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QUANTITATIVE ASSESSMENT OF THE EFFECTIVENESS OF PHASE 1
ORTHODONTIC TREATMENT UTILIZING THE ABO DISCREPANCY
INDEX
Nefeli D. Vasilakou, D.D.S.
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
2014
ABSTRACT
Purpose: The purpose of this study is to quantify the changes obtained from the First
Phase of Orthodontic treatment and determine how much improvement, if any, has
occurred before the initiation of the Second Phase. Additionally, all variables
constituting the DI score were measured to investigate which components of
malocclusion undergo the most change. Finally, the three Angle classification groups
will be compared to investigate if any of these groups would benefit more from an Early
treatment phase. Materials and Methods: For the purpose of this retrospective study,
pre-Phase 1 and pre Phase 2 records of 300 individuals who received a 2-Phase treatment,
were gathered. All cases were measured using the Discrepancy Index and a score was
given for each Phase (T1DI before Phase 1 and T2DI before Phase 2). The difference of
T1D1-T2DI demonstrates the quantitative change of the case complexity. Paired t-tests
were used to compare the initial and final scores overall and for each component of the
DI separately. Additionally the sample was categorized in three groups according to the
molar Angle classification (Class I, II and III) and the same statistics were used to
identify significant changes between T1 and T2. An ANOVA was applied to compare
the three groups and determine which one underwent the most change. Lastly,
percentages of change were calculated for the total score and each variable as well as for
the total scores and for the DI components of each group individually. Results: The
total DI score overall and the scores of all three groups were significantly reduced from
T1 to T2, which indicates a significant reduction in complexity. Overall, 42%
improvement was observed. The Class I group showed 49.3% improvement, the Class II
group 34.5% and the Class III group 58.5%.Several components of the DI (overjet,
anterior open bite, crowding, occlusal relationship, lingual crossbite, ANB angle and the
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category “Other” complexities) improved significantly while few ( IMPA in the Class II
group and occlusal relationship in the Class I group) showed negative change. Between
the three groups, the Class III proved to undergo the most significant change and benefit
the most from early treatment. Conclusion: A significant reduction of DI score was
observed in our sample overall and in all Angle Classification groups, which indicates
that Early treatment reduces the case complexity. Only two components of the DI
showed negative change which shows that controlled mechanics are required during
treatment.
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QUANTITATIVE ASSESSMENT OF THE EFFECTIVENESS OF PHASE 1
ORTHODONTIC TREATMENT UTILIZING THE ABO DISCREPANCY
INDEX
Nefeli D. Vasilakou, D.D.S.
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
2014
COMMITTEE IN CHARGE OF CANDIDACY:
Professor Eustaquio Araujo,
Chairperson and Advisor
Associate Professor Ki Beom Kim
Associate Clinical Professor Donald R. Oliver
i
DEDICATION
This work is dedicated to my wonderful parents, Ourania and Dimitri, who have
always encouraged me to pursue my dreams and have supported me in every possible
way to make them come true. My love and appreciation for you is ever growing.
To my beloved grandmother, Aggeliki.
To the loving memory of my grandfather, Stavro.
Lastly, to the faculty of Saint Louis University, whose guidance and instruction
have built a strong foundation for me to grow a fulfilling practice and future.
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ACKNOWLEDGEMENTS
I would like to thank Dr. Eustaquio Araujo, my mentor and committee chair, for all of his
guidance through this process and for giving me confidence with his trust and support.
My other committee members, Dr. Donald Oliver and Dr. Ki Beom Kim, for all of their
help with this work, their guidance and the constructive criticism. Thank you to Dr.
Heidi Israel for her help with the statistical analyses and to Dr. Patrick Foley for his help
with the calibration process. I also need to thank the entire faculty, staff and
administration who have played a role in my acceptance to this program and in my
orthodontic education. Special appreciation goes to my co-residents for their friendship
and support throughout the years that we studied together.
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TABLE OF CONTENTS
List of Tables .......................................................................................................................v
List of Figures .................................................................................................................... vi
CHAPTER 1: INTRODUCTION ........................................................................................1
CHAPTER 2: REVIEW OF THE LITERATURE
Early Treatment in Orthodontics ................................................................3
ABO Discrepancy Index (DI) …..……………………..………………..13
Statement of Thesis…........................................................……..............30
Literature Cited.........................................................................................31
CHAPTER 3: JOURNAL ARTICLE
Abstract ....................................................................................................37
Introduction ..............................................................................................39
Early Treatment ..................................................................................39
ABO Discrepancy Index ....................................................................41
Materials and Methods .............................................................................43
Results ......................................................................................................46
Discussion ................................................................................................56
Conclusion……………………………………………………………....62
Overall............………………………................................................62
Groups………………………………………………………………62
Literature Cited.........................................................................................63
Vita Auctoris……………………………………………………………………………..65
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LIST OF TABLES
Table 3.1.
Overall DI Score differences……………………..…………………..…47.
Table 3.2.
Discrepancy Index Score differences for the Class I group…...……......48.
Table 3.3.
Discrepancy Index Score differences for the Class II group…..…...…...49.
Table 3.4.
Discrepancy Index Score differences for the Class III group…...………50.
Table 3.5.
Percentages of change (%)……………...…………………………….…51.
Table 3.6.
ANOVA………………..………………………………......……...….....52.
Table 3.7.
Post-Hoc test………………..………………………………………...…54.
Table 3.8.
Percentages of contribution to the total improvement....…......................58.
Table 3.9.
Percentages of contribution in Class I group……………………………59.
Table 3.10.
Percentages of contribution in Class II group…………………………..60.
Table 3.10.
Percentages of contribution in Class III group………………………….61.
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LIST OF FIGURES
Figure 2.1.
Discrepancy Index Instructions Form …...……………………….……....15
Figure 2.2.
Discrepancy Index Worksheet ………...…………………..…………..…16
Figure 2.3.
Example model articulating………………...…………………..…..…….17
Figure 2.4.
Discrepancy Index score for overjet ………...…………………………...18
Figure 2.5.
Measurement of anterior positive and negative overjet……...……..….....18
Figure 2.6.
Overbite …………………….….…..…………………………………….19
Figure 2.7.
Edge to edge and open bite relationship of anterior teeth….…..…........…19
Figure 2.8.
Posterior teeth in open bite relationship…….…………………………….20
Figure 2.9.
Crowding…………….…………………..………………………...………21
Figure 2.10. Discrepancy Index score for occlusal relationship…...………....………...22
Figure 2.11. ABO Operational Definition for occlusal relationship…….…….…..……22
Figure 2.12. Lingual posterior crossbite……………………………...………………...23
Figure 2.13. Buccal posterior crossbite…………...……….…………...……………….23
Figure 2.14. Cephalometric measurements…………...……..…………...………...…...24
Figure 2.15. Supernumerary teeth…….……………...……...………………………….25
Figure 2.16. Ankylosis of permanent teeth………………………….………...…...…...25
Figure 2.17. Anomalous morphology of tooth size and shape…….……………………26
Figure 2.18. Impaction of teeth ………………….…….....….......…...……………...…26
Figure 2.19. Congenitally missing teeth……………….………………..……………...27
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Figure 2.20. Midline discrepancy…..…………………..………………………………27
Figure 2.21. Midline diastema and generalized spacing…………...….…......………....28
Figure 2.22. Tooth transposition…………...…………….………...…………………...28
Figure 2.23. Skeletal asymmetry………………...……………………..………………29
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CHAPTER 1: INTRODUCTION
The American Board of Orthodontics was founded in 1929 and is the oldest
specialty board in dentistry. It was first established by Albert Ketcham and his
colleagues who believed that the specialty of orthodontics should have a certifying body.
The primary purpose has always been "to elevate the standards of the practice of
orthodontia; to familiarize the public with its aims and ideals; to protect the public against
irresponsible and unqualified practitioners".1 In order to accomplish this, the ABO
established national standards of orthodontics through a certifying process.
