Accuracy of impressions and framework marginal fit of implant-supported complete-arch fixed dental prostheses fabricated by using direct and indirect workflows.

Abstract

Purpose To compare the scan trueness and marginal gaps of monolithic zirconia implant-supported fixed complete prostheses (iFCPs) fabricated using direct and indirect digital workflows. In addition, to compare average marginal gap values of digital analysis and stereomicroscopic image analysis, performing 1-screw test, evaluating potential correlations between them. Methods A master model of an edentulous maxilla with four implants following the all-on-4 concept was fabricated and digitized to design a 12-unit zirconia iFCP for evaluating scan accuracy and marginal fit. Two digital workflows-direct (multi-unit abutment level intraoral scanning) and indirect (digitized stone casts from conventional impressions)-were used to design iFCPs (n=8). iFCPs were milled out of zirconia discs in a centralized milling center. Scan trueness and marginal fit were assessed using 3D analysis software through trueness evaluation and vertical gap measurements, including 1-screw test. Vertical gaps were measured also using stereomicroscope images. The scan trueness and vertical gap were analyzed with two-way ANOVA with Bonferroni post hoc, Mann-Whitney U and Dunn's tests, and Spearman's Rho was used for correlation. Results The IOS scans showed significantly higher scan body distance deviations than LBS scans overall (P ≤ 0.001) and at abutments 13 and 16, with significant effect of scanner-scan body location interactions at y- and z-axes (P ≤ 0.018). Marginal gap values at abutments 13, 16, and 23 were higher for IOS scans in both stereomicroscope and TSP analyses (P =0.038, P =0.001, and P =0.015, respectively), except at abutment 23, where similar marginal gap values were found with TSP. Positive correlations were found between scan body deviations and average gap values using both measurement methods, and between the two methods themselves. Conclusions Indirect digital workflows resulted in superior trueness and marginal fit compared to direct digital workflows using IOS. TSP enabled marginal gap values mostly comparable and correlated to those from stereomicroscope, which revealed promising findings for the validity of the technique. Clinical Significance Investigated indirect digital workflow may provide superior impression trueness and marginal fit for monolithic zirconia implant-supported complete-arch fixed dental prostheses, compared with tested digital workflow, potentially reducing the risk of mechanical and biological complications related to misfit.