A Study On Buccal Surface Morphology Of The Mandibular Premolar In A Three-dimensional Digital Model

ObjectiveThe preadjusted appliance shape is relative to the tooth facial contour morphology adjacent, the suitability is the fundamental of accurately bracket placing and the expression of torque, as well as in normal occlusion. Mandibular premolars have lager curvature variations, the bracket shape differ between the contours of facial morphology would produce a differing coronal long axis orieatation which do not facilitate for the placement of the cusp tips in maxillary premolars, and the bracket is frequently fall out. The researches on tooth contour morphology is yet inadequate and there is still no standards for bracket shape designing based on Chinese. In order to establish such database, this research used three-dimensional digital models and ArtForm 3D software to measure the curvature radius, which will be supportive for preadjusted appliance designing for the future reference.Materials and Methods:117 orthodontic patients were randomly selected at Stomatological Hospital of ShanDong University, aged 13 to 18, their skeletal types were assessed by ANB angle from cephalometric analysis, which divided into the following groups:skeletal Class Ⅰ, ANB angle was from 0° to 5°, skeletal class Ⅱ ANB angle>5°, and skeletal class Ⅲ, ANB angle<0°. Each plaster model was scanning by inEos Lab (Sirona, German, Precision<15μm). The data were saved in STL (STereoLithography,STL) format, and imported into ArtForm 3D to measuring the curvature radius:horizontal-coronal, rAC (r stands for radius, AC is the contour between the 2 points), horizontal-middle, horizontal-gingiva, vertical-mesial, vertical-middle, and vertical-distal. Finnally, established the database of these three experiment groups.Results:1. Established database of three experiment groups.2. There is no statistic difference in the curvature radius of the bilateral teeth. (P> 0.05).3. Statistic differences of RAC and rAG were found in 1st premolar (P<0.05), and rCE in 2nd premolar (P<0.01), no differences were found in the rest curvature radius in the 3 groups (P>0.05)4. There was a significant difference among 3 vertical curvature radius,so as to 3 horizontal curvature radius in mandibular premolars(P<0.01).5. rAC、rGE、rAG、rCE were different between the 1 st and 2nd mandibular premolars (P<0.05)Conclusion:This study shows that establishing database of facial curvature radius is necessary, which will be supportive for preadjusted appliance designing for the future reference. The bracket shape should be consistant along with the difference of the tooth facial contour morphology, and the bilateral tooth’s bracket shape would be similar, but the bracket of 1st and 2nd should be discriminatory, moreover, it is necessary to establishing curvature radius database with different skeletal types.