Initial Transient Accumulation of M2 Macrophage–associated Molecule-expressing Cells after Pulpotomy with Mineral Trioxide Aggregate in Rat Molars

Abstract

IntroductionM2 (alternatively activated) macrophages are known to participate in wound healing and tissue repair. This study aimed to analyze the temporospatial changes in the distribution and density of M2 macrophage–associated molecule-expressing cells after pulpotomy with mineral trioxide aggregate (MTA) in rat molars to ascertain the role played by M2 macrophages in the healing of MTA-capped pulp tissue. MethodsThe maxillary first molars of 8-week-old Wistar rats were pulpotomized and capped with MTA. After 1–14 days, the teeth were examined after hematoxylin-eosin staining or immunoperoxidase staining of CD68 (a general macrophage marker) and M2 macrophage markers (CD163 and CD204). The density of positively stained cells was enumerated in the surface and inner regions (0–100 μm and 300–400 μm, respectively, from the wound surface). ResultsMTA capping initially caused mild inflammatory changes and the formation of a degenerative layer followed by progressive new matrix formation and calcified bridging. At 1–2 days, CD68-, CD163-, and CD204-positive cells started to accumulate beneath the degenerative layer, and the density of these cells was significantly higher in the surface region than in the inner region (P < .05). From 7 days onward, the 3 types of cells displayed an almost normal distribution beneath the newly formed dentinlike matrix. ConclusionsAfter the pulpotomy of rat molars with MTA, M2 macrophage–associated molecule-expressing cells transiently accumulated beneath the degenerative layer under the MTA. This suggests that M2 macrophages participate in the initial phases of the healing of MTA-capped pulp tissue.