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COMPARISON OF THE EFFECTS OF AN ESSIX AND HAWLEY
RETAINER ON POST-ORTHODONTIC OCCLUSION
Collin Tsai
An Abstract Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirement for the Degree of
Master of Science in Dentistry
2010
Abstract
Purpose:
To evaluate and compare the posterior
occlusal changes between the Essix and Hawley retainer
during the first 3 months of retention.
Methods: This
randomized trial evaluated 40 patients who had completed
full orthodontic treatment and been assigned to wear
either Essix or Hawley retainer.
They were evaluated at
three time points, debond (T1), one month after debond
(T2) and three months after debond (T3). Duplicate bite
registrations were used to quantity posterior areas of
contact and near contact (ACNC).
The patient’s
perceptions about their occlusion and compliance with
retainers wear were evaluated using a 5 item
questionnaire.
Results:
Both the Essix and the Hawley
retainers produced slight decreases in ACNC from T1 to
T2.
At T2, there were significant (p<.05) group
differences of cumulative ACNC at ≤50 µm and ≤100 µm,
with the Hawley group having greater ACNC.
showed increases in ACNC from T2 to T3.
Both groups
At T3,
significant group differences of cumulative ACNC were
observed at ≤50 µm, ≤100 µm, ≤150 µm and ≤200 µm, again
with the Hawley group showing greater ACNC than the Essix
group. Total cumulative ACNC of the Essix group decreased
from 19.3 mm² at T1 to 17.5 mm² at T3; ACNC of the Hawley
1
increased from 21.2 mm² at T1 to 22.1 mm² at T3. Group
differences in ACNC at T3 were not statistically
significant.
Conclusion:
The Hawley retainer produced
greater ACNC than the Essix retainer, especially at or
below the 200 µm level, but the differences are small.
2
COMPARISON OF THE EFFECTS OF AN ESSIX AND HAWLEY RETAINER
ON POST-ORTHODONTIC OCCLUSION
Collin Tsai
A Thesis Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirement for the Degree of
Master of Science in Dentistry
2010
COMMITTEE IN CHARGE OF CANDIDACY:
Adjunct Professor Peter H. Buschang,
Chairperson and Advisor
Professor Estaquio Araujo
Assistant Professor Ki Beom Kim
i
DEDICATION
I would like to dedicate to the two most important
people in my life.
To my mother, Helen Chan, for motivating me, showing
me that nothing is unachievable with hard work and giving
me the best on the little that she had.
To my fiancée, Angeline Chow, for always supporting
me, giving me great advice, and making me laugh when life
was stressful.
ii
ACKNOWLEDGEMENTS
Dr. Buschang, for helping me substantially in the
design, the statistical analysis and the interpretation
of my results.
Dr. Araujo and Dr. Kim, for their time, interest,
and help in this study.
Dynaflex for their sponsor in making retainers for
this study.
iii
Table of Contents
List of Tables..........................................v
List of Figures........................................vi
CHAPTER 1: INTRODUCTION.................................1
CHAPTER 2: LITERATURE REVIEW
Ideal Occlusion and Posterior Occlusal Contacts.........3
Methods to Measure Posterior Occlusion..................7
Visual Assessment..................................7
Articulating Indicators............................8
Photo-occlusion...................................10
T-Scan............................................11
Polyether Impression Material.....................13
Silicone-based Impression Material................14
Optical Scanning..................................16
Retention..............................................17
Retention Appliances...................................19
Hawley Retainer...................................19
Wrap Around Retainer..............................20
Positioner........................................20
Perfector.........................................21
Spring Retainer...................................22
Fixed Lingual Retainer............................22
Essix/Vacuum Formed Retainer/Clear Overlay Retainer
..................................................23
Post-Orthodontics Occlusion: Settling..................24
Past Studies......................................25
Studies Comparing Hawley Retainer to Essix (Vacuum
Formed) Retainer.......................................33
Conclusion.............................................40
References.............................................43
CHAPTER 3: JOURNAL ARTICLE
Abstract...............................................48
Introduction...........................................50
Materials and Methods..................................53
Statistical Analyses...................................56
Results................................................57
Discussion.............................................60
Conclusions............................................66
References.............................................67
Appendix...............................................69
Vita Auctoris..........................................81
iv
List of Tables
Table 1: Areas of contact and near contact (ACNC) of
posterior occlusion with Essix and Hawley
retainers at debond (T1), 1 month after debond
(T2) and 3 months after debond (T3)...........70
Table 2: Changes in the areas of contact and near contact
(ACNC) of posterior occlusion with Essix and
Hawley retainers at debond (T1), 1 month after
debond (T2) and 3 months after debond (T3)....71
Table 3: Patient perception of posterior occlusion at at
debond (T1), 1 month after debond (T2) and 3
months after debond (T3) using a visual analogue
scale.........................................72
Table 4: Changes in patient perception of posterior
occlusion at at debond (T1), 1 month after
debond (T2) and 3 months after debond (T3) using
a visual analogue scale.......................73
v
LIST OF FIGURES
Figure 1:
Photo of registration.......................74
Figure 2:
Scan of registration........................74
Figure 3:
Tracing of occlusal table...................74
Figure 4: Calibration Curve: step-wedge thickness (Y)
estimated from grey scales (X0.........................75
Figure 5: Median cumulative areas of contact and near
contact of Essix and Hawley retainers at ≤350 µm
thickness at T1 (debond), T2 (1 month post-debond) and T3
(3 months post-debond).................................76
Figure 6: Median cumulative areas of contact and near
contact of Essix and Hawley retainers at ≤50 µm and ≤100
µm thickness at T1 (debond), T2 (1 month post-debond) and
T3 (3 months post-debond) .............................77
Figure 7: Median absolute areas of contact and near
contact of Essix and Hawley retainers at T1 (debond) and
T2 (1 month post-debond)...............................78
Figure 8: Median cumulative areas of contact and near
contact of Essix and Hawley retainers at ≤150 µm and ≤200
µm thickness at T1 (debond), T2 (1 month post-debond) and
T3 (3 months post-debond)................. ............79
Figure 9: Median absolute areas of contact and near
contact of Essix and Hawley retainers at T1 (debond) and
T3 (3 month post-debond).............. ................80
vi
Chapter 1: Introduction
One of the many goals of orthodontic treatment is to
establish proper occlusion, allowing the patient to have
healthy masticatory function and stability.
Once the
teeth are brought into an esthetically pleasing alignment
and proper occlusion, the appliance is removed.
A
retainer is then prescribed to the patient by the
orthodontist.
This marks the beginning of the retention
phase of orthodontic treatment.
changes occur.
During this phase, many
The purpose of prescribing a retainer is
to prevent undesirable changes such as rotational
relapse, while allowing desirable changes, such as
establishing stability and allowing settling of the
occlusion.
Many different types of retainers are available for
the orthodontist to prescribe.
Currently, the Essix and
the Hawley retainer are the two most commonly prescribed
retainers in the United States and the United Kingdom.
It has been determined from previous studies that both
Hawley and Essix retainers are equally as effective in
preventing post-treatment irregularity and relapse.
However, there are no studies that have objectively
attempted to determine which type of retention method is
more effective in allowing settling of the posterior
1
occlusion using the same retention protocol.
The purpose
of this study is to objectively quantify the posterior
occlusal changes that occur with Essix and Hawley
retainers from debond to one and three months post-debond
and to determine if one is superior in allowing settling
to occur in the dentition.
2
Chapter 2:
Review of the Literature
Ideal Occlusion and Posterior Occlusal Contacts
Crooked and irregular teeth have been around for
over 50,000 years.
Since 1000 BC, there have been many
attempts and successes in correcting the irregularity of
teeth, but little emphasis was placed on correcting the
occlusion.1,2
It was not until about 100 years ago that
orthodontists focused on and realized the importance of
correcting the occlusion.
In 1900, Angle devised a way
to classify the occlusion based on the antero-posterior
position of the maxillary first molar relative to the
mandibular first molar.
According to Angle, a normal
occlusion occurred when the mesiobuccal cusp of the
maxillary first molar occluded with the buccal groove of
the mandibular first molar.
Three types of malocclusion
existed under Angle’s classification.
A Class I
malocclusion is when there is a normal molar
relationship, but the teeth are not in alignment.
A
Class II malocclusion is present when the mandibular
first molar is distally positioned relative to the
maxillary first molar.
A Class III malocclusion exists
when the mandibular first molar is mesially positioned to
the maxillary first molar.3
In 1972, Andrews added to
Angle’s definition of normal occlusion by noting that the
3
distal surface of the distobuccal cusp of the maxillary
first molar should occlude with the mesial surface of the
mesiobuccal cusp of the mandibular second molar.4
Okeson
added that posterior occlusion should focus on the
relationship between cusp tips and central fossae, as
well as the relationship between cusp tips and marginal
ridges.5
The function of the posterior teeth is to
effectively break up food when chewing and to maintain
vertical dimension.
The function of the anterior teeth
is to incise food and guide the mandible through
excursive and protrusive movements.
The incisors guide
the mandible into protrusive contact, thereby
disocclusing the posterior teeth.
The canines guide the
mandible during excursive movements.
For this reason,
contacts between the anterior teeth are much lighter than
the contacts for posterior teeth and can even be
absent.5,6
The anterior tooth contacts that guide the
mandible through protrusive and extrusive movements are
called anterior guidance.5
Besides esthetics, another goal of orthodontic
treatment is ideal occlusion.
Ideal occlusion can be
defined as Class I molar relationship, anterior guidance,
maximum occlusal contacts and no occlusal
4
interferences.6-8
Maximum intercuspation is the occlusal
position when the teeth are in maximum contact and can
also be called centric occlusion or the patient’s most
comfortable bite.
Retruded contact position is the
occlusal position when the first tooth contact occurs on
the mandibular path of closure with the condyles in the
retruded axis position.7
Some orthodontists believe that
an ideal treatment goal is to have maximum intercuspation
coincident with retruded contact position.8-10
An
association between non-coincidence of maximum
intercuspation, retruded contact position and
temporomandibular disorders has been shown.11
Other
studies support the notion that the non-coincidence of
the two can be considered normal.12,13
Clarke concludes
that there is no evidence to show any disadvantage in
patients when maximum intercuspation that does not
coincide with a retruded contact position.7
In maximum
intercuspation, Ricketts described the ideal occlusion
having a maximum of 48 contacts between the cusp tips and
opposing marginal ridges, with third molars excluded.
According to Rickets, 32-48 contacts are adequate for a
good balanced occlusion.14
This is in agreement with
Okeson who states that there are 34-48 contacts in ideal
occlusion.5
5
Providing patients with an ideal occlusion is
important in orthodontics because it directly affects
masticatory performance and function.
Occlusal contacts
of maxillary and mandibular teeth during mastication,
swallowing and speech is called functional occlusion.7
English et al. found that the ability to process and
break down food is dependent upon the molar
relationship.15
They found that a normal Class I molar
relationship was most efficient in breaking down food,
followed by Class I and II malocclusions, with Class III
malocclusion being the most inefficient in mastication.
Toro and co-workers also showed that children with a
Class I malocclusion do not break down food as well as
those with normal occlusion and children with severe
malocclusions cannot break down food as well as those
with less severe Class I malocclusions.16
Besides molar relationship, the number of tooth
contacts and area of tooth contacts also affects
masticatory function.
Yurkstas and Manly were the first
to identify a correlation between occlusal contact areas
and masticatory performance.17
Bakke and collegues have
also shown a positive correlation between adult bite
force and occlusal contact area.18
Positive correlations
between bite force and occlusal contact area also hold
true for children as well, with stronger correlations for
6
girls than boys.19
A study by Julien et al. concluded
that greater height of the ramus, larger occlusal contact
area and stronger bite force all contribute to increased
masticatory performance.20
Using a silicone based
impression material to record the bite and measure areas
of contact and near contact (ACNC), Owens et al. defined
actual contact areas at a thickness at or below 50 µm and
areas of near contact at thicknesses between 50 µm and
350 µm.21
They demonstrated that Class III subjects had
the smallest ACNC and also had the most difficultly
breaking down food.
Conversely, subjects with normal
occlusion had the largest ACNC and were able to break
down food into the smallest pieces.
This led them to the
conclusion that subjects with more closely fitting
posterior occlusion and larger ACNC were better able to
break down food.