The certificate is not a professional or academic degree but it shows the voluntary
will of an individual to pursue continued proficiency in orthodontic knowledge and
clinical ability. Only dentists who have completed an advanced education program in
orthodontics approved by the Commission on Dental Accreditation of the American
Dental Association are eligible to go through the certification process. The examination
consists of two parts, one written and one clinical. The written examination has evolved
into a well-respected testing procedure that is now used by many graduate orthodontic
programs to evaluate the residents’ academic knowledge. The clinical examination has
gone through many changes. Currently, the examinee is required to submit case reports
with an oral defense of the treatment and pass an oral examination of cases presented by
the Board for analysis.2
In order to evaluate the complexity of the cases that the examinees bring to the
Board and the quality of the final result of their treatment, two indices were developed
over the years that have been used since 1998, the Discrepancy Index Score (DI) and the
Objective Grading System (OGS). The DI is used by the ABO to determine whether the
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cases, before treatment, are complex enough to be considered for the certification
process. The OGS is utilized in determining whether the post-treatment results qualify
for passing or failing. The DI is an index that is intended to quantify the problem list and
give a score that can simplify the understanding of the complexity of any case.3
The cases that are accepted by the American Board of Orthodontics can be treated in a
single phase or in two phases. The record requirements for the two-phase cases are a
complete set of records taken prior to the beginning of the first phase of treatment (or
prior to extractions if it is a serial extraction case), a complete set of records as interim
records prior to the second phase of treatment, and a complete set of records after second
phase appliance removal.4 Essentially, it is the clinician’s choice to decide if an early
phase of treatment is required for each patient. The importance of the early treatment has
been discussed many times and it has been a controversial issue among clinicians.
The purpose of this study is to use the DI as an objective method to quantify the
changes obtained from the first phase of orthodontic treatment and determine if there is a
reduction in complexity before the initiation of the second phase. The question to be
answered is: Does an early phase of treatment make a case less complicated to treat in the
second phase?
2
CHAPTER 2: REVIEW OF THE LITERATURE
Early treatment in Orthodontics
In orthodontics, practitioners have their own preferences when it comes to
treatment timing, techniques and appliances. The treatment timing is one of the
controversial issues that have been discussed among many clinicians and researchers who
either support an early phase of orthodontic treatment or believe that treatment should be
completed in one single phase during the permanent dentition. One of the reasons for the
debate may be the lack of research regarding early treatment outcomes.
Several definitions have been used to describe early treatment, which some also
refer to as phase 1. The American Association of Orthodontists’ Council of Orthodontic
Education, in 1971, defined interceptive orthodontics as “that phase of the science and art
of orthodontics employed to recognize and eliminate potential irregularities and
malposition in the developing dentofacial complex.” Early treatment in orthodontics has
been understood as the intervention with removable or fixed appliance in the primary,
early mixed (permanent first molars and incisors present), or mid mixed period, (before
the emergence of first premolars and permanent mandibular canines).5, 6 The onset of
treatment in a late-mixed dentition stage treatment (before the emergence of second
premolars and permanent maxillary canines) is largely accepted by many clinicians as
well.7 The definition that this study will be using is the treatment initiated during the
primary or mixed dentition with the purpose of preventing, intercepting, or correcting a
specific orthodontic problem or set of problems.
3
This definition contains different aspects that refer to different treatment strategies
when examining a young patient. A preventive orthodontic treatment mainly refers to
patients’ education (e.g. stopping digit sucking habits) and simple appliances used for
passive maintenance of a favorable orthodontic condition (e.g. space maintenance
appliances). An interceptive early treatment is intended to stop, deflect, or interrupt the
progress of a certain problem (e.g. guidance of eruption, serial extractions, habit
appliances among others), but may also attempt to correct developing intra- and interarch problems. (e.g. transverse problems and severe anterior posterior and vertical
deviations).
The objectives of early orthodontic treatment may include the establishment of a
correct occlusion in both deciduous and permanent dentition, the prevention of problems
that would result in irreversible damage to the dentition and supporting structure, the
correction of any transverse asymmetry, the modification of growth, the reduction of
trauma risk to anterior teeth and the improvement of the patient’s self-esteem in the
sensitive young age.8 The most important advantage of early treatment occurs when one
makes use of the patient growth potential and when a patient is better able to comply.9
On the other hand, the disadvantages of these approaches include the increased cost and
duration of overall treatment, increased risk of caries and fatigue from both the child and
the parents.5, 10, 11
According to the latest guidelines by the AAO, a child should receive an
orthodontic check- up no later than age 7. The reason for this visit is the early diagnosis
of dental and facial irregularities that may be prevented from developing. A study done
in Germany in 2004 showed the prevalence of different types of malocclusion in a large
4
group of children, age 6 to 8 years old. Open bites with ranges from 1 to 12 mm was
recorded in 17.7 per cent of the children. Deep bites with and without gingival contact
was registered in 46.2 per cent of those examined and bilateral crossbites occurred in 7.7
per cent. Class III malocclusion (skeletal) with reverse overjet was found in 3.2 per cent.
Overjet ranged from 0.5 to 14.0 mm. Overjets greater than 3.5 mm (Class II division 1)
were registered in 31.4 per cent of cases. Anterior crowding greater than 3 mm was
recorded in the mandible in 14.3 per cent of the subjects and 12 per cent in the maxilla.12
The conclusion of this study is that the orthodontist can detect a problem when the child
is still young and make a decision about the timing of the treatment.
The mixed dentition period is the time that most arch and dental changes are
happening and it may provide the opportunity for orthodontic intervention and
modification of the development. At 6 years of age, the transition from the primary to
permanent dentition begins with the eruption of the first permanent molars followed soon
by the eruption of the permanent incisors. The maxillary permanent incisors are larger
than the primary ones they replace and during this transition growth adaptations occur.13
In the maxillary arch the permanent incisors erupt more labially and as a result, there is a
slight increase in the dental arch of 1-2 mm in the average child.14
In the mandibular arch, there is not much gain as the incisors erupt since the
permanent ones follow the same inclination of their predecessors. In both arches the
presence of interdental and primate spaces , when they exist in the deciduous dentition
may allow for the early adjustment of occlusion.15
5
The mandible in reality presents the potential for more loss of space due to the
late adjustment of the leeway space. The early mesial shift as well as the late mesial shift
contribute for the reduction of the mandibular arch length. The sum of the permanent
premolars’ width is smaller than the sum of the primary predecessors’ one and this
difference represents around 2.00 mm of extra space per side in the maxillary arch and
around 2.5mm per side in the mandibular arch.16, 17
Apparently, there is a continuous mesial drift of the permanent teeth that tends to
reduce arch length. In addition, the lower incisors tend to upright due to the differential
growth of the maxilla and the mandible. Mandibular growth occurs distal to the first
molars and it does not contribute to any gain of space. 18, 19
It is obvious that preserving the leeway space during the time of transition of the
dentition may provide space for the solution of crowding as described by Gianelly.
According to the author, 77% of the cases with an average mandibular crowding of 4.5
mm would have enough space to align all teeth by preventing the molars from drifting
forward with a lingual holding arch.20 In the maxillary arch, a Nance button would be
able to hold the molars and preserve the space. Space maintenance is even more
necessary in cases of premature loss of primary teeth. Early loss of primary second
molars normally allows the mesial drifting of the permanent molars and decrease the arch
perimeter. On the other hand, early loss of primary canines causes an immediate
uprighting of the lower incisors, which produces the same result.21 In these cases, a
holding arch is indicated to prevent both the molars from drifting and the incisors from
uprighting.
6
Gianelly also stated that an additional 7% of the cases would require 2 mm of
extra space for the crowding to be resolved, which could be obtained with a lip bumper
used to move the molars distally on average 1mm.20 Lip bumpers also alter the
equilibrium between the lips and the tongue and can alter the inclination of the incisors as
well as produce some transverse expansion of the mandibular arch.
On the maxillary arch, arch perimeter can be increased and extra space can be
gained through maxillary expansion. Adkins has shown that every millimeter of
transpalatal width increase in the premolar region produces a 0.7 mm increase in
available maxillary space.22
In those cases with excessive crowding, in the range of 10 mm according to
Proffit17, when extractions will not be avoided in the future, a progressive extraction
method is indicated to allow the teeth to erupt in a more favorable position in the arch.
This planned and timely procedure is referred to as “serial extraction”, a term introduced
by Kjellgren in 192923 and adopted by several authors.24-28 Serial extraction is indicated
for Class I occlusions in patients with a balanced or mildly protruded face. It is most
often initiated with the extraction of primary canines to allow the alignment of the
permanent incisor, followed by the extraction of primary first molars to accelerate the
eruption of the permanent first premolars. In most cases the sequence is finished with the
extraction of the premolars, once they erupt. If the lower permanent canine emerges in
the arch prior to the eruption of the first premolar, the result could be the impaction of the
premolar and enucleation of the tooth used to be the treatment of choice.29 Nowadays,
due to the aggressiveness of this procedure, the insertion of a holding lingual arch or use
7
of multibonded appliances and the subsequent extraction of the primary lower second
molars are more recommended.29
Early orthodontic intervention may also allow for some skeletal modification.
