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Relationship between facial asymmetry and masseter reflex activity
Naoki Machida1, Kazuhiro Yamada, Yoshiyuki Takata
1Division of Orthodontics, Department of Oral Biological Science, Course for Oral Life Science, Niigata University Graduate School of Medical and Dental Sciences, Niigata City, Japan. orthomac@pop02.odn.ne.jp
Summary
Facial asymmetry in orthognathic patients alters the tonic vibration reflex (TVR) of masseter muscles. A higher TVR index on the deviated side suggests a link between craniofacial morphology and reflex responses.
Area of Science:
- Biomedical Engineering
- Neurology
- Orthodontics
Background:
- Facial asymmetry can impact neuromuscular function.
- The tonic vibration reflex (TVR) is a measure of muscle spindle activity.
Purpose of the Study:
- To evaluate the tonic vibration reflex (TVR) of masseter muscles in individuals with and without facial asymmetry.
- To investigate the relationship between facial asymmetry, mandibular deviation, and masseter muscle reflex responses.
Main Methods:
- TVR was elicited in 10 healthy volunteers and 12 orthognathic patients with facial asymmetry.
- Electromyography recorded masseter muscle activity during TVR and maximum voluntary contraction (MVC).
- Mandibular deviation was quantified using frontal cephalograms; TVR index and ratio were calculated.
Main Results:
- Patients with facial asymmetry exhibited a significantly higher TVR index on the deviated side compared to the non-deviated side.
- A negative correlation was observed between the degree of mandibular deviation and the side-to-side difference in TVR index (r = -0.536, P <.05).
- Individuals with lower MVC on the deviated side showed a higher TVR ratio than controls.
Conclusions:
- Masseter muscle TVR differences between sides may be associated with frontal craniofacial morphology.
- TVR assessment could provide insights into neuromuscular adaptations in facial asymmetry.
- Findings suggest potential clinical applications in evaluating and managing facial asymmetry.