Temporal alteration of chewing jaw movements after a reversible bite-raising in guinea pigs

Previous studies analysed the temporal changes of occlusal vertical dimension (OVD) with natural molar tooth contacts in bite-raised guinea pigs and found that the OVD is strictly maintained in the growing guinea pigs. Since the OVD is considered to be the influencing factor for performing mastication, we hypothesised that a control of the OVD is integrated with maintenance of an appropriate chewing behavior. In young adult guinea pigs with or without bite-raised treatment, the OVD was measured by micro-CT and stable chewing movements were recorded during 11 days after the removal of the bite-raising appliance. In control animals, the OVD increased developmentally up to 10.5 ± 6.0% for 11 days. In the bite-raised animals, the increased OVD was increased by 19.1 ± 6.7% with the bite-raising appliance, and the OVD rapidly decreased to the same level as that of controls within 4 days after the removal of the appliance. During chewing on the first day after the removal of the appliance, the most closed position of the jaw was lower in bite-raised animals than in controls while the most opened position did not differ between the two groups, i.e., the jaw gape was decreased. These changes disappeared when OVD returned to the same level as that of controls. Any other variables for movements (e.g., rhythm) did not differ between the both groups throughout the experimental period. These results suggest that there is a robust association between an innate OVD and a centrally-programmed pattern of chewing movements for functional integrity.