The purpose of this controlled clinical trial was to compare the clinical efficacy of 3 treatment modalities in the treatment of deep interproximal intrabony defects. Forty-five (45) defects in 45 patients were randomly assigned to 1 of 3 treatment groups by blocking to prognostic variables. The test group was treated with titanium reinforced membranes positioned just apical to the cemento-enamel junction and the modified papilla preservation technique; the second group received conventional expanded polytetrafluoroethylene (ePTFE) barrier membranes applied at the alveolar crest; the third group was treated with an access flap procedure. The groups were well balanced with respect to all prognostic variables. During the 1-year observation period, patients were subjected to a stringent infection control program including: professional tooth cleaning every week for the first 6 weeks (all groups) and in the 4 weeks following membrane removal (guided tissue regeneration groups), then at monthly intervals (all groups). The results indicated that: 1) all treatment modalities resulted in clinical and statistically significant improvements in clinical attachment level (CAL) and probing depths (PD) at 1 year; 2) a significantly greater amount of CAL gain (P = 0.0003, analysis of variance) was observed in the test group (5.3 +/- 2.2 mm) with respect to both the ePTFE group (4.1 +/- 1.8 mm) and the flap control group 2.5 +/- 0.8; 3) in the test group the 1 year CAL (4.7 +/- 1.8 mm) was located more coronally than the baseline position of the interproximal alveolar crest (5.9 +/- 2 mm; P = 0.003, t test).(ABSTRACT TRUNCATED AT 250 WORDS)