Transient receptor potential melastatin 8 (TRPM8) plays a crucial role in innocuous cool sensation, acute cold pain and cold-induced hyperalgesia during pathologic conditions. To help understand TRPM8-mediated cold perception in the dental pulp and periodontal tissues, we examined the distribution of TRPM8-immunopositive (+) axons in molar and incisor pulp and periodontal tissues using transgenic mice expressing a genetically encoded axonal tracer in TRPM8+ neurons. In the radicular pulp of the molar teeth, a small number of TRPM8+ axons were observed. TRPM8+ axons branched frequently and extensively in the core of coronal pulp, forming a network in the peripheral pulp. Some TRPM8+ axons ascended between odontoblasts and were observed in the dentinal tubule. TRPM8+ axons were linear-shaped in the radicular pulp, whereas many TRPM8+ axons showed portions shaped like beads connected with thin axonal stands at the peripheral pulp. TRPM8 was densely expressed in the bead portions. In the incisor pulp, TRPM8+ axons were occasionally observed in the core of the coronal pulp and rarely observed at the peripheral pulp. TRPM8+ axons were occasionally observed and showed a linear shape rather than a bead-like appearance in the periodontal ligament and lamina propria of the gingival tissue. These findings, showing differential distribution of TRPM8+ axons between radicular and coronal portions of the molar pulp, between incisor and molar pulp, and between dental pulp and periodontal tissues, may reflect differential cold sensitivity in these regions.

As pulp calcification occurs at least fifty percent of total teeth, the focal calcification in pulp chamber usually appears in all age groups. However, the pulp calcification is one of the important pathologic changes affecting the pulp vitality. In order to elucidate the mechanism of pulp calcification during the retrogressive degeneration of pulp tissue we performed an immunohistochemical study for proteases (MMP-3, MMP-10, and cathepsin-G), antiproteases (TIMP-1, α1- AT) and proteins involving tissue protection (TGase-2 and HSP-70). In the normal pulp tissue MMP-3 and MMP-10 were weakly expressed, but cathepsin-G and TIMP-1 were rarely expressed. Around the calcifying tissue of MMP-3, MMP- 10, and α1-AT were predominant, but TIMP-1 and cathepsin-G were sparsely expressed. On the other hands, TGase-2 and HSP-70 were condensed in the proximal fibrous tissue. These data suggest that the pulp calcification is related to retrogressive pulp degeneration, which could be resulted in the incomplete digestion of the degenerated stromal tissue by different proteases. We presume that the aberrant protease digestion of chronic pulpal pathosis, i.e., sclerotic fibrosis, chronic pulp degeneration, etc., may enhance the dystrophic calcification in dental pulp.