TREATMENT EFFECT ON SKELETAL CLASS 11

LOW ANGLE PATIENTS

Peter George Dueckman, BA., D.M.D. Division of Graduate Orthodonties

Submitted in partial fiifilment of the requirements for the degree of

Master of Clinical Dentistry

Faculty of Graduate Studies The University of Western Ontario

London, Ontario, Canada February 1998

QPeter George Dueckman 1998

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The purpose of this study was to investigate the effects of non-extraction k e d

appliance orthodontie treatment on low mandibular plane angle Class II, Division 1 patients.

Serial lateral cephalograms taken pre-treatment (Tl), at end of treatrnent (T2), and

2 years post-treatrnent (T3) for 18 females and 18 males were compared to s e d

cephaiograrns of skeletally and dentally sirnilar, untreated subjects, 12 females and 12 males

from the Burhgton Growth Centre, taken at ages 12, 14, and 16. Treatment effects were

assessed by cornparison of changes in skeletal and dental parameters between treated and

untreated groups over the treatment intewai (Tl to TZ), the post-treatment interval (T2 to

T3), and the overd tirne penod (Tl to T3). Angular rneasurements were: SNA, SNB, ANB,

mandibular plane angle to Frankfort Horizont al v), facial axis angle (FA), maxillary incisor

angulation to S-N plane (ISN), and mandibular incisor angulation to rnandibular plane (IMP).

Linear measurements were: postenor face height (PFH), antenor face height (AFH), upper

face height (WH), lower face height (LFH), upper dental height (UDH), and lower dental

height (LDH).

Both fernale and male treatment groups showed effects during the treatment period

that rebounded slightly during post-treatment. Statistically significant changes for the

treatment groups compared to control groups during the Tl to T2 interval were: 1) a

decreased SNA for both females and males; 2) a decreased ANB for females only; 3) an

increased MP coincident with a decreased FA in males only; 4) an increased LFH with an

increased AFH for both females and males; and 5 ) an increased [MP in males only.

Digerences between treatment and control groups for the overd T l to T3 interval were:

1 ) a decreased SNA and AM3 for females; 2) a decreased FA for males; 3) an increased UDH

and a decreased ISN for females; and 4) an increased IMP for the males.

The correction of Class II, Division 1 malocclusion differed slightly between the

females and males. Reduction of AM3 by retraction of protrusive incisors and inhibition of

horizontal maxillary growth was more successfùl for the females. Bite opening effects caused

greater backward and downward rotation of the mandible in the males and necessitated

increased mandibular incisor proclination to achieve desired overjet reduction. Appropriate

mechanotherapy was used to correct anteroposterior and vertical skeletal and dental

discrepancies.

Key Words

Class II division 1 malocclusion Low mandibular plane angle Non-extraction

Orthodonties Cephaiometrics

ACKNOWLEDGEMENTS

1 would like to thank the mernbers of my thesis committee, Dr. David Banting, Dr. Jeff

Dixon, Dr. John Murray and Dr. Eung-Kwon Pae for their questions and constructive

comments. A special word of appreciation goes to my committee chairman, Dr. Antonios

Mamandras for his support and guidance throughout the preparation of this thesis.

1 would like to acknowledge the use of material fiom the Burlington Growth Centre

at the Faculty of Dentistry, University of Toronto which was supported by: (1) National

Hedth Grant (Canada) No.605-7-299, (2) Province of Ontario Grant PR33 and (3) the

Varsity Fund.

1 am indebted to Mrs. Patti-JO Blake for her indispensable assistance in editting,

fonnatting and copyhg the thesis manuscript.

To my classrnates Dr. EbfE Aynaciyan and Dr. N d r Lalani 1 Say thanks for the

cornradene, encouragement and helpfùl instructions.

1 extend my most hearfelt gratitude to my wife Irene and my sons Samuel, Thomas,

James and David for their love and patience in spite of the disruptions imposed on them.

TABLE OF CONTENTS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Certificate of Examination u

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements v

Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

ListofTables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VÜ . .

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vlt i

List o f Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MethodsandMaterials 4

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Vita . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

LIST OF TABLES

Table Description

1 Means and standard deviations of initial age and three intervals in months for control and treatment group females and males

Means and standard deviations of initiai cephaiometric values compared between females and males in control and treatrnent groups

Means and standard deviations of initial cephalometnc values cornpared between control and treatrnent groups for females and males

Mean changes in cephalometnc values with standard deviations for three time intervals, in female subjects

V Mean changes in cephaiometric values with standard deviations for three t h e intervals, in male subjects

VI Analysis of covariance for selected outcome variables

VI1 Standard error of measurements

vii

LIST OF FIGURES

Description

Laterai cephalometric landmarks

Angular cephalometric measurements

Linear cep halometric measurement s

Pane

26

27

28

LIST OF APPENDICES

A ~ ~ e n d i x Description

A Dennitions of cephalometric landmarks and planes

B Definitions of angular and linear cep halometric measurements

C Control and treatrnent groups

INTRODUCTION

Orthodontists are often called upon to treat patients with Class II, Division 1

malocclusion and there are rnany reports in the orthodontic literature that describe the

characteristi~sl~ of this problem and the effects of its treatment.9*'332 A number of cross-

s e c t i ~ n a l ~ ~ " ' * ' ~ ~ ~ and l~ngitudinal'*~*~~*~*~~*~~~~ cornparisons oftreated and untreated individuals

have been previously pubtished, but relatively few reports have included comparison of

treated patients to untreated Class II control s u b j e c t ~ . ~ * ~ " ~ ~ ' ~ ~ " * ~

