10.5005/jp-journals-10021-1039
ORIGINAL ARTICLE
Rohit Khanna et al
Position and Orientation of Hyoid Bone in Class II
Division 1 Subjects: A Cephalometric Study
1
Rohit Khanna, 2Tripti Tikku, 3VP Sharma
ABSTRACT
Objective: The present study was undertaken to compare the pharyngeal dimensions in Angle’s Class I normal and Angle’s Class II division
1 samples, and to correlate it with the dentoskeletal parameters in both the groups.
Materials and methods: The sample consists of 92 pretreatment lateral cephalogram, which were categorized into two groups, Group A
and Group B, that they should present Angle’s Class I and Angle’s Class II molar relationship. Each group consists of 25 males and 21
females. Descriptive statistics for 14 variables were calculated. Results obtained from this study imply that Angle’s Class II Division 1
samples with retrognathic mandible showed an inferoposterior displacement of hyoid bone.
Results: The positional alteration of hyoid was prevalent in skeletal malrelationship rather than dentoalveolar malocclusion. The anteroposterior
dimension of pharynx at hyoid level was more in males than in females, and it was relatively less in Angle’s Class II Division 1 samples to
Class I samples. No significant sexual dimorphism exists in angular measurements of hyoid positioning.
Keywords: Hyoid bone, Dentofacial Pattern, Facial morphology, Pharyngeal dimension.
How to cite this article: Khanna R, Tikku T, Sharma VP. Position and Orientation of Hyoid Bone in Class II Division 1 Subjects: A
Cephalometric Study. J Ind Orthod Soc 2011;45(4):212-218.
INTRODUCTION
Attempts have been made to visualize the position of hyoid
bone in various dentofacial patterns.1-5 In almost all previous
studies, hyoid bone was related to the cranium, due to which a
great variability was observed in its position even on slight
movement of the head. To minimize the variability in its position,
Bibby1 in 1981, related the hyoid bone to mandibular symphysis
and third cervical vertebra in individuals with Class I
malocclusions.
Precise measurement of hyoid bone position by cephalometric means is considered difficult. Graber2 stated that slight
variations in head position in the cephalostat, the postural
position of the spine, and the state of function all affect the
position of the hyoid bone. Stepovich3 reported that when
roentgenograms of the same person were taken at different time
intervals, the hyoid bone was found to be positioned differently
in each film. Ingervall and associates4 believe that Stepovich
exaggerated the lack of precision in recording the hyoid bone
1
Professor, 2Professor and Head, 3Former Head and Ex-Dean
1,2
Department of Orthodontics and Dentofacial Orthopedics
Uttar Pradesh Dental College and Research Centre, Lucknow
Uttar Pradesh, India
3
Department of Orthodontics, Faculty of Dental Sciences, Chhatrapati
Shahuji Maharaj Medical University, Erstwhile King George’s Medical
College, Lucknow, Uttar Pradesh, India
Corresponding Author: Rohit Khanna, Professor, Department of
Orthodontics and Dentofacial Orthopedics, Uttar Pradesh Dental
College and Research Centre, Lucknow, Uttar Pradesh, India
e-mail: rohitkhanna@doctor.com, rohitkhanna.dr@gmail.com
Received on: 5/11/11
Accepted after Revision: 10/11/11
212
position, although they admit that the hyoid position will vary
even under standard conditions. King5 noted that changes in
head position lead to changes in the position of the hyoid bone
in the same person. If the head is extended back, then the hyoid
bone moves back; if the head is tipped forward, then the hyoid
bone moves forward. This confirmed the postulate of Negus6
who found that the hyoid bone to elevate when the head was in
dorsiflexion and to move down when the head was in
ventriflexion. Ingervall7 found a positive correlation (although
not always significant) between the anteroposterior distance
between retruded contact and intercuspal positions of the
mandible and the vertical movement of the hyoid bone between
these positions. In another study, Ingervall7 compared the hyoid
bone positions when the mandible is in intercuspal position
and when it is in postural position. He found that the hyoid
bone was higher in postural position than in intercuspal position.
