Dental implants were placed in 30 subjects who have 1 or 2 missing teeth in both side of posterior mandible. Implants with a length of 11.5 and a diameter of 4.5 mm will be inserted in both sides. In one side PRF will be instilled after surface treatment with PRF before implant placement, while no PRF was added in other side to serve as control group. All implants will be followed with stability measurement by means of resonance frequency analysis at baseline, and every two weeks up to 3 months. Bone height was measured on medial & distal side on standardized IOPA x-rays.