One of the most common deviations is related to the transverse dimension. Posterior
crossbites can be of skeletal or dental origin and they are prone to cause occlusal
interferences. This condition should be corrected as soon as it is observed in the late
deciduous or early mixed dentition.30 Removal of functional interferences has been
shown to be useful also in patients under the age of five, with success rates ranging from
27% to 64%.31-33 In a study of 76 four-year-old children with posterior crossbite, Lindner
reported 50% correction after selective grinding to eliminate any premature interference.
The greatest chance of correction after selective grinding occurred when the maxillary
intercanine width was at least 3.3 mm greater than the corresponding mandibular
intercanine width.34 Although this method is effective in some cases with a functional
interference, most of the time expansion of the arch is necessary. One of the most
common appliances utilized for expansion is the Haas palatal expander (RPE).35 During
the primary or mixed dentition, the expansion of a constricted maxillary arch can be
achieved through the orthopedic separation of the mid-palatal suture which is less
interdigitated and as a result it is less resistant to the expanding forces.36 In older ages,
the correction is not skeletal but mostly due to the bending of the alveolar process and the
stretch of the periodontal ligament resulting in tipping of the posterior anchor teeth.37
The orthopedic and orthodontic forces of RPE have an impact on the mandibular position
and the result in an autorotation of the mandible in a downward and backward direction
caused by the extrusion and tipping of maxillary posterior teeth. Additionally, the lower
8
posterior teeth follow the inclined planes of the maxillary teeth during the expansion and
an increase of the lower intermolar width is noted.38 A different type of expander with
occlusal coverage, a bonded expander, eliminates the interdigitation of the teeth and
when compared to the banded expander. It does not produce any mandibular arch width
gain.39
Antero-posterior discrepancies are also commonly identified in the mixed
dentition stage. A skeletal Class II relationship can be the result of a protruded maxilla, a
retrusive mandible or a combination of both. When the origin of the problem is the
maxilla, headgears have been one of the appliances of choice. They were introduced in
the late 1800s by Kingsley. The headgear uses extra-oral anchorage to distalize the
maxillary molars but in a younger age, it may also restrict the maxillary development. It
is shown that “A point” in the maxilla is repositioned posteriorly with the use of
headgear.40-42 The amount of force applied and duration of wear is crucial for the
anticipated result. It is necessary to apply a force level of 12-16oz per side in order to
produce molar movement.6 The direction of the extra-oral force can produce different
results during treatment. A cervical pull headgear has an extrusive force on the upper
molars and if the force is below the center of resistance of the molars, it causes distal
tipping of the teeth. Often it is combined with a bite plate to eliminate any dental
interference and allow the mandible to come forward while the maxillary growth is
restricted.42 A high pull headgear is used when intrusion of the molars is necessary and
allows for autorotation of the mandible, which may maximize the horizontal expression
of mandibular growth.29
9
When the Class II relationship is a result of mandibular deficiency, an attempt to
advance the mandible is made with functional appliances. Among the many different
types of appliances presently used one can find activators, monoblocs, Herbst, bionator,
Frankel, twin-block or MARA. Functional appliances in early treatment have been used
since the early 1900s. Their main attempt is to jump the bite and unload the condyles,
which may stimulate earlier mandibular growth. The result on this growth has long been
a controversial issue that many authors have addressed. There are studies that have
shown that there is an increase in mandibular length with functional appliance therapy 43,
44
, although most authors tend to agree that the effect is an acceleration of mandibular
growth combined with a restriction of maxillary retrusion caused by dentoalveolar
compensation.45 The most effective time to treat with functional appliances is the late
mixed dentition when there can be a modification of growth.43,46, 47 However the gains
observed by the early intervention seem to produce no long-term advantage when
compared to treatment started at a later time normally around 12 years of age.46,48
Other factors, however, should be taken into consideration during the decision
making process for Class II treatment. O’Brien has shown that children who had early
treatment were perceived to be more attractive by peers49 and thus there was an
improvement in self-esteem.50 Also prevention of trauma in a young age should be taken
into account because prominent incisors seem to be more prone to injuries.51, 52
Class III relationship has been identified in 5% of the North American population and it
has a strong familial inheritance.53 This type of malocclusion is due to maxillary
retrusion, mandibular protrusion or a combination of both with a posterior or anterior
crossbite frequently displayed. Maxillary retrusion is best treated with a protraction
10
facemask, an appliance used for over 100 years and popularized by Delaire in the 1970s.
Delaire’s approach meant to apply traction to maxillary sutures using extra-oral
anchorage provided by the forehead and the mandible. Maxillary expansion is usually
attempted at the same time, using a bonded expander with occlusal coverage or banded
expander with a splint covering the mandibular teeth to eliminate the interdigitation of
the teeth. Attached to the expanders are hooks for the use of elastics that secure the mask
on the face and anchor the traction force. The timing of treatment is an important factor
for the result. Late deciduous to early mixed dentition is the age that a facemask
treatment is believed to be most effective for a skeletal result while after 11 years of age
the result is mostly dental movement. The treatment effects are also evident in the
mandible, where a downward and backward rotation results in an increase of the lower
anterior facial height.54,55
In those cases that the mandibular protrusion is the reason for the Class III
relationship, the chin cup therapy has been introduced and utilized for centuries as an
attempt to apply pressure on the temporomandibular joint to inhibit or redirect condylar
growth.56 Chin cup appliances can be divided in two different types, the occipital-pull
chin cup which is used in instances of mandibular prognathism and the vertical-pull for
cases with a steep mandibular plane angle. The occipital-pull headgear is most effective
in those patients who can bring the anterior teeth in an edge-to-edge relationship and the
vector of the force can modify the result. When the force is directed through the condyle,
the chin cup may interfere in the mandibular growth. In low angle cases, when opening
of the mandibular plane angle is desired, the force should be directed below the condyle
producing a downward and backward movement of the mandible. One of the concerns
11
for this appliance is whether it can restrict or not the mandibular growth. In several
studies a decrease in the mandibular growth during treatment in mixed dentition has been
noted 57, 58 whereas other authors showed no difference between treated and untreated
adolescent patients.59 Another topic of discussion is the effect of the chin cup at the
temporomandibular joint. Most studies have concluded that the percentage of patients
developing some symptoms from the joint, mostly clicking, does not exceed the
percentage in the general untreated population. Therefore, the treatment should not be
considered causal for TMD symptoms.60-62
There are several orthodontic problems seen in childhood that could be addressed
with various treatment strategies. Many clinicians and authors have taken interest and
embraced the early treatment techniques but it is crucial to control the mechanics, choose
the appropriate treatment protocol and decide the most appropriate time to complete the
phase 1. Precise treatment goals must be implemented as well as a thorough study of the
benefits one may get from a preliminary phase of orthodontic treatment. The purpose of
this study is to quantify treatment changes obtained after phase 1 treatment using the
Discrepancy Index (DI) as by the American Board of Orthodontics.
12
The ABO Discrepancy Index (DI)
As guidelines for achieving board certification, the ABO needed to develop an
objective measure of malocclusion complexity to ensure uniform interpretation and
application of criteria. Numerous orthodontic indices have been used for many years that
mostly attempt to determine the need for treatment. The Peer Assessment Rating (PAR)
index estimates the deviation of a case from normal alignment and occlusion; it has good
reliability and validity but it excludes several aspects of a malocclusion.63 The Index of
Orthodontic Treatment Need (IOTN) and the Dental Health Component (DHC) are
indices that are designed to evaluate treatment need. The Standard Component of
Aesthetic Need (SCAN) is also used to determine treatment need but includes a
subjective judgment of esthetics, which might compromise its reliability.64 The ABO’s
main purpose was to use an index that would evaluate the complexity of the pretreatment
records of the cases that were submitted for the clinical examination.
