Unifying intraoral scanner, computer-aided manufacturing, and final crown accuracy: A virtual-fit method for marginal gap evaluation

Abstract

Objectives

To validate a high-resolution virtual-fit method for evaluating marginal gap (MG) across CAD/CAM crown fabrication stages and to determine whether the Root Sum of Squares (RSS) method can reliably estimate total error from independent intraoral scanning (IOS) and manufacturing (CAM) steps.

Methods

A typodont model with a prepared maxillary first premolar was scanned 12 times using the EmeraldS IOS. Cement space settings from 30 to 140 µm (in 10 µm steps) were applied to CAD designs. Thirty-six hybrid-ceramic crowns were milled using only the 70, 100, and 140 µm settings. Final crowns and the reference model were scanned using both the MeditT710 lab scanner and the ATOSQ industrial scanner. A unified marginal gap assessment method was applied after non-penetrative alignment (virtual-fit) to measure MG at the IOS, CAM, and final (IOS+CAM) stages. The total error was estimated using the RSS formula. A sensitivity analysis was conducted to verify statistical power.

Results

MG was significantly overestimated when the MeditT710 scanner was used compared to ATOSQ, particularly in the IOS stage. The RSS estimate (52.0 ± 5.7 µm) slightly overestimated the final MG at 70 µm spacing by 4.7 µm (p < 0.01), likely due to STL mesh artifacts. At 100 µm and 140 µm spacing, no significant difference was observed. The virtual-fit method demonstrated high statistical power, capable of detecting differences as small as 6 µm. At the final stage, MG at 140 µm spacing was 6 µm higher than at 100 µm (p < 0.05).

Conclusions

The virtual-fit method provides consistent, high-resolution marginal fit measurement throughout the CAD/CAM workflow and supports cumulative error modeling via the RSS approach.

Clinical significance

RSS modeling enables clinicians and researchers to assess whether new IOS or CAM systems meet clinical accuracy thresholds without physically testing all device combinations. Cement spacing between 70–100 µm provides reasonable accuracy for chairside CAD/CAM crown fabrication.