Periodontal Masseteric Reflex is Changed by Periodontal Sensory Modification during Occlusal Hypofunction in Rats

The purpose of this study was to investigate changes in the periodontal masseteric reflex (PMR) after experimentally induced occlusal hypofunction. Wistar rats were divided into control groups (CGs) and hypofunction groups (HGs). Rats in the HGs had their lower incisors cut down every other day for 6 weeks. Electrical stimulation was given to the periodontal ligaments of an upper incisor or the left trigeminal mesencephalic nucleus (MeV) in the CGs and HGs. Recordings of masseter motor unit responses were performed at 0, 1, 2, 4 and 6 weeks after hypofunction. Compared with the CGs, significant longer latencies in the PMR were found in the 4w- and 6w- HGs. After MeV stimulation, no significant difference in latency was found between HGs and CGs. After periodontal stimulation, the threshold value of masseteric motor-unit responses was higher in HGs than in CGs in 4and 6 weeks respectively. These results suggest that the PMR can be changed by periodontal sensory modification during occlusal hypofunction