To address this need, in 1998, the DI was developed by eight ABO directors and
six consultants who were sharing the same vision of clinical excellence.65, 66 In 1999, a
pilot study that included 100 cases scored by two directors was done and the results were
reviewed by the committee that modified the Index. During the years 2000 to 2003, the
DI was still being tested and for this purpose; all directors and examiners were measuring
every case that was submitted to the Board. It was also required that the examinees to
score a number of cases in 2002 and all their cases in 2003, which all led to the final
modification that made the DI the official alternative for the ABO case submission in
2004. It was decided that the DI would be used initially as an alternative and three years
later it would be used as the main index for acceptance of the cases that would be
13
considered. In the beginning, a DI of 25 and above was required for two cases, a DI of
16 and above for six cases and a DI of 7 and above for two cases67. In 2005, the
acceptance criteria changed to three cases of DI of 10 and above and three cases of 20
and above.
The DI is widely used today to evaluate the complexity of a case by taking into
account both dental and skeletal irregularities measured on dental casts as well as
panoramic and cephalometric x-rays. It includes the evaluation of 12 features that should
be part of the problem list that every clinician considers when examining a new case.
Those include overjet, overbite, anterior open bite, lateral open bite, crowding, occlusal
relationship, lingual posterior crossbite, buccal posterior crossbite, ANB angle, IMPA,
SN-GoGn and an “Other” category, which evaluates further complexities such as
ankylosed, supernumerary or malformed teeth etc. These features are the most common
characteristics of any malocclusion and were chosen because they are considered as
“clinical entities that are measurable and have generally accepted norms”.4
Each feature receives a score and the sum of all individual scores constitutes the
DI score, which indicates the level of complexity of the case. The score that is assigned
to each of those features is explained in detail in the following instructions that were
directly drawn from the ABO website’s Clinical Examination Case Report Work File.4
(See Figure 2.1 and 2.2)
14
Figure 2.1. Discrepancy Index Instructions Form from the Case Report Work File on the
ABO website4
15
Figure 2.2. Discrepancy Index Worksheet from the Case Report Work File on the ABO
website.4
16
Occlusion is determined by placing the backs (bases) of the pre-treatment dental casts on
a flat surface after they have been pushed together in occlusion. All measurements must
be made from this position. (Figure 2.3)
Figure 2.3. Example model articulation.
OVERJET: Overjet is a measurement between two antagonistic incisor teeth comprising
the greatest overjet and is measured from the facial surface of the most lingual tooth
(Maxillary or Mandibular) to the middle of the incisal edge of the more facially
positioned tooth (Maxillary or Mandibular). For overjet of 0 – 0.9 mm. (edge-to-edge),
1 point is scored; for overjet of 1 to 3 mm., no points are scored; for 3.1 – 5 mm., 2 points
are scored; for 5.1 – 7 mm., 3 points are scored; for 7.1 – 9 mm., 4 points are scored and
if over 9 mm., 5 points are scored. If there is a negative overjet (anterior crossbite), the
score is recorded as 1 point per mm. per anterior tooth in crossbite. (See Figures 2.4 and
2.5)
17
Figure 2.4. Discrepancy Index score for overjet.
Figure 2.5. Measurement of anterior positive and negative overjet.
OVERBITE: For overbites of up to 3 mm, no points are scored. If the overbite is
between 3.1 to 5 mm, 2 points are scored; if between 5.1 to 7 mm, 3 points are scored. If
the lower incisors are impinging on the palatal tissues and/or 100% overbite, then 5
points are scored. (See Figure 2.6)
18
Figure 2.6. 1.5 mm overlap yields no points.
A. Represents an overlap of greater than 3 mm therefore 2 points are given.
B. Represents an overlap of greater than 5 mm therefore 3 points are given.
C. Represents 100% overbite or vertical tissue impingement therefore 5 points are given.
ANTERIOR OPEN BITE: For each anterior tooth (canine to canine) that is in an edgeto-edge relationship (overbite = 0), 1 point. is scored per tooth. For each additional full
mm. of open bite, 1 point is scored for each maxillary tooth involved. No points are
scored for any tooth that is blocked-out of the arch or simply not fully erupted. (See
Figure 2.7)
Figure 2.7. Edge to edge and open bite relationship of anterior teeth.
19
LATERAL OPEN BITE: For each maxillary tooth (from the 1st premolar to 3rd molar)
in an open bite relationship with the lower arch, 2 points are scored per mm. of open bite
for each tooth. No points are scored for any tooth that is blocked-out of the arch or
simply not fully erupted. (See Figure 2.8)
Figure 2.8. Posterior teeth in open bite relationship.
CROWDING: When scoring, measure the most crowded arch circumference (only one
arch) between the first molars. From 0 to 1 mm, 0 points are scored; from 1.1 to 3 mm.,
one point is scored; from 3.1 – 5 mm., 2 points are scored; from 5.1 – 7 mm, 4 points are
scored. If the crowding is greater than 7 mm, 7 points are scored. (See Figure 2.9)
Figure 2.9. Measure the most crowded arch (only one arch) from the mesial contact point
of the right first molar to the mesial contact point of the left first molar
20
OCCLUSION: When scoring occlusion, the Angle classification is used. If the
mesiobuccal cusp of the maxillary first molar occludes with the buccal groove of the
mandibular first molar or anywhere between the buccal groove and the mesiobuccal or
distobuccal cusps, no points are scored. If the mesiobuccal cusp of the maxillary first
molar occludes with the mesiobuccal (Class II end-to-end) or distobuccal (Class III endto-end) cusps of the mandibular first molar, then 2 points per side are scored. If the
relationship is a full Class II or III, then 4 points per side are scored. If the relationship is
greater or beyond Class II or III, then 1 additional point per mm. ] is scored. Each side
should be scored individually and included in the point accumulation for this category.
(See Figure 2.10 and 2.11)
Figure 2.10. Discrepancy Index score for occlusal relationship
21
Figure 2.11. ABO operational definition of occlusal relationship.
For DI scoring per side, the location of the cusp within the zones is an estimation. If the
relationship is beyond Class II or III, measure the additional distance, round up to next
full mm, then score 1 additional point per mm per side
LINGUAL POSTERIOR CROSSBITE: For each maxillary posterior tooth where the
maxillary buccal cusp is lingual to the buccal cusp tip of the opposing mandibular tooth
(from the first premolar to the third molar), 1 point is scored. (See Figure 2.12)
Figure 2.12. Lingual posterior crossbite
22
BUCCAL POSTERIOR CROSSBITE: For each maxillary posterior tooth (from the first
premolar to the third molar) in complete buccal crossbite, 2 points are scored. (See
Figure 2.13)
Figure 2.13. Buccal posterior crossbite
CEPHALOMETRICS:
•
If the ANB angle is 6° or greater or -2° or less, then 4 points are scored. An
additional point is scored for each degree above 6° or below -2°.
•
If the SN-MP angle is between 27° and 37°, zero points are scored.
•
If the SN-MP angle is 38° or greater, then 2 points are scored for each degree
above 37°.
•
If the SN-MP angle is 26° or less, then 1 point is scored for each degree below
27°.
•
If the Lower Incisor to MP angle is 99° or greater, then 1 point is scored for each
degree above 98°. (See Figure 2.14)
23
Figure 2.14. Cephalometric measurements.
OTHER:
•
Supernumerary teeth – 1 point for each extra tooth (See Figure 2.15)
Figure 2.15. Supernumerary teeth – 1 point each
•
Ankylosis of permanent teeth – 2 points per tooth (See Figure 2.16)
24
Figure 2.16. Ankylosis of permanent teeth
•
Anomalous morphology of tooth size & shape (e.g. peg lateral incisor) - 2 points
per tooth. (See Figure 2.17)
Figure 2.17. Anomalous morphology of tooth size and shape
•
Impaction (except third molars) of teeth –2 points per tooth (See Figure 2.18)
25
Figure 2.18. Impaction of teeth (except 3rd molars)
•
Missing teeth (except third molars) – 1 point per tooth;
•
Congenitally missing teeth – 2 points per tooth (See Figure 2.19)
Figure 2.19. Congenitally missing teeth
•
Midline discrepancy – 2 points for 3 mm or more (See Figure 2.20)
26
Figure 2.20. Midline discrepancy.
