Temporospatial localization of dentine matrix protein 1 following direct pulp capping with calcium hydroxide in rat molars

AimTo examine the temporospatial expression of dentine matrix protein 1 (DMP1; a noncollagenous protein involved in mineralized tissue formation), osteopontin (another noncollagenous protein detected during reparative dentinogenesis) and nestin (a marker of differentiating/differentiated odontoblasts), following direct pulp capping with calcium hydroxide in rat molars. MethodologyThe maxillary first molars of 8-week-old Wistar rats had their pulps exposed and capped with calcium hydroxide. The pulp-capped teeth were collected from 6h to 14days postoperatively and processed for immunohistochemistry for DMP1, osteopontin and nestin. Cell proliferation was monitored using 5-bromo-2-deoxyuridine (BrdU) labelling. ResultsThe capped pulps initially exhibited superficial necrotic changes followed by the formation of new matrix and its mineralization. DMP1 immunoreactivity was observed in the matrix beneath the necrotic layer from 6h onwards and present in the outer portion of the newly formed mineralized matrix from 7days onwards. Osteopontin displayed a similar expression pattern, although it occupied a narrower area than DMP1 at 6 and 12h. Nestin-immunoreactive cells appeared beneath the DMP1-immunoreactive area at 1day, were distributed beneath the newly formed matrix at 5days and exhibited odontoblast-like morphology by 14days. BrdU-positive cells significantly increased at 2 and 3days (P<0.05) and then decreased. ConclusionsThe deposition of DMP1 at exposed pulp sites preceded the appearance of nestin-immunoreactive cells, active cell proliferation and new matrix formation after pulp capping with calcium hydroxide in rat molars, suggesting that DMP1 acts as a trigger of pulp repair. The colocalization of DMP1 and osteopontin suggests that these two proteins play complementary roles.