Download QUANTITATIVE ASSESSMENT OF CLASS II MALOCCLUSION

QUANTITATIVE ASSESSMENT OF CLASS II MALOCCLUSION
IN MIXED DENTITION
by
Pius Jwn-Young Kim
Divisionof Graduate Orthodontics
Submitted in partial llfilment
ofthe requirements for the degree of
Master ofClinical Dentistry
Faculty of Graduate Studies
The University of Western Ontario
London, Ontario
February 1997
BPius Joon-Young Kim 1997
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Abstrret
The purposeofthis study was to investigate cepbalometrically the facial components
associated with Class II malocclusions and compare the &dings with previously published
studies.
The sample consisted of 46 msks and 59 fbdes in mixed dentition (range: 8.0- 11-0
years) with Class I1 molar and cuspid relationships. Lateral cephalometric radiographs for
these subjects were obtained tiom the files o f the Graduate Orthodontic Clinic, at the
University of Western Ontario (London, Ontario). In 40 of these subjects, posteroanterior
(P-A) cephalometric radiographs were also available to investigate the rmutillomandibular
transverse skeletal relationships.
A wide variation was evident fiom the various measurements. In comparison to the
established cephalometric norms, the maxilla was more prognathic in 35.2% of the subjects
based on SNA and 21 -0% based on A point to nasion perpendicular measurements. The
mandible was retrogrdic in 76.2% based on SNB and 55.2% based on pogonion to nasion
perpendicular measurements. The lower f-
height was short to normal in 26.7% and
exoessive in 73.3% ofthe subjects mpechely.
The Pearson correlation coefficients between
the transverse dimensions of maxilla and
to the lower anterior face height were 0.40
and 0.46, respectively. Compared to cephalometric norms, the maxillary incison were
protrusive in 23.8% with reference to A point vertical and 98.1% with respect to A pointpogonion line while the madicbular incisors were retnrsive to A point-pogonion line in 44.8%
of the sample.
Key words: Class I1 Malocclusion, Mixed Dentition, Cephalometry, Facial dimensions
I would like to atpress my sincere gratitude to my thesis advisor and the chairperson
of the orthodontic program, Dr. AH. hrlamaadras for his constant support, guidance and
encouragement in this study.
I would like to extent my thanks to the following members of my cornminee, Dr.
D.W. Banting, Dr. TF. Foley, Dr. W.S. Hunter and Dr.J. R Murray for their valuable and
constructive comments-
Special thanks to my classmates, Drs. P.J. Karl and U P .Meehan and their f d e s
for the support and Wendships during the past three years.
I would like to acknowledge alI the staff members and personnel involved with the
Graduate Orthodontic Program at the University of Western Ontario. A special gratitude to
Mrs. P.J. Blake for her technical support with this thesis.
To my wife, Sylvia and our children, Rachel, Kathryn and William, for their love,
encouragements and shariag this memorable time in our lives together.
finally, to my mother and late fhther, who d a d and made everything possible for
our education.
Page
Certificate ofE x m i d o n . . ... - . . . .. . . . ... . - .. . .. . . . . . . . . . . .. . . . . . . . . . . ii
Abstra~t.................................................~..........
..-
ur
Acknowledgments . . . . . . . . . .. . . . . . . . . . . . . . . . . .. .. . .. . . . . . . . . . . . . . . . . . . iv
Table ofContents . . .. ,, , , . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . - . . . . . .. . . .. . v
List of Tables . . . . . . . - . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
,,
,
,,
ListofFigures ....................................................... vii
List of Appendices . . . . .. . . . .. . . . . . . . . . . . . . . . . . .. . ... . . . . . . . .. . . . . . . . . . ix
Introduction . . . . . . . . . . . . . . . . . . . , . . - . . . . . . . . .. . . ... . . , . , . . . . . . . . . . . . . - 1
Materials and Methods . . . . . . . . . . . . .
- . . . . . . . . . . . . . .. . .. . . . . . . . . . . . . . . . . 4
Results ........,.....,.,............,............................... 6
Discussion ...........,.................................,............. 9
Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Tables ........,..........,....,....-....-.,.................,.,...- 16
Figures ............................................................ 24
Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
References . . . . . . . . .. . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. , . . . 46
Vita ............................................................... 50
Table
1
Standard errors of manual measurements
2
Lateral cephelomeaic measurements d
subgroup measurements by gender
Maxillary and mandibular transverse dimensions (mm)
and me& ratios between maxillary basal to man&bdar
basal dimensions; total sample and subgroup
measurements by gender
M d a r y length end mandibular length measurements (rnm),
and 9 year old cephalometric norm fiom Bolton, Burlington
and Michigan Growth studies with associated percent
enlargements
Pearson correlation coefficients for various cephalometric
skeletal variables
Pearson correlation coefficients for rmucillary and mandibular
transverse dimensions to lower anterior face heights
21
Correlations between measurements from condylion and articulare
to A point and gnathion
22
Subgroup measurements with angle ANB < 4.5" versus angle
23
ANB > 4.5"
LIST OF FIGURES
Figure
1,
Lateral cepbalometric landmarks
2.