Methods to Measure Posterior Occlusion
Visual Assessment
The most basic method to evaluate posterior
occlusion is gross visual assessment.
As simple and
unsophisticated as this may be, it is still routinely
used by orthodontist to evaluate the posterior dentition.
Orthodontists commonly use gross visualization to
7
determine the relationship of the molars based on Angle’s
classification.
Orthodontists also rely on visual
assessment to evaluate tooth contact of the posterior
occlusion.
This may be the quickest way to grossly
evaluate the posterior occlusion, but it is neither
accurate nor reliable.
Besides visual assessment, researchers have
developed and used various other methods to measure
posterior occlusion and tooth contact.
Among these
methods used include articulating indicators (paper, film
or silk), photo-occlusion, T-scan, polyether impression
material and silicone-based impression material.
Although advances have been made in terms of methodology
to measure posterior occlusion, the accuracy and
reliability of these methods remain questionable.
Articulating Indicators
Articulating indicators are routinely used in all
fields of dentistry to record contacts between the teeth.
Articulating indicators can be made out of paper, silk or
plastic.
They can be found in various thickness, colors,
and texture.
They can be single-sided or double-sided.22
Articulating indicators are typically placed between the
maxillary and mandibular teeth and the patient is
instructed to bite down with the indicator between the
8
teeth.
This transfers color to the area(s) on the teeth
that are in occlusal contact with their antagonists.
The clinician can then visualize and evaluate the marked
areas to make gross adjustments as needed.
Although articulating indicators may seem simple to
use, Carossa et al. demonstrated that the assessment of
interocclusal contacts is significantly affected by
operator experience.23
They also showed that the
thickness of the articulating indicators, bite force of
the patient and duration of the bite all have an
influence on the contact area obtained from articulating
indicators.
This is in agreement with Millstein’s
results, who found that depending on thickness, color and
type of material, articulating indicators can produce
various quantities of markings.24
A more recent study by
Millstein and Maya yielded similar results.
They noted
that near occlusal contacts may appear as actual contacts
depending on the thickness of the marking indicator,
suggesting that articulating indicators differ and that
physical difference among articulating indicators will
affect their ability to mark areas of contact.22
The most
recent article on articulating indicators demonstrated
that the occlusal markings obtained by articulating
indicators are not reflective of the occlusal load and
operator subjectiveness is “tantamount to clinical
9
guessing.”25
The available evidence suggests that
articulating indictors may not be a reliable and accurate
mean of measuring posterior occlusion.
Photo-occlusion
In 1985, Gazit and Lieberman developed the photoocclusion technique to measure posterior occlusion.
The
technique consisted of biting into an occlusal wafer for
10 seconds.
This was repeated twice to enhance accuracy.
The occlusal wafer, with the bite indentations, was then
viewed on a polariscope and traced.
The quantitative
analysis was based on the number of contacts as viewed on
the polariscope.
The qualitative analysis was based on
the colored stress pattern produced by the occlusal
wafer.
This pattern depends on the degree of light
penetration into the occlusal wafer.
The authors
considered 40% penetration as light contact, 60%
penetration as medium contact and over 60% as heavy
contact.26
A later study by Gazit et al. examined the
reproducibility and reliability of the photo-occlusion
technique and compared it to the articulating markers.
They measured the posterior occlusion and tooth contacts
of 11 subjects with Class I occlusion using both
techniques.27
Measurements were taken at the beginning of
10
the study and one month later. They concluded that the
photo-occlusion technique had a higher degree of
reproducibility than articulating markers.
The photo-
occlusion technique also produced more contacts than
articulating markers, especially in the premolar areas.
However, the results indicated that neither the photoocclusion technique nor articulating makers were highly
reproducible.27
T-Scan
In 1987, Maness et al. introduced the T-Scan, a
computerized device developed to capture and record
occlusal contacts.28
The T-Scan system is composed of a
piezoelectric foil sensor, a sensor handle, the
computerized system unit and software to view, record and
analyze the data.
The disposable sensor, which is less
than 100 µm thick, is made of conductive ink on a
polyester film substrate.
The polyester film substrate
is thin, yet strong, resistant to tear and possess
elastic properties to resist permanent deformation.
According to Maness et al., these attributes makes it
superior to other types of polyester registration strips.
The patient bites onto, but not through the disposable
sensor, and the information is relayed to the computer.28
The software provides a three-dimensional representation
11
of tooth contacts, along with when they occlude.
This
makes it possible to determine the first tooth contact
and the sequence of tooth contacts thereafter.
The
software also allows comparison of occlusal patterns at
different time points, such as before and after
treatment.
Hsu and collegues conducted a study to evaluate the
sensitivity and reliability of the T-Scan.29
The occlusal
patterns of 47 patients were analyzed by the T-Scan.
The
sensitivity and reliability of the sensor in recording
occlusal contact was tested with an articulator using
reproducible forces.
The results showed that the number
of occlusal contacts varied within the same patient.
On
average, the number of occlusal contacts obtained from
the T-Scan was less than the actual number of contacts
present.
They concluded that the sensor of the T-Scan
lacked the sensitivity to reliably measure the number of
tooth contacts in occlusion.29
This is in agreement with
the findings of Lyons et al., who compared the force
applied to the sensor for subjects at increasing forces.30
Lyons et al. also found that the number of contacts
recorded by the T-scan was not consistent with the force
being applied.30
12
Polyether Impression Material
Utilizing impressions to obtain information about
the dentition is common practice in dentistry.
Impression material, such as polyether can also be used
to measure the posterior occlusion in maximum
intercuspation.
Durbin and Sadowsky used polyether
rubber impression material to record the posterior
occlusion.31
The patient was seated upright and polyether
impression material was injected onto the occlusal
surfaces of the mandibular teeth.
The patient was then
instructed to bite firmly onto their posterior teeth and
to hold the position for 2 minutes.
The bite
registration was then transferred to study models with a
pencil, using the perforations as a guide.
The total
numbers of tooth contacts were quantified.
However, no
attempt was made to investigate areas of near occlusal
contact.
Razdolsky et al. also used polyether to measure
posterior occlusion in a follow up study to the one
conducted by Durbin and Sadowsky, using a similar
protocol.32 The bite registrations were positioned on a
light box in a dark room.
Areas of actual contact were
identified as perforations in the polyether occlusal
registrations and transferred to the study models using a
red marker. Razdolsky et al. found no significant
13
differences between the contacts of the polyether bite
registration and the actual patient.32
In this follow-up,
areas of near occlusal contact were also counted.
Areas
of near contact were identified by a change in color of
the Ramitec material from yellow to a transparent white.
The white transparent centers were transferred onto the
study models with a black marker.
However, Razdolsky et
al. did not have a method to check for errors in
identifying areas of near contact.32
The evaluation of
color change also introduces subjectivity to the
evaluation of near contacts.
Silicone-based Impression Material
Silicone-based impression materials have been used
in several studies to evaluate and measure occlusal
contacts.
In 1992, Haydar et al. used a soft silicone-
based impression material to take occlusal records of 20
patients.33
The silicone based impression material was
loaded into two separate syringes and applied on the
occlusal surfaces of the mandibular teeth.
The patients
were then asked to bite firmly for 30 seconds.
The bite
registration was held up to sun light, perforations
signified actual contacts, while very thin transparent
sections without perforations were considered areas of
near occlusal contact.
The bite registration was then
14
transferred onto the upper cast of the patients.
Photographs of the occlusal view of the models were taken
and standardized.
Actual contacts and near contacts were
then traced on acetate paper.
Sauget et al. used vinyl polysiloxane to record the
occlusal contacts.34
Again, the impression material was
applied on the occlusal surface of all mandibular teeth.
The patient was told to bite firmly in maximum
intercuspation for 2 minutes.
The bite registrations
were examined on a light box.
Perforations in the
impression material were counted as actual contacts.
Near contacts were counted only if the size of the thin
translucencies on the bite registration were under 0.20
mm, when measured with an Iwanson caliper.
Dincer and co-wokers used a silicon putty impression
material to measure the occlusal contacts.
The material
was placed over the mandibular teeth and the patients
were instructed to close tightly on their back teeth and
also slide the lower jaw to the right, to the left and
slide their jaw forward.35
Perforations in the impression
material were identified as actual contacts.
Translucent
areas in the impression material were identified as near
contacts.
All contacts were transferred to lower study
models using different colors for each type of contact.
15
Optical Scanning
Manually counting perforations and evaluating
translucencies in bite registrations can introduce
subjectivity and error.
Recently, several researchers
have utilized optical scanning of occlusal bite
registration to quantify contacts and near contacts.
Optical scanning of occlusal bite registrations provides
a more objective and accurate method to measure and
evaluate contacts and near contacts.20,21,36
The method of
optical scanning involves a silicone-based impression
material, called Blu Mousse, to obtain the bite
registration.
Blu Mousse is applied on the occlusal
surface of mandibular posterior teeth (1st molars and both
premolars) and the patient is instructed to bite down
firmly and maintain maximum intercuspation until the
material has set.
The occlusal registrations are then
placed onto the scanner with the mandibular surface
facing down.
The scanned image of the bite registration
is then traced using Image Tool software developed by the
University of Texas Health Science Center, San Antonio.
The software calculates the platform area of the teeth
traced and determines the frequency distributions of the
pixels corresponding to each of the 256 gray scales.
Calibration step wedges of Blu Mousse impression material
of known thickness are used to establish a calibration
16
curve corresponding to the thickness of the impression
material and each of the 256 gray scales.
This
calibration curve, allows the software to analyze the
thickness of the occlusal bite registration and determine
the thickness based on gray scale values of the area
scanned.
The thickness of the impression material is
typically measured in 50 µm increments, from 0 µm to 350
µm.
The increments of 50 µm are significant because
pixel densities are only detectable in increments of 50
µm.37
The upper limit of light penetration is between 350
µm and 400 µm.
Actual contacts were defined as 50 µm or
less and near contacts were defined as greater than 50
µm, but less than 350 µm.
Retention
Even after the active phase of orthodontic
treatment, during which the teeth are properly aligned
with fixed appliances, treatment is far from over.
Removal of appliances marks the beginning of the most
challenging aspect of orthodontics, the retention phase.
The primary purpose of retention is to maintain teeth in
their corrected positions.
Without a retention phase,
there is a tendency to the teeth to go back to their
pretreatment positions.
This tendency is called relapse.
The importance of retention was recognized as early as
17
1919, when Hawley wrote that, “if anyone would take my
cases when they are finished, retain them and be
responsible for them afterwards, I would gladly give them
half the fee.”38
The goal of the retention phase is to
prevent relapse, maintain the alignment and esthetics of
the dentition and allow for post-treatment settling of
the occlusion.
After the removal of appliances, retention is needed
because the gingival and periodontal fibers, which are
disrupted by orthodontic movement, require time to
reorganize.
Reitan demonstrated that fibers of the
gingival attachment requires 4-6 months to reorganize,
while supracrestal periodontal fibers may take over 232
days to adapt to the new teeth position.39
Retention is
critical during and even after the first post-treatment
year to prevent relapse of the dentition.
Even with
retention, it has been shown that incisor crowding and
irregularities increased and alignment of teeth was
variable and unpredictable in the long run when appliances
for retention have been removed.40,41
Another important reason for retention is growth.
Not only does growth or lack of growth have the potential
to affect the initial malocclusion, it also has the
potential to cause malocclusion post-treatment.
Class
II, Class III, open-bite and deep-bite growth patterns at
the start of treatment can still persist when treatment
18
is finalized.42
Selection of retention devices must be
based on the patients’ maturational status and any
anticipated future growth to prevent unfavorable changes
of the dentition.
Discoll-Gilliland and collegues has
shown that there is significant vertical growth in
posterior and lower anterior face height after completion
of orthodontic treatment, which was related to increases
in lower incisor irregularities in both orthodontically
treated and untreated populations.43
Melrose and Meillett
concluded that total stability does not exist in the
craniofacial skeleton or dentition after treatment, and
relapse in saggital, vertical or lateral skeletal
dimensions may occur.44
Retention Appliances
Hawley Retainer
Perhaps the most common type of retainer used is the
Hawley retainer or some variation of it.
and introduced in the 1920s.
It was designed
The Hawley retainer is a
removable retainer and consists of an adjustable labial
bow at the canines and an acrylic base lingual to the
teeth.45
Retentive features to hold the retainer include
ball clasps, Adam’s clasp or circumferential clasps.
