Download VALIDATION OF AGE INTERVAL CRANIOFACIAL VERTICAL GROWTH SINGLE-TOOTH IMPLANTS

VALIDATION OF AGE INTERVAL CRANIOFACIAL VERTICAL GROWTH
PREDICTION TABLES FOR THE AID OF PLACEMENT OF
SINGLE-TOOTH IMPLANTS
Jaclyn M. Scroggins, B.S., D.M.D.
An Abstract Presented to the Graduate Faculty of
Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2012
ABSTRACT
Introduction:
The purpose of this study was to test
the accuracy of a growth prediction scheme.
The scheme
developed by Fudalej, Kokich and Leroux is the current
recommendation to determine the cessation of vertical
growth of the craniofacial structures to facilitate
placement of single-tooth implants.
The purpose of the
present investigation is to test the accuracy of the
current recommendation using a new sample.
Subjects and
Methods: Fifty-seven post-treatment orthodontic patients
were recalled from one private practice. Each subject had
lateral cephalograms taken pre-treatment, immediately posttreatment and a mean of 23.4 years in retention. To compare
the predicted amounts of vertical growth of the
craniofacial structures to the actual growth values, the
same anatomic landmarks as the original study were utilized
and distances between the respective points were measured.
A paired t-test was applied to each measured variable for
statistical analysis.
Tables and graphic representations
were created to compare the predicted versus the actual
measurements.
Results: There were two statistically
significant paired t-test measures: the anterior facial
height and the eruption of maxillary molar.
Grouped by age
intervals, there were 4 out of 16 statistically different
1
measures.
Conclusions:
In comparison to the actual sample
measurements, the growth prediction system by Fudalej et al
overestimated the amount of growth in anterior facial
height and underestimated the amount of eruption of the
maxillary molar.
There was no significant difference
between the actual and predicted measurements for the
eruption of the maxillary and mandibular incisors. In
conclusion, in agreement with the conclusions of the
original study, growth of the craniofacial skeleton is a
continuous process that decreases in amount with time.
However, more practically speaking, the risk of failure due
to a development of a perceivable asymmetric discrepancy
between of the implant and adjacent teeth may be greater
than we once believed.
In this study, one out of every
four implants would have failed if the recommendations of
the original study were taken that only clinically
insignificant amounts of growth are observed after the
second decade of life.
2
VALIDATION OF AGE INTERVAL CRANIOFACIAL VERTICAL GROWTH
PREDICTION TABLES FOR THE AID OF PLACEMENT OF
SINGLE-TOOTH IMPLANTS
Jaclyn M. Scroggins, B.S., D.M.D.
A Thesis Presented to the Graduate Faculty of Saint
Louis University in Partial Fulfillment of
the Requirements for the Degree of
Master of Science in Dentistry
2012
COMMITTEE IN CHARGE OF CANDIDACY:
Professor Rolf G. Behrents,
Chairperson and Advisor
Associate Clinical Professor Donald R. Oliver
Professor Eustaquio A. Araujo
i
DEDICATION
I dedicate this to my husband, Kenneth, who supported
me endlessly through my extensive education, whose love and
unwavering devotion made the completion of this project and
this chapter of my life possible.
I express immense gratitude to my parents for their
years of love, support, dedication and encouragement
throughout my life that has given me the opportunity to
pursue my dreams and become the person I am.
I also dedicate this to my teachers who have laid the
foundation and provided the encouragement and confidence to
achieve my goals of becoming an orthodontist.
ii
ACKNOWLEDGEMENTS
This research project would not have been possible without
the leadership and guidance of many important people:
Dr. Rolf G. Behrents, my thesis committee chair, for
your direction to this thesis topic, guidance through the
experimental process and your hours of dedication to my
thesis construction.
The opportunity you provided me with
to attend the finest institution in orthodontic education
is invaluable.
Your encouraging leadership throughout my
orthodontic education has led me to develop confidence in
myself, which I have always struggled.
Dr. Donald R. Oliver, for the dedication you have to
the program and the residents.
You have spent hours of
your personal time brainstorming and reading to make my
thesis possible.
Your instruction, encouragement and
support in the clinic have given me the needed skills and
assurance in my orthodontic skills to be a proficient
practitioner in private practice.
Dr. Eustaquio A. Araujo, for the assistance with this
thesis and your tremendous guidance in my clinical
education.
It has been a privilege and an honor to learn
from you, one of the best clinicians and teachers.
iii
The
skills and lessons I have learned from you are invaluable
and will be never forgotten.
Mr. Dan Kilfoy, for hours of technical help with the
configuration of the computer software and programs.
Dr. Heidi Israel, for your assistance and dedication
to the statistical analysis for this thesis.
Dr. James Vaden, for the use of your records in this
study, and your dedication to maintain pristine ongoing
records to allow me this unique opportunity to study this
long-term sample.
iv
TABLE OF CONTENTS
List of Tables ...........................................vi
List of Figures .........................................vii
CHAPTER 1: INTRODUCTION....................................1
Problem.........................................3
CHAPTER 2: REVIEW OF LITERATURE............................5
Osseointegration of Dental Implants.............5
Ankylosed Teeth in Growing Individuals..........9
Dental Implants in Growing Individuals.........11
Risks of Early Placement....................11
Benefits of Early Placement.................15
Facial Growth..................................18
Maxillary Growth............................18
Mandibular Growth...........................22
Post Adolescent Changes........................25
Mesial Migration of Teeth...................25
Continued Eruption of Teeth.................26
Facial Types................................28
Current Recommendations........................30
Need for Project...............................31
Statement of Thesis............................32
Literature Cited...............................34
CHAPTER 3: JOURNAL ARTICLE................................40
Abstract.......................................40
Introduction...................................41
Sample and Methods.............................45
Sample......................................46
Cephalometric Technique and Analysis........48
Statistical Analyses...........................53
Results........................................54
Anterior Facial Height......................56
Incisors....................................57
Molars......................................62
Discussion.....................................63
Summary and Conclusions........................70
Literature Cited...............................73
Vita Auctoris............................................75
v
List of Tables
Table 1.
Sample demographics (yrs).....................46
Table 2.
Age distribution of sample....................47
Table 3.
Error of measurement of variables (mm)........52
Table 4.
Descriptive statistics for the total sample
population and paired t-tests for the null
hypothesis....................................55
Table 5.
Descriptive statistics for the various age
ranges in years and paired t-test for the
null hypothesis...............................55
vi
List of Figures
Figure 1:
Reconstructed distribution of number of
patients with regard to the degree of
infraposition.................................13
Figure 2:
Reconstructed distribution of the degree
of vertical infraposition of single implant
crown restoration showing gender differences..14
Figure 3.
Landmarks and reference planes................49
Figure 4.
Measurements..................................50
Figure 5.
Comparison of the predicted growth amounts
and actual growth amounts for linear
measurements N-Me, U1e-PP, L1e-MP and
U6c-PP in mm for the sample as a whole........54
Figure 6.
Comparison of the predicted growth amounts
and actual growth amounts grouped by age
for the linear measurement N-Me in mm.........56
Figure 7.
Comparison of the predicted growth amounts
and actual growth amounts grouped by age
for the linear measurement U1e-PP in mm.......58
Figure 8.
Comparison of the predicted growth amounts
and actual growth amounts grouped by age
for the linear measurement L1e-MP in mm.......58
Figure 9.
The distribution of the sample illustrating
the amount of eruption of the maxillary
incisors from T2 to T3 ........................59
Figure 10. The distribution of the sample illustrating
the amount of eruption of the mandibular
incisors from T2 to T3 ........................60
Figure 11. The percentage of the sample with the amount
of eruption of the maxillary incisors from
T2 to T3 of increments of 0 mm, 0-1 mm,
1-2 mm or >2.0 mm, grouped by age at T2.......61
vii
Figure 12. The percentage of the sample with the amount
of eruption of the mandibular incisors from
T2 to T3 of increments of 0 mm, 0-1 mm,
1-2 mm or >2.0 mm, grouped by age at T2.......61
Figure 13. Comparison of the predicted growth amounts
and actual growth amounts broken down by age
for the linear measurement U6c-PP in mm.......63
viii
CHAPTER 1: INTRODUCTION
Facial growth prediction is considered an important
subject in the specialty of orthodontics. The success of
many treatment methodologies depends on proper timing
relative to skeletal growth. The amount, direction and
timing of growth are important in determining predictable
and successful treatment and for most cases constitute a
determinant of treatment time. In 1938, Brodie et al wrote,
“There seems to be a definite correlation between success
of treatment and growth.”1
Growth prediction schemes have been studied at length
for accuracy. Unfortunately, the most common finding is
that most growth prediction schemes are no more accurate
than random chance alone.2
A prediction equation is
typically developed using one sample and then tested for
efficiency using that same sample.
Using this method,
prediction efficiency is usually high.
To actually put the
prediction equation to real test, the prediction scheme
must be applied to another sample so that the predicted
result can be compared to the actual result.
The
correlation between the predicted and actual values will
measure the efficiency of the facial growth scheme.
Growth prediction systems are often based on
chronologic age or maturational stage.