The Angle classification of maiocclusion descnbes problems in the anteropostenor

plane of space but does not differentiate on the basis of vertical differences. l2icketts9

sudivided his Class 11, Division 1 malocclusion group into two facial types, with either

prognathic or retrognathic tendencies based on a combination of values of X Y axis, facial,

and mandibular plane angles. Schudylo proposed that it would be logical to use vertical

growth as the bais for facial typing. He felt that the angle SN-MF (sella-nasion plane to

mandibular plane) should be used for identifjnng types as either "hypodivergent" (low angle)

or "hyperdivergent" (high angle). While differing on semantics both Ricketts9 and Schudy "

modified treatment according to extreme facial types, finding that treatment, particularly the

type of extra-oral traction to the maxillary first molar, could influence the eruption of teeth

and have an effect on the position of the chin and rnandible.

Isaacson et al? studied skeletal and dental parameters of orthodontic patients

exhibiting extreme variations in vertical facial type based on SN-MP angle. They examined

the low SN-MP group in comparison to the high SN-MP group and found that the height of

the posterior rnaxillary first molar and alveolar process was the best predictor of SN-MP

angle. The authors included specific suggestions as to the type of rnechanotherapy and

particularly the type of headgear best suited to the correction of malocclusion in patients with

extreme variations in facial growth.

Researchers have reported the effects of various types of headgear in the treatment

of Class II, Division 1 malocclusions. Wies1anderl3 observeci that with ceMcal headgear

treatment the whole mailla was positioned relatively more downward or downward and

backward and that the lower face height change was greater than in the untreated Class I

control group. Wieslander and Buck" in a six-year follow-up of cervical headgear treatment

changes showed relative stability and minimal physiologie retum of the rnaxillary molar and

basal maxilla. The rnandibular plane angle increased during treatment, then decreased post-

treatment, but the overall decrease was considerably less than in the untreated Class II control

P U P - Melsenls used maxillary and mandibular implants to study the effects of extra-oral

forces. During treatment the maxilla grew downward and backward, the maxillary molar

extruded and the mandible rotated posteriorly. When observeci 7 to 8 years later, the growth

direction of both maxilla and mandible was found to have changed dramatically. The maxilla

had grown fonvard and downward, on average more forward than expected in a typical

population, and similarly the growth direction of the mandible had changed to a more forward

direction in al1 but a few patients.

Mills et al. l6 evaluated the effect of heavy intermittent ceMcal traction applied to the

maxillary arch via 'TV hooks. Assessed for treatment and post-treatment changes, males and

females showed a stable decrease in SNA and ANB. The mandible was rotated downward

and backward slightly during treatment and returned to a more normaf pattern of forward

rotation post-treatment.

Baumrind et al.17*18 examined five systems of maxillary retraction that al1 appeared to

slightly increase the mandibular plane angle relative to both Frankfort plane and SN plane but

with no statistically significant dserences between means. The authors noted that variability

of change in mandibular plane angle was greatest with the cervical and straight pull devices

and suggested that their use might require careful m~nitonng.'~ Further investigation showed

that variability of change in mandibular plane angle was predictively linked to mandibular

proportions and distal positioning of the maxillary first molar, more so than eruption-

extrusion of the upper first molar. Ig

When the same data were revisited by Baumrind et al. l9 to analyze changes in facial

dimensions associated with m d a r y retraction it was found that the cenical group had

increased measurements of both anterior and posterior face height compared to the controls.

This implied that cervical treatment caused facial elongation with relatively unchanged

rnandibular plane orientation.

Numerous researchers have reported on cephdometric changes in Class II, Division

1 non-extraction patients treated with fked appliances, most often including extra-oral

traction forces to the rna~illa.'~~* Some of these specifically differentiated treatment groups

by facial but generally the low angle, brachycephaiic, or deep-bite Class II, Division

1 treatment groups were smd and none were compared to untreated Class II, Division 1

control groups of simila. facial type.

The purpose of this study was to investigate the effect of non-extraction, dved

appliance orthodontie treatment on a group of Iow mandibuiar plane angle Class II, Division

1 patients by examining facial changes Iongitudinally and comparing them to changes in a

skeletally and dentally similar, untreated control group.

METHODS AND MATERIALS

Sample

The data used in this study were compiled from lateral cephalograms of

orthodonticaiiy treated subjects and untreated controls. The treatment group was derived

kom the files of the Graduate Orthodonties Clinic at The University of Western Ontario and

consisted of 18 females and 18 d e s who underwent non-extraction orthodontic treatrnent

with fixed appliances. The control group was made up of 12 females and 12 males from the

Burlington Growth Centre who had either no orthodontic treatment or only minimal early

preventive treatment discontinued several years pnor to the period under study.

Lateral cephalograms of the treatment group were available at three distinct times:

pre-treatment (Tl), at the end of active treatment (T2), and two years post-treatment (T3).

Serial radiographs of the control group available at 12, 14 and 16 years of age corresponded

weil with these three times for purposes of cornparison.

The following inclusion cnteria applied to both samples:

1. Class II molar and skeletai relationship with AM3 angle greater than 3 O .

2. Ove jet at the central incisors greater than or equal to 4 mm as measured

from the pretreatment 1 12 year (T 1) radiograph.