Brodie8 brought attention to the suprahyoid muscles which
suspend the hyoid bone, the larynx, the pharynx, and the tongue,
since these muscles are attached at or near the symphysis of
the mandible, it follows that, should the hyoid bone passively
follow the course of the chin, all of the above structures would
fall back and thus tend to shut off the airway. This is prevented
by shortening of the suprahyoid muscles. Grant9 studied the
position of the hyoid bone in Class I, II and III malocclusions.
He concludes that the hyoid bone position is constant in all
three classes and that the position of the hyoid bone is
determined by the musculature and not by the occlusion of the
teeth.
Durzo and Brodie10 showed that the relationship between
the hyoid bone and the mandible is maintained from the age of
3 years. According to them the hyoid bone is positioned at a
level opposite to the lower portion of the third cervical vertebrae
and the upper portion of the fourth cervical vertebrae. Its
anteroposterior position, it is dependent on the relative lengths
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Position and Orientation of Hyoid Bone in Class II Division 1 Subjects: A Cephalometric Study
of the muscles running to it and also on gravity acting on the
larynx. Bench11 found that the hyoid bone gradually descends
from a position opposite the lower half of the third and the
upper half of the fourth cervical vertebrae at the age of 3 years
to a position opposite the fourth cervical vertebrae in adulthood.
King5 found that the distance between the hyoid bone and the
cervical vertebrae is constant until puberty, when the hyoid bone
moves slightly forward. Bibby1 postulated that since hyoid is
not related to cranial reference plane (as in all previous studies)
the incorrectness stem from changes in head postures is
minimized. Apart from establishing norms for the hyoid triangle,
he found that bony pharynx at the level of PNS and hyoidale to
have the same anteroposterior dimension with 0.98 coefficient
of correlation. He did not find any sexual dimorphism in hyoid
position. Bibby RE12 found that hyoid bone has a stable position
and is independent of any posture alterations due to tonguethrusting or mouth breathing.
Haralabakis et al13 strongly suggest that hyoid bone moves
in close conjunction with the pharynx, cervical spine, and
mandibular plane in patients with entirely different skeletal
patterns.
Erdinc et al 14 found that hyoid bone location in the
hypodivergent group was not changed vertically, however, it
had more of a posterior placement with the increase of Pg-H
distance. Bucchieri15 investigated that the altered hyoid bone
position may influence tongue position and upper airway
patency of OSA patients. Ferraz16 concluded that the hyoid bone
keeps a stable position, probably in order to secure correct ratios
in the airways, and it does not depend on the respiratory pattern.
Pae17 investigated that changes in hyoid position over time were
significant in dolichofacial subjects but not in brachyfacial
subjects.
Ritu Duggal et al18 concluded that the anteroposterior
position of the hyoid bone was more forward in subjects with
short face syndrome and the vertical position of the hyoid bone
was comparable among subjects with different vertical jaw
dysplasias and axial inclination of the hyoid bone closely
followed the axial inclination of the mandible.
The present study was undertaken to compare the pharyngeal
dimensions in Angle’s Class I normal and Angle’s Class II
division 1 samples, and to correlate it with the dentoskeletal
parameters in anteroposterior dimension irrespective of facial
divergence and to find the role of sagittal mandibular positioning
in hyoid bone position.
1. Group A: Subjects having Angle’s Class I molar relationship
with ideal occlusion, and no significant abnormalities in
the vertical dimension of facial form. This group comprised
of 25 male and 21 female subjects from the records of
control group of previous conducted studies.
2. Group B: Subjects having Angle’s Class II division 1
malocclusion. This group comprised of 25 male and 21
female subjects from the patients reporting at the
Department of Orthodontics, King George’s Medical
College, Lucknow.
The subjects of entire sample mentioned above fell in the
age group of 16 to 24 years, with the mean age of 18 years for
females and 20 years for males.
METHODS
The following osteometric landmarks were used in the present
study (Fig. 1).