1
Ricketts used a
pattern-extension methodology to estimate future skeletal
changes. This scheme assumed the continued patterns of the
preceding facial growth and was based on chronologic age.3
The Johnston methodology scheme for predicting facial
growth used a grid system of incremental skeletal
projections that were also based on chronologic age.4
The
Fishman system of maturation assessment was based on
maturational age rather than chronologic age, and developed
projections based on percentage values of total completed
maxillary and mandibular growth as related to combinations
of maturational stages and levels derived from hand-wrist
radiographs.5
It has been shown that individualizing prediction by
assessing maturational development rather than chronologic
age can increase the accuracy of prediction by
significantly reducing physiologic variability between
children of the same chronologic age.
Turchetta, Fishman
and Subtelny demonstrated that using maturational age, as
used in the Fishman analysis, is superior to both the
chronologically based Johnston grid and Ricketts analysis
for short- and long-term predictions.
However, maturation
age did not produce efficient predictions in all cases.2
2
The Problem
Many adolescent patients present with congenitally or
acquired missing teeth and the resultant treatment plans
often intend to maintain the related space for
prosthodontic replacement after treatment.
There are
multiple restorative options for missing teeth; however,
single-tooth implants are becoming the gold standard due to
their high success rate and because such replacements do
not require tooth preparation of the adjacent teeth.
One
potential problem, however, is that dental implants are
similar to an ankylosed teeth. If they are placed before
the cessation of growth, the dental implant will submerge
in relation to the adjacent teeth.
A submerged dental
implant not only leaves an unesthetic restorative result,
but can also destroy the adjacent alveolar bone resulting
in a periodontal bony defect around the adjacent teeth.
Many orthodontic patients finish treatment with years of
remaining potential growth, therefore, the question is at
what age are alveolar changes small enough so as not to
affect the esthetic and functional long term outcome of a
dental implant.
Fudalej, Kokich and Leroux studied changes in vertical
alveolar growth and continued tooth eruption to develop
prediction tables for that intent to predict the change of
3
a measurement between two age intervals.
Derived tables
are supposed to be the guide for quantifying the amount of
vertical growth of the facial skeleton and the amounts of
eruption of the central incisors and first molars after
puberty so proper recommendations about dental implant
placements can be made.6
To date, however, the accuracy of
the prediction tables has not been subject to tests of
accuracy.
4
CHAPTER 2: REVIEW OF LITERATURE
Osseointegration of Dental Implants
In today’s esthetically driven society, choosing a
correct patient-specific treatment plan must consider both
the best esthetic outcome for the patients, as well as, the
most stabile long-term result.
Many patients present for
orthodontic treatment with congenital or acquired missing
permanent teeth. Tooth loss is a disadvantage, and living
with the stigma of missing teeth has been proven to
negatively influence quality of life as such damages a
person’s self-image and limits their lifestyle. Statistics
reveal that 5% of the population has a congenitally missing
tooth and nearly 70% of adults 35 to 44 years of age have
lost at least one permanent tooth.
According to Shimizu
and Maeda, congenitally missing permanent teeth occur in 3%
to 11% of European and Asian populations.
Additional data
indicates that almost 30% of adults will lose all of their
teeth by age 74.7,8
So, there is an immense need for
replacement of acquired or congenitally missing teeth.
There are multiple restorative options for replacement
of missing teeth: dental implants, space closure
orthodontically, fixed partial dentures, removable partial
dentures, and autotransplantations.
Single-tooth dental
implants are becoming a popular restorative option due to
5
their high success rate, lower future maintenance, and they
do not require preparation of adjacent teeth.
However, the
timing of dental implant placement is an age and
developmental related procedure that has been proven to be
challenging technically and esthetically, especially in the
long term.9
Even though the term osseointegration is used
differently among many researchers, it is an established
fact that dental implants anchor themselves to the bone via
a process of functional ankylosis. Osseointegration occurs
when the outer surface oxide layer of the dental implant is
in direct contact with the osseous tissue of the bone
without an intervening layer of connective tissue.
The
clinical success of dental implants relies on the
osseointegration process where the bone attaches to the
surface of the dental implant.10,11,12
Even though osseointegration is essential for the
survival of a dental implant, osseointegration results in a
condition similar to ankylosed teeth. The ankylotic nature
of dental implants was first observed in growing pig jaws.
Odman and coworkers were the first to study the effect of
osseointegrated dental implants on vertical dento-alveolar
development. Clinical and radiographic evidence
demonstrated that dental implants do not behave like
6
normally erupting teeth during development of the dentition
and supporting alveolar bone.
It was noted that dental
implants do not erupt similar the adjacent teeth, but
“submerge” into the bone while the adjacent teeth continue
to erupt; this is similar to the behavior of an ankylosed
tooth.13
Thilander and co-investigators studied this topic
further by placing four dental implants in each region of
the maxilla and mandible, and focused their observations on
the horizontal effects of dental implants during growth.
They found that osseointegrated dental implants do not
become secondarily displaced in sagittal and transversal
dimension and do not act like normal erupting teeth.
As
the jaws grows in the transverse direction in the molar and
premolar areas by buccal bone apposition and lingual
remodeling and resorption, dental implants appear to be
lingually displaced due to progressive translocation of the
bone of the alveolus in a buccal direction.
In this
situation, bone is added to the buccal side and resorbed
from the lingual side of the stationary dental implant.
As
the adjacent teeth erupt occlusally and buccally it will
appear that the dental implant is moving lingually and
submerging in relationship to the adjacent teeth.
During
periods of accelerated growth, dental implants risk failure
7
due to the relative translocation of the bone buccally and
resorption of the lingual side of the bone.
Due to this
physiological process, a recommendation was made such that
placement of dental implants in buccal regions of young
children should be avoided. However, dental implants placed
anterior to the canine of the maxilla propose less risk of
failure due to the majority of the increase of transverse
dimension occurring at the intermaxillary suture, thus not
affecting an dental implant placed in the alveolus of the
anterior portion of the maxilla.14
Another study, using dental implants inserted in
growing pig jaws, focused on the affect of posterior
vertical alveolar bone development.
Compared to adjacent
teeth, dental implants in the mandibular premolar region
were found to be inferiorly and lingually angulated, while
in the maxillary premolar region they were positioned
inferiorly, but centrally located in the alveolar process.15
In summary, osseointegrated dental implants when
placed in growing jaws do not change in position while the
adjacent teeth move vertically or laterally consistent with
alveolar process development.
At some distance from the
dental implants the alveolus develops normally, however, in
the immediate vicinity of the dental implant development of
the alveolar process may be negatively impacted.
8
The
overall effect of dental implant placement is loss of
occlusal contact and development of angular bony defects
around adjacent teeth.15
Ankylosed Teeth in Growing Individuals
The studies discussed previously, involving dental
implants in young pigs, raised concern about the placement
of dental implants in children and their affect on
remaining growth.
Ankylosed teeth display several
similarities to dental implants.
For example, ankylosed
teeth have a complete or partial lack of periodontal
ligament fusing the teeth to bone, they submerge in
relationship to adjacent teeth, and they cause angular bony
defects adjacent to the ankylosed tooth.
Because children
frequently experience ankylosed teeth, children with
ankylosed teeth have been studied in order to understand
the effects of an ankylosed tooth in growing children.
A
study completed by Malmgren and Malmgren, used cephalograms
of 42 children to observe the rate of infraposition
occurring over 10 years.
These subjects had experienced
reimplantation of incisors that subsequently became
ankylosed.
Originally, this study intended to provide a
guideline for the timing of extraction of ankylosed teeth.
It was hypothesized that a relationship exists between the
9
rate of infraposition and age at the time of injury, growth
intensity and facial growth.
Four periods of growth
intensity were established: before the growth spurt, from
initial to maximal growth spurt, from maximal to the end of
the growth spurt and after the growth spurt.
Growth
intensity was determined by an analysis of annual body
height measurements.
The findings of the study suggested
that infraocclusion of more than 3.5 mm was observed in
group one, more than 2.5 mm in group two, 2.5 mm in group
three and 1 mm in group four.
The degree of infraocclusion
and growth intensity was not directly correlated, showing
large variability between individuals especially for
horizontal and vertical growers.
No specific age
recommendation could be made due to this high degree of
variation in growth.16
Kawanami and coworkers found a similar phenomenon in a
longitudinal study of 52 patients involving study casts.
Significant infraposition was identified if the tooth was
traumatized and subsequently ankylosed before the age of 14
in females and 16 in males.
Furthermore, Kawanami et al
studied patients aged 20 to 30 years of age, discovering
that infraposition was also observed after puberty, at a
rate of 0.07 mm per year.
This finding also emphasized the
importance of the concept of slow continuous eruption of
10
teeth especially adjacent to and opposed to dental
implants.
In the study’s conclusions, the phenomenon of
continued eruption of teeth was noted to have implications
not only for the treatment of traumatized teeth, but also
for the treatment of tooth loss using osseointegrated
dental implants; such represents an analogue to
the ankylosed replanted tooth.17
The atypical pattern for
the development of infraocclusion and the ongoing movement
of teeth in an occlusal direction after puberty has also
been observed in studies by Ainamo and coworkers18 and
Bjerklin and Bennett.19
Dental Implants in Growing Individuals
Risks of Early Placement
Several longitudinal studies of young adults who
received implant-supported restorations have documented
disharmonies between adjacent teeth and dental implants.