•
Spacing – 2 points for maxillary central diastema of 2 mm or more; 2 points per
arch for generalized spacing of 4 teeth or more. (See Figure 2.21)
Figure 2.21. Midline diastema and generalized spacing
•
Tooth transposition – 2 points for each event (See Figure 2.22)
27
Figure 2.22. Tooth transposition
•
Skeletal asymmetry (treated nonsurgically) – 3 points (See Figure 2.23)
2.23. Skeletal asymmetry
•
Additional treatment complexities – 2 points each
28
It should be clarified that the DI is intended to be used for the evaluation of the
complexity of a case and not the difficulty.65 The level of difficulty is a subjective
perception that each clinician is assessing based on the experience and the treatment
techniques that are routinely used in their practice. While this aspect has been
emphasized by the ABO, there have been studies that show that the initial DI score
correlates to the quality of the final treatment result for the most difficult cases.64, 68, 69
29
Statement of Thesis
The purpose of this study is to quantify the changes obtained from the first phase
of orthodontic treatment and determine how much improvement, if any, has occurred
before the initiation of the second phase. Additionally, all variables constituting the DI
score will be measured to investigate which components of malocclusion undergo the
most change. Finally, the three Angle classification groups will be compared to
investigate if any of these groups would benefit more from an early treatment phase.
30
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65. Cangialosi TJ, Riolo ML, Owens SE, Jr., Dykhouse VJ, Moffitt AH, Grubb JE, Greco
PM, English JD, James RD. The ABO discrepancy index: a measure of case
complexity. Am J Orthod Dentofacial Orthop. 2004;125:270-8.
66. Riolo ML, Owens SE, Jr., Dykhouse VJ, Moffitt AH, Grubb JE, Greco PM, English
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35
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36
CHAPTER 3: JOURNAL ARTICLE
Abstract
Purpose: The purpose of this study is to quantify the changes obtained from the first
phase of orthodontic treatment and determine how much improvement, if any, has
occurred before the initiation of the second phase. Additionally, all variables constituting
the DI score were depicted and measured to investigate which components of
malocclusion undergo the most change. Finally, the three Angle classification groups
were compared to investigate if any of these groups would benefit more from an early
treatment phase. Materials and Methods: For the purpose of this retrospective study,
pre-phase 1 and pre-phase 2 records of 300 individuals who received a 2-phase treatment,
were gathered. All cases were measured using the ABO Discrepancy Index (DI) and a
score was given for each phase (T1DI before phase 1 and T2DI before phase 2). The
difference of T1D1-T2DI indicates the quantitative change of the case complexity.
Paired t-tests were used to compare the initial and final scores overall and for each
component of the DI separately. Additionally the sample was categorized in three groups
according to the molar Angle classification (Class I, II and III) and the same statistics
were used to identify significant changes between T1 and T2. An ANOVA was applied
to compare the three groups and determine which one underwent the most change.
Lastly, percentages of change were calculated for the total score and each variable as well
as for the total scores and for the DI components of each group individually. Results:
The total DI score overall and the scores of all three groups were significantly reduced
from T1 to T2, which indicates a significant reduction in complexity. Overall, 42%
improvement was observed. The Class I group showed 49.3% improvement, the Class II
37
group 34.5% and the Class III group 58.5%. Several components of the DI (overjet,
anterior open bite, crowding, occlusal relationship, lingual crossbite, ANB angle and the
category “Other” complexities) improved significantly while few (IMPA in the Class II
group and occlusal relationship in the Class I group) showed negative change. Among the
three groups, the Class III proved to undergo the most significant change and benefit the
most from early treatment. Conclusion: A significant reduction of DI score was
observed in the total sample and in all Angle Classification groups, which indicates that
early treatment reduces the complexity of the malocclusions. Only two components of
the DI showed negative change which shows that controlled mechanics are required
during treatment.
38
Introduction
Early Treatment
The questions about the importance of early treatment, also known as phase 1,
have not been fully answered. Many clinicians and researchers are still skeptical about
the benefits of an early phase of treatment. One of the reasons for the debate is probably
the inadequate evidence about the favorable effects on the case progression.
Several definitions have been proposed to describe phase 1 treatment. Most of them tend
to agree on early treatment as the treatment initiated during the primary or mixed
dentition with the purpose to prevent, intercept, or correct a specific orthodontic problem
or problems.
This definition refers to three different treatment strategies used to achieve the
goals of phase 1. A preventive early treatment refers to the intervention on a developing
malocclusion through the cessation of a harmful habit or the maintenance of a favorable
orthodontic condition. On the other hand, interceptive early treatment techniques are
intended to interrupt the progress of a certain problem by the use of early corrective
mechanics. It encompasses an attempt for complete correction or minimizing of an
orthodontic problem that has already occurred restoring better conditions for normal
growth and development.
Evidently, this early intervention cannot be an effortless process with an unclear
treatment plan. On the contrary, it should be an opportunity to interrupt a developing
malocclusion through well-designed treatment goals and accurate application of the
appropriate mechanics. The clinician who starts treating a younger patient, should have
well-defined objectives for this phase which include the establishment of a good
39
occlusion, the prevention of problems that could potentially damage the dentition and
supporting structures, the reduction of trauma risk to anterior teeth, the management of
the leeway space, the correction of any transverse asymmetry and the correct use of the
evidenced based theories of growth and development.1-13
It is also important to emphasize the psychological factors affecting patients and
families, which in certain cases is a strong component of reasons to seek orthodontic
help. Enhancing the self-confidence of a young child sometimes is the key factor for the
psychosocial growth and the development of a balanced personality.14
Researchers and clinicians, who are in favor of the early treatment, claim that there are
certain advantages associated with the young age of those patients. Among those, we
may depict the assumption of greater compliance and cooperation, which seems to cease
during the teenage years, the opportunity to modify growth or control its direction and the
possibility to manage the E-space (leeway space) to accommodate the permanent teeth
and resolve some crowding.
On the other hand, among the disadvantages of a first phase of treatment are the
increased cost and overall treatment time that may lead to the patient’s “burn out” before
the second phase, especially if the first phase does not have a well-defined end. The oral
hygiene is also an important factor to be taken into consideration when fixed appliances
are required to stay for longer time, since it may increase the chances of caries and white
spot lesions at the end of treatment.
40
ABO Discrepancy Index
A tested and established way of measuring the complexity of malocclusions is the
Discrepancy Index introduced by the American Board of Orthodontics (ABO) in 1998.
The ABO’s vision has always been "to elevate the standards of the practice of
orthodontia; to familiarize the public with its aims and ideals; to protect the public against
irresponsible and unqualified practitioners".15
In order to accomplish this goal a certifying process with the establishment of national
standards was created. The orthodontics board examination comprehends a written exam
and a clinical assessment, which requires the submission of treated cases for evaluation.16
Within the framework of this evaluation a Discrepancy Index (DI) was developed to
evaluate the complexity of the pretreatment records of the cases that are submitted for the
exam.
Numerous orthodontic indices have been used for many years, the Peer
Assessment Rating (PAR) Index, the Index of Orthodontic Treatment Need (IOTN), the
Dental Health Component (DHC) and the Standard Component of Aesthetic Need
(SCAN), that were not suitable because they are mostly designed to determine the
treatment need and they exclude certain aspects of a malocclusion.16, 17
The DI is used to evaluate the complexity of a case by taking into account both
dental and skeletal irregularities measured on dental casts, panoramic and cephalometric
x-rays. It includes the evaluation of 12 features, which are the most common
characteristics of malocclusion and were chosen because they are considered to be
“clinical entities that are measurable and have generally accepted norms”.18 Those are
overjet, overbite, anterior open bite, lateral open bite, crowding, occlusal relationship,
41
lingual posterior crossbite, buccal posterior crossbite, ANB angle, IMPA, SN-GoGn and
a category “Other”, which evaluates other complexities such as ankylosed,
supernumerary or malformed teeth etc. Each feature receives a score and the sum of all
individual scores constitutes the DI score, which indicates the level of complexity of the
case.18
The purpose of this study is to employ the Discrepancy Index to quantify the
degree of the discrepancies before the first phase of orthodontic treatment and determine
if any improvement can be quantified when compared to numbers obtained before the
initiation of the second phase. Additionally, all variables constituting the DI score will be
compared to investigate which components of malocclusion undergo the most change.
Finally, the three Angle classification groups will be analyzed to investigate the potential
benefits of early treatment for each malocclusion group separately.
