Posterior scissors-bite: masticatory jaw movement and muscle activity

Area of Science:

• Dentistry
• Orthodontics
• Biomechanics

Background:

• Scissors-bite malocclusion involves buccal inclination of maxillary posterior teeth or linguoversion of mandibular posterior teeth.
• This condition can lead to reduced occlusal contact and excessive vertical overlap of posterior teeth.

Purpose of the Study:

• To investigate masticatory jaw movement and muscle activity in patients with unilateral posterior scissors-bite.
• This is the first case-control study to evaluate these factors in unilateral posterior scissors-bite.

Main Methods:

• A case-control study involving 30 adult patients with unilateral posterior scissors-bite and 18 healthy controls.
• Recorded jaw movement variables and surface electromyography data for masseter and temporalis muscles.

Main Results:

• Chewing patterns on the affected side differed significantly, showing narrower angles, longer closing duration, and slower closing velocity.
• Reduced activity was observed in both temporalis and masseter muscles on the working (affected) side.
• 96% of patients preferred chewing on the non-scissors-bite side.

Conclusions:

• Unilateral posterior scissors-bite is associated with distinct masticatory chewing patterns and altered jaw muscle activity.
• The findings highlight a significant preference for the non-affected side in chewing among patients with this malocclusion.