Choice Of Premolar Extraction Patterns In ClassⅡ Division1Patients

Objictive:To find the pretreatment factor influencing the premolar extraction pattern and provide some clinical and academic reference for the premolar extraction choice before treatment.Methods:In the study25patients involved the extraction of four first premolars and25patients involved the extraction of two first maxillary premolars and two second mandibular premolars. Both groups of patients were class II division1without protruding maxillary and the treatment effects were satisfactory.The lateral cephalometric taken before and after treatment were traced and measured.46typical values of hard and soft tissue were measured and statistical analysis was carried by spss software.After the statistically significant differences were searched, stepwise discriminant analysis was applied to identify the key factors for discriminating the two groups.Results:L1_AP(mm)>TLL_E、congestion Pos_NFL>L1_MP, the five measurements were into the logistic regression equation, Choice of extraction model most closely, in determining the extraction mode selection plays an important role. The logistic regression equation was derived:logitP=0.056+0.0037L1_MP+0.125L1_AP(mm)-0.022Pos_NFL+0.056TLL_E+0.052congestion, The five measurements of the extraction model selected in decreasing order of L1_AP (mm)、TLL_E、congestion、 Pos NFL、L1MP.Conclusion:During the Class II Division1malocclusion deformity correction combined design, the lower incisors protrusion, lower lip protrusion, congestion, jaw and soft tissue chin,lower incisor inclination to the tongue were closely contact with the extraction model, the five measurements together determine the extraction model choice. In order to make the right choice, design and clinical treatment must be considered for the five measurements, from three aspects of the teeth,the bone and the soft tissue comprehensive analysis.Measurement of the above project on behalf of five into the regression equation, the estimated probability, the probability of greater than0.5, select the extraction model44/44; probability is less than0.5, select the44/55tooth extraction mode.