3. Mandibular plane angle to Frankfort Horizontal less than or equal to 23 O .

4. No extractions of permanent teeth for orthodontic purposes.

5. Lateral cephalograms available with teeth in maximum intercuspation at three

times: pre-treatment / 12 years (T 1 ), end of treatment / 14 years (T2), and

two years post-treatment 1 16 years (T3).

Methods

The lateral cephaiograms were traced on matte acetate fiIm with a 0.5 mm HB lead

mechanical pencil and digitized with the RMO JOEa program. Calculation of the majority

of the measurements of skeletal morphology depicted in Figures II and III and defined in

aJifQ Orthociontic Evaluation. Version 5.0. RMO Diagnostic Services. 1996.

Appendix B was carried out by the JOE program, accurate to *O. 1 O and *O. 1 mm for angular

and linear measurements respectively. The upper facial height (UFH), upper dental height

W H ) , and lower dental height (LDH) were measured directly &om the acetate tracings with

electronic calipersb accurate to IO.0 1 mm and reported to the nearest tenth of a millimeter in

the result tables.

Data for seven angular and six lineu measurements for each cephalogram were

entered into the SPSSc program for calculation of dflerences over the time intervals Tl to

T2, T2 to T3, and T l to T3. Statistical analysis was then carried out with the SPSS program

to determine the means and standard deviations of the cephdometric parameters at T 1, at T2,

and at T3, and also the means and standard deviations of the differences or changes over time:

from Tl to T2 corresponding to the active treatment phase; from T2 to T3 corresponding to

the post-treatment or retention phase; and fiom Tl to T3 corresponding to the overall

treatment and retention period.

The comparison of means between females and males in the control group and females

and males in the treatment group was carried out as a t-test for independent sarnples for each

ofthe cephalometric measurements at Tl, T2, and T3, and for their calculated changes in the

intervals T l to T2, T2 to T3, and T l to T3. A t-test for independent sarnples was also used

to compare means between females in the control and treatment groups, and between males

in the control and treatment groups for each of the sarne cephalometnc parameters.

The critical p value for statistical significance for comparisons of cephalometric

measurements was set using the Bonferroni adj~strnent'~ of the usually accepted p s 0.05.

In this case 0.05 was divided by 13 (the number of interrelated cephalometric measurements)

to give a value of 0.0038. Statistical significance was achieved if p s 0.003 when multiple

statistical comparisons were performed.

The SPSS program was also used to calculate the mean ages at Tl, T2, and T3, and

the means of the intervals T 1 to T2, T2 to T3, and Tl to T3 for the females and males in the

bMirutoyo Digimatic Caiiper. # 5 0 - 197. MI1 Corporation, lapan.

'SPSS for MS WiNDûWS, version 6.1.3.

control and treatment groups. Digerences between control and treatment groups were teaed

for statistical significance using t-tests.

Analysis of covariance (ANCOVA) was used to analyze the contribution of covariates

on treatment effect. Covariates were those variables that showed statistically significant

differences between the treated and non-treated groups for initial (T 1 ) cephalometric values.

Al1 radiographs were traced and digitized by the same operator. Outlines of bilateral

images were bisected except in the case of central incisors where the most antenorly

protmsive tooth was traced.

An error study was carried out to assess the meanirement error of tracing and

digitking cephalograms. Thirty lateral cephalograms (T 1, T2, and T3 radiographs of ten

randomly chosen subjects, 5 female and 5 male) were traced and digitized a second time a

month after the original tracings were done. The rneasurement error was caiculated according

to the formula for standard e r r o r based on the 30 duplicate values as follows: S = m2/2n

where d is the difference between the pairs and n is the number of pairs.

RESULTS

Idormation on initial age and elapsed t h e intervais between radiographs is presented

in Table 1. Male treated subjects comprised the oldest group with a rnean age of 154.1

months (1 2 years, 10 months) and femaie treated subjects comprised the youngest group with

a mean age of 139.8 months (1 lyears, 8 months) at the start of the study. The mean ages for

the female and male control groups were quite consistent, 145.6 months for females and

144.9 months for males. The mean age of the treated males was about 9 months older than

the control males, enough of a dBerence to be statistically significant @ = 0.003). The half

year (5.8 months) dflerence in mean age between treated females and control females did

not quite achieve statistical significance ( p = 0.057).

Statistical evaluation of the Tl to T2, T2 to T3, and T l to T3 mean time intervals

showed a significant difference for the T 1 to T2 intervai between control females at 2 1.6

months and treated females at 27.8 months. No other interval cornparisons showed

statistically significant differences with p s 0.05.

Comparisons of the means of the initial cephalometric values between females and

males identified several çtatistically signuicant differences (Table II). Treated females differed

from the treated males in three linear measurements: antenor face height (1 08.6. mm to 1 1 8.0

mm), upper face height (50.0 mm to 54.1 mm), and upper dental height (25.6 mm to 28.9

mm). Because of these observed differences females and males were analyzed separately.

Untreated females did not differ in a statistically significant manner frorn their male control

counterparts in any of the measurements.

Cornparisons of initial cephalometric means between control and treatment groups

(Table III) reveaied that females differed significantly in mandibular plane angle (2 1.1 O to

1 7.5 O) and in maxiilary incisor angulation to SN plane (1 0 1 -6 O to 1 1 1 -8 O ) and that males

differed in upper face height (50.8 mm to 54.1 mm). The effect of these initial merences on

changes during Tl to T2 and Tl to T3 was tested by analysis of covariance. Age at Tl was

also included as a covariate for the males because of the significant difference in age between

control and treatment groups.

