BACKGROUND: The objective of this study was to place bone graft materials in cranial defects in a rabbit model and compare their bone regenerating ability according to the size and density of demineralized dentin matrix (DDM). METHODS: We selected nine healthy male rabbits that were raised under the same conditions and that weighed about 3 kg. Two circular defects 8 mm in diameter were created in each side of the cranium. The defects were grafted with DDM using four different particle sizes and densities: 0.1 mL of 0.25- to 1.0-mm particles (group 1); 0.2 mL of 0.25- to 1.0-mm particles (group 2); 0.1 mL of 1.0- to 2.0-mm particles (group 3); and 0.2 mL of 1.0- to 2.0-mm particles (group 4). After 2, 4, and 8 weeks, the rabbits were sacrificed, and bone samples were evaluated by means of histologic, histomorphometric, and quantitative RT-PCR analysis. RESULTS: In group 1, osteoblast activity and bone formation were greater than in the other three groups on histological examination. In groups 2, 3, and 4, dense connective tissue was seen around original bone even after 8 weeks. Histomorphometric analysis of representative sections in group 1 showed a higher rate of new bone formation, but the difference from the other groups was not statistically significant. RT-PCR analysis indicated a correlation between bone formation and protein (osteonectin and osteopontin) expression. CONCLUSIONS: DDM with a space between particles of 200 μm was effective in bone formation, suggesting that materials with a small particle size could reasonably be used for bone grafting.