Comparative Evaluation of Fit Accuracy of Milled Versus 3D-Printed Provisional Crowns over Endodontically Treated Abutments

Abstract

Background: Provisional crowns placed over endodontically treated abutments must provide a precise marginal fit to preserve the coronal seal, prevent bacterial microleakage into the obturated canal system, and protect the structurally weakened tooth during the interim period. Computer-aided design and computer-aided manufacturing (CAD/CAM) milling and additive manufacturing (three dimensional (3D) printing) are now the two principal digital workflows used for fabricating these restorations, but comparative data on their fit performance specifically over endodontically treated abutments remain limited.

Objective: To compare the marginal and internal fit accuracy of provisional crowns fabricated by subtractive milling (CAD/CAM) and additive manufacturing (digital light processing (DLP) 3D printing) over endodontically treated abutments using the silicone replica technique.

Methods: Sixty extracted, single-rooted human premolars that had received standardized orthograde root canal treatment were randomly allocated into two groups of 30 specimens each. Group I received milled polymethylmethacrylate (PMMA) provisional crowns from pre-polymerised CAD/CAM blocks, while Group II received 3D-printed crowns fabricated from a DLP printable resin. A standardized tooth preparation with a 1 mm chamfer finish line, 6 degree taper, and a 2 mm ferrule was completed. All crowns were designed from a single STL file with a 50 µm cement spacer. The marginal gap, axial gap, occlusal gap, and absolute marginal discrepancy were measured at 16 reference points per specimen using the silicone replica technique under a digital microscope at ×100 magnification. Data were analysed using independent t-tests with significance set at p < 0.05.

Results: The mean marginal gap was 58.4 ± 9.7 µm in the milled group and 76.2 ± 12.3 µm in the 3D-printed group, a difference that was statistically significant (p < 0.001). The mean axial and occlusal gaps were also significantly smaller in the milled group (axial: 71.5 ± 10.8 µm vs 89.6 ± 13.4 µm; occlusal: 112.4 ± 18.6 µm vs 138.9 ± 22.1 µm; p < 0.001 for both). All values, however, fell within the clinically acceptable threshold of 120 µm for the marginal interface. Inter-examiner reliability for replica measurements was high (intraclass correlation coefficient (ICC) = 0.92).

Conclusion: Milled provisional crowns demonstrated superior marginal and internal fit compared with their 3D-printed counterparts when seated on endodontically treated abutments, although both fabrication methods produced restorations within the clinically acceptable range. The choice of fabrication technique should consider the duration of provisionalization, restorative complexity, and chairside efficiency, with milling preferred where prolonged interim service over a structurally compromised tooth is anticipated.