Response of the somatosensory cortex following thermal stimuli to dental implants.

In the current study, we investigated the cortical response of the somatosensory cortex following thermal stimuli to dental implants. Five implants were inserted at the site of the left upper canine with immediate implant placement protocols in five cats. Intrinsic signal optical imaging was applied to measure the cortical responses evoked by thermal sensing via dental implants. The cortical response evoked by 60 g of tactile stimulus to implants was also examined. The response strength and activated location were compared between implants and natural teeth. Thermal stimuli via the implant could evoke reliable cortical responses in the tooth-related region. However, the response amplitude evoked by the cold stimuli applied to the implants was significantly lower than that evoked by the cold stimuli applied to the natural teeth, indicating that the implants were less sensitive to thermal change than the natural tooth. The response evoked by tactile stimuli to implants was significantly stronger than that evoked by cold stimuli. Thermal and tactile stimuli activated the same location of the tooth-related somatosensory cortex in both the implants and natural teeth. Therefore, the thermal change in implants could be detected at the cortical response level. Multimodal sensory integration of thermal and tactile functions existed for implants.

The role of gingival mechanoreceptors in the tactile function of dental implants.

Dental implants seem to restore some degree of tactile function. The aim of this study was to investigate the role of gingival mechanoreceptors in dental-implant osseoperception at the cortical-response level. The gingiva of the upper-left canine implant was stripped off under local anesthesia in five cats. We used intrinsic-signal optical imaging (ISOI) to measure the population-response characteristics of the feline oral-related cortex when separately applying punctate mechanical stimuli to the left canine implant and right intact natural canine. These response characteristics were compared under local anesthesia after removal of the gingiva. Under local anesthesia, the signal strength of the implant was significantly weaker than that of the tooth under weak but not under strong stimulus. After the gingiva was stripped off, the signal strength of the implant was significantly weaker than that of the tooth at all strengths of stimulus. Based on the evoked cortical responses, the gingiva was involved in the maximal tactile function of the implant.

Investigating the role of gingiva in the tactile function of teeth at the cortical level.

The role of the gingiva in the tactile perception of teeth is unclear, and the physiological basis of tooth tactile function needs to be examined at the cortical response level. In the presented study, gingiva from the upper left canine was removed under local anesthesia from five cats. Intrinsic signal optical imaging was used to measure population response characteristics of the cat oral-related cortex when punctate mechanical stimuli were separately applied to the left gingiva-stripped canine and right intact canine. Then, their response characteristics were compared. There were no significant differences in the cortical response strength between the anesthetized and unanesthetized canines. Signal strength of the gingiva-stripped tooth was significantly weaker than that of the intact tooth at low stimulus strength. However, no significant differences between the gingiva-stripped tooth and intact tooth were found after saturation. Based on the evoked cortical responses, the gingiva is involved in low-intensity tactile perception of teeth, which could explain the reason why chronic gingivitis results in the paresthesia of natural teeth.