Reliability of chewing kinematic measurements in the neutral and forward head posture

Abstract

Aim: The purpose of this study was to examine the within and between-sessions reliability during chewing in two different head-neck postures. Methods: Asymptomatic participants were recruited for this study. Mandibular movements were tracked using a 12-camera three-dimensional motion analysis system. Twelve retro-reflective markers (including a technical marker placed on the chin) were placed on specific landmarks and used to define the local coordinate systems for the cranium and the mandible. Participants were asked to chew gum (1.4gram pellets) for 4 minutes while maintaining two different head-neck positions (neutral head posture (NHP) and forward head posture (FHP)) during two separate recording sessions, one week apart. The order of the head-neck positions was randomized. Mandibular movements were described with regards to the cranium using a customized code written in Matlab®. Ten representative chewing cycles were identified visually, processed and analysed as three separate time intervals (i.e. first, second and third minute time intervals). Mandibular rotations (degrees) around the x, y and z axis were used as the main outcome measure. The most reliable time interval within and between-sessions reliability was determined with the participants registered in NHP as determined by intraclass correlation coefficient (ICC) values. The influence of change in head-neck postures on the between-sessions reliability of measurements in the most reliable time interval was also evaluated on the basis of ICC values. Results: Seven participants, aged between 19 to 33 years of age, took part in the study. Of the three chewing time intervals examined, the third minute was found to be the most reliable in measuring the range of mandibular rotation (within-sessions ICC values ranged between 0.84 to 0.97 and between-session ICC values ranged between -0.74 to 0.97). Changes in head-neck posture from NHP to FHP reduced between-sessions ICC values in the x-axis (NHP = 0.56; FHP = -0.74) and y-axis (NHP = 0.97; FHP = 0.83), while the z-axis increased (NHP = 0.32; FHP = 0.38). Conclusion: When collecting kinematic mandibular rotation data during chewing, the time interval in which the data is collected are important factors to be taken accounted of. The reliability of measuring the range of mandibular rotation during chewing tasks in the NHP was found to be the most reliable after three minutes of chewing gum. Furthermore the registration of head-neck posture in the NHP provides improved reliability when compared with data obtained during chewing with these same participants registered in the FHP. The findings of this study may be a useful benchmark for future chewing kinematic studies involving patient populations.