Objective: This study aims to evaluate the effect of fibrin, which is formed with an alteration to the standard PRF centrifugation protocol, on the bone formation. The study additionally aims to assess cell-distribution, and to evaluate the effects of alterations in the speed and duration of centrifugation on the changes in cell-distribution and the formation of hard tissue, by making histological investigations. Materials and methods: Ten New Zealand rabbits were used in this experimental animal study. PRF (2700 rpm, 12 min) and APRF (1500 rpm, 14 min) were placed in the standard bone defects that formed in the right corpus of the mandible randomly. No additional material was placed in the left mandible defect, as a control group. Rabbits were sacrificed after two months, the histological evaluation was performed. Results: There were no marked differences between groups in regard to the quantity of bone formation and bone quality. The quantities of new bone formation were (mean) 56.9%, 55%, 42.5%. Discussion: It may be considered that PRF and its variations have positive effects on the new bone tissue and cell number, and may lead to more rapid ossification compared to the unprocessed bone defects.