Narrow-diameter implants for treatment with fixed restorations in the posterior region: A systematic review and meta-analysis

PURPOSE To evaluate the survival and complication rates of narrow-diameter implants (NDIs) for treatment with fixed restorations in premolar and molar sites. METHODS A systematic review and meta-analysis were conducted following the preferred reporting items of systematic reviews and meta-analyses (PRISMA) guidelines. Searches were performed according to a Population-Intervention-Outcome (PIO) format in MEDLINE, Scopus, and Cochrane Library, supplemented by manual cross-referencing. Inclusion criteria encompassed clinical studies on NDIs (<3.75 mm diameter) restored with fixed dental prostheses (FDP) in the posterior region. Random-effect models were employed to pool survival and complication rates, and heterogeneity was assessed using the Q test and I$^{2}$ statistic. Subgroup analyses explored variations by jaw location, implant material, and follow-up. The risk of bias was evaluated using the Cochrane tool for randomized controlled trials (RCTs) and the MINORS tool for non-randomized studies. RESULTS Thirty-six trials involving 2741 NDIs were included in the systematic review and 29 in the meta-analysis. Survival rates (SRs) ranged from 92.73% to 100% with follow-up periods from 10.8 months to 12 years. Pooled SRs for maxillary (97.0%; 95%CI: 96.2%-97.8%) and mandibular (96.5%; 95%CI: 95.7%-97.3%) NDIs were not significantly different (p = 0.688). Comparing NDIs in the premolar and molar sites, jaw location demonstrated similar SRs of 97.5% (95% CI: 95.9%-99.1%) and 98.6% (95% CI: 96.5%-99.6%), respectively. Technical complication rates varied from 0% to 23.5%, with follow-up periods ranging from 1 to 12 years. These complications primarily included screw loosening, fractures, and detachment of restorations. Data on biological complications were notably limited, and due to the heterogeneity in reporting, comparisons were not feasible. CONCLUSION NDIs demonstrate high survival and low complication rates for therapy of the partially edentulous patient with FDPs in posterior sites. The clinical performance is consistent across jaw location and implant materials.