1. Nasion (N)
2. Sella (S)
3. Articulare (Ar)
4. Gonion (Go)
5. Menton (Me)
6. Capitulare (C): Center of the head of the condyle
7. Xi: Geometrically determined centroid of the ramus
8. Pt. D: Located by inspection as the center of body of the
mandibular symphysis seen on lateral cephalogram.
MATERIALS AND METHODS
The present study was based on lateral cephalograms of 92
individuals selected on the conviction that they should present
Angle’s Class I and Angle’s Class II molar relationship. The
cephalograms for the purpose were obtained from records
maintained in the Department of Orthodontics, Faculty of Dental
Sciences, King George’s Medical College, Lucknow, India.
The cephalograms of the subjects were categorized into the
following two groups:
Fig. 1: Osteometric landmarks
The Journal of Indian Orthodontic Society, October-December 2011;45(4):212-218
213
Rohit Khanna et al
9. C3: The point at the most inferior anterior position on the
third cervical vertebra.1
10. Hyoidale (Hy): The most superior, anterior point on the
body of the hyoid bone.1
11. AA’: The most anterior point on the body of the atlas
vertebra, seen on the lateral cephalogram.1
12. PNS
13. Subspinale (Point ‘A’).
For the location of point ‘C’, a ‘template’ with concentric
circles on a graph was designed on the basis of geometric
visualization. The circle which most nearly coincided with the
perimeter of condylar head was superimposed and the geometric
center of condyle was located. Similarly, for the location of
‘point D’, the inner cortical plate was traced and the center of
this circumscribed area was located with the help of the
‘template’.
For the linear and angular measurements, a scale and
protractor were used and readings were recorded to the nearest
of 0.5 mm and half degree respectively. Tracings of the
cephalograms of each group were repeated after an interval of
2 weeks and both sets of measurements were subjected to
t-test. p-value was found to be 0.1, i.e. significant for all the
measurements, signifying that the location of the points and
lines were correct.
MEASUREMENTS
Following five linear and seven angular measurements were
analyzed:
Linear Measurements (in mm)
1. Sella-Nasion (S-N)—it is drawn from selected point Sella
to Nasion. It represents the anterior-posterior latent of the
anterior cranial base.
2. Capitulare-Xi (C-Xi)—line connecting center of condyle,
i.e. capitulare to the geometric center of the ramus of
mandible, i.e. Xi. This line will be named as Capitulare
axis in this study.
3. C3-Hy(C3-Hy)—formed by joining most inferior-anterior
point on the third cervical vertebrae to most superior,
anterior point on the hyoid bone.1
4. Hyoidale-Pt. D (Hy-D)—line connecting most superior
anterior point on the hyoid bone to center of mandibular
symphysis.
5. AA’-PNS—line adjoining the most anterior point on body
of atlas vertebrae and posterior nasal spine designating
upper bony nasopharynx.1
Angular Measurements (in degree)
1. Saddle angle (NSAr)—the angle formed by joining Nasion,
Sella and Articulare is an assessment of the relationship of
anterior and posteriolateral cranial base.
2. Articulare angle (SArGo)—the angle is constructed by
joining sella, articulare and gonion.
3. Gonial angle (ArGoMe)—the angle formed by tangents of
body of the mandible and posterior border or ramus.
214
4. SNA—the angle formed with sella nasion plane and the
line joining nasion and point A.
5. SND—the angle formed between sella-nasion plane and
nasion-point D plane.
6. Hyoidale angle (C3HyD)—the angle formed by C3 to
Hyoidale plane and Hyoidale Pt. D. The angle formed
superiorly by two planes is read as hyoidale angle.
7. Hyoid plane angle—formed by intersection of long axis of
greater horn of hyoid with C3-Pt. D line.
RESULTS
The data obtained by the linear and angular measurements from
tracings of lateral cephalograms was subjected to statistical
analysis. The arithmetic means and standard deviations of the
linear and angular measurements are given in Table 1.
The Hy-D dimensions does not reveal any statistically
significant changes between the Groups A and B both in male
and female samples. In Table 2, the significance of difference
(t-value) of angular and linear measurements in Group A and
Group B has been depicted.
