|Year : 2019 | Volume
| Issue : 4 | Page : 161-167
Assessment and correlation of the position and orientation of the hyoid bone in Class I, Class II, and Class III Malocclusions
Aishwarya Prashant Gundawar, Deven Mahesh Rawlani, Amol S Patil, Anand Sabane
Department of Orthodontics, Bharati Vidyapeeth Dental College and Hospital, Pune, Maharashtra, India
|Date of Submission||21-Oct-2019|
|Date of Acceptance||07-Nov-2019|
|Date of Web Publication||17-Dec-2019|
Dr. Aishwarya Prashant Gundawar
Department of Orthodontics, Bharati Vidyapeeth Dental College and Hospital, Pune-Satara Road, Katraj-Dhankawadi, Pune - 411 043, Maharashtra
Source of Support: None, Conflict of Interest: None
Objective: This study aims to examine and correlate the position and orientation of the hyoid bone in Class I, Class II and Class III malocclusions.
Materials and Methods: A total of 90 pretreatment digital lateral cephalograms were chosen in accordance with the established criteria and categorized into three groups, namely: Class I (n = 30), Class II (n = 37), and Class III (n = 23) malocclusions. The lateral cephalograms were traced and various linear and angular parameters such as MPH, H-NL, H-Go, H-Me, H-FH, H-C3, NSH, and H-NL were measured. The standard deviation and arithmetic mean values were computed for every measurement, after which independent t-test was conducted to study the variations between the skeletal classes of malocclusions.
Results: The linear measurements of H-Me and H-C3 were found to be statistically significant. The angular measurements of SNA and ANB were also statistically significant and indicated the dissimilarities in the different classes of malocclusions. The anteroposterior position of hyoid bone was established, but the superoinferior positioning was found to be statistically insignificant.
Conclusion: A significant difference occurs in the position and orientation of Hyoid Bone in relation to its surrounding structures in Class I, II, and III malocclusions. The hyoid bone is more anteriorly placed in Class III malocclusions than Class II which is more posteriorly placed. The superoinferior positioning of hyoid bone was found to be statistically insignificant in this study.
Keywords: Growth patterns, hyoid position, orthodontics, skeletal malocclusion
|How to cite this article:|
Gundawar AP, Rawlani DM, Patil AS, Sabane A. Assessment and correlation of the position and orientation of the hyoid bone in Class I, Class II, and Class III Malocclusions. Int J Orthod Rehabil 2019;10:161-7
|How to cite this URL:|
Gundawar AP, Rawlani DM, Patil AS, Sabane A. Assessment and correlation of the position and orientation of the hyoid bone in Class I, Class II, and Class III Malocclusions. Int J Orthod Rehabil [serial online] 2019 [cited 2020 Jan 22];10:161-7. Available from: http://www.orthodrehab.org/text.asp?2019/10/4/161/273312
| Introduction|| |
To ensure the success of an orthodontic or orthognathic treatment, an accurate diagnosis of the entire craniofacial region is essential. The entire treatment is customized for an individual based on the relation between the hard and soft tissues of the craniofacial region.
It has been recognized that there may be significant differences in physiologic function of individuals with different craniofacial anatomical relationships. In orthodontics, cephalometric radiography has become one of the most essential tools for recognizing the craniofacial anatomical relationships. It has been utilized extensively to quantify the dental, skeletal, and soft tissue relationships of the craniofacial complex, before the beginning of orthodontic treatment and throughout growth. Less often, in clinical research, cephalometry is used to evaluate craniocervical angulation, pharyngeal relationships, soft palate dimensions, and hyoid bone and tongue position.,,, In recent times, the position of hyoid bone in relation to its surrounding structures has gained significant amount of attention.
The hyoid bone is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies at the level of the base of the mandible in the front and the third cervical vertebra (C3) behind. The hyoid bone does not have a direct bony articulation with any other bone. It is suspended in the midline neck with muscles and ligaments from all directions. The hyoid bone serves as attachment to various muscles of the tongue, floor of the mouth, larynx, epiglottis, and the pharynx. It aids in various functions such as swallowing, breathing, and speech. It has also been related to obstructive sleep apnea (OSA) such that a more inferiorly positioned Hyoid bone increases the presence and severity of OSA. According to Brodie, the upright posture of the head involves the balance between the tensions of posterior neck muscles and anterior muscles such as masticatory, suprahyoid, and infrahyoid groups in relative to occipital condyles. Hyoid bone position is, thus, a reflection of the relative tensions of the muscles, ligaments, and fascia attached to it.
