Objective: To evaluate trio efficacy of p-tricalcium phosphate (beta-TCP) (Synthograft, Bicon USA) in periodontal osseous defects in comparison to open flap debridement (OFD). Method and Materials: Twelve patients showing clinical and radiographic evidence of almost identical bilateral infrabony defects were selected. The infrabony defects in the 12 patients were treated with OFD+beta-TCP on one side and OFD on the other side. Clinical evaluation was performed at baseline and 6 months following therapy. Results: No differences in probing depth (PD) reduction or clinical attachment level (CAL) gain were observed, although a. statistically significant difference was observed for the defect fill between the two groups. Six months after therapy, sites treated with OFD+beta-TCP showed a reduction in mean PD from 9.67 +/- 2.35 mm to 4.00 +/- 1.60 mm (P < .05), a change in mean CAL from 9.92 +/- 3.15 mm to 5.00 +/- 3.86 mm (P < .05), and the mean defect fill was 2.92 +/- 0.90 mm. In the sites treated with only OFD, the mean PD was reduced from 7.58 +/- 1.08 mm to 2.67 +/- 0.65 mm (P < .05), the mean CAL changed from 6.83 +/- 1.34 mm to 1.83 +/- 1.64 mrn (P < .05), and the mean defect fill was 0.83 +/- 0.39 mm. Reduction of 5 mm in PD was observed in 5 of the 12 defects (42%); 4 of the 12 defects (33%) gained 3 mrn of CAL in the test sites. PD reductions and CAL gains of 3 to 6 mm were measured in the majority of the cases (60% to 75%) regardless of treatment modality. Conclusion: Within the constraints of this study, both therapies resulted in significant PD reductions and CAL gains 6 months after surgery. Sites treated with OFD+beta-TCP showed a significant defect fill compared to those treated with OFD alone. (Quintessence lot 2011:42:291-300)