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doi: 10.1013/IJCO/1701-0005
International Journal of Contemporary Orthodontics
Original Research
The Hyoid Triangle: Importance and Evaluation of normalcy
in different skeletal malocclusions in the Indian Population.
Nakul R Raval1, Jee-Hun Kim1, Amol S Patil2
1
2
Interns, Bharati Vidyapeeth Dental College and Hospital, Pune, India
Professor, Department of Orthodontics and Dentofacial Orthopedics, Bharati Vidyapeeth
Dental College and Hospital, Pune, India
Abstract
OBJECTIVE : The aim of the study was to investigate the normalcy of the hyoid triangle in the Indian Population and
compare the relationship of the hyoid triangle with the different skeletal malocclusion.
MATERIALS AND METHODS: A total of 60 pretreatment digital lateral cephalograms were selected according to the
criteria and grouped into 3 groups, group 1: Class I (n=20), group 2: Class II (n=20) and group 3: Class III(n=20).
Lateral cephalograms were traced and analysed on basis of the hyoid triangle i.e. the following linear and angular
measurements were recorded: C3-H, C3-RGn, H-RGn, H-H’, Angle H, AA’-PNS. The arithmetic mean and standard
deviation values were calculated for each measurement. Independent sample t- test was performed to compare the
difference between the skeletal classes. Statistical tests were performed.
RESULT: The normalcy of the different readings were established by statistically finding the mean and the standard
deviation. The normalcy shows similar reading shown in different studies in Non-Indian population. The linear
measurements of H-C3 and C3-RGn showed statistically significant differences in Class I, Class II, and Class III (pvaule=0.07 and 0.011 respectively). The angular measurements of Angle H was also statistically significant (pvalue=0.002) indicating the differences in respective class malocclusions. However, H-H’, H-RGn and AA’-PNS
showed no significant statistical difference in the groups.
CONCLUSION: The importance of the Hyoid triangle is established and shows the three dimensional use of this
analysis and the reliability of the statistics. The normalcy is set by statistical analysis and the standard values are given
for the dimensions of the hyoid triangle in the Indian Population. The bony pharynx at the level of the PNS and hyoidale
was found to have statistically similar anterioposterior dimensions.In Skeletal Class III or prognathic mandible the
hyoid is placed more anteriorly. In Skeletal Class II the hyoid is placed more posteriorly. Anterior Posterior relation by
C3-H remains to be very constant with the least deviation.
Introduction
The complexity of the stomatognathic system is so high that a
brief but specific knowledge of the anatomy, physiology and
cranofacial growth theories is both necessary and indispensable
for understanding the complexity. The evolution of the upright
posture and the bipedal walking has been associated with
notable changes that characterise many human bones and
Correspondence: Amol S Patil, PhD, Professor, Department of
Orthodontics and Dentofacial Orthopedics, Bharati Vidyapeeth
University Pune
Email [email protected]
muscles.[1] The hyoid bone is one such variety in the path of
evolution that unlike other mammals is in unison with the larynx
and hence give us the ability to talk.[2] However, it has a unique
structure in man, unlike all other bones of the head and neck, the
hyoid has no bony articulations.[3] The hyoid bone presents
approximately as a horseshoe-shaped bone, located in the
midsagittal plane of the neck, just inferior to that mandible and
above the thyroid cartilage. The bones forming the adult hyoid
are the unpaired body, the paired greater horns (thyrohyals).[4]
Developmentally, the hyoid bone is part of the pharynx, with the
inferior half of the hyoid body and the greater horns originating
Patil et al.
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form the third pharyngeal arch and the superior half of the hyoid
The hyoid triangle employs the planes between the third cervical
body and the lesser horns arising from the second pharyngeal
vertebrae and the mandibular symphysis which markedly
arch.[5] Two major
group of muscles, the suprahyoid and
reduces the effects of the varied cranial base points/reference
infrahyoid attach to the hyoid bone. The digastric muscles
points and hence eliminated the variation that may be caused
increases the anteroposterior dimensions of the oropharynx
due to head posture. The triangle is formed by the joining of 3
during deglutition, whereas the posterior belly of the digastric
points that is C3, Hyoidale and Retrognathion. The
and the stylohyoid muscles act together to prevent regurgitation
anterioposterior position is determined by H-RGn and H-C3.
