Trueness of Crown Preparation Dies in Dental Models: An In Vitro Assessment of Digital and Analog Workflows.

PURPOSE: To assess crown die trueness using additive manufacturing (AM) based on intraoral scanning (IOS) data and compare it with stone models.

MATERIALS AND METHODS: Crown dies with four finish line types- equigingival shoulder (SAE), subgingival shoulder (SAS), equigingival chamfer (CAE), and subgingival chamfer (CAS)-were incorporated into a reference model and scanned with a coordinate measurement machine (CMM; n = 1 scan). Trios4 (3Shape) scans generated a second reference dataset (IOS; n = 10 scans). Using scans, crown dies were produced with two different 3D printers (MAX UV385 [Asiga] and NextDent 5100 [3DSystems]; n = 10 per system). Stone dies were created from conventional impressions (n = 10). Specimens were digitized with a laboratory scanner (E4, 3Shape). Trueness was evaluated with Geomagic Control X (3DSystems). Data analysis was done using Shapiro-Wilk, Levene, ANOVA, and t tests (α < .05).

RESULTS: All crown dies fell within the clinically acceptable trueness range (150 μm). IOS exhibited significantly lower (P < .05; Δ ≤ 21.7 μm) or similar trueness compared to stone models. Asiga dies demonstrated similar and NextDent significantly lower marginal trueness than IOS (P < .05; Δ ≤ 57.3 μm). Most AM margin areas had significantly lower trueness than stone (P < .001; Δ ≤ 57.2 μm). Asiga outperformed NextDent (P < .001). Shoulder trueness surpassed chamfer in optical scans (P = .01). Finish line design and gingiva location did not have a significant impact on AM and stone models (P > .05).

CONCLUSIONS: Combining IOS and AM achieves clinically acceptable crown die trueness for single molar teeth. The choice of AM device is critical, with Asiga outperforming NextDent. Finish-line design has an impact on optical scans. Finish-line design and marginal gingiva location have little effect on AM trueness.