Distraction osteogenesis offers an alternative approach for the correction of craniofacial deformities, yet little substantive data is available regarding mineralization of the forming regenerate. The purpose of this study was to evaluate, by plain film radiography and digital subtraction radiography, the mineralization dynamics of regenerate bone during osteodistraction. Thirteen skeletally mature male beagle dogs underwent 10 mm of bilateral mandibular distraction osteogenesis, at which time the bone was allowed to consolidate for either 4, 6, or 8 weeks. The tissues were then evaluated clinically and radiographically. The results demonstrate that several different types of regenerate are evident during mineralization of the distraction gap. A classification system is presented based on the length, width, and density of the mineralizing regenerate, as well as the presence or absence of an interzone. It appears that important factors for determining regenerate stability are the presence or absence of an interzone, as well as the width of the regenerate relative to the host bone segments. Finally, in cases where an interzone is present, subtraction radiography may provide a means of evaluating the level of mineralization within the interzone as well as the dynamics of mineralization over the course of distraction and consolidation.