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

Objective: 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. Materials and methods: 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. Results: <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. Conclusion: 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. Clinical relevance: 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.