Spatial control of biting behavior : to bite and not to slip

Sammanfattning: Background: During biting and chewing the periodontal mechanoreceptors (PMRs) signal sensory information about the point of attack, the direction of the tooth loads and the intensity of the force with a high sensitivity to very low forces. The sensory information from the PMRs is used by the central nervous system (CNS) to control and position the food morsels and direct the force vectors during biting and chewing. In the absence of this information as for example in subjects with dental implants, control of food positioning, bite force direction and magnitude of force is hampered. Aims: The present thesis examines the sensorimotor mechanisms involved in the spatial aspects of human jaw movements during biting and chewing. Further, it aims to identify specific sensorimotor impairments in patients rehabilitated with fixed prostheses supported by dental implants or natural teeth. Material and methods: In a series of studies we investigated the effects of short-term training (Study I) and of transient sensory input deprivation due to local anesthesia (Study II) on oral fine motor performance in individuals with normal healthy dentition. Further, we evaluated sensorimotor impairments in patients with fixed tooth- and implant-supported prostheses during tasks involving biting (Study III) and chewing (Study IV). Results: These results of the present studies revealed that short-term training of oral fine motor tasks increased the accuracy of task performance and decreased the duration of jaw movements required to complete the biting task (Study I). Transient deprivation of sensory inputs decreased the accuracy of task performance, yet had no impact on the duration of jaw movements required to complete the biting task (Study II). Sensorimotor impairment was observed in subjects with fixed tooth- and implant-supported prostheses compared to subjects with natural dentition during the oral fine biting task. This impairment was apparent from lower accuracy of task performance and a shorter duration of jaw movements compared to those with natural dentition (Study III). Moreover, when attempting to crush the food morsel during a chewing task, the subjects in the fixed tooth- and implant-supported groups exhibited significantly longer total duration of the jaw movement phases than individuals with natural dentition, owing to food morsel slippage (Study IV). Conclusion: The findings of these studies indicate that short-term training leads to superior spatial control reflected in better performance and optimization of jaw motor functions. However, transiently or permanently altered inputs of sensory information from the PMRs perturbs the spatial aspects of oral fine motor control. It is apparent that lack of peripheral afferent input to the CNS attenuates fine-motor control of the jaws.