Angular measurements for lateral cephalometric
radiographs
Linear measurements for lateral cephalomemc
radiographs
Frontal (posteroanterior) cephalometric landmarks
with linear measurements
Distniution of maxillary position, measured with
angle SNA
Distribution of maxillary position, measured by
linear distance fiom nasion perpendicular to A point
Distribution of mandibular position, measured with
angIe SNB
Distribution of mandibular position, measured by
linear distance fiom nasion perpendicular to B point
Distribution of mandibular position, measured by
the angle between Frankfort plane and mandibular plane
Distribution of linear vertical dimension, fkom anterior
nasal spine to menton
Distribution of mandibular position in vertical and
anteroposterior dimensions, measured by the posterior
angle between basion-nasion plane and
pterygomaxillaxy-gnathion plane
Distribution of vertical mandibular position, measured
by the angle between sella-aasion plane and mandibular plane
vii
35
List of Figures cont'd.
13,
Distributionof maxillary incisor position in
anteroposteriorposition, measured tiom A point vertical
to most facial sudhce of maxillary incisor
Distniution of maxillary incisor position in
anteroposterior position, measured fiom A pointpogonion line to incisal tip of maxillary incisor
Distribution of mandibularincisor position in
anteroposteriorposition, measured &omA pointpogonion line to incisal tip of mandiiular incisor
LIST OF APPENDICES
A
Definitions of l a n a , angles and planes utilized
39
B
Cephelometric norms fiorn various analyses
40
C
Corrected linear measurements of the sample (1 1%)
41
D
Mardllary length and mandibular length, corrected
measurements of the sample and corrected cephalometric
nonns fiom Bolton, Burlington and Michigan Growth studies
42
E
List of individuals in the sample from the Graduate
Orthodontic Clinic, UWO
Introduction
The prevalence ofclass I1 malocclusions is reported fiom 15% to 38.6% in children
6 to 11 years of age?
A broad spearurn of treatment philosophies and modalities are
available for the treatment of Class II malocclusions. These include various dentofacial
orthopedic appliances for growing individuals, extraction of bicuspids, or orthognathic
surgery where the growth potential is limited or udavourable. It is important to recognize
and address variations in size, position, form and proportions of the dentofacial complex in
the diagnosis of Class II malocclusions.
It has been suggested by various investigators that the Class 11malocclusion is not a
single entity, but rather a combination of various skeletal and dental components.zCD In
1941, ~aldridge'proposed four possible conditions associated with Class 11malocclusions:
1.
Over-development of the maxilla in conjunction with a mandible being n o d in
position and size.
..
11.
Mamllary teeth are forward in relation to the maxilla. The relationship of the maxilla
to mandiiiile is normal.
iii.
The mandible is underdeveloped or smaller than normal in size. The maxilla is
normal.
iv.
The mandible is in a posterior position with respect to a normal maxilla.
In 1948, Elsasser and Wylie6 suggested an additional condition associated with Class II
malocclusion.
v.
The maxilla and mandible are average in size and position but the mandibular dental
2
arch is posteriorly placed on the mandiiufar base.
Some studies,zGc18have reported that the major component of Class II malocclusion is the
skeletal mandibular retmsion. Protrusive skeletal maxilla has been suggested by some
hrvestigatodvWDas a primary causative k t o r in Class 11rnalocdusion, while
have attributed Class I1 malocclusion to a maxilla that is either neutral or slightly
retrognathic. Interestingly, EElsasser and Wylie6 reported a neutral maxillary position for
females but a prognathic maxilla for males.
Sassouni2' summarized the interaction of size, position, form and proportions of
various dentofacial structures of verticai and horizontal deviations. He descnied and
classified vertical disproportions (skeletal open-bite and skeletal deep-bite) with
anteroposterior disproportions (skeletal Class I1 and skeletal Class III malocclusions).
Moyers et al* used sophisticated cluster analyses to subgroup 697 Class I[ subjects.
They described six horizontal and five vertical facial types and proposed an arborization to
subgroup C l w II malocclusions with similar skeletal and dental characteristics. They
concluded, "AU vertical types are not found with each horizontal type, but there is a strong
relationship between horizontal and vertical features permitting identification of Ween
subtypes with distinguishing features." An increase of the anterior face height in Class II
malocclusion has also been reported by some investigator^.^^*^^'^
Sujmimposed on various skeletal relationships is the position of dentoalveolar units
in their respective basal bones. Many s t ~ d i e s ~ *have
" * ~reported protrusive maxillary
dentition within the maxillary basal bone. ~ t h e r ~ ' ~ * 'observed
""
a retrusive position of the
mandibular dentoalveolar units within the basal mandible in Class II maloccfusion.