Thilander and coworkers performed three studies following
18 patients with 47 dental implants over a 10-year period
with photographs, study casts, periapical radiographs,
lateral cephalograms and body height.
Measurements were
collected annually for four years and then every two years
thereafter.
Infraocclusion of the dental implant
restorations was noticed in patients with residual
11
craniofacial growth. Thus, a recommendation was made that
the dental and skeletal maturation, not a fixed
chronological age of the patient, must be taken into
consideration to avoid infraocclusion of implant-based
restorations.
Additionally, in the maxillary incisor region,
especially in those patients with no incisor contact,
slight continuous eruption of adjacent teeth was noted.
Craniofacial changes post-adolescence over time produced
noticeable infraocclusion of single implant-supported
prosthesis.
Thus, it was deemed important to finish
treatment with good incisor coupling and stability to
reduce the risk of an infraoccluded position of the
implant-supported crown.
Orthodontic relapse can cause an
implant-supported crown to be out of position in relation
to the adjacent teeth. However, evidence derived from these
studies showed that infraocclusion might also occur in
adult patients receiving single dental implants with no
history of orthodontics.
Therefore, careful analysis is
needed on an individual case basis before implant placement
to achieve the best possible long-term result.
Another
finding was that marginal bone loss, observed on the
adjacent teeth, was directly proportional to the distance
between the adjacent teeth and the dental implant.
12
This
study recommended that sufficient space be established and
root paralleling should be completed before the placement
of dental implants so that the least amount of angular bone
defect occurs around the adjacent teeth.20,21,22
Likewise, by comparing dental implants placed in
“young adults” and “mature adults,” Bernard and coworkers
found that with anterior osseointegrated restorations,
mature adults, thought to have only small amounts of
residual growth or aging alterations, could experience
major vertical steps between a dental implant and adjacent
teeth to the same extent as adolescents or young adults.
8
6
Amount of
infraocclusion
5
>1.0 mm
4
<1.0 mm
7
3
<0.5 mm
2
1
0
18-25
26-35
36-45
>45
Age in years
Figure 1. Reconstructed distribution of number of patients
with regard to the degree of infraposition (at the age of
crown placement in 34 patients (adapted from Andersson et
al23).
13
The young adult group ranged from 15.5 to 21 years of age
and all showed infraocclusion of implant-supported crowns.
These defects were measured on radiographs and found to be
between 0.1 and 1.65 mm.
During ages from 40 to 55 years,
the mature adult group displayed vertical steps ranging
from 0.12 to 1.86 mm.
There was no statistically
significant difference found in the amounts of the vertical
step between male and female patients or comparing the
location of the dental implant.24
Andersson et al23 and Jemt
et al25 reported similar findings.
In Figures 1 and 2, one
can see that for any age or sex there is a risk for
infraposition of a single implant crown.
60
50
40
Total
Females
30
Males
20
10
0
0 mm
<0.5 mm
<1.0 mm
>1.0 mm
Figure 2. Reconstructed distribution of the degree of
vertical infraposition of single implant crown restoration
showing gender differences (results compiled from Andersson
et al23 and Jemt et al25).
14
In summary, the consequences of early placement of a
dental implant may be infraocclusion, jeopardized
esthetics, destruction of supporting bone, and insufficient
gingival contours. Thus, reports in the literature on both
ankylosed teeth and osseointegrated dental implants should
draw the periodontist, orthodontist and oral surgeon’s
attention during the treatment planning phase.
The changes
in vertical and horizontal dimension between naturally
erupting teeth and dental implants and ankylosed teeth
needs to be understood and factored into the treatment plan
to prevent disharmony and poor esthetic and functional
outcomes.
Benefits of Early Placement
One recommendation is to postpone the placement of a
dental implant until after puberty or after the growth
spurt of a child.
However, some conflicting factors
warrant possible early placement of dental implants.
first factor is alveolar bone resorption.
The
Within four
months of a single tooth extraction, the buccolingual width
of the alveolar crest can show resorption up to 3 mm.
In
other words, this amounts to 40% of the entire horizontal
width of the crest.
Total resorption of alveolar bone
volume totals about 34% over five years.
15
In some
instances, delaying the placement of an endosseous implant
may eventually render a dental implant in an extraction
site impossible because of lack of sufficient bone volume
due to resorption.26,27
Conversely, it has not been proven
that immediate placement of a dental implant in an
extraction site can prevent such resorption.
On the other
hand, Spear and colleagues has shown that the resorption of
alveolar bone occurs much more slowly in a space created
orthodontically.
A rate of bone volume resorption of about
1% was observed in spaces opened orthodontically versus
about 34% in an extraction socket over a five year period.28
Some will argue that alveolar bone grafting is a
solution for the alveolar bone resorption and will provide
sufficient bone for the dental implant placement.
Jemt and
coworkers studied buccal bone grafting and soft tissue
volume associated with single tooth implant restorations.
They found that bone grafting of a single tooth gap could
create good initial bone volume for a dental implant
placement.
On the other hand, after crown placement most
patients showed both initial shrinkage, as well as, slow
long-term resorption of the apical part of the crestal
graft.
They also observed that local bone grafting failed
to restore the crest in a vertical direction resulting in a
significantly longer clinical implant crown compared to
16
adjacent and contra-lateral crown.
Similarly, looking at
buccal tissue volume, after abutment placement there was a
significant increase in buccal tissue however this increase
of buccal contour was reduced after one year.29,30
In addition to bone height and volume considerations,
early placement of dental implants is often based on the
psychosocial benefits.
Ectodermal dysplasia, caused by
more than 170 clinically distinct hereditary syndromes,
leaves patients with extended syndromal hypodontia
involving multiple missing permanent teeth.
Accompanying
the missing teeth, the alveolar processes are severely
atrophied and exhibit a reduced growth rate.
Conventional
prosthodontic treatment is challenging due to the irregular
distribution and abnormal shape of the remaining teeth used
to support bridges or crowns.
Under such conditions dental
implants placed in the anterior mandible, for example, at
the age of eight years old result in increase retention of
removable prosthesis and high patient satisfaction.
Even
in these severe cases, it is recommended that it is best to
allow as much growth as possible before initiating dental
implant placement.
In addition, it is recommended that
dental implants not be placed in the maxilla, and the
maxillary midline should not be crossed when a fixed
17
prosthesis is placed.
Doing so produces detrimental growth
defects involving the developing structures.31
Facial Growth
Most of what we know about facial growth is rooted in
the classic studies by Björk and Skieller.
They used
metallic implants fixed in the jawbones as fixed reference
points to study the longitudinal growth of craniofacial
complex.
Growth of the face and jaws was found to occur in
three planes of space: transverse, sagittal and vertical.
In both the maxilla and the mandible, growth is first
completed in the transverse plane, followed by the
sagittal, and lastly, in the vertical direction.
In
general, growth of the maxilla is related to the growth of
the cranial structures, and the mandible is more closely
associated with the growth of the axial skeleton.32
Björk
and Skieller also noted continuing eruption of teeth.
Iseri and Solow described this phenomenon as continued
passive eruption of teeth and distinguished that such
occurred after the emergence of the teeth into occlusion.33
Maxillary Growth
Growth of the maxilla is a result of apposition of
bone at both the suture connecting the two halves of the
18
maxilla as well as those articulating with the cranial
base, and by surface remodeling.
After the age of seven,
the majority of the changes, however, are a result of
remodeling.
In the transverse direction, the maxilla increases in
width by way of the median suture and buccal eruption of
the posterior teeth.
The transverse growth of the
midpalatal suture mirrors the curves that represent somatic
growth.
Thus, most of the growth at the midpalatal suture
is completed around the termination of the pubertal growth
spurt (around the age of 13 to 15 years) and then is
followed by continued apposition mostly apparent in the
posterior maxilla until 18 years of age.
Continued
apposition of the maxilla contributes to what seems like
minimal changes in the transverse dimension of the maxilla,
but such has been proven to be statistically significant.34
Changes in the anterior portion of the arch, in the
premaxillary area, occur mostly at the midpalatal suture
and such growth is usually completed prior to the
adolescent growth spurt, changing minimally after the age
of 10.
Thus, dental implants placed in the central incisor
area before age 10 can lead to a diastema with the adjacent
natural central incisor and subsequent shifting of the
midline toward the implant side.
19
In the posterior portion
of the maxilla, transverse growth gained from sutural
widening is smaller than that in the anterior maxilla.
Rather, the increase in transverse width is directly
related to the increase in intermolar width.
The eruption
of permanent molars in a buccal occlusal direction, in a
more posterior position in the dental arch, results in
relative wider transverse position.32,35,36
Sagittally, the maxilla increases in length through
sutural growth and bony apposition.
The maxilla increases
in length posteriorly by bone apposition at the maxillary
tuberosity.
The anterior part of the maxilla is relatively
stable; however, via bone resorption during remodeling, up
to 25% of sutural growth is lost at the anterior site.
Consequently, dental implants placed in the anterior
maxilla before remodeling of the anterior maxilla is
complete are at risk of resorption causing gradual loss of
bone on the labial side of an implant.
This has been shown
in case reports involving an 11.5 year old girl and a 13
year old boy.
