Effects of occlusal loading on ankylosis, bone, and cementum formation during bone morphogenetic protein-2-stimulated periodontal regeneration in vivo

Background: The purpose of this study was to investigate the influence of occlusal loading on recombinant human bone morphogenetic protein-2 (BMP-2)-induced bone and cementum formation in a previously established rat model of periodontal regeneration during the early and late stages of wound healing. Methods: 64 Wister rats were divided into 8 groups and had surgically created fenestrated defects on the right side of the mandible involving the removal of bone and exposure of the first and second molar roots. Four groups had their right maxillary molars extracted 2 weeks prior to surgery. Ten mu 1 of 100 ug/ml BMP-2 in a collagen membrane was placed in extracted (hypofunctional) and non-extracted (functional) groups (BMPe and BMPf, respectively) while control groups had collagen membrane only (CONe and CONf). Groups were sacrificed at 10 (BMPe, BMPf, CONe, CONf) or 35 days (BMP35e, BMP35f, CON35e, CON35f) postoperatively and tissues processed for histological examination. Transverse 5 mu m sections were stained for identification of new bone, ankylosis and cementum formation. Results: At 10 days, CONe developed greater bone growth compared with CONf (P <0.05), while both BMP groups developed greater bone compared with controls. However, BMPe developed more ankylosis compared with both CONe and CONf while BMPf was significantly greater than CONf only (P <0.05). BMPf only developed significantly greater new cementum compared with controls. At 35 days, BMP35f developed greater bone growth compared with all other groups including BMP35e (P <0.05) and unlike results at 10 days, no differences were apparent between CON35f and CON35e. Unwanted bone growth beyond the defect margin anteriorly was significantly greater in BMP35f. Conclusions: Results suggest hypofunction stimulates early bone formation. Furthermore, hypofunction and BMP-2 increase the development of transient ankylosis. However, after wound healing is complete, function augments the early effects of BMP-2-induced new bone growth indicating remodeling to physiological levels does not occur. Finally, occlusal loading is both an important stimulus for remodeling and establishment of the periodontal ligament space during early wound healing as well as enhancing BMP-2-induced cementogenesis.