ABSTRACT
AIM: To investigate if treatment outcome in patients with Class II division 1 malocclusion treated by a variety of approaches is affected by masticatory muscle capacity. MATERIALS: Seventy-four children with Class II division 1 malocclusion were included in the present study. These were divided into 54 children (10.4 ± 1.6 years of age) treated with fixed appliances including headgear and/or Class II intermaxillary elastics, 12 children (9.9 ± 1.9 years of age) treated with functional appliances and 8 children treated with fixed appliances and other means of treatment. Ultrasonographic masseter muscle thickness measurements were taken before treatment, while lateral cephalograms were taken before and after treatment. STATISTICS: Multivariate linear regression analysis was used to assess the association between masseter muscle thickness and treatment outcomes, as well as the gonial angle and treatment outcomes. CONCLUSION: In children with Class II division 1 malocclusion treated by means other than functional appliances, treatment outcome is not associated with masseter thickness. This may be the case since the application of intermaxillary forces and torque application may offset the functional component in tooth movement. Outcomes following functional appliance treatment may be partly determined by the masticatory muscles. During functional treatment, children with a weaker masticatory system show greater dentoalveolar compensation. This is however not maintained during the second phase of fixed appliance treatment.
Subject(s)
Malocclusion, Angle Class II , Orthodontic Appliances, Functional , Cephalometry , Child , Humans , Malocclusion, Angle Class II/diagnostic imaging , Malocclusion, Angle Class II/therapy , Mandible , Masseter Muscle/diagnostic imaging , Treatment OutcomeABSTRACT
The aims of this study were to assess the thickness of the masseter muscle by means of ultrasonography and to investigate the relationship between masseter electromyographic activity and muscle thickness bilaterally, during maximum voluntary clenches. Participants in the study consisted of 52 young female adults (mean age 23.7 +/- 2.5 years) without craniomandibular disorders and with full natural dentitions. The thickness of the masseter muscle was measured with a real-time ultrasound equipment. Electromyographic activity was recorded with bipolar surface electrodes, during maximum voluntary clenches. The error of the methods was calculated by double recordings in 15 subjects in a 4-week interval. The measurement error for the right muscle was 0.16 mm in thickness and 16.44 microV in electromyographic activity. For the left masseter the corresponding values were 0.19 mm and 18.01 microV. The relationship of masseter muscle thickness to its electromyographic activity was estimated by Pearson's correlation coefficient. The mean masseter thickness under contracted conditions was 13.9 +/- 1.5 mm for the right side and 13.9 +/- 1.4 mm for the left side. The mean maximum electromyographic activity was 379.0 +/- 56.0 microV for the right muscle and 372.3 +/- 73.2 microV for the left. Muscle thickness was strongly correlated to electromyographic maximum activity in the right masseter (r = 0.721, P < or = 0.001) and moderately correlated in the left muscle (r = 0.407, P < or = 0.01). The difference between the two sides is possibly because of the larger method error in the left side. It is apparent that ultrasonography can be used as a useful tool to assess masseter muscle functional capacity during full effort in healthy individuals.
