Study on relationships between use of dentures and cerebral function in the elderly by means of positron CT

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Positron Emission Tomography (PET) with 18F-fluoro-D-deoxy glucose (FDG) was performed in healthy volunteers in order to investigate activities of the brain and the skeletal muscles in relation to masticatory function during gum chewing. As a result, it was found that activities of the masseter, temporal, medial pterygoid, lateral pterygoid, and tongue muscles could be simultaneously measured and quantified. PET images of the brain during gum chewing were also analyzed using SPM96 according to Friston et al. To clarify the characteristics of the brain activities. The primary sensorimotor areas, the premotor areas and the cerebellum were highly and bilaterally activated during arbitrary chewing while those activities were different in the left and right sides of the brain during the right side chewing. There were statistically significant differences in the brain activities during arbitrary chewing and the right side chewing. The activity of the right primary sensorimotor areas showed significantly higher during arbitrary chewing compared to the right side chewing. When the brain activities during the right side chewing was compared to those during arbitrary chewing, the left thalamus and mid brain, and the right putamen and cerebellum showed significantly higher activities. Thus it was appear that the brain activities differed depending on the chewing manner and this suggests that use of removable dentures also affect the brain activities.On the other hand, a force transducer was developed to measure denture retention that was one of the evaluating factors for removable dentures. The transducer was proved to be useful when it was applied to the measurement of retention force for an experimental palatal plate in 10 subjects. The average retention force and the standard deviation ranged 0.71 to 1.00 N and 0.16 to 0.61, respectively. Whereas the retention forces showed wide variations between subjects, reproducibility of the measurement was acceptable.