Preliminary study of neural excitation with positron emission tomography after tooth mechanical stimulation

Dentists often cannot objectively find abnormalities in patients who complain of discomfort or abnormal sensation in their dental occlusion. We hypothesized that abnormal neural transmission from the tooth is related to this occlusal discomfort sensation. Chronic tooth contact habits may induce neural excitation from the tooth to the central nervous system, and may aggravate the sensation of discomfort in the central nervous system. However, the details of neural transmission from the tooth to the central nervous system are still unclear. In this study, we stimulated a rat premolar mechanically and observed activated bran sites using positron emission tomography (PET) and 18F-2-fluoro-2-deoxy-D-glucose (FDG). We anesthetized 5-7-week-old male rats using isoflurane inhalation anesthesia and stimulated the upper right premolar mechanically with an electric von Frey system (Model 1601C, IITC Instruments) by measuring mechanical pressure. Before the tooth mechanical stimulation, we injected FDG through the rat’s caudal vein and then used a stimulation intensity of 100, 200 or 300 g. We recorded FDG accumulation with PET. The PET brain images were separated into four parts (right higher, left higher, right lower and left lower) for analysis and the peak value of striatal uptake (SUV) in each part was analyzed. The PET images showed that the accumulated FDG in the right lower part of the brain was higher with 300 g tooth stimulation than with 100 or 200 g. The data showed that the tooth stimulation site in the lower part of the brain was activated with tooth stimulation by comparing it with the other parts. We also measured SUV in the right and left sensory areas, motor area, hippocampus, trigeminal ganglia (TG) and spinal cord. The TG and sensory area showed more FDG accumulation compared with mouth opening.

咬合違和感を訴えて来院した患者に対して，歯科医師は咬合状態に客観的な異常を見つけることができないこともよくある．我々は歯からの神経伝達が咬合違和感と何らかの関連をしているのではないかと仮説を立てて研究を行っている．慢性的な歯への刺激が歯から中枢における神経興奮に関連しており，中枢での咬合違和感を悪化させるのかもしれないと考えられる．しかしながら，歯から中枢への神経伝達の詳細は不明である．この研究ではラットの小臼歯を機械的に刺激して，脳の活動部位を18F-2-フルオロ-2-デオキシ-D-グルコース （FDG）を用いて放射断層撮影法（PET）により計測した．5〜7 週齢のラットをイソフルレンを用いて全身麻酔し，電気的フォンフレイ刺激装置を用いて刺激圧を計測しながら上顎右側小臼歯を刺激した．歯の刺激前にFDG を尾静脈から注射し，100，200，300g の刺激力を用いて刺激した． 脳PET 画像は脳を4 分割（右上，左上，右下，左下）して，ピーク値を計測したところ，右下部においては300g の刺激力は100，200g よりもFDG の集積が観察された．この結果は歯の刺激により脳の右下部位が活動することを示していると考えられる．また，知覚部位，運動部位，海馬，三叉神経節，脊髄に分類して観察したところ，三叉神経節と知覚部位においてFDG の集積が観察された．