Mandibular rest position in subjects with high and low mandibular plane angles

Area of Science:

• Dentistry
• Orthodontics
• Biomechanics

Background:

• Facial morphology and mandibular posture have been investigated, but conclusive findings are limited.
• Understanding the relationship between facial types and jaw resting positions is crucial for diagnosing and treating various dental and orthodontic conditions.

Purpose of the Study:

• To investigate the influence of distinct facial morphologies on both clinical and electromyographic rest positions of the mandible.
• To determine if facial skeletal patterns correlate with differences in mandibular resting posture.

Main Methods:

• Recruited 20 subjects, divided into low-angle (Frankfort-to-mandibular plane <20°) and high-angle (>30°) facial morphology groups.
• Measured clinical rest position using soft tissue landmarks and electromyographic (EMG) rest position via EMG integrator and kinesiograph.
• Maintained consistent head posture relative to the subject's visual axis during measurements.

Main Results:

• Clinical rest position was significantly greater in the low-angle group (4.6 mm) compared to the high-angle group (3.1 mm).
• No significant differences were found in EMG rest positions between the low-angle (9.9 mm) and high-angle (9.7 mm) groups.
• These findings challenge simple mechanical explanations for jaw posture.

Conclusions:

• Contrasting facial morphologies influence the clinical, but not the electromyographic, rest position of the mandible.
• The results indicate that factors beyond simple mechanics may govern mandibular posture.
• Further research is recommended, including assessments with subjects allowed to select their preferred head inclination.