Download POSTERIOR OCCLUSAL CHANGES WITH A HAWLEY VS PERFECTOR/HAWLEY RETAINER: A FOLLOW-UP STUDY

POSTERIOR OCCLUSAL CHANGES WITH A HAWLEY VS
PERFECTOR/HAWLEY RETAINER:
A FOLLOW-UP STUDY
Elizabeth M. Bauer, D.M.D.
An Abstract Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2008
Abstract
The purpose of this study is to characterize postorthodontic settling of the posterior occlusion by
comparing patients wearing Hawley retainers against
patients initially wearing Perfector retainers and then
switching to Hawley retainers.
This follow-up study was
based on 40 patients (25 Perfector and 15 Hawley) evaluated
at four time points over eight months.
They were part of a
larger sample of 50 patients randomly assigned to wear
either Hawley or Perfector retainers. The Perfector
patients were given Haley retainers two months post-debond.
Objective and subjective measures were collected at the end
of treatment (T1), two months post debond (T2), six months
post-debond (T3) and eight months post-debond (T4).
Occlusal bite registrations were scanned and traced to
quantify posterior areas of contact and near contact
(ACNC).
A seven-item questionnaire was used to assess the
patient’s perception of occlusion.
Results showed that
ACNC increased during the first six months of retainer
wear. The Hawley group showed a 129% increase in ACNC,
while the Perfector/Hawley group showed a 104.9% increase
in ACNC over eight months of retention.
No significant
differences in ACNC were found between the Hawley and
1
Perfector/Hawley groups.
Both the Hawley and
Perfector/Hawley groups showed the greatest rates of
increase in ACNC between T1-T2.
While the Perfector/Hawley
group perceived greater improvements in their occlusion
than the Hawley group, group differences after eight months
were small and related to the changes that occurred during
the first two months of retention.
2
POSTERIOR OCCLUSAL CHANGES WITH A HAWLEY VS
PERFECTOR/HAWLEY RETAINER:
A FOLLOW-UP STUDY
Elizabeth M. Bauer, D.M.D.
A Thesis Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2008
COMMITTEE IN CHARGE OF CANDIDACY:
Adjunct Professor Peter H. Buschang,
Chairperson and Advisor
Professor Rolf G. Behrents,
Assistant Clinical Professor Donald R. Oliver
i
DEDICATION
I dedicate this project to my husband Ben, who has
supported and encouraged me throughout this entire process.
ii
ACKNOWLEDGEMENTS
I would like to acknowledge the following individuals:
Dr. Peter Buschang for chairing my thesis committee.
Dr. Rolf Behrents and Dr. Donald Oliver for serving on my
thesis committee.
Dr. Jennifer Horton, Laura Wiley, Celia Giltinan,
Daniel Kilfoy, and Dr. Heidi Israel for their assistance
with this project.
Parkell Bio-Materials for supplying the Blu Mousse
impression material used in this experiment.
The Orthodontic Education and Research Foundation for
contributing to the funding of this project.
iii
TABLE OF CONTENTS
List of Tables...........................................vi
List of Figures.........................................vii
CHAPTER 1: INTRODUCTION...................................1
CHAPTER 2: REVIEW OF THE LITERATURE
Review of Topics..........................................6
Ideal Occlusion...........................................7
Introduction.........................................7
Definitions..........................................9
Methods to Measure Posterior Occlusion.......... ........13
Introduction........................................13
Articulating Indicators.............................14
Photoocclusion......................................16
T-Scan..............................................18
Polyether Impression Material.......................19
Silicone-based Impression Material..................20
Optical Scanning....................................22
Summary.............................................23
Importance of Posterior Occlusion: Function..............24
Importance of Posterior Occlusion: Stability.............27
Immediate Post-orthodontic Occlusion.....................31
Retention................................................34
Introduction........................................34
Significance of Retention...........................35
Retention Devices...................................36
Post-Orthodontic Occlusion and Retention.................40
Introduction........................................40
Past Studies........................................41
Conclusion..........................................55
References...............................................59
CHAPTER 3: JOURNAL ARTICLE
Abstract.................................................66
Introduction.............................................67
iv
Materials and Methods....................................71
Statistical Analyses................................74
Results..................................................74
Discussion...............................................78
Conclusions..............................................84
Literature Cited.........................................94
Vita Auctoris............................................97
v
LIST OF TABLES
Table 1:
Comparison of areas of contact and near
contact (ACNC) of posterior occlusion with
Hawley and Perfector groups at T1 (posttreatment), T2, T3 and T4 (approximately
eight months later).......................86
Table 2:
Comparison of areas of contact and near
contact (ACNC) of posterior occlusion with
Hawley and Perfector groups from T1-T2, T2T3, T3-T4 and T1-T4.......................87
Table 3:
Patient perception of posterior occlusion
with Hawley and Perfector groups at T1
(post-treatment),T2, T3 and T4
(approximately eight months later)using a
visual analogue scale.....................88
Table 4:
Changes in patient perception of occlusion
in Hawley and Perfector groups from T1-T2,
T2-T3, T3-T4, and T1-T4 using a visual
analogue scale............................89
vi
LIST OF FIGURES
Figure 1:
Median cumulative areas of contact and near
contact measured in 50µm thickness intervals
between T1(end of treatment) and T4 (eight
months)for patients initially wearing Hawley
retainers.................................90
Figure 2:
Median cumulative areas of contact and near
contact measured at 50µm thickness intervals
between T1 (end of treatment) and T4 (eight
months) for patients initially wearing
Perfector retainers.......................91
Figure 3:
Median absolute changes in areas of contact
and near contact at 50µm thickness intervals
between T1 (end of treatment) and T4 (eight
months) for patients initially wearing
Hawley and Perfector retainers............92
Figure 4:
Median cumulative changes in areas of
contact and near contact at 50µm thickness
intervals between T1 (end of treatment) and
T4 (eight months) for patients initially
wearing Hawley and Perfector retainers....93
vii
CHAPTER 1:
INTRODUCTION
The goal of orthodontics is an esthetic result that
establishes proper occlusion so as to maximize masticatory
health, function and stability.
Through active orthodontic
treatment, the teeth are brought into proper occlusion.
Once the appliances are removed, the teeth are held in the
attained position with some type of device during the
retention phase of treatment.
Although active tooth
movement is not usually occurring during this phase, there
may be slight or even large changes in the position of the
teeth.
Some of these changes, such as settling of the
occlusion, are desirable, while other changes, such as
rotational relapse, are not.
Since post-orthodontic
changes are anticipated, it is an accepted procedure for
the orthodontist to prescribe a retainer and continue
observation until the teeth have settled into their final
position.
Most orthodontists develop a “retention
protocol” based on their own beliefs concerning posttreatment changes and how long these changes may be
expected to occur.
The Hawley retainer and the Perfector ® , which is a
modified version of the Tooth Positioner, are two
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appliances used in orthodontics during the retention phase
of treatment.
Several retention studies have been
conducted with the intention of clarifying the advantages
of various retention devices; however, most of them have
not objectively evaluated the effects of the Hawley and
Perfector ®
teeth.
retainers on the occlusion of the posterior
Furthermore, it is unclear which retention method
is more effective in encouraging post-orthodontic settling.
It is important for orthodontists to know the effectiveness
of different retention designs, the nature of postorthodontic changes that occur, and how long these changes
are expected to continue after active treatment in order to
prescribe the optimal retention protocol.
A previous study by Horton et al.1 evaluated changes in
the posterior occlusion over two months of retention in an
attempt to determine if there were quantitative or
qualitative differences in the posterior occlusion in cases
where the Perfector ® and Hawley retainer were used.
No
differences were found between the two groups after two
months of retention. Although the differences between the
Hawley and Perfector ® appliance after two months has been
examined by Horton et al.1, it has not yet been determined
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what changes may occur thereafter in the Perfector ® group,
especially after the occlusal coverage of the Perfector ®
appliance is removed.
Furthermore, it is currently not clear what happens
after Perfector ® use is discontinued and retention is
continued with a Hawley retainer.
During the time the
Perfector ® is worn, the patient is instructed to perform
chewing exercises for several hours a day and then sleep
with the Perfector ® at night.
This process is supposed to
align the teeth into a more ideal position, which in
theory, should result in increased occlusal contacts.
However, the Perfector ® by design has occlusal coverage,
which may inhibit actual settling.
There has not been a
study that examines what happens to the amount of settling
after the Perfector ® patient is given a Hawley retainer.
The teeth, in theory have been moved into a more ideal
position.
By removing the occlusal coverage of the
Perfector ® , it is possible that the teeth may then be able
to settle, and actually produce increased occlusal contacts
months later.
®
There has not yet been a study that compares
TP Orthodontics, Inc.
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the Hawley and Perfector ® group’s months later, after both
groups are given identical Hawley retainers.
There is a
possibility that although there were no apparent
differences initially, the Perfector ® group may provide
better occlusion in the long run.
Knowing the nature of
occlusal changes over time and the qualitative and
quantitative differences between the Hawley and Perfector ®
retainers will assist the orthodontist in making an
informed decision when prescribing a retention protocol.
The current study is a follow-up study to Horton et
al.1 While the same sample of patients will be used, each
patient will be given identical Hawley retainers at the
beginning of the current follow-up study (2 months postdebond).
Identical materials and methods as Horton et al.1
will be used to maintain continuity of the data. The goal
of this follow-up study is to further investigate whether
and how the retention device used after active orthodontic
treatment affects posterior occlusion after two different
retention groups (Perfector ® and Hawley) are given
identical Hawley retainers at two months and again assessed
six and eight months post-debond.
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Occlusal bite
registrations of silicone-based impression material will be
analyzed using optical scanning and Image Tool® software to
assess 1) area of occlusal contacts (actual and near
contacts) at 6 and 8 months post-debond, 2) differences in
settling between the Hawley and Perfector ® groups after
both retention groups are given identical retainers, 3)
quantify the rates of post-orthodontic settling to
determine the nature of the changes that occur over time
and 4) patient perception of occlusion.
It is hypothesized
that post-orthodontic settling will continue to increase
over time; however, the nature of these changes may differ
between the two retention groups.
It is expected that both
the Hawley and Perfector ® patients will both show increased
occlusal contacts over time, with the Perfector ® patients
showing more overall settling later in the post-orthodontic
phase.
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CHAPTER 2:
REVIEW OF THE LITERATURE
Review of Topics
This review of the literature will begin by discussing
the importance of ideal occlusion, as this concept has been
a cornerstone of orthodontics since the specialty was
founded.
To thoroughly understand this topic, the
definition of ideal occlusion will be reviewed along with a
description of anterior and posterior occlusion.
While
anterior occlusion is often the focus in orthodontics, this
study will focus on posterior occlusion for two reasons: 1)
the important role of posterior occlusion in overall
masticatory health, function and stability and 2) the lack
of orthodontic literature pertaining to post-orthodontic
posterior occlusion. Next, the review will review the
different methods that have been used to measure posterior
occlusion.
These concepts are fundamental for
understanding the research methods used in the present
study and will also aid in illustrating the drawbacks and
benefits of previously used methods.
This section will
illustrate the importance of using a more objective and
quantifiable method of measuring posterior occlusion.
The
review will then describe the importance of occlusion as it
6
relates to function and stability.
It will then explore
the condition of the occlusion immediately following
orthodontic treatment.
This is important because it is
useful to know how these discrepancies will change over
time, and how long these changes take place.
sections will focus on retention.
The final two
First, a brief history
of retention will be provided, followed by descriptions of
various retention methods.
Finally, there will be a review
of retention studies evaluating post-orthodontic posterior
occlusion.
It will be shown that we currently do not have
a clear understanding of post-orthodontic occlusal changes
produced by Hawley and Perfector retainers.
Ideal Occlusion
Introduction
Throughout the history of orthodontics the importance of
occlusion has been emphasized and well documented. The
definition of ideal occlusion has been a topic of debate
among dental professionals for several years and still
remains an issue today.
The concept of ideal occlusion has
changed over the years and has been influenced by many
theories. In 1900, Angle published Treatment of
Malocclusion of the Teeth and Fractures of the Maxillae,
7
edition 6, which greatly assisted dentists in their
diagnosis and treatment of various malocclusions.
In this
textbook, Angle described the antero-posterior relationship
of the maxillary and mandibular molars and established the
Angle classification system that is still widely used today
among orthodontists.2 Another innovator in orthodontics,
Charles Tweed, published the article titled “Indications
for the extraction of teeth in orthodontic procedures” in
1944,
which suggested that the stability of orthodontic
treatment was influenced by the attainment of good occlusal
contacts.3 In 1972, Andrews introduced the six keys to
normal occlusion.4
These ideas further emphasized the
importance of ideal occlusion and aided in the development
of the straight-wire appliance that many orthodontists use
today.
The concept of ideal occlusion is multifactorial, with
occlusal contacts being one of the major contributors.
Through thorough evaluation of the various aspects of
occlusion, Okeson5 describes ideal occlusion as:
1)the presence of even and simultaneous contacts of all
teeth when the mandibular condyles are in their most
superoanterior position resting on the posterior slopes
of the articular eminences with the discs properly
interposed, the anterior teeth should contact but more
lightly than the posterior teeth 2) each tooth should
contact so that occlusal forces are directed through the
long axis of the tooth, 3) the presence of canine
guidance in laterotrusive movements, 4) the presence of
8
anterior guidance in protrusive movements and 5) heavier
posterior than anterior contacts in the alert feeding
position.
These concepts of ideal occlusion have played an important
role in orthodontics since the specialty was established
and are still valued and strived for by orthodontists
today. It was recently stated in a modern orthodontic
textbook that the “operational goal” of orthodontics is to
obtain optimal occlusion.6 On this basis, it is important
that future research continues to focus on developing
methods for identifying, describing and better
understanding occlusion.
Definitions
Occlusion can be divided into two types: anterior and
posterior.