42
Material and Methods
This retrospective study includes a sample of 300 randomly selected cases from
the archived records of Saint Louis University graduate orthodontic clinic, from 1990 to
2012. All cases had phase 1 treatment at an early age that was followed by
comprehensive treatment. The sample included 164 females and 136 males, who started
phase 1 treatment at a mean age of 9.3 years. The mean treatment duration was 14.5
months. The inclusion criteria were available pre-phase 1 and pre-phase 2
(comprehensive phase) casts as well as cephalometric and panoramic radiographs. The
records preceding phase 2 were either taken at the end of phase 1 or at the beginning of
phase 2, if this was within two years after the completion of the first phase of treatment.
Any cases with casts that had been damaged or non-measurable radiographs were
excluded. The degree and type of malocclusion, the treatment method chosen and the
clinician, who treated the patient, were not taken into consideration for the selection of
the cases. Once all inclusion and exclusion were met, 300 records were gathered to be
measured according to the ABO’s Discrepancy Index.
The principal investigator was initially trained and calibrated in the ABO
Discrepancy Index (DI) using the ABO board preparation CD ROM from October 2000
as well as the online tutorial. For further training and calibration, the principal
investigator blindly selected and graded 10 cases. The same cases were also graded by an
ABO examiner. A tutorial session was arranged in which those scores were compared
and the reasons for the discrepancies were discussed. This process was repeated for any
areas of discrepancy until an agreement on the reasons for the deductions was achieved
and calibration was confirmed. For intra-examiner reliability, 30 cases were re-measured
43
and an intraclass correlation coefficient test was performed as a replication error
procedure.
The ABO measuring gauge was used to measure the models for all 300 cases with
the ABO Discrepancy Index instructions and form. Since all pre-phase 1 and many of the
pre-phase 2 models were in mixed dentition, the Tanaka-Johnston prediction for the
mesio-distal size of unerupted canines and premolars was used to calculate the amount of
dental crowding.19 Another area of special consideration was the grading of anterior and
lateral open-bite because several teeth were in the process of eruption. No points were
scored for those teeth that were not fully erupted.
The study of radiographs and the tracing of cephalometric x-rays were done in
two different ways due to the records availability. Cases that were treated before 2003
had hard copies of radiographs while cases that were treated after 2003 had digital form
of radiographs. Hard copies of cephalometric radiographs were traced using a light box,
tracing paper and a protractor whereas digital x-rays were uploaded and traced with the
Dolphin Imaging orthodontic software (Version 11.5, Chatsworth, CA). All the
cephalometric measurements that were used were angular (ANB, SN-MP, Lower Incisor
to MP). Consequently, the difference of the tracing method is not expected to affect the
values.
All measurements were input in to Microsoft Excel 2010 (Redmond, WA), in a
spreadsheet, which was programmed to automatically calculate the points that are scored,
according to the DI, for each of the twelve measurements on the models and the x-rays.
Additionally, the sums of points that were assigned to each case prior to phase 1 (T1) and
prior to phase 2 (T2), were calculated, along with the differences of these scores between
44
the two phases. The subtraction of T1DI – T2DI provided numbers, which demonstrate
the quantitative change of each variable that constitutes the DI as well as the change of
the total score after the first phase of treatment.
Descriptive statistics, means and standard deviations, of the score differences at
the two time points, were used to identify the change. Positive mean values indicated
improvement after treatment whereas negative mean values indicated deterioration.
Paired t-test were employed to compare the overall DI score at T1 and T2, as well as the
individual scores for each variable, in order to identify the statistically significant
changes before and after phase 1 treatment. Due to the large number of variables (13), in
order to avoid a type-1 statistical error, the α was set as 0.004 according to the Bonferroni
correction for multiple comparisons.
The data were then categorized in three different groups according to Angle
classification, Class I (81 subjects), Class II (165 subjects) and Class III (54 subjects). A
one-way ANOVA between the differences of the scores, T1DI-T2DI, was applied to
determine which of those three groups underwent the most change with phase 1
treatment. The Bonferroni Post-Hoc test was used to identify between which groups
there was a statistically significant difference. The α for these tests was set at 0.05.
All statistical analysis, together with the histograms that are generated from the data, was
made with the SPSS software.
Furthermore, a percentage of change for each feature of the DI and for the total
score was figured to demonstrate in a simple way the difference in complexity before and
after the first phase of treatment. The same percentage measurements were calculated for
each of the three Angle Classification groups.
45
Results
The American Board of Orthodontics Discrepancy Index (DI) has been widely
accepted and tested as a reliable tool to indicate the severity of a malocclusion. The
purpose of this study was to apply the DI to a sample of patients before phase 1
orthodontic treatment (T1) to determine the severity of each malocclusion and then to
repeat the same methodology on the same sample before the beginning of phase 2 and/or
the end of phase 1(T2). The changes were statistically analyzed and the results
interpreted. An increase of the DI score shows an increase in complexity, while a
decrease shows a reduction in complexity.
Means from the total score and from each of the variables of the DI, before and
after phase 1, were calculated for 300 cases and were evaluated for descriptive
characteristics. The difference of the initial and final mean score produced a number,
which represents the mean difference between the initial and final score. If the total DI
score was reduced at T2, it indicates that there was a reduction in the complexity of the
data analyzed. If the total DI score increased at T2, it indicates a greater complexity of
the sample analyzed. Table 3.1 displays the initial and final mean values for the total
score and the scores of each individual component of the DI, as well as the mean
differences of those scores. Additionally, paired t-tests were used to compare T1 and T2
means and a p-value is added to the table, to indicate if the difference in points was
statistically significant. All significant values are marked with an asterisk.
The mean total score at T1 was 17.26 points and the mean total score at T2 was
9.98 points that indicates a mean reduction of 7.28 points in the DI score, which
according to the t-test was a statistically significant change. Each of the variables of the
46
DI were assessed individually in the same way and the ones that showed a statistically
significant reduction of their score were the overjet, the anterior open bite, the crowding,
the occlusal relationship, the posterior lingual crossbite, the ANB angle and the category
“Other”. The variables that underwent non-significant changes were the overbite, the
lateral open bite, the posterior buccal crossbite and the SN-MP and IMPA angles. (See
Table 3.1)
Table 3.1. Overall DI Score differences.
Mean
SD
P Value
2.19
2.64
<0.001*
0.77
0.17
1.13
0.008
1.32
0.41
0.9
3.00
<0.001*
Lateral open
bite
0.21
0.21
0
1.59
0.971
Crowding
1.92
1.25
0.67
1.76
<0.001*
Occlusal
relation
Posterior
lingual
crossbite
Posterior
buccal
crossbite
3.49
1.96
1.54
2.73
<0.001*
0.91
0.083
0.83
1.37
<0.001*
0.02
0.11
-0.09
0.62
0.016
ANB
1.32
0.75
0.57
2.04
<0.001*
SN-MP
2.15
2.27
-0.12
2.59
0.410
IMPA
0.66
0.85
-0.19
2.26
0.146
Other
1.26
0.46
0.80
1.29
<0.001*
Total
17.26
9.98
7.28
7.06
<0.001*
Mean T1
Mean T2
Overjet
3.06
0.87
Overbite
0.94
Anterior
open bite
Difference
*Statistically significant difference at p<0.004
The sample was then categorized in three different groups according to the Angle
Classification (Class I, II and III) and the same descriptive statistics were used. The
47
Class I group included 81 subjects. The mean total DI score at T1 was 11.74 points and
at T2 it was 5.94 points, showing a mean reduction of 5.79 points, which also proved to
be a statistically significant change. All variables were analyzed with the same
methodology and the ones that showed a statistically significant change were the overjet,
the anterior open bite, the crowding, the occlusal relationship, the posterior lingual
crossbite and the category “Other”. All the significant changes pointed towards a
reduction of the DI score at T2. The variables that showed non-significant changes were
the overbite, lateral open bite, the posterior buccal crossbite and all cephalometric
measurements ( ANB, SN-MP, IMPA). (See Table 3.2)
Table 3.2. Discrepancy Index Score differences for the Class I group.
