Data sourcesMedline, the Cochrane Library, Google and hand-searches of systematic reviews and bibliographies from related journals in English and German up to August 2012.Study selectionThree reviewers independently searched for clinical trials that assessed the success rates of placing two anterior and two posterior tilted dental implants in humans either in the maxilla or mandible according to the all-on-four treatment concept. Inclusion limited studies with a minimum follow-up period of one year.Data extraction and synthesisThe primary outcome measure was the failure rate of implants. The secondary outcomes were prosthesis failure and marginal bone loss/bone level changes assessed through radiological examination. Failure rate was used to calculate standard deviations (SDs) of implants, whereas the mean success rate was used for dental implants and prostheses. Evaluation and quality assessment of articles and data extraction were performed by three independent reviewers. These reviewers estimated risk of bias by assessing the trial quality using a criteria form focused on the trial design, specification of inclusion/exclusion criteria, performance of surgery, outcome measure provided, radiographic examination of marginal bone level change as well as its evaluation and completeness of follow-up. Outcome measures were based on weighted means using a variance components analysis.ResultsThirteen studies, including 4,804 dental implants (2,000 maxilla and 2,804 mandible) placed in 1,201 jaws met the inclusion criteria. Nine were prospective trials, three retrospective studies and one longitudinal trial. All studies except one were considered to be at high risk of bias. Seventy-four (37 axially, 37 tilted) dental implants failed, with most failures (74%) within the first 12 months. Fifty-seven out of 1,201 prostheses failed but were repairable. The major prosthetic complication was the fracture of the all-acrylic prostheses. At 36 months the mean cumulative survival rates for implants and prostheses were 99.0 ± 1.0% (SD) and 99.9 ± 0.3% (SD), respectively with an average bone loss of 1.3 ± 0.4 mm (SD). There were no statistically significant differences in the clinical outcomes between maxillary versus mandibular arches and axially versus tilted placed implants.ConclusionsThe available evidence shows a promising short-term prognosis for the all-on-four treatment concept. However the evidence is limited by the quality of the available studies and the paucity of clinical trials of greater than five years. © 2016 Macmillan Publishers Limited.