BACKGROUND: Conventional treatment of destructive periodontal (gum) disease arrests the disease but does not regain the bone support or connective tissue lost in the disease process. Guided tissue regeneration (GTR) is a surgical procedure that aims to regenerate the periodontal tissues when the disease is advanced and could overcome some of the limitations of conventional therapy. OBJECTIVES: To assess the efficacy of GTR in the treatment of periodontal infra-bony defects measured against the current standard of surgical periodontal treatment, open flap debridement. SEARCH STRATEGY: We conducted an electronic search of the Cochrane Oral Health Group specialised trials register and MEDLINE up to October 2000. Hand searching included Journal of Periodontology, Journal of Clinical Periodontology, Journal of Periodontal Research and bibliographies of all relevant papers and review articles up to October 2000. In addition, we contacted experts/groups/companies involved in surgical research to find other trials or unpublished material or to clarify ambiguous or missing data and posted requests for data on two periodontal electronic discussion groups. SELECTION CRITERIA: Randomised, controlled trials of at least 12 months duration comparing guided tissue regeneration (with or without graft materials) with open flap debridement for the treatment of periodontal infra-bony defects. Furcation involvements and studies specifically treating early onset diseases were excluded. DATA COLLECTION AND ANALYSIS: Screening of possible studies was conducted independently by two reviewers (RT & IN) and data abstraction by three reviewers (RT, IN & EGL). The methodological quality of studies was assessed in duplicate (RT & IN) using both individual components and a quality scale (Jadad 1998) and agreement determined by Kappa scores. Methodological quality was used in sensitivity analyses to test the robustness of the conclusions. The Cochrane Oral Health Group statistical guidelines were followed (HW) and the results expressed as weighted mean differences (WMD and 95% CI) for continuous outcomes and relative risk (RR and 95% CI) for dichotomous outcomes calculated using random effects models where significant heterogeneity was detected (P < 0.1). The final analysis was conducted using STATA 6 in order to combine both parallel group studies and intra-individual (split-mouth) studies. The primary outcome measure was gain in clinical attachment. Any heterogeneity was investigated. MAIN RESULTS: We initially included 23 trial reports. Twelve were subsequently excluded. Of these, seven presented six-months data only, three were not fully randomised controlled trials, one used a non-comparable radiographic technique. Eleven studies were finally included in the review, ten testing GTR alone and two testing GTR+bone substitutes (one study had both test treatment arms). For attachment level change, the weighted mean difference between GTR alone and open flap debridement was 1.11 mm (95% CI: 0.63 to 1.59), chi-square for heterogeneity 31.4 (df = 9), p<0.001) and for GTR+bone substitutes was 1.25 mm (95% CI: 0.89 to 1.61, chi-square for heterogeneity 0.01 (df = 1), p=0.91). GTR showed a significant benefit when comparing the numbers of sites failing to gain 2 mm attachment, with relative risk 0.58 (95% CI: 0.38, 0.88, chi-square for heterogeneity 5.72 (df = 3), p=0.13). The number needed to treat (NNT) for GTR to achieve one extra site gaining 2 mm or more attachment over open flap debridement was 8 (95% CI: 4, 33), based on an incidence of 32% of sites in the control group failing to gain 2 mm or more of attachment. For baseline incidences in the range of the control groups of 10% and 55% the NNTs are 24 and 3. Probing depth reduction demonstrated a small but statistically significant benefit for GTR, weighted mean difference 0.80 mm (95% CI: 0.14,1.46, chi-square for heterogeneity 10.0 (df = 4), p=0.04) or GTR+bone substitutes, weighted mean difference 1.24 mm (95% CI: 0.89, 1.59, chi-square for heterogeneity 0.03 (df = 1), p=0.85). No significant difference was noted for gingival recession between GTR and open flap debridement. Regarding hard tissue probing at surgical re-entry, a statistically significant greater gain was found for GTR compared with open flap debridement. This amounted to a weighted mean difference of 1.39 mm (95% CI: 1.08, 1.71, chi-square for heterogeneity 0.85 (df = 2), p=0.65). For GTR+bone substitutes the difference was greater, with mean difference 3.37 mm (95% CI: 3.14, 3.61). Heterogeneity between studies was highly statistically significant for all principal comparisons and could not be explained satisfactorily by sensitivity analyses. The quality of study reporting was poor with seven out of 11 studies graded as poor using the Jadad score. (ABSTRACT TRUNCATED)