Impacts Of Extraction And Nonextraction On The Front View Of Facial Soft Tissue In Class Ⅰ

Objective The controversy of extraction or nonextraction is lasting forone-hundred-year time during the orthodontic history. Orthodontists andresearchers often focus on lateral profile or cephalometric analysis whendrawing up the treatment plan and assessing the results. But people facethe anterior view far more than profile in the daily life whencommunicating with each other. So lateral profile is insufficient forevaluating the results of orthodontic treatment. This research aims topreliminary discuss the method of marking the gonion on photographicfront view and measuring the mandible width via anthropometry methodfirst, and then assess the impacts of extraction and nonextraction on thefacial front view of Class Ⅰ female adolescent patients based on theproposed approaches. Methods First, in experiment Ⅰ,60normal teenagers are selectedbased on the criteria. We mark the gonion on the mandible andphotograph their facial front views. By observing and measuring theprojection position of the marked point, a hypothesis of the method forfixing the set-point of the gonion and measuring the mandible width onfacial front view is developed to provide the basis for the followingexperiment.Secondly, in experiment Ⅱ,50female adolescent patients who metthe inclusion criteria are extracted from the sample pool,25cases forextraction group and25cases for nonextraction group. The extractiongroup consists of bimaxillary protrusion cases with4first premolarsextracted. The standardized front view photograph for pretreatment andposttreatment of each patient are selected. We fix the points and measure12parameters, including6relative linear variables: facial width(Zy-Zy), mandiblewidth(Go-Go), nose width(Ac-Ac), mouth width(Ch-Ch), facial height(G-Me),lower facial height(Sn-Me);6index variables: facial index(G-Me/Zy-Zy),mandible index(Sn-Me/Go-Go), Zy-Zy/Go-Go, Go-Go/G-Me, Ch-Ch/ Go-Go, Sto-Me/Sn-Sto. The statistical analysis of the resulting data isproposed by using the statistical software SSPS13.0. Paired t-test is used toevaluate the treatment changes within each group. Group t-test of independentsamples is used to compare the differences between groups.Results we can find that the position gonion projected on Zy-Mesegment follows some regularities, which is located in or close to themidpoint of the segment. The Zy-pedal/Zy-Me percentage frequencycurve approximates to the normal distribution and the average value islocated in the midpoint of the line. No significant difference existsbetween the different genders.After orthodontic treatment, nonextraction group indicates that,facial height(G-Me) increases (P<0.05); mandible index(Sn-Me/Go-Go)increases significantly (P<0.01). In the extraction group of bimaxillaryprotrusion, the variables including mandible index(Sn-Me/Go-Go) andZy-Zy/Go-Go increase (P<0.05); Go-Go/G-Me decreases (P<0.05);Sto-Me/Sn-Sto increases significantly (P<0.01). The comparison resultsbetween groups show that after treatment, the statistical difference of Zy-Zy and Go-Go exist in both two groups, which are larger in thenonextraction group than those in the extraction group. The variablesG-Me/Zy-Zy, Sto-Me/Sn-Sto are statistically different before thetreatment, but then insignificant after treatment between groups. Otherparameters show no differences within or between groups.Conclusion(1) For the beautiful population, the position gonion projected on Zy-Mesegment should be located in or close to the midpoint of the segment. Nosignificant difference exists between different genders;(2) The nonextracton treatment can increase the facial height;(3) After extraction treatment, the bimaxillary protrusion patients showchanges on both horizontal and vertical version. The most remarkableeffect on the facial front view is that Sto-Me/Sn-Sto index increases,much improving the facial proportion and harmony.(4) No matter which method of the two—extraction ornonextraction—is selected, mandible index (Sn-Me/Go-Go) will increaseafter treatment, which modifying the lower face as slightly longer and narrower.