Dental implants protruding 2 mm were covered with dome-shaped stiff occlusive titanium barriers filled with demineralized freeze-dried bone allograft (DFDBA)+saline (7 rabbits), DFDBA + rifamycin (8 rabbits), or DFDB +PRF (8 rabbits). After 4 weeks, the animals were sacrificed, and undecalcified histomorphometric examination with toluidine blue staining was performed.