[6]
of food after swallowing. . The suprahyoid muscles depress the
Vertical position of the hyoid bone is recorded by the help of H-
mandible by contacting to a fixed platform while they also play
H’ which is a perpendicular dropped on C3-RGn from hyoidale.
an important and equal part in maintaining cranial balance. The
[27]
fibrous mylohyoid raphe and stylohyoid ligament act as “rigging
given my Angle H which also incorporates the greater horns of
line” that dictate the range of the possible movements of the
the hyoid bone. Thus by the use of this triangle the position and
hyoid bone. Brodie[7] in 1950 explained the importance of the
orientation of the hyoid bone can be fixed in space and the three
hyoid in deglutition and the active role in the stabilising of the
directional view of the bone can be assessed and the use of
cranial base. Hence the importance of the hyoid bone is self
cranial reference points be reduced.
The angular position or the orientation of the hyoid bone is
evident and its functions of maintaining airway, swallowing and
preventing regurgitation, and maintaining the natural head
Material and Methods
position is evident.
60 pretreatment digital lateral cephalograms were selected on
Since major amount of studies[8-26] have employed the cranial
the criteria as mentioned below. All cephalograms were of the
structures to define the plane from which the position of the
same dimension, magnification and printed from the same
hyoid bone is measured the variation of the results is not
machine. Criteria for selection of the Cephalograms are as
surprising. Cranial points are further away from the hyoid which
follows:
increases it’s chances of a variation, thus a smaller variation in
the position of the bone leads to a greater apparent variation in
the readings. Thus the object of this article to use the hyoid
triangle to see the normalcy of the hyoid bone and the variation
in different skeletal classes is to minimise the effect of the head
position on the analysis of the hyoid bone as no cranial points
are used in the study. This analysis was first given by Bibby and
Preston[3] in 1981. The hyoid bone position reflects the relative
tension of the
1.
Subject should be of Indian Origin.
2.
Subject should be healthy with no systemic diseases,
signs of trauma or a congenital disease.
3.
Subject should show no sign of previous orthodontic
treatment.
4.
Subject should be between the age group of 16years to
30years.
5.
All Class I malocclusion patients had an ANB value
between 1° to 4°.
6.
All Class II malocclusion patients had an amplitude of
ANB value more 4°.
7.
All Class III malocclusion patients had an amplitude of
ANB value less than 1°.
muscle, ligaments and fascia around this bone
and hence is used to assess the physiological normal position
and functional space of the hyoid bone, which may be important
in orthodontic and post surgical relapse. As the position of the
hyoid bone remain the same post surgical any excess forces from
the supra hyoid muscles may lead to a relapse due to soft tissue
forces. This can be treated by balancing of the muscle forces by
making it more favourable by myectomy or myotomy to reduce
Cephalograms were categorised into 3 major groups on Group
soft tissue relapse.
1: Class I malocclusion, Group 2: Class II malocclusion,
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Patil et al.
Table 1 : Cephalometric points and planes
Group 3: Class III malocclusion. All Lateral cephalograms
were taken by skilled and experienced technicians in a
standard natural head position as recommended by Broadbent
et al.[28] The cephalograms were manually traced by a single
researcher with the help of a 0.5mm thick lead pencil and a
millimetre scale for the planes on Orthodontic tracing paper.
