Methods: An incision in the bony palate of healthy wild-type (WT) and inducible NO synthase knockout (iNOS KO) mice was made with a piezotome (Satelec). In separate groups of WT and iNOS KO mice bur osteotomy was also performed for comparison. Bone volume and bone density of the maxilla was measured with microCT at various time points.
Results: There was a marked drop in bone density 1 week after piezotomy in both WT and iNOS KO mice. Bone density recovered to control levels by week 3 in both mouse strains. By week 8 bone density was significantly increased at the piezotomy site compared to the untreated side in WT mice (untreated: 1190±39mgHA/cm2, piezotomy: 1235±14mgHA/cm2, P=0.04). We found no significant increase in bone density in iNOS KO mice at 8 weeks (untreated: 1189±49mgHA/cm2, piezotomy: 1194±9mgHA/cm2, P=0.85). A separate set of WT and iNOS KO mice underwent palatal osteotomy with a carbide bur and micro CT analysis was performed after 8 weeks. Bur osteotomy did not induce significant change in bone density in WT (untreated: 1272±27mgHA/cm2, bur osteotomy: 1264±15mgHA/cm2, P=0.60) or iNOS KO mice (untreated: 1323±25mgHA/cm2, bur osteotomy: 1301±23mgHA/cm2, P=0.14). Bone volume fraction of total sample volume (BV/TV) decreased 1 week after piezotomy and recovered to control levels 3 weeks after. No significant changes were noted in BV/TV at weeks 3, 5 and 8 and no significant differences between WT and iNOS KO mice were found. Bur osteotomy on the other hand induced significant increase in BV/TV in iNOS KO mice at 8 weeks (untreated: 0.75±0.05, 8 week: 0.82±0.4, P=0.03).
Conclusion: Piezotomy significantly increases bone density. Nitric oxide mediates the piezotomy-induced increase in bone density.