Within 11 months in the girl and 19 months
in the boy after placement of dental implants in the
anterior maxilla, a problem with labial fenestrations was
encountered.37
The vertical dimension of the maxilla reaches its
mature dimension around the age of 17 to 18 years in girls
20
and somewhat later in boys.
The growth of the maxilla in
the vertical direction is an accumulation of sutural growth
causing displacement, bone remodeling, and the continued
eruption of teeth.
Björk and Skieller found that the
orbital floor undergoes bony apposition, whereas the nasal
floor has resorptive remodeling over time.
When they
precisely measured these changes they found that the ratio
between orbital floor apposition and nasal floor resorption
was on average three to two, consequently the maxilla is
displaced downward, away from the cranial base.32
Between the ages of 9 and 25, the maxillary incisors
move downwards about 6.0 mm reaching an average eruption
velocity of 1.2 to 1.5 mm during active growth phase, and
0.1 to 0.2 mm per year afterwards.33
Ranley discovered that
a dental implant placed in the anterior maxilla at the age
of seven would be located 10 mm more apically than the
adjacent teeth nine years later.
Dental implants placed at
the age of 12 showed a 5.0 to 7.0 mm infraocclusion four
years later.
noted.38,39
In the molar region, similar changes were
Delaying dental implant placement until the age
of 18 years of age would help prevent the complications in
the vertical plane especially related to remodeling.
21
Mandibular Growth
The timing and direction of mandibular growth is not
identical to that of the maxilla.
In general, in girls,
mandibular growth is nearly completed two to three years
after menarche, while for boys, growth can continue into
the early 20s but usually reaches adult size by age 18.
Due to the longer growth of the mandible in the sagittal
plane, a conversion of a child’s convex profile to the
straighter adult profile is apparent.
This is referred to
differential jaw growth as the mandible outgrows the
maxilla.
In the transverse direction, unlike the maxillary
suture, the mandibular symphysis closes within the first
year of life causing the anterior region of growth to cease
very early in life.
After the eruption of the permanent
canines, almost no change in width occurs in the
intercanine region.
Due to bone apposition on the buccal
side and resorption on the lingual side, growth in the
transverse dimension in the molar and premolar areas tends
to extend for a longer period of time.
The eruption of the
permanent molars and premolars adds an additional small
amount to the transverse dimension.
If a dental implant is
placed in the premolar or molar area before the end of
growth, it may become displaced lingually in relation to
22
the other teeth as the bone remodeling causing an increase
in the transverse dimension.
Due to the early
establishment of the anterior transverse dimension, a
dental implant placed in this area should not show any
displacement in the transverse relationship.40
The growth of the mandible in the sagittal direction
is an indirect result from the growth at the condyle and
remodeling of the mandibular ramus.
The corpus remodels in
the sagittal direction only in length as resorption at the
ventral side and bone apposition at the dorsal side of the
ramus occurs.
The increase in length at the condyle and
the corpus by bone remodeling has no impact on dental
implant placement.
Early dental implant placement would be most affected
by the vertical dimension of growth. Similar to the
sagittal direction most of the vertical growth of the
mandible occurs at the condyle.
While condylar growth
would not directly affect a dental implant placed in the
alveolar ridge, what is called the dentoalveolar
compensation mechanism would significantly affect an
implant’s position.
The dentoalveolar compensation
mechanism is defined as a system that attempts to maintain
a normal inter-arch relationship.
When applied to
mandibular growth, it involves alveolar growth and tooth
23
eruption of the mandibular posterior alveolus and dentition
to compensate for the growth at the condyle and the
rotation of the mandible.
In result, a normal intra-arch
relationship, as well as occlusion between the maxillary
and mandibular teeth, is preserved during growth of the
mandible.41
As the condyle grows up and back into the fossa, one
would think the resultant displacement of the chin would be
down and forward.
However, due to mandibular bony
remodeling and mandibular rotation there is little change
at the chin button in normal facial types.42
In varying
facial types, mandibular rotation varies in amount and
direction, such that the resultant displacement of the
mandible and chin varies in direction.
A larger amount of
dentoalveolar compensation of the dentition is needed in
these cases in order to maintain proper occlusion.
Therefore, the more the facial type is deviated from normal
the more positive or negative rotation occurs, and the more
compensatory alveolar growth and tooth eruption occurs.43,44
Since dental implants cannot move along with alveolar bone
growth and tooth eruptions, variations in the compensatory
amount and direction can dramatically affect the position
of the implant in relation to the adjacent teeth.
24
Post Adolescent Changes
Large changes occur in the dento-facial complex during
early facial growth and development.
After the adolescent
growth spurt, many believe only insignificant changes occur
in the dentofacial complex.
For this reason, it is
recommended that surgeries and implant placement be delayed
until two years after the completion of the growth spurt,
which is thought to be the period of time when adult levels
of growth are complete.45
However, even though most of the
growth is complete two years after the growth spurt, small
amounts of change over a short period of time can add up to
significant changes over a longer period of time.
These
seemingly insignificant changes transpire post adolescence
as mesial migration of teeth, continued eruption of teeth,
and continued alveolar growth.
Mesial Migration of Teeth
Spontaneous mesial drift of teeth is an accepted
phenomenon.
By studying the relationship between
unilateral posterior ankylosed deciduous teeth and normal
teeth, the mesial drift of teeth can be determined. In all
cases, there is an increase in arch length on the side with
the retained ankylosed tooth.
The increase in length
displays itself as either one large space directly anterior
25
to the ankylosed tooth or as space divided interdentally
and randomly in the arch.46
On average, between the ages of
ten and twenty one, the buccal segments move about 5 mm
mesially and the incisors move about 2.5 mm facially.42
In studies by Chirstou and Kiliaridis, a significant
mesial and palatal displacement and of unopposed molars
without mesial and distal adjacent teeth was observed.
Mesial displacement was also observed in a control group
consisting of occlusally and adjacently opposed teeth.
A
mesial vector of the occlusal force has been suggested as
the reason for this mesial displacement of teeth.
Since
they act similarly to ankylosed teeth, a dental implant in
the posterior region could cause inhibition of the mesial
drift of teeth distal in position resulting in an
asymmetric arch anteriorly and contralaterally.
A dental
implant in the anterior would not inhibit the mesial
movement of teeth but could become lingually displaced in
relationship to the adjacent teeth.47
Continued Eruption of Teeth
In addition to the teeth drifting mesially, the teeth
continue to erupt, even after occlusal contact has been
established.
As teeth wear and the dento-facial complex
continues to change over time, teeth continue to erupt in
26
order to maintain occlusal contact.
Classic studies about
continued eruption, have documented the eruption of teeth
over time in relationship to marker implants placed in the
jaws as fixed reference points.
In relationship to marker
implants, Iseri and Solow found that on average, between
the age of 9 and 25 the central incisor erupts vertically 6
mm and the molar 8 mm.
In total, the upper incisor
translocates in relationship to the cranial base 9.5 mm and
the molar translocates about 12.5 mm.33 The difference
between the eruption and translocation was apparently due
to lowering of the maxilla in relationship to the cranial
base.
Another way to study the eruption of molars is to
study unopposed molars compared to teeth with opposing
molars in the same patient.
Christou and Kiliaridis
studied patients with the mean age of approximately 46
years and found vertical displacement of unopposed molars
to be 0.8 mm compared to controls who exhibited 0.4 mm of
movement over a mean period of 10 years.47
Kiliaridis and
colleagues found similar results measuring 84 unopposed
molars over a period of 10 years.
They found 24% of the
teeth showed moderate to severe over eruption.
In
addition, molar rotation was frequently noted in the
maxilla and molar tipping was common in the mandible.48
27
Facial Types
Most of the changes previously discussed were means or
average data collected from large samples of subjects.
When these averages and means are applied to individual
patients, predictive accuracy declines especially in
patients with deviating facial types.
Three facial types
are recognized in the orthodontic literature: normal, short
(described as the horizontal grower or the forward
rotator), and long facial types (described as the vertical
grower or the backward rotator).
To determine the facial
type of a patient the proportion of upper and lower
anterior facial heights are compared to the total anterior
facial height.
In addition, the angle between a line
connecting sella and nasion to a line connecting gonion and
menton can be used.
Facial features distinguishing a short
facial type includes an enlarged nasolabial angle, a well
developed chin point, a concave profile with retro-position
of the lips, thin curly lips, a deep plica labiomentalis, a
broad nose and a toothless look.
A long facial type is
characterized by a heightened lower facial hump, hump on
the nose, decreased chin point, convex profile, enlarged
interlabial distance, a small nose, and a gingival smile.49
There are numerous important skeletal growth
differences between short and long facials types.
28
Arat and
Rubenduz discovered that vertical alveolar development
exhibits regional differentiation during pubertal growth.
These changes are crucial for establishing normal facial
patterns and occlusal relations. Because of the deviations
in jaw growth, differential alveolar growth is needed to
maintain normal occlusal relationships.50
Specifically, studies have shown that short facial
types exhibit more growth in the transverse direction (1.5
mm compared to 0.3 mm in long facial types); the difference
occurs at the midpalatal fissure due to later closure.41
Similarly, Björk and Skieller found large variation in
appositional growth in the height of the alveolar process
(ranging from 9.5 to 21 mm) and is indirectly related to
the transverse dimension of the maxilla.32
Fields, Proffit
and Nixon studied facial pattern differences in long faced
children and adults.