Changes in cephalornetric values from Tl to T2 correspond to changes during the

period of orthodontic treatrnent in the treated subjects and were cornpared to changes in the

controls between ages 12 and 14. The diierences frorn T2 toT3 occurred during the post-

treatment or retention period in the treatment group and between ages 14 and 16 in the

control group. Overall dserences fiom Tl to T3 reflect the combined changes d u ~ g

orthodontic therapy and during retention for the treatment group and the changes over 4

years from age 12 to 16 for the control group (Table IV and Table V).

SNA angie decreased during Tl to T2 in a statisticaily significant rnanner in both

female and male treatment groups (2.0" and 1.2" respectively), increased slightly during T2

to T3 (0.4" and 0.2"), and resulted in net decreases from T 1 to T3 of 1.6 O for the females and

1.0 O for the males. The change for the treated females was statistically significant compared

to the control group, while that of the males was not.

S M 3 angle changes were not significantly Werent for any group dunng any interval

although SNI3 increased 0.7" for the control group males and decreased O.ZOfor the treated

males during Tl to T2 @ = 0.004).

The ANI3 angle decreased 2.3' in the female treatment group during Tl toT2, then

increased slightly from T2 to T3. The net ANB change from T l to T3, a decrease of 2.1 O ,

was statistically significant compared to the controls who exhibited a mean decrease of O. 1 O .

The mean mandibular plane angle (MP) decreased over al1 time intervals for al1 groups

except from Tl to T2 for the treated males. During that interval it increased 0.5" for the

treated males and decreased 1 .5" for the control group males, a statisticaily significant

dserence of 2.0". From T2 to T3 the M . decreased more for the treated males than the

untreated controls. The difference in TI to T3 change in MP between treated and untreated

males (1 .2 " difference of means) was not statistically significant .

Facial axis angle (FA) changes were statistically significant for the male treatment

group compared to the control group for both Tl to T2 and Tl to T3. FA decreased dunng

treatment and increased during the post-treatrnent period of the treatment group males, while

it increased through both intervals for the control group. The 1.9' difference of means

between treated and untreated males in the T 1 to T2 interval (- 1.2 O to 0.7") increased slightly

to 2.0' ( -0.7" to 1.3 ") for the interval Tl to T3.

Female and male treatment groups both showed statistically si@cant differences in

the increases in anterior face height (ARI) compared to untreated control groups for the Tl

to T2 interval but not for the T2 to T3 or Tl to T3 intervais. The difference of the means for

the females for T 1 to T2 of 2.8 mm decreased to 2.2 mm for the overall interval T 1 to T3,

and the corresponding values for the males decreased from 3 -6 mm to 1 .O mm.

A very sirnilar pattern was observed for Iower face height ( L w increases. Female

and male treatment groups had T l to T2 changes that differed in a statistically sipflcant

m m e r compared to their respective control groups. Because of greater increases in the

control groups during T2 to T3, a statisticaliy significant difference between control and

treatment groups was not maintained through the entire Tl to T3 interval. For the females

a difEerence of means between treated and untreated groups decreased fiom 1.8 mm for the

Tl to T2 interval to1.2 mm. for the Tl to T3 interval, while for the males the dzerence of

means decreased fiom 3.0 mm to 1.6 mm for the same intemals.

Upper dental height W H ) and upper incisor angulation to SN plane (ISN) both

differed in a statistically significant manner between female treatment and control groups in

the Tl to T3 interval. UDH increased an average of 1.5 mm more for the female treatment

group than for the control group and mean upper incisor angulation decreased 8.0" in the

treated females, while it increased a minimal O. 1 " in the untreated females for a difference of

8.1".

Lower incisor angulation to mandibular plane (IMP) exhibited significant ciifferences

between male treatment and control groups for intervals Tl to T2 and Tl to T3. The

dserence of the means of 5.5" (4.9" to -0.4") decreased slightly to 4.7" (4.0" to -0.7") but

maintained statisticai significance, indicating a fairly stable proclination of mandibular incisors

with treatment.

Results of the analysis of covariance are shown in Table VI. The difference related

to change in ISN in females between treated and control groups for the overail treatment and

retention penod (TI to T3) was found to be significant @ = .001) using a t-test. When the

initial ISN values were taken into account, this difference disappeared. The differences in

ISN at Tl accounted for the observed dinerences in ISN change from Tl to T3. In

orthodontie terrns, the teeth that were more proclined at the stari of treatment changed the

most and the treated group had more prociined maxi11ary incison on average.

The results of the error study are listed in Table W. shown as the standard error for

each cephdometric measurement, deterrnined from 30 double measurernents. The standard

mors for the six tinear meanires are quite consistent and ail fdl within 0.1 mm of each other,

from 0.36 mm to 0.45 mm, while the standard errors of the angular measures are more

disparate. SNA, SNB, ANB, and FA al1 have similar standard errors, ranging from 0.24" to

0.34". but MP, ISN, and IMP have considerably larger SE values, 0.70". O.86", and 1 -36"

respect ively .

DISCUSSION

The chief aim in this study was to investigate the effects of non-extraction, 6xed

appliance orthodontic treatment in a group of low mandibular plane angle Class II, Division

1 patients. Skeletal and dental changes were assessed using serial lateral cephalogram.

