α-tricalcium phosphate (a TCP) with the addition of antimicrobials such as ciprofloxacin, metronidazole, and cefaclor (3Mix) has been applied to sterilize the infected dentin and pulp in vivo. Both clinical and animal experiments have shown that 3Mix is effective for sterilizing infected tissues. However, the responses of the infected dental pulp to 3Mix remain to be fully determined at the cellular level. This study aims to clarify the responses of neural elements and immune cells to antimicrobials during the healing process of infected pulp using immunohistochemistry for protein gene product (PGP) 9.5 and class II major histocompatibility complex molecules using both light and electron microscopy. An artificial pulp exposure was prepared on the maxillary molar of 14-week-old rats and maintained without any treatment for 12 - 24 h. Subsequently, the exposed pulp was covered with αTCP or α TCP containing 3Mix, followed with glass ionomer cement. A pulp abscess lacking both dendritic cells and PGP 9.5-reactive nerve fibers was induced after pulp capping with α TCP; in contrast, numerous dendritic cells accumulated along the pulp-dentin border followed by the differentiation of odontoblast - like cells and matrix deposition after the application of α TCP containing 3Mix. PGP 9.5-reactive nerve fibers were also densely distributed and surrounded the accumulated dendritic cells in the medial dental pulp beneath α TCP containing 3Mix. The findings indicate that the application of α TCP containing 3Mix to the infected pulp induces an intense accumulation of dendritic cells, suggesting that these cells play crucial roles in the differentiation of odontoblast like cells under pathological conditions.
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