Even though vertical facial patterns
can be identified clinically and documented
morphologically, they found that events could occur during
adolescence to magnify or maintain these differences.
Consequently, a simple explanation of complex biologic
phenomena is inadequate.
Fundamentally, when including
data of patients with varying facial types, facial growth
is even more difficult to predict.51
29
Current Recommendations
The literature shows that predicting the amount of
remaining growth is pertinent to the esthetic and
functional result of dental implants.
Children and
adolescent growth has been extensively studied, but no
facial growth predication system has been established that
is more accurate than pure chance.
Growth prediction is
accurate in the short term but varies greatly when studied
over a longer period of time.
This is especially true for
deviating facial types as discussed earlier.
Studies have
been performed studying late facial growth in adults.
The
most recent studies have shown that although the risk for
infraposition is due to growth changes, it is not
completely age dependant.
As discussed previously, mature
adults can exhibit major vertical steps in anterior
restorations to the same extent as young adults.
So, what
do we recommend to our patients about the appropriate
timing for dental implant placement?
Should we continue to
use Ricketts’ traditionally naive belief that facial growth
is complete after the age of 15 in females and 19 in males?3
Similarly, Love, Murray and Mamandras recommend that growth
is highly correlated at each age period and growth is
directly proportional to age.52
Or, do we believe the more
recent studies showing that alveolar bone growth is not
30
completely age dependent and has been observed to occur in
higher age groups.
Need for Project
Fudalej, Kokich and Leroux completed the most
influential existing study that intended to determine the
predicted amount of change in vertical growth and tooth
eruption between specific ages.
A sample of 301 subjects
from 12 to 40 years of age was evaluated.
Linear
regression models were used to determine changes in the
anterior facial height and displacement of teeth with
increasing age.
Measurements were taken from lateral
cephalograms at pretreatment, post-treatment and 10 years
post-retention.
Measured changes over the various age
intervals for each measured parameter were calculated,
inserted into the fitted regression equations, and
prediction tables were developed.
The main conclusion
drawn indicate that after puberty the facial skeleton
continues to grow in progressively diminishing amounts that
become clinically insignificant after the second decade in
life.6
The accuracy of the prediction tables was tested,
however, on the original sample and thus it is not
surprising that high prediction efficiency was claimed.
31
Other limitations of the study were that the sample
used was a treated sample, therefore whether the relative
eruption of the teeth was due to eruption of the teeth or
due to relapse cannot be determined.
Incisor angulations
were not taken into consideration, which can also affect
the height of the teeth.
Differing growth patterns also
were not taken into consideration.
Lastly, the
measurements did not assess the remodeling of the
mandibular border of the mandible and the palatal plane of
the maxilla.
Thus, the points and measurements based on
these lines may be inaccurate.53
Statement of Thesis
Treatment planning for missing teeth occurs daily in
most orthodontic practices.
There are several restorative
options for missing teeth; when a dental implant is
selected, the timing of placement is important.
Recent
literature reports that the risk for a dental implant to
develop an infraposition in relation to the adjacent teeth
is not completely age dependant.
Studies have revealed
that adults, who originally were thought to have minimal
remaining growth and dental compensations, have developed
significant discrepancies between dental implants and
adjacent teeth. The currently used recommendations for the
32
timing of single-tooth implant placement was developed by
Fudalej et al, who concluded that growth of the facial
skeleton continues after puberty, but the amount of growth
decreases steadily and after the second decade of life
seems to be clinically insignificant.6
The purpose of the
present investigation, therefore, is to test the accuracy
of the current recommendation using a new sample.
33
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Vertical position, rotation, and tipping of molars
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49. Op Heij DG, Opdebeeck H, van Steenberghe D, Quirynen M.
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Facial pattern differences in long-faced children and
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39
CHAPTER 3: JOURNAL ARTICLE
Abstract
Introduction:
The purpose of this study was to test
the accuracy of a growth prediction scheme.
The scheme
developed by Fudalej, Kokich and Leroux is the current
recommendation to determine the cessation of vertical
growth of the craniofacial structures to facilitate
placement of single-tooth implants.
The purpose of the
present investigation is to test the accuracy of the
current recommendation using a new sample.
Subjects and
Methods: Fifty-seven post-treatment orthodontic patients
were recalled from one private practice. Each subject had
lateral cephalograms taken pre-treatment, immediately posttreatment and a mean of 23.4 years in retention. To compare
the predicted amounts of vertical growth of the
craniofacial structures to the actual growth values, the
same anatomic landmarks as the original study were utilized
and distances between the respective points were measured.
A paired t-test was applied to each measured variable for
statistical analysis.
Tables and graphic representations
were created to compare the predicted versus the actual
measurements.
Results: There were two statistically
significant paired t-test measures: the anterior facial
height and the eruption of maxillary molar.
40
Grouped by age
intervals, there were 4 out of 16 statistically different
measures.
Conclusions:
In comparison to the actual sample
measurements, the growth prediction system by Fudalej et al
overestimated the amount of growth in anterior facial
height and underestimated the amount of eruption of the
maxillary molar.
There was no significant difference
between the actual and predicted measurements for the
eruption of the maxillary and mandibular incisors. In
conclusion, in agreement with the conclusions of the
original study, growth of the craniofacial skeleton is a
continuous process that decreases in amount with time.
However, more practically speaking, the risk of failure due
to a development of a perceivable asymmetric discrepancy
between of the implant and adjacent teeth may be greater
than we once believed.
In this study, one out of every
four implants would have failed if the recommendations of
the original study were taken that only clinically
insignificant amounts of growth are observed after the
second decade of life.
Introduction
Facial growth prediction is considered an important
subject in the specialty of orthodontics. The success of
many treatment methodologies depends on proper timing
41
relative to skeletal growth. The amount, direction and
timing of growth are important in determining predictable
and successful treatment and for most cases constitute a
determinant of treatment time. In today’s esthetically
driven society, choosing a correct patient-specific
treatment plan must consider both the best esthetic outcome
for the patients, as well as the most stabile long-term
result.
Many adolescent orthodontic patients present with
congenitally or acquired missing permanent teeth.
Missing
or lost teeth is a disadvantage, and living with the stigma
of missing teeth has been proven to negatively influence
quality of life as such damages a person’s self image and
limits their lifestyle. There are multiple restorative
options for replacement of missing teeth: dental implants,
space closure orthodontically, fixed partial dentures,
removable partial dentures, and autotransplantations.
Single-tooth dental implants are becoming a popular
restorative option due to their high success rate, lower
future maintenance, and they do not require preparation of
adjacent teeth.
However, implants have been proven to be
an age specific procedure that can be challenging
technically and esthetically, due to their ankylotic
characteristic.1
42
Dental implants have been shown to fuse to the bone
and exhibit many qualities as an ankylosed tooth.
The
ankylotic nature of dental implants was first demonstrated
in growing pig jaws.2,3,4
Such effects in growing humans
were sequentially studied via ankylosed teeth.5
Clinical
and radiographic evidence demonstrated that dental
implants, like ankylosed teeth, do not behave like natural
erupting teeth during the development of supporting
alveolar bone and the dentition.
Rather they “submerge”
into the developing alveolar bone and the adjacent teeth
continue to erupt causing the dental implant to be
relatively displaced.
A submerged dental implant not only
leaves an unesthetic restorative result, but can also
destroy the surrounding alveolar bone resulting in a
periodontal bony defect around the adjacent teeth.
The
more growth of the dentofacial complex and supporting
alveolus, the more the position of the dental implant is
affected.
Many orthodontic patients finish treatment with years
of remaining potential growth.
A classic study by Iseri
and Solow’s reported from the age 9 to 25, incisors have
the potential to erupt 6 mm incisal and 2.5 mm forward and
molars 8 mm occlusal and 3 mm forward.6
Consequently, the
placement of dental implants in adolescents is not
43
recommended.
While the effects of growth on dental
implants in adolescents have been well documented and
accepted, the changes that occur post adolescence is not
well understood. It has been assumed that adults are stable
and do not change, however, there is documented evidence
that mature adults can exhibit major defects resulting from
osseointegrated fixtures.7
Studies done by Behrents,
Bishara et al and Forsberg et al confirm that growth
continues post adolescent into adulthood.8,9,10
Therefore,
the question is at what age, if ever, are alveolar and
eruptive changes small enough so as not to affect the
esthetic and functional long term outcome of dental
implants.
Growth prediction systems have been studied at length
for accuracy, unfortunately the most common finding is that
most growth prediction systems have limited accuracy.11
Schulhof and Bagha studied the classic prediction schemes
in comparison to refined computer methods, even taking in
account the individual facial patterns, and they found
range of accuracy from 50 to 70%.
Such accuracy in the
practical sense is principally not much greater than chance
alone.12
Prediction equations are usually developed using one
sample and then tested for efficiency using that same
44
sample.
Using this approach, prediction efficiency is
usually high.
To actually put the prediction equation to
real test, the prediction scheme must be applied to another
sample so that the predicted result can be compared to the
actual result.
The correlation between the predicted and
actual values will measure the efficiency of the facial
growth scheme.
