Microdamage in porcine alveolar bone due to functional and orthodontic loading.

Bone remodelling has been associated with microdamage. The aim of this study was to investigate the presence of microdamage in the alveolar bone and its potential role in the initiation of bone remodelling following the application of an orthodontic load. The three-dimensional morphology of the alveolar bone was investigated by means of high resolution micro-CT scanning. In 25, 3-month-old, male Danish land-race pigs, the alveolar bone around the lower right and left first molars was analysed. The right first molar was moved buccally with a force of 130 cN by means of a custom-made cantilever made of a TMA 0.017 x 0.025 inch wire. The left molar was left untreated. After 1, 2, 4, 7 and 15 days of treatment the regions containing the right and left molars were excised and en bloc stained in basic fuchsin and the presence of microdamage detected. Diffuse damage was present in the alveolar bone of both the treated and the untreated teeth on both sides. On the lingual sides, diffuse damage showed the same orientation as the periodontal fibres. Bone microcracks were also detected on both the treated and untreated teeth. On the buccal surfaces they where often observed in close proximity to scalloped resorption surfaces. After 1 day of treatment, the presence of microcracks on the buccal-treated side was particularly marked. To conclude, bone microdamage is present in porcine alveolar bone in form of both microcracks and diffuse damage, suggesting that microdamage-driven remodelling also occurs in the alveolar bone. The presence of bone microcracks in the direction of the orthodontic force at day 1 suggests that they could represent the first damage induced by the orthodontic load that has to be repaired.