Does Splinting the Direct Copings Increase the Impression Accuracy of Two-Unit Nonparallel Implant Restorations? A Systematic Review and Meta-analysis

Purpose: The purpose of this systematic review and meta-analysis was to evaluate the effects of splinting impression copings on the accuracy of conventional impressions for two-unit nonparallel implant restorations.
Materials and methods: MEDLINE via PubMed, Embase, and Web of Science databases were searched with no publication year or language limits, and studies comparing the accuracy of conventional impressions for two-unit nonparallel implant restorations made using splinted impression copings and nonsplinted impression copings were identified. A meta-analysis was performed using Review Manager software. The mean difference (MD) with 95% confidence interval (95% CI) for the framework strain and marginal gap of the implant-framework connection between impressions using splinted and nonsplinted copings were statistically analyzed (α = .05).
Results: Initially, 142 articles were identified after the removal of duplicates. Five in vitro studies were included in the systematic review, and four in vitro studies were included in the meta-analysis. All the included studies were focused on internal-connection implants and implant-level impressions. The implant angulation in the included studies ranged from 8 to 30 degrees. Impressions using splinted impression copings exhibited significantly smaller marginal gaps than those using nonsplinted impression copings (P = .02; mean difference [MD] = -13.34; 95% CI = -24.31 to -2.36). Moreover, with respect to the framework strain, no significant differences were found between impressions using splinted impression copings and nonsplinted impression copings (P = .47; MD = -12.64; 95% CI = -47.32 to 22.03).
Conclusions: Significantly larger marginal gaps were found in the impressions using splinted impression copings, but the clinical significance was low. Based on the limited number of studies included, splinting copings is unnecessary when making conventional impressions for two-unit nonparallel implant restorations.