19
The
labial bow can be shortened to close small spaces and
bent to correct minor rotations.
If retention clasps are
bent properly and do not cross the occlusal table,
maxillary and mandibular Hawley retainers may allow the
posterior teeth to contact.46
Hawley retainers are
typically worn 24 hours per day for the first 6 months
after active orthodontic treatment, and then only at
night for 12 hours.
Wrap-around Retainer
Another type of removable retainer is the wraparound retainer.
It is similar to the Hawley retainer
except there is a plastic bar along the labial and
lingual surfaces of maxillary and mandibular teeth.46
There are no clasps that extend over the occlusal
surface, therefore permitting the posterior teeth to come
into occlusion.
Positioner
The tooth positioner is a removable appliance that
functions as a finishing appliance, a retainer or both.
After a cast is made from the impression, the teeth can
be reset to ideal positions to improve arch form,
angulation of teeth and minor irregularities.
20
It is a
one-piece rubber appliance for both the maxillary and
mandibular teeth.
Positioners are worn 24 hours per day
during the first two days.
The patient then wears it for
4 hours during the day and while sleeping.
During the 4
hours, the patient is instructed to clench onto the
appliance every 30 seconds, repeatedly.47
According to
Kesling, clenching into the rubber moves the teeth into
position dictated by the appliance and also into more
ideal occlusion to allow post-treatment settling.48
However, a common complaint among patients is that the
positioner is too bulky, uncomfortable and interferes
with speech.47
Perfector
The Perfector is a modified version of the
positioner.
It is made from silicone in order to enhance
patient comfort and acceptance.
The Perfector also has
an anterior labial bow covered with acrylic and seating
springs to enhance retention.
Fabrication of the
Perfector is similar to the Positioner and also has a
patient wear protocol very similar to the positioner.
It
also involves active clenching for 4 hours during the day
and passive wear at night.49
21
Spring Retainer
The spring retainer is a removable retainer that
resembles the Hawley retainer in structure and the
positioner in function.
Like the Hawley retainer, it has
an acyclic base and an adjustable labial bow.
Like the
positioner, the anterior teeth can be reset to ideal
positions.
Acrylic covers the labial bow, actively
positioning the teeth into the preset alignment.
Spring
retainers, depending on design, may also have clasps that
prevent posterior teeth from contacting.
Spring
retainers are typically worn 24 hours per day until
irregularities are corrected.
After that they are worn
only at night, for 12 hours per day.
Fixed Lingual Retainer
Permanent or fixed retention can be used in
situations where there is doubt about patient compliance
in removable retainer wear.
A fixed retainer can be
fabricated a number of different ways.
Knierim first
reported the use of a 0.030 mm stainless steel wire,
adapted to the teeth and bonded to the lingual surface of
the teeth with composite.50
Since then, many clinicians
have incorporated the same technique, but with different
wires.
Alexander uses a 0.0215-inch multistraned
22
stainless steel wire as a fixed retainer for the
mandibular arch.51
A lighter 0.0175 or 0.0195-inch wire
can be used to retain closure of maxillary diastema.46
Booth et al. have shown that patients who have worn a
bonded lingual retainer for over 20 years exhibited no
periodontal problems.52
Essix/Vacuum Formed Retainer/Clear Overlay Retainer
The vacuum formed retainer was introduced by Ponitz
in 1971.
Ponitz called it the “invisible retainers”
because it is made from clear plastic.53
Three decades
after it was first introduced, the vacuum formed retainer
is still fabricated the same way.
the impressions of the patient.
Casts are poured from
A sheet of plastic is
heated until the plastic slumps and the vacuum unit
exerts negative pressure to adapt the plastic over the
patient’s cast.
In 1993, Sheridan introduced the Essix
retainer, which is essentially the same as the vacuum
formed retainer of previous years, except the material is
thinner and stronger.54
Essix retainers are made from
0.030 inch sheets of copolyester plastic.
It covers the
occlusal surface of all teeth and does not allow the
posterior teeth to contact.
Sheridan recommends that the
Essix retainer be worn full-time for a short period and
23
then only at night.54
However, there is no consensus
among clinicians concerning Essix retainer wear.
Post-Orthodontics Occlusion: Settling
The active phase of orthodontic treatment can
produce many positive changes such as better alignment of
teeth, correction of crossbites, correction of impacted
teeth, enhanced esthetics and Class I occlusion.46
Even
though the occlusion may be corrected to Class I
relationship, the active phase of orthodontic treatment
can also have a negative effect on the occlusion.
While
esthetics generally improves, studies have shown that
orthodontic treatment can decrease the number of occlusal
contacts.36,55
The number of occlusal contacts then
increase during the retention phase.
This is a type of
“beneficial” relapse commonly referred to as
“settling.”26,31-33
The literature suggests that the type of
retention device used and the duration of wear also has
an effect on the amount of settling of the posterior
teeth.26,31,32,34
24
Past Studies
Most post-orthodontic occlusal studies demonstrate
that occlusal contacts increase during the retention
phase, after fixed appliance removal and completion of
orthodontic treatment.
Using the photo-occlusion
technique, Gazit and Lieberman measured the occlusal
contacts of the anterior and posterior teeth immediately
after completion of orthodontic treatment on 12 patients
between 14 and 16 years of age.26
Measurements were made
at time of appliance removal, one month after, and one
year after appliance removal.
They reported an average
of 11.2 contacts at the time of appliance removal.
After
one month, 4 patients showed a decrease in the number of
contacts, while 8 showed increases.
At one year after
appliance removal and completion of orthodontic
treatment, all 12 patients showed increases in the number
of contacts, with an average of 17.4.
The 6.2 gain
represents a 56% increase in contacts of both anterior
and posterior teeth.
However, the authors report that no
retention device was used for 3 months prior to the
measurement at one year.
The authors did not specify the
type of retention device used.
A study by Dincer et al. in 2003 produced similar
results pertaining to post-orthodontic occlusal contact
changes.35
In this study, 20 individuals with ideal
25
occlusion served as the control group and were compared
to 20 patients with Class I malocclusion who all had four
premolar extractions and had been treated with standard
edgewise mechanics.
The treated patients were all given
maxillary and mandibular Hawley retainers at time of
appliance removal and were instructed to wear them fulltime for the first six months and nighttime only for the
last three months of the study.
Silicone putty was used
to take the bite registration and measure the posterior
occlusion.
Perforations in the bite registration were
counted as actual contacts and translucent areas were
considered near contacts.
Dincer et al. reported that at
the time of appliance removal, the average number of
posterior contacts (both actual and near) was 11.4.
At
the end of the nine month period after appliance removal,
they reported an average of 19 posterior contacts (both
actual and near), an increase of 67%.
According to the
authors, this was considered a significant increase in
the number of posterior contacts.
However, they noted
that one-third of the increases in posterior contacts
were not in ideal locations.35
Post-orthodontic occlusal studies have also
investigated occlusal contact changes comparing different
retention devices.
In 1986, Durbin and Sadowsky
investigated the post-treatment occlusal changes in 38
patients, 3 months after appliance removal.31
26
The
patients were divided into two groups; 23 were given
maxillary and mandibular Hawley retainers, and 15 were
given tooth positioners as retention device.
The
patients given Hawley retainers were instructed to wear
the appliance at all times except when eating.
The
patients given tooth positioners were instructed to wear
the positioner while sleeping and as much as possible
while awake for the first 2 days; followed by 4 hours,
while awake, for the first 2 weeks; 3 hours for the next
4 weeks, and 2 hours for the last 6 weeks of the study,
while awake.
The authors reported that the patients were
compliant to a large degree and the that the three who
were not compliant were removed from the study.31
The
occlusal bite registration was obtained using polyether
rubber impression material.
The authors reported an
increase in the average number of total contacts from
10.11, at the end of treatment to, 11.53, at 3 months
after appliance removal, regardless of the type of
retention device given.
This represents an overall
increase of 14.05% and was due mostly to increase in
posterior contacts from an average of 8.70 to 10.12
contacts.
The study also showed that patients who had
fewer teeth in contact at the end of treatment developed
more contacts over the 3 month post-treatment period than
those who had more contacts.
27
In the same study, Durbin and Sadowsky also reported
an increase in the average total number of contacts from
7.77 to 8.87 in the tooth positioner group.
This
represents a total increase of 1.10 contacts or 14%.
Hawley group increased from 9.3 to 10.93.
The
This
represents a total increase of 1.63 or 18% from appliance
removal to 3 months post-orthodontic treatment.31
The
average number of posterior teeth in contact increased
from 9.73 to 10.66 (total increase of 0.93 or 10%) in the
positioner group, while the increase in the Hawley
retainer group was from 10.65 to 11.39 (total increase of
0.73 or 7%).
Even though the average number of total
contacts increased significantly more in the Hawley group
(p<.05), the authors reported that the tooth positioner
was statistically more effective than the Hawley retainer
(p<.05) in establishing additional teeth in contact, but
the gain was minimal.
The author concluded that the
interdigitation of teeth improved after orthodontic
appliance removal as settling occurs.
A follow-up to the study by Durbin and Sadowsky
was conducted by Razdolsky et al. in 1989.
In this
study, 28 of the 38 patients originally evaluated by
Durbin and Sadowsky, along with an additional 12 patients
were evaluated from 11 to 21 months after orthodontic
appliance removal.32
During the period of the study, 28
patients had a maxillary Hawley retainer and a mandibular
28
fixed lingual retainer.
Three patients had tooth
positioners, followed by maxillary Hawley retainers and 8
patients had maxillary and mandibular Hawley retainers.
One patient had only a maxillary Hawley retainer.
Patients with removable retainers were instructed to wear
the retainers full-time for 6-12 months and then at night
only, for the remainder of the study.
Similar to the
original study, the occlusal bite registration was
obtained using polyether rubber impression material and
the actual contacts were recorded as perforations in the
bite registration.
Unlike the original study, Razdolsky
et al. also recorded areas of near contact as a change in
the color of the bite registration material from yellow
to transparent white.
The results showed that the mean
number of teeth in contact increased from 17.5 at the
time of appliance removal to 20.7 (18% increase),
approximately 21 months later, which was statistically
significant (p<0.01).
They also reported that the mean
number of contacts (actual and near contacts combined)
increased from 36.6 to 58.2, a total increase of 59% or
21.6 total contacts, between the two time points of
measurement (p<.001).
Haydar et al. also compared the tooth positioner to
the Hawley retainer.33
In this study, 10 patients were
assigned maxillary and mandibular Hawley retainers and 10
patients were assigned tooth positioners after completion
29
of orthodontic treatment.
A non-treated control group of
10 people was also examined.
The authors did not specify
whether or not the patients were randomly assigned.
Bite
registrations, using a soft silicone-based impression
material, were obtained at the time of appliance removal
and again at 3 months after appliance removal.
The bite
registrations were evaluated visually by holding them up
to daylight.
Perforations were counted as actual
contacts and thin transparent sections were counted as
near contacts.
The total number of contacts at time of
appliance removal was 21.2 for the Hawley group, 24.8 for
the tooth positioner group and 39.4 for the untreated
control group.
At 3 months post-appliance removal, the
total number of contacts was 22.4 for the Hawley group,
27.0 for the tooth positioner group and 40.5 for the
untreated control group.
This represents an increase of
6%, 9%, and 3% respectively.
The authors concluded that
there were no statistically significant differences in
posterior contacts between the 3 groups studied.33
In 2009, Horton et al. published a study comparing
the short-term changes in posterior occlusion produced by
the Perfector and Hawley retainer.56
In this study, 50
patients who completed orthodontic treatment were
randomly assigned to either a Perfector/Spring aligner
group or a Hawley retainer group.
Twenty-two patients
received maxillary and mandibular Hawley retainers and
30
instructed to wear the retainer full-time.
Twenty-eight
patients received a Perfector and mandibular spring
retainer and instructed to wear both devices at night,
while sleeping.
According to the manufacturer’s
instructions, the patients were to perform clenching
exercises 3-4 hours during the first two weeks, followed
by 2-3 hours during the next 4 weeks, and for 2 hours the
final two weeks of the study.
However, during the
interim period (about 4 weeks), while the retainers were
being made, both groups were where given Essix retainers
and instructed to wear them full-time.
Occlusal bite
registrations were taken with Blu Mousse at time of
orthodontic appliance removal and 2 months postorthodontic appliance removal.
