Bone strain above a threshold increases bone mass, while bone loss is evident with reduced bone strain. It has been suggested that orthodontic appliances may induce an osteopenic effect on bone due to stress-shielding. In this study, we investigated the molecular basis of osteopenia of alveolar bone with an inactive spring attached to maxillary molars in a rat model.
Method:
For this purpose, thirty-two 6 week-old male Wistar rats were used. The experimental group were implanted with passive helical coil springs bonded to the maxillary molars and sacrificed after 4 or 8 days. A further group of sixteen rats were similarly treated for histological analysis. The serum was collected and the levels of bone resorption markers, Deoxypyridinoline (DPD) and Tartrate-resistant acid phosphatase 5b (TRACP 5b) as well as Alkaline phosphatase (ALP), a biomarker of bone formation were investigated by Enzyme linked Immunosorbent Assay (ELISA). ELISA was also used to measure Leptin, a hormone associated with regulation of bodyweight and inhibition of bone formation.
Result: While the experimental group demonstrated higher DPD levels at 4 days, no difference was observable at 8 days. Increased levels of Leptin were observed in the experimental group at 8 days while no changes in TRACP 5b levels were evident. The levels of bone formation factor, ALP were significantly reduced at both time points. Correspondingly, osteopenia was evident in the histological section for the experimental group. Taken together, while bone loss was due to a reduction in bone formation, bone resorption remained mostly unchanged – in other words, the normal remodelling cycle of bone formation and bone resorption had been uncoupled.
Conclusion: These findings suggest that the osteopenia resulted from stress shielding of the interradicular bone by the appliance, and a consequent reduction in occlusal loading below the critical threshold required for maintaining normal osseous architecture