Hydroxylapatite as a bone graft substitute in orthognathic surgery: histologic and histometric findings

The use of porous hydroxylapatite (HA) as a substitute for bone in grafting associated with orthognathic surgical procedures was studied histologically and histometrically. The surgical procedures included maxillary downgrafting, advancement, setback, superior repositioning with expansion, and mandibular advancement and chin augmentation. Seventeen biopsies were obtained from nine patients after successful healing from 4.7 to 16.4 months postoperatively. Anatomic sites of the biopsies included maxillary wall, interdental region, palatal midline, chin, and mandible. In addition, nine implants representing six planned and three unplanned exposures were retrieved from nine patients. One biopsy from a successful implant was decalcified and thin-sectioned to provide better cell detail of the antral lining of the implant. The remaining biopsies were sectioned undecalcified to permit backscattered electron imaging with a scanning electron microscope. Each of the 17 biopsy specimens contained bone ingrowth. The decalcified specimen showed an intact submucosa with loss of the mucosal epithelium due to prolonged acid exposure. The biopsies were composed of 48.5% HA matrix, 18.0% bone ingrowth, and 33.5% soft tissue or vascular space. The HA matrix surface area averaged 9.4 mm2/mm3 with 62.1% of the surface covered by appositional bone ingrowth. The nine exposed implants contained connective tissue ingrowth only at their margins, with little or no bone being present. This graft-like biologic response to a porous HA matrix confirmed its ability to serve as a bone graft substitute in clinical applications. The absence of any decrease over time confirmed the relative permanence of the HA matrix. The lack of inflammatory cells in the biopsies, along with the formation of a connective tissue protective barrier in the exposed specimens, suggests that host responses to contamination were not impaired by the porous HA matrix.