The bite registrations
were scanned and evaluated using Image Tool software.
The results indicated that the areas of contact and near
contact (ACNC) in the Hawley group increased from 6.7
mm², at time of appliance removal, to 11 mm² at 2 months
post-orthodontic treatment; a 64% increase. The ACNC for
the Perfector/Spring Aligner group also increased from
8.4mm² at time of appliance removal to 13 mm² at 2 months
post-orthodontic treatment; a 55% increase.
Although,
the gain in number of ACNC were statistically significant
(p<.05) in both groups during the 2 months of this study,
there was no significant difference (p<.05) between the
two groups.
The patient’s perception of occlusion was
31
also assessed using a seven-item questionnaire.
Patients
in the Perfector/Spring Aligner group 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.
Horton et
al. concluded that ACNC increased substantially and
similarly in patients wearing Hawley retainers and
Perfector/Spring Aligners and there was no difference
between the two groups in post-orthodontic settling.56
Bauer et al. conducted a follow-up study to the
original study by Horton et al.56,57
In this study, Bauer
et al. recalled 40 of the 50 patients from the original
study.
Twenty-five were from the Perfector/Spring
aligner group and 15 were from the Hawley group.
Patients in the Perfector/Spring aligner group were given
Hawley retainers at 2 months post-orthodontic treatment.
Methods to obtain the bite registration and quantitative
analysis of ACNC were identical to the original study by
Horton et al.
However, measurements were taken at 4 time
points: (T1), at the end of orthodontic treatment, (T2),
2 months post-orthodontic treatment, (T3), 6 months postorthodontic treatment and (T4), 8 months post-orthodontic
treatment.
The results indicated that the Hawley group
showed a 129% increase in ACNC, while the
Perfector/Hawley group showed a 105% increase in ACNC
during the 8 months of the study.
32
The greatest increase
in ACNC was between T1-T2.
The Hawley group showed
greater increases in ACNC from T2-T3, while the
Perfector/Hawley group showed slightly greater increases
from T3-T4.
In agreement with Horton et al., the authors
of this study concluded that the gain in ACNC were not
significantly difference between the two groups after 8
months of retention wear.56,57
Studies Comparing Hawley Retainer to Essix (Vacuum
Formed) Retainer
The Hawley retainer and the vacuum formed retainer
(Essix) are the 2 most commonly prescribed retainers in
the United States and the United Kingdom.58
Despite their
popularity and frequency of use, only a few studies have
been conducted comparing the effectiveness of these two
retention devices.
In 1998, Lindauer and Shoff published
the first study comparing Hawley and Essix retainers.59
In this study, 19 patients were given Essix retainers
after full orthodontic treatment. They were instructed to
wear the mandibular Essix retainer full-time and the
maxillary Essix retainers at least half-time for the
first 4 weeks, and both retainers only at night
afterwards.
Twenty-one patients were given Hawley
retainers and instructed to wear the retainers full-time
for the first 3 months and only at night, or 12 hours per
33
day afterwards.
Study casts were taken at the end of
orthodontic treatment and 6 months post-orthodontic
treatment.
The casts were used to measure anterior
crowding using Little’s Irregularity Index, overbite and
overjet.
The results showed that at 6 months post-
orthodontic treatment, patients in the Hawley retainer
group showed slightly more incisor irregularity in both
arches than the Essix, but the difference was
statistically significant only in the maxillary arch
(p<.05).
They also reported that there were no
significant differences between groups in the amount of
change in overbite or overjet that occurred.
No patients
in either group developed anterior open bites. The
authors concluded that Essix retainers are just as
effective as Hawley retainers in maintaining orthodontic
corrections and preventing relapse of the dentition.59
A more recent study comparing the effectiveness of
Hawley to Essix retainers in maintaining orthodontic
corrections and preventing relapse was conducted in 2007
by Rowland et al.58
This study was a randomized trial and
used a much larger sample size than Lindauer and
Shoff’s.59
After completion of orthodontic treatment, 196
patients were randomly assigned Hawley retainers and
instructed to wear them full-time for the first 3 months,
and only at night for the next 3 months.
A total of 201
patients were randomly assigned Essix retainers, which
34
they were instructed to wear full-time for the first
week, and only at night, or 12 hours per day for the
remainder of the study.
At the end of the study, only
155 patients remained in each group.
The others were
dropped from the study due to loss, damaged, noncompliance, or withdrawal from the study.
Study models
of the patients were taken at orthodontic appliance
removal and at 6 months post-orthodontic appliance
removal.
The results showed no statistically significant
difference between the two retainer groups in the changes
that occurred in overbite, overjet, intercanine width,
and intermolar width.
However, a statistically
significant difference was found between the retainers in
the maintenance of incisor irregularity; the Hawley group
demonstrated almost twice as much the change in incisor
irregularity over the 6 month period.
The Hawley group
had a 0.51 mm change in incisor irregularity, while the
Essix group had a 0.26 mm change in incisor irregularity.
The authors concluded that the Essix or vacuum formed
retainers were more effective than Hawley retainers at
preventing incisor irregularity, but that the two
retainers were equally effective in maintaining overjet,
overbite, intercanine width, and intermolar width.58
Hichens et al. conducted a study comparing
effectiveness and patient satisfaction of Essix and
Hawley retainers.60
A total of 196 patients were randomly
35
assigned to the Hawley group, and 201 patients were
randomly assigned into the Essix group.
assessed after 3 months and 6 months.
time points, all patients were given
Each group was
At the respective
questionnaires to
fill out; cost analysis was based on patient records and
national databases.
A total of 352 questionnaires
(Hawley 171, Essix 181) were completed at the 3 month
time point.
No significant difference was found between
the two retainer groups at that time.
At the 6 month
time point, a total of 350 questionnaires (Hawley 168,
Essix 182) were completed.
At the 6 month time point,
the results showed that patients in the Essix group wore
their retainers as instructed more often than the Hawley
group.
Patients also indicated that the Hawley retainers
caused more embarrassment in terms of speech and
esthetics.
More patients in the Hawley group broke their
retainers than patients in the Essix group.
It was also
determined through cost analysis that the Essix retainer
was more cost-effective than the Hawley retainer to the
clinician and the patients over the 6 months period.
The authors concluded that Essix retainers are less
likely to be broken, cause less embarrassment, and are
more cost effective for the clinician and the patient
than Hawley retainers over the first 6 months posttreatment.
36
A very limited amount of research exists comparing
the posterior occlusal changes of the Hawley and Essix
retainer.
A clinical trial of unknown duration by
Sheridan et al. reported that 11 out of 407 patients
given Essix retainers developed a slight anterior open
bite.54
Sauget et al. conducted a study in 1995
comparing the occlusal contacts of clear overlay
retainers and Hawley retainers.34
Thirteen patients
received maxillary and mandibular Hawley retainers; two
patients received maxillary Hawley retainers with
mandibular fixed lingual retainers, and 15 patients
received maxillary and mandibular clear overlay
retainers.
The patients who received Hawley retainers
were instructed to wear them full-time.
The patients who
received clear overlay retainers were instructed to wear
them full-time for the first 3 days then nightly
afterwards.
Vinyl polysiloxane was used to record
occlusal contacts at 3 time points; at the time of
appliance removal (T1), at the time of retainer delivery,
one week later (T2), and at 3 months after retainer
delivery (T3).
The bite registrations were viewed using
a light box; perforations were counted as actual contacts
and thin translucencies were counted as near contacts if
they were 0.20 mm or less thick.
This evaluation of
translucencies may be affected by the subjectivity of the
authors.
At T1, the Hawley retainer group had a mean of
37
34.3 total contacts (actual and near), while the clear
overlay retainer group had 31.8 total contacts.
There
were no significant changes between T1 and T2.
At T3,
after 3 months retention, the Hawley group had a mean of
45.7 total contacts and the clear overlay retainer group
had a mean of 36.7 total contacts.
Based on posterior
contacts only, the Hawley group had an average increase
of 10.6 contacts from T1 to T3; a 33% increase. The clear
overlay retainer group only had an average increase of
4.2 contacts; an increase of 13%.
These changes in
posterior occlusion were statistically significant.
It
was concluded that the Hawley retainer allowed
significantly more settling of the occlusion than the
clear overlay retainer.34
The authors did not discuss
whether the two patients given maxillary Hawley retainers
and mandibular fixed lingual retainers skewed the data.
They also failed to mention whether the patients in the
two retainer groups were randomly allocated.
Dincer and Aslan published the most recent study
investigating the effects of Essix retainers on posterior
occlusion.61
They investigated the long term changes in
occlusal contacts with Essix retainers.
Fifteen Class I
patients with four premolar extractions completed
orthodontic treatment and were given Essix retainers.
Fifteen Class I untreated individuals served as the
controls.
Patients were given maxillary and mandibular
38
Essix retainers at the time of appliance removal and were
instructed to wear them full-time for 6 months and then
only at night for the next 3 months.
Occlusal records
were taken using the methods described by Razdolsky et
al. at the time of retainer delivery (T0), at the end of
the 9 month retention period (T1) and 2.5 years after
removal of appliance (T2).32
viewed under a light box.
The bite registration was
Perforations and thin
transparent sections without perforations were also
counted.
was 21.80.
The average number of posterior contacts at T0
At T2 the average number of posterior
contacts was 22.13 indicating no significant changes
compared to T0.
However, at T3, the average number of
posterior contacts increased to 27.67, a 27% increase;
exceeding the number of average posterior contacts in the
untreated control group.
It was concluded that in the
long term, the number of occlusal contacts increased with
Essix retainers.61
The authors did not take records at
any time during full-time Essix wear, nor did they
indicate whether patients continued to wear the Essix
retainer at night after the 9 month retention period.
Similar to the study by Sauget et al., this study was
also affected by the subjectivity of the authors in
counting the contacts they considered to be actual and
near.
39
Overall, there have been very few studies evaluating
the Essix retainer as a retention device.
Two studies
indicate that the Essix retainer is slightly superior to
the Hawley retainer in preventing incisor
irregularities.58,59
However, this may be due to the Essix
being more readily accepted by patients than the Hawley
retainer.
One study showed that Essix retainers
increased the number of occlusal contacts over the long
term, but they did not indicate whether patients
continued to wear the Essix retainers after the retention
period.61
The study may also have been affected by the
subjectivity of the authors in quantifying actual and
near occlusal contacts.
Only one study exists comparing
the Essix retainer to the Hawley retainer and the method
of evaluation may also be affected by the subjectivity of
the authors and lack of random allocation of the
patients.34
Conclusion
The goals of the retention phase are to prevent
relapse, maintain the alignment and esthetics of the
dentition and allow for post-treatment settling of the
occlusion.
Currently, there are many different types of
retention devices available for the orthodontist to
prescribe.
It is up to the orthodontist to prescribe a
40
retainer that will best achieve this goal.
Clinical
experience gives orthodontists a preference in retention
device, but that preference is subject to bias.
A review
of the literature shows that there is very limited
evidence based research that directly compares different
types of retention devices.
Among these studies, there
is even less that reaches a definite conclusion as to
which retainer is best for the retention phase.62
As previously stated, one of the goals of the
retention phase is to allow for post-treatment settling
of the posterior occlusion.
Many of the past studies
used unreliable methods, such as articulating indicators,
photo-occlusion method and T-scan to evaluate the
settling of the occlusion during retention.
Also, the
samples in the study were not randomly allocated.
More
importantly, these studies relied on visually evaluating
the bite registration and counting the contacts,
introducing bias and subjectivity in to the study.
Despite the fact that Hawley retainers and Essix
retainer remain the two most commonly prescribed
retainers, there is little evidence as to which is best
for the posterior occlusion.
Two studies have shown that
the Essix and Hawley retainer are as equally effective in
maintaining alignment of the dentition; the Essix may
even be slightly superior in preventing incisor
irregularity when compared to the Hawley retainer.58,59
41
Only one study compared settling of the occlusion with
the Essix retainer and the Hawley retainer.34
Although it
was determined by the authors of this study that the
Hawley retainer allowed more posterior settling than the
Essix retainer, the method of visually counting and
evaluating the contacts introduces subjectivity and bias.
Also, this study placed patients who received Essix
retainers and Hawley retainers on different wearing
protocols.