Fudalej, Kokich and Leroux studied changes in vertical
alveolar growth and continued tooth eruption to develop
prediction tables intended to predict the change of a
measurement between two age intervals.
Derived tables are
supposed to be the current recommendation for quantifying
the amount of vertical growth of the facial skeleton and
the amounts of eruption of the central incisors and first
molars after puberty.
It is thought that using these
tables proper recommendations for the timing of dental
implant placements can be made.13
To date, however, the
accuracy of the prediction tables has not been subject to
tests of accuracy.
Sample and Methods
The purpose of the present investigation is to test
the accuracy of the current recommendations of age specific
dental implant placement based on growth prediction tables
45
by Fudalej, Kokich and Leroux.13
The amount of vertical
growth of the facial skeleton and the amount of eruption of
the central incisors and maxillary first molars after
puberty will be measured. The actual measurements of the
sample will be compared with the predicted values to test
the accuracy of the prediction tables.
Sample
The sample consisted of 57 subjects, selected from
pre-treatment, post-treatment and retention records.
The
sample was treated and retained by the same orthodontist.A
Each subject had cephalograms taken pre-treatment (T1),
immediately post-treatment (T2) and at least 18 years, but a
mean of 23 years 5 months in retention (T3).
The
cephalograms at T1 were not used in this study.
The
cephalograms at T2 and T3 time points were used to select
the sample and collect the data.
Table 1.
A
Sample demographics (yrs).
Time/Interval
Mean
SD
Range
T2
16.3
2.8
12-27.4
T3
39.7
4.1
32.2-52.2
T3-T2
23.4
3.2
16.1-25.5
Dr. James L. Vaden, Cookeville, TN
46
The mean age of the sample was 16 years 4 months at T2
and 39 years 9 months at T3.
The sample was predominately
female with a gender distribution of 52 females and 5
males. The age demographic breakdown of the sample is shown
in Tables 1-2. The sample fit the same inclusion criteria
outlined in the study performed by Fudalej, Kokich and
Leroux including: (1) T2 Age 12 or later; (2) non-surgical
orthodontic treatment; (3) no additional orthodontic
treatment between T2 and T3; (4) no more than two teeth lost
or extensive prosthodontic treatment; (5) satisfactory
orthodontic treatment with regards to overbite and overjet
at T2; and (6) quality lateral cephalometric radiographs.13
Table 2.
Age distribution of the sample at T2.
Age range (years)
Number in Sample
12-15
15
15-18
34
18-21
4
21+
4
The Angle classification of the starting malocclusion
was not considered in the selection of the sample. Both
extraction and nonextraction orthodontic therapy was
included in the sample.
The subjects were Caucasian
females and males who returned to the practice at the own
47
discretion and expense between the years of 2005 and 2008.
The orthodontic treatment was performed with edgewise
appliances and using Tweed mechanics involving but not
limited to J-hook headgear, tip-back bends and Class II
elastics.
Cephalometric Technique and Analysis
The following landmarks were identified on each
cephalograms and traced on 0.003 acetate tracing paper:
nasion (N), menton (Me), gonion (Go), anterior nasal spine
(ANS), posterior nasal spine (PNS), maxillary central
incisor incisal edge (U1e), mandibular central incisor
incisal edge (L1e), and maxillary first permanent molar
mesial buccal cusp tip (U6c).
Templates were constructed
outlining the most clearly discernible maxillary and
mandibular incisors and maxillary first molars in each of
the two film series.
A second observerB examined the finished tracings
before the Cephalometric digitization and numerical
analysis.
Disagreements were resolved by discussion,
retracing and re-measurement if needed.
The cephalometric
tracings were digitized on a transparent digitizer
B
Dr. Rolf Behrents
48
(Numonics Digitizing Board, Model A30B1.H, Numonics
Corporation, Montgomeryville, PA).
were constructed:
Two reference planes
palatal plane (PP), line running through
ANS and PNS; and mandibular plane (MP), line running
through Me and Go.
The traced landmarks were digitized and
the references lines were constructed using a commercial
Figure 3. Landmarks and reference planes: S, sella; N,
nasion; Me, menton; Go, gonion; ANS, anterior nasal spine;
PNS, posterior nasal spine; U1e, maxillary central incisor
incisal edge; L1e, mandibular central incisor incisal edge;
U6c, Maxillary first permanent first molar CEJ; PP, palatal
plane connecting ANS and PNS; MP, mandibular plane
connecting Go and Me (adopted from Fudalej et al).13
49
software program (Dentofacial Planner 7.0, version 5.32,
Dentofacial Software, Toronto, Canada).
These landmarks
and planes are diagrammed in Figure 3.
From the landmarks and reference planes, four linear
measurements were derived and computed by the software:
Anterior facial height (N-Me), measuring from nasion to
Figure 4. Measurements: anterior facial height (N-Me),
eruption of maxillary incisor (U1e-PP), eruption of
mandibular incisor (L1-MP), and eruption of maxillary molar
(U6c-PP) (adopted from Fudalej et al).13
50
menton; eruption of maxillary teeth (U1e-PP) and (U6c-PP),
measuring the incisal edge of the maxillary incisor and the
cusp tip of the first molar perpendicular to the palatal
plane respectively; and eruption of mandibular teeth (L1eMP), measuring the incisal edge of the mandibular incisors
perpendicular to the mandibular plane.
These measurements
are diagrammed in Figure 4.
The data was corrected for magnification differences
between T2 and T3 on an individual basis.
Lesser
measurements at T3 compared to T2 were observed in 37 of
the 57 patients.
This illustrated that there was a
magnification discrepancy with the cephalograms.
All of
the films were taken with a constant anode to object
distance of five feet, but a varying midline-lateral film
distance (distance from the patient’s midsagittal plane to
the film), contributing to the varying magnifications.
The
use of different cephalostats at T2 and T3 also contributed
to the difference in magnification.
The percentage of enlargement was corrected based on
equalizing the distances from sella to nasion (S-N).
The
following equation was used to calculate the percentage of
enlargement:
Percentage of enlargement = (S-N at T2) – (S-N at T3)
(S-N at T3)
51
The T3 measurements were multiplied by this enlargement
factor for each individual patient, such that no patient
decreased in size from T2 to T3 in regards to S-N. The
percent enlargement of the T3 measurements ranged from zero
to 6.8% with an average enlargement of 1.3%.
The reproducibility of the measurements was assessed
by statistically analyzing the difference between
reproduced measurements taken two weeks apart on 13
cephalograms selected at random.
The error of the method
(Si) was calculated from the equation:
Si=√(∑d²/2N)
where d is the difference between the repeated measurement
and N is the number of repeated measurements.
The mean
error for the cephalometric measurements was 0.25 mm and
ranged from 0.18 mm to 0.33 mm for the individual
measurements.
The individual measurements can be found in
Table 3.
Table 3.
Error of measurement of variables (mm).
Measurement
Error
N-Me
U1e/PP
L1e/MP
U6c/MP
0.33
0.30
0.18
0.19
52
Statistical Analysis
Statistical analysis was computed using commercially
available spreadsheet program (Microsoft Excel 2007) and
statistical software (SPSS, version 18.0, SPSS Inc.,
Chicago, IL).
For each measured parameter, actual growth
changes over the various age intervals were calculated by
subtraction of the T2 time point from the T3 time point
measurements.
The predicted growth changes were collected
from the prediction tables in the article written by
Fudalej et al.13
For each individual in the sample, they
were matched with the values in the table using the post
treatment and retention ages and the predicted changes were
recorded.
A Q-Q plot was used to determine the distribution of
the data.
Due to the data lying along the X-axis it was
determined to be normally distributed.
Means and standard
deviations were calculated for all cephalometric
measurements.
Paired t-tests were employed to test the
null hypothesis: the sample’s linear changes in growth from
post-treatment to retention did not differ significantly
from predicted amounts forecasted by Fudalej et al.13
type-I error was set at α = 0.05.
The
The data was analyzed as
a whole and as groups based on age intervals: 12-15, 15-18,
18-21 and 21 plus years of age.
53
Results
The descriptive statistics, means and standard
deviations, for the actual and predicted growth changes
between post-treatment and retention linear cephalometric
measurements are presented in Table 4.
The actual and
predicted changes and standard deviation as a whole sample
are graphically presented in Figure 5.
The results grouped
by age are presented in Table 5.
Whole Sample
3.5
3.0
2.5
2.0
Predicted
1.5
Actual
1.0
0.5
0.0
-0.5
N-Me
*
U1e-PP
L1e-MP
U6c-PP
*
Figure 5. Comparison of the predicted growth amounts and
actual growth amounts for linear measurements N-Me, U1e-PP,
L1e-MP and U6c-PP in mm for the sample as a whole.
*Indicates statistically significant group difference
(P≤.05).
54
Table 4. Descriptive statistics for the total sample
population and paired t-tests for the null hypothesis.
Predicted
Error
Actual Change
Change
(Actual - Paired t
(T3 minus T2) (T3 minus T2) Predicted) (Ho:δ=0)
Measures Mean
S.D.
Mean
S.D. Mean S.D.
