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

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

Marginal adaptation of 3D-printed crowns: influence of preparation geometry and digitization workflow

This in vitro study evaluated the impact of different workflow and finish line design on the marginal adaptation of 3D printed resin matrix ceramic crowns. Forty extracted mandibular molars were randomly allocated into two groups according to finish line design (n = 20); heavy chamfer 0.8 mm (H) and conservative chamfer 0.2 mm (C). Each main group was divided into 2 subgroups (n = 10) according to workflow; direct digital intraoral scanning workflow (D) and semi-digital workflow (S). Crowns were 3D printed from hybrid resin and cemented using adhesive resin cement. Marginal adaptation was evaluated for all groups using a stereomicroscope before cementation and after the combined cementation and artificial aging. Statistical analysis was performed with 3-way ANOVAs and post hoc Tukey test, (P < 0.05). Significant effects were found for finish line design, workflow, and the combined cementation and artificial aging (P < 0.05), with no significant interaction between finish line design and workflow (P = 0.552). Mean marginal gaps (µm) of test groups before cementation and after the combined cementation and aging protocol were: HD, (71.72 ± 4.82), (84.5 ± 2.75); CD, (82.16 ± 3.76), (97.32 ± 3.16); HS, (92.51 ± 3.64), (111.8 ± 3.37); and CS, (106.1 ± 3.57), (123.4 ± 2.58). All groups showed significant increases thereafter (P < 0.05). Heavy chamfer finish line and direct digital workflow each yielded significantly smaller marginal gap than conservative chamfer and semi-digital workflow at both time points (P < 0.05). Within the limitations of this in vitro study, finish line design and workflow type each independently influenced the marginal adaptation of 3D-printed resin matrix ceramic crowns. A heavy chamfer and a direct digital workflow were each associated with smaller marginal gaps.

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.

Effect of cement space on 3D-printed fixed prostheses: an in vitro evaluation of accuracy and tensile strength

ABSTRACT Objective: This in vitro study evaluated the internal adaptation and the influence of different internal cement space parameters on dimensional accuracy and tensile retention strength of 3D-printed provisional crowns. Methods: Three internal cement spaces (40 μm, 80 μm, and 120 μm) were digitally designed using MeshMixer software for a cylindrical abutment compatible with an implant-supported cementation post. Twenty specimens were printed per group. After standardized post-processing, specimens were internally scanned and STL files were analyzed using CloudCompare software to assess internal accuracy. Specimens were cemented onto abutment analogs and divided into two subgroups (n=10): storage in saline solution for seven days or thermocycling for 3,000 cycles between 5°C and 55°C. Tensile bond strength testing was performed to evaluate cementation stability. Results: The 120 μm group showed significantly greater internal distortion in total surface area and cervical third compared with the 40 μm and 80 μm groups (p<0.001). All crowns demonstrated clinically acceptable accuracy. Increased cement space significantly reduced tensile retention, with the 80 μm group exhibiting the highest bond strength. Thermocycling significantly reduced tensile strength in all groups. Conclusion: The 80 μm internal spacing showed superior accuracy, while thermocycling negatively affected the tensile strength of all 3D-printed provisional crowns, with the 120 μm group exhibiting the lowest tensile resistance.

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.