Anterior occlusion involves the incisors and
canines and exists when the incisal edges of the mandibular
incisors contact the lingual surfaces of the maxillary
incisors.5
The maxillary and mandibular incisors act to
guide the mandible into protrusive movements while the
maxillary and mandibular canines guide the mandible during
excursive movements, providing anterior guidance.5 In
comparison to posterior occlusion, the contacts on the
anterior teeth are much lighter, and sometimes may not even
9
be present.5
Ideal occlusion has often been described based
on the complete absence of anterior occlusal contact.7-9
The anterior teeth, mainly the incisors, are inclined
labially, as they are not designed to withstand heavy
occlusal forces. The posterior teeth consist of maxillary
and mandibular premolars and molars, and have a much
different function than the anterior teeth. The posterior
occlusion, as described by Okeson,5 pertains to the
relationships between cusp tips and their opposing central
fossae and marginal ridges.
The posterior teeth establish
and maintain the vertical dimension of occlusion and are
designed to withstand the heavy forces of mastication.5
The
posterior occlusion has been closely related to masticatory
function and occlusal stability.
As previously stated, Angle developed a classification
system using the antero-posterior relationship of the
maxillary and mandibular first molars to define occlusion.
According to Angle, the mesiobuccal cusp of the maxillary
first molar should occlude with the buccal groove of the
mandibular first molar. This was classified as a “Class I”
molar relationship.
If the maxillary and mandibular first
molars have a normal relationship, but the teeth are
crowded or rotated, a “Class I malocclusion” exists.
A
“Class II” relationship exists if the lower first molar is
10
positioned distally in relation to the maxillary first
molar. Finally, if the mandibular first molar is positioned
mesially in relation to the maxillary first molar, a “Class
III” relationship exists.2
The American Board of Orthodontics has implemented a
grading system to evaluate the quality of finished
orthodontic cases.
The objective grading system (OGS) was
implemented in 1999 in order to provide a fair and
objective means of evaluating occlusion for the ABO phase
III examination.10
In the ABO OGS, seven occlusal criteria
are measured on plaster models to assess the patient’s
final occlusion.
The criteria included tooth alignment,
vertical positioning of marginal ridges, buccolingual
inclination of posterior teeth, occlusal relationship,
occlusal contacts, overjet, and interproximal contacts.10
The eighth criterion is root angulation,
which is measured
using a panoramic film.10,11 Points are assigned for each of
the eight criteria. A case will pass if fewer than 20
points are deducted and fail if more than 30 points are
deducted.10,11
On this basis, occlusion is a major component
in determining the acceptability of a case for the ABO
phase III examination as well as diagnosis, treatment
planning and overall case management.10
11
Depending on the extent of anterior contact and whether
the cusp tips contact one or two opposing marginal ridges,
the total number of ideal occlusal contacts may vary.
ideal
occlusions,
if
a
cusp
tip
contacts
two
In
opposing
marginal ridges, two contacts on the cusp tip will result,
but if the cusp tip only contacts one opposing ridge only
one
contact
on
the
cup
tip
will
result.5
Ricketts12
reported that an ideal occlusion will produce 48 contacts,
while Okeson5 reported ideal occlusions as having between 34
and 48 contacts, with each cusp tip contacting either one
or two marginal ridges.
Haydar et al.13 reported 40.50 +/-
9.68 contacts in patients with ideal occlusion.
Maximum intercuspation occurs when the maxillary and
mandibular teeth are brought together into occlusion.
The
posterior occlusion is often evaluated by having the
patient bite into maximum intercuspation, which has been
shown to be a repeatable position.14 Occlusal contacts of
maxillary and mandibular teeth during function is referred
to as functional occlusion, which is important during
mastication, swallowing and speech.15
12
Methods to Measure Posterior Occlusion
Introduction
Orthodontists commonly evaluate posterior occlusion using
Angle’s classification, which helps to determine the
relationship between the upper and lower first molars in
the saggital plane. While this method is helpful in
evaluating how well the maxillary and mandibular teeth
relate to each other, it does not quantify the amount of
occlusal contact, which can only be assessed in the
vertical plane between the maxillary and mandibular teeth.
Occlusal contacts, which can vary in size and number,
provide a measure of how forces may dissipate during
function. This also cannot be measured in the saggital
plane.
Studies measuring posterior occlusion have used various
methods of evaluating tooth contact including photoocclusion, the T-scan method, articulating indicators
(paper, film or silk), and polyether or silicone bite
registrations.
Despite the information these methods can
provide, the accuracy and reliability of some of these
methods remain questionable.
The following section will
explore the various methods of measuring posterior
occlusion along with the problems and benefits associated
13
with each.
The section will conclude by describing optical
scanning of silicon-based impression materials, which is a
newer and more reliable method of measuring posterior
occlusal contacts.
Articulating Indicators
Articulating indicators are routinely used in dentistry
to register occlusal contacts and to assess the patient’s
occlusion.
They are made of various materials such as
paper, nylon or silk that transfer color from the
articulating indicator to the teeth marking occlusal
contacts.16
Articulating indicators are also fabricated
with different surface characteristics (smooth vs. coarse)
and thicknesses which might affect the marking ability of
the indicator.1
An advantage of using articulating
indicators is that they are very easy to use.
After the
indicator is placed over the teeth the patient is
instructed to bite together onto the articulating
indicator.
This action transfers color to the areas of
occlusal contact.
After the markings are registered, the
number and location of occlusal contacts can be evaluated.
While articulating indicators allow for gross assessment of
contact size and location, it has been reported that this
method is less reliable than other methods because of
14
variations in film thickness, the character of the ink, the
surface texture of the indicators, and the condition of the
occlusal surfaces in contact.17,18 Carossa et al.19 examined
the effect of articulating strip thickness on the number of
posterior contacts. Two different thicknesses (8μm and 40
µm) of articulating indicators were used to register the
contacts. The force and time of biting were also recorded.
Operator-dependent factors were evaluated by using thirteen
dental students and thirteen expert dental professionals to
register and record the data.
It was found that when using
the thinner articulating strips, dental students applied
stronger and shorter bites than experts. Furthermore, the
biting time impacted the number of occlusal markings when
the thinner strips were used.
However, the thicker
articulating strips produced greater contact areas,
regardless of the operator.
Overall, the results showed
that when using articulating indicators to register
occlusal contacts, paper thickness, operator experience,
biting force, and time all have an effect on the occlusal
markings.
Similar results were reported by Millstein and
Maya,16 who compared the effects of articulating indicators
consisting of different materials (paper, film, silk and
nylon), colors and thicknesses on occlusal markings.
Images were recorded using articulator-mounted casts and a
15
video camera. It was found that the size of occlusal
markings was significantly affected by the color, thickness
and material of the articulating indicator. Based on ten
indicators, it was demonstrated that the markings were not
repeatable, suggesting that the use of articulating
indicators may not be the most dependable method to record
and measure posterior contacts.
Photoocclusion
The photoocclusion technique was introduced in 1985 by
Gazit and Lieberman as a method of measuring occlusal
contacts using an occlusal wafer and a polariscope, which
measures the polarization of light.1
Using the
photocclusion method, subjects are instructed to bite onto
an occlusal wafer with continuous pressure for 10 seconds.
After two consecutive bite registrations are taken, the
occlusal wafer is projected onto the polariscope and
analyzed.18 Each contact that appears on the polariscope is
traced and recorded.
This information serves as a
quantitative analysis.
The occlusal contacts can also be
evaluated qualitatively by interpretation of the colored
stress patterns, which are dependent on the degree of
occlusal penetration into the occlusal wafer.
16
These
patterns can then be translated into percentages using a
visual interpretation chart.18
Gazit and Lieberman
considered light contact to be up to 40% penetration into
the wafer, medium between 40% and 60% penetration into the
wafer, and heavy contact as over 60% penetration into the
occlusal wafer.18
However, in 1986, Gazit, Lieberman and Fitzig20 conducted
a follow-up study in which they examined the
reproducibility and reliability of the photocclusion
technique. Results of their study indicated that the
photocclusion technique was a fairly inaccurate method of
evaluating occlusal contacts.
The photocclusion technique
was also compared to articulating indicators in recording
occlusal contacts.
Using both the photoocclusion technique
and the articulating indicator technique, occlusal records
were taken on 11 male dental students with Class I
occlusion at the beginning of the study and again one month
later.
It was found that neither the photoocclusion nor
the articulating indicator technique were highly
reproducible. However, the photocclusion technique was more
reliable than the articulating indicator technique.20
17
T-Scan
The T-Scan, a computerized occlusal analysis device, was
introduced in 1987 by Maness et al.21
The T-Scan is a
computerized system for recording occlusal contacts and the
force of occlusal contact.21
This system consists of a 60
μm thick piezoelectric foil sensor made from conductive ink
on a polyester film substrate, a sensor handle, hardware
and software for recording, viewing and analyzing the
data.22
film.
A plastic intra-oral carrier is used to hold the
The sensor is connected to a computer, which
provides information regarding position, strength,
frequency and timing of occlusal contacts.23 Information
pertaining to bite force can be measured using the T-scan
system software.
This information can be measured as
either a force movie, which is a 3-second recording of
force, or a force snap shot, which is an immediate
measurement.22
The sensitivity and reliability of the T-Scan system for
occlusal analysis was tested by Hsu et al.23 The sensitivity
threshold of the sensor was analyzed and the sensor’s
reliability in recording occlusal contacts was measured in
an articulator using reproducible forces.
It was
determined that the T-Scan sensor did not have a uniform
sensitivity throughout its surface.
18
Furthermore, the
number of registered occlusal contacts varied from sensor
to sensor, within the same sensor and between trials.23
Finally, it was found that the T-Scan continually recorded
fewer occlusal contacts than actual existed;23 Similar
results were reported by Lyons et al.22 After examining the
sensitivity and reliability of the T-Scan method, several
authors have concluded that the T-Scan system is an
inconsistent method for recording occlusal contacts.22,23
Polyether Impression Material
Impression materials such as Polyether have been widely
used to register posterior occlusion in maximum
intercuspation. For instance, Durbin and Sadowsky24
measured the posterior occlusion using polyether impression
material to fabricate occlusal bite registrations.
Polyether impression material was injected onto the
occlusal surfaces of the mandibular teeth and patients were
instructed to “bite firmly on your back teeth and hold the
position” for two minutes.24
Using the polyether bite
registrations, perforations in the material were
transferred to study models with a pencil. These markings
were counted to determine the number of contacts.
In a follow-up to Durbin and Sadowsky’s study, Razdolsky
et al.25
also measured posterior occlusion by injecting
19
polyether impression material onto the mandibular occlusal
surfaces. As in the previous study, the patients were
instructed to “bite firmly on their back teeth and hold the
position” for two minutes.25
In this follow-up study, near
contacts were evaluated as well as actual contacts.
However, the method used to identify near contacts was very
subjective; they were identified as a “change in color from
yellow to transparent white.”25
Near contacts were
transferred to the study models with a black marker and
counted.
The actual contacts, defined as “perforations” in
the polyether bite registration, were evaluated using a
radiographic viewing screen in a dark room and transferred
to study models with a red marker.
Silicone-based Impression Material
Several studies have used silicone-based impression
materials to assess occlusal contacts.
For example, using
a silicone putty impression material, Dincer et al.26
counted the number of contacts and near contacts by
evaluating perforations and translucent areas in the
silicone material.
Actual contacts were classified as
perforations and near contacts were identified as
translucencies. Using the bite registrations, the contacts
20
and near contacts were then transferred onto study models
for further evaluation.
Sauget et al.27 also fabricated occlusal bite
registrations using polysiloxane impression material to
register and assess occlusal contacts.
They instructed
subjects to “bite firmly” in maximum intercuspation after
injecting the material over the occlusal surfaces of the
mandibular teeth.
Similar to the previous study,
perforations in the bite registration were identified as
actual contacts.
However, a caliper was used to measure
near contacts, which consisted of a material thickness of
0.20 mm or less.
Haydar et al.13 also evaluated occlusal contacts using
silicone-based impression material.
As in previous
studies, the patients were instructed to bite “firmly” onto
their back teeth for 30 seconds after the impression
material was injected onto the mandibular occlusal
surfaces.
To evaluate occlusal contacts, the bite
registrations were simply held up to the light.
Perforations in the material that allowed light to pass
through were counted as contacts, while the
thin/transparent areas without perforations were classified
as near contacts. The actual contacts were transferred to
the maxillary cast; the near contacts were recorded by
21
marking their midpoints on the cast.
Occlusal photographs
of the models were then taken, the photographs were
standardized and the contacts were traced on acetate paper.
Finally, all contacts were counted and combined for the
evaluations.
Optical Scanning
Several recent studies have abandoned counts of occlusal
contacts and have used optical scanning to quantify areas
of contacts.17,28,29
Optical scanning of occlusal bite
registrations provides a more objective method of
evaluating contacts and near contacts.
A silicone-based
material, called Blu Mousse is applied to the mandibular
posterior teeth and, as in previous studies, the subjects
were instructed to bite down “firmly” and hold in order to
fabricate an occlusal bite registration. The occlusal
registrations are then placed onto a scanner with the
mandibular occlusal surface facing downward.
After the
bite registration has been scanned, the platform area of
the mandibular first molar and premolars is traced using
the software program Image Tool, (University of Texas
Health Science Center, San Antonio) which computes the
platform area and determines the frequency distributions of
pixels delimited by the platform area in gray scales.
22
A
calibration curve, which relates known thicknesses of Blu
Mousse to a gray scale, is developed using calibration
wedges of Blu Mousse impression material.
Using this
curve, the investigators were able to determine the
thickness of sample registrations based on gray scale
values of the area scanned.
Therefore, instead of
subjectively classifying contacts and near contacts, they
were quantified “optically” on the basis of light
transmitting through the registration material and
thickness was measured up to 350μm.28,29 When scanning
silicone-based impression materials, it has been shown that
pixel densities are only detectible in increments of 50μm.30
In other words, a thickness of 40μm can be distinguished
from 90μm and a thickness of 90μm can be distinguished from
140μm, but a thickness of 90μm cannot be distinguished from
100μm.
Summary
Dental research has used several different methods for
measuring the posterior occlusion and areas of contact and
near contact, including articulating paper or film, silk,
the photo-occlusion technique, visual assessment and the TScan method. Although these techniques have provided
23
valuable information, they are not as accurate as more
recently developed methods of evaluating occlusal contacts.
Studies evaluating occlusion and occlusal contacts often
use silicone-based impression materials because they
provide more accurate registrations.31
To date, most
studies have used counts to evaluate the bite
registrations.