Various authors , have proved that the mandibular changes influence hyoid bone position during the entire postsurgical period, whereas stretching of suprahyoidal musculature seems to contribute to skeletal relapse. Being aware of the position of hyoid in different malocclusion and factors affecting its position can result in better orthodontic treatment without relapse and possible deficient pharyngeal airway space after orthodontic treatment as well as orthognathic surgery.
Although similar studies have been performed before, disagreements over the position and orientation of hyoid bone still occur. This study aims to assess the position and orientation of the hyoid bone in Class I, II, and III malocclusions.
| Materials and Methods|| |
The present study is an in-vitro retrospective study and did not involve any intentional radiation exposure to any patient.
A total of 90 pretreatment lateral cephalograms were selected from the records in the Department of Orthodontics, Bharati Vidyapeeth (Deemed to be University) Dental College and Hospital, Pune. These radiographs were selected by simple random sampling after satisfying the established criteria of selection. Lateral cephalograms were taken by skilled and experienced technicians in a standard natural head position as recommended by Broadbent. All cephalograms were printed from the same machine with unaltered standard settings of magnification and dimensions.
Criteria for selection
- Good quality radiographs were selected
- Subject should be between the age group of 18–30 years
- Subject must not show any sign of previous orthodontic treatment.
- The cephalograms with signs of trauma, congenital disease, cyst, tumors or any maxillofacial abnormality were excluded
- The radiographs of patients undergoing orthodontic treatment were excluded.
Method of data collection
- The 90 cephalograms were classified into three categories: Class I malocclusion, Class II malocclusion, and Class III malocclusion
- It was found that of a total of 90 cephalograms, 30 had Class I malocclusions, 37 had Class II malocclusions, and 23 had Class III malocclusions
- The cephalograms were traced by a single researcher using a lead pencil of 0.5 mm thickness and a millimeter scale for marking and measuring various points and planes on an orthodontic tracing paper. The angles were measured using a geometric protractor
- The cephalometric points and planes that were traced have been enumerated in [Table 1]. The linear and angular measurements that were recorded have been listed in [Table 2]. The schematic representation in the form of a tracing is shown in [Figure 1]
- All the linear measurements were recorded and the arithmetical mean of these readings was taken as the standard value for statistical evaluation
- All data collected was compiled, tabulated, and analyzed statistically
- The tests applied were independent t-test for analysis for variance and post hoc (Bonferroni) for multiple comparisons. The significance level was at P < 0.05.
|Figure 1: A tracing of a lateral cephalogram which shows all the cephalometric points, planes and landmarks related to this study of hyoid bone|
Click here to view
| Results|| |
- The resultant values obtained from the linear and angular measurement findings have been tabulated in [Table 3]
- The linear measurements of H-C3 and H-Me were statistically significant with their P < 0.05. The angular measurements of SNA and ANB were also statistically significant and indicated the dissimilarities in the different classes of malocclusions. The P values have been tabulated in [Table 4] for comparison
- These findings show that hyoid bone is more inferiorly placed in Class I malocclusions than Class II which is more superiorly placed. However, since the P > 0.05, the data are statistically not significant
- The position of hyoid in relation to mandible using H-Me and H-C3 as the parameters has shown that hyoid is more anteriorly placed in Class II malocclusion; and it is more posteriorly placed in Class I malocclusion [Figure 2]
- The linear measurement from cervical vertebra to the Hyoid was most in Class III and the least in Class I, which confirms the above finding. The distance from Menton to the hyoid bone was also least in Class III and most in Class I, which supports the more forward positioning of hyoid bone in Class III malocclusion patients.
|Figure 2: A chart comparing the position of the Hyoid bone in Class I, II and III malocclusions with respect to H-Me and H-C3|
Click here to view
| Discussion|| |
In the early stages of life, the hyoid bone is placed at the inferior edge of mandibular border, but with the aging process, it gradually descends and eventually is fixed next to the fourth cervical vertebra (C4). The position of hyoid bone also differs as a result of any changes in the body gesture, head position and other physiological states. In addition, the hyoid bone moves in response to mouth's different functions such as respiration and ingestion.
Extensive research has been conducted in order to identify the position of the hyoid bone in various dentofacial patterns. The studies have shown that changes in the position of the mandible are related to those in the hyoid bone and the position of hyoid bone adjusts to anteroposterior changes in the head posture., Moreover, published studies have determined that there is a strong relation between the hyoid bone position and the size of respiratory tract; therefore, great consideration has to be given to this before orthognathic surgery.,,,
In this study, a sample size of 90 lateral cephalograms was selected. These cephalograms were categorized into Class I, Class II, and Class III malocclusions. The cephalograms were traced, measured, and the values were tabulated. After statistical analysis, a conclusion was reached. In the course of the study it was found that, the linear measurements of H-C3 and H-Me were found to be statistically significant with their P < 0.05. The statistical values obtained show that hyoid bone is more posteriorly placed in Class I and more anteriorly placed in Class III malocclusion cases. The values for superoinferior positioning of hyoid bone were found to be statistically insignificant in this study, due to the P value being > 0.05. In the literature, several studies have been conducted in the past related to the positioning of hyoid bone.
