Particulated bone grafts -: effectiveness of bone cell supply

Objective: The objective of this study was to measure the amount of viable bone cells present in different types of bone graft. Material and methods: Bone chips were harvested from the trabecular or cortical bone of the mandible or the iliac crest and either milled or not. The average size of unmilled bone particles was 5x5x5 mm and that of milled was 2x2x2 mm. Drill sludge was obtained using either a ball reamer, a diamond ball or an implant drill (the latter from mandibular bone and of average dimension 1x1x1 mm). A measure of 0.5 g of each category was cultured in Dulbecco's modified Eagle's medium with additives for four weeks. Cell counts were performed. An analysis of the osteocalcin synthesis, the alkaline phosphatase (ALP) activity, the collagen types and the concentration of bone-specific collagen cross-links in medium supernatants was performed. Results: Cells stained positively for osteocalcin and ALP in all groups. Bone-specific collagen cross-links could be quantified and collagen of types I and V was present with no difference in all groups. Unmilled spongy bone chips revealed greater cell counts than milled (P<0.05). Spongy bone chips revealed greater cell counts than cortical bone chips (P<0.05). Drill sludge obtained by hard alloy ball reamer showed the least amount of viable cells (P<0.05). Conclusions: Bone milling reduces the quantity of osteoblasts. Bone obtained by the ball reamer supplies a smaller number of cells than bone obtained by other methods. Unmilled spongy bone chips appear to offer the greatest amount of viable osteoblasts.