3
Fisk et ai" in 1953, and McNamara4 in 1981, reviewed and reported on Class II
malocclusions. McNamara investigated 277 subjects with Class II malocclusion in mixed
dentition stage. He concluded that the most common components in a Class II malocclusion
include; (
i
J
skelaal retrusion, (ii) neutral positioning of skeletal rmodlla, and (iii)
excessive lower face height.
Some investigatof~~~
have discussed the conflicting and inconsistent reports of Class
II malocclusions in the Literature. Facton that may contribute to these variations include but
are not limited to:
1.
variations in age of samples studied
.11..
sexual dimorphism
ILL
...
differences in the methods of investigations
iv.
lack of valid statistical analysis and interpretations
v.
insufficient sample size@)
vi.
lack of stable reference plane
vii.
natural variation of Class II malocclusion^
In considerations of the above factors and many diversified opinions respecting the
constitution of Class II malocclusion, the purpose of this study was to investigate
cephalometricaUy which facial components are associated with Class I1 malocclusion and
compare the findings with previously published studies.
hlrteriais and Method@
Lateral beadfilms of 46 males and 59 females were cepbalometridy analyzed. The
subjects ranged in age &om 8 years, 0 months to 1 1 years, 0 months, with an average age of
9 years, 10 months. All 105 l a t d cepbalometric radiographs ofthese subjects were obtained
from the files of the Graduate Orthodontic C h i c at the University of Western Ontario
(London, Ontario, Canada). The Class II occlusal relationship was determined fiom the
headfilms and study models with at leest endsn molar and cuspid relationships. Although
all subjects included in this study were class%edas Class II malocclusion, 99 exhibited Class
11, Division 1 and 6 exhibited Class II, Division 2 characteristics.
In 40 of these subjects, posteroanterior (P-A) cephalometric radiographs were
available to investigate the maxiuoman'bular
transverse skeletal relationships.
Initially, each film was traced by one investigator and digitized using a computer
cephalometric program' Due to unforeseen technical dficdties, the digitized data were
discarded and each tracing was nmeasuredby the same investigator manually with Mitutoyo
dial caliperAwith accuracy of 0.05 mm and a protractor with accuracy of 0.5". The
landmarks, angles and planes utilized in this study have been previously reported2' and their
definitions can be found in Appeadix A Various cephalometric measurements were analyzed
with Student's t-test and Pearson correlation coefficient (SPSS for MS WINDOWS Release
6.1.3).
bentofacid Planner, version 6.5 1;RDT 1212 Saiptel Digitizer, Columbus, Ohio; Packard &U 586
Computer
^MTI Corporation, Japan
The eniargernent fhctor at the midsagittal plane was 11.0%.
Reliability of Method
The error mdy for landmark identification and measurement involved retracing and
remeasuring 28 l a t d and 15 P-A cephalometricradiographs with a 4 week interval W e e n
first and second measures. The error variance was computed using both standard errors of
the mean and Dahlberg's formula?
where d is the Merence between duplicate measures and n is the number of duplications.
m!!&
The standard errors for the m u d reproducibilityare found in Table 1. The largest
standard ertor for angular measurement was the mandibular plane angle at 0.2P,and for
linear measurement, pogonion to nasion perpendicular at 1.01 mm. The corresponding
Dahlbergs standard errors wen 0.99" and 3.77 nun, respectivelyrespectively
These large values of error
of measurements were most likely due to difllidty in locating the reference landmarks,
namely orbitale and porion."
Uncorrected cephalometric measurements are reported for comparison with other
published data.4*24v2744 The summary of cephalometric values and subgroups for males and
females are presented in Table 2.
The mean SNA for r n d a r y position was 8 1.2" (Figure 5). The A point to nasion
perpendicular was -0.44 rnm (Figure 6). Both of these values indicate average to mildly
retrusive madary position compared to the ideal cephalornetric norms (AppendomBU*27-M).
The mean SNB (Figure 7) and pogonion to nasion perpendicular (Figure 8)
measurements were 75.3" and -9.49 mm respectively, suggesting moderate skeletal
mandibular retrusion with respect to anterior cranialbase.
The means of vertical measurements,the rnandr'bular plane angle (Figure 9) and lower
anterior face height (Figure 10) wen 25.0" and 65.77 mm, respectively. The facial growth
axis was 87-90 (Figure 11). The angle between SN-GoGn was 33.3" (Figure 12).
The mean madllary basal width was 63.21 mm. The mean mandibular basal widths
were 81.25 mm and 90.50 mat the antegod and gonial points respectively, as determined
from the P-A cephalometric measurements of 40 subjects (Table 3).