Referring to Table 1, the differences in means show the
C3-D is lesser in Group B. In Table 3, the anteroposterior
measurements of pharynx (C3-Hy) showed highly significant
difference between males and females in both the groups.
The highly significant change was observed in hyoidale
angle due to the inferiorly positioned hyoid bone in Group B to
Group A (Table 2). Thus, it was decided to correlate the hyoidale
angle to certain angular measurements contributing to Class II,
division 1 tendencies (Tables 4 and 5).
The angle SND-relating mandible to the cranium showed a
very highly significant coefficient of correlation to hyoidale
angle both in males and females in Group A (Table 4), and a
high level of significance in Group B (Table 5), confirming
that distally positioned mandible contributes mainly to the
inferior drop of hyoid bone.
The angle SNA shows significant correlation in Group A
(Table 4) in both males and females, while no significant
correlation was observed in Group B (Table 5). This showed
that the Class II, division 1 relationships in the given sample
were due to a retruded mandible rather than the procumbency
of the maxilla (Fig. 2).
The saddle angle (NS Ar) and articulare angle (S Ar Go)
showed low level negative correlation to hyoidale angle in
Group A (Table 4) and Group B (Table 5). The negative
correlation indicates that with increase in saddle angle and
articulare angle there is simultaneous decrease in hyoidale angle
in Groups A and B (Table 5). The gonial angle showed no
significant correlation in Groups A and B (Tables 4 and 5) for
both males and females (Fig. 2).
The hyoid plane angle (posterior superior angle between
long axis of greater horn of hyoid and C3-D line) when correlated
to hyoidale angle (C3HyD) showed a negatively high level of
significance, i.e. with the decrease in the hyoidale angle
(C3HyD) there was simultaneous increase in hyoid plane angle.
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Position and Orientation of Hyoid Bone in Class II Division 1 Subjects: A Cephalometric Study
Table 1: Arithmetic means and standard deviations of angular and linear measurements
Sl. No.
Variables
Group A
Males (n = 25)
Mean
SD
Group B
Females (n = 21)
Mean
SD
Males (n = 25)
Mean
SD
Females (n = 21)
Mean
SD
Angular measurements (in degree)
C3HyD
SNA
SND
NSAr
S-Ar-Go
Ar-Go-Me
Hyoid plane angle
1.
2.
3.
4.
5.
6.
7.
178.36
81.28
76.70
125.88
141.00
120.32
16.90
8.38
2.86
2.61
3.37
5.19
5.55
8.38
180.80
78.81
75.76
128.48
139.05
124.62
22.00
9.38
3.36
2.33
5.95
6.94
5.44
9.25
158.50
81.40
73.40
128.12
139.84
119.70
21.72
16.30
3.45
3.67
4.43
6.42
5.23
9.82
155.57
78.50
70.85
127.47
142.33
127.10
28.12
12.07
3.87
3.40
6.69
5.76
5.79
12.45
Linear measurements (in mm)
1.
2.
3.
4.
5.
6.
7.
C3Hy
AA’-PNS
S-N
C-Xi
C3Hy:HyD
HyD
C3D
37.48
35.06
71.84
38.12
0.858
44.06
81.98
4.19
4.35
3.95
2.85
0.11
6.42
9.21
32.02
33.40
69.57
34.05
0.78
41.05
75.17
2.78
3.03
3.44
3.49
0.12
5.05
6.16
36.30
35.12
72.46
38.18
0.82
44.16
76.89
3.83
3.91
3.54
2.76
0.136
6.01
9.30
32.88
33.95
69.67
33.62
0.818
40.20
68.12
3.66
3.17
3.65
2.61
0.21
7.68
8.92
Table 2: Mean difference of measurements in Groups A and B and their level of significance
Sl. No.
1.
2.
3.
4.
5.
6.
7.
8.