Mean T1
Mean T2
Overjet
2.27
0.57
Overbite
0.53
Anterior
open bite
Mean
SD
P Value
1.7
1.6
<0.001*
0.39
0.14
0.89
0.174
2.04
0.42
1.62
3.49
<0.001*
Lateral open
bite
0.32
0.07
0.25
1.53
0.150
Crowding
1.49
0.87
0.62
1.76
0.001*
Occlusal
relation
Posterior
lingual
crossbite
Posterior
buccal
crossbite
0
0.35
-0.35
1.58
0.002*
0.89
0.10
0.79
1.31
<0.001*
0
0.02
-0.02
0.22
0.320
ANB
0.57
0.58
-0.01
1.57
0.944
SN-MP
1.96
2.08
-0.12
2.44
0.650
IMPA
0.55
0.33
0.22
1.73
0.252
Other
1.11
0.15
0.96
1.52
<0.001*
Total
11.74
5.95
5.79
5.30
<0.001*
Difference
*Statistically significant difference at p<0.004
48
The Class II group included 165 subjects. The mean total DI score at T1 was
19.13 points and at T2 it was 12.53 points, showing a mean reduction of 6.60 points,
which also proved to be a statistically significant change. All features of the DI were
described with the same statistics and the ones that showed a significant reduction in DI
score were the overjet, the anterior open bite, the crowding, the occlusal relationship, the
posterior lingual crossbite, the ANB and the category “Other”. In this group, the IMPA
angle demonstrated a statistically significant increase in score, which indicates that after
treatment the position of the lower incisors was less favorable. The features that
underwent non-significant changes were the overbite, the lateral open bite, the posterior
buccal crossbite and the SN-MP angle. (See Table 3.3)
Table 3.3. Discrepancy Index Score differences for the Class II group.
SD
P Value
1.08
Mean
Difference
1.54
1.76
<0.001*
1.41
1.15
0.26
1.32
0.01
0.91
0.24
0.67
2.43
<0.001*
0.17
0.27
-0.10
1.63
0.418
2.33
1.68
0.65
1.88
<0.001*
Occlusal
relation
Posterior
lingual
crossbite
Posterior
buccal
crossbite
ANB
5.13
2.80
2.33
2.87
<0.001*
0.62
0.07
0.55
1.12
<0.001*
0.04
0.18
-0.14
0.81
0.023
1.57
0.82
0.75
2.03
<0.001*
SN-MP
2.31
2.42
-0.11
2.31
0.523
IMPA
0.78
1.37
-0.59
2.58
0.004*
Other
1.25
0.44
0.81
1.25
<0.001*
Total
19.13
12.53
6.60
6.60
<0.001*
Mean T1
Mean T2
Overjet
2.62
Overbite
Anterior
open bite
Lateral open
bite
Crowding
*Statistically significant difference at p<0.004
49
The last group was composed of 54 Class III subjects. The mean total score at T1
was 19.85 points, which was reduced to 8.24 points at T2. The mean difference was 11.6
points, which was a statistically significant change. Descriptive statistics were applied to
all variables and the ones that underwent a significant change were the overjet, the
crowding, the occlusal relationship, the posterior lingual crossbite and the category
“Other”. The variables that demonstrated non-significant changes were the overbite, the
anterior open bite, the lateral open bite and all cephalometric measurements (ANB, SNMP, IMPA). The t-test for the posterior buccal crossbite was not possible because there
was no change. (See Table 3.4)
Table 3.4. Discrepancy Index Score differences for the Class III group
Mean T1
Mean T2
Mean
Difference
SD
P Value
Overjet
5.61
0.68
4.93
4.05
<0.001*
Overbite
0.13
0.18
-0.05
0.73
0.582
Anterior
open bite
Lateral open
bite
1.48
0.92
0.56
3.64
0.267
0.148
0.18
-0.03
1.58
0.864
Crowding
1.33
0.48
0.85
1.64
<0.001*
Occlusal
relation
Posterior
lingual
crossbite
Posterior
buccal
crossbite
3.74
1.78
1.96
2.73
<0.001*
1.83
0.11
1.72
1.76
<0.001*
0
0
0
0
-
ANB
1.67
0.74
0.92
2.5
0.009
SN-MP
1.94
2.09
-0.15
3.50
0.757
IMPA
0.46
0.05
0.41
1.61
0.068
Other
1.5
1
0.50
0.95
<0.001*
Total
19.85
8.24
11.6
8.96
<0.001*
*Statistically significant difference at p<0.004
50
Percentages were also calculated to describe the amount of change comparing T1
and T2. The initial score was marked as 100 and the final score was calculated as a
percentage of the initial score with the formula 100 x mean T2DI/ mean T1DI. The
difference between the initial (100) and final percentage, showed the change of the score
in form of percentage. Positive value suggests that the cases obtained a lower DI score at
T2, thus the complexity was reduced, whereas a negative value shows the opposite. The
change for all 300 patients was 42.19%. The Class I group showed an overall
improvement of 49.32%, while the Class II group and the Class III group showed an
improvement of 34.5% and 58.89%, respectively. (See Table 3.5)
Table 3.5. Percentages of change (%)
Total
Class I
Class II
Class III
Overall
49.3*
34.5*
58.5*
42.2*
*Statistically significant differences as shown by the t-tests at p<0.004
51
Lastly, a one-way ANOVA was used to compare all variables between the three
groups. This test revealed significant differences between the three malocclusion groups
for the total score, the overjet, the occlusal relationship, the posterior lingual crossbite,
the ANB and the IMPA. (See Table 3.6)
Table 3.6. ANOVA
ANOVA
Overjet
<0.001*
Overbite
0.181
Anterior
open bite
Lateral
open bite
0.055
Crowding
0.711
Occlusal
relation
Posterior
lingual
crossbite
Posterior
buccal
crossbite
<0.001*
ANB
0.008*
SN-MP
0.997
IMPA
0.003*
Other
0.120
Total
<0.001*
0.266
<0.001*
0.185
*Statistically significant difference at p<0.05
The Bonferroni Post-Hoc test was used to identify between which groups
specifically these differences were found. (See Table 3.7.) According to this test, the
difference in the overjet was significantly more for the Class III group, whereas the Class
52
I and II groups had the same amount of change. The changes of the overbite, lateral open
bite, crowding, buccal posterior crossbite, SN-MP and the category “Other” were similar
for all three groups. The change in the occlusal relationship was significantly more in the
Class II and Class III groups compared to the Class I group. However, there was no
statistical difference of the changes between the Class II and Class III groups. The
changes observed in the posterior lingual crossbite were significantly more for the Class
III group while there was no significant difference between the Class I and Class II
groups. As far as the cephalometric measurements are concerned, change of the ANB
was significantly more pronounced for the Class II and Class III groups and change of the
IMPA was significantly more important for the Class II group. The changes for the
overall score are significantly more for the Class III group, while there is not statistically
significant difference between the Class I and Class II group.
53
Table 3.7. Post-Hoc test
Bonferroni
Overjet
Anterior
open bite
Occlusal relation
Posterior lingual
Crossbite
ANB
IMPA
Total
Mean
Differences
P value
I
II
0.16
1.000
I
III
-3.2*
<0.001*
II
III
-3.39*
<0.001*
I
II
0.94
0.13
I
III
1.06
0.06
II
III
-0.94
1.000
I
II
-2.67*
<0.001*
I
III
-2.31*
<0.001*
II
III
0.36
1.000
I
II
0.24
0.538
I
III
-0.93*
<0.001*
II
III
-1.17*
<0.001*
I
II
-0.76
0.018*
I
III
-0.94
0.025*
II
III
-0.18
1.000
I
II
0.81
0.023*
I
III
-0.19
1.000
II
III
-0.99
0.014*
I
II
-0.81
1.000
I
III
-5.82*
<0.001*
II
III
-5.01*
<0.001*
*Statistically significant difference at p<0.05
I: Class I, II: Class II, III: Class III
On the reliability test the Cronbach’s Alpha was 0.98 which is >0.8 and shows good
reliability for the principal investigator.
54
Discussion
A quantitative assessment of interceptive orthodontic treatment (phase 1) has not
been found in the literature. The American Board of Orthodontics has developed and
tested the Discrepancy Index with the purpose to quantify the severity of each case to
be examined for board certification. The purpose of this study was to evaluate the DI
of a sample of developing malocclusions at two different points in time, T1 and T2,
before the first phase of treatment and before the phase 2 treatment respectively and
quantify the changes observed by treatment. Thus, the efficacy of the treatment was
assessed utilizing the DI to register positive or negative results.
The sample included 300 patients, 164 females and 136 males, who started phase
1 treatment at a mean age of 9.3 years. The mean treatment duration was 14.5
months. The type of treatment performed was not taken into consideration and could
probably be part of another study of the same type.
