CONFLICT-OF-INTEREST STATEMENT: Marco Esposito, Pietro Felice and Paul Coulthard are among the authors of four of the included trials, however, they were not involved in the quality assessment of these trials. This review is based on a Cochrane systematic review entitled 'Interventions for replacing missing teeth: augmentation procedures of the maxillary sinus' published in The Cochrane Library (see http:// www.cochrane.org/ for information). Cochrane systematic reviews are regularly updated to include new research and in response to comments and criticisms from readers. If you wish to comment on this review, please send your comments to the Cochrane website or to Marco Esposito. The Cochrane Library should be consulted for the most recent version of the review. The results of a Cochrane Review can be interpreted differently, depending on people's perspectives and circumstances. Please consider the conclusions presented carefully. They are the opinions of the review authors, and are not necessarily shared by the Cochrane Collaboration. BACKGROUND: Insufficient bone volume is a common problem encountered in the rehabilitation of the edentulous posterior maxillae with implant supported prostheses. Bone volume is limited by the presence of the maxillary sinus together with loss of alveolar bone height. Sinus lift procedures increase bone volume by augmenting the sinus cavity with autogenous bone and/or commercially available biomaterials. OBJECTIVES: To test whether and when augmentation of the maxillary sinus is necessary and which are the most effective augmentation techniques for rehabilitating patients with implant-supported prostheses. SEARCH METHODS: The Cochrane Oral Health Group's Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and EMBASE were searched. Several dental journals were hand searched. The bibliographies of review articles were checked, and personal references were searched. More than 55 implant manufacturing companies were also contacted. The last electronic search was conducted on 7th January 2010. SELECTION CRITERIA: Randomised controlled trials (RCTs) of different techniques and materials for augmenting the maxillary sinus for rehabilitation with dental implants reporting the outcome of implant therapy at least to abutment connection. DATA COLLECTION AND ANALYSIS: Screening of eligible studies, assessment of the methodological quality of the trials and data extraction were conducted independently and in duplicate. Authors were contacted for any missing information. Results were expressed as random-effects models using mean differences for continuous outcomes and odds ratios for dichotomous outcomes with 95% confidence intervals. The statistical unit of the analysis was the patient. RESULTS: Ten RCTs out of 29 potentially eligible trials were suitable for inclusion. One trial including 15 patients, evaluated whether 5-mm-long implants with a diameter of 6 mm could be an alternative to sinus lift in bone having a residual height of 4 to 6 mm. Nine trials with 235 patients compared different sinus lift techniques and, of these, four trials (114 patients) evaluated the efficacy of platelet-rich plasma (PRP). Since different techniques were evaluated in different trials, only two meta-analyses evaluating the efficacy of PRP could be performed for implant failures (two trials) and complications (three trials). No statistically significant difference was observed for any of the evaluated interventions. CONCLUSIONS: Conclusions are based on few trials, usually underpowered, having short follow-ups, and often judged to be at high risk of bias, therefore they should be viewed as preliminary and interpreted with great caution. It is still unclear when sinus lift procedures are needed. Short implants (5 mm) can be successfully loaded in maxillary bone with a residual height of 4 to 6 mm, but their long-term prognosis is unknown. Elevating the sinus lining in the presence of 1 to 5 mm of residual bone height without the addition of a bone graft may be sufficient to regenerate new bone to allow rehabilitation with implant-supported prostheses. Bone substitutes might be successfully used as replacements for autogenous bone. If the residual alveolar bone height is 3 to 6 mm, a crestal approach to lifting the sinus lining and placing 8 mm implants may lead to less complications than a lateral window approach and placing implants at least 10 mm long. PRP treatment does not seem to improve the clinical outcome of sinus lift procedures with autogenous bone or bone substitutes.