Comparisons were made to untreated subjects of similar age and skeletal and dental pattern

in an effort to be able to discem treatrnent effects ftom changes related to normal growth.

Horizontal Skeletal Changes

The first noted, and perhaps most hoped for, effect was the decrease in SNA

experienced by both females and males. Extraorai force was applied to the maxilla in nearly

every case, rnost ofken in the form of cervical traction headgear, although requested hours

of wear, force application, and general cornpliance varied. A decrease in SNA had the same

net effect on ANB since SNB remained relativeiy unchanged for the treated females and

males. Skeletal Class II malocclusions can exhibit maxillary protrusion ~ i t h ' " ~ ' or withoutl*'

mandibular deficiency and in these patients growth modification was directed at the maxilla,

with restraint of maxillary growth and retraction of rnaxillary incisors a top prionty. The

magnitude of change in SNA (about 2" in females) was in very close agreement to values

reported in other s t ~ d i e s . " " ~ ~ ~

Although SNB changes were not dramatic in any interval, the control group males

experienced a cumulative increase of 1.1 " over 4 years of growth with the same net decrease

of ANB, SNA rernaining relatively constant. This finding is stnkingly sirnilar to Carter's3

observed changes in untreated Class 4 Division 1 males. In contrat, the treated males made

only srnail net gains in SNB with their 1.4" decrease in ANB largely attributable to the

decrease in SNA. Two explanations for this difference in trends are plausible: the untreated

males were considerably younger on average than the treated males and therefore had more

incremental mandibular growth lefi; and the orthodontic treatment afTected the B point

position, most likely by rotating the rnandible down and backward as previously r e p o ~ t e d . ~ - " ~ ~ ~

Vertical Skeletal Changes

Mandibular plane angle (MP) and facial axis angle (FA) are related to the position of

the mandible, as are posterior face height (PFH) and anterior face height (AFH). Vertical

changes cm occur in the face without affecting the general orientation of the mandible and

thus both MF and FA may remain unchanged, while increased dimensions can be noted for

PFH and AFH. Most oflen though, changes in mandibular position are reflected by changes

in al1 four measures. Conversely, changes in any or al1 of these measures can also be caused

by changes in other parts of the head and face.

Treated males and females both showed a trend to less counterclockwise rotation of

the mandible (viewed fiom the right) than the controls dunng the treatment phase. The males

actually increased MP slightly (0.5 O ) dunng treatment, then revened rotation of the mandible

dunng the retention phase (-2.0°), ending with only slightly less reduction of MP than the

controls. Mandibular plane changes of this type were reported with headgear treatment

alone"16 and also in fidi fixed appliance treatment".". Changes in FA roughly paralleled Ml?

changes but inversely; increased MF correponded to decreased FA and vice versa. It is

interesting to note that the difference in change in FA for treated males remained statistically

significant for the overall Tl to T3 period, while M . change did not. The distinction is that

MP ultimately decreased in the treated males, much as the controls did, while FA also

remained decreased overall in the treated males but increased in the control males. Ricketts9

reported that use of neckstrap or inter-maxillary elastics opened the XY axis (Y axis, sella-

gnathion, measured as an angle to basion-nasion line) on average - 1 .O0. similar to the FA

change seen in the treated males. The 2.0" decrease of MP during the post-treatment period

with only minimal increase of FA (0.5 O) indicates that the mandibular border rotated counter-

clockwise, but the symphysis of the rnandible grew mostly downward and forward with less

horizontal projection of the chin for the treated males than their controls, corroborating the

findings related to SNB discussed above. Treatment in the males rotated the mandible down

and back and post-treatment growth re-established lower mandibular border orientation

without increasing horizontal chin projection.

The geometric relationship of PRI and AFH to MP is self-evident in that the two

former measurements terminate at landmarks that define the latter. A change in proportions

of PFH to ARI is directly related to change in MP as long as the Fraddort Horizontal (RI)

plane is unchanged in angulation to the S-N plane. Thus, as can be seen fiom Tables IV and

V, both treated females and males had p a t e r changes in AFH than PFH compared to their

respective control groups during Tl to T2. This trend distinctly reversed during T2 to T3

with PFH increasing more than AFH for the treatrnent groups, but with PFH and ARI

changes very similar to each other in the control groups. These data provide confhation

that the treated males and femaies experienced AFH increases that, in conjunction with

incrementaily smaller PFH increases, caused the mandible to rotate downwards and

backwards (clockwise) during treatment, then rebound back &er active treatment was ended.

It is particularly noteworthy that the proportion of PFH changes to AFH changes

fiom Tl to T3 was 1 : 1 for al1 treatment and control groups. Treated groups had slightly

larger increases than their control counterparts, but not at statistically significant Ievels and

males exceeded females overall simply because of larger physique. There are at least two

implications of such well baianced PFH and AFH increases over the entire T 1 to T3 interval.

The first is that angulation of the mandible in the face is perhaps better measured relative to

S-N plane than to the FH plane, partly because landmark identification is easier and more

consi~tent'~, but also because relating upper and lower limits of the growing face (ie. anterior

cranial base to lower border of the mandible) seems conceptually more valuable than relating

the lower Iimit to an intemal plane variably afTected by growthM and which in clinical terms

often poorly approximates horizontal orientation of natural head posture. Secondly, the data

in this study indicated that MP decreased in differing amounts over time in ail treatment and

control groups, an observation of rnandibular rotation descnbed by ~jorl?'. Yet the PFH and

AF'H increases within each group were so consistently alike at the end of the post-treatment

period as to suggest that compensatory growth mechanisms may have played a role in

ultimately maintainhg the orientation of the lower border of the mandible to the anterior

cranial base. Baumrind et dg ciaimed to be the first to make "this observation of the

geometry for maintainhg constancy of the mandibular plane angle". They found that in the

ceMcai treatment group rarnus height and anterior face height both increased significantly

compared to the control group, essentially keeping mandibular plane orientation unchanged.

