One aspect of relapse commonly observed in orthodontic practice is space reopening in cases treated with dental extractions. Once there's a lack of studies on the prevalence and etiology of extraction space reopening after corrective orthodontic treatment, the aim of this study is to evaluate its prevalence in cases of Class I malocclusion treated with extraction of four premolars; identify the most common location and dental arcade; evaluate the behavior of these spaces in 1, 5 and 10 years post-treatment; to verify the association with factors such as the amount of initial crowding, anterior retraction and crowns angulations of adjacent teeth in the end of treatment. The sample will be comprised by orthodontic models of 40 patients selected from 4000 orthodontic files of Orthodontics discipline, Faculty of Dentistry of Bauru, University of São Paulo. It will be selected models before and after treatment, as well as control of 1, 5 and 10 years after treatment, in a total of 200 plaster casts. Later, the models are going to be organized into two groups: Group I, composed by cases there was extraction space reopening after treatment and Group II, corresponding to cases there was no reopening of spaces. These models will be scanned by a 3D scanner 3Shape R700 (3Shape A / S, Copenhagen, Denmark), and measured via 3D software OrthoAnalyzerTM. The evaluation of lower incisors retraction during treatment will be performed using initial and final cephalometric radiographs which will be drawn by one examiner. These lateral cephalograms will be scanned and the measurements performed using the Dentofacial Ortho Side Planner 7022 standard program. In the statistical analysis, the prevalence of relapse such as the average size of reopened space, will be calculated. The changes between phases will be evaluated by the Analysis of variance for repeated measures. Descriptive statistics for quality variables will be calculated using absolute frequency and relative frequency, and for comparison between phases of these variables, the McNemar test. The independent t test will be applied to compare groups regarding the initial amount of crowding, amount of retraction and crowns angulation of adjacent teeth. All statistical tests will apply the significance level of p <0.05.
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