Objective: To test the hypothesis that platelet rich plasma (PRP) injection can minimize relapse of orthodontically moved
teeth. Material and Methods: Thirty rabbits were randomly and equally divided into three groups (A, B and C). The mock group C (n=10) was further equally divided into C1 and C2 subgroups. A mesializing force was applied to the first molar on both sides in all groups. After achieving orthodontic movement, in groups A and B, (PRP) was injected on the experimental side while normal saline was injected on the control side. Animals in group C did not receive any injections. Animals in groups A and C1 were sacrificed after 1 week and animals in groups B and C2 were sacrificed after four weeks. Amount of first molar relapse in all groups was measured and compared. Results: After 1 week and 4 weeks relapse periods; the distance of relapse in the experimental group was reduced significantly (P <0.001) when compared with the control and mock groups. No statistically significant difference was found between the relapse observed in the experimental groups in 1 week and 4 weeks relapse periods; (29.09%) and (39.16%) respectively. However, relapse increased significantly (P <0.001) in both the control and mock groups from 1 week to 4 weeks relapse period intervals. Conclusion: The injection of platelet rich plasma can significantly reduce the amount of orthodontic relapse following removal of the orthodontic force.