Tissue Remodelling and Gene Expression in Tooth Eruption

Tooth eruption is a multifactorial process that involves the movement of existing tissues and the formation of new tissues coordinated by a complex set of genetic events. Objectives: We have used the model of the un-opposed rodent molar to study morphologic and genetic mechanisms of tooth eruption. Methods: Left maxillary molar teeth of 35-day old Swiss-Webster mice were extracted under anesthesia. Mandibular molars were allowed to super-erupt for 1, 3, 6, 10, and 12 days. To trace areas of tissue remodeling and to determine areas of new tissue formation, mice were injected with fluorescent dyes, tetracycline, alizarin red, calcein blue, and chlor-tetracycline. Subsequent to sacrifice, mandible tissue blocks were prepared for ultrathin ground sections and fluorescent microscopy. A second set of specimen was prepared for RNA extraction and microarray analysis. Results: Labeled tissue sections revealed significant differences in bone and cementum apposition between the experimental and the control side as measured in mid-sagittal root cross-section (p<0.001). There was 64µm +/-11µm alveolar bone deposition in coronal direction and 72µm +/-21µm cementum deposition in apical direction in the experimental group. In contrast, there was 28µm +/-5µm alveolar bone deposition in coronal direction and 25µm +/-4µm cementum deposition in apical direction in the control group. Microarray analysis demonstrated a significant (more than 2-fold) increase in gene expression of collagen I, integrin beta 5, and SPARC, as revealed by comparison between the experimental and the control group. Conclusion: In this study we have established the un-opposed mouse molar as a model to study tissue dynamics in tooth eruption. Our data indicated significant new formation of bone and cementum in tandem with increased expression of extracellular matrix genes. This study was supported by NIDCR grant DE15425 to TGHD.