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

To quantitatively evaluate the cortical bone thickness at upper molar miniscrew sites.

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.

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).

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.