Research On Arch Width In Skeletal Class Iii Malocclusion Among Different Vertical Facial Skeletal Types

Objective:The aim of this study was to analyze the features of the dental and alveolar widths of skeletal Class Ⅲ malocclusion patients, and furthermore to discuss the correlation between arch width and different vertical facial skeletal types in individual normal occlusion and skeletal Class Ⅲ malocclusion, to provide a theoretical basis for clinical treatment design.Methods:56 patients with skeletal Class Ⅲ malocclusion(female 29, male 27)were selected from dental hospital of Lanzhou University as the test group. 52 undergraduate and graduate students with individual normal occlusions(female 31, male 21)were selected from Stomatological Department of Lanzhou University as the control group. The original plaster models and cephalometric x-ray(control group taken CBCT) were taken. According to the value of mandibular plane angle(MP-FH,SN-MP), the test group and control group were separately divided into three groups(high-angle,average-angle and low-angle groups). 12 parameters were measured for each sample, including maxillary and mandible arch width and alveolar arch width between canines, first premolars and first molars, and the differences between the maxillary width and mandibular width were also measured. The statistic analysis was finished by independent samples t-test and Pearson’s correlation test.Results:1, High-angle groups: in all maxillary measurements,there was no any difference in dental arch and alveolar arch width between the test group and control group(P> 0.05), mandibular first molar arch width and all mandibular alveolar arch width of test group were larger than that of control group,(P <0.05), maxillary and mandibular alveolar arch width differences were significant between the test group and control group(P <0.05), while maxillary and mandibular arch width differences showed no statistical difference(P> 0.05).2, Average-angle groups:the alveolar arch width in the maxillary of the test group were smaller than that of the control group, mandibular canine alveolar arch width was larger in testgroup than that of in control group(P <0.05), and the rest of measurements have no significant difference(P> 0.05). maxillary and mandibular alveolar arch width differences were significant between the test group and control group(P <0.05). The arch width differences of maxilla and mandible between first molar have statistical difference(P <0.05).3, Low-angle groups: there was no any difference in maxillary dental arch and alveolar arch width between the test group and control group(P> 0.05), mandibular canines and first premolar alveolar arch width were larger in test group than that of in control group(P <0.05), maxillary and mandibular alveolar arch width differences were significant between the test group and control group(P <0.05), while maxillary and mandibular arch width differences showed no statistical difference(P> 0.05).4, The test group:maxillary first premolar arch width and mandibular plane angle was negatively correlated, maxillary and mandibular alveolar arch width differences in first premolars area were negatively correlated with mandibular plane angle, the maxillary middle arch widths was decreased with the increasing of mandibular plane angle.5, The control group: the alveolar arch width of maxillary canine and maxillary first premolar was negatively correlated with mandibular plane angle, the arch width between two upper premolars was also negatively correlated with mandibular plane angle, upper and lower alveolar arch width differences in canine and first premolars area were negatively correlated with the mandibular plane angle, The maxillary middle arch widths were decreased with the increasing of mandibular plane angle.Conclusion:1, Skeletal Class Ⅲ malocclusion in high-angle and low-angle greater than normal with mandibular alveolar arch width, in average-angle smaller than normal with maxillary alveolar arch width,indicate mandibular alveolar arch width of Skeletal Class Ⅲ malocclusion in high-angle and low-angle has tendency of excessive development,in average-angle maxillary alveolar arch width has tendency of underdevelopment.2, The maxillary middle arch width of skeletal Class Ill malocclusion was related with mandibular plane angle.3, The upper anterior and middle area arch width of individual normal occlusion was related with vertical facial type.