| Objective:The purpose of this study is to assess the height and width of mandibular cross-sections and the thickness of cortical bone for young females with the different vertical skeletal patterns by using cone-beam computed tomography (CBCT), compare the differences of the morphology of mandibular cross-sections with different vertical skeletal patterns, and determine the correlation of these parameters with the vertical skeletal pattern.Methods:A total of64females with a CBCT scan were enrolled from Department of Orthodontic of school of Stomatology of Shandong University, aged from19to40years old, which were divided into3groups according to the mandibular plane, the ratio of between the posterior face height and the anterior face height (14in the low-angle group,31in the average-angle group,19in the high-angle group). The morphology of the mandibular cross-sections was evaluated, including the height and width of the mandibular cross-sections, the thickness of cortices in8regions (13sites). SPSS16.0(Statistic Package for Social Science) was used to compare the differences, the parameters among the different vertical skeletal pattern. All the values are statistically analysed by the means of SPSS16.0. The statistical methods used in this study are One-way ANOVA and multiple comparisons between groups (LSD), Paired T-test, Pearson correlation analysis, which used to compare the differences of the morphology of mandibular cross-sections with different vertical skeletal patterns, and determine the correlation of these parameters with the vertical skeletal pattern.Results:1. The height of the cross-sectional area of the mandible decreased from the mandibular symphysis to the posterior segments, the variation trend of high-angle group was significant than the other two groups. Compared to the low-angle group, the mandibular cross-sectional height of the mandibular symphysis and the lateral incisor segments in the high-angle group was higher, but the height of molar segments were lower (P<0.05, P<0.01). The results of correlation reveal that there is a significantly positive relationship between FH-MP angle and the height of the mandible of the mandibular symphysis, lateral incisor and canine segments (P<0.01); There is a significantly negative relationship between FH-MP angle and the height of the first and second molar segments (P<0.05, P<0.01).2. The upper one third width (wl) of the cross-sectional area of the mandible increased from the mandibular symphysis to the posterior segments; however, the lower one third width (w2) of the cross-sectional area of the mandible decreased from the mandibular symphysis to the premolar segments, and increased gradually to the molar segments. Compared to the low-angle group, the cross-sectional upper one third width of the anterior and premolar segments and the cross-sectional lower one third width of the mandibular symphysis and lateral incisor segments were narrowed in the high-angle group (P<0.05, P<0.01). The results of correlation reveal that there is a significantly negative relationship between FH-MP angle and the width of the mandible of the mandibular symphysis, lateral incisor and canine segments (except the lower one third width of second molar segments)(P<0.01).3.There are some regular pattern in the thickness of cortical bone:the thickness of the buccal cortical bone, the upper one third (a) increased from the mandibular symphysis to the posterior segments, the lower one third (b) was thinnest in the lateral incisor, and increased gradually to the posterior segments; the thickness of the lingual cortical bone, the upper one third (e) increased from the mandibular symphysis to the first premolar segment, and decreased to the posterior segments, the lower one third (d) decreased from the mandibular symphysis to the posterior segments; the thickness of the base of the cortical bone (c) increased from the mandibular symphysis to the cranial segment, and decreased from the cranial segment to the posterior segments; In addition, the high-angle group compared to the lower-angle group, there were no differences in the incisor segments of the thickness of the labial cortical bone; the thickness of the buccal cortical bone, the upper one third (a) of the cranial, premolar, molar segments and the lower one third (b) of the canine, second molar segments were thinner than the lower-angle group (P<0.05, P<0.01); the thickness of the lingual cortical bone, the upper one third (e) of the premolar, molar segments and the lower one-third (d) of the mandibular symphysis were thinner than the lower-angle group (P<0.05, P<0.01); the thickness of the base (c) were significant thinner than the lower-angle group except of the premolar segments (P<0.05, P<0.01). The results of correlation reveal that there is a significantly no relationship between FH-MP angle and the buccal lower one third cortical thickness of the lateral incisor, first molar segments (32b,36b), the lingual lower one third cortical thickness of the canine, the premolar, first molar segments (33d,34d,35d,36d) and the lingual upper one third cortical thickness (35e), there is a significantly negative relationship between FH-MP angle and the other sections (P<0.05,P<0.01).Conclusion:1. There are some regularity from the media to the distance of the height, width of the mandibular cross-sections and the thickness of the cortical bone of the young females.2. There are some differences of the parameters of the mandibular cross-sections of the young females.(1) Compared to the low-angle group, the mandibular cross-sectional height of the mandibular symphysis in the high-angle group was higher, but the height of molar segments was lower. As the angle of FH-MP increases, the mandibular cross-sectional height of the anterior teeth segments increase, the mandibular cross-sectional height of the molar segments decrease.(2) Compared to the low-angle group, the cross-sectional upper one third width of the anterior and premolar segments and the cross-sectional lower one third width of the mandibular symphysis and lateral incisor segments were narrowed in the high-angle group. As the angle of FH-MP increases, the mandibular cross-sectional width decrease (except the lower one third width of the second molar segment).(3) The high-angle group compared to the lower-angle group, there were no differences in the incisor segments of the thickness of the labial cortical bone, the other areas which were thinner than the lower-angle group. As the angle of FH-MP increases, the thickness of more areas of the cortical bone decrease.Thus it can be seen, the morphological conditions of the cross-sectional area of the mandible of the high-angle patients of the young females exist the larger risk in which the oral therapies, for example, the limitation of the teeth movement in orthodontics, bone anchorage implant, implant restoration, genioplasty and the trauma surgery of mandible. |
PDF Full Text Request