For the linear measurements a millimetre precision digital
vernier calliper for the registration of the reading, for the
angular measurements a geometric protractor was used with a
half degree approximation. They were again evaluated by a
second researcher and the arithmetical mean of these readings
were taken as the standard value for statistical evaluation and
assessment. Beside routine anatomical designs the
Cephalometric points and planes traced are given in table 1
Statistical Methods
Table 2 : Cephalometric points and planes
population as given in the Table 2. The linear measurements of
H-C3 and C3-RGn showed statistically significant differences
in Class I, Class II and Class III (p-vaule = 0.011
and 0.007
respectively). The angular measurement of Angle H were
statistically significant with p-value 0.000 indicating the
differences in respective class malocclusions. P-values have
been paired for comparing the measurements in different
classes and have been shown in Table 2(i). The position of
hyoid in relation to mandible and cervical vertebrae using C3RGn and H-C3 as the parameters has shown that hyoid is more
The data was statistically analysed with NCSS 11 Software
(NCSSST, Kaysville, Utah, USA). Data was subjected to
descriptive analysis for mean and standard deviation of all
variables and ranges. Multiple t-test and a post hoc test
(Bonferroni) was used for multiple comparisons. P<0.05 was
considered as the level for statistically significant data.
Results
anteriorly placed in Class III malocclusion; and it is more
posteriorly placed in Class II. The angular measurement of
angle H shows the change in orientation in different planes of
the skeletal malocclusion. Linear measurement from cervical
vertebra to the symphysis was least in Class III and the most in
Class I, indicating vertical growth of mandible in class III
which approximate the level of the cervical vertebra. The
anterior-posterior position of the hyoid bone in relation to the
cervical vertebra (C3-H) again confirmed the previous reading
The linear and angular measurements of the study have been
tabulated in Table 2. The mean and the standard deviation is
given in Table 2 and this sets the normalcy of the hyoid
that the patient with the class III malocclusion has more
anteriorly placed hyoid bone. Class II, however, showed most
close position with the cervical vertebra indicating its most
triangle and the standards were derived in the Indian
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Discussion
The samples consisted of a large number of Lateral
cephalograms that is 60 in number. The skeletal characteristics
presented a homogenous behaviour in this study and showed a
statistically valuable anteroposterior dimension. The high
frequency by which the craniofacial changes justices the
functional orthodontic treatment of the maxilla should be
considered as Meredith[29] puts it, that the growth of the cranial
structures is completed by the age of 9 years for this aspect is
necessary to consider the preventive aspects of the
diagnostic
phase because one of the etiological agents of malocclusion is
atypic deglutition, and makes the hyoid position an important
tool for diagnosis. Anteroposterior position of the Hyoid with
Fig 1: Hyoid triangle is shown with blue line. The cephalometric points are 1:
C3, 2: RGn (retrognathion), 3: H (hyoidale) 4: H’ (perpendicular to C3-RGn
from H), 5: AA (atlas), 6: PNS (posterior nasal spine). Red line shows the
hyoid axis. Dotted green line shows the perpendicular from H to C3-RGn
line.
posterior position among the classes. On the other hand the
comparative relation of Class I and Class III in H-RGn with pvalue=0.039 shows that the hyoid is more anteriorly placed in
the patients with a prognathic mandible. On the contrary the
AA-PNS is statistically non-significant showing the relation of
the upper limit of that respiratory tract remains the same in all
the classes of skeletal discrepancy. As well as with H-H’
shows no significant variation in the vertical plane. All three
directions can be explained with this triangle without the use of
cranial reference points. Measurement of the angular and
vertical position shows a greater range than compared to the
horizontal dimensions. A correlation was established between
the angular and vertical position (i.e. Angle H and H-H’ of the
bone with a correlation coefficient of 0.5608 was statistically
significant and indicated that the hyoid bone may see-saw
about an axis through its greater horns. Anteroposterior
relation with the cervical vertebrae was very constant with a
mean of 30.90mm and standard deviation of ±2.4. The
correlation coefficient between the two anteroposterior
dimensions of the pharynx (AA-PNS and C3-H) was 0.7206
this finding indicates the hyoid bone represents the anterior
the 3rd cervical vertebra was relatively constant in this
population with a mean value of 30.90 and standard deviation
of
±2.4 which suggest that osseous structure to be constant in
a population group but still showing a significant difference in
the different skeletal classes suggesting the variation due to the
surrounding tissue and muscle activity. The vertical as well as
angular values had a high standard deviation as the previous
authors have mentioned like Bibby and Preston[3] who
recognised the greater variation than the linear ones. The
measurement with AA-PNS was relatively constant with no
significant difference statistically with a mean value of 31.95
and standard deviation of ±2.03 also correlating with Bibby
and Preston[3] and Coelho-Ferraz[27]. Additionally is thought to
have been determined at the age of 9 years and shows the least
deviation is the population. Correlation coefficient between the
bony ends of the pharynx (C3-H and AA-PNS) was r=0.7206
in accordance to Bibby and Preston[3] was r=0.98. The vertical
behaviour presented was also in accordance with Bibby and
Preston[3], Bibby[23] and Coelho-Ferraz[27] that showed a
irregular behaviour in the vertical position as it shows a
unstable behaviour of the hyoid bone. The correlations
coefficient between the angular measurements and the vertical
measurements also shows a moderately positive coefficient
bone boundary of the pharynx at a lower level than the PNS.