Measurements
Males (n = 25)
Females (n = 21)
Mean difference
t-value
p-value
Mean difference
t-value
p-value
19.86
1.18
0.06
0.036
0.1
5.09
0.62
0.06
5.43
1.41
0.055
1.028
0.057
1.95
0.58
0.07
***
NS
NS
NS
NS
*
NS
NS
25.24
0.86
0.55
0.038
0.85
7.05
0.1
0.38
7.56
0.84
0.57
0.72
0.32
2.98
0.08
0.41
***
NS
NS
NS
NS
C3HyD (in degree)
C3-Hy (in mm)
AA’-PNS (in mm)
C3Hy:HyD (in mm)
Hy-D (in mm)
C3D (in mm)
S-N (in mm)
CXi (in mm)
NS
NS
*p < 0.05: Significant; ***p < 0.001: Very highly significant; NS: Not significant
Table 3: Mean difference of measurements in Groups A and B and their level of significance
Measurements
Males (n = 25)
C3Hy (in mm)
AA’-PNS (in mm)
C3HyD (in degrees)
Hyoid plane angle (in degrees)
Mean
difference
t-value
5.48
1.66
2.44
5.10
4.76
1.51
0.97
1.92
Females (n = 21)
p-value
**
NS
NS
NS
Mean
difference
t-value
3.92
1.17
2.94
6.50
3.54
1.07
0.70
1.92
p-value
**
NS
NS
NS
**p < 0.01: Highly significant; NS: Not significant
Table 4: Coefficient of correlation ‘r’ of angle C3-HyD with following angular measurements in Group A and their level of significance
Sl. No.
Angular measurements
Sex
‘r’
p-value
1.
SND
Male (n = 25)
Female (n = 21)
0.798
0.703
***
***
2.
SNA
Male
Female
0.445
0.573
*
**
3.
N-S-Ar
Male
Female
–0.034
–0.116
NS
NS
4.
S-Ar-Go
Male
Female
–0.172
–0.164
NS
NS
5.
Ar-Go-Me
Male
Female
0.04
0.19
NS
NS
6.
Hyoid plane angle
Male
Female
–0.687
–0.59
**
**
*p < 0.05: Significant; **p < 0.01: Highly significant; ***p < 0.001: Very highly significant; NS: Not significant
The Journal of Indian Orthodontic Society, October-December 2011;45(4):212-218
215
Rohit Khanna et al
Table 5: Coefficient of correlation ‘r’ of C3-Hy (in mm) with following
linear measurements in Group A and their level of significance
Sl. No.
Linear measurements
1.
AA’-PNS
2.
S-N
3.
C-Xi
Sex
‘r’
p-value
Male
Female
Male
Female
Male
Female
0.85
0.71
0.41
0.51
0.35
0.23
***
***
*
*
NS
NS
*p < 0.05: Significant; ***p < 0.001: Very highly significant; NS: Not significant
Table 6: Coefficient of correlation ‘r’ of C3Hy (in mm) with following
linear measurements in Group B and their level of significance
Sl. No.
Linear measurements
1.
AA’-PNS
2.
S-N
3.
C-Xi
Sex
‘r’
p-value
Male
Female
Male
Female
Male
Female
0.55
0.49
0.25
0.35
0.175
0.22
**
*
NS
NS
NS
NS
*p < 0.05: Significant; **p < 0.01: Highly significant; NS: Not significant
Fig. 2: Difference in facial morphology in normal and
Class II div 1 malocclusion
This value of hyoid plane angle was found in bxoth males and
females (Tables 4 and 5) (Fig. 2).
The anteroposterior dimension of pharynx (C3-Hy) was
further correlated with linear measurements (Table 6). When
correlated with AA’-PNS it revealed a very highly significant
level in Group A both in males and females, indicating that the
hyoid bone represents the anterior bony boundary of the pharynx
at a lower level. While the drop in level of coefficient of
correlation was observed in Group B, which was probably due
216
to change in dimension of either C3-Hy or AA’-PNS, but on
visualizing the significance of difference in means of AA’-PNS
(Tables 1 and 2) it was observed to be statistically not significant
between Groups A and B, i.e. change was probably due to
decrease in anteroposterior dimension of C3-Hy in Group B.
