Department of Orthodontics, University of Geneva Dental School, 19 rue Barthélemy-Menn, Geneva, Switzerland.
Orthod Craniofac Res. 2010 Nov;13(4):203-13. doi: 10.1111/j.1601-6343.2010.01496.x.
To estimate the association of initial masseter muscle thickness with treatment outcomes using functional appliances and the effect of treatment on masseter muscle thickness.
Twenty-two children, aged 8-12, with skeletal and dental class II relationships and increased overjet were treated with twin-block appliances for 9-17 months, until a class I molar relationship and decreased overjet was achieved. Dental casts, lateral cephalograms, and ultrasonographic measurements of the masseter muscle were performed before and after treatment. Twenty-two children, aged 8-12, without immediate need for orthodontic treatment, served as controls. They were observed for 11-17 months, and ultrasonographic masseter muscle measurements were taken before and after the observation period.
Masseter muscles in treated children were thinner at the end of treatment, while untreated controls showed an increase in thickness. Treated children with thinner pre-treatment muscles showed greater mandibular incisor proclination, distalisation of maxillary molars, and posterior displacement of the cephalometric A point during treatment.
Treatment of a dental class II relationship with functional appliances leads to mild atrophy of the masticatory muscles, possibly because of their decreased functional activity. The initial condition of the muscles may be associated with mandibular incisor proclination, and the position of maxillary first molars and A point.
评估使用功能矫治器治疗时，咬肌初始厚度与治疗效果的关系，以及治疗对咬肌厚度的影响。
22 名 8-12 岁的儿童，存在骨骼和牙齿的 II 类关系以及较大的覆盖，使用双板矫治器治疗 9-17 个月，直到获得 I 类磨牙关系和减少覆盖。在治疗前后进行了牙模、侧位头颅侧位片和咬肌超声测量。22 名 8-12 岁没有立即需要正畸治疗的儿童作为对照组。他们观察了 11-17 个月，并在观察期前后进行了咬肌超声测量。
治疗结束时，治疗组儿童的咬肌较薄，而未治疗的对照组则显示出厚度增加。治疗组中治疗前肌肉较薄的儿童在治疗过程中下颌切牙更前倾、上颌磨牙远移和头影测量 A 点后移。
功能性矫治器治疗 II 类错颌关系会导致咀嚼肌轻度萎缩，可能是因为其功能活动减少。肌肉的初始状态可能与下颌切牙前倾、上颌第一磨牙和 A 点的位置有关。