AFH changed sigruficantly in both females and males during the treatment penod

(Table VI) and treatment groups differed considerably in age fiom control groups. Nanda3""

noted that females tended to have their adolescent growth spurt before males and that short-

face subjects experienced their pubertal growth spun later than long-face subjects. Changes

in ARI may thus have been affected by individual timing and growth variations of adolescent

growth spurts. Did younger females and older males outgrow their 12 year old control group

counterparts? The treatment group females also had a longer Tl to T2 interval during which

to expenence both growth and treatment effects. Treatment group males were significantly

older than the control group and aiready had larger AFH dimensions at the start of treatment.

Certainly it would seem that the catch-up of AFT3 change for control group males during T2

to T3 (age 14 to 16) could be partly attributed to a growth surge in the younger group as

both their PFH and AFH changes outpaced the treated males.

Perhaps the most revealing parameter of treatment effect was the lower face height

( L m measurement. Initiai pre-treatment values were very similar for al1 groups except for

the older, and presumably bigger, treatment group males. During the treatment period UFH

changes were numencally similar between treatment and control groups while LFH changes

differed for both males and females. n?is is an acceptable and logicai finding since the focus

of orthodontic treatment, the dentition, is located in the lower face. The farniliar reversai

trend of the T2 to T3 interval, not statistically significant by itself, was enough to reduce

statistical significance of the differences in LFH of the treated groups over the total Tl to T3

interval.

LFH changes were indeed the greater component of AFH changes which in tum

directly affected MP and FA values. Significant differences in skeletal vertical changes were

thus at least partly caused by orthodontic effects on the dentition.

Dental Changes

The parameters that were used in this study to evaluate dental changes focused on the

anterior dentition. Incisor changes are of considerable interest to orthodontists and patients

alike when dealing with Class LI, Division 1 maiocclusion. Upper dental height (UDK) and

lower dental height (LDH) are reasonable divisions of LFH and the difference between LFH

and the sum of UDH and LDH is a good approximation of depth of bite &RI - (UDH +

LDH) = OB). However, UDH and LDH changes were affected by vertical alveolar growth

changes, dental extrusion or intwion, and angular changes brought about by dental tipping.

Evaluation of incisor angulation changes in conjunction with dental height changes helped

elucidate orthodontic effects on the incisors.

Femaies and males showed a relatively large decrease in mean maxillary incisor

proclination with treatment, while only the males exhibited a sizeable mean increase in

mandibular incisor proclination. Individual variation was considerable, especiaily for upper

incisor angulation to S-N plane (ISN).

The initial ISN was a significant covariate for overall Tl to T3 ISN change in the

females (Table VI); those with the most proclined incisors would be expected to need the

greatest correction and the female treatment group was significantly worse initially with

respect to incisor angulation than the female controls. Many of the original femde patients

in the Burlington Growth Centre snidy who had significant onhodontic problerns received

treatment, therefore biasing the untreated control çample toward less severe cases. With a

better matched control group, one in which mean ISN was very similar to the treatment group

initially, the change with treatment could well have been the sarne in which case the results

of ANCOVA would likely have indicated statistical significance based on treatment aione.

UDH increased concurrently with ISN decrease in treated femaies, indicating that

orthodontic tipping of incisors can affect their relative length. According to treatment

records, intrusive orthodontic forces were used in most cases to counter the lengthening

effect othenvise the mean dserence might have been greater than 1.5 mm. Similarly, in the

treated males the LDH showed slightly smaller but not statistically significant increases than

in the controls (a relative decrease) as the MP increased. Relative intrusion of lower incisors

is often necessary to level the curve of Spee that can be quite marked in low angle Class iI,

Division 1 malocclusion cases. In both females and males the lack of significant differences

in LDH between treated and untreated groups concurrent with significant differences in LFH

during Tl to T2 suggests that not much tme intrusion of lower incisors took place. The

increased eruption or extrusion of posterior teeth was the more u d rnethod of levelling the

mandibular dentition, thereby affecthg Lm AFH, MP and FA.

The pattern of anterior dental changes fits well with the obsewed skeletal changes in

the treated groups. Females showed greater change in SNA and thus also ANB, partly

attributable to retraction of severely proclined incisors as well as possible inhibition of

fomard maxillary growth. Orthodontic effects on the maxillary dentition reduced incisor

anguiation while increasing relative incisor length. Correction of the skeletal Class II

relationship and ove jet reduction was achieved primarily with effects to the rnaxilla and its

teeth, making it unnecesçary to proche or advance the mandibular dentition. Males on the

other hand experienced less success with maxillary traction with smaller reduction of SNA

and ANB. Dental extrusion or eruption lead to bite opening effects causing downward and

backward mandibular rotation and reduced chin projection. Ovejet reduction was

accomplished by retroclining maxillary incisors and by advancing the mandibular dentition.

