下切牙内收与牙槽骨厚度变化间的相关分析

Correlationship between the retraction of lower incisors and the thickness of the alveolar of symphysis

目的分析拔牙矫治后下切牙内收量与下颌颏联合处牙槽骨厚度变化间的相关关系。方法从矫治完成的安氏Ⅱ1类错[牙合]患者中，选取拔除4个第一双尖牙（组1），拔除上颌第一、下颌第二双尖牙（组2）以及下颌未矫治的非拔牙（组3）患者各15例，进行矫治前后的X线头影测量分析。结果两拔牙组牙槽点、B点及根尖处的牙槽骨厚度都明显减小（P〈0．01），而下颌未矫治组无明显变化；组1的下切牙内收量与B点及根尖处的牙槽骨厚度减小呈正相关，而组2仅与根尖处的牙槽骨厚度减小正相关。结论下切牙内收后，B点与根尖点处的牙槽骨厚度明显减小，且内收量越大该处厚度减少的越多，在临床诊疗与设计时应予以考虑。

Objective To investigate the correlationship between the retraction of lower incisors and the change of symphysis in patients with Class Ⅱ division 1 malocclusion. Methods Forty-five patients were divided into 3 groups, 15 patients in each group. The extraction protocols included that extraction of 4 first premolars （group 1 ）, extraction of upper first premolars and lower second premolars （group 2）, and nonextraction （group 3）. Cephalograms were analyzed for all patients. Results In the two extraction groups, the thickness of symphysis at infradentale, apex, β point were decreased significantly. In the nonextraction group, no significant change was found. In Group 1, a positive correlation was found between the retraction of lower incisors and the reduction of the thickness at B point, apex point of symphysis; In Group 2, a positive correlation was only found between the retraction of lower incisors and the thickness of symphysis at apex： Conclusions The more retraction of the lower incisors, the more reduction of the thickness of symphysis was achieved in the extraction groups.