GTR has a greater effect on probing measures of periodontal treatment than open flap debridement, including improved attachment gain, reduced pocket depth, less increase in gingival recession and more gain in hard tissue probing at re-entry surgery. However there is marked variability between studies and the clinical relevance of these changes is unknown. As a result, it is difficult to draw general conclusions about the clinical benefit of GTR. Whilst there is evidence that GTR can demonstrate a significant improvement over conventional open flap surgery, the factors affecting outcomes are unclear from the literature and these might include study conduct issues such as bias. Therefore, patients and health professionals need to consider the predictability of the technique compared with other methods of treatment before making final decisions on use. Since trial reports were often incomplete, we recommend that future trials should follow the CONSORT statement both in their conduct and reporting. 
There is therefore little value in future research repeating simple, small efficacy studies. The priority should be to identify factors associated with improved outcomes as well as investigating outcomes relevant to patients. Types of research might include large observational studies to generate hypotheses for testing in clinical trials, qualitative studies on patient-centred outcomes and trials exploring innovative analytic methods such as multilevel modelling. Open flap surgery should remain the control comparison in these studies.
Evaluation of guided tissue regeneration in the treatment of paired periodontal defects.
The aim of the present study was to compare guided tissue regeneration with conventional surgery in matched periodontal defects within the same subject. Twenty pairs of sites in nine subjects were treated. Surgery was performed at both test and control sites on the same visit. Random allocation was not performed until all preparation and root instrumentation had been completed. Test defects were covered with e-PTFE membranes (Gore-Tex) and secured with sutures. Membranes were removed after 5-6 weeks with a second surgical procedure, whereas the control sites were not re-operated. At 12 months probing depth reductions were significantly greater at the Gore-Tex treated sites (P<0.05) but no difference in probing attachment level gains were found when compared with conventional flap surgery.