N-Me
0.9
2.0
2.4
0.8 -1.5
2.0
.000*
U1e-PP
1.4
1.3
1.3
0.5
0.1
1.2
.570
L1e-MP
0.8
1.0
0.7
0.5
0.1
1.1
.400
U6c-PP
1.2
0.9
0.7
0.5
0.5
0.9
.000*
*Indicates statistically significant group difference
(P≤.05).
Table 5. Descriptive statistics for the various T2 age
ranges in years and paired t-test for the null hypothesis.
Predicted
Error
Actual Change
Change
(ActualPaired t
(T3 minus T2) (T3 minus T2) Predicted) (Ho:δ=0)
Measures Mean
S.D.
Mean
S.D.
Mean S.D.
12-15
N-Me
2.2
2.4
3.1
0.8
-0.9
2.5
.202
U1e-PP
1.9
1.4
1.7
0.5
0.2
1.3
.524
L1e-MP
1.0
1.1
1.1
0.5
-0.1
1.3
.864
U6c-PP
1.7
1.0
1.1
0.5
0.6
1.1
.034*
15-18
N-Me
0.5
1.7
2.4
0.5
-1.9
1.7
.000*
U1e-PP
1.4
1.3
1.3
0.2
0.1
1.3
.589
L1e-MP
0.8
1.0
0.7
0.3
0.1
1.0
.580
U6c-PP
1.0
0.7
0.7
0.3
0.3
0.7
.007*
18-21
N-Me
0.9
1.7
1.5
0.3
-0.6
1.0
.335
U1e-PP
0.1
0.4
0.6
0.2
-0.5
0.5
.133
L1e-MP
0.9
0.6
0.2
0.2
0.7
0.6
.104
U6c-PP
1.4
0.7
0.2
0.2
1.2
0.6
.025*
21+
N-Me
-0.3
1.2
0.7
0.5
-1.1
1.2
.171
U1e-PP
0.2
0.7
0.3
0.2
-0.1
0.7
.807
L1e-MP
0.4
1.1
-0.2
0.1
0.6
1.1
.383
U6c-PP
1.0
0.9
-0.2
0.1
1.2
0.9
.098
*Indicates statistically significant group difference
(P≤.05).
55
Anterior Facial Height
Anterior facial height (AFH) is the distance measured
from nasion to menton (N-Me).
The actual changes in AFH
were calculated by subtracting post-treatment distances
from retentions distances.
The mean actual changes were
compared to the mean predicted changes collected from the
tables provided by Fudalej et al13 and shown in Table 4 and
Figure 5 for the sample as a whole.
The result grouped by
post-treatment age is shown in Table 5 and Figure 6.
N-Me
5.0
4.0
3.0
2.0
Predicted
1.0
Actual
0.0
12-15
-1.0
15-18
18-21
21+
*
-2.0
Figure 6. Comparison of the predicted growth amounts and
actual growth amounts grouped by T2 age for the linear
measurement N-Me in mm. *Indicates statistically
significant group difference (P≤.05).
56
As a whole in the sample group, AFH (N-Me) increased 0.9 mm
(SD = 2.0 mm) during the observation period.
When compared
to the predicted value of 2.4 mm (SD = 0.8 mm), the error
in the growth prediction scheme (calculated by the actual
minus the predicted mean value for N-Me) was -1.5 mm (SD =
2.0 mm). The predicted change was significantly larger than
the actual amount of growth, accordingly, the growth
prediction scheme over-estimated the amount of growth from
post-treatment to retention. Grouping by age, the 15 to 18
age interval was the only groups with a significant
difference between the predicted and actual measures.
Consequently, the prediction scheme over-estimated the
amount of growth by 1.9 mm (SD = 1.7 mm).
Incisors
The amount of eruption of the maxillary (U1e-PP) and
mandibular incisors (L1e-MP) of the measured sample
compared to the predicted values of the growth prediction
scheme by Fudalej et al13 are presented as a whole in Table
4 and Figure 5 and broken down by age group in Table 5 and
Figures 7 and 8.
In the sample group, the mean eruption
distance of the maxillary and mandibular incisors over the
observation period was 1.4 mm (SD = 1.3 mm) and 0.8 mm (SD
= 1.0 mm) respectively.
When compared to the predicted
57
U1e-PP
3.5
3.0
2.5
2.0
1.5
Predicted
1.0
Actual
0.5
0.0
-0.5
12-15
15-18
18-21
21+
-1.0
Figure 7. Comparison of the predicted growth amounts and
actual growth amounts grouped by T2 age for the linear
measurement U1e-PP in mm. *Indicates statistically
significant group difference (P≤.05).
L1e-MP
2.5
2.0
1.5
1.0
Predicted
Actual
0.5
0.0
12-15
15-18
18-21
21+
-0.5
-1.0
Figure 8. Comparison of the predicted growth amounts and
actual growth amounts grouped by T2 age for the linear
measurement L1e-MP in mm. *Indicates statistically
significant group difference (P≤.05).
58
eruption of the maxillary and mandibular incisor values of
1.3 mm (SD = 0.5 mm) and 0.7 mm (SD = 0.5 mm) respectively,
the error in the prediction scheme is 0.1 mm for both
measures.
The actual measurements of the samples were not
significantly difference from the predicted values of the
growth prediction scheme for the eruption of the incisors.
Categorized by age, comparing the actual to the predicted
measures, there was no significant difference in the
measurements.
U1e-PP
35
30
25
>2.0 mm
20
<2.0 mm
<1.0 mm
15
0 mm
10
5
0
12-15
15-18
18-21
21+
Figure 9. The distribution of the sample illustrating the
amount of eruption of the maxillary incisors from T2 to T3,
grouped by age in years at T2 and by increments of eruption
of 0 mm, <1.0 mm, <2.0 mm, or >2.0 mm.
59
L1e-MP
35
30
25
>2.0 mm
20
<2.0 mm
<1.0 mm
15
0 mm
10
5
0
12-15
15-18
18-21
21+
Figure 10. The distribution of the sample illustrating the
amount of eruption of the mandibular incisors from T2 to T3,
grouped by age in years at T2 and by increments of eruption
of 0 mm, <1.0 mm, <2.0 mm, or >2.0 mm.
The distribution of the amount of eruption of the
maxillary and mandibular incisors from T2 to T3 of the
measured sample, grouped by age at T2 and increments of
eruption from 0 mm, 0 to 1.0 mm, 1.0 to 2.0 mm, and greater
than 2.0 mm, is presented in Figures 9 and 10 respectively.
The distributions illustrating the percentages of the
sample with specific increments of eruption of maxillary
and mandibular incisors are presented in Figures 11 and 12
60
U1e-PP
80
70
60
0 mm
50
<1.0 mm
40
<2.0 mm
30
>2.0 mm
20
10
0
12-15
15-18
18-21
21+
total
Figure 11. The percentage of the sample with the amount of
eruption of the maxillary incisors from T2 to T3 of
increments of 0 mm, 0-1 mm, 1-2 mm or >2.0 mm, grouped by
age at T2.
L1e-MP
50
45
40
35
0 mm
30
<1.0 mm
25
<2.0 mm
20
>2.0 mm
15
10
5
0
12-15
15-18
18-21
21+
total
Figure 12. The percentage of the sample with the amount of
eruption of the mandibular incisors from T2 to T3 of
increments of 0 mm, 0-1 mm, 1-2 mm or >2.0 mm, grouped by
age at T2.
61
respectively. Looking at the sample as a whole, 59% and 48%
of the patients experienced greater than 1 mm of eruption
of the upper and lower incisors respectively. After the age
of 21, 25% of the patients developed a discrepancy of
greater than 1 mm for both the maxillary and mandibular
incisors.
Molars
The eruption distances of the maxillary molars (U6cPP) of the measured sample compared to the predicted values
of the growth prediction scheme by Fudalej et al13 are shown
in Table 4 and Figure 5.
The results for the eruption U6c-
PP broken down by age group is presented in Table 5 and
Figure 13.
As a whole, the actual change in the eruption of the
maxillary molar was 1.2 mm (SD = 0.9 mm) compared to the
predicted value of 0.7 mm (SD = 0.5 mm).
The actual change
was significantly larger than the predicted amount of
growth showing the growth prediction scheme under-estimated
the amount of growth from post-treatment to retention.
Grouped by age, the age groups with a significant
difference between the predicted and actual measures were
those with a post-treatment age of 12 to 15, 15 to 18 and
18-21.
The prediction scheme under-estimated the amount of
62
growth by 0.6 mm (SD = 1.1 mm), 1.2 mm (SD = 0.7 mm) and
1.4 mm (SD = 0.6 mm) respectively.
U6c-PP
3.0
2.5
2.0
1.5
Predicted
1.0
Actual
0.5
0.0
-0.5
12-15
*
15-18
*
18-21
*
21+
Figure 13. Comparison of the predicted growth amounts and
actual growth amounts grouped by T2 age for the linear
measurement U6c-PP in mm. *Indicates statistically
significant group difference (P≤.05).
Discussion
The accuracy of the prediction tables constructed by
Fudalej et al13 was tested with a sample of 57 treated
orthodontic patients.
The conclusions of this study were
based on the premise that if the predicted values (acquired
from the original study’s growth prediction tables) were
equal to the actual values (measured in this study) then
the error in prediction scheme would equal zero.