Optical scanning of occlusal registrations
provides a more objective and precise alternative for
measuring occlusal contact areas.1
Importance of Posterior Occlusion:
Function
Achieving an ideal posterior occlusion is a very
important factor in orthodontic treatment because it
directly affects masticatory function.
Occlusal contact
area has been shown to be among the most important factors
determining masticatory performance.32
Although the
occlusal contact area is only a fraction of the total
occlusal surface area, it represents the most important
fraction of the total area involved in mastication.32
Yurkstas et al.32 found that the occlusal contact area was
the major factor in accounting for variation in masticatory
performance. They also showed that masticatory performance
24
was related to the occlusal contact area in a curvilinear
manner. Because the correlation between occlusal contact
area and masticatory performance is highly significant,
performance can be predicted with a relative degree of
certainty.32 It has also been shown that the contact and
near contact areas form the actual food platform and that
there is a high correlation between this small area and
chewing performances.33
Toro et al.34 and English et al.35
demonstrated that subjects with normal occlusion are able
to break down foods more efficiently than those with
malocclusion.
When comparing the masticatory efficiency
and ability of subjects with normal occlusion to patients
with Class II malocclusions, Henrikson et al.36 found that
subjects with normal occlusion presented significantly
better masticatory efficiency and ability in comparison to
the Class II subjects.
It was concluded that fewer
occlusal contacts and a larger overjet were the factors
most closely associated with reduced masticatory
efficiency.
Owens et al.29 found that patients with
malocclusions had smaller areas of contact and near contact
than patients with normal occlusions and that the patients
with smaller areas of contact and near contact were less
efficient in their ability to break down food during
mastication.
Near contacts are important because they
25
provide a measure of near occlusion, which may be a more
important factor in masticatory performance than actual
contacts.29
During mastication, near contacts may become
contacts with flexure of the mandible and movements of the
teeth within the PDL space.
Omar et al.37
found a significant correlation between
masticatory efficiency scores and occlusal analysis scores,
showing that deviations from normal occlusion affect
masticatory efficiency. When investigating the effects of
age, posterior occlusal contacts, occlusal force, and
salivary flow on masticatory performance in 328 adults,
Ikebe et al.38 found that masticatory performance was
significantly associated with posterior occlusal contacts,
occlusal force and salivation.
It was concluded that
decreases in posterior occlusal contacts and occlusal force
were associated with reduction of masticatory performance.
Mastication involves heavy forces that sometimes
exceed 100 pounds and pressures that have been estimated at
over 10,000 pounds per square inch.32 Such forces emphasize
the importance of ideal occlusion.
It is important that
these forces are vertically directed down the long axis of
the teeth.
This is why both contacts and near contacts are
important during function; near contacts maximize the total
contact area.
Maximizing tooth contacts minimizes the
26
stresses distributed among the teeth and ideally located
contacts help to distribute forces of mastication parallel
to the long axis of the dentition providing maximum
periodontal support.26
Therefore, the location of occlusal
contacts and increased number and size of occlusal contacts
are important.
A strong correlation between bite force and
occlusal contacts in adults was found by Bakke et al.39 A
positive correlation between bite force and the number of
interocclusal contacts was also reported by Ingervall and
Minder.40
Julien et al.28 demonstrated that masticatory
performance in adults was affected by posterior ramus
height, contact area, and bite force, and that those with
greater contact areas had better masticatory performance.
Collectively, these studies emphasize the importance of
ideal occlusion as it relates to occlusal function and the
role of occlusal contacts in masticatory performance and
efficiency.
Importance of Posterior Occlusion:
Stability
Maintaining post treatment alignment has been a goal of
orthodontics since the specialty came into being.
been hypothesized
It has
that post treatment crowding is not
27
necessarily due to relapse, but to a phenomenon known as
instability.41
Relapse occurs when the teeth move back
toward their original position after orthodontic treatment
is finished.
Driscoll-Gilliland et al.41 attribute
instability to vertical growth of the craniofacial complex,
and the consequent eruption and migration of teeth
necessary to reestablish occlusion. For instance, as the
patient grows there is vertical eruption of the teeth which
in turn, changes the relationship between the teeth.
Therefore, the occlusion is less stable, and as a result,
the relationships between adjacent and opposing teeth
change and crowding results.35
It has been suggested that good intercuspation and
occlusal contacts may be essential for stable orthodontic
results.
Parkinson et al.17 assessed the relationship
between posterior occlusion and post treatment changes by
examining pretreatment, post treatment and post retention
records of 49 Class I and Class II extraction cases.
Overbite, overjet, mandibular incisor irregularity, right
and left molar deviations, midline deviation, and
mandibular arch length were measured and occlusal
registrations were made of each set of dental casts.
It
was concluded that post treatment contact and near contact
areas may be factors in overbite and overjet stability.
28
Deng and Fu42 examined occlusal contacts before and
after orthodontic treatment in 32 eight to seventeen year
old patients by utilizing silicone occlusal bite
registrations. The registrations were analyzed using a
computer imaging system called Add-Picture.
After
comparing the images before and after treatment,
significant differences were noted in the number, type,
location and size of contacts.
Results indicated that
orthodontic treatment has a positive effect on the
distribution of occlusal contacts in intercuspal position.
They interpret the findings to suggest that treatment
contributes to the establishment of occlusal stability and
that the location of contacts in intercuspation is one of
the main factors responsible for maintaining correct
alignment of the teeth and stabilization of the mandible.
It was also noted that failure to provide adequate centric
stops may cause occlusal instability, resulting in a
shifting of the teeth as well as disturbances in the
muscles and joints.
Dincer et al.26 hypothesized that one of the most
important factors in occlusal stability is the existence of
centric stops.
Centric stops on functional cusps were
thought to ensure the stability of orthodontic treatment.
Upper and lower removable Hawley retention appliances were
29
given to 20 treated orthodontic patients and their occlusal
contact points were determined from occlusal registrations
taken at the beginning and end of 9 months of retention.
Subjects were compared to 20 untreated controls with ideal
occlusion.
Results showed a significant increase in the
number of posterior contacts and a significant increase in
the number of contacts in ideal locations during the 9
month retention period. The authors suggested that these
results provide important signs of occlusal stability. It
was concluded that in order to maintain the occlusal
stability that is needed for the success of orthodontic
treatments, ideal occlusal contacts and localization of
contacts in centric and eccentric occlusion should be
considered.
Conversely, Ormiston et al.43 suggest that finishing
occlusal relationships to perfection might not ensure postretention stability. When evaluating ABO and post-treatment
PAR scores for stable and unstable groups, the analysis of
the ABO scores at T2 demonstrated a regression to the mean,
in which subjects with low T2 scores tended to increase
their score (deteriorate) at T3, and those with high T2
scores tended to decrease their score (improve) at T3.
Although the post treatment PAR, incisor irregularity and
ABO scores were all lower for the stable group, the
30
differences were not large.
These results show that both
the stable and unstable groups were finished to comparable
levels and that the post treatment condition was not the
most important or influential factor in long-term
stability.
If this is true, other factors might play more
important roles in stability, such as treatment and
retention methods, compliance, the tendency to return to
pre-treatment condition, and growth.
Only a small number of studies have addressed the
important contributions of occlusal contacts to maintaining
functional and structural stability.
Although it is
commonly accepted by orthodontists that ideal occlusion
enhances long-term stability, there is little scientific
support of the relationship between occlusion and
stability.
Furthermore, it is a possibility that the
studies that show increased stability in untreated subjects
may not have finished the treated patients to an ideal
occlusion.
Immediate Post-orthodontic Occlusion
Based on the premise that ideal occlusion is necessary
for optimal function and stability, it is important to know
31
the quality of occlusion after active orthodontic
treatment.
Using the photocclusion technique on 12
orthodontically treated patients, Gazit and Lieberman18
showed widely varying numbers of occlusal contacts.
However, the study casts showed close to ideal buccolingual
and mesiodistal relationships for all the cases.
This
study illustrates a common mistake orthodontists may make;
a patients’ occlusion may look satisfactory upon clinical
observation, but when closely examined, the occlusion may
not be as ideal as it appears.
After measuring 138 post-treatment models of Class I
non-extraction patients using the ABO OGS criteria
(interproximal contacts and root angulations were
excluded), Fleming et al.44 reported a mean overall OGS
score of 24.9 +/- 8.0.
The highest point deduction (6.25
+/- 3.75) from the model analysis was due to occlusal
contacts. The lowest point deduction was associated with
occlusal relationships (1.74 +/- 1.83).
Overall, occlusal
contacts contributed to approximately 26% of the total
deductions.
Approximately 56.2% of the variation in the
total score was due to the occlusal contact component.44
This illustrates that occlusal contacts were the most
important component contributing to and explaining
32
variability in the overall OGS scores in the study.
Previous studies have also shown occlusal contacts to be
important determinants of overall post-treatment OGS
scores.45-48
When comparing treatment results between orthodontists
and general dentists, Abei et al.45 found that neither group
consistently produced the level of quality required to pass
the ABO phase III examination.
According to ABO standards,
when using the OGS method of grading, patients who score
more than 30 points are likely to fail the ABO phase III
examination.
When comparing treatment outcomes between two
orthodontic programs, Deguchi et al.46 found that only 45.1%
of finished patients from Okayama University (OU) and 46.6%
of patients from Indiana University (IU) had OGS scores of
less than 30.
These results show that fewer than half of
the patients had passable immediate post-treatment results
according to ABO examination criteria.
After examining 115
consecutively finished cases obtained from nine Board
certified orthodontists, Cook49 found that according to ABO
OGS standards, 18% of the cases passed, 47% were
undetermined and 35% failed.
In that study, alignment and
root angulation contributed most to the overall score.
Interestingly, Parkinson et al.17 found that despite
excellent treatment results, the proximity of posterior
33
occlusal surfaces lessened during orthodontic treatment.
Haydar et al.13 reported that the total mean number of
contacts at the end of active treatment was 21.20 for the
Hawley group and 24.80 for the Perfector group, which were
much less than the 39.4 contacts of the untreated group.
Assuming that occlusion is not ideal immediately posttreatment, it is important to know how certain aspects of
occlusion will change over the long term.
Existing studies
suggest that little attention has been given to this aspect
of finishing.
This emphasizes the importance of post-
orthodontic settling. It leads to the important question of
how much settling can we expect and rely on over time.
Retention
Introduction
The retention phase is a very important and challenging
part of orthodontic treatment.
Retention devices are
typically given to patients following orthodontic treatment
to prevent relapse, promote further “settling” of the
occlusion and to make minor corrections in the dentition.50
Different types of retainers can be used to accomplish
these goals including removable, fixed, passive and active
34
retention devices, all of which will be discussed in the
following sections.
Significance of Retention
Several factors contribute to orthodontic relapse.
After
active appliances are removed, the teeth must be retained
in their new positions long enough for the periodontal and
gingival fibers to reorganize. For example, by studying the
periodontal tissues of dogs with orthodontically rotated
teeth, Reitan51 found that the connective tissue fibers in
the supracrestal periodontal tissues continued to persist
after 232 days. Furthermore, it has been shown that tissue
changes and post treatment tooth position contribute to
relapse after active orthodontic treatment.51 Bone also
needs time for reorganization and maturation.
It has been
shown that after the teeth have been moved through the bone
they have a strong tendency to relapse.52
For this reason
it is important to hold the teeth in their new position to
enhance future stability.
Another important factor in retention is growth.
It has
been shown that certain growth patterns can contribute to a
patient’s malocclusion.53 Growth has been shown to continue
into adulthood, which could affect a patients occlusion
after orthodontic treatment is finished.53
35
For instance, it
has been shown that post-treatment relapse may be affected
by continued Class II, Class III, open bite or deep bite
growth patterns.54 Furthermore, it has been demonstrated in
both treated and untreated subjects that there is a
significant amount of growth in lower facial height even
after adolescence, which may contribute to lower incisor
irregularity in late adolescents through middle adulthood.41
As such, retention is required to ensure that growth does
not alter the final orthodontic result.
Retention Devices
The Hawley retainer is one of the most commonly used
retainers today.
It consists of a stainless steel labial
bow with adjustment loops at the canines.55
Various
retentive clasps may be utilized in the molar and premolar
regions to enhance retention of the device, which is
especially important if the Hawley retainer is used to
actively move a tooth, such as a rotated incisor.
The wire
extensions from the labial bow and accessory clasps are
embedded in acrylic, which covers the patient’s palate and
further aid in maintenance of the retainer. Hawley
retainers allow for occlusal contact between the maxillary
and mandibular teeth because they do not cover the occlusal
36
surfaces of the teeth.
Following removal of fixed
appliances, patients are typically instructed to wear
removable Hawley retainers full-time for the first few
months, and at nighttime only thereafter.56
Another type of removable retainer, the wrap-around
retainer, consists of a circumferential labial bow with
full coverage acrylic over the palate.57
The design of the
wrap-around retainer is very similar to the Hawley
retainer; however the clasps and labial bow do not cross
over the occlusion, which further enhances interocclusal
contact between the maxillary and mandibular teeth.
The clear overlay retainer, in contrast to the Hawley and
wrap-around retainers, provides full occlusal coverage of
the maxillary and mandibular teeth.
It is fabricated by
vacuum forming a heated plastic sheet over a stone model.58
It is recommended that patients wear the clear overlay
retainer full time for a few months, followed by nighttime
only wear.56
When long term retention is needed in cases with expected
instability, such as severely rotated incisors or large
diastemas, fixed retention is often indicated. Fixed
retainers are usually fabricated from 0.030 round steel
wire which is adapted to the lingual surfaces of the teeth
from canine to canine.
The wire is then either bonded to
37
the lingual surfaces of the canines and rests passively
against the incisors, or is bonded to each tooth from
canine to canine.
Another commonly used appliance is the tooth positioner.
Unlike the previously described retention devices which
hold the teeth in their debanded position, the positioner
is used to move the teeth after the orthodontic appliances
are removed.
