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Impact of orthodontic forces on masseter muscle morphology and function: A CBCT and electromyographic study
Pascal Ubuzima1, Quancheng Han2, Yuhe Cheng2
1Department of Orthodontics, College & Hospital of Stomatology, Anhui Medical University, Key Lab. of Oral Diseases Research of Anhui Province, Hefei 230032, China; School of Dentistry, College of Medicine and Health Sciences, University of Rwanda, Kigali, Rwanda.
Background:
Orthodontic treatment is important in restoring facial balance and harmony. The morphology and function of masticatory muscles influence facial aesthetics. This study aimed to assess the morphological and functional adaptation of masseter muscle during orthodontic treatment.
Methods:
Two hundred and seventy-six fixed orthodontic patients aged 8-42 years were included and grouped into teenagers and adults. Pretreatment (T0) and three-month post-bonding (T1) masseter muscle morphology and function were assessed using Cone-Beam Computed Tomography (CBCT) and Electromyography (EMG). Assessments were performed at rest, maximum clenching and chewing. Independent t-test and Mann-Whitney U test were used for comparisons. Statistical significance was set at p < 0.05.
Results:
Morphologically, CBCT data showed no initial gender-based differences at T0. At T1, adult males exhibited a significant increase in masseter muscle length (MML), whereas adult females showed a notable reduction in masseter muscle thickness (MMT) and masseter muscle cross-sectional area (MMCA) on both sides. Teen females displayed a significant MMCA reduction (left). Functionally, mandibular postural position (MPP) and maximum voluntary bite position (MVBP) at the right side showed significant differences in adult patients at T0. In adult females, significant changes were observed in MPP (left) and masticatory movement (MM) (both sides), while adult males exhibited significant differences in MPP (left), MVBP (both sides), and MM (both sides). No significant functional differences were noted between orthodontic teenagers and adults as revealed by EMG data.
Conclusion:
Altered masseter muscle activities and reductions in apparent dimensions, particularly in the female patients appeared within three months of orthodontic fixed treatment.
