Accuracy of Direct Intraoral Versus Reverse Scanning for Abutment-Level Implant Impressions: an In Vitro Study

The aim of the study was to compare the relative accuracy of direct intraoral scanning and reverse scanning techniques (RST) for abutment-level implant impressions, with specific evaluation of putty-only impressions and alginate casts.

An in vitro study was conducted using a 3D-printed mandibular edentulous model with four multiunit abutments. Three techniques were compared (five scans per technique; 15 digital datasets in total): (1) direct IOS (iTero Element 5D) with manufacturer-provided scan bodies; (2) reverse scanning of a putty-only impression (addition silicone); and (3) reverse scanning of an alginate cast (Cavex Cream) poured in Type IV dental stone. Both reverse scans were performed using a laboratory scanner (Medit T510). Linear distances between the scan body center points were measured in the anterior (canine-to-canine) and posterior (molar-to-molar) regions using exocad software. As no independent gold standard was used, outcomes represent relative differences between techniques. Statistical analysis was performed using a two-way repeated measures ANOVA with Tukey's HSD post-hoc test.

All pairwise comparisons were statistically significant (p <0.05). Direct IOS produced the smallest relative deviations, followed by reverse scanning of alginate casts, while putty-only impressions exhibited the greatest relative deviations, particularly in the posterior region. Posterior deviations were significantly greater than anterior deviations. A significant technique and region interaction indicated that putty-only impressions were disproportionately affected in the posterior region.

Within the limitations of this in vitro study, direct IOS demonstrated the highest relative accuracy. Reverse scanning of alginate casts showed intermediate accuracy, whereas putty-only impressions exhibited substantially greater relative deviations, particularly in the posterior regions. Material and technique selection significantly influence impression accuracy; direct IOS should be preferred when clinically feasible.

Accurate implant impressions are critical for achieving a passive fit and long-term success of implant-supported prostheses. This study indicates that direct intraoral scanning provides superior accuracy compared with RSTs, particularly in the posterior regions. When digital workflows are not feasible, alginate casts may offer a more reliable alternative to putty-only impressions, thereby helping clinicians select appropriate impression techniques to improve clinical outcomes.