This appliance was developed by Kesling, who
believes that by using “functional forces,” which are
generated by chewing exercises, the teeth can be
successfully repositioned into a more ideal occlusion.59
This can only be accomplished if the appliance is properly
worn by the patient and the prescribed clenching exercises
are performed.60
The positioner is fabricated from a model
in which the teeth have been dissected and reset in wax
with improved positions, arch form, axial inclinations, and
occlusion.60
The tooth positioner is then constructed from
the reset models as a single rubber appliance that fits
over the maxillary and mandibular teeth.
The patient is
instructed to perform clenching exercises into the
appliance and, according to Kesling,60
the “resiliency” of
the rubber material allows the teeth to move toward their
new ideal position.
38
The Perfector ® is a newer, modified version of the
positioner. It is fabricated in the same manner as the
positioner; however some changes have been made to its
overall design.
Unlike the positioner, which is made out
of a rubber material, The Perfector ® was made out of
silicone, which, according to the manufacturer, is a more
pliable material.
To increase retention of the device, a
wire bow, seating springs and labial acrylic were added to
the design.
These added features not only help with
retention, but are also thought to aid in controlling
overjet.
While wearing the Perfector ® , the patient must perform
clenching exercises during the day and sleep with it at
night. The protocol is as follows: For the first 2 weeks,
the patient is instructed to perform clenching exercises
for 3-4 hours a day; for the next 4 weeks, the patient is
instructed to perform clenching exercises for 2-3 hours a
day, and; for the final 2 weeks, the patient is instructed
to perform 2 hours of clenching exercises a day.
Throughout, the Perfector ® is worn at night.
Corrections
with the Perfector ® are usually obtained during the first
®
TP Orthodontics, Inc.
.
39
six weeks.61 After 2-3 months of Perfector ® wear, patients
are given Hawley retainers or other, more low profile
retention devices. It has not yet been determined what
occlusal changes occur after the occlusal coverage of the
Perfector ® appliance has been removed.
Post-Orthodontic Occlusion and Retention
Introduction
The nature of orthodontic treatment produces changes in
a patient’s occlusion.
Although most of the changes are
positive, some studies have shown that occlusion is not
ideal immediately following orthodontic treatment and that
the number of occlusal contacts might actually
decrease.17,42,44
Post-orthodontic occlusion studies remain
controversial.
While most indicate that contacts increase
during the retention period,13,18,24,25 some show that there
are no improvements or the occlusion may worsen or regress
to the mean.17,62-64
In addition to holding the teeth in a
desired position, another aim of the retention phase is to
allow settling of the occlusion. The available data suggest
that the amount of settling that occurs during retention is
®
TP Orthodontics, Inc.
40
largely affected by the type of appliance prescribed and
the duration that the appliance is worn.13,18,24,25
Past Studies
The majority of post-orthodontic studies have shown that
occlusal contacts increase during the retention phase.
Post-orthodontic settling typically improves the occlusion
and the interdigitation of the dentition over time.
However, this remains a controversial issue, as other
studies have produced contradictory results.
Various studies support the findings that ideal occlusal
relationships should be established during active
orthodontic treatment and should not be expected to change
during the retention phase.
Sultana et al.65 reported that
occlusal force and occlusal contact area in the total
dental arch significantly increased during retention, due
primarily to increases in the molar region.
These findings
support previous reports showing an increase in the number
of occlusal contacts in the molar region in the retention
phase.25 However, Sultana et al.65 reported no changes in the
occlusal force and occlusal contact area in the premolar
regions during the retention period and after retention.
Therefore, eruption and settling in the premolar region
after orthodontic treatment should not be expected to
41
occur.
If this is true, it suggests that occlusal contacts
in the premolar region should be established during active
orthodontic treatment.
When examining pre-treatment, post-treatment and
post-retention (average of 14.2 years post-treatment)
models of 49 subjects to assess the relationship between
posterior occlusion and post-treatment changes, Parkinson
et al.17 found that the area of actual and near contacts at
or below 300um did not significantly increase during the
post-treatment period.
This indicates that practitioners
should not expect the proximity of posterior occlusal
surfaces to improve post-treatment with long term settling.
A study by Nett and Huang,62 who examined long-term
(minimum 10 years post retention) post-treatment changes,
found a statistically significant improvement in overall
occlusal relationships.
On average, alignment scores
worsened, while scores for marginal ridge, bucco-lingual
inclination, occlusal contacts and overjet criteria all
significantly improved during the post-retention period.
However, based on a sample of 100 subjects, it was
concluded that well finished cases tended to worsen over
time while acceptable or poorly finished cases tend to
improve in the long term, illustrating a regression to the
mean.66
These results are supported by similar findings by
42
Ormiston et al.43
A study by Otuyemi and Jones67 reported
that PAR scores in well treated patients tend to get worse
over time, with only 38% of patients maintaining treatment
results at T3.
However, it has been shown by Weiland68 that
occlusal shifts decrease from T2 to T3, suggesting that
some discrepancies at T2 will diminish in severity by T3.
Dincer et al.26 found that there was an increase in the
number of contacts in “not ideal” locations throughout the
retention period.
These contacts represented one-third of
the total posterior contacts.
They concluded that rather
than expecting the occlusion to settle into correct contact
positions, the occlusion should be finished as close to the
ideal as possible before the orthodontic appliances are
removed.
These findings are supported by Haydar et al.13
who found no major changes in occlusion after orthodontic
treatment.
The findings of these studies suggest that the
final occlusion should be as ideal as possible at the end
of orthodontic treatment and that only minimal changes can
be expected to occur during the retention phase.
Although there are studies that do not demonstrate
increased settling and improved occlusal relationships
during the retention phase, the majority of retention
studies show improvements.
43
Gazit and Lieberman18 measured occlusal contacts on 12
patients between the ages of 14 and 16 years of age who had
been orthodontically treated for approximately 18 months.
Occlusal recordings were taken at debond, one month postdebond, and one year post-debond. Anterior and posterior
occlusal contacts were recorded and analyzed using the
photo-occlusion technique.
Prior to the last recording
(one year), all patients were retainer-free for 3 months.
Importantly, the authors did not report the type of
retention that was used in the study.
Results showed that
there were an average of 11.2 contacts on the day of
debond.
One month later, four patients demonstrated
decreases in the number of contacts and eight demonstrated
increases in number of contacts.
When records were taken
one year after debond, the average number of contacts had
increased to 17.4.
This represents a gain of 6.2 anterior
and posterior contacts. Throughout the study, only 3 of the
12 subjects had anterior contacts.
Similar results were reported by Dincer et al.,26 who
evaluated occlusal contacts of 20 orthodontically treated
patients at debond and after 9 months of retention.
All of
these patients had Class I malocclusion, four premolar
extractions and had been treated with standard edgewise
mechanics. The treatment group was compared to a
44
nontreatment group of 20 subjects with ideal occlusion, who
served as controls.
The treated patients were instructed
to wear the maxillary and mandibular Hawley retainers fulltime for the first six months of retention and then
nighttime only for the last three months of the study.
Occlusal records were taken in centric and eccentric
occlusion with silicone putty (Optosil plus) impression
material. Actual contacts were identified as perforations
in the material and translucent areas were counted as near
contacts.
Using different colors, both actual and near
contacts of the premolar, first molar and second molar
regions were transferred to study models. During the 9
month retention period, a total gain of 7.6 posterior
contacts was reported. Before retention, patients
registered a total number of 11.4 posterior contacts
(actual and near) and at the end of the 9 month retention
period, there were a total of 19 posterior contacts (actual
and near).
The gain of 7.6 posterior contacts during nine
months of retention was considered a significant increase.
However, as previously mentioned, one third of these
posterior contacts occurred in “not ideal” locations.
Not only is it important to evaluate post-orthodontic
occlusion and the gain in occlusal contacts over time, but
it is also important to evaluate if the type of retention
45
device used has an affect on occlusal contacts and posttreatment settling. Durbin and Sadowsky24 accomplished this
by evaluating post-treatment occlusal changes of 38
patients at the time of debond and three months postdebond.
The patients were divided into two groups; 23
patients were given upper and lower Hawley retainers while
the other 15 patients were instructed to wear tooth
positioners.
It is important to note that, due to specific
preferences of the instructors and patient acceptance, the
subjects were not randomly assigned to the two retention
groups. This suggests that there may have been group
differences in the quality of post-orthodontic occlusion.
Occlusal contacts were recorded using polyether rubber
impression bites and the locations of the contacts were
subsequently transferred to study models.
It is also
important to note that areas of near contact were not
measured. They reported that the total number of contacts
in the combined sample increased from 10.11 at the end of
orthodontic treatment to 11.5 during the 3 month post
treatment period, which represents a total increase of
14.1%.
This change was due entirely to an increase in the
number of contacts on posterior teeth, which increased from
8.7 to 10.1, representing a 16.3% increase in posterior
contacts.
Over the three months of retention, the number
46
of anterior teeth in contact and the number of contacts on
the anterior teeth decreased in 37% of the cases.
It was
also shown that those cases with fewer teeth in contact at
the end of treatment developed more contacts over the 3
month post-treatment period.24 The positioner group showed
an increase in posterior contacts from 7.8 to 8.9, which
represented a gain of 1.0 posterior contacts. The posterior
contacts in the Hawley group increased from 9.3 to 10.9,
representing a gain of 1.6 posterior contacts.
When
examining the total number of posterior teeth in contact
before and after 3 months of retention, Durbin and
Sadowsky24 found that the positioner group increased from
9.7 to 10.7 while the Hawley group increased from 10.7 to
11.4.
Although the authors concluded that the group
retained with the tooth positioner demonstrated a greater
gain in the total number of teeth in contact over time and
was statistically more effective than the Hawley retainer
(p<.05), the differences were small.
To evaluate the continued settling of the occlusion,
Razdolsky et al.25 conducted a follow-up study to Durbin and
Sadowsky’s study.24 In addition to recording the actual
contacts, Razdolsky et al.25 also recorded near contacts and
the location of contacts.
Because only 28 of the 38
patients from the original study were available for this
47
follow up study, an additional 12 patients were included.
The retention protocols for this follow-up study varied.
Maxillary Hawley retainers along with mandibular fixed
lingual retainers were worn by 28 patients, tooth
positioners were worn by 3 patients who then changed to a
maxillary Hawley retainer, 8 patients wore maxillary and
mandibular Hawley retainers and one patient wore a
maxillary retainer only.
Following the removal of
orthodontic appliances, the patients were instructed to
wear the retainers full-time for the first 6 to 12 months
and then at night only. The study did not compare the
different retention devices and their effects on occlusal
contacts. Occlusal bite registrations were taken using
polyether rubber impression material at two timepoints; T1
was within two hours after removal of fixed appliances and
T2 was obtained after approximately 21 months of retention.
The time between T1 and T2 ranged from 11 to 28 months.
The number of actual and near contacts on the second
molars, first molars, premolars, canines and incisors were
registered by positioning the polyether bite registrations
on a radiographic viewing screen in a dark room.
Areas of
actual contact were counted as perforation in material and
were transferred to a study model with red marker, while
the areas of near contacts were counted as a change in the
48
registration material from yellow to transparent white, and
were transferred onto the models with a black marker.
From
the day of debond (T1) to the follow up visit an average of
21 months later/(T2), the total number of contacts (actual
and near) increased from 36.6 to 58.2, showing a total
increase of 21.6 total contacts.
This overall gain in
occlusal contacts can be explained as an increase in the
number of actual and near contacts on the posterior teeth.25
Haydar et al.13 also compared the tooth positioner to the
Hawley retainer. Twenty patients were equally divided into
two groups, a Hawley group and a Positioner group, and were
compared to a control group of 10 subjects with normal
occlusion. It was not stated whether the subjects were
randomly assigned to their respective retention groups.
Anterior and posterior contacts were registered at the end
of active orthodontic treatment (T1) and 3 months into the
retention period (T2) by having patients bite down into a
silicone-based impression material.
These bite
registrations were then held up to daylight, the number of
contacts were counted, and the perforations were
transferred to maxillary casts.
At T1, the total number of
contacts was 21.2 for the Hawley group, 24.8 for the
Positioner group and 39.4 for the control group.
The mean
number of contacts at T2 was 22.4 for the Hawley group,
49
27.0 for the Positioner group and 40.5 for the control
group, resulting in a gain of 2.2 contacts in the
positioner group and 1.2 contacts in the Hawley group.
However, the authors reported that there were no
statistically significant differences between the Hawley
and positioner groups with regard to the increase of
contacts, concluding that there were no group differences
based on post-orthodontic occlusion.
The Hawley retainer has also been compared to the clear
overlay retainer based on changes in the number of occlusal
contacts following orthodontic treatment.
Sauget et al.27
examined 30 patients who were randomly assigned at the time
of appliance removal into either the Hawley group or the
clear overlay retainer group. Occlusal bite registrations
in maximum intercuspation were taken with vinyl
polysiloxane at three timepoints; at the time of debond
(T1), at retainer delivery 1 week post-debond (T2), and
after three months of retention (T3).
Occlusal contacts
were evaluated and classified as follows; contacts were
defined as actual perforations in the material while near
contacts appeared as thin translucencies and had a material
thickness of 0.20 mm or less.
contacts were evaluated.
Both anterior and posterior
At the time of debond (T1), the
Hawley group had a total of 34.3 contacts (actual and near,
50
anterior and posterior) while the clear overlay retainer
group had a total of 31.8 contacts.
One week later, at the
time of retainer delivery (T2), there were no significant
differences between the two retainer groups. After three
months of retention (T3), there were 45.7 total contacts in
the Hawley group and 36.7 total contacts in the clear
overlay retainer group.
Based on
posterior contacts only
(actual and near), there was a reported change in the
Hawley group from 25.3 at T1 to 35.9 contacts at T3 and a
change in the clear overlay retainer group from 23.7 at T1
27.9 at T3.
It was concluded that, when compared to the
clear overlay retainer, the Hawley retainer allowed more
settling of the occlusion during the retention phase.
These findings suggest that if one of the objectives of
retention is to allow for relative vertical tooth eruption
and settling, particularly in the posterior teeth, a Hawley
retainer should be prescribed, as the clear overlay
retainers tend to hold the teeth in their debond position.
These differences between the Hawley and clear overlay
retainer were statistically significant.