Adamidis and Spyropoulos  studied the cephalometric radiographs of two groups exhibiting Class I and Class III malocclusions. He found that hyoid bone tends to be more anteriorly placed in the group exhibiting Class III malocclusions, which was similar to our study. Opdebeeck et al. analyzed and compared linear and angular measurements for short face and long face syndrome and concluded that the characteristics of the long face and short face syndrome group can be explained by movement of hyoid bone in concert with the movement of mandible, tongue, and cervical spine in both groups.
Amayeri  observed that the hyoid bone is more inferiorly placed in Class III malocclusion, compared to Class II, where it is more superiorly placed. Lngervall et al. only used the mandible as a reference for the comparison which is not a stable landmark which was further changed by Bibby and Preston  in the introduction of the hyoid triangle. Graber  on the other hand found the correlation between the position of the hyoid bone and and the mandibular morphology and hence found an affirmative explanation between the positive correlation. Stepovich  also said that the hyoid bone assumes variable position from a person to another, and the difference in it may also occur in a same sample of the patients after a short space of time. That is why the relation between the mandibular symphysis and the 3rd cervical vertebrae was considered into the relation by Bibby and Preston.
The lower hyoid position in Class III malocclusion in relation to the anterior cranial base (SN plane) and the Frankfort plane (FH plane) could justify that the hyoid bone did not follow the mandibular movements completely. Thus it appears that, as the mandible is moved posteriorly in relation to the other craniofacial structures, the tongue and the hyoid bone do not follow this movement in a similar manner. Otherwise it would encroach upon the vital oropharyngeal and laryngeal spaces. As a functional compensation, the hyoid bone and related structures are guided to an inferior position to avoid compromising the airway space. This suggests the stability and potency of the pharyngeal airway are primary factors in the hyoid bone position. This is consistent with the results of Tourné and Battagel et al.
An increase in the distance between the hyoid bone and the cervical vertebrae (C3) in Class III subjects were similar to the study conducted by Trenouth and Timms  and also Abu Alhaija et al. that showed that the hyoid bone moves more posteriorly with the increase in ANB angle. The explanation of this phenomenon lies with the genioglossus muscle that protrudes the tongue and generates upper airway dilating forces to maintain the patency and as the hyoid bone moved forward would pull the tongue anteriorly en mass, leading to increase in tongue pressure and maintaining the pharyngeal spaces at the level of the base of the tongue.
In a study by Jose et al. in 2015, it was concluded that the position of hyoid bone in antero-posterior dimensions does not have any statistical difference among individuals with skeletal I, II and III patterns. In a study by Kim et al. in 2016, it was concluded the Hyoid bone was more antero-inferiorly placed in Class III malocclusions and it was more postero-superiorly placed in Class II malocclusions.
The position of the Hyoid bone in class III patients is more anteriorly and inferiorly placed due to the prognathic mandible and the pull from the suprahyoid and the tongue muscles attaching to the Hyoid. In Class II malocclusions, the mandible is more posteriorly positioned and the pull from the supra hyoid muscles is lesser. Thus, the hyoid is more posteriorly and superiorly placed.
If the hyoid bone is in the same position before and after orthodontic treatment, the soft tissue must still be in the same balance, thus possibly reducing the chance of relapse from the soft tissue forces. If the hyoid position is altered, a longer retention period than normal may be indicated. Any alteration in the hyoid position following mandibular surgery may be indicated for the balancing of the muscles forces to be made more favorable by myectomy or myotomy to reduce surgical relapse.
The hyoid bone is a mobile structure which changes position with various physiologic processes such as swallowing, speech, or respiration. This study lacked the potential to assess the hyoid bone while in function. We promote further research for a more accurate assessment of hyoid bone position and orientation in different skeletal malocclusions.
| Conclusion|| |
A significant difference occurs in the position and orientation of hyoid bone in relation to its surrounding structures in Class I, II, and III malocclusions.
- In Class II malocclusion, the hyoid bone is placed more anteriorly, while in Class I malocclusions, it is positioned more posteriorly. It is positioned most anteriorly in Class III malocclusion cases
- In Class I malocclusion, the hyoid bone is more inferiorly placed as compared to Class II and III malocclusions. However, these data are statistically insignificant in this study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]