Similarly, when C3-Hy was correlated to S-N plane and
C-Xi, it was found that level of correlation changes from
Group A to Group B. The mean difference of S-N and C-Xi
amongst the groups was negligibly small (Table 1), indicating
the probable changes in C3-Hy dimension.
Referring to Table 2, the low level of significance in the
mean difference of C3-Hy in Group A and B was observed.
Although the t-value was statistically nonsignificant but the
difference in values establishes that change exists in
anteroposterior dimension of C3-Hy in Group A to Group B.
DISCUSSION
Whenever vital functions of respiration and deglutition are
imposed upon by morphological alteration, the compensations
in morphology and physiological activities are integrated upon
modification in neurological pathway. This discussion will deal
mainly with the variations in mandibular morphology and
concurrent changes in associated structures in Class I subjects
and subjects with Angle’s Class II division 1 malocclusion.
Hoffman and Hoffman19 believed that the hyoid bone was
important for tongue position, since most of the extrinsic
muscles of the tongue are attached to it and it also maintains
the pharyngeal airway, which is essential to life. It was found
that the positioning of hyoid was variable in Class I and Angle’s
Class II division 1 malocclusion. To evaluate the shift of hyoid
and its effect on the patency of airway, the anteroposterior
dimension of pharynx (C3-Hy) was compared with upper bony
airway (AA’-PNS). It was observed that coefficient of
correlation was lesser in Class II division 1 samples than in
normal subjects (Fig. 2). The slight decrease (statistically
nonsignificant) in anteroposterior dimension of pharynx at level
of hyoid. The probable reason for this decrease was the posterior
movement of hyoid bone as mandible attains distal position in
Class II division 1 sample. The patency of the airway is to be
maintained for the survival, hence the further posterior
displacement of hyoid was resisted.
To compare the relative change in distance of hyoid to
cervical vertebrae (C3-Hy) and hyoid to center of mandibular
symphysis (Hy-D) in Class I and Class II division 1 samples.
The ratio (C3Hy: HyD) was calculated for each sample and
subjected to statistical analysis, which showed no significant
difference in means (Table 2) was observed. While the distance
between cervical vertebrae and mandibular symphysis (C3-D)
was significantly decreased in samples with Class II division 1
malocclusion (Tables 1 and 2). The position of hyoid was altered
in order to accommodate the muscles geniohyoid and anterior
belly of diagastric, which could be the probable reason for
posterior displacement of hyoid and slight decrease in C3-Hy
dimension. The decrease in C3-Hy was not sufficient to
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Position and Orientation of Hyoid Bone in Class II Division 1 Subjects: A Cephalometric Study
accommodate the hyoid and hence the change was expected in
either superior or inferior direction. It was further noticed that
the angle formed by C3-Hy line and Hy-D (C3HyD-Hyoidale
angle) superiorly at the hyoid decreases in Class II division 1
subjects indicating the inferior positioning of the hyoid bone.
The very highly statistically significant difference in hyoidale
angle (C3HyD) was noticed among Class I normal and Angle’s
Class II division 1 samples (Table 2). Grant9 also reported the
difference in hyoid bone position, and found hyoid bone was
higher in Class III than in Class II subjects in relation to cervical
vertebrae.
It was observed that retrognathic mandible leads to inferioposterior displacement of hyoid bone. This inferior-posterior
displacement of hyoid might affect the tongue posture in oral
cavity and stretching of the pharyngeal wall, because hyoglossus
muscles and middle constrictor muscles of pharynx take their
attachments on greater horn of hyoid bone.
The hyoidale angle was also correlated to angle SNA
showed a significant correlation in Class I normal subjects, while
in Class II division 1 samples it was statistically not significant
(Tables 4 and 5). The above findings showed that Class II
division 1 tendency of samples in the present study was due to
mandibular retrusion rather than maxillary procumbency. Two
of the samples revealed the higher positioning of hyoid similar
to that found in Class I normal subjects. On further investigation,
the Class II division 1 tendency in those samples was due to
maxillary procumbency rather than distal mandibular
positioning. It was thus interpreted that for change in position
of hyoid it was necessary that the subjects should possess
retrognathic mandible.