Many of the effects observed in the treatment groups were sirnilar to those found in

a previous study in which treatment effects on hi& mandibular plane angle Class II, Division

1 patients were investigated." The results of the high angle study indicated that orthodontic

treatment increased antenor face height and in particular the lower face height, but postenor

face height growth did not keep Pace with the anterior increases. Mandibular plane angle

increased and facial axis angle decreased, indicating a downward and backward mandibular

rotation. Dental changes included maxillary incisor retraction and mandibular incisor

proclination but antero-postenor skeletal correction was deemed to be minimal.

Clinically, the most relevant difference between the low and high mandibular plane

angle patients is the ability of low angle patients to tolerate or even benefit fiom, in terms of

facial esthetics, an increase in lower face height. A short face with a deep bite is readily

improved by opening the bite, and thereby lengthening the lower face, but a long face can be

worsened in appearance by bite-opening effects and treatment must be p lmed accordingly.

Isaacson et al." recommended ceMcal headgear with a high outer bow as an ideal

force system for low angle, deep bite patients but warned that it would be contraindicated for

high angle patients since molar extrusion, while favourable in low angie cases, would be

undesirable in high angie ones. The preferred treatment for high angle patients was high pull

headgear with a short outer bow that would exert an intrusive force to maxillaq molars.

Further control of vertical parameters was suggested; in low angle, deep bite patients, reverse

cuves in archwires, full-arch banding including second molars, and intemaxillary elastics that

cause posterior extrusion are reasonable treatment. In high angie patients with open bite

tendencies it is better to Ieave some occlusal curve in the archwires, to leave second molars

unbanded, and to avoid use of intermaxillary elastics. The ability to control vertical facial

growth through orthodontie mechanotherapy is the key to producing good results in patients

with severe vertical skeletal pattern discrepancies.

SUMMARY AND CONCLUSIONS

Senal laterd cephalograms were used to compare facial changes in 36 non-extraction

orthodontically treated subjects and 24 untreated control subjects. Treatment and control

groups exhibited Class II, Division 1 dental and skeletal characteristics with a low mandibular

plane angle. The findings of the study may be surnmarized as foilows:

SNA decreased with treatment in both femdes and males, while SNB remained

relatively unchanged.

SNA and AM3 decreases at the end of the cornbined treatment and retention

penod were statistically significant only for females.

Males experienced a statistically significant increase in rnandibular plane angle and

a decrease in facial axis angle with treatment; oniy the decrease in facial axis angle

rernained si@cant at the end of the combined treatment and retention period.

Lower anterior face height and consequently also total anterior face height were

increased with ?reatment in females and males. By the end of the combined

treatment and retention penod postenor and anterior face height changes had

equalized.

Lower incisors were proclined during treatment in the males and remained proclined

at the end of the combined treatment and retention period.

In females, maxiIlary incisors were uprighted by retraction that increased upper dental

height. The effect initiated with treatment increased during the retention period to

become statistically significant over the combined treatment and retention perîod.

Considerable variation was observed in changes of the cephalometric measures but the

correction of Class II, Division 1 malocclusion was achieved in a slightly different manner for

females than for males. On average, the inhibition of horizontal maxillary growth and

retraction of proclined incisors was more pronounced for the females. The males experienced

greater relative posterior mandibular rotation ffom bite opening effects that increased antenor

and particularly lower face height. Decreased chin projection necessitated increased

mandibular incisor proclination to achieve desired overjet reduction. Appropriate

mechanotherapy was used to correct horizontal and vertical skeletal and dental discrepancies.

Table 1. Means and standard deviations of initial age and three intervals, in months, for control and treatment group females and males

Initial age

TI to T2

T2 to T3

Tl to T3

Females 1 Treatment

group (n = 18)

Males

t-test I .-

Control Treatrnent 1 t-test 1 Contra1

46.7 3.6 1 51.8 10.9 1 .O78 1 48.5 1 . 1 * les than critical p value, p r 0.050

(n = 12)

Mean / SD

145.6 3.7

(n = 18)

Mean j SD

139.8 11.3

y value

.O57

(n = 12) . Mean i SD

144.9 1.0

Table IL Means and standard deviations of initial cephalometric values compared between fernaies and males in control and treatrnent groups

SNA

SNI3

ANB

MP

FA

PFH

AFH

UFH

LFH

UDH

LDH

ISN

ma?

Control Group

Males (n = 12)

t-test

p value

Treatment Group

Females ( n = 18)

Mean ! S D

Males (n = 18)

t-test

p value

.O38

-285

.O13

.O53

.O15

.O09

-000'

.O0 1 *

.O04

. OOO*

.O04

.307

-166 *less than cnticai p value, p < 0.003

Table IIL Means and standard deviations of initial cephalometric values compared between control and treatment groups for femaies and males

SNA

Sm

ANS

MP

FA

PFH

AFH

UFH

LFH

UDH

LDH

ISN

IMP

Control W'UP

(n = 12)

Mean i SD 84.6 3.7

79.0 2.7

5.5 1.9

21.1 2.3

91.4 1.8

74.7 3 .6

109.1 2.9

50.9 2.4

61.0 2.5

26.8 1.9

3 8 . 2 1.7

101.6 7.7

102.2 4.3

- -

Treatment P U P

(n = 18)

Mean j SD

t-test

p value

- - -

Control P U P

(n = 12)

Mean j SD

Males

Treatment P U P

(n = 18)

t-test

p value - .120

-277

. I52

-253

.O30

.O16

.O04

-001"