While, most clinicians agree that the Hawley
retainer requires full-time wear, there is no agreement
on the protocol for Essix wear.62-64
Another aspect that
has not been investigated is the patient’s perception of
the posterior occlusion during retention.
The goal of the present study was to evaluate and
compare the effects of two different types of retainers
on the posterior occlusion 1 month and 3 months postorthodontic treatments using the same wear regimen.
Occlusal bite registration were obtained using siliconebased impression material and analyzed using optical
scanning and Image Tool to avoid subjectivity of the
investigator.
The area of occlusal contacts and near
contacts were measured to access whether or not a there
is a difference in the posterior settling between the
Essix retainer and the Hawley retainer given identical
wear regimen.
The patient’s perception of their
posterior occlusion were also evaluated.
42
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Unilateral, isometric bite force in 8-68-year-old women
and men related to occlusal factors. Scand J Dent Res.
1990;98:149-158.
19. Ingervall B, Minder C. Correlation between maximum
bite force and facial morphology in children. Angle
Orthod. 1997;67:415-422.
20. Julien K, Buschang P, Throckmorton G, Dechow P.
Normal masticatory performance in young adults and
children. Arch Oral Biol. 1996;41:69-75.
21. Owens S, Buschang P, Throckmorton G, 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.
22. Millstein P, Maya A. An evaluation of occlusal
contact marking indicators. A descriptive quantitative
method. J Am Dent Assoc. 2001; 132:1280-1286.
23. 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.
24. Millstein P. An evaluation of occlusal contact
marking indicators: a descriptive, qualitative method.
Quintessence Int Dent Dig. 1983; 14:813-836.
25. Kerstein R. Articulating paper mark misconceptions
and computerized occlusal analysis technology. Dent
Implantol Update. 2008; 19:41-46.
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26. Gazit E, Lieberman M. Occlusal contacts following
orthodontic treatment. Measured by a photocclusion
technique. Angle Orthod. 1985;55:316-320.
27. Gazit E, Lieberman M, Fitzig S. Reproducibility of
occlusal marking techniques. J Prosthet Dent. 1986;
55:505-509.
28. Maness W, Benjamin M, Podoloff R, Bobick A, Golden R.
Computerized occlusal analysis: a new technology.
Quintessence Int. 1987;18:287-292.
29. Hsu M, Palla S, Gallo L. Sensitivity and reliability
of the T-scan system for occlusal analysis. J
Craniomandib Disord Facial Oral Pain. 1992;6:17-23.
30. Lyons M, Sharkey S, Lamey P. An evaluation of the TScan computerised occlusal analysis system.Int J
Prosthodont. 1992;5:166-172.
31. Durbin D, Sadowsky C. Changes in tooth contacts
following orthodontic treatment. Am J Orthod Dentofacial
Orthop. 1986;90:375-382.
32. Razdolsky Y, Sadowsky C, BeGole E. Occlusal contacts
following orthodontic treatment: a follow-up study. Angle
Orthod. 1989; 59:181-186.
33. 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.
34. Sauget E, Covell DJ, Boero R, Lieber W. Comparison
of occlusal contacts with use of Hawley and clear overlay
retainers. Angle Orthod. 1997;67:223-230.
35. Dincer M, Meral O, Turner N. The investigation of
occlusal contacts during the retention period. Angle
Orthod. 2003;73:640-646.
36. Moller E, Bakke M. Occlusal harmony and disharmony:
frauds in clinical dentistry? Int Dent J. 1988; 38:7-18.
37. Sakaguchi R, Anderson G, Delong R. Digital imaging
of occlusal contacts in the intercuspal positon. J
Prosthodont. 1994;3:193-197.
38. Riedel R. A review of the retention problem. Angle
Orthod. 1960;30:179-199.
45
39. Reitan K. Clinical and histologic observations on
tooth movement during and after orthodontic treatment. Am
J Orthod. 1967;53:721-745.
40. Little R, Riedel R, Artun J. An evaluation of changes
in mandibular anterior alignment from 10-20 years
postretention. Am J Orthod Dentofacial Orthop.
1988;93:423-428.
41. Little R, Wallen T, Riedel R. Stability and relapse
of mandibular anterior alignment-first premolar
extraction cases treated by traditional edgewise
orthodontics. Am J Orthod. 1981;80:349-365.
42. Nanda R, Nanda S. Considerations of dentofacial
growth in long-term retention and stability: is active
retention needed?. Am J Orthod Dentofacial Orthop.
1992;101:297-302.
43. Driscoll-Gilliland J, Buschang P, Behrents R. An
evaluation of growth and stability in untreated and
treated subjects. Am J Orthod Dentofacial Orthop.
2001;120:588-597.
44. Melrose C, Meillett D. Toward a perspective on
orthodontic retention? Am J Orthod Dentofacial Orthop.
1998; 113:507-514.
45. Hawley C. A removable retainer. Dent. Cosmos.
1919;61:449.
46. Proffit W, Fields H, Sarver D. Contemporary
Orthodontics 4th edition. St. Louis: Mosby;2007.
47. Binder R. Retention and post-treatment stability in
the adult dentition. Dent Clin North Am. 1988;32:621-641.
48. Kesling H. The philosophy of the tooth positioning
appliance. Am J Ortho and Oral Surg. 1945;31:297-304.
49. Elasser W. Some observations on the history and uses
of the Kesling positioner. 1950;36: 368-374.
50. Knierim R. Invisible lower cuspid to cuspid retainer.
Angle Orthod. 1973;43:218-220.
51. Alexander R. The 20 Principles of the Alexander
Discipline. Chicago: Quintessence; 2008.
52. Booth F, Edelman J, Profitt W. Twenty-year follow-up
of patients with permanently bonded mandibular canine-to46
canine retainers. Am J Orthod Dentofacial Orthop.
2008;133:70-76.
53. Ponitz R. Invisible retainers. Am J Orthod.
1971;59:266-272.
54. Sheridan J, LeDoux W, McMinn R. Essix retainers:
fabrication and supervision for permanent retention. J
Clin Orthod. 1993;27:35-45.
55. Deng Y, Fu M. Occlusal contact changes before and
after orthodontic treatment of a group of children &
adolescent patients with TMJ disturbance. Aust Orthod J.
1995;13:231-237.
56. Horton J, Buschang P, Oliver D, Behrents R.
Comparison of the effects of Hawley and perfector/spring
aligner retainers on postorthodontic occlusion. Am J
Orthod Dentofacial Orthop. 2009;135:729-736.
57. Bauer E, Buschang P, Oliver D, Behrents R. Posterior
occlusal changes with a Hawley vs Perfector/Hawley
retainer. 2007. Angle Orthod. (pending).
58. Rowland H, Hichens L, Williams A, et al. The
effectiveness of Hawley and vacuum-formed retainers: a
single randomized controlled trial. Am J Orthod
Dentofacial Orthop. 2007;132:730-737.
59. Lindauer S, Shoff R. Comparison of Essix and Hawley
retainers. J Clin Orthod. 1998;65:95-97.
60. Hichens L, Rowland H, Williams A, et al. Costeffectiveness and patient satisfaction: Hawley and
vacuum-formed retainers. Eur J Orthod. 2007;29:372-378.
61. Dincer M, Aslan B. Effects of thermoplastic
retainers on occlusal contacts. Eur J Orthod. 2009; Epub
ahead of print.
62. Littlewood S, Millet D, Doubleday B, Bearn D,
Worthington H. Orthodontic retention: a systematic
review. J Orthod. 2006; 33:205-212.
63. Ledvinka J. Vacuum-formed retainers more effective
than Hawley retainers0. Evid Based Dent. 2009;10:47.
64. Kau C. Orthodontic retention regimes: will we ever
have the answer? Evid Based Dent. 2006;7:100.
47
Chapter 3: Journal Article
Abstract
Purpose:
To evaluate and compare the posterior
occlusal changes between the Essix and Hawley retainer
during the first 3 months of retention.
Methods:
This
randomized trial evaluated 40 patients who had completed
full orthodontic treatment and been assigned to wear
either Essix or Hawley retainer.
They were evaluated at
three time points, debond (T1), one month after debond
(T2) and three months after debond (T3). Duplicate bite
registrations were used to quantity posterior areas of
contact and near contact (ACNC).
The patient’s
perceptions about their occlusion and compliance with
retainers wear were evaluated using a five item
questionnaire.
Results:
Both the Essix and the Hawley
retainers produced slight decreases in ACNC from T1 to
T2.
At T2, there were significant (p<.05) group
differences of cumulative ACNC at ≤50 µm and ≤100 µm,
with the Hawley group having greater ACNC.
showed increases in ACNC from T2 to T3.
Both groups
At T3,
significant group differences of cumulative ACNC were
observed at ≤50 µm, ≤100 µm, ≤150 µm and ≤200 µm; again,
with the Hawley group showing greater ACNC than the Essix
48
group. Total cumulative ACNC of the Essix group decreased
from 19.3 mm² at T1 to 17.5 mm² at T3; ACNC of the Hawley
increased from 21.2 mm² at T1 to 22.1 mm² at T3. Group
differences in ACNC at T3 were not statistically
significant.
Conclusion:
The Hawley retainer produces
greater ACNC than the Essix retainer, especially at or
below the 200 µm level, but the differences are small.
49
Introduction
Ideal occlusion has been defined as Class I molar
and canine relationships, along with a maximum number of
contacts between the cusp tips and marginal ridges of
maxillary and mandibular teeth.1,2
Obtaining ideal
occlusion is an important goal of orthodontic treatment
because patients with Class I molar relationship are able
to break down foods better than patients with Class II or
Class III molar relationship.3
Individuals who possess
normal occlusion are able to break down foods better than
those with malocclusion because they have larger areas of
contact and near contact (ACNC) between opposing teeth.4,5
Masticatory performance and bite force are also directly
related to the number of occlusal contacts.6-8
While there is no debate regarding the importance of
ideal occlusion, post-orthodontic retention remains as
one of the most controversial issues in orthodontics.
The goal of the retention phase is to prevent relapse,
maintain esthetics of dentition and allow for posttreatment settling of the occlusion.
It is well
established that relapse of the dentition relates to
periodontal factors, the stability of the occlusion and
growth.9,10
While there is no disagreement that retainers
are needed to prevent relapse of the dentition, a
spectrum of wavering opinions exists as to the which
50
retention device will be most efficient in allowing
settling of the occlusion.11,12
Studies have shown that occlusal contacts decrease
during orthodontic treatment, but increase during
retention.13-15
The type of retainer used has been shown
to have a direct influence on the amount of occlusal
contacts gained during retention.
For example, Dincer et
al. reported a 67% increase in contact and near contact
numbers for patients wearing Hawley retainer nine months
post-orthodontic treatment.16
Durbin and Sadowsky showed
a greater increase in the number of tooth contacts for
subjects wearing tooth positoners(18% increase) than
those wearing Hawley retainers(14% increase) at three
months post-debond.15
In contrast, Haydar et al. found no
statistically significant difference between the
positioner (6% increase) and the Hawley retainer (3%
increase) three months after orthodontic treatment.17
Importantly, the samples in each of these studies were
not randomized, making the results susceptible to bias,
and the data were subjectively tallied based on the
researchers’ visual assessment of occlusal contacts and
near contacts.
Horton et al. recently conducted a randomized study
comparing the occlusal changes between patients wearing
Perfector/Spring Aligner or Hawley retainers.18
They
found that areas of contact and near contact (ACNC)
51
increased less with the Perfector/Spring Aligner (55%)
than with the Hawley retainer (64%) two months postdebond, but the group differences were not statistically
significant.
However, there was an interim period of 4
weeks, from debond of braces to delivery of retainers,
during which the subjects in both groups wore Essix
retainers while their retainers were being fabricated.
Despite the fact that the Essix and Hawley retainer
are the two most commonly prescribed retainers in the
United States and the United Kingdom19, there has been
only one study directly comparing their effects on the
posterior occlusion.
Sauget et al. found that Hawley
retainers (33%) produce significantly greater contact and
near contact numbers than Essix retainers (13%) three
months post-debond.20
However, their patients were not
randomized and the authors visually counted the contacts
and near contacts rather than quantifying the total ACNC.
The purpose of this study was to objectively
evaluate and compare the posterior occlusal changes in
patients who have been randomly allocated to wear either
an Essix or Hawley retainer.
This information is
important because the Essix and Hawley retainer are the
two most commonly prescribed retainers, even though their
effect on the posterior occlusion have not been well
established.
