Comparison of digital vs. conventional impression systems for marginal accuracy

Objective: The purpose of this study was to compare marginal accuracy and fit of Lava Zirconia (3M ESPE) copings using the Lava Chairside Oral Scanner (LCOS) vs. Polyvinyl Siloxane Impression (PVS) material.

Methods: Tooth #30 was prepared with a 360-degree chamfer finish line design on a half-arch articulated typodont mimicking a clinical situation. A digital file was used to create simulated models replicas of the prepared tooth (n=30) via computer aided manufacturing. All models randomly were assigned to two groups (n=15/gp), Group A: LCOS; Group B: PVS(Aquasil Ultra Heavy and LV Fast Set, Dentsply). Impressions were taken, evaluated for accuracy by two trained clinicians and sent to commercial laboratory. The LCOS impressions were used to fabricate stereolithographic (SLA) models. The PVS impressions were used to fabricate type IV gypsum models. All models were utilized to manufacture Lava Zirconia copings. Copings were seated and held with finger pressure. Qualitative measure of marginal accuracy was determined at 4 designated locations (mid buccal, mid lingual, mid distal and mid mesial) using USPHS criteria with a scaling of Alfa, Bravo, & Charlie by visual inspection and tactile perception. Measurements were recorded by two calibrated, blinded examiners using sharp explorers and 3.0 magnified loupes.

Results: Mann-Whitney U test was used to analyze the effect of the impression systems on copings and marginal integrity. There were no statistically significant differences between the two impression systems at any of the four sites. Both mid-mesial and mid-distal showed a slight trend for improved integrity in the digital impression system, but the results were not statistically significant (0.07 and 0.15, respectively).

Conclusion: The use of LCOS was equivalent to PVS impressioning in this in-vitro study. Further clinical research is necessary to validate this new system. Supported by a grant from 3M/ESPE.