Journal of Periodontology on CD-ROM (Copyrights © 1998, AAP), 1998 Nov (1183 - 1192): Generalizability of the Added Benefits of Guided Tissue Regenerat Generalizability of the Added Benefits of Guided Tissue Regeneration in the Treatment of Deep Intrabony Defects. Evaluation in a Multi-Center Randomized Controlled Clinical Trial Maurizio S. Tonetti, Pierpaolo Cortellini, Jean E. Suvan, Patrick Adriaens, Carlo Baldi, Dominik Dubravec, Alberto Fonzar, Ioannis Fourmousis, Cristina Magnani, Veronique Muller-Campanile, Stefano Patroni , Mariano Sanz, Tine Vangsted , Iohn Zabalegui, Giovanpaolo Pini Prato , and Niklaus P. Lang Background: Several studies have shown that GTR therapy of intrabony defects results in significantly better outcomes than access flap alone. Most of the available data, however, have been produced in highly controlled research environments by a small group of investigators. Generalizability of results to different clinicians and different subject populations has not been evaluated so far. Methods: This parallel group study involved 143 patients recruited in a practice-based research network of 11 offices in 7 countries. It was designed to evaluate: 1) the applicability of the documented added benefits of GTR in the treatment of intrabony defects to different populations, and 2) the generalizability of the expected results to different clinicians. GTR was compared to access flap alone. Defects, one in each patient, were accessed with a previously described papilla preservation flap in both the test and control group. In addition, GTR sites received application of a bioabsorbable poly-D,L-lactide-co-glycolide membrane. A stringent plaque control regimen was enforced in all patients during the 1-year observation period. Outcomes included gains in clinical attachment (CAL) and reductions in probing depth. Results: Observed gains in CAL were 2.18 ± 1.46 mm for access flap and 3.04 ± 1.64 mm for the GTR-treated group. The treatment-associated difference was statistically significant ( P = 0.03) after correcting for both center effect and defect anatomy. Among the various centers, a 1.73 mm difference in CAL gain was observed. This is a clinically relevant amount, which underlines the significance of center variability in the outcome of periodontal surgical procedures. A frequency distribution analysis of the obtained CAL gains indicated that GTR treatment of deep intrabony defects decreased, with respect to the access flap control, the probability of obtaining only a modest attachment gain at 1 year. Conversely, CAL gains of 4 mm or more were observed in more than 40% of GTR-treated defects and in less than 20% of the controls (P < 0.0001). Conclusions: These data indicate that GTR therapy of deep intrabony defects performed by different clinicians on various patient populations resulted in both greater amounts and improved predictability of CAL gains than access flap alone. J Periodontol 1998;69:1183-1192. Key Words: Guided tissue regeneration; periodontal diseases/surgery; periodontal diseases/therapy; surgical flaps; comparison study; clinical trials; clinical research; periodontal attachment; outcome assessment. A recent meta-analysis of 18 investigations on the clinical outcomes following application of Article Text 1