Three-dimensional fit of self-glazed zirconia monolithic crowns fabricated by wet deposition

Evaluation of fit and accuracy of single crowns fabricated from self-glazed zirconia compared with milled zirconia

STATEMENT OF PROBLEM

Self-glazed zirconia is a novel dental material fabricated with a combination of subtractive and additive manufacturing techniques. However, how the marginal and internal fit of these restorations compare with conventionally fabricated zirconia is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the marginal and internal fit and internal accuracy of single crowns made from self-glazed zirconia compared with those made from