7
Dentally, the maxillary incisors were on average, 5-95 mm ahead of A point
perpendicular (Figure 13). The mean distance between d a r y incisors to A pointpogoaion line mgure 14) was 8.62 nrm. The mean distance between mandibular incisors to
A point-pogonion line (Figure 15) was 4-16mm behind this line.
The r m x i h y and mandibular lengths were measured &om condylion and artidare.
For maxilla, the mean measurements were 90.78 mm and 87.81 mm fiom A point to
condylion and to artidare, respeaively. The mean mandiiular lengths were 109.39 mm and
101.77 mrn h
m gnathionto condylion and to artidare, respectively (Table 2). The sample
maxillary and mandibular lengths were compared to other published studies24s (Table 4).
In Table 5, various cephalometric skeletal variables fiom lateral cephalometric
radiographs were correlated. SpeciGcdly, the correlation values between the anteroposterior
position of maxilla to vertical dimension were not stathically significant, with r values of 0.07
between SNA and LAFH, and 0.09 between A point to nasion perpendicular and LAFH.
In Table 6, Pearson correlation coefficients were calculated between maxillary and
mandibular transverse dimensions and lower anterior face height. The r value was 0.40 for
maxillary transverse dimension to LAFH. In mandible, the r values were 0.43 and 0.46 for
mandibular basal 1 (AG-GA)
to
LAFH and mandibular basal 2 (GO-GO)to L
m
respectively.
In Table 7, Pearson correlation coefficients were calculated to determine the
relationships of-
and mandibular length measurements fiom articulare and condylion.
For maxillary length measurements, the r value was 0.93. For mandibular length
measurements, the r value was 0.91.
8
In Table 8, various cephalomeaic values between the skeletal Class I1 (ANB > 4.5")
and the skeletal Class I (ANB 5 4.5")ere
compared.
The correctedd u e s for various lhreer measurements are in Appendices
B and C for
comparison with other published data with different enlargement fkctors. The published
magnification factors were subtracted from the reported values of various growth studies.
Y
Discussion
Describ'mg craniofiwiai associations, various i n v e s @ t t ~ n ~have
' ~ *stated
~
that the
mean values and wious ldfttiStical analyses represent oniy the overall average picture. Also,
absolute values are not as important as the variability seen among individual^?^ Only by
examidon of individual cases can one truly appreciate the extent of the variation seen within
each class of maloodusion. Therefore, comparisons of means and conclusions derived from
statistical analysis should be tempered by the concept of individual variations. This study and
many other^^*^^*'^"*^^* have previously reported an extensive variation of the dentofacial
complex. Hence, most of the cephalometric variables were presented in histograms to
demonstrate the variability associated with each of the measurements.
Consistent with previous report^:^*^^" the most significant component of Class II
malocclusion was the mandibular retrusion. The mandible was retrognathic in 76.2% with
SNB as reference measurement. When the pogoclion to nasion perpendicular measurement
was dyed, 55.2% demonstrated a retrognathic mandible. These values concurred with
McNamara's report4 of 78.5% and 60.W with respect to SNB and pogonion to nasion
have reported that the glenoid
perpendicular measurements respectively. Investigator~~*'~
fossa in their sampleswas posteriorlypositioned, while other^^^"^^^ have reported that the
smaller size and funn of the mandible were the significant factors in mandibular retrusion.
Based on embryological and biochemical studies, McNamara4postulated a possible etiology
of skeletal mandibular retrusion. He stressed the developmental difrence between the
condylar cartilage, which is secondary in origin embryologically, and other primary
cartilaginous skeletons of both the craniofkcial and the appendidar skeletons. Furthermore,
10
he discussed the condylar d a g e respond to alterations in the environment similar to that
of periosteum and these altered hctioaal environments may aEict the size and shape of
mandible.
Although the mean SNA value for maxilla of 81.2" indicated orthoguathism, if not
slight maxillary retrognathisrn, the range of values obsemd indicated that the number of
subjects exhiiited various degrees of maxillary prognathism (Figwe 5). These observations
support McNamara's findings4. Not only was the mandible retrognathic, but more often than
not, the mardlla was deficient in the anteroposterior dimension. MaxiUary retrusion was also
reported by others.10i41g Consistent with Solow and Kreiborg's (1977)
which
suggested the inhibition of the forward development of the nasomaxillarycomplex in mouth
breathers due to stretchmg of the fjlciel soft tissue layer, McNamara discussed the association
of maxillary retrusion in conjunction with excessive vertical development in his repon.' To
investigate this relationship, the anteroposterior maxillary position measurements, SNA, A
point to nasion perpendicular were related to the vertical dimensions, lower anterior face
height, facial axis, mandibular plane angle, and the angle between SN to mandibular plane.