Basciftci et al.69 conducted a study comparing a modified
wraparound Hawley retainer to the Jenson plate.
This was a
follow up study to evaluate the number of contacts in
centric occlusion during a 1-year retention period in
51
subjects using two different retention protocols.
In this
study, 20 patients received modified wraparound Hawley
retainers and 20 patients received maxillary Jensen plates
along with a mandibular fixed retainer. A Jensen plate
consists of a removable palatal plate of acrylic with cclasps on the second molars and an outer labial bow
extending between the lateral incisors.
Due to the fact
that some clinicians in the postgraduate clinic had a
preference between retention devices, the patients were not
randomly assigned to their retention groups. Patients were
instructed to wear the retainers full time for 6 months and
then nighttime only for the next six months.
The two
retention groups were also compared to a control group of
20 subjects with normal occlusions.
Occlusal bite
registrations were taken with Zeta plus, a soft siliconebased impression material, at the following timepoints; In
the treated groups, T1 was taken within 2 hours after
debond and T2 was obtained approximately 14 months later.
In the control sample, the two sets of occlusal records
were taken 12 months apart. Occlusal records were taken by
having the patient bite into the silicon based impression
material in maximum intercuspation for one minute.
The
interocclusal bite registration was held up to a light box
to view the occlusal contacts.
52
Actual contacts were
identified as perforations in the bite registration that
let the light through, and thin, transparent areas that did
not perforate the material were recorded as near contacts.
After the contacts were classified, they were transferred
to a model of the maxillary teeth.
At each of the two
timepoints, the following variables were recorded from the
study models:
total number of contacts (actual and near),
number of actual contacts on second molars, first molars,
premolars, canines, and incisors; and the number of near
contacts on the previously mentioned teeth.
Results of the
study indicate that when compared to the control group,
total and posterior contacts (actual and near) increased
during the retention period.
In the Hawley group, there
were statistically significant increases in actual contacts
on the second molars, near contacts on the premolars, and
total contacts on the first molars and premolars.
In the
maxillary Jensen plate and mandibular fixed retainer group,
there were statistically significant increases in actual
contacts on the first molars, second molars, premolars and
canines, and total contacts on the first and second molars.
The control sample demonstrated slight occlusal changes
which may have been due to growth and development.
Overall, Basciftci et al.69 concluded that both retention
protocols allow settling of the occlusion and that no
53
statistically significant differences exist between the
groups.
Horton et al.1 evaluated the short term changes in
posterior occlusion when 50 patients were given either a
Hawley retainer or a Perfector ® and mandibular spring
aligner. Patients who had full orthodontic treatment were
randomly assigned to one of the two retention groups.
Objective and subjective measures were taken at two
timepoints: the day the retainers were delivered (T1) and
approximately two months later (T2). To quantify posterior
areas of contact (less than 50um) and near contact (50350um), occlusal bite registrations were taken with Blu
Mousse at both timepoints.
Each occlusal bite registration
was scanned and traced using Image Tool software. It was
shown that in the Hawley group, areas of contact and near
contact (ACNC) was 6.7 mm2 at T1 and 11 mm2 at T2.
ACNC for
the Perfector ® /Spring Aligner group were 8.4 mm2 at T1 and
13 mm2 at T2. There were statistically significant increases
in ACNC in both the Hawley and Perfector ® retention groups
after two months.
To assess the patient’s perception of
occlusion, a seven item questionnaire was given at both
timepoints.
®
Results from this qualitative analysis showed
TP Orthodontics, Inc.
54
that patients who wore the Perfector ® /Spring aligner
retainers reported significantly greater improvements in
how well their back teeth fit together, how well they could
chew tough meats, and how much pain they felt when biting
down.1
It was concluded by Horton et al.1 that there were
no differences between the Hawley and Perfector ® retainers
in terms of post-orthodontic settling.
similar amounts of improvement.
Both produced
However, patients wearing
the Perfector ® perceived greater and more beneficial
occlusal changes over time.
Overall, these studies tend to show conflicting
results on post-orthodontic changes, indicating the need
for further research in this area.
Conclusion
Various studies have evaluated post-orthodontic occlusion
and the effects of different retention devices.
However,
these studies use varying methods to record and measure
occlusal contacts. Some of these methods have proven to be
more reliable than others. Considering the differences in
protocol among the studies, it is difficult to draw
55
concrete conclusions. Only broad statements regarding postorthodontic settling and the affects of different retention
devices can be made.
These include that: 1) during the
retention phase of treatment the number of posterior
occlusal contacts tend to increase and 2) contacts increase
for several months after removal of fixed appliances and 3)
different types of retention devices may have different
effects on post-orthodontic occlusion and settling.
It is currently not clear what happens after the
Perfector ® patients are given Hawley retainers.
As stated
earlier, the patient is instructed to perform chewing
exercises for several hours a day and then sleep with the
Perfector ® at night.
This process is supposed to align the
teeth into a more ideal position, which should result in
increased occlusal contacts.
However, the Perfector ® by
design has occlusal coverage which may inhibit actual
settling.
There has not been a study examining what
happens to the amount of settling after the Perfector ®
patient is given a Hawley retainer.
With proper use of the
Perfector ® , the teeth, in theory, have been moved into a
more ideal position.
®
By removing the occlusal coverage of
TP Orthodontics, Inc.
56
the Perfector ® , there is a possibility that the teeth will
then be able to further settle, and in turn produce
increased occlusal contacts months later.
There have been
no studies comparing the effects of Hawley and Perfector ®
retainers months after both groups are given identical
Hawley retainers.
There is a possibility that although
there were no apparent differences initially, the Perfector ®
group may provide better occlusion in the long run.
Knowing the nature of occlusal changes over time and the
qualitative and quantitative differences between the Hawley
and Perfector ® retainers will assist the orthodontist in
making an informed decision when prescribing his or her
retention protocol.
The goal of this follow-up study is to further
investigate whether and how the retention device used after
active orthodontic treatment affect posterior occlusion
after two different retention groups (Perfector ® and Hawley)
are given identical Hawley retainers at two months and are
assessed six and eight months post-debond.
Occlusal bite
registrations of silicone-based impression material will be
analyzed using optical scanning and Image Tool software to
assess the differences in 1) area of occlusal contacts
®
TP Orthodontics, Inc.
57
(actual and near contacts) at eight months post-debond, 2)
differences in settling between the Hawley and Perfector ®
groups after both retention groups are given identical
retainers, and 3) patient perception of occlusion.
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TP Orthodontics, Inc.
58
References
1. Horton J, Buschang P, Behrents R, Oliver D (in press). Comparison of the effects of a
hawley and perfector/spring aligner retainers on post orthodontic occlusion . Am J
Orthod Dentofacial Orthop.
2. Angle E. Treatment of malocclusion of the teeth and fractures of the maxillae.
Philadelphia: SS White Dental Manufacturing; 1900.
3. Tweed C. Indications for the extraction of teeth in orthodontic procedures. Am J
Orthod 1944;30:405-408.
4. Andrews LF. The six keys to normal occlusion. Am J Orthod 1972;62:296-309.
5. Okeson J. Management of temporomandibular disorders and occlusions. St. Louis: CV
Mosby; 2003.
6. Sarver D, Proffit W, Ackerman J. Diagnosis and treatment planning in orthodontics.
In: Graber T, Vanarsdall R, editors. Orthodontics; current principles and techniques. St.
Louis: Mosby; 2000.
7. Roth RH. Functional occlusion for the orthodontist. J Clin Orthod 1981;15:32-40, 4451
8. McHorris WH. Occlusion with particular emphasis on the functional and
parafunctional role of anterior teeth. Part 2. J Clin Orthod 1979;13:684-701.
9. Beyron H. Occlusal relations and mastication in Australian Aborigines. Acta Odontol
Scand 1964;22:597-678.
10. Costalos P, Sarraf K, Cangialosi T, Efstratiadis S. Evaluation of the accuracy of diital
model analysis for the American Board of Orthodontics objective grading system for
dental casts. Am J Orthod Dentofacial Orthop 2005;128:624-629.
59
11. Casko J, Vaden J, Kokich V, Domone J, James R, Cangialosi T. Objective grading
system for dental casts and panoramic radiographs. Am J Orthod Dentofacial Orthop
1998;114:589-599.
12. Ricketts RM. Occlusion--the medium of dentistry. J Prosthet Dent 1969;21:39-60.
13. Haydar B, Ciger S, Saatci P. Occlusal contact changes after the active phase of
orthodontic treatment. Am J Orthod Dentofacial Orthop 1992;102:22-28.
14. Moller E, Bakke M. Occlusal harmony and disharmony: frauds in clinical dentistry?
Int Dent J 1988;38:7-18.
15. Clark JR, Evans RD. Functional occlusion: I. A review. J Orthod 2001;28:76-81.
16. Millstein P, Maya A. An evaluation of occlusal contact marking indicators. A
descriptive quantitative method. J Am Dent Assoc 2001;132:1280-1286; quiz 1319.
17. Parkinson CE, Buschang PH, Behrents RG, Throckmorton GS, English JD. A new
method of evaluating posterior occlusion and its relation to posttreatment occlusal
changes. Am J Orthod Dentofacial Orthop 2001;120:503-512.
18. Gazit E, Lieberman MA. Occlusal contacts following orthodontic treatment.
Measured by a photocclusion technique. Angle Orthod 1985;55:316-320.
19. Carossa S, Lojacono A, Schierano G, Pera P. Evaluation of occlusal contacts in the
dental laboratory: influence of strip thickness and operator experience. Int J Prosthodont
2000;13:201-204.
20. Gazit E, Fitzig S, Lieberman MA. Reproducibility of occlusal marking techniques. J
Prosthet Dent 1986;55:505-509.
21. Maness WL, Benjamin M, Podoloff R, Bobick A, Golden RF. Computerized occlusal
analysis: a new technology. Quintessence Int 1987;18:287-292.
22. Lyons MF, Sharkey SW, Lamey PJ. An evaluation of the T-Scan computerised
occlusal analysis system. Int J Prosthodont 1992;5:166-172.
60
23. Hsu M, Palla S, Gallo L. Sensitivity and reliability of the T-scan system for occlusal
anaysis. J Craniomandib Disord Facial Oral Pain 1992;6:17-23.
24. Durbin DS, Sadowsky C. Changes in tooth contacts following orthodontic treatment.
Am J Orthod Dentofacial Orthop 1986;90:375-382.
25. Razdolsky Y, Sadowsky C, BeGole EA. Occlusal contacts following orthodontic
treatment: a follow-up study. Angle Orthod 1989;59:181-185; discussion 186.
26. Dincer M, Meral O, Tumer N. The investigation of occlusal contacts during the
retention period. Angle Orthod 2003;73:640-646.
27. Sauget E, Covell DA, Jr., Boero RP, Lieber WS. Comparison of occlusal contacts
with use of Hawley and clear overlay retainers. Angle Orthod 1997;67:223-230.
28. Julien KC, Buschang PH, Throckmorton GS, Dechow PC. Normal masticatory
performance in young adults and children. Arch Oral Biol 1996;41:69-75.
29. Owens S, Buschang PH, Throckmorton GS, Palmer L, English J. Masticatory
performance and areas of occlusal contact and near contact in subjects with normal
occlusion and malocclusion. Am J Orthod Dentofacial Orthop 2002;121:602-609.
30. Sakaguchi RL, Anderson GC, DeLong R. Digital imaging of occlusal contacts in the
intercuspal position. J Prosthodont 1994;3:193-197.
31. Wright PS. Image analysis and occlusion. J Prosthet Dent 1992;68:487-491.
32. Yurkstas AA. The Masticatory Act. a Review. J Prosthet Dent 1965;15:248-262.
33. Yurkstas AA, Manly R. Measurement of occlusal contact area effective in
mastication. Am J Orthod 1949;35:185-195.
34. Toro A, Buschang PH, Throckmorton G, Roldan S. Masticatory performance in
children and adolescents with Class I and II malocclusions. Eur J Orthod 2006;28:112119.
35. English JD, Buschang PH, Throckmorton GS. Does malocclusion affect masticatory
performance? Angle Orthod 2002;72:21-27.
61
36. Henrikson T, Ekeberg E, Nilner M. Masticatory efficiency and ablility in relation to
occlusion and mandibular dysfunction in girls. Int J Prosthodont 1998;11:125-132.
37. Omar SM, McEwen JD, Ogston SA. A test for occlusal function. The value of a
masticatory efficiency test in the assessment of occlusal function. Br J Orthod
1987;14:85-90.
38. Ikebe K, Matsuda K, Morii K, Furuya-Yoshinaka M, Nokubi T, Renner R.
Association of masticatory performance with age, posterior occlusal contacts, occlusal
force and salivary flow in older adults. Int J Prosthodont 2006;19:475-481.
39. Bakke M, Holm B, Jensen BL, Michler L, Moller E. Unilateral, isometric bite force in
8-68-year-old women and men related to occlusal factors. Scand J Dent Res
1990;98:149-158.
40. Ingervall B, Minder C. Correlation between maximum bite force and facial
morphology in children. Angle Orthod 1997;67:415-422; 423-414.
41. Driscoll-Gilliland J, Buschang PH, Behrents RG. An evaluation of growth and
stability in untreated and treated subjects. Am J Orthod Dentofacial Orthop
2001;120:588-597.
42. Deng Y, Fu MK. Occlusal contact changes before and after orthodontic treatment of a
group of child & adolescent patients with TMJ disturbance. Aust Orthod J 1995;13:231237.
43. Ormiston J, Huang G, Little R, Decker J, Seuk G. Retrospective analysis of long-term
stable and unstable orthodontic treatment outcomes. Am J Orthod Dentofacial Orthop
2005;128:568-574.
44. Fleming J. An analysis of variability in Class I non-extraction treatment outcomes in
a resident clinic using the American Board of Orthodontics Objective Grading System.
Masters Thesis. Saint Louis: Saint Louis University; 2006.
45. Abei Y, Nelson S, Amberman B, Hans M. Comparing orthodontic treatment outcome
between orthodontists and general dentists with the ABO index. Am J Orthod Dentofacial
Orthop 2004;126:544-548.
