EFFECT OF ER-YAG LASER HOLES ON OSTEOINDUCTION IN DEMINERALIZED RAT CALVARIAL ALLOGRAFTS

Massive cortical autografts and allografts have been found to incorpor ate into host bone very slowly and thus are subject to complications s uch as fatigue fracture and infection. In order to understand and impr ove the process of osteogenesis in these types of bone grafts, a new e xperimental model was developed using bone discs from rat calvaria pre pared by demineralization and drilling of 0.5 mm diameter holes with a pulsed, 2.94 mu m wavelength Erbium:Yttrium-Aluminum-Garnet laser. Fo ur types of bone discs were analyzed: untreated (Type I): demineralize d (Type II), laser-ablated (Type TIT), and laser-ablated then deminera lized (Type IV). The discs were transplanted into a subcutaneous site in adult Sprague-Dawley rats and followed for as long as 6 weeks. Hist ologic analysis of the discs at weekly intervals with use of hematoxyl in and eosin staining confirmed the presence of new bone growth in Typ e-II and Spe-IV discs. The amount of new bone growth in each disc was estimated by determining the mineral x-ray attenuation coefficient, wh ich is proportional to mineral density, from digitized radiographs of the discs. The results showed that the processes of demineralization ( p < 0.001) and laser ablation with demineralization (p < 0.05) were bo th significant in enhancing new bone growth in this model. This study demonstrated that osteoinduction can be fostered in cortical bone thro ugh the processes of demineralization and laser ablation. To the exten t that laser ablation may allow maintenance of structural integrity wh ile altering the surface geometry in such a way as to promote ingrowth of new bone, this experimental model represents an advance in underst anding how osteogenesis in cortical bone grafts might be improved.