[MRI analysis of the effect on mandibular retrusion with anterior disc displacement treated by using Herbst appliance].

Objective: To investgate the effect of Herbst appliance on the growth and remodeling of the temporomandibular joint (TMJ) in class Ⅱ patients with mandibular retrusion by using MRI. Methods: Between December 2010 and October 2014, 12 class Ⅱ patients (11-16 years old) with mandibular retrusion were chosen. The patients were divided into two groups. The control group included 7 patients (14 joints) with normal disc condyle relationship and the anterior disc displacement (ADD) group included 5 patients (10 joints) with anterior disc displacement. The MRI images of TMJ were measured, including condylar height, joint space index and disc position ratio, before and after the treatment. Results: The condylar height of the patients in the control group was significantly increased (P<0.001) after treatment, and no significant difference in joint space index (P=0.821) and disc position ratio (P=0.146) was found. The joint space index of the patients ([-14.70±8.82]% and [4.90±11.35]%) in ADD group changed significantly (P<0.001) after treatment, and no significant difference in condylar height (P=0.294) and disc position ratio (P=0.120) was found. Conclusions: The normal disc condyle relationship was beneficial to the reconstruction of the condylar process, and the increase of the condylar height. The condyle moved forward in patients with anterior disc displacement after treatment.目的：通过MRI评价颞下颌关节盘前移位对Herbst矫治器矫治安氏Ⅱ类错牙合畸形下颌后缩患者关节生长改建的影响，为临床提供参考。方法：回顾2010年12月至2014年10月于上海交通大学医学院附属第九人民医院就诊的11~16岁安氏Ⅱ类错牙合畸形下颌后缩患者12例（共24侧关节）。7例共14侧关节的关节盘-髁突关系正常，为对照组；5例共10侧关节伴关节盘前移位为ADD组；测量Herbst功能矫治前后MRI影像的髁突高度、关节间隙指数及关节盘位置比，评估患者颞下颌关节的生长改建情况。结果：对照组矫治后髁突高度为（5.46±1.13）mm，比矫治前[（4.50±1.12）mm]显著增加（P<0.001）；关节间隙指数和关节盘位置比矫治前后差异均无统计学意义（P=0.821、0.146）。ADD组关节间隙指数矫治前后[分别为（-14.70±8.82）%和（4.90±11.35）%]差异有统计学意义（P<0.001），即矫治后髁突位置前移；髁突高度和关节盘位置比矫治前后差异均无统计学意义（P=0.294、0.120）。结论： Herbst矫治器可矫治安氏Ⅱ类错牙合畸形下颌后缩，正常的关节盘-髁突关系有利于髁突改建，促进髁突高度增加；ADD患者矫治前后髁突-关节窝关系变化显著，髁突位置前移。.