63
However,
if the error of prediction scheme was not equal to zero
then the prediction scheme either underestimated or
overestimated the amount of growth.
In this study, significant differences were found
between the actual and predicted measurements of N-Me and
U6c-PP.
The prediction scheme overestimated the amount of
growth of the anterior facial height by 1.5 mm and
underestimated the amount of eruption of the maxillary
first molar by 0.5 mm.
There was no statistical difference
between the actual and predicted measurements of U1e-PP and
L1e-MP.
Thus, the prediction scheme was accurate for the
prediction of the amount of eruption of the maxillary and
mandibular incisors.
Even though we found similarities and differences in
the predicted and actual values, the results were variable.
For all variables, the standard deviations were larger than
the mean result of error of the prediction scheme.
When
dealing with small numbers, any variation in the data
decreases the reliability of the data.
Additionally,
grouping the sample into age intervals further reduces the
sample size, decreasing it below the needed size to have
sufficient statistical power to make definitive
conclusions.
For those reasons, as stated in the
conclusions of the original study,13 the changes in the
64
means are for the population and should not be interpreted
as a predicted range of values for the change in a single
patient.
Looking at the larger picture, this study’s findings
are similar to those found in the original study by Fudalej
et al.13
The age interval 12 to 15 years of age for all
measured variables resulted with the largest growth changes
over the observation period and the values decreased with
subsequent age intervals.
As well, in the age group 21
years and older there was no significant difference between
the actual and predicted measures.
Consequently, the
results of this study were in agreement with the
conclusions that growth of the craniofacial skeleton is a
continuous process that decreases in amount with time and
after the second decade of life the amount of growth may be
clinically insignificant for the average patient.
On the contrary and more practically speaking, one
should determine the risk of failure of a dental implant
before giving recommendations about the procedure.
According to a study by Kokich et al, dental professionals
and laypersons can detect discrepancies as small as 0.5 and
1.0 mm.
Furthermore, asymmetric esthetic discrepancies are
more perceptible than symmetric discrepancies.
Such
information can be used as an aid to determine whether to
65
recommend treatment to the patient.14
In this study as a
whole, 59% of the maxillary and 48% of the mandibular
incisor change position greater than 1 mm.
After the age
of 21, 25% of the patients developed a change in position
greater than 1 mm for both the maxillary and mandibular
incisors.
Thus, 60% of the whole sample and 25% of the
patients 21 years and older experienced an amount of
eruption of the incisors at a magnitude that could
potentially cause a perceivable discrepancy in position.
Such discrepancy between a tooth and an immobile dental
implant would risk failure of the implant.
A clinical
failure of 25 to 50% is a significant problem.
The original study predicts that after the age of 18
the maxillary incisor will continue to erupt 0.8 mm in
females and 0.5 mm in males, while the mandibular incisors
continue to erupt 1.1 mm in females and 1.5 mm in males.13
Consequently, can a recommendation be made that after the
second decade of life the amount of eruption of the
incisors are clinically insignificant when the study
predicts a perceptible difference in the position of the
incisors to occur?
Dental professionals should consider
this information when advising patients on the risk of
failure of dental implants.
66
Since the error of measurement ranges from 0.18 to
0.33 mm, it gives the impression that the error of
measurements is small and thus insignificant.
However,
relative to the small changes in measurements from T2 to T3,
the error in the measurements becomes a significant factor.
In some cases, the measurement error is larger than the
growth changes.
Such magnitude of error has implication of
the accuracy of actual values, as well as, the prediction
values.
One may speculate the underlying cause of the variable
results, but the study had multiple limitations.
Since
there were no rulers or consistence structures on all the
cephalograms, the only means of correction of the
magnification was based on equalizing S-N.
Conversely,
Behrents’ thesis showed the majority of the population
experience an increase in the S-N distance throughout
adulthood.8
Thus, a percent enlargement correction based on
equalizing the S-N measurement between T2 and T3, is a
conservative method of correction and under-values the
amount of enlargement.
Since this correction was made on
37 of the 57 patients (65% of the T3 data), the resulting
corrected measurements could be smaller than their true
values.
Therefore, the actual changes in growth from T2 to
T3 could be larger in value than reported in this study.
67
Incisal wear was not considered as a factor in the
study.
According to Magne et al, the difference in length
between worn and unworn teeth can range up to 1.02 mm.15
Since the calculated amounts of eruption over the
observation period decreased with age, incisal wear could
be the reason rather than the cessation of eruption.
Furthermore, the uprighting of the incisors is a
physiological event not accounted for in the study.
According to Bonevik, significant changes in the position
of teeth occur between 23 and 34 years of age.
Changes
such as the retroclination of the maxillary incisors by
1.44 degrees and a decrease in the mandibular anterior
perimeter by 2.5 mm could have a substantial effect on the
vertical and horizontal position of an incisors.16
Such
factors would significantly change the resulting data in
this study.
Moreover, the study did not consider differing facial
types.
A study by Malmgren and Malmgren studying the
infraposition of ankylosed teeth found that there is a
difference in the rate of infraposition between horizontal
and vertical growers.
They concluded that annual body
height measurements is a good indication of intensity of
skeletal growth and can aid in the assessment of the risk
of infraposition, but a cephalograms is important for
68
evaluation the direction of growth.17
This fact adds reason
to the variability of the sample data.
The reality that the sample was taken from postorthodontic treatment patients is a further concern about
the reliability of the results.
The amount of intrusion or
extrusion of teeth during treatment has a potential to
relapse changing the vertical position of the teeth.
Considering the sample was treated with pure Tweed
mechanics, involving tip backs in the molars, technique
related settling of the molars that necessary in most cases
to fully seat the posterior buccal occlusion would have
been measured as physiological eruption in the data that in
actuality is relapse from orthodontic treatment.
Such
eruption may account for the difference in eruption of the
maxillary molar found in this study compared to the
original study.
A non-treated sample may have resulted in
a different and more accurate finding.
An ideal study design would measure an untreated
sample, thus eliminating the possibility of relapse or
settling as a potential error in the study.
Using the
center of the tooth instead of the incisal edge or cusp tip
to measure the amount of eruption would remove the problems
involving tooth tipping and incisal and occlusal wear.
Finally, radiographs with consistent magnification without
69
the need for adjustment would be ideal and eliminate
possible enlargement error.
Summary and Conclusion
The present investigation was a test of accuracy of a
growth prediction scheme.
The accuracy of the scheme
affects the timing of placement of dental implants and
affects the long-term esthetic result of the restorations.
Underestimating the amount of post adolescent growth can
cause a dental implant to submerge and result in an
unesthetic and structurally damaging result.
In conclusion:
1.
In comparison to the actual sample measurements, the
growth prediction system by Fudalej et al13
overestimated the amount of growth in the anterior
facial height and underestimated the amount of eruption
of the maxillary molar.
There was no significant
difference between the actual and predicted measurements
for the eruption of the maxillary and mandibular
incisors.
2.
In general, the age interval 12 to 15 years of age
resulted in the largest growth changes over the
observation period, agreeing with the conclusion of
Fudalej et al13 study that growth of the craniofacial
70
skeleton is a continuous process that decreases in
amount with time.
3.
According to the findings in this study, alveolar and
eruptive changes are small enough after the second
decade of life not to affect the esthetic and functional
long-term outcome of the dental implants in the average
patient.
4.
More practically speaking, 60% of the whole sample and
25% of the patients 21 years and older experienced an
eruption of the incisors to a magnitude such that an
esthetic discrepancy would develop if a dental implant
were placed at T2.
According to the recommendations
made by Fudalej et al13, one out of four implants placed
would risk failure, which is not clinically acceptable.
Due to the large variation in measurements for small
differences, the reliability of the data is of concern.
Multiple limitations of the study have been outlined in the
discussion.
However, as long as it is realized that the
growth prediction tables fabricated by Fudalej et al13 are
recommendations for the population as a whole and should
only be used as a guide to determine when serial
cephalograms should be taken to assess the cessation of
skeletal growth, the tables are a useful guide.
However,
the restoring doctor and patient need to know the risk of
71
the failure of dental implants in regards to the
development of perceivable discrepancies may be greater
than we originally believed.
The original thought
maintains true that it is difficult to make predictions,
especially about the future.
72
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VITA AUCTORIS
Jaclyn Scroggins was born on October 2, 1982 in
Bartlett, Illinois. She completed her undergraduate studies
at Francis Marion University, in Florence, South Carolina
obtaining a Bachelor of Science in Biology while playing
division two volleyball. Coming back closer to home, she
continued her education at Southern Illinois University
School of Dental Medicine where she earned her Doctor of
Dental Medicine degree in 2009. In dental school, she met
her future husband, Kenneth, causing her to relocate to the
Saint Louis Metro East following graduation.
She worked a
year as a general dentist in Litchfield, Illinois where she
gained invaluable experience in the general dental field.
In search of further knowledge, in the fall of 2010, she
began the orthodontic residency program at Saint Louis
University in pursuit of a Certificate in Orthodontics and
a Master of Science in Dentistry Degree. Kenneth and Jaclyn
were married during her first year of her orthodontic
residency in July of 2010. Upon her graduation from Saint
Louis University, they will remain in the Saint Louis area
to begin dental and orthodontic careers and start a family.
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