Study On Occlusal Contacts Of Three Basic Mandibular Movement In ClassⅡ Division Ⅰ Malocclusions

Objective: The purpose of this study was to analyse the occlusal contacts in ClassⅡDivisionⅠMalocclusions during opening/closeing, protrusive and lateral movement of the mandibible and investigate the dentofacial morphological factors related to the ICP -MCP discrepancy and occlusal interferences.Methods: A total of 60 ClassⅡDivisionⅠMalocclusions with no history of orthodontic treatment were employed. T-Scan II system was used to record and analyse the occlusal contacts during opening/closeing, protrusive and right/left lateral movement of the mandibible.Dentofacial morphological data was dertermined by measuring plaster mold and the lateral cephalometric radiography.SPSS 12.0 for windows was used for the statistics.Results:①There was no significant difference among three repeated measurements of the vertical distance from the center of occlusive force to the midline,the D-value of occlusive force between the right and the left side , the numbers of occlusal contacts in the intercuspal position.②Significant difference of the later arch-widths was observed between the group with and without ICP–MCP discrepancy.③There was significant difference in Y-angle,MP-FH, U1-L1,A-ptm,the ratio of front arch-widths and the molar mesiodistal indexs between the group with and withnot protrusive occlusal interference. Logistic analysis showed that MP-FH is the dangerous factor in the protrusive occlusal interference,while A-ptm served as the protect one.④Significant differences ofA-ptm, U1-SN, the front upper/lower arch-widths,the molar mesiodistal indexs were found between the group with and without lateral occlusal interference.Conclusions:①C lassⅡDivisionⅠMalocclusions is characterized by intercupided occlusion stability, abnormal later arch-width may associate with ICP–MCP discrepancy.②"High-angle"patients are more likely to incur protrusive occlusal interference,Mandibular plane angle is the dangerous factor for the occlusal interference.③Maxillary length is negative correlated to protrusive and lateral occlusal interference, and it's the protective factor of the occlusal interference.④C uspid-cuspid molar distoclusion is more likely to occur occlusal interference than complete post-normal occlusion do.