The descriptive statistics showed a mean reduction of 7.28 points in the DI score
from T1 to T2. This indicates an overall decrease in complexity of the
malocclusions, which was confirmed by the percentage of change measured to
represent 42% of improvement. Regarding the different components of malocclusion
measured in the DI, several of them were found to have significantly changed and
with the results pointed towards improvement. The overjet, the anterior open bite,
the crowding and the molar occlusal relationship showed significant improvement.
How much was the contribution of the correction of each aspect to the result? It
seems that the improvement in overjet and occlusal relationship were the
characteristics that contributed the most to the treatment result by 30% and 21%
55
respectively. The posterior lingual crossbite was one of the features that underwent
great change, which represented the 11% of the total improvement. This change was
highly expected since posterior crossbites are one of the most common malocclusions
and need to be corrected as soon as they are observed. Many clinicians target this
specific feature with the purpose to re-establish normal development at a very early
age.
The correction of the anterior open bite also showed great change, which
was the 12% of the total improvement. In many cases, the open bite was the result of
a habit and ceased after the habit was interrupted either by educating the patient or by
the use of appliances.
Cephalometric measurements are also part of the DI and the ANB angle improved
significantly, which combined with the occlusal relationship improvement shows that
the anteroposterior (AP) dimension is routinely addressed in phase 1 with good
results. The ANB correction represented the 8% of the total improvement.
The category “Other” includes unusual developmental features normally not
treated (e.g. Congenital missing teeth or anomalous morphology of teeth) but also
important in the assessment of the severity of a malocclusion. Another consideration
for the category is the presence of a maxillary central diastema ≥ 2mm, which adds 2
points to the DI score. Since the pretreatment records were taken before the
permanent maxillary canines erupt, this diastema could close spontaneously later on,
without any orthodontic intervention and these points would be deducted from the
score. This category also showed a significant improvement, which was the 11% of
the total improvement after phase 1. The percentages of the contribution of the
56
improvement of each feature to the total improvement do not add up to 100% because
the result is also affected by the variables that underwent a non-significant change.
(See Table 3.8.)
While all the previous features showed positive change, there were certain
components of the DI (SN-MP, IMPA, buccal posterior crossbite) that underwent a
negative change. These changes can be considered side effects of the mechanics used
to correct different occlusal problems and may be transitory or not. However, none of
these measurements proved to be statistically significant.
Table 3.8. Percentages of contribution to the total improvement.
Overall
Overjet
30%
Anterior
Posterior
Occlusal
open
Crowding
lingual
relationship
bite
crossbite
12%
9%
21%
11%
ANB
Other
8%
11%
After the assessment of the overall scores, the sample was categorized in three
different groups according to their Angle molar classification (Class I, II and III) and
the same scores were analyzed to investigate how phase 1 treatment affected the
complexity of malocclusions.
The first group included 81 Class I molar subjects (48 females and 33 males) with
a mean age of 9.3 years. This group displayed a 49.3% of total improvement, which
was expressed as 5.79-point reduction of the DI total score from T1 to T2. The
analysis of each feature individually showed that overjet had a statistically significant
improvement, which represented the 29% of the total improvement in this group. A
large contribution to this correction was the alignment of anterior teeth by partial
57
bonding. The anterior open bite and the category “Other” also showed improvement,
which represented the 28% and 17% of the total improvement respectively. The
crowding and the posterior lingual crossbite were the main features of Class I
malocclusion and they both improved significantly. Their contribution to the total
result was 11% and 14% respectively. On the contrary, the occlusal relationship
showed a negative change, which actually attenuated the total improvement by 6%.
(See Table 3.9.) The rest of the features and all cephalometric measurements
underwent changes that were statistically insignificant. These results for Class I were
expected since no anteroposterior major change was projected.
Table 3.9. Percentages of contribution to the total improvement in Class I group.
Class I
Overjet
Anterior
open bite
Crowding
Occlusal
relationship
Posterior
lingual
crossbite
Other
29%
28%
11%
-6%
14%
17%
The second group consisted of 165 Class II molar subjects (89 females and 76
males) with the mean age of 9.6 years. Class II was categorized by the presence of
an end-on or full step molar relationship. For this group the total change from T1 to
T2 was also positive with a mean improvement of 34.5%. The examination of the
individual components of this malocclusion, showed that the overjet, the anterior
open bite, the crowding, the lingual posterior crossbite and the category “Other”
improved significantly. The contribution of the improvement of each component to
the total improvement of the Class II group was 23% for the overjet, 10% for the
anterior open bite, 10% for the crowding, 8% for the posterior lingual crossbite and
58
12% for the category “Other”. The main components of the DI that express the
severity of the Class II malocclusion are the occlusal relationship and the ANB angle.
Both features displayed a significant improvement and contributed to the result by
35% and 11%. On the contrary, the IMPA showed a negative change, which could
be seen as a side effect of mechanics used to reduce the overjet or “advance” the
mandible. The change of this feature reduced the total improvement by 9%. (See
Table 3.10.)
Table 3.10. Percentages of contribution to the total improvement in Class II group.
Class
II
Overjet
Anterior
open bite
Crowding
Occlusal
relationship
Posterior
lingual
crossbite
23%
10%
10%
35%
8%
ANB IMPA Other
11%
-9%
12%
The third group included 54 Class III molar subjects (27 females and 27 males)
with a mean age of 9 years. Class III cases were categorized by the presence of small
to full step molar relationship. This group demonstrated a total improvement of
58.5% and a reduction of the total score of 11.6 points. The features that were mostly
affected in the Class III malocclusion were the overjet, which is usually negative or
edge-to-edge, the posterior crossbite and the occlusal relationship All these features
showed significant improvement, which represented the 43%, 15% and 17% of the
total improvement respectively. This change can be attributed to the most common
treatment with a reverse-pull facemask combined with expansion of the upper arch.
A significant change was also expected for the ANB angle, which improved indeed
with a mean score of 0.92 points, but the change was not statistically significant. The
59
reason is that only an ANB≤ -2 is getting a score ≥ 4 point, according to the DI
instructions. This skeletal discrepancy is anticipated in more severe Class III cases
and it was not very common in the sample of this study. Additionally, the crowding
and the category “Other” improved significantly and they contributed by 7% and 4%
to the total result.
Table 3.11. Percentages of contribution to the total improvement in Class III group.
Class III
group
Overjet
Crowding
Occlusal
relationship
Posterior
lingual
crossbite
43%
7%
17%
15%
Other
Total
4%
100%
In all groups, there was a reduction of complexity after the completion of
treatment. In order, to investigate which of the three groups underwent the most
change from T1 to T2, an ANOVA was used to make the comparison. This test
revealed that the Class III group benefitted the most from early treatment compared
to the Class I and II groups, which demonstrated similar amount of improvement.
This could be an indication that the mechanics used for Class III correction are more
predictable and the changes are more pronounced due to the more severe initial
malocclusion. The overjet and the posterior lingual crossbite correction were more
distinct in the Class III group; the molar occlusal relationship and ANB angle were
corrected in the Class II and III groups equally. The IMPA angle was significantly
increased at the Class II group and therefore exacerbated compared to the other two
groups.
60
Conclusion
Overall
•
An overall 42.5% reduction of the DI score was observed, which indicates that
early treatment significantly reduced the complexity of the cases.
•
Most features of malocclusion that consist the DI (overjet, anterior open bite,
crowding, lingual crossbite, occlusal relationship, ANB angle and the “Other”
complexities) showed statistically significant improvement.
•
The components that showed negative change did not prove to be statistically
significant.
Groups
•
The Class I, Class II and Class III groups showed a total improvement of 49.3%,
34.5%, and 58.5%, respectively.
•
In the analysis of the groups certain measurement (IMPA in Class II group,
occlusal relation in Class I) showed significant negative change.
•
The Class III group underwent the most improvement.
61
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Vita Auctoris
Nefeli Vasilakou was born on April 25, 1985 in Athens, Greece. She attended National
and Kapodistrian University, in Athens, Greece for her dental education. In 2009, she
received a D.D.S. degree from Kapodistrian University School of Dentistry. She started
her graduate studies in orthodontics at Saint Louis University’s Center of Advanced
Dental Education in Saint Louis, Missouri in 2011. She currently is a candidate for the
degree of Master of Science in Dentistry.
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