The r values ranged fkom -0.37 to 0.15 (Table 5) and thus, do not support the relationship
between the mx&y retmion and excessive vertical development with this sample of Class
II malocclusions.
~ ~ sample
~ ' ~ of Class I1 malocclusion exhibited
Consistent with other ~ t u d i e s , this
longer Lower face height than the McNamaragscephalometric norm for this age, of 6062
mmw Similarly, the mean facial axis value was less, at 87.9". However, other vertical
measurements, mandibular plane angle and SN-GoGn angle were comparable to the
11
cephalometric mxms o f ~ c ~ a m a f a~ickettsfi
,"
and ~ i e d e l s These
. ~ Merences in various
cephalometric measurements demonstrated the variability due to different methods of
measurements. Interestingly, the lower face height pigwe 10) showed a tendency to
skewness toward the shorter lower f'hce height vatues (i.e. Lebard skewness; a median
value is greater thpn the mean value), while the kcid axis (Figure 11) demonstrated an
asymmetrical distniution pattern.
The mandibular incisors were more retruded by 1.5 m m than McNarnara's sample4
(+I .3 mm versus -0.16 mm with respect to A point-pogonion line). In contrast, maxillary
incisors with respect to A point-pogonion and A point vertical were remarkably similar but
slightly more protruded than McNamata's sample. The distribution patterns of incisor
positions were demonstrated in Figures 13-15. The majority of upper incisor positions to A
point-pogonion Line were closely distributed about the mean value of 8.62 mm ( 74.3% of
sample between values, 6.00 to 11.00 mm ), whereas the lower incisor positions were not
appeared to be normally distributed. The upper incisor to A point vertical appeared to be
normally distributed about the sample mean value of 5.95 mm.
The relative inaeases in protrusion of maxillary incisors and remsion of mandibular
incisors in Class I?malocclusion were partially due to the retruded mandible, which is causing
the posterior positioning of the A point-pogonion reference line.'
Similarly,a protrusive
maxilla will have the same relative effect as a retrusive mandiile. The size of anatomic
pogonion will also modify the position of A point-pogonion reference line. In a Class I1
malocclusion, a dimensionally large pogonion will place both the mandibular incisors and the
mdIary incisors in relatively more retrusive position.
12
Clinically, orthodontists have postulated that there may exist a relationship between
the constricted skeletal basal dimensiona d the iaaepse m lower anterior f-
height. Linder-
A.ronson3' described in detail, f m e s of adenoid f m in a typical mouth breather. These
subjects have changed their jaw, tongue a d head postures such that they exhibit a long lower
face height secondary to ova-enrpted posterior teeth, narrow maucilla, increased overjet,
clockwise (down and back) rotated mandible. In the present sample, the mean maxillary
width (JR-K)was 6321 mm and 81-25 mrn for the mean mandibular width (AG-GA). The
Rickett's P-A cephalometric analysip has values for the normal transverse dimensions for
maxilla (TR-JL) and mandible (AG-GA) at 61.9-62.5 mm and 76.1-77.5 mm for 9 to 10 years
old children, respectively. Therefore, the differences between mandibular base to maxillary
base are, 14.2 nunfor 9 years and 15.0 mm for 10 year n o d subjects. The mean dEerence
for the same rneesuremeats in this sample was 18.04 mm This large Merence may also be
due to a large m a n d i i width compared to a n o d maxillary transverse width. However,
Moyers' t e e has the normal bigonial width measurements for this age group as 92.13 to
94.60 mm for males and 88.50 to 90.61 mm for females. The bigonial width measurements
of the sample were 92.26 mm for males and 89.19mm for females, which were comparable
to Moyers' cephalometric norms.
Furthermore, the skeletal width ratios, maxillary
basaVrnandibular basal 1 (JR-JL/ AG-GA), for this sample of Class I1 malocclusion was
0.705 0.04 (Table 3). This ratio value is less than 0.73-0.74 reported by Ghafari et al."
They reported that this ratio may be more accurate indicator than the absolute differences
between maxillary and mandibular widths. Hence, this Class II sample had on average, a
constricted maxilla
The Pearson correlation d c i e n t values between the transverse maxilla
13
and mandibular dimensions to lower anterior face height were &om 0.40 to 0.46 (Table 6).
Thus,no clinicaUy significant conelation was present between the transverse dimensions and
lower anterior tkce height, at least in this sample.'