62
46. Deguchi T, Honjo T, Fukunaga T, Miyawaki S, Roberts W, Takano-Yamamoto T.
Clinical assessment of orthodontic outcomes with the peer assessment rating, discrepancy
index, objective grading system, and comprehensive clinical assessment. Am J Orthod
Dentofacial Orthop 2005;127:434-443.
47. Djeu G, Shelton C, Maganzini A. Outcome assessment of Invisalign and traditional
orthodontic treatment compared with the American Board of Orthodontics objective
grading sytem. Am J Orthod Dentofacial Orthop 2005;128:292-298.
48. Yang-Powers L, Sadowsky C, Rosenstein S, BeGole E. Treatment outcome in a
graduate orthodontic clinic using the American Board of Orthodontics grading system.
Am J Orthod Dentofacial Orthop 2002:451-455.
49. Cook M. Evaluation of Board-certified orthodontist's sequential finished cases with
the ABO objective grading system. Masters Thesis. Saint Louis: Saint Louis University;
2003.
50. Binder RE. Retention and post-treatment stability in the adult dentition. Dent Clin
North Am 1988;32:621-641.
51. Reitan K. Principles of retention and avoidance of posttreatment relapse. Am J
Orthod 1969;55:776-790.
52. Riedel RA. A review of the retention problem. Angle Orthod 1960;30:179-199.
53. Behrents R. A treatise on the continuum of growth in the aging craniofacial skeleton:
University of Michigan Center for Human Growth and Development; 1984.
54. Nanda RS, Nanda SK. Considerations of dentofacial growth in long-term retention
and stability: is active retention needed? Am J Orthod Dentofacial Orthop 1992;101:297302.
55. Hawley C. A removable retainer. Int J Orthod 1919;5:291-298.
56. Lindauer SJ, Shoff RC. Comparison of Essix and Hawley retainers. J Clin Orthod
1998;32:95-97.
57. Collett T. A rationale for removable retainers. J Clin Orthod 1998;32:667-669.
63
58. Ponitz RJ. Invisible retainers. Am J Orthod 1971;59:266-272.
59. Kesling H. The tooth positioner as the means of final positioning of teeth to a
predetermined pattern. J Dental Child 1944;11:103-105.
60. Kesling H. The philosophy of the tooth positioning appliance. Am J Ortho and Oral
Surg 1945;31:297-304.
61. TP Orthodontics. La Porte, Indiana.
62. Nett BC, Huang GJ. Long-term posttreatment changes measured by the American
Board of Orthodontics objective grading system. Am J Orthod Dentofacial Orthop
2005;127:444-450.
63. Otuyemi O, Jones S. Long term evaluation of treated Class II Division I
malocclusions utilizing the PAR index. Br J Orthodont 1995;22:171-180.
64. Ormiston J, Huang G, Little R, Decker J, Seuk G. Retrospective analysis of long-term
stable and unstable orthodontic treatment outcomes. Am J Orthod Dentofacial Orthop
2005;128:568-574.
65. Sultana M, Yamada K, Hanada K. Changes in occlusal force and occlusal contact
area after active orthodontic treatment: a pilot study using pressure-sensitive sheets.
Journal of Oral Rehabilitation 2002;29:484-491.
66. Nett BC, Huang GJ. Long-term posttreatment changes measured by the American
Board of Orthodontics objective grading system. Am J Orthod Dentofacial Orthop
2005;127:444-450.
67. Otuyemi O, Jones S. Long term evaluation of treated Class II Division I
malocclusions utilizing the PAR index. Br J Orthodont 1995;22:171-180.
68. Weiland F. The role of occlusal discrepancies in the long-term stability of the
mandibular arch. Eur J Orthod 1994;16:521-529.
64
69. Basciftci FA, Uysai T, Sari Z, Inan O. Occlusal contacts with different retention
procedures in 1-year follow-up period. Am J Orthod Dentofacial Orthop 2007;131:357362.
65
CHAPTER 3:
JOURNAL ARTICLE
Abstract
Purpose:
To characterize post-orthodontic settling of the
posterior occlusion by comparing patients wearing Hawley
retainers against patients initially wearing Perfector
retainers and then switching to Hawley retainers. Methods:
This follow-up study was based on 40 patients (25 Perfector
and 15 Hawley) evaluated at four time points over eight
months.
They were part of a larger sample of 50 patients
randomly assigned to wear either Hawley or Perfector
retainers. The Perfector/Hawley patients were given Hawley
retainers two months post-debond.
Objective and subjective
measures were collected at the end of treatment (T1), two
months post debond (T2), six months post-debond (T3) and
eight months post-debond (T4).
Occlusal bite registrations
were scanned and traced to quantify posterior areas of
contact and near contact (ACNC).
A seven-item
questionnaire was used to assess the patient’s perception
of occlusion.
Results: ACNC increased during the first six
months of retainer wear. Both the Hawley and
Perfector/Hawley groups showed the greatest rates of
increase in ACNC between T1-T2. Overall, the Hawley group
showed a 129% increase in ACNC, while the Perfector/Hawley
66
group showed a 104.9% increase in ACNC over eight months of
retention.
While the Hawley group showed greater increases
in ACNC from T2-T3 and the Perfector/Hawley group showed
slightly greater increases from T3-T4, overall group
differences were not statistically significant.
While the
Perfector/Hawley group perceived greater improvements in
their occlusion than the Hawley group, group differences
after eight months were small and related to the changes
that occurred during the first two months of retention.
Conclusions: Settling occurred at decelerating rates until
six months after which they stabilized.
No significant
differences in ACNC were found between the Hawley and
Perfector/Hawley groups after eight months of retainer
wear.
Introduction
Achieving an ideal posterior occlusion is an important
outcome of orthodontic treatment.
Posterior occlusion
pertains to the relationships between cusp tips and their
opposing central fossa and marginal ridges.1
These
relationships are important because the posterior teeth
establish and maintain the vertical dimension of occlusion
and are designed to withstand the heavy forces of
mastication.1 Posterior occlusal contact area has been shown
67
to be among the most important factors determining
masticatory performance.2-5
relatively small,
Occlusal contact area, albeit
represents the most important fraction
of the total area involved in mastication.2
This explains
why subjects with normal occlusion are able to break down
foods more efficiently than subjects with malocclusion.6,7
Good intercuspation and occlusal contacts may also be
essential for stable orthodontic results, especially for
maintaining overbite and overjet.8,9
Furthermore, the
location of contacts in intercuspation is one of the main
factors responsible for stabilization of the mandible;
failure to provide adequate centric stops may cause
occlusal instability.9
Our understanding of posterior occlusion during the
retention phase of orthodontic treatment remains limited.
While most studies indicate that contacts increase and that
occlusion improves,10-14 some studies show that there are no
improvements, others show that the occlusion worsens, and
some show that occlusion regresses to the mean.8,15-17 Because
most studies have evaluated posterior occlusion at only two
timepoints, the patterns of occlusal change that occur
remain unknown.
Does the settling occur rapidly; does it
increase at a regular rate; when might settling be expected
to stop?
It is also controversial how the type of
68
retention device used affects post-orthodontic settling.
Sauget et al.18 reported that Hawley retainers allowed more
settling of the occlusion than clear overlay retainers
after three months of retention.
In contrast, Basciftci et
al.14 found no differences in the number of posterior
occlusal contacts between Hawley retainers and the Jenson
plate 1 year post-treatment. Based on changes in the number
of occlusal contacts three months post-debond,
Durbin and
Sadowsky12 reported significantly more settling with the
active positioner retainers than with passive Hawley
retainers; Haydar and coworkers10 found no differences
between these two retainers over the same time period.
The controversies pertaining to post-orthodontic
occlusion may relate to the study designs.
First, most
studies could not adequately control for selection bias
because patients have not been randomly assigned to their
respective retention groups. For instance, Durbin and
Sadowsky12 allocated subjects to either the Hawley or
positioner groups depending on the preferences of the
instructors and patient acceptance.
Both factors could
introduce group differences in the quality of postorthodontic occlusion.
Furthermore, most studies have used
counts or visual assessments of occlusal contacts, which
69
might be expected to be less discriminating than areas of
occlusal contact and near contact(ACNC).6,7,19,20
In a recent randomized controlled trial, Horton et al19
found no differences in ACNC between patients wearing
Perfector or Hawley retainers, but their study was limited
to two months.
It remains unknown whether ACNC change when
patients switch from active Perfector ® retainers to passive
retainers, as they commonly do after two or three months.
Comparisons of active and passive retainers are important
for determining whether noticeable treatment effects are
limited to the anterior dentition only, or if they produce
differences in posterior occlusion as well.
Based on the foregoing, a follow-up study was designed
to evaluate the long-term occlusal changes that occurred
for the patients evaluated by Horton et al.19
this are twofold:
The goals of
1) to evaluate the time-course of the
occlusal changes that occur over the first eight months of
retention, and 2) to determine if the posterior occlusion
of patients who switch from the Perfector to the Hawley
retainers after two months differs from the occlusion of
patients who wore only Hawley retainers for eight months.
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Materials and Methods
Fifty subjects who had completed full orthodontic
treatment to class I molar and canine relationships were
recruited by Horton et al.19
Subjects were excluded if they
had any history of temporomandibular dysfunction, large
restorations on the posterior teeth, allergies to any
materials used in the study, periodontal disease and/or
muscular dysfunction or if they were non-compliant with
retainer wear.19
They were randomly assigned, with 22
receiving Hawley retainers (9 males and 13 females) and 28
patients receiving Perfector/Spring Aligners (13 males 15
females) and followed for two months. Forty-four patients
completed the first part of the study and consented to
participate in this follow-up study, which lasted for an
additional six months.
Due to patient dropout and missed
appointments, 40 patients completed the second part of the
study, including 25 patients (11 males and 14 females)
originally assigned to the Perfector/Spring aligner group
and 15 patients (5 males and 10 females) assigned to the
Hawley group.
The Hawley group wore the same retainers throughout the
eight month observation period.
After the first two
months, maxillary and mandibular alginate impressions were
taken for each of the subjects in the Perfector group and
71
Hawley retainers were delivered within two weeks. This
group (Perfector/Hawley) was instructed to wear the
maxillary and mandibular Hawley retainers full-time for the
duration of the follow-up study.
Data were collected at four timepoints: Immediate posttreatment (T1),two month post-debond (T2), 6 months postdebond (T3), and 8 months post-debond (T4). At each
timepoint, duplicate bilateral posterior occlusal bite
registrations were taken in maximum intercuspation using
Blu Mousse,® a silicone impression material (Parkell BioMaterials, Farmingdale, NY).
The Blu Mousse® was applied to the occlusal surfaces of
the mandibular premolars and first molars and the patient
was instructed to bite firmly on their back teeth for 30
seconds.10,18,19
Using a holder, each registration was placed
in a standardized position and scanned at 300 DPI with the
mandibular occlusal surfaces facing downward.
The
mandibular premolars and first molars on the scanned image
were traced using Image Tool® (University of Texas Health
Science Center, San Antonio) software, which calculated the
platform area of the outlined teeth and the frequency
distribution of pixels within the platform area based on
256 possible gray scales.
Because all methods and
72
procedures were the same, the calibration curve developed
by Horton et al.19 was used to establish the relationship
between the 256 gray scales and ACNC at thicknesses ranging
from 0μm to 350μm. The upper limit for scanned light
penetration through the impression was approximately 400µm.
The thicknesses were recorded in increments of 50µm, with
0-50µm representing contacts and the other increments
representing areas of near contacts.
Patient perception of occlusion was assessed using the
seven item questionnaire developed by Horton et al19 to
measure how well their teeth fit together, their level of
occlusal discomfort, and their masticatory function.
A
148mm visual analogue scale was used with the following
seven questions:
Q1.
How well do your back teeth fit together when
you bite down hard?
Q2.
Do your back teeth contact each other evenly when
you bite down hard?
Q3.
How well can you chew tough meats, such as steak
or chops, with your back teeth?
Q4.
How well can you chew fresh vegetables, such as
carrots or celery, with your back teeth?
Q5.
How much pain do you feel when you bite down hard
on your back teeth?
73
Q6.
How much discomfort do you experience when you
bite down hard on your back teeth?
Q7.
When you bite down hard, do you feel your back
teeth slide?
The terms “very well” or “very poor”, “none” or “very
much”, and “no slide” or “large slide” served as anchors
for the visual analogue scale.
Statistical Analysis
Based on their skewness and kurtosis, the variables
showed significant (p<.05) departures from normality.
As
such, they were described by medians (50th percentile) and
interquartile ranges (25th and 75th percentiles). Wilcoxon
signed ranks tests evaluated changes over time; the MannWhitney U was used to compare the two retainers.
Results
Hawley Group:
Wilcoxon signed ranks tests showed significant (p<.05)
increases in ACNC with Hawley retainers between T1-T2 and
T2-T3 for all thickness intervals except 50-100 um (Tables
74
1 &2; Figure 1). The changes that occurred after 6 month
(i.e. T3-T4) were not statistically significant. The
greatest overall absolute increase (1.49 mm2) in ACNC
occurred between T2-T3 at the 300-350 um interval.
The
majority of changes in ACNC occurred during the first six
months. At the 350um level the total cumulative ACNC
increased from 7.01 mm2 immediately post-treatment to 10.7
mm2 at T2, to 16.6 mm2 at T3, to 16.0 mm2 at T4, with all
changes being significant (p<.05) except those from T3-T4
(Table 2, Figure 1). At the thinnest ACNC (<150 um),
increases tended to be greater from T1-T2, while they
tended to be greater at the thickest (>300 um) ACNC from
T2-T3 (Figure 1).
Perfector/Hawley Group:
The Perfector/Hawley group showed increases in ACNC
similar to those of the Hawley group. Increases in ACNC
were significant (p<.05) at all thickness levels between
T1-T2 and T2-T3.
The Perfector/Hawley group also showed
small but significant increases in ACNC > 200 um from T3-T4
(Table 2). Increases were greatest from T1-T2 at the 300350 um level, with an increase of 0.74 mm2. The total
cumulative ACNC increased from 8.3 mm2 at T1, to 13.2 mm2 at
T2, to 16.3 mm2 at T3, and to 17.0 mm2 at T4 (Figure 2). The
75
cumulative increases in ACNC were significant at all levels
between T1-T2 and T2-T3.
