Relationship Between Occlusal Vertical Dimension And Mandibular Morphology Among Different Vertical Facial Types

Objective:Research on mandibular morphological characteristics of different vertical facial types can help clinicians restore occlusal vertical dimensions correctly and then determine the inclination of occlusal plane during treatment.Nevertheless individual teeth arrangement will be decided by the difference of width of mandibular arch and the inclination of OP.In this study,three-dimensional reconstructive images of CBCT were used to measure the morphological characteristics of mandible,and regression equation was formed by the regression analysis of relevant mandibular morphological parameters.Methods:73 adults with different vertical facial types,who were patients of Nanjing Stomatological Hospital,were included into this study.Inclusion criteria includes:1.Complete dentition 2.Adults or growing development has ended 3.Basically symmetrical maxillofacial.Exclusion criteria:1.Obviously asymmetrical maxillofacial;2.Orthodontic,orthognathic,cleft lip and palate treatment history 3.Unhealed severe oral disease.39 hard tissue landmarks and 2 soft tissue landmarks were marked on the 3D reconstructive image.The morphological parameters of mandible in sagittal and coronal directions were obtained by measuring the linear distance and angle between landmarks.Each group of data was measured twice by different researchers and then averaged.Similarities and differences of mandibular morphological parameters of adults with different vertical facial types were analyzed by single factor ANOVA via SPSS 23.0 software.Pearson correlation test was used to construct the correlation among morphological parameters.Finally,the mandibular morphological parameters directly related to occlusal reconstruction and orthodontic treatment,such as occlusal vertical dimension and inclination of occlusal plane,were used as dependent variables to construct regression equation.Results:.1.In this study,according to the sagittal parameters of different vertical facial types,we found the FH-MP angle,FH-GOP angle,ANS-LXI-Pm angle,ANS-RXI-Pm angle,ANS-Gn distance and Sn-Mes distance of high angle group were statistically larger than average angle group and lower angle group.H4,H3 and H1 of high angle group were higher than those in the low angle group(P<0.01),but there was no statistical difference between the high and average angle group.H5 of high angle group were higher than those in the low angle group(P<0.05)5but there was no statistical difference between the high and average angle group.There was no statistical difference in the H6(P>0.05).In the coronal variation,High angle group shares a greater ANB,GoL-Gn-GoR angle than the low group accompanied with a lesser ANB,Go-Gn distance,CRL-Gn-CRR angle,L4U-Gn-R4U angle,L3U-Gn-3UD angle,the difference was statistically significant(P<0.05)2.In this study,ANS-LXI-Pm angle and ANS-RXI-Pm angle had a strong positive correlation between FH-MP angle,FH-GOP angle,ANS-Gn distance,Sn-Mes distance,H5,H4,H3,H1(P<0.001),and a moderate positive correlation between ANS-XI-Pm angle and H6(P<0.05).At the same time,the inclination of functional occlusal plane FH-GOP angle has a strong positive correlation with FH-MP,ANS-LXI-Pm,ANS-RXI-Pm,ANS-PM and Sn-Mes(P<0.001);has a moderate positive correlation with H5,H4,H3,H1;has no statistical correlation with H6.3.The regression equation of the occlusal vertical dimension of bilateral occlusion was ANS-LXI-Pm=9.326+0.597ANS-Gn+0.187FH-MP-0.286H3;ANS-RXI-Pm=9.046+0.615ANS-Gn+0.173FH-MP-0.309H3.The regression equation of inclination of functional occlusal plane was FH-GOP=4.928+0.770MP-FH-0.311ANS-XI-Pm.Conclusions:1.There are differences in mandibular morphology among different vertical facial types,which were mainly reflected in sagittal direction.The high angle group had greater occlusal vertical dimension,anterior facial height and steep occlusal plane.Vertical facial types should be taken into consideration while accessing occlusal vertical dimension and inclination of occlusal plane in clinics.2.In this study,the height of mandible body of the high-angle group is shorter than that of average angle group and lower angle group in the middle and posterior section of mandible.The mandibular height of the high angle group is higher than that of the average angle and lower angle group in the anterior section of mandible.From posterior to anterior,mandible of high angle group tends to be a triangle when measuring the height of mandible body,while that of low angle group tends to be a rectangle.3.In this study,the morphological variation of mandible in coronal direction is comparatively mild.The length of mandibular body in lower angle group was larger than that in high angle group and average angle group.In three-dimensional craniofacial morphology measurement,angular measurements may take some advantages over linear measurements in exactment and symbolic meanings.