IADR Abstract Archives
Effect of Occlusal Interferences on Orthodontic External Root Resorption
Objectives:
To test the effects of occlusal interference (OI) during orthodontic movement and find patterns of apoptosis, necrosis and clast cell activity associated with increased OERR.
Methods: For 15 days, 24 inbred rats were randomly distributed into 4 groups: Implant controls (with 2 subgroups), spring only, occlusal interference only, interference+spring. The Finite element (FE) models of the first maxillary molars were constructed from μCT scans to calculate PDL stresses delivered by the spring to the mesio-buccal root. We used an apoptotic/necrotic cell evaluation assay (APOPTAG) and TRAP histochemistry to evaluate the tissue response.
Results: Occlusal Interferances resulted in up to 2.4x and 3.6x increased OERR in the apical region compared to controls and spring alone, respectively (p<0.001), but not in the cervical region of the sampled root. There was no significant statistical interaction between the effect of spring and the effect of OI. Areas of increased OERR were associated with higher stresses and increased visualization of clast-type and necrotic cells, as evidenced by FE models, TRAP and APOPTAG assays. Apoptotic, but not necrotic cells were observed in areas of low stress.
Conclusions: OIs, when concentrated on a single tooth, can significantly aggravate OERR in the apical region, and the effects in this region are additive to a simple orthodontic force. I.e., intermittent high compressive stresses in the apex causes by occlusal loading can increase apical OERR.
To test the effects of occlusal interference (OI) during orthodontic movement and find patterns of apoptosis, necrosis and clast cell activity associated with increased OERR.
Methods: For 15 days, 24 inbred rats were randomly distributed into 4 groups: Implant controls (with 2 subgroups), spring only, occlusal interference only, interference+spring. The Finite element (FE) models of the first maxillary molars were constructed from μCT scans to calculate PDL stresses delivered by the spring to the mesio-buccal root. We used an apoptotic/necrotic cell evaluation assay (APOPTAG) and TRAP histochemistry to evaluate the tissue response.
Results: Occlusal Interferances resulted in up to 2.4x and 3.6x increased OERR in the apical region compared to controls and spring alone, respectively (p<0.001), but not in the cervical region of the sampled root. There was no significant statistical interaction between the effect of spring and the effect of OI. Areas of increased OERR were associated with higher stresses and increased visualization of clast-type and necrotic cells, as evidenced by FE models, TRAP and APOPTAG assays. Apoptotic, but not necrotic cells were observed in areas of low stress.
Conclusions: OIs, when concentrated on a single tooth, can significantly aggravate OERR in the apical region, and the effects in this region are additive to a simple orthodontic force. I.e., intermittent high compressive stresses in the apex causes by occlusal loading can increase apical OERR.