Changes of masseter muscle thickness during orthodontic treatment with fixed appliances: a prospective controlled study in growing children

Abstract

Objectives To examine the effects of orthodontic treatment with fixed appliances on masseter muscle thickness in growing children. Subjects and method Forty children with a mean pre-treatment age of 12.9 ± 1.19 years with mild to moderate malocclusions were treated with fixed appliances. Forty untreated children served as the control group, with a mean age of 9.14 ± 0.91 years at the start of the study. Masseter muscle thickness was measured by ultrasonography at treatment start and 1 year later in the patient group, and at equivalent times in the control group. Differences within and between the groups were evaluated using paired and independent sample t-tests, respectively. Multiple regression analysis was conducted to examine associations between different variables, including age, gender, and treatment. Results Masseter thickness at the beginning of the study was smaller (P =. 004) in the control group (10.57 ± 1.04 mm) than in the treatment group (11.26 ± 1.03 mm), an observation that can be partly explained by the initial age difference between the groups. One year later, masseter muscle thickness increased in the control group (0.38 ± 0.50 mm, P