Three-dimensional evaluation of masseter muscle in different vertical facial patterns: a cross-sectional study in...

Area of Science:

• Orthodontics and Dentofacial Orthopedics
• Human Anatomy
• Biomedical Imaging

Background:

• Facial vertical patterns significantly influence craniofacial development.
• The masseter muscle, a key masticatory muscle, plays a role in facial morphology.
• Understanding masseter muscle anatomy in relation to facial types is crucial for orthodontic diagnosis and treatment planning.

Purpose of the Study:

• To analyze the three-dimensional (3D) anatomical characteristics of the masseter muscle in growing individuals with varying vertical facial patterns using ultrasound (US).
• To investigate the relationship between mandibular plane angle (FMA) and masseter muscle dimensions in prepubertal subjects.

Main Methods:

• Sixty prepubertal subjects (mean age 11.5 ± 1.6 years) with Class I occlusion were categorized into brachyfacial (FMA < 22°), mesofacial (22° ≤ FMA ≤ 28°), and dolichofacial (FMA > 28°) groups based on lateral cephalograms.
• Ultrasound (US) scans were performed to measure masseter muscle width, thickness, cross-sectional area, and volume during relaxation and contraction.
• Analysis of variance (ANOVA) with Tukey's post hoc tests were used to compare measurements between groups.

Main Results:

• Masseter muscle dimensions (width, thickness, area, volume) were significantly smaller in dolichofacial subjects compared to brachyfacial and mesofacial subjects.
• Masseter muscle volume showed a significant 10% decrease from brachyfacial to mesofacial, and from mesofacial to dolichofacial groups.
• A significant negative correlation was observed between US measurements and the Frankfort-mandibular plane angle (FMA), indicating reduced masseter size with increased facial divergence.

Conclusions:

• Ultrasound is a reliable in vivo method for evaluating masticatory muscles in children.
• Growing individuals with a dolichofacial vertical pattern exhibit reduced masseter muscle dimensions compared to their brachyfacial and mesofacial counterparts.
• These findings highlight the association between facial morphology and masticatory muscle development, offering valuable insights for orthodontic assessment.