~ o y and
d other i n ~ e s t i g a t o f lhave
~ ' ~obsewed, in general, Class I1 patients
have smaller hces or components of craniofacid dimensions. The values for lower anterior
face height, maxillary and mandibular lengths were compared to published reports by
McNamara et
and an Rid0 et ala (TabIe 4). There were no significant differences for any
of the measurements of the sample of Class II malocclusions as compared to previous
reported data.24a Therefore, this study does not support the observations made by the
previous a~thors,~
4'3*'6" that the Class II malocclusions exhibit smaller dimensions, at least
with lower anterior face height, maxillary and mandibular lengths. However, all linear
dimensions for males were larger compared to females (Tables 2,3,4). This observation of
sexual dimorphism supports tindings of other
investigator^."'^
The Pearson correlation coefficients for maxillary length and mandibular length
measurements fiom condylion and articulare were 0.93 and 0.9 1, respectively (Table 7). Such
values are highly clinically significant,' and thus support the interchangeability of
measurements for maxillary and mandibular length measurements from candylion or
artidare. These values m higher than previously reported data by Foley and Mamandra~,~~
0.59 to 0.75 for Co-GniAr-Gn measurements at diierent age groups of Class I females.
Others have reported correlation values any where from 0. I6 to 0.64 by CoUins," 0.87 by
Pollard and Mamandras" and 0.70 to 0.87 by Love et al."
Finally, to examine if there was any difference between the skeletal Class 11
14
(ANB>4.S0) versus Class 1 skeletal with dental Class II relationships ("Pseudo Class ~ " 9 ,
the sample was divided into 2 subgroups (Table 8). The mean SNB measurements were
75-722.8"and 75.122.8" for skeletal Class 1and skeletal Class II subgroups, respectively.
The main difference between these 2 subgroups was not the position of the mandible but
rather the position of the maxilla with respect to anterior cranial base (SNA values of
78.7+3.2" for skeletal Class I and 81-9-12-7"
for skeletal Class LC). Similar observation was
reported by Blair," in comparing Class I versus Class II, Division 2 malocclusions with
respect to SNA measurement Furthermore, the A point was 2.53 mm fbrther posterior in
the skeletal Class I subgroup compared to skeletal Class II subgroup, with respect to nasion
perpendicularplane in this study. Other significant cephalometric differences between theses
two subgroups were; (i) the fUcia axis angle was greater, (ii) the mandibular plane angle was
smaller and (iii the upper incison were fUrther posteriorly positioned with respect to A pointpogonion line in skeletal Class I malocclusion-
It is abundantly clear that a great deal of variation exists among Class II type of
malocclusion. Detailed examinations, appropriate diagnosis and carefbl treatment planning
are of paramount importance. Treatment modalities should parallel and reflect the nature of
the Class II maloccIusions. A skeletal imbalance should be differentiated &om a dental
disharmony and only then can one plan appropriate treatment toward improving form and
hction.
Summanr and Conclusions
The purpose of this study was to investigatethe components of Class I1 malocclusion,
using lateral cephalometric radiographs fiom patients at the Graduate Orthodontic Clinic,
University of Western Ontario. The following obsewations and conclusions can be drawn
&om this investigation:
Extensive variations of the skeletal and the dental patterns were associated with Class
II malocclusion in this study.
The most significant component to Class II malocclusion was the mandibular
retrusion,
The distribution o f m d a y position was slightly more retrusive than protrusive in
this sample ofclass 11 malocclusion.
The vertical skeletal measurementswere slightly higher than the cephalometric norms
for this age group.
There were no correlations b e w e n maxillary or mandibular transverse dimensions
and lower anterior face height.
This study does not support the smaller tscial dimensions reported in previous studies
with respect to maxillary length, mandibular length and lower anterior facial height.
This study supports the sexual dimorphism in facial dimensions.
Clinically sigdicant correlations exist for m d a r y and mandibular length
measurements from articuIare or condylion and thus support the interchangeability of
these landmarks in these measurements.
