[Combination of NITI cantilever arm and casting frame in correcting lingually inclined mandibular molar].

PURPOSE: To study the effect of NITI cantilever arm in correcting lingually inclined mandibular molar. METHODS: Sixteen patients whose single mandibular second molar was lingually inclined were chosen. The intra-mandibular anchorage was achieved by means of cast frame which connected the bilateral mandibular posterior teeth. The splint disoccluded the lingually inclined second molar with the antagonist. The cantilever arm of 0.018 inch×0.025 inch or 0.019 inch×0.025 inch NITI wire was used to provide buccal rotation moment and intrusion force. Graphpad Prism 6.0 software was applied for data analysis. RESULTS: All the lingually inclined second molars were uprighted, the axial change relative to the sagittal plane was 24°±1.2°(P<0.01).The change of the distance from the mesial lingual cusp of the lingually inclined second molar to the sagittal plane was 3 mm±0.8 mm (P<0.05). The anterior overbite was almost unchanged and the periodontal condition was healthy. CONCLUSIONS: Combination of casting frame with NITI cantilever arm can provide effective mechanics to correct lingually inclined mandibular molars.

[Cone beam computed tomographic analysis of cortical bone thickness of upper molar region for miniscrew].

PURPOSE: To quantitatively evaluate the cortical bone thickness at upper molar miniscrew sites. METHODS: Sixty Angle's Class II division I patients were involved in this study(30 males and 30 females), measurements of cortical bone thickness were done with cone beam computer tomography(CBCT) scanning. The contact point of upper second premolar and upper first molar was chosen for center of coordinate. Totally 20 layers of cortical bone were measured every 1 mm. Paired t test was performed with SPSS 15.0 for Windows to evaluate the differences between both sides, and one-way ANOVA was performed to compare the changes in different layers. RESULTS: The cortical bone thickness had no significant difference between left and right side. Below the 7th layer, cortical bone could not be seen or very thin (less than 0.5mm). Above the 10th to 12th layers, thickness of cortical bone was more than 1.5mm. The average cortical bone thickness was 2.12±0.72mm in male, and 1.86±0.83mm in female (above 7th layer). In the cortical area above the 6th layer, 13 layers of cortical bone thickness were significantly different(P<0.05) and only 2 layers had no significant difference(P>0.05). CONCLUSIONS: In this area, the cortical bone thickness is gradually increased from occlusal to gingival directions; and the cotical bone is thicker in male than in female at the same level.