Effect of build orientation on marginal and internal discrepancies of zirconia crowns fabricated by using digital light processing 3D printing: A clinical study.

Three-Dimensional Evaluation of Marginal Gap in Prefabricated Zirconia and 3D-Printed Pediatric Crowns

3D-printed resin crowns exhibited superior marginal adaptation compared to prefabricated zirconia crowns, and among the evaluated materials, the SLA-fabricated Formlabs crowns exhibited the lowest marginal gap values.

Marginal and Internal Adaptation of Crowns Fabricated on Models From Digital and Conventional Impressions: An In Vitro Study.

OBJECTIVE To evaluate the marginal and internal adaptation of monolithic crowns fabricated from lithium disilicate (LD), zirconia (Zr), and fiber-reinforced composite (FRC) using five different model types derived from digital and conventional impressions. MATERIALS AND METHODS A maxillary first molar was prepared on a phantom model for full-coverage crown restoration. Conventional and digital impressions were used to produce five types of working models: scanned impression STL (CS), plaster (CP), 3D-printed resin from scanned impressions (CR), direct digital STL (DS), and 3D-printed resin from digital impressions (DR). A total of 150 crowns (n = 10 per group) were fabricated using CAD/CAM. The marginal and internal adaptation were assessed using the silicone replica technique and analyzed under a light microscope (×40). Data were statistically analyzed using two-way MANOVA and ANOVA (α = 0.05). RESULTS Both model type and restorative material significantly affected adaptation values (p < 0.05). The best adaptation was observed in LD crowns fabricated on 3D-printed resin models derived from digital impressions. In general, crowns fabricated on digitally derived 3D-printed resin models demonstrated lower gap values than those fabricated on plaster and STL models. FRC crowns on plaster models exhibited the highest gap values. All measured gap values remained within clinically acceptable limits (< 120 μm). CONCLUSIONS Crowns fabricated on 3D-printed resin models derived from digital impressions showed the most favorable adaptation among tested groups. Both model type and restorative material significantly influenced restoration fit. Based on the findings of this in vitro study, digital workflows incorporating 3D-printed resin models may be considered reliable alternatives to conventional plaster models in CAD/CAM systems.

From milling to printing: evaluating the applicability of zirconia in restorative dentistry

PURPOSE This study compared the mechanical and optical properties of 3D-printed and milled zirconia, and evaluate the marginal and internal adaptation of crowns fabricated with 3Y-TZP and veneers fabricated with 5Y-TZP. MATERIALS AND METHODS Ninety-two disc specimens and thirty-six monolithic restorations (crowns and laminate veneers) were fabricated using standardized CAD-CAM workflows. Biaxial flexural strength was measured, and optical properties were evaluated using the translucency parameter (TP), total transmittance (TT), and haze. Marginal and internal adaptations were assessed using a silicone replica technique. RESULTS Printed 3Y-TZP showed flexural strength comparable to milled zirconia (1211.4 ± 114.3 MPa vs. 1120.3 ± 93.3 MPa; P = .067), and no significant differences were observed between fabrication methods for 5Y-TZP (P = .442). TP values were significantly higher in milled zirconia for both 3Y-TZP and 5Y-TZP (all P < .001). For 5Y-TZP specimens only, TT was higher in the milled group (P < .001), whereas haze values did not differ between fabrication methods. All restorations demonstrated marginal gaps within clinically acceptable limits (< 120 µm). Printed crowns exhibited significantly smaller occlusal internal gaps (P = .029), and printed laminate veneers showed favorable marginal adaptation at multiple sites. CONCLUSION 3D-printed zirconia showed flexural strength comparable to milled zirconia and demonstrated favorable adaptation in selected regions, although optical properties were lower.

Adjustment Efficiency and Internal Fit of Screw-Retained Zirconia Crowns on Additively Manufactured Dental Casts: An In Vitro Study on the Effect of Printing Layer Thickness and Digital Implant Analog Design.

PURPOSE To evaluate how the layer thickness of additively manufactured casts and implant analog design influence the adjustment efficiency and internal fit of screw-retained zirconia crowns, compared with those adjusted on conventional stone casts. MATERIALS AND METHODS A master mandibular model with an implant and its antagonist were digitized to additively manufacture implant casts with 50 µm or 100 µm layer thicknesses and either proprietary friction-retained (S) or third-party screw-retained (N) analogs (S-50, S-100, N-50, N-100), along with their corresponding maxillary casts. Conventional stone casts (CNV) served as the control (n = 10). Screw-retained zirconia crowns were fabricated for each cast, and the duration of interproximal and occlusal contact adjustments was recorded. Crown fit on the master model was evaluated using the triple-scan protocol, followed by a qualitative assessment of interproximal and occlusal contacts. Crowns with heavy contacts were readjusted and timed, then reevaluated to determine whether interproximal adjustments affected the fit. Comparisons among resin casts were performed using a generalized linear model with Bonferroni-adjusted post hoc tests, while comparisons with CNV casts were made with 1-way analysis of variance and Dunnett's tests. Qualitative contact data were analyzed using the chi-square test (α = .05). RESULTS Crowns on 50 µm-layer casts needed less adjustment and exhibited smaller gaps than those on 100 µm-layer casts; S analogs led to smaller gaps (P ≤ .010). Compared to CNV, 50 µm-layer casts led to lower adjustment duration and S-50 led to lower internal gaps (P ≤ .020). Only mesial interproximal contacts differed significantly on the master model (P = .001); crowns from S analog casts showed normal contacts, while at least 50% those from other casts had light contacts. At least 50% of the crowns exhibited normal distal contacts, and those with heavy contacts (3 on the mesial and 16 on the distal side) showed improved fit after adjustment. No occlusal adjustments were required on the master model. CONCLUSIONS Reduced printing layer thickness and the use of proprietary friction-retained analogs improved the adjustment efficiency and internal adaptation of screw-retained zirconia crowns.

Effect of the build angle on the accuracy of 3D-printed definitive composite resin crowns, onlays, and laminate veneers: An in vitro study.

OBJECTIVE This in vitro study evaluated the effect of the build angle on the accuracy of 3D-printed definitive composite resin crowns, onlays, and laminate veneers. MATERIALS AND METHODS Phantom models of a maxillary first premolar, first molar, and central incisor were prepared for crown, onlay, and laminate veneer restorations. The restorations were fabricated using an LCD printer and a definitive composite resin at five build angles (0°, 30°, 45°, 70°, and 90°; n = 15 per group) Trueness and precision were evaluated using root mean square (RMS) values from 3D superimposition analyses of the intaglio, external, and overall surfaces. RESULTS For the crown restorations, the lowest RMS values were observed at a 45° build angle, whereas the highest values were observed at 90°. The build angle did not significantly affect crown precision (P ≥ 0.091). For the onlay and laminate veneer restorations, the lowest RMS values were observed at a 30° build angle, whereas the highest values were observed at 90°. Regarding precision, the 30° build angle for the onlays and the 0° and 30° build angles for the laminate veneers resulted in significantly lower RMS values for the external and overall surfaces (P ≤ 0.012). All the RMS values remained below the clinically acceptable threshold of 100 μm. CONCLUSION The build angle significantly influenced the accuracy of 3D-printed definitive composite resin restorations. The optimal build angle depended on the restoration type, with 45° for crowns and 30° for onlays and laminate veneers. CLINICAL SIGNIFICANCE Appropriate build angle selection may improve the manufacturing accuracy and clinical fit of 3D-printed definitive composite resin restorations.

Digital Evaluation of Marginal Adaptation of 3D-Printed and Milled Endocrown Restorations: An In Vitro Study.