-101

-328

.O 17

.242

.73 1 *less than cntical p value, p r 0.003

Table VI. Analysis of covariance for selected outcorne variables

Cephalometnc

Female MP Tl toT2

Female MP Tl toT3

Female ISN TI toT2

Female ISN TI to T3

Male UFH 11 TItoT2

t-test p value

-143

-378

.O09

.001*

.450

.146

- -

Covariate (Initial value)

MP

M P

ISN

ISN

UFH, Age

UFH, Age

ANCOVA p value

.357

.56 1

.562

.20 1

.602

.506

* less t han cntical p value, p s 0.003

Table VIL Standard error of measurernents

S.E. = a d 2 / 2 n , n = 30

Angular (degrees) : SNA

SNB

ANB

ME'

FA

ISN

IMP

Linear (mm) Pm

AFH

UFH

LFH

UDH

LDH

Standard error

Figure 1 : Lateral cephaiometric landmarks

Figure 2: Angular cephalomeîric measurements

1 . SNA 5. Facialaxisangle 2. S N B 6 . Upper incisor to S-N plane 3 . ANB 7. Lower incisor to mandibular plane 4. Mandibulu plane angle

Figure 3: Linear cephaiometric measurements

1 . Posterior face height 2. Anterior face height 3. Upper face height

4. Lower face height 5. Upper dental height 6. Lower dental height

Appendix A: Definitions of cephalometnc landmarks and planes

A point (A)

Anterior Nasal Spine (ANS)

Articulare (Ar)

B point (B)

Basion (Ba)

Gnathion (Gn)

Gonion (Go)

Iderior Gonion (IGo)

Menton (Me)

Nasion (N)

Orbitale (Or)

Pogonion (Pg)

Porion (PO)

Posterior Nasal Spine PNS)

Landmarks

The most posterior point on the curve of the antenor maxilla.

The most anterior point ofthe maxilla at the lower margin of the anterior aperture of the nose.

The point of intersection of the infenor surface of the cranial base and the posterior surface of the mandibular condyle.

The point most posterior to a line from the crest of the alveolus to pogonion on the anterior surface of the symphyseal outline of the mandible.

The most infenor, postenor point on the anterior margin of forarnen magnum.

The most anterior and inferior point on the contour of the bony chin symphysis. Determined by drawing a line from pterygoid point to the intersection of the mandibular plane and a line through nasion and pogonion.

The point of intersection of the mandibular plane and a line through articulare and tangent to the mandibular ramus inferior to it.

A point tangent to the inferior border of the mandible located on the gonial curve.

The most inferior point on the symphyseal outline.

The junction of the fiontonasal suture at the most postenor point on the curve of the bridge of the nose.

The lowest point on the average of the right and Iefi borders of the orbit.

The most antenor point on the symphysis of the mandible determined by a line from nasion tangent to the symphysis.

The most superior point of the bony extemal auditory meatus.

The most posterior point of the bony hard palate.

Appendir A: Definitions of cephalometric landmarks and planes cont'd.

Pterygoid point (Pt)

Sella Turcica (S)

Basion-Nasion plane (Ba-N)

Frankfort Horizontal (FH)

Mandibular plane (MP)

Sella-Nasion plane (S-N)

The intersection of the infenor border of foramen rotundum with the posterior wail of the pterygomaxillary fossa.

The center of the piniitary fossa of the sphenoid bone as determined by inspection.

Planes

A line joining basion and nasion.

A line joining pterygoid point and gnathion.

A line joining porion and orbitale.

A line joining inferior gonion and menton.

A line joining sella turcica and nasion.

Appendix B: Definitions of angular and linear cephalornetric measurements

Anmlar Measurements

SNA

SNB

ANB

MP

ISN

PF'H

AFH

UFH

LFH

UDH

LDH

The angle formed by the points Sella - Nasion - A point.

The angle formed by the points Sela - Nasion - B point.

The angle formed by the points A point - Nasion - B point.

Mandibular plane angle: the angle formed by the intersection of the mandibuiar plane and the Frankfort Horizontal plane.

Facial axis angle: the iderior angle formed by the intersection of the Basion-Nasion plane and the line through pterygoid point and constructed gnathion.

Upper incisor to S-N: the postenor angle formed by the intersection of the long axis of the most prominent maxillary incisor and the Sella- Nasion plane.

Lower incisor to mandibuiar plane: the postenor angle formed by the intersection of the long axis of the most prominent lower incisor and the mandibular plane.

Linear Measurements

Posterior face height: sella to constmcted gonion.

Anterior face height: nasion to menton.

Upper face height: nasion to anterior nasal spine.

Lower face height: anterior nesal spine to menton.

Upper dental height: linear distance from the incisal edge of the maxillary central incisor to the palatal plane dong a perpendicular to palatal plane.

Lower dental height: linear distance fiom the incisal edge of the mandibular central incisor to the mandibular plane dong a perpendicular to mandibular plane.

Appendix C: Control and treatment groups

Burlington Growth Centre

Patient Chart Number

Female Male

44 409

257 615

423 804

482 865

571 877

806 897

840 954

847 1 085

848 1144

942 1316

1024 2523

1363 2561

University of Western Ontario

Orthodontie Patient Chart Number

Female Male

88 21

97 197

184 538

417 634

420 678

447 849

480 889

48 1 89 1

682 945

683 1141

739B 1189

1018 1335

1101 1376

121 1 1477

1443 1509

1537 1541

1632 1677

1633 1679

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