Clinical validity of measuring jerk-cost of jaw movement during speech: effect of mouthguard design on smoothness of jaw movements

Improvement of movement smoothness is indicated by reduction of movement jerk-cost. Although jerk-cost of masticatory jaw movement is known to be a sensitive indicator of occlusal abnormalities, an applicability of the jerk-cost measurement to diagnose speech jaw movement is uncertain. The jaw movement during speech is modified in adaptation to oral applications such as complete denture, orthodontic appliances and mouthguards. This study aimed to test sensitivity of the jerk measurement to distinguish between speech jaw movements that are performed in response to insertions of varied types of the mouthguards. Five subjects participated in this study. Mandibular incisor-point movements during speech were recorded at sampling rate of 100 Hz by a stereotaxic device. The subject was asked to read a prescribed Japanese sentence including 170 characters aloud with a normal pitch. Normalized values of the jerk-costs were calculated and compared. The results showed that the jaw movement smoothness was impaired by the insertions of mouthguards. However, the movement smoothness was improved by size reduction of lingual part of the mouthguards. It is concluded that the measurement is capable of sensitive monitoring of the smoothness of the jaw movement in speech articulation.