Rotational head motion concurrent to rhythmical mandibular opening movements.

Area of Science:

• Biomechanics
• Craniofacial Kinesiology
• Head and Neck Anatomy

Background:

• Previous research established a functional-rhythmical coupling between the head and mandible using incisal tracking.
• However, prior studies lacked data on whole-head motion and the instantaneous center of rotation.

Purpose of the Study:

• To determine if the head exhibits rotational motion during mouth opening.
• To identify the instantaneous center of rotation for head movement during jaw opening and closing.

Main Methods:

• Utilized a 6 degree of freedom (d.f.) measuring device to analyze head and mandibular movements in five adult males.
• Assessed sagittal plane motion by tracking reference points on the head (incisor, cranial base, occipital, parietal) and mandible during maximal mouth opening and closing.
• Calculated motion vectors and defined the instantaneous center of rotation as the point with minimal motion around head reference points.

Main Results:

• Observed concomitant movements of the mandibular and maxillary incisal points during jaw opening and closing.
• Identified distinct displacement patterns for head reference points (O, P, C) during opening and closing.
• Determined that the head undergoes clockwise rotation during opening and counter-clockwise rotation during closing in the sagittal plane.

Conclusions:

• The head exhibits a rotation-like sagittal movement during mouth opening.
• The instantaneous center of rotation appears to be located superior to the cranial base reference point.
• The precise location of the head's center of rotation varies with the magnitude of mouth opening.