52
Materials and Methods
Sixty subjects were recruited from Saint Louis
University, Center for Advanced Dental Education,
Department of Orthodontics, between March 1, 2009 and
August 15, 2009.
All subjects had completed full
orthodontic treatment to Class I molar and canine
relationships.
Subjects were excluded from the study if
they had any history of temporomandibular disorder, large
restorations on posterior teeth, allergies to any
materials used this study and periodontal disease and /or
muscular dysfunction.
Subjects were also withdrawn from
the study if they were non-compliant with regards to
retainer wear, lost their retainers, or did not have
longitudinal records.
This study was approved by the
Biomedical Institutional Review Board at Saint Louis
University.
The 60 subjects were randomly assigned to either to
the Hawley retainer group or to the Essix retainer group;
30 in the Hawley group and 30 in the Essix group.
Those
in the Hawley group received maxillary and mandibular
Hawley retainers; those in the Essix group received
maxillary and mandibular Essix retainers.
Ten subjects
in the Essix group and 10 subjects in the Hawley group,
who either lost their retainers or failed to show up for
their follow-up appointment, were excluded from the
53
study.
A total of 20 subjects in Essix group and 20
subjects in the Hawley group fully participated in the
study.
Each group had two subjects with 4 premolar
extractions.
Maxillary and mandibular Essix retainers for the
patients in the Essix group were immediate fabricated and
delivered at the same appointment.
All Essix retainers
were fabricated using Essix C+ and were trimmed 2 mm
below the gingival margins.
Subjects assigned to the
Hawley group had alginate maxillary and mandibular
impressions taken one appointment prior to debonding the
braces.
The Hawley retainers were all fabricated by the
same laboratory with ball clasps mesial to the first
molar.
Subjects in the Hawley group also received their
retainers at the debonding appointment.
Both groups were
instructed to wear their retainers full-time, except when
eating and brushing.
Data were collected at three time points: At debond
of braces (T1), one month post-debond (T2) and three
months post-debond (T3).
At each time point, two sets of
bilateral posterior bite registrations were taken in
maximum intercuspation using Blu Mousse (Parkell BioMaterials, Farmingdale, NY), a silicone bite registration
material.
Blue Mousse was applied to the occlusal
surface of mandibular 1st and 2nd premolars and 1st molars.
54
The subjects were instructed to bite down firmly and hold
in maximum intercuspation for approximately 1 minute.
Each occlusal registration was placed in holders
with the mandibular occlusal surface facing down and
scanned at 300 DPI.
The mandibular premolars and 1st
molars were traced using Image Tool (University of Texas
Health Science Center, San Antonio) software, which
calculated the platform area of the traced teeth and the
frequency distribution of pixels within the platform
based on 256 possible gray scales (See Appendix for all
tables and figures; Fig. 1-3).
The calibration curve
developed by Horton et al. was used to correlate the 256
gray scales obtained from Image Tool and ACNC thickness
of the occlusal registration obtained from the
subjects(Fig. 4).18
The thickness of the occlusal
registration ranges from 0 µm to 350 µm, with the upper
limit for scanned light to be at approximately 350 µm.
The thicknesses were analyzed in increments of 50 µm.
thickness of 0-50 µm represents actual contact of teeth
A
and any increments above that represents areas of near
contacts.
Patient perception of their occlusion was also
accessed at the 3 time points (T1, T2 and T3) using
questions from a seven-item questionnaire developed by
Horton et al to assess opinions about their occlusion,
level of discomfort with their occlusion, their
55
masitcatory function and compliance with retainer wear.18
A 148 mm analogue scale was used with the following
questions:
Q1.
How often do you wear your retainer as
instructed by your orthodontist? (Asked at T2 and T3
only)
Q2.
How well do your back teeth fit together when
you bite down hard?
Q3.
Do your back teeth contact each other evenly
when you bite down hard?
Q4.
How well can you chew tough meats, such as
steak or chops, with your back teeth?
Q5.
How much pain do you feel when you bite down
hard on your back teeth?
The terms “very often” or “never,” “very well or very
poor,” and “none” or “very much” served as anchors for
the visual analog scale.
Statistical Analysis
Central tendencies and dispersions were described
using medians and interquartile ranges due to the
skewness and kurtosis of the data.
The five perception
questions were changed to percents ranging from 0-100 by
dividing each response by 148.
The Wilcoxon signed
ranked test was used to evaluate changes over time and
56
the Mann-Whitney test was used to evaluate group
differences.
Results
At debond, there were no significant differences
between the Hawley and the Essix retainer groups in ACNC
or cumulative ACNC.
Cumulative ACNC 350 µm in the Essix
and Hawley groups decreased 24% and 3%, respectively,
during the first month, but neither of the changes was
statistically significant (Table 1,2).
The decreases in
ACNC during the first month were followed by a 20%
increase in cumulative ACNC for the Essix group and an 8%
increase for the Hawley group during the second and third
month (Table 1, Fig. 5).
One month after debond, cumulative ACNC showed
statistically significant (p<.05) group differences
between the Essix and Hawley retainer groups at the ≤50
µm and the ≤100 µm levels (Table 1, Fig 6).
Areas of
contact (≤50 µm) of the Essix group (0.3 mm²) were
significantly smaller than the areas of contact of the
Hawley group (0.9 mm²).
For ACNC, the Essix group also
had significantly smaller ACNC ≤100 µm than the Hawley
group (1.2 mm² versus 2.4 mm²).
There were also
statistically significant group differences at the 50-100
µm and the 300-350 µm levels, with the Hawley group
57
having greater ACNC than the Essix group at each level
(Table 1, Fig. 6, 7).
At three months post-debond, there were
statistically significant group differences in cumulative
ACNC at the ≤50 µm, ≤100 µm, ≤150 µm and ≤200 µm levels,
with consistently greater ACNC for the Hawley than the
Essix retainers (Table 1, Fig. 8).
The Hawley group had
significantly greater ACNC at the 0-50 µm and 50-100 µm
levels than the Essix retainer group (Table 1, Fig 9).
Total cumulative areas of contact and near contact
(ACNC  350 µm) of the Essix group decreased from 19.3
mm² at debond to 17.5 mm² three month post-debond,
representing a decrease of 9%.
In contrast, the Hawley
showed a slight (5%) increase in total cumulative ACNC
over the same three month period, from 21.2 mm² at debond
to 22.1 mm² (Table 1, Fig. 1).
However, group
differences in the total cumulative changes ACNC that
occurred between debond and three months post-debond were
not statistically significant. The only statistically
significant group difference was at the 100-150 µm level,
where the Essix group demonstrated a 0.4 mm² decrease and
the Hawley showed a 0.1 mm² increase (Table 2).
At the time of debond, patients in both the Essix
and Hawley retainer group reported that their back teeth
fit together very well when they bit down hard (Q2),
contacted each other very evenly when they bit down hard
58
(Q3), they were able to chew tough meats very well (Q4),
and had little or no pain when they bite down hard (Q5).
Patients in the Hawley group reported that their teeth
fit together significantly better than the patients in
the Essix group; the other questions showed no
statistically significant group differences at the time
of debond (Table 3).
Both groups reported small
improvements during the first month.
Patients in the
both groups indicated a worsening of their occlusion
during the second and third months (Table 3). However,
there were no statistically significant group differences
at T2 or T3 in changes that occurred (Table 4).
After the first month, both the Essix group (93%)
and the Hawley group (91%) reported that they wore their
retainers as instructed by their orthodontist (Q1).
Little or no change in compliance of retainer wear
occurred during the second and third months.
Reported
compliance for the Essix and Hawley groups were 88% and
90%, respectively, at the three month assessment.
There
were no statistically significant group differences in
the patients’ perception of how well they wore their
retainers at either of the time points or in the changes
that occurred over time (Table 4).
59
Discussion
Three months after orthodontic appliance removal,
the ACNC of the Essix group showed an overall decrease of
1.8mm², representing 9% decrease.
This differs from the
13% increase in ACNC reported by Sauget et al. at three
months post-appliance removal.20
While both studies
evaluated the subjects at the same time point.
Sauget et
al. instructed their subjects to wear the Essix retainers
only at night, while the subjects in the present study
instructed the subjects to wear their retainers fulltime.20
A greater increase for subjects wearing the Essix
only at night might be expected, due to increase in the
posterior occlusion as subjects transition from full-time
to part-time wear.
The decrease in ACNC between the time
of debond and three months later is likely a due to the
fact that Essix retainer covers the occlusal surface and
not only prevents the posterior teeth from settling, but
actually disoccluded the teeth slightly.
In fact, the patients in the Essix group experienced
a substantial (24%) decrease in ACNC during the first
month after debond, followed by an increase of 20% during
the subsequent three months.
At the end of the three
months of retention, the ACNC were still below, but
closely approximated, the ACNC at debond.
Dincer and
Aslan found no significant changes overtime, but their
60
measurements were take nine months after debond, the last
three months of which patients only wore their Essix
retainers part-time.21
It is not unreasonable to assume
that if measurements were taken while patients were still
wearing Essix retainers full-time that they would also
observe an initial rate of decrease in ACNC, followed by
an increase of ACNC close to the value at debond.
The
initial, decreases in ACNC may have been due to the
posterior teeth being unaccustomed to the Essix
retainers, as the dentition adjusted to the retainers,
the ACNC returned near the amount at debond.
The Hawley group demonstrated an overall increase of
0.9 mm² over the three months of retention, representing
a 5% increase.
The findings compares well with those of
Haydar et al who reported a 6% increase over a period of
3 months in subjects wearing Hawley retainers full-time.17
Dincer et al. reported a 67% increase in contacts and
near contacts, but their measurements were taken nine
months after debond, the last three months of which the
patients only wore their Hawley retainers part-time.16
Despite using similar methods to measure the
posterior occlusion, a disparity exists between the
present results and those of Horton et al., who reported
a 63% increase in ACNC after 2 months.18 The difference
could be due to the fact that Horton and colleagues kept
their patients in Essix retainers for approximately 4
61
weeks while the retainers for the study were being made.
Based on the present results, which indicate that there
is an initial 24% decrease in ACNC for patients wearing
Essix retainers during the first month, the 66% increase
in ACNC reported by Horton et al. may include a
compensation for the initial decrease, along with the
lesser increase associated with Hawley retainers.
This
further supports the finding that Essix retainers may
initially decrease ACNC because it covers the occlusal
surface of all teeth.
In addition, the Hawley retainers
in the present study were made in a different lab and it
is also possible that the lab used different size ball
clasps for retention of the Hawley retainers.
According to Sheridan et al., the minimum bulk
thickness of the first Essix retainer was 0.015”.
then, the material has become thicker.
in the present study is 0.040”.
Since
The Essix C+ used
According to Raintree
Essix, after the plastic conforms to the impression
model, the thickness of the retainer is 0.030” (762 µm),
yielding a bulk thickness of 1524 µm that covers the
occlusal surface of all maxillary and mandibular teeth.22
The ball clasps used for the Hawley retainers in the
present study has a maximum thickness of 0.032” (812 µm),
yielding a maximum thickness of 1624 µm that can
potentially lie across the occlusal surface for both
arches.
However, since ball clasps seat in the occlusal
62
embrasure between teeth and are also staggered, the
maximum thickness may decrease substantially.
This might
explain why the Hawley retainer had significantly greater
cumulative ACNC at ≤50 µm and ≤100 µm levels at one month
and three months post-debond, as well as greater ACNC at
≤150 µm and ≤200 µm levels at the third month. The ball
clasps of the Hawley retainers are staggered and can also
conform to the occlusal embrasure of the teeth minimizing
the distance the posterior teeth are disoccluded.
The
full coverage of all teeth of the Essix retainer – the
plastic is minimally 1624 µm thick – may prevent the
teeth from contacting each other and settling at levels
less ≤200 µm.
Patients wearing the Essix retainers and patients
wearing the Hawley retainers all perceived that their
teeth fit together well, contacted each other evenly,
they could chew tough meats well and felt little or no
pain when biting down hard at the time of debond.
was no significant changes overtime.
There
Horton et al. also
reported no changes over time in the perception of
occlusion for patients wearing Hawley retainers.18
This suggests that patients are insensitive to small
changes in their occlusion if their occlusion fits well.
Initially, patients in the Essix group perceived
that their teeth did not fit together as well when they
bit down hard compared to the Hawley group.
