Correlative Study Between Position And Shape Of Chin And Orthodontic Treatment Plan About Extraction

Objective:The purpose of this study was to investigate and analysis the correlation between position of chin and orthodontic treatment plan about extraction treatment. To develop a discriminant method to predict probability of orthodontic extraction.Methods:A total of 50 patients were collected from the orthodontic department, TianJin oral hospital. 28 females, 22 males. The average age of them is sixteen point five. Thirty-eight parameters were measured. Conventional Cephalometric analysis was made to compare hard and soft tissue structures before orthodontic treatment between extraction cases and non-extraction.The mean and standard deviation of each measurement were calculated for all the variables with SPSS. The correlation analysis, T-test and Logistic regression analysis were applied. In order to evaluate the accuracy of the developed function,ten patients were randomly selected to form a "verifying sample" before stepwise Discriminant Analysis.Results:1. The parameters Pog-NB and Pog-NFL Show the statistical significant differences of the before-treatment cephalometry betweenextraction and nonextraction. 2. Logistic regression analysis showed that the probability of orthodontic extraction is significantly correlated with Pog-NB, ANB, ANS-Me,Ll-NB,Ul-Ll, Ll-NP and a high correlation with the vertical distance between position of Pognion and N. B. line. 3. The parameter of Pog-NB shows a highly correlation with the parameters of Ll-NB^ Ll-NP. U1-1STC\ L1-AP> A-NFL> UL-EP.Conclusions of this study are as follows: 1. If the degree of maxillary incisor protrusion of two cases is identical, the degree of prominence of the chin should contribute tremendously to a determination of the placement of the mandibular incisor. 2. The vertical distance between Pognion and nasion-B. Suparomental line plays an important role in determing treayment plan about orthodontic extraction or non-extraction. The probability of orthodontic extraction decreases with the increasing in the degree of chin protrusion. The standardized discriminant function about orthodontic extraction was as follows:_<sub><sub><sub><sub><sub><sub><sub><sub><sub><sub><sub><sub><sub><sub>1_<sub><sub><sub><sub><sub><sub><sub><sub><sub><sub><sub><sub>P -1 -(^.07Po/NB+0.43ANB+O.37ANS/Me-0.13Ul/Ll+1.25Ll/NB-2.22Ll/NP)...