Primary stability of mini-screw：buccal cortical thickness in maxillary posterior area of malocclusion

Zou Shuang-shuang; Lei Yong-hua; Zhang Ya-mei; Liu Lu

doi:10.3969/j.issn.2095-4344.2015.12.007

Abstract：BACKGROUND:Mini-screw stability is primarily related to alveolar bone cortical thickness. It is necessary to learn cortical thickness to choose suitable implanting sites and predict success rate. OBJECTIVE:To evaluate the buccal cortical thickness in maxilary posterior area of Class II Division I malocclusion adolescents. METHODS: Fifty-two adolescents (including 26 male and 26 female) of Class II Division I malocclusion scanned by Cone Beam Computer Tomography were involved in this study. The buccal cortical thickness of six posterior interradicular sites (14-15, 15-16, 16-17, 24-25, 25-26, 26-27) at four bone levels (2, 4, 6, 8 mm) from the alveolar crest in both boys and girls were measured. RESULTS AND CONCLUSION: (1) There was no statisticaly significant difference in alveolar cortical thickness between left and right sides in the girls (P > 0.05); cortical thickness of 5-6 and 6-7 at 8 mm was thicker than that at 2 mm (P < 0.05) and cortical thickness of 6-7 at 2 mm was smaler than that at 8 mm (P < 0.05). The cortical thickness increased from crest to base of alveolar crest and reached the peak at 8 mm. Cortical thickness of 6-7 was thicker than 4-5 at 8 mm depth (P < 0.05). The results of males were the same as females. (2) There was no statisticaly significant difference in alveolar cortical thickness of the same site between males and females (P > 0.05). Al sites in this study were suitable for mini-screw implantation; from the first molar to posterior dental arch, buccal cortical thickness is wel-distributed; it is dangerous for implantation in the areas around the first molar more than 6 mm, where the frequent presence of the maxilary sinus is observed. There is an increase of buccal cortical thickness from crest to base of alveolar crest, obtaining good initial stability.