Table 1
Standard errors of manual measurements
Measurements
Standam
of the mean
("1
=
0.1 1
(0)
0.08
SN-GoGn (")
0.14
A point to nasion perpendicular (mm)
0-34
pogonion to nasion perpendicular (mm)
t -01
lower anterior face height (mm)
0.15
mandibular plane angle (")
0-27
facial axis (0)
0.13
upper incisor to A point vertical (mm)
0-12
upper incisor to A point-pogonion(rnm)
0.19
lower incisor to A point-pogonion (mm)
0.25
condylion-A point (rnm)
0.18
artidare-A point (mm)
0.10
condylion-gnathion (mm)
0.14
artidare-gnathion (mm)
0.10
d a r y basal (IR-JL) (mrn)
0.25
mandibular basal 1 (AG-GA) (mrn)
0-44
mandibular basal 2 (GO-GO)(mrn)
0.26
Table 2
Lateral cepbatometric measurements and subgmap mcwunmeats by gender
SNA (O)
81.2
* 3.1
81.1
* 3.4
81.2
2.9
SNB (O)
75.3
2.8
75.1
3.0
75.4
2.7
SN-GoCn (O)
33.3 =t 5.2
32.9
5.2
33.6
5.2
Md Plane (O)
25.0
24.8
* 4.7
25.2
5.2
5.0
64.41
* 4.7St*
Table 3
M u i l l v g .ad mandibular transverse dimensions (ma) and
mean ratios between m a d b y basal to mandibuhr b u r l dimension;
total sample and subgraup measurements by gender
max basal
1-(
mand basal 1
(AC-CA)
maad basal 2
(GO-GO)
LAFH
(ANS-Me)
Total
n=40
8
Q
n=17
as23
63.21 4.14
64-40+ 3 -45
62.33
* 4.45
80.47
* 4.77
81.25
* 4.95
82.30
5- 14
90.50
* 5.32
92.26
* 5-57
66.3 1 5.33
67.73
5-28
0.70 0.04
*
0.70
0.04
0.70
0.05
* 0.04
0.78
* 0.04
0.78
0.05
*
89-19 4-83
65.26
5.24
I
mar bas&
mand basal 1
max basal
0.78
mand b a d 2
J~
Table 6
Pwsoa corrda@ioncoeffidents for mlrillrry and mandibular
tm~wversedimensions to lower anterior f.cc heigbts
I
LGE'EI
(ANS-Me)
max basal
1
-
(AG-GA)
-
I
KAB~~D)
-
Table 7
Comlrtionr between measurements fmm comdylion
and articdare to A point and gnathion
Subgroup measurements with angle ANB a 4.5' venus angle A N '> 4.S0
A to N L (mm)
Pg to N I (mm)
UI to A I (mm)
UI to A-Pg (mm)
LI to A-Pg (mm)
Ar-A (mm)
Ar-Gn (mm)
Co-Gn (mm)
Figurn I
Lateral cephalomenie landmarkr
Angulat mcisurements for
IateraI ctphalometric radiographs
1.
2.
3.
4.
5.
SNA
SNB
SN-GoGn
Mandibular plane angle
Facial axis
Figure 3
Linear meaSunments for
lateral cephalometric radiographs
I.
2.
ApoiattoN~
Pg to N L
3.
4.
5.
UI to A point vertical
UI to Apg
L I to Apg
6.
Ar-A point
7. Ar-Gn
8. Co-A point
9. Co-Gn
10. ANSMe
Figure 4
Frontal(postemanteriot) cephalonettic
landmarks with linear measurements
1.
2.
3.
M a r i U ~ yb u d (JR-JL)
Mandibular basal L (AGGA)
Mandibular basal 2 (GO-GO)
Figure 5
Dbtribution o f m a d a y position, measured with angle SNA
N = 105
Mean = 81.2'
S.D. = 3. lo
SNA
Figure 6
Distribution of muill.ry position, measured by
linear distance from nuion perpendicular to A point
A point to nasion perpendicular
Distribution of mandibular position, measured with angle SNB.
SNB
Distributionof mandibular position, measured by
linear distance fmm nrsion pvpcadiculv to B point
N = 105
Mean = -9.49 m m
S,D. = 5.29 m m
Pogonion to nasion perpendicular
Figure 9
Distribution of mandibulr position, measured by
the angle between Franklor&plane and mandibular plane
N = 105
Mean = 25.0"
S.D. = 5.00
Mandibular plane angle
Figure 10
DMbutioa of lincu vertical dimension,
N = 105
Mean = 65.77 mm
S.D. = 4.91 mm
Lower anterior face height
Figure 11
Distribution of mandibular position in v d d and
antemposterior dimensions, m&red by the posterior angle
between basion-nuiou p h e and pttrygomadhy-gnathion plane
Facial axis angle
Distribution of vertical mandibular position, measured by
the mgk betwan s&-nuion plant and mandibular plane
N= 105
Mean = 33.3'
S.D. = 5.2'
Angle between SN-GoGn
,l'n--T
Figure 13
Distribution of mmrilllry incisor position in anteroposterior dimension,
measured from A point vertical to most facial sudace o f maxillary incisor
N = LO5
Mean = 5.95 mm
S.D. = 2.23 m m
Figure 14
Distribution o f m u i l l v y incisor position in antemposterior position,
measured from A point-pogonion Uae to incM tip of muillmy incisor
N = 105
Mean = 8.62 mm
S.D. = 2.82 mm
Upper incisor to A-Pg line
Figure 15
Distributioa o f mandibular incisor position in anternposterior dimension,
measured from A point-pogonion line to inciul tip of mandibulu incisor
N = 105
Mean = 4.16 mm
S.D. = 2.46 mm
Lower incisor to A-Pg line
Appendix A
Definition o f landmarks, angles and planes utilized
Nasion (N):
Thejunction ofthe t i o n t o d suture at the most posterior point on the
curve of the bridge of the nose.
PterygomaxiUaty The intersecfion of the inferior border offoramen rotundurn with the
posterior w d of the pterygomaxillary fossa.
