Narrow-Diameter Implants for Partial Fixed and Removable Prostheses: A Systematic Review and Meta-Analysis

To answer the following focus question: Are narrow-diameter implants feasible to support fixed dental prostheses (FDPs) and partial removable dental prostheses (PRDPs)?

This review followed the PRISMA statement and was registered in the PROSPERO database (CRD42020153729). Six databases and the gray literature were searched through October 2021 without language, publication time, or follow-up restrictions. The main outcomes were survival, success, and marginal bone loss (MBL). Risk of bias was assessed for each study design, and random-effects meta-analyses were performed (α = .05).

Seventeen studies were included in the qualitative analysis, and 3 were included in the meta-analyses. In total, 1,624 NDIs and 339 standard-diameter implants (SDIs) were placed in 1,060 patients. Follow-up varied from 1 to 10 years, and 17 failures (implant loss) were recorded. No differences in survival rate for FDPs supported by NDIs vs SDIs were found (odds ratio [OR] = 0.59, 95% CI: 0.18 to 1.92, P = .38). However, Kaplan-Meier analysis evaluating only NDI performance revealed a higher survival rate of NDIs ≥ 3.3-mm diameter (P = .002), placed with delayed loading (P = .024), and placed in the maxilla (P = .014). FDPs supported by NDIs vs SDIs presented similar success rates (OR = 1.48, 95% CI: 0.41 to 5.34, P = .55); however, MBL was lower in the NDI group (mean difference = -0.23 mm, 95% CI: -0.41 to -0.06, P = .01). Insufficient data regarding PRDPs were available.

Despite the limited studies available, FDPs supported by NDIs presented survival and success rates comparable to those supported by SDIs, with slightly lower MBL. For PRDPs, strong conclusions were not possible.