Expression of extracellular matrix molecules, MMPs and TIMPs in alveolar bone, cementum and periodontal ligaments during rat tooth eruption

Tooth eruption involves extensive degradation and reorganization of extracellular matrix (ECM) components. It is not known how ECM-degrading enzymes are coordinated with each other or how they are regulated in the event. The present study was designed to investigate mRNA expression of inhibitors of metalloproteinases (TIMPs) in comparison with matrix metalloproteinases (MMPs) as well as ECM molecules during rat first molar eruption using in situ hybridization. We also examined how TIMPs are involved in the process of tooth eruption, root formation, cementogenesis and alveolar bone remodelling. Expressions of type-I collagen, osteocalcin, MMPs 2 and 8, and TIMPs 1, 2 and 3 were shown in osteoblasts, osteocytes, cementoblasts, cementocytes and periodontal ligament fibroblasts, and the concomitant high expressions of the ECM molecules, MMPs and TIMPs in alveolar bone, cementum and periodontal ligaments were identified in the middle of first molar eruption. The remodelling of ECM in these periodontal tissues might be regulated through balance among the production of ECM molecules, the degradation of ECM by MMPs and the inhibition of MMPs by TIMPs during tooth eruption.