Ronen Shika Igaku

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According to a survey of old people, those healthy and mentally active invariably have 20 or more of their own teeth, which leads to a hypothesis that mastication may exert a positive influence on the brain. In fact, in our aging society there is a strong demand for a healthy life, using one's own teeth for biting and chewing. Recently positron emission tomography,(PET) has been developed and applied to brain researches. PET is a diagnostic method in which the subject is administered with radiopharmaceuticals (radioactive drugs) labeled with positron emitting radionuclides, and their distribution within the brain is imaged in slices using positron tomograph (PETcamera). Regional organ function can be evaluated from regional radioactivity distribution. Oxygen-15 water (H₂¹⁵O) is the radiopharmaceutical used to measure the regional cerebral blood flow (rCBF). Since the half life of oxygen-15 is very short (2minutes), the radioactivity decays out after the measurement, allowing repeated measurements of rCBF under different conditions. Comparing rCBF in stimulated state with baseline can reveal which specific s timulus increases the blood flow in which part of the brain. This technique is known as the H₂¹⁵O-PET activation study. Since the rCBF is known to be adjusted according to the regional neuronal activity, this technique can be used to study brain functional anatomy. In this report this technique was applied to rCBF measurements during mastication.
Method: The subject was a 30-year-old normal volunteer. Inspection of the oral cavity revealed a complete natural dentition with no missing teeth, and no abnormalities were observed in the oral mucosa. A specially designed training gum “Gumm's” (Lotte) was used for mastication. The subject's rCBF was measured with PET and intravenous injection of H₂¹⁵O under “gum mastication” and “resting” conditions with 15 minutes intervals.
The PET camera “Headtome IV” (Shimadzu) was used, providing 14 slices of tomographic images of the brain with spatial resolution of 7mm (Fig.1). Using a standard method the rCBF was calculated and mapped.
Results and Discussion: The rCBF image in gum mastication showed increased blood flow in the bilateral lower frontal and parietal lobes, compared to the resting rCBF images as shown by the arrow in the illustration (Fig.2). This area, lower part of the Rolandic area (or primary sensorimotor area), is believed to receive sensory input from the lips, tongue, oral mucosa, gingiva, teeth, periodontal ligaments, mandible and temporomandibular joint and to control the movement of the masticatory, lingual and facial muscles, and may be called “masticatory center”.

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