Group Comparisons:
Absolute and cumulative ACNC showed no significant
group differences at any of the four time points (Table 1).
Changes in ACNC were significantly greater between T2-T3
for the Hawley than for the Perfector/Hawley at the 200-250
um, 250-300um and 300-350 um levels (Table 2).
In
contrast, the Perfector/Hawley showed significantly greater
increases in contact areas (<50µm) between T3-T4.
Cumulative changes in areas of near contact showed no
significant group differences. Even though there was a
tendency for the Hawley group to show greater increases
than the Perfector/Hawley group in absolute (Figure 3) and
cumulative areas (Figure 4) of near contact between T1-T4,
the differences were not statistically significant.
Questionnaire Data:
The only significant (p=0.035) change of perception
for the patients in the Hawley group occurred between T2-T3
for Q6, indicating that they experienced increased
discomfort when they bit down hard on their back teeth.
The Perfector/Hawley group showed significant improvements
76
from T1-T2 in how well their back teeth fit together
(Q1;p=.001), how well their back teeth contact each other
when they bite down hard (Q2;p=.012) and how well they can
chew tough meats with their back teeth (Q3;p=.026). From
T3-T4, the Perfector/Hawley patients also perceived less of
a slide when they bit on their back teeth (p=.026;Q7).
From T1-T4 Perfector/Hawley patients showed significant
(p<.05) improvements in all questions except Q5.
At the time of debond (T1), the Perfector/Spring
Aligner group perceived significantly more difficulty
chewing tough meats (Q3;p=.029)and more pain when
biting(Q5;p=.004)than the Hawley group (Table 3). The only
other significant group difference at the other time points
was at T4, with the Perfector/Hawley group reporting
significantly more pain when biting (Q5;p=.047)than the
Hawley group.
With respect to the changes in perception over time
(Table 4), the Perfector/Hawley group perceived greater
improvements than the Hawley group from T1-T2 in how well
their back teeth fit together (Q1;p=.009), how well they
could chew tough meats (Q3;p=.021), and how much pain they
felt when they bite down (Q5;p=.025).
The only other
significant (p<.05) group difference occurred from T1-T4,
with the Perfector/Hawley group showing greater
77
improvements in how well their back teeth fit together
(Q1;p=.026).
Discussion
The Hawley group demonstrated a substantial settling
during the first six months of retention. ACNC increased
from 7.0mm² to 16.6mm²,representing an increase of over
130%.
The changes were greatest at the thicker levels of
near contact and least at the level of contacts (Figure 3).
The increases observed are substantially larger than
previously reported for Hawley retainers, which range from
6%-67%.10,12,18,21
The differing results can be partially
explained by the duration of time that the patients were
followed. Most retention studies of shorter duration (3
months or less) have reported increases ranging from only
6% to 42%.10,12,18 In contrast, Gazit and Lieberman11 reported
a 55% gain in anterior and posterior contacts over one year
while Dincer et al.21 reported a 67% gain of posterior ACNC
over nine months. In addition, the different methods used
to measure posterior occlusion could explain some of the
variability across studies. Horton et al,19 showed an
overall increase in posterior ACNC of 63% over two months,
which is substantially higher than relative increases based
on counts over comparable time periods.10,12,18
78
This suggests
that ACNC are more discriminating for evaluating posterior
occlusion than counting the number of contacts and near
contacts.
The Perfector/Hawley group also demonstrated
substantial increases in settling over the first eight
months of retention, with ACNC increasing over 104%. The
changes were also greater at the thicker levels of near
contact and least at the level of contacts (50 µm)(Figure
3). The overall increases observed were again substantially
greater than previously reported.
Haydar et al.10 reported
a 9% gain in anterior and posterior ACNC after three months
of positioner wear; Durbin and Sadowsky12 reported a 14%
gain in posterior occlusal contacts after three months of
retention; Horton et al.19 reported a 53% increase in
posterior ACNC after two months of Perfector wear.
The
differences between studies may again be explained by the
different methods used to evaluate posterior occlusion and
the study duration. The differences could also be partially
due to the materials used. The Perfector appliance is
fabricated from silicone material, which is a softer, more
pliable material than the rubber used to fabricate the
tooth positioner.
The added resiliency may increase the
movements of the teeth under functional forces, resulting
in a gain in posterior contacts.
79
The Perfector’s seating
springs and a labial bow may have also led to increased
amount of settling.
The rates of increase in ACNC for both the Hawley and
Perfector retainers were greater from T1-T2 than T2-T3.
In
other words, ACNC increased at decelerating rates until six
months, after which they stabilized (Figure 1 and 2). It is
possible that rates were greater during the second two
months than during the third two months, but the data do
not allow such a comparison. Unfortunately, there are no
longitudinal data with multiple observations available for
comparison.
The decreasing rates of settling observed may
be explained by the law of diminishing returns. Immediately
after debond, the teeth are the furthest away from their
“settling” point, and therefore have a further distance to
potentially move. In other words, the greatest potential
for increasing ACNC is when braces are initially removed;
as ACNC decrease, their potential to increase decreases
proportionately.
This may explain why the majority of
settling was observed early in the retention phase, and
also why the majority of increases occurred at the thicker
near contact level (350µm).
It was hypothesized at the beginning of the study
that the Perfector group would show a greater amount of
settling after the occlusal coverage of the Perfector was
80
no longer present.
There was a tendency for the Hawley
group to show greater increases in ACNC during the first
six months, while the Perfector/Hawley group tended to show
greater increases during the last two months. In fact, the
Perfector/Hawley group showed significant changes between
T3 and T4 at thickness levels >200um, while the Hawley
showed no changes over the same time period. Over the same
time periods, the Perfector/Hawley group also showed
significantly greater increases in contact areas (<50um)
than the Hawley group. This shows that even though the
differences are small, a certain amount of settling
continued to occur late in the retention phase for the
Perfector/Hawley group. The lack of statistical
significance between groups could be partially due to
patient compliance.
While all patents were repeatedly
instructed to wear their Hawley retainers full-time, it was
difficult to assess how long the patients had actually worn
their retainer.
Sample sizes could also have reduced the
power of the comparisons.
During the first part of the
study, six Hawley patients were dropped and the Perfector
patients were over-sampled due to expected non-compliance.
The combination of over-sampling and dropouts produced an
unequal numbers of patients in each retention group, which
81
may have had an effect on the ability to identify
differences.
Overall post-treatment increases in posterior ACNC
were similar for the Hawley and Perfector groups. This
suggests that during the retention phase, the teeth have a
limited amount of settling, no matter if the Hawley or
Perfector retention device is used.
These findings are
similar to Haydar et al.,10 who after comparing the tooth
positioner to the Hawley retainer after three months, found
that there were no statistically significant differences in
the number of contacts.
In contrast, Durbin and Sadowski12
reported that the positioner produced a greater increase in
the total number of teeth in contact over time than the
Hawley retainer, but the differences were small.
Although there were no significant differences between
the Hawley and Perfector groups in regards to the ACNC,
other dimensions of occlusion may benefit from Perfector
wear, such as axial inclination, rotations, etc.
These
factors could affect the patients’ perception of occlusion
and help explain the overall improvements observed for the
Perfector/Hawley group. Whereas patients wearing the Hawley
retainer generally did not perceive any changes over time,
patients initially wearing the Perfector/Hawley noted
significant improvements in how well their back teeth fit
82
together. The Perfector/Hawley patients demonstrated
significant improvements for all questions except one over
the eight month observation period. However, it must be
emphasized that the overall improvements that occurred in
the Perfector/Hawley group closely reflect the changes that
occurred during the first two months of Perfector wear.
To better understand the lack of group differences and
the changes in patient perception that occurred, it is
important to emphasize that, as reported by Horton,19 the
Perfector/Hawley group initially reported more pain and
discomfort than the patients assigned to the Hawley group.
This suggests a potential sampling bias, with the
Perfector/Hawley group having a greater potential to
improve than the Hawley group. The initial group
differences in perception could also explain, at least
partially, the lack of group differences after eight months
of retention. The lack of long-term group differences may
be further explained by the slight improvements that the
Hawley group showed over time, which decreased the overall
group differences.
Nevertheless, it is important to
emphasize that the Perfector is designed to influence many
aspects of occlusion such as rotations, axial inclinations,
alignment, interproximal space closure, crossbite
correction, arch coordination and overjet correction.22
83
Such changes may have altered patients’ perceptions of
occlusion, which could also explain the improvements
identified for those patients who initially wore the
Perfector. This suggests that the Perfector/Hawley
combination may be a useful retention protocol for patients
needing additional corrections other than settling of the
occlusion.
The Hawley appliance, on the other hand,
maintains the buccolingual positions of the teeth, but
allows vertical movements.
This may explain why the Hawley
showed an increased amount of settling, but did not show
improvements in patient perception of occlusion and comfort
over eight months of retention.
Conclusions
1.
Areas of contact and near contact (ACNC) increased
at decelerating rates over the first six months,
with little or no change thereafter.
2.
The greatest increases in ACNC occurred at the
thicker near contact levels (300-350um).
3.
Overall, ACNC increased 130% for the Hawley group
and 104% for the Perfector/Hawley group after 8
months, but the group differences were not
statistically significant.
84
4.
While the Perfector/Hawley group perceived greater
improvements in their occlusion than the Hawley
group, the differences after eight months of
retention were not statistically significant.
Because the majority of post-treatment settling of the
occlusion occurs during the first six months, it is
recommended that Hawley and Perfector/Hawley retainers
should be worn for at least this amount of time before
switching to other retention protocols.
Moreover, many
practitioners prefer to perform equilibrations after
orthodontic treatment, but do not know when settling is
complete.
Based on the results of this study, it is
recommended that the practitioner wait six months before
occlusal equilibration.
85
Table 1.
Areas of contact and near contact (ACNC) of posterior the occlusion at T1, T2, T3 and T4.
T1 areas (mm2)
Hawley
Thickness
(µm)
Median
T2 areas (mm2)
Perfector
IQR
Median
Hawley
IQR
Median
T3 areas (mm2)
Perfector
IQR
Media
n
IQR
Hawley
Median
T4 areas (mm2)
Perfector
IQR
Median
IQR
Hawley
Median
Perfector
IQR
Median
IQR
Absolute Thickness
≤50
0.66
0.23/1.42
0.71
0.28/1.21
1.35
0.71/2.27
1.25
0.76/1.96
1.80
1.25/3.51
1.84
0.88/2.60
1.74
1.35/2.73
1.83
1.15/3.43
50-100
0.73
0.30/1.88
1.14
0.44/1.82
1.67
1.17/2.96
1.76
1.08/2.26
2.22
1.51/3.84
2.38
1.41/3.21
2.33
1.89/3.90
2.29
1.77/3.53
100-150
0.89
0.37/2.00
1.17
0.44/1.83
1.74
1.28/3.00
1.72
1.04/2.47
2.03
1.53/3.24
2.22
1.42/3.12
2.35
1.64/3.08
2.37
1.80/3.29
150-200
0.90
0.46/1.92
1.03
.49/1.63
1.54
1.28/2.77
1.73
1.11/2.60
1.98
1.47/3.28
2.21
1.44/2.90
2.12
1.58/3.24
2.44
1.75/3.02
200-250
1.08
0.46/2.02
1.18
0.46/1.58
1.71
1.33/2.73
1.87
1.14/2.43
2.09
1.60/3.74
2.34
1.51/2.65
2.13
1.60/3.62
2.42
1.91/3.12
250-300
1.30
0.45/2.17
1.33
0.55/1.73
1.77
1.46/2.98
1.99
1.22/2.66
2.29
1.82/4.42
2.57
1.75/3.21
2.47
1.95/4.0
2.87
2.18/3.82
300-350
1.60
0.63/2.62
1.62
0.69/2.01
1.94
1.66/3.56
2.30
1.38/2.90
2.97
2.21/5.85
3.19
2.09/3.73
3.14
2.43/5.33
3.16
2.83/5.14
Cumulative Thickness
≤50
0.66
0.23/1.42
0.71
0.28/1.21
1.35
0.71/2.27
1.25
0.76/1.96
1.80
1.25/3.51
1.84
0.88/2.60
1.74
1.35/2.73
1.83
1.15/3.43
≤100
1.23
0.63/3.10
1.96
0.69/2.97
3.02
1.80/5.12
2.92
1.96/4.21
4.24
2.76/7.67
4.37
2.21/5.95
4.40
2.72/8.06
4.17
2.85/7.16
≤150
2.12
1.15/5.22
2.96
1.15/4.73
4.46
3.30/8.24
4.89
2.79/6.20
6.11
4.32/11.66
6.36
3.67/9.45
6.17
5.41/11.14
6.25
4.96/10.21
≤200
3.01
1.63/7.37
4.12
1.73/6.47
5.72
4.65/11.10
6.68
3.63/8.69
8.03
5.92/15.16
8.45
5.20/11.97
8.50
7.48/14.38
8.13
6.79/13.83
≤250
4.10
2.15/9.41
5.36
2.19/8.03
7.26
6.20/13.85
8.56
4.85/11.12
10.59
7.74/18.91
10.68
6.72/14.45
10.53
8.91/18.13
10.63
8.73/17.10
≤300
5.38
2.77/11.47
6.69
2.67/10.03
8.89
7.72/16.72
10.83
6.18/13.79
13.40
9.77/23.32
13.42
8.48/17.53
13.10
10.73/22.30
13.50
10.99/20.87
≤350
7.01
3.37/13.90
8.30
3.40/11.80
10.67
9.37/20.26
13.16
7.62/16.64
16.61
12.57/29.17
16.33
10.68/22.29
16.03
12.84/27.64
17.00
13.89/26.43
86
Table 2.
Changes in areas of contact and near contact (ACNC) from T1-T2, T2-T3, T3-T4 and from T1-T4.
