Head movements in the occlusal phase of mastication.

It has been recognized that mandibular movements evoke head movements during jaw tapping. However there have been only a few studies that investigated the aspects of head movements during mastication. The objective of this study was to demonstrate the hypothesis that the head moves actively in mastication in order to achieve effective destruction of a food bolus. Head and mandibular movements during gum, gummi candies and kelp chewing among nine adult volunteers have been recorded as time series data with a three-dimensional motion capture system and the vertical components of the movements have been analyzed. To focus on occlusal phase of mastication, the following parameters have been examined: time lag of the head movements at the beginning of occlusal phase, perpendicular velocity of the head at the beginning of the phase of occlusion, and average velocity of the head during occlusal phase. The results showed that the head moved downward in mastication and the velocity of the head movements increased in the order of gum, gummi candies and kelp chewing. There is a possibility that the elasticity of a food bolus affects the activity of head movements, and the kinetic energy was increased to achieve effective destruction of a food bolus.