Increase in saddle angle (NSAr) and articulare angle
(SArGo) leads to retrognathic mandibular pattern. On
correlating these angular measurements to hyoidale angle, they
showed statistically insignificant negative correlation in Class I
normal subjects and Class II division 1 samples (Tables 4 and 5).
The gonial angle (ArGoMe) showed no significant correlation
with hyoidale angle in both the Classes (Tables 4 and 5). These
findings strengthens the fact that the skeletal malrelationship
causes the change in hyoid position, i.e. sagittal malformation
has highly significant role in inferoposterior positioning of hyoid
bone.
The possible explanation for the low level correlation of
saddle angle to hyoidale angle is that, large saddle angle is
compensated with a change in articulare angle and length of
ramus. While the articulare angle apart from affecting the
anteroposterior positioning of mandible, also changes in closing
and opening of bite. In Class II division 1 malocclusion, the
distal mandibular position increases the articulare angle, while
the deep overbite compensate this increase resulting in a
relatively less change in articulare angle.
The hyoid plane angle (long axis of greater horn of hyoid
to C3-D line). When correlated with hyoidale angle (C3HyD)
revealed a highly significant negative coefficient of correlation
(Tables 4 and 5). The increase in hyoid plane angle with an
inferior drop of body of hyoid in Class II division 1 malocclusion
was noticed, thereby maintaining the relative length of middle
constrictor muscle of pharynx and hyoglossus muscle, which
takes its attachments on greater horn of the hyoid bone.
However, the decrease in hyoidale angle was to accommodate
geniohyoid, anterior belly of diagastric and mylohyoid muscles.
The slight posterior displacement is justifiable due to stylohyoid
muscle and ligaments attached to the body of hyoid, which pulls
the hyoid bone posteriorly when it is displaced inferiorly,
encroaching upon pharyngeal space in Class II division 1
subjects, resulting the decrease in anteroposterior dimension
of pharyngeal space.
The anteroposterior linear dimension of pharynx (C3-Hy)
showed a marked sexual dimorphism. The highly significant
values of difference in means in both Class I and Class II subjects
were observed (Table 3). The anteroposterior dimension was
found more in males than in females (Table 1) as also observed
by King, EW.5 His roentgenographic study of pharyngeal
growth, revealed an increase of 7.8 mm in males and 2.3 mm in
females between three months and sixteen years of life. While
AA’-PNS showed statistically no significant changes in males
and females. Though small difference in means was observed
in AA’-PNS both in normal and Angle’s Class II division 1
malocclusion.
The hyoid plane angle and hyoidale angle revealed no
statistically significant difference in means amongst males and
females both in Class I normal subjects and Class II division 1
malocclusion (Table 3). Bibby1,12 also observed the lack of
sexual dimorphism, in hyoid plane angle.
Hence, it could well be concluded that slight change in linear
dimension of pharyngeal space at the level of hyoid occurs in
skeletal Class II division 1 malocclusion. The change was due
to the inferior-posterior displacement of hyoid, the position of
which is governed by certain skeletal parameters of dentofacial
complex. Furthermore, sexual dimorphism exist in C3-Hy linear
measurement, but the angular measurement hyoidale angle and
hyoid plane angle did not reveal marked difference in male and
female samples.
CONCLUSION
The following conclusions were drawn:
1. Angle’s Class II division 1 samples with retrognathic
mandible showed an inferoposterior displacement of hyoid
bone.
2. The positional alteration of hyoid was prevalent in skeletal
malrelationship rather than dentoalveolar malocclusion.
3. The anteroposterior dimension of pharynx at hyoid level
was more in males than in females, and it was relatively
less in Angle’s Class II division 1 samples to Class I samples.
4. No significant sexual dimorphism exists in angular
measurements of hyoid positioning.
The Journal of Indian Orthodontic Society, October-December 2011;45(4):212-218
217
Rohit Khanna et al
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