T1-T2 areas (mm2)
Hawley
Thickness
(µm)
Median
T2-T3 areas (mm2)
Perfector
IQR
Median
T3-T4 areas (mm2)
Hawley
IQR
Median
Perfector
IQR
Median
Hawley
IQR
Median
T1-T4 areas (mm2)
Perfector
IQR
Median
Hawley
IQR
Median
Perfector
IQR
Median
IQR
Absolute Thickness
≤50
0.49
0.25/1.24
0.52
0.05/1.10
0.65
0.55/2.29
0.29
-0.09/0.76
-0.12
-0.60/0.24
0.36
-0.19/0.80
1.02
0.56/2.04
1.19
50-100
1.10
-0.09/1.49
0.38
-0.02/0.73
0.66
0.47/1.39
0.69
0.17/1.01
0.37
-0.21/0.92
0.18
-0.43/0.71
1.60
1.23/2.01
1.17
0.33/2.67
0.64/2.15
100-150
0.91
0.15/1.42
0.21
-0.06/1.20
0.43
0.14/0.99
0.65
0.21/0.81
0.19
-0.12/0.46
.04
-0.25/0.33
1.54
0.68/2.12
1.11
0.42/1.84
150-200
0.81
0.06/1.29
0.29
-0.02/1.03
0.98
0.24/1.13
0.51
0.11/0.94
0.07
-0.14/0.33
0.14
-0.17/0.29
1.36
0.66/1.81
1.09
0.43/1.45
200-250
0.98
0.14/1.38
0.53
-0.01/0.96
0.86
0.40/1.45
0.42
0.01/0.71
0.19
-0.38/0.34
0.19
-0.06/0.47
1.48
0.76/1.79
1.29
0.63/1.51
250-300
1.03
0.11/1.29
0.57
-0.04/0.96
0.99
0.54/1.75
0.52
0.10/0.98
0.04
-0.65/0.44
0.18
-0.05/0.51
1.70
0.75/2.45
1.38
0.65/2.04
300-350
0.97
0.04/1.41
0.74
0.15/1.11
1.49
0.63/2.88
0.71
0.20/1.37
-0.26
-0.70/0.64
0.19
-0.14/0.74
2.00
0.90/3.65
1.76
0.95/2.89
≤50
0.49
0.25/1.24
0.52
0.05/1.09
0.65
0.55/2.29
0.29
-0.09/0.76
-0.12
-0.60/0.24
0.36
-0.19/0.80
1.02
0.56/2.04
1.19
0.33/2.67
≤100
1.51
0.12/3.06
0.81
0.22/1.95
1.37
0.83/3.67
0.94
-0.02/1.73
0.02
-0.62/1.16
0.48
-0.52/1.50
2.99
1.89/5.25
2.41
1.19/3.84
≤150
2.96
0.35/4.13
1.19
0.27/2.77
1.65
0.91/4.01
1.69
0.24/2.37
0.21
-0.76/1.66
0.51
-0.49/1.75
4.82
2.18/7.40
3.55
1.51/6.28
≤200
4.07
0.45/5.05
1.43
0.48/4.18
2.11
1.36/4.99
1.94
0.69/3.26
0.26
-0.88/2.01
0.56
-0.57/1.68
6.18
2.83/9.07
4.80
2.13/7.36
≤250
5.33
0.57/6.43
1.90
0.60/5.14
3.27
1.75/6.64
2.08
1.10/2.08
-0.16
-0.78/2.32
0.73
-0.64/1.89
7.83
3.60/10.80
6.28
2.57/8.78
≤300
6.47
0.64/8.11
2.66
0.60/5.93
5.13
2.37/8.86
2.68
1.35/4.79
-0.22
-1.03/2.28
1.00
-0.67/2.39
9.60
4.32/13.12
7.86
3.22/10.81
≤350
7.43
0.68/10.46
3.77
0.32/6.67
6.42
3.16/11.69
3.34
1.57/5.79
-0.27
-1.75/2.71
1.36
-0.93/3.15
11.28
5.08/17.69
9.62
4.04/13.70
Cumulative Thickness
87
Table 3.
Patient perception of posterior occlusion at T1, T2, T3 and T4 using a visual analogue scale.
T1 areas (mm2)
Hawley
Questio
n
number
Median
1
2
T2 areas (mm2)
Perfector
Hawley
Median
T3 areas (mm2)
Perfector
IQR
Hawley
Perfector
Median
Hawley
IQR
Median
IQR
124.75
110.25/139.31
118.75
101.13/131.88
125.25
112.75/138.08
125.00
118.13/136.50
119.50
97.88/137.19
129.25
124.25/139.38
3
141.88
139.13/145.50
134.50
128.13/142.50
139.00
130.38/144.38
4
139.25
125.75/144.00
132.50
127.63/143.13
139.50
131.13/144.63
139.25
128.50/144.75
145.00
127.00/147.50
142.75
135.50/146.00
5
145.25
143.00/147.75
138.00
131.88/143.75
143.00
130.75/145.63
143.25
137.00/146.75
143.00
131.00/148.00
141.25
132.75/145.00
6
137.75
111.50/145.94
135.00
115.50/142.38
142.13
117.19/143.75
141.75
124.56/143.50
142.50
134.00/148.00
142.63
133.25/145.63
7
138.00
125.19/144.88
140.00
125.75/142.50
139.38
125.38/145.00
138.75
131.00/142.75
145.00
140.00/148.00
136.50
131.38/143.38
88
Median
T4 areas (mm2)
IQR
Median
Perfector
IQR
Media
n
IQR
IQR
Median
IQR
134.75
127.00/140.00
138.00
124.50/146.50
137.13
128.00/142.50
135.50
124.25/147.50
138.50
131.25
120.38/138.00
130.00
111.00/147.50
134.75
125.31/140.00
142.00
117.75/146.75
138.00
132.00/141.50
139.50
131.50/143.19
146.00
140.00/147.50
140.00
136.00/144.50
143.00
131.50/148.00
139.50
137.00/146.00
145.00
138.00/148.00
141.00
137.50/145.00
145.00
141.50/148.00
141.00
134.50/145.50
143.00
126.50/147.00
143.00
131.00/144.00
143.00
132.00/148.00
141.00
136.00/145.00
136.00/142.50
Table 4. Changes in patient perception of occlusion from T1-T2, T2-T3, T3-T4 and from T1-T4 using a visual
analogue scale.
T1-T2 areas (mm2)
Hawley
Question
Number
Median
T2-T3 areas (mm2)
Perfector
IQR
Median
IQR
Hawley
Median
T3-T4 areas (mm2)
Perfector
IQR
Median
IQR
Hawley
Median
T1-T4 areas (mm2)
Perfector
IQR
Median
IQR
Hawley
Median
Perfector
IQR
Median
IQR
1
-0.75
-9.94/11.75
13.63
1.75/36.88
3.50
0.00/21.50
0.25
-5.19/3.19
1.00
0.00/5.00
0.13
-1.94/8.75
3.50
-4.63/18.50
13.75
10.00/29.00
2
-0.50
-7.75/14.25
8.50
-4.38/34.38
0.50
-0.00/4.00
0.25
-8.50/10.25
0.00
-1.00/4.00
3.50
-2.13/6.25
2.00
-6.75/23.25
11.00
3.25/24.50
3
-0.25
-7.88/1.38
3.50
-1.69/11.00
1.00
0.00/8.00
1.63
-2.50/6.75
0.00
-2.00/1.00
0.25
-5.00/3.25
0.00
-0.50/3.25
5.00
-0.75/11.00
4
0.50
-5.38/4.25
2.00
-1.75/10.88
1.00
-1.00/8.00
2.00
-0.88/7.88
0.50
-0.50/4.50
0.38
-0.63/1.00
4.00
-0.25/17.25
8.25
2.50/14.50
5
-0.50
-5.81/0.75
2.75
-1.75/9.00
0.00
-0.50/7.00
-1.50
-8.00/1.50
0.50
0.00/8.00
1.00
-1.38/3.75
0.00
-0.50/1.50
2.00
-3.00/9.00
6
0.25
-10.25/10.75
8.00
-2.50/23.63
2.00
0.00/17.75
-0.25
-5.00/4.81
0.00
-7.50/1.75
0.25
-3.25/2.63
2.50
-0.13/23.25
8.00
1.00/23.75
7
-0.25
-7.06/12.94
-0.13
-7.75/8.50
0.00
-1.00/19.25
-1.25
-4.63/8.63
0.00
-5.50/4.00
2.00
-1.00/7.63
3.50
-1.00/20.13
2.50
-1.00/10.00
89
Area (mm2)
≤50
18.5
16.5
14.5
12.5
10.5
8.5
6.5
4.5
2.5
0.5
0
≤100
2
≤150
≤200
4
≤250
6
≤300
≤350
8
10
Time Interval (months)
Figure 1. Median cumulative areas of contact and near contact measured at 50
um thickness intervals between T1 (end of treatment) and T4 (8 months) for
patients initially wearing Hawley retainers.
90
2
Area (mm )
≤50
≤100
≤150
≤200
≤250
≤300
≤350
18.5
16.5
14.5
12.5
10.5
8.5
6.5
4.5
2.5
0.5
0
2
4
6
8
10
Time Interval (months)
Figure 2. Median cumulative areas of contact and near contact measured at 50
um thickness intervals between T1 (end of treatment) and T4 (8 months) for
patients initially wearing Perfector retainers.
91
Areas (mm2)
2.1
Hawley
1.9
1.7
1.5
1.3
Perfector
1.1
0.9
0.7
0.5
≤50
50-100 100-150 150-200 200-250 250-300 300-350
Thickness (um)
Figure 3. Median changes in areas of contact and near contact at 50 um
thickness intervals between T1 (end of treatment) and T4 (8 months) for
patients initially wearing Hawley and Perfector retainers.
92
12.5
Hawley
2
Area (mm )
10.5
Perfector
8.5
6.5
4.5
2.5
0.5
≤50
≤100
≤150
≤200
≤250
≤300
≤350
Thickness Interval
Figure 4. Median cumulative changes in areas of contact and near contact at
50 um thickness intervals between T1 (end of treatment) and T4 (8 months)
for patients initially wearing Hawley and Perfector retainers.
93
Literature Cited
1. Okeson J. Management of temporomandibular disorders and
occlusions. St. Louis: CV Mosby; 2003.
2. Yurkstas AA. The Masticatory Act. a Review. J Prosthet
Dent 1965;15:248-262.
3. Yurkstas AA, Manly R. Measurement of occlusal contact
area effective in mastication. Am J Orthod 1949;35:185-195.
4. Owens S, Buschang PH, Throckmorton GS, Palmer L, English
J. Masticatory performance and areas of occlusal contact
and near contact in subjects with normal occlusion and
malocclusion. Am J Orthod Dentofacial Orthop 2002;121:602609.
5. Ikebe K, Matsuda K, Morii K, Furuya-Yoshinaka M, Nokubi
T, Renner R. Association of masticatory performance with
age, posterior occlusal contacts, occlusal force and
salivary flow in older adults. Int J Prosthodont
2006;19:475-481.
6. Toro A, Buschang PH, Throckmorton G, Roldan S.
Masticatory performance in children and adolescents with
Class I and II malocclusions. Eur J Orthod 2006;28:112-119.
7. English JD, Buschang PH, Throckmorton GS. Does
malocclusion affect masticatory performance? Angle Orthod
2002;72:21-27.
8. Parkinson CE, Buschang PH, Behrents RG, Throckmorton GS,
English JD. A new method of evaluating posterior occlusion
and its relation to posttreatment occlusal changes. Am J
Orthod Dentofacial Orthop 2001;120:503-512.
9. Deng Y, Fu MK. Occlusal contact changes before and after
orthodontic treatment of a group of child & adolescent
patients with TMJ disturbance. Aust Orthod J 1995;13:231237.
94
10. Haydar B, Ciger S, Saatci P. Occlusal contact changes
after the active phase of orthodontic treatment. Am J
Orthod Dentofacial Orthop 1992;102:22-28.
11. Gazit E, Lieberman MA. Occlusal contacts following
orthodontic treatment. Measured by a photocclusion
technique. Angle Orthod 1985;55:316-320.
12. Durbin DS, Sadowsky C. Changes in tooth contacts
following orthodontic treatment. Am J Orthod Dentofacial
Orthop 1986;90:375-382.
13. Razdolsky Y, Sadowsky C, BeGole EA. Occlusal contacts
following orthodontic treatment: a follow-up study. Angle
Orthod 1989;59:181-185; discussion 186.
14. Basciftci FA, Uysai T, Sari Z, Inan O. Occlusal
contacts with different retention procedures in 1-year
follow-up period. Am J Orthod Dentofacial Orthop
2007;131:357-362.
15. Nett BC, Huang GJ. Long-term posttreatment changes
measured by the American Board of Orthodontics objective
grading system. Am J Orthod Dentofacial Orthop
2005;127:444-450.
16. Otuyemi O, Jones S. Long term evaluation of treated
Class II Division I malocclusions utilizing the PAR index.
Br J Orthodont 1995;22:171-180.
17. Ormiston J, Huang G, Little R, Decker J, Seuk G.
Retrospective analysis of long-term stable and unstable
orthodontic treatment outcomes. Am J Orthod Dentofacial
Orthop 2005;128:568-574.
18. Sauget E, Covell DA, Jr., Boero RP, Lieber WS.
Comparison of occlusal contacts with use of Hawley and
clear overlay retainers. Angle Orthod 1997;67:223-230.
95
19. Horton J, Buschang P,
Comparison of the effects
aligner retainers on post
Orthodontics. Am J Orthod
Behrents R,
of a hawley
orthodontic
Dentofacial
Oliver D (in press).
and perfector/spring
occlusion
Orthop.
20. Julien KC, Buschang PH, Throckmorton GS, Dechow PC.
Normal masticatory performance in young adults and
children. Arch Oral Biol 1996;41:69-75.
21. Dincer M, Meral O, Tumer N. The investigation of
occlusal contacts during the retention period. Angle Orthod
2003;73:640-646.
22. Kesling H. The philosophy of the tooth positioning
appliance. Am J Ortho and Oral Surg 1945;31:297-304.
96
VITA AUCTORIS
Elizabeth Bauer was born in Edwardsville, IL on October 21,
1977.
She graduated from the University of Alabama in 1999
with a B.S. degree in Psychology.
In 2005, she graduated
from Southern Illinois School of Dental Medicine and began
her residency in orthodontics at Saint Louis University.
She married Benjamin R. Hite on September 29, 2007.
97