(Pearson correlation)
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Patil et al.
between the morphology of the mandible and the position of
the hyoid bone is argued over by various authors. Graber[8]
gives desperate results, while some find a correlation others
contradict the relativity. Authors [18, 19, 20, 21, 22, 23, 24, 25] reported a
statistically significant difference in Class I and Class III and
reported that the in Class III the hyoid shows a more anterior
position as well as decreased inclination. Tallgren and
Solow[26] have suggested that the position of the hyoid bone
might be influenced by two postural systems: the change in
mandibular position and change in cervical inclination as well
as the craniocervical angulation.
According to this study the Hyoid is more anteriorly placed in
the ClassIII skeletal malocclusion and shows the prognathic
mandible pulls the hyoid anteriorly due to that effects of the
Table 2 : Cephalometric points and planes
suprhyoid muscle and hence proving the functional matrix
of r=0.4608 and showing the correlation between the two
theory right. This shows the importance of the hyoid triangle in
invariable and non constant values. Precise measurement of the
diagnostic tools as it shows the same reliability as it has shown
position and the orientation of the hyoid bone is difficult due to
with the Cranial reference points that author like King[11],
the mobility of the mandible as well as the hyoid. Graber
[8]
Bench[17], Bibby[23], Grant[18], Smith[32] and Kim et al[25] used
states the variation of the head position in the cephalostat,
and have shown similar readings regarding the position of that
position of the spine, opening of the mouth and the postural
hyoid bone in the anteroposterior plane. Some authors[24, 25, 34,
position affects the position of the hyoid bone but within the
35]
limit of these errors a define conclusion concerning the
depending upon the malocclusions. Adamidis et al24] studied
[9]
reported the significant difference in position of hyoid bone
position of the hyoid bone can be made. Stepovich reported
the cephalometric radiographs of two groups of exhibiting
that the position of the hyoid bone taken in the same patient in
Class I and Class III malocclusions. He found that hyoid bone
different lateral cephalograms at different time interval varied.
tends to be more anteriorly placed in the group exhibiting
Thou some authors[10,11] state otherwise and said that the data
Class III malocclusions. Opdebeeck et al[35] analysed and
was exaggerated by Stepovich. Various authors[7, 12-15] studied
compared linear and angular measurements for short face and
at the position of the hyoid in function as well as rest and
long face syndrome and concluded that the characteristics of
showed various factors that affect the position of the hyoid
bone. Brodie[7] was the first to assess the translation of that
hyoid along the chin due the supra hyoid muscles and its
shortening.
Various author[7, 11, 16, 17] also studied the relation of the hyoid
bone with the cervical vertebrae and found it to be constant
after the age of 3 years and only at puberty does it more
anteriorly. They also studied the translation of the hyoid bone
from third cervical vertebrae to the fourth cervical vertebrae
along the course of the patients age. The possible tie up
5
Graph 1 : Mean Triagle Parameters by Class
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Patil et al.
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posteriorly.
the long face and short face syndrome group can be explained
by movement of hyoid bone in concert with the movement of
5.
mandible, tongue, cervical spine in both groups. Jee Hun Kim
Anterior Posterior relation by C3-H remains to be very
constant with the least deviation.
et al[25] found significant difference in Class III and Class II
skeletal malocclusions and states that that the mandible is more
anteriorly placed in case of Class III patients. According to
them, the changes in mandibular position are related to hyoid
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