Point (Pt):
A Point (A):
The point in the median sagittal plane where the lower fiont edge of the
anterior4 spine meets the &ont wall of the maxillary alveolar process.
B point (B):
The deepest midline point on the mandible between idadentale and
pogonion.
Pogonion (Pg):
The most anterior point on the symphysis of the mandible in themedian
plane determined by a line fiom nasion tangent symphysis.
Gnathion (Gn) :
The most anterior and iaferior point on the contour of the bony chin
symphysis. Determined by biseaing the angle fonned by the mandibular
plane and a line through nasion to pogonion.
Menton (Me):
The most inferior point on the symphysis of the mandiile in the median
plane.
Gonion (Go):
The external angle of the mandible, located on the lateral and P-A
cephafograms by bisecting the angle formed by tangents to the posterior
border of the ramus and the Senor border of the mandible.
Merior
Gonion (I-):
A point at a tangent to the inferior border of the mandible near gonion.
The lowest point on the anterior margin of the foramen magnuqon the
midsagittal plane.
Anterior Nasal
Spine (ANS):
The most anterior position of the maxilla at the lower margin of the
anterior aperture of the nose.
Porion (Po):
The most superior point of the bony external auditory meatus.
Condylion (Co): The most superior posterior point of the average of the tight and left
condylar head.
Upper lacisor
Tip 0:
The incisal tip of the d q central incisor.
Lower Incisor
Tip O:
The incisal tip of the mandibular central incisor.
Upper Incisor
Apex (UIA):
The root apex of the maxillary central incisor. If root formation
is not complete,then the midpoint ofthe fomriag root is used.
Lower Incisor
Apex (LLA):
The root apex of the mandibular central incisor. If root formation
is not complete, then the midpoint of the fonning root is used.
Orbitale (Or):
The lowest on the average ofthe right and left borders of the bony orbit.
Posterior Nasal
Spine (PNS):
The most posterior point of the bony hard palate.
The point of intersection of the inferior cranial base sUTface and the
averaged posterior surfhces of the mandibular borders.
SeUa Turcica (S): The centre of the pituitary fossa of the sphenoid bone.
Jugale
Bilateral points on the jugal process at the intersection of the
outline ofthe tuberosity of the maxilla and the zygomatic buttress.
Antegonion
(AG,GA):
The deepest point of the antegonial notch.
(JWu:
Andes
SNA:
The angle formed by the points S, N and A.
SNB:
The angle formed by the points S, N and B.
Facial Axis:
The posterior inferior angle formed by the intersection of basionnasion plane facial axis plane (Pt-Gn).
The angle formed by the points A, N and B.
The angle formed by the intersection ofthe S-Nplane and the
Go-Gn plane.
Mandibular
Plane Angle:
The angle formed by the intersection of the Frankfort plane and
the Go-Gn plane.
Frankfort Horizontal:
A line joining porion and orbitale.
A line joining basion and nasion.
Facial Axis:
A Line joining pterygoid point and gnathion
Mandibular Plane:
A line joining menton and inferior gonion.
A line joining sella and nasion.
Lower Anterior
A line j o h g anterior nasal spine and menton.
Face Height:
Mandibular (# 1)
Length (Co-Gn):
A linejoining condylion to gnathion.
Mandibular (#2)
Length (Ar-Gn) :
A linejoining articulare to gnathion.
M a r y (#1)
Length (Co-A):
A linejoining condylion to A point.
Maxillary (#2)
Length (Ar-A):
A line joining hculare to A point.
M d a r y Basal
Width (JR-JL):
A line joining J(R) to J(L).
Mandibular Basal 1
Width (AG-GA):
A linejoining AG-GA
Mandibular Basal 2
Wldth (GO-GO):
A Linejoining Go@)-Go&).
Appendix B
Cepbdometric norms from various anrlyse-'
Measurtments
SNA (0)
SJVB("1
SN-GOGn (O)
A point to mion perpendicular (mm)
pogonion to nasion perpendicular (mm)
lower fjlce height (mm)
mandibular plane angle (0)
facial axis (")
upper incisor to A point vertical (mm)
upper incisor to A point-pogonim (am)
lower incisor to A poiat-pogonion (mm)
condylion-A point (mm)
articulare-A point (mm)
condylion-gnathion (mm)
artidare-gnathion(mm)
max basal (JR-JL) (mm)
maad basal 1 (AG-GA) (mm)
mand basal 2 (Go-Go) (mm)
Normal values
List of individuals inthe sample fiom the Graduate Orthodontic Clinic. UWO
Lateral cephalometric radiographs N=105
Chart numbers
P-A cephalometric radiographs N=40
Chart numbers
139
175
351
386
467
497
644
696
1105
1466
148
181
354
395
472
499
654
701
1309
1493
150
233
357
449
482
SO5
664
741
1395
1518
151
244
382
464
495
542
691
996
1463
1626
I
,
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