A Three-dimensional Study On Upper Airway And Hyoid Bone In Adult Skeletal Class Ⅱ Patients

The upper and lower jaw bone, which craniofacial bone structure is mainlycomposed of, constitute a hard upper airway stent. The hyoid bone is the uniquedissociative bone tissue which connects craniofacial bone and the upper airway.Craniofacial morphology interact with upper airway. Craniofacial bone dysplasiainevitably leads to the development of the upper airway abnormalities, it also causeposition changes of the hyoid bone. Meanwhile, the hyoid bone link with bone tissue ofcraniofacial structure through muscles, fascia and ligaments. Its position changesinfluence the balance and coordination of muscle chain of stomatognathic system,thereby affecting the airway morphology. Therefore, the position of the hyoid can beconsidered an important indicator to assess airway physiological function. Skeletal ClassII malocclusion are frequently found in clinical practice, which seriously affect thepatient’s oral function and looks and can be regarded as risk factors for OSAHSmorbidity. It is found that such patients confront with a problem that their oropharyngealcross-sectional area are structural narrow, and the hyoid bone position are posterior andinferior. However, previous research mainly focused on relationships among sagittalfacial types, upper airway morphology and hyoid position, while the features of upper airway and hyoid bone in different vertical facial types of Class II malocclusion have notbeen reported in the literature. Because of limited conditions, previous studies are basedon two-dimensional imaging of lateral cephalometric radiographs, thus making it unableto measure and study the upper airway volume and diameter. Researches on hyoid boneare also limited to its position, and the effects of morphology changes on upper airwayare unclear.Now, the application of cone beam computed tomography (Cone-beamcomputer tomography, CBCT) in dental clinical has provided a new way to study therelationships among the craniofacial,the upper airway and the hyoid bone.Purposes:In this paper, select adult skeletal Class II malocclusion patients without snoring asresearch subjects. For patients meeting the standards, CBCT scans are conducted underthe same condition. Rebuild3D models of upper airway and hyoid bone, compare thedifference of position and morphology of upper way and hyoid bone in different verticalfacial skeletal class II patients, getting some references for orthodontic treatment to theskeletal class II patients and research to pathogenesis of OSAHS.Methods:For this study, adult skeletal Class II(ANB angle>5°)malocclusion patients wereselected as research subjects.60skeletal Class II patients including30male and30female were selected.They were divided into3groups by GoGn-SN angle: low-anglegroup (GoGn-SN≤22°), average-angle group (22°≤GoGn-SN≤32°) and high-anglegroup (32°≤GoGn-SN). They were treated with CBCT examinations under the samecondition in our hospital. We applied software MIMICS10.01to build3D models forupper way and hyoid bone, selected21related indicators to be measured.Next,we usedstatistical software SPSS17.0to analyze data of upper airway and hyoid bone,comparingthe differences among the three groups.Finally,we took a further LSD pairwisecomparison between indexes which are significant differences. Correlation analysisbetween hyoid bone related indicators and and upper airway were performed.Results:In the upper airway linear measurement indicators, there exists a significant difference (P <0.05) among velopharyngeal upper bound plan sagittal diameter length(PNSL) of different vertical skeletal facial types. And there are significant differences (P<0.01) between both upper airway velopharyngeal and oropharyngeal lower bound plansagittal diameter length (UTL, ETL) of high-angle group and that of average-angle andlow-angle group.With vertical facial type increasing, the above value seems to be a trend:high angle <average angle <lower angle. Comparison of both the height (UTH, ETH)and width (PNSW, UTW, ETW) of each segment of the upper airway is no significantdifference (P>0.05). Velopharyngeal and oropharyngeal volume of high-angle group areobvious smaller than that of average-angle and low-angle group, and the difference isstatistically significant (P <0.05). Pairwise comparison find that difference only existsbetween the high-angle group and the low-angle. Both hyoid bone morphology andlocation are no difference (P>0.05) between different vertical facial types. There is apositive correlation between hyoid bone morphology and all the measurements of upperairway, and a negative correlation between hyoid bone position and the sagittal diameter,transverse diameter and volume of upper airway.Conclusions:The growth and development of craniofacial morphology will have an impact onboth velopharyngeal and oropharyngeal segment of upper airway. Among differentvertical facial types, sagittal diameter of the upper airway seems to be a trend: high angle<average angle <low angle. Both velopharyngeal and oropharyngeal segment of upperairway are no significant difference among the three groups, indicating that effect of thevertical growth and development on upper airway transverse diameter is limited. Hyoidbone position and morphology are no significant differences among the different verticalfacial types, which means that hyoid bone position and morphology stay relatively stableafter completing growth and development, thus may be related to self-regulation andcompensation of the suprahyoid, and infrahyoid muscle groups. In the correlationanalysis of the upper airway and hyoid bone, upper airway and hyoid bone are shown tocorrelate significantly with each other in skeletal Class II malocclusion; a differentpositive relationship exists between the sagittal diameter, transverse diameter and volume of upper airway and the hyoid bone morphology; and a different negativerelationship exists between hyoid bone position and all measurements of upper airway.