Bone Cells and Mast Cells Express MMP-9 During Tooth Eruption In Vivo

Abstract

Context: Tooth development takes place inside a bony crypt in the alveolar bones. Tooth eruption requires, therefore, the removal of bone and lamina propria to establish the eruptive pathway. Matrix metalloproteinases (MMPs) belong to a family of enzymes responsible for the degradation of the extracellular matrix (ECM). MMP-9 is a member of this family and is secreted by a variety of cells, including mast cells. Both have been identified as possible collaborators for tissue remodeling during tooth eruption. Aims: The aim of this study is to analyze the bone remodeling, MMP-9 expression, and the prevalence of mast cells throughout the eruptive process of rat molars. Materials and Methods: Twenty-eight rats (4–17 days old) were used in this study. Histomorphometric analyses were performed to determine the bone area in the basal and coronal regions of the bony crypt and the prevalence of mast cells at the lamina propria along the eruptive process. Immunohistochemistry was performed to detect MMP-9 expression in the lamina propria and alveolar bone. Results: Increased bone apposition at the base of the bony crypt was observed at 14 days and increased resorption of the coronal bone was detected after 9 days. An elevated number of mast cells was observed in 9-day-old rats, and MMP-9 was strongly expressed in mast cells and osteoclasts. Conclusion: Taken together, we suggest that mast cells may contribute to the recruitment of osteoclast precursors during tooth eruption and that MMP-9 is possibly involved in the removal of the ECM during the eruptive process.