63
This
difference might explain the differences in ACNC observed
for Essix (19.3 mm²) versus the Hawley group (21.2 mm²),
supporting the notion that individuals are able to
perceive differences in ACNC.
Similar to all studies involving removable
retainers, a limitation to this study is patient
compliance.
Even though all patients reported from the
questionnaire that they wore their retainers full-time
consistently, it is unknown whether or not their answers
actually reflected the time they wore their retainers.
Due to the inability to accurately assess amount of time
patients actually wore their retainers and the veracity
in their answers, a larger sample size was needed.
Sixty
patients were recruited, but due to dropouts and lost
retainers, only 40 were used in the study.
Another
limitation is the lack of consistency in retainer wear
protocol among clinicians, especially with the Essix
retainer.
There is no consensus with respect to the
protocol for Essix wear; it can range from full-time wear
to part-time wear only.
11,12,22,23
Since patients were
instructed to wear the Essix retainers full-time
throughout this study, it is unknown whether part-time
wear would have yielded a different result.
Clinically, the results imply that the Essix
retainer may prevent settling of the dentition at
interocclusal distances of ≤200 µm during the first three
64
months of retention compared with the Hawley retainer.
However, at interocclsual distances of ≤350 µm, no
statistically significant differences between the two
retainers exist.
Occlusal equilibration should not be
performed prior to three months post-debond as the ACNC
can increase or decrease depending on the type of
retention device.
65
Conclusions
1.
After one month of retention, the Hawley retainer
produced significantly greater ACNC than the Essix at
cumulative ACNC ≤200 µm; after three months of retention
the Hawley retainer produced significantly greater ACNC
at ≤50 µm, ≤100 µm, ≤150 µm and ≤200 µm levels.
The full
coverage of all teeth by the Essix retainer may prevent
tooth contacts and settling at occlusal distances of ≤200
µm.
2.
During the first three months of full-time retainer
wear, areas of contact and near contact (ACNC) decreased
9% in patients wearing the Essix retainers and increased
5% in patients wearing the Hawley retainers.
Because the
absolute differences were small (4.6 mm²) and the
variability was larger, the group differences was not
statistically significant.
3.
Both groups reported that they wore their retainers
consistently throughout the study, their teeth fit
together well, their teeth contacted each other evenly,
they could chew tough meats well, and they felt little or
no pain when biting down hard at debond. No significant
changes in the patients’ subjective perceptions of
retainer wear occurred.
66
Literature Cited
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occlusions. 5th ed. St. Louis: CV Mosby; 2003.
2. Roth R. Functional occlusion for the orthodontist. J
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malocclusion affect masticatory performance? Angle
Orthod. 2002;72:21-27.
4. Toro A, Buschang P, Thorckmorton G, Roldan S.
Masticatory performance in children and adolescents with
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5. Owens S, Buschang P, Throckmorton G, 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.
6. Yurkstas A, Manly R. Measurement of occlusal contact
area effective in mastication.Am J Orthod. 1949;35:185195.
7. Bakke M, Holm B, Jensen B, Michler L, Moller E.
Unilateral, isometric bite force in 8-68-year-old women
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1990;98:149-158.
8. Julien K, Buschang P, Throckmorton G, Dechow P. Normal
masticatory performance in young adults and children.
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orthodontic retention? Am J Orthod Dentofacial Orthop.
1998; 113:507-514.
10. Reitan K. Clinical and histologic observations on
tooth movement during and after orthodontic treatment. Am
J Orthod. 1967;53:721-745.
11. Littlewood S, Millet D, Doubleday B, Bearn D,
Worthington H. Orthodontic retention: a systematic
review. J Orthod. 2006; 33:205-212.
12. Kau C. Orthodontic retention regimes: will we ever
have the answer? Evid Based Dent. 2006;7:100.
67
13. Moller E, Bakke M. Occlusal harmony and disharmony:
frauds in clinical dentistry? Int Dent J. 1988; 38:7-18.
14. Deng Y, Fu M. Occlusal contact changes before and
after orthodontic treatment of a group of children &
adolescent patients with TMJ disturbance. Aust Orthod J.
1995;13:231-237.
15. Durbin D, Sadowsky C. Changes in tooth contacts
following orthodontic treatment. Am J Orthod Dentofacial
Orthop. 1986;90:375-382.
16. Dincer M, Meral O, Turner N. The investigation of
occlusal contacts during the retention period. Angle
Orthod. 2003;73:640-646.
17. 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.
18. Horton J, Buschang P, Oliver D, Behrents R.
Comparison of the effects of Hawley and perfector/spring
aligner retainers on postorthodontic occlusion. Am J
Orthod Dentofacial Orthop. 2009;135:729-736.
19. Rowland H, Hichens L, Williams A, et al. The
effectiveness of Hawley and vacuum-formed retainers: a
single randomized controlled trial. Am J Orthod
Dentofacial Orthop. 2007;132:730-737.
20. Sauget E, Covell DJ, Boero R, Lieber W. Comparison
of occlusal contacts with use of Hawley and clear overlay
retainers. Angle Orthod. 1997;67:223-230.
21. Dincer M, Aslan B. Effects of thermoplastic
retainers on occlusal contacts. Eur J Orthod. 2009; Epub
ahead of print.
22. Sheridan J, LeDoux W, McMinn R. Essix retainers:
fabrication and supervision for permanent retention. J
Clin Orthod. 1993;27:35-45.
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than Hawley retainers0. Evid Based Dent. 2009;10:47.
68
Appendix
69
Table 1. Areas of contact and near contact (ACNC) of posterior occlusion with Essix and Hawley retainers at debond (T1), 1
month after debond (T2) and 3 months after debond (T3).
Thickness
(µm)
Debond Areas (mm²)
Essix
Hawley
Median
IQ Range
Median
IQ Range
1 Month Post-Debond Areas (mm²)
Essix
Hawley
Median
IQ Range
Median
IQ Range
3 Months Post-Debond Areas (mm²)
Essix
Hawley
Median
IQ Range
Median
IQ Range
70
Individual
≤ 50
50-100
100-150
200-250
250-300
300-350
0.9
1.5
1.9
2.7
3.9
7.6
0.6/1.7
1.0/2.8
1.3/3.4
1.9/4.3
2.9/5.9
5.4/11.0
1.1
2.0
1.9
2.6
4.0
7.7
1.0/1.9
1.3/2.4
1.2/2.6
1.5/3.6
2.2/5.7
5.1/10.4
0.3
0.7
1.2
2.2
3.2
5.4
0.2/0.7
0.3/1.8
0.5/2.4
0.8/3.2
1.2/4.3
3.4/8.3
0.9
1.5
1.7
2.8
4.0
7.3
0.4/1.7
1.1/2.2
1.3/2.5
2.0/3.6
3.0/5.2
6.2/10.4
0.4
0.8
1.3
2.3
3.5
7.2
0.2/0.7
0.4/2.0
0.4/2.6
0.6/3.8
1.2/5.8
3.4/11.4
1.1
2.0
2.1
3.0
4.0
7.9
0.8/1.7
1.5/2.6
1.6/3.2
2.4/4.7
3.3/5.8
5.5/9.9
Cumulative
≤ 50
≤ 100
≤ 150
≤ 200
≤ 250
≤ 300
≤ 350
0.6
2.4
4.1
6.3
9.2
12.6
19.3
0.6/1.7
1.3/4.8
2.6/7.8
4.1/11.8
6.2/15.8
9.2/22.3
15.2/34.1
1.2
3.2
5.2
7.1
9.6
13.0
21.2
1.0/1.9
2.4/4.5
3.6/6.9
4.8/10.1
6.3/13.8
8.5/19.6
13.0/30.0
0.3
1.2
2.2
3.9
6.1
9.4
14.6
0.2/0.7
0.5/2.4
1.0/1.8
1.6/7.8
2.4/10.9
3.8/15.2
6.8/23.4
0.9
2.4
4.2
6.4
9.1
12.7
20.5
0.4/1.7
1.5/3.8
2.7/6.2
4.4/9.1
6.8/12.1
9.8/17.2
17.0/27.1
0.4
1.4
2.2
4.3
6.8
10.3
17.5
0.2/0.7
0.6/2.7
1.1/4.9
1.6/8.4
2.3/11.9
3.4/17.1
6.9/28.8
1.1
3.2
4.8
7.1
10.2
14.2
22.1
0.8/1.7
2.6/4.0
4.5/7.1
6.6/11.1
9.0/16.0
12.3/22.2
17.3/32.1
Table 2. Changes in the areas of contact and near contact (ACNC) of posterior occlusion with Essix and Hawley retainers at
debond (T1), 1 month after debond (T2) and 3 months after debond (T3).
Thickness
(µm)
Debond to 1 Month After Debond Changes
(mm²)
Essix
Hawley
Median
IQ Range
Median
IQ Range
1 Month to 3 Months After Debond Changes
(mm²)
Essix
Hawley
Median
IQ Range
Median
IQ Range
Debond to 3 Months After Debond Changes
(mm²)
Essix
Hawley
Median
IQ Range
Median
IQ Range
71
Individual
≤ 50
50-100
100-150
150-200
200-250
250-300
300-350
-0.3
-0.2
-0.4
-0.3
-0.5
-0.6
-0.8
-0.9/0.0
-1.4/0.3
-1.1/0.3
-1.0/0.0
-1.1/0.0
-1.6/0.3
-3.8/1.1
-0.3
-0.3
-0.1
-0.1
-0.1
-0.1
0.4
-0.6/0.0
-0.6/0.2
-0.5/0.1
-0.6/0.4
-0.7/0.5
-1.1/1.6
-1.6/1.6
0.1
0.1
0.0
0.0
0.0
0.3
1.5
0.0/0.2
-0.3/0.4
-0.3/0.6
-0.3/0.7
-0.4/0.7
-0.5/1.4
-1.1/2.5
0.3
0.2
0.3
0.1
0.2
0.1
-0.2
0.0/0.5
0.0/0.9
-0.2/0.8
-0.3/0.8
-0.4/0.7
-0.6/0.9
-1.3/1.4
-0.3
-0.5
-0.4
-0.5
-0.3
-0.5
0.9
-0.7/0.0
-1.5/0.3
-1.1/0.1
-0.9/0.5
-0.9/0.5
-1.4/0.8
-3.0/2.4
0.1
0.0
0.1
0.2
0.2
0.0
0.4
-0.2/0.2
-0.2/0.5
-0.2/0.5
-0.3/0.8
-0.5/1.0
-0.6/1.2
-2.0/1.7
Cumulative
≤ 50
≤ 100
≤ 150
≤ 200
≤ 250
≤ 300
≤ 350
-0.3
-0.5
-0.7
-1.0
-1.6
-2.5
-3.0
-0.9/0.0
-2.4/0.2
-3.6/0.4
-4.9/0.2
-6.0/0.0
-7.7/0.3
-10.9/1.3
-0.3
-0.7
-0.8
-0.7
-0.7
-0.6
-1.1
-0.6/0.0
-1.1/0.4
-1.8/0.3
-2.3/0.2
-3.2/0.5
-4.4/0.9
-4.2/2.1
0.1
0.2
0.1
0.4
0.6
1.0
1.5
0.0/0.2
-0.2/0.7
-0.6/1.1
-1.1/1.8
-1.4/2.4
-1.7/3.5
-2.5/7.7
0.3
0.5
0.8
0.8
0.9
1.0
1.1
0.0-0.5
-0.1/1.7
0.0/2.3
-0.3/3.0
-0.6/3.7
-1.3/4.4
-3.1/7.1
-0.3
-0.6
-0.9
1.5
-2.3
-2.9
-2.2
-0.7/0.0
-2.2/0.2
-3.4/0.1
-4.5/0.5
-4.8/1.5
-4.9/2.6
-7.8/5.3
0.1
0.0
0.4
0.5
0.5
0.8
0.7
-0.2/0.2
-0.3/0.3
-0.6/0.8
-0.8/1.2
-1.2/2.4
-1.7/2.7
-1.6/4.7
Table 3. Patient perception of posterior occlusion at debond (T1), 1 month after debond (T2) and 3 months after debond (T3)
using a visual analogue scale, converted to percentages.
Debond Values (mm)
Essix
Hawley
Question Medium
IQ
Medium
IQ
Range
Range
72
Teeth
Fit
Teeth
Contact
Evenly
Chew
Tough
Meats
Pain
Biting
1 Month After Debond values (mm)
Essix
Hawley
Medium
IQ
Medium
IQ
Range
Range
3 Months After Debond values (mm)
Essix
Hawley
Medium
IQ
Medium
IQ
Range
Range
24
19/43
24
14/32
17
10/23
8
6/20
17
6/46
13
8/29
31
17/41
16
7/24
19
6/44
10
7/21
17
9/38
16
8/34
10
2/30
9
7/15
5
2/24
6
3/9
10
3/19
8
2/12
6
1/10
5
1/17
2
1/12
3
2/13
4
2/22
5
1/30
Table 4. Changes in patient perception of posterior occlusion at debond (T1), 1 month after debond (T2) and 3 months after
debond (T3) using a visual analogue scale, converted to percentages.
Debond to 1 Month After Debond
Changes (mm)
Essix
Hawley
Question Medium
IQ
Medium
IQ
Range
Range
73
Teeth
Fit
Teeth
Contact
Evenly
Chew
Tough
Meats
Pain
Biting
1 Month After Debond to 3 months
After Debond Changes (mm)
Essix
Hawley
Medium
IQ
Medium
IQ
Range
Range
Debond to 3 Months After Debond
Changes (mm)
Essix
Hawley
Medium
IQ
Medium
IQ
Range
Range
-1
-18/2
-13
-23/0
0
-7/8
1
-3/13
-8
-18/7
-5
-18/6
-8
-21/23
-2
-10/-13
0
-7/8
6
0/13
-10
-21/0
3
-7/14
-3
-23/8
-3
-8/0
0
-9/5
-1
-3/8
0
-20/6
-3
-8/1
0
-5/6
-1
-8/2
2
-1/9
0
-2/5
1
-4/14
0
-4/4
74
Fig. 1 Photo of registration.
Fig. 2 Scan of registration.
Fig. 3 Tracing of occlusal table.
75
Fig. 4 Calibration Curve: step-wedge thickness (Y) estimated from grey scales (X).
76
Fig. 5 Median cumulative areas of contact and near contact of Essix and Hawley retainers at ≤350 µm thickness at T1 (debond),
T2 (1 month post-debond) and T3 (3 months post-debond).
77
Fig. 6 Median cumulative areas of contact and near contact of Essix and Hawley retainers at ≤50 µm and ≤100 µm thickness at
T1 (debond), T2 (1 month post-debond) and T3 (3 months post-debond).
78
Fig. 7 Median absolute areas of contact and near contact of Essix and Hawley retainers at T1 (debond) and T2 (1 month postdebond).
79
Fig. 8 Median cumulative areas of contact and near contact of Essix and Hawley retainers at ≤150 µm and ≤200 µm thickness at
T1 (debond), T2 (1 month post-debond) and T3 (3 months post-debond).
80
Fig. 9 Median absolute areas of contact and near contact of Essix and Hawley retainers at T1 (debond) and T3 (3 month postdebond).
81
Fig. 10 Median absolute areas of contact and near contact of Essix and Hawley retainers at T2 (1 month post-debond) and T3 (3
month post-debond).
Table 1. Areas of contact and near contact (ACNC) of posterior occlusion with Essix and Hawley retainers at debond (T1), 1 month after
debond (T2) and 3 months after debond (T3).
Thickness
(µm)
Individual
≤ 50
50-100
100-150
150-200
200-250
250-300
300-350
Cumulative
≤ 50
≤ 100
≤ 150
≤ 200
≤ 250
≤ 300
≤ 350
Debond Areas (mm²)
Essix
Hawley
Median
IQ
Median
IQ
Range
Range
1 Months After Debond Areas (mm²)
Essix
Hawley
Median
IQ
Median
IQ
Range
Range
3 Months After Debond Areas (mm²)
Essix
Hawley
Median
IQ
Median
IQ
Range
Range
0.9
1.5
1.9
2.2
2.7
3.9
7.6
0.6/1.7
1.0/2.8
1.3/3.4
1.5/3.6
1.9/4.3
2.9/5.9
5.4/11.0
1.1
2.0
1.9
2.0
2.6
4.0
7.7
1.0/1.9
1.3/2.4
1.2/2.6
1.4/2.8
1.5/3.6
2.2/5.7
5.1/10.4
0.3
0.7
1.2
1.7
2.2
3.2
5.4
0.2/0.7
0.3/1.8
0.5/2.4
0.6/2.7
0.8/3.2
1.2/4.3
3.4/8.3
0.9
1.5
1.7
2.2
2.8
4.0
7.3
0.4/1.7
1.1/2.2
1.3/2.5
1.6/3.2
2.0/3.6
3.0/5.2
6.2/10.4
0.4
0.8
1.3
1.8
2.3
3.5
7.2
0.2/0.7
0.4/2.0
0.4/2.6
0.6/3.1
0.6/3.8
1.2/5.8
3.4/11.4
1.1
2.0
2.1
2.3
3.0
4.0
7.9
0.8/1.7
1.5/2.6
1.6/3.2
1.9/3.6
2.4/4.7
3.3/5.8
5.5/9.9
0.6
2.4
4.1
6.3
9.2
12.6
19.3
0.6/1.7
1.3/4.8
2.6/7.8
4.1/11.8
6.2/15.8
9.2/22.3
15.2/34.1
1.2
3.2
5.2
7.1
9.6
13.0
21.2
1.0/1.9
2.4/4.5
3.6/6.9
4.8/10.1
6.3/13.8
8.5/19.6
13.0/30.0
0.3
1.2
2.2
3.9
6.1
9.4
14.6
0.2/0.7
0.5/2.4
1.0/1.8
1.6/7.8
2.4/10.9
3.8/15.2
6.8/23.4
0.9
2.4
4.2
6.4
9.1
12.7
20.5
0.4/1.7
1.5/3.8
2.7/6.2
4.4/9.1
6.8/12.1
9.8/17.2
17.0/27.1
0.4
1.4
2.2
4.3
6.8
10.3
17.5
0.2/0.7
0.6/2.7
1.1/4.9
1.6/8.4
2.3/11.9
3.4/17.1
6.9/28.8
1.1
3.2
4.8
7.1
10.2
14.2
22.1
0.8/1.7
2.6/4.0
4.5/7.1
6.6/11.1
9.0/16.0
12.3/22.2
17.3/32.1
100
Table 2. Changes in the areas of contact and near contact (ACNC) of posterior occlusion with Essix and Hawley retainers at debond (T1), 1
month after debond (T2) and 3 months after debond (T3).
95
Thickness
(µm)
Individual
≤ 50
50-100
100-150
150-200
200-250
250-300
300-350
Cumulative
≤ 50
≤ 100
≤ 150
≤ 200
≤ 250
≤ 300
≤ 350
Debond to 1 Month After Debond
Changes (mm²)
Essix
Hawley
Median IQ Range Median
IQ
Range
1 Month to 3 Months After Debond
Changes (mm²)
Essix
Hawley
Median
IQ
Median
IQ
Range
Range
Debond to 3 Months After Debond
Changes (mm²)
Essix
Hawley
Median
IQ
Median
IQ
Range
Range
-0.3
-0.2
-0.4
-0.3
-0.5
-0.6
-0.8
-0.9/0.0
-1.4/0.3
-1.1/0.3
-1.0/0.0
-1.1/0.0
-1.6/0.3
-3.8/1.1
-0.3
-0.3
-0.1
-0.1
-0.1
-0.1
0.4
-0.6/0.0
-0.6/0.2
-0.5/0.1
-0.6/0.4
-0.7/0.5
-1.1/1.6
-1.6/1.6
0.1
0.1
0.0
0.0
0.0
0.3
1.5
0.0/0.2
-0.3/0.4
-0.3/0.6
-0.3/0.7
-0.4/0.7
-0.5/1.4
-1.1/2.5
0.3
0.2
0.3
0.1
0.2
0.1
-0.2
0.0/0.5
0.0/0.9
-0.2/0.8
-0.3/0.8
-0.4/0.7
-0.6/0.9
-1.3/1.4
-0.3
-0.5
-0.4
-0.5
-0.3
-0.5
0.9
-0.7/0.0
-1.5/0.3
-1.1/0.1
-0.9/0.5
-0.9/0.5
-1.4/0.8
-3.0/2.4
0.1
0.0
0.1
0.2
0.2
0.0
0.4
-0.2/0.2
-0.2/0.5
-0.2/0.5
-0.3/0.8
-0.5/1.0
-0.6/1.2
-2.0/1.7
-0.3
-0.5
-0.7
-1.0
-1.6
-2.5
-3.0
-0.9/0.0
-2.4/0.2
-3.6/0.4
-4.9/0.2
-6.0/0.0
-7.7/0.3
-10.9/1.3
-0.3
-0.7
-0.8
-0.7
-0.7
-0.6
-1.1
-0.6/0.0
-1.1/0.4
-1.8/0.3
-2.3/0.2
-3.2/0.5
-4.4/0.9
-4.2/2.1
0.1
0.2
0.1
0.4
0.6
1.0
1.5
0.0/0.2
-0.2/0.7
-0.6/1.1
-1.1/1.8
-1.4/2.4
-1.7/3.5
-2.5/7.7
0.3
0.5
0.8
0.8
0.9
1.0
1.1
0.0-0.5
-0.1/1.7
0.0/2.3
-0.3/3.0
-0.6/3.7
-1.3/4.4
-3.1/7.1
-0.3
-0.6
-0.9
1.5
-2.3
-2.9
-2.2
-0.7/0.0
-2.2/0.2
-3.4/0.1
-4.5/0.5
-4.8/1.5
-4.9/2.6
-7.8/5.3
0.1
0.0
0.4
0.5
0.5
0.8
0.7
-0.2/0.2
-0.3/0.3
-0.6/0.8
-0.8/1.2
-1.2/2.4
-1.7/2.7
-1.6/4.7
101
Table 3. Patient perception of posterior occlusion at at debond (T1), 1 month after debond (T2) and 3 months after debond (T3) using a visual
analogue scale.
96
Debond Values (mm)
Essix
Hawley
Question Medium
IQ
Medium
IQ
Range
Range
Teeth
Fit
Teeth
Contact
Evenly
Chew
Tough
Meats
Pain
Biting
1 Month After Debond values (mm)
Essix
Hawley
Medium
IQ
Medium
IQ
Range
Range
3 Months After Debond values (mm)
Essix
Hawley
Medium
IQ
Medium
IQ
Range
Range
24
19/43
24
14/32
17
10/23
8
6/20
17
6/46
13
8/29
31
17/41
16
7/24
19
6/44
10
7/21
17
9/38
16
8/34
10
2/30
9
7/15
5
2/24
6
3/9
10
3/19
8
2/12
6
1/10
5
1/17
2
1/12
3
2/13
4
2/22
5
1/30
102
Table 4. Changes in patient perception of posterior occlusion at at debond (T1), 1 month after debond (T2) and 3 months after debond (T3)
using a visual analogue scale.
Debond to 1 Month After Debond
Changes (mm)
Essix
Hawley
Question Medium
IQ
Medium
IQ
Range
Range
Teeth
Fit
Teeth
Contact
Evenly
Chew
Tough
Meats
Pain
Biting
1 Month After Debond to 3 months
After Debond Changes (mm)
Essix
Hawley
Medium
IQ
Medium
IQ
Range
Range
Debond to 3 Months After Debond
Changes (mm)
Essix
Hawley
Medium
IQ
Medium
IQ
Range
Range
-1
-18/2
-13
-23/0
0
-7/8
1
-3/13
-8
-18/7
-5
-18/6
-8
-21/23
-2
-10/-13
0
-7/8
6
0/13
-10
-21/0
3
-7/14
-3
-23/8
-3
-8/0
0
-9/5
-1
-3/8
0
-20/6
-3
-8/1
0
-5/6
-1
-8/2
2
-1/9
0
-2/5
1
-4/14
0
-4/4
103
Vita Auctoris
Collin Tsai was born in San Francisco, California on the 26th of May 1979.
He graduated from the University in San Francisco in 2001 with a B.S. degree in
Biology and a minor in Chemistry. He entered dental school at the University of
California, Los Angeles in 2003 and graduated in 2007. After dental school, he began
his residency in orthodontics at Saint Louis University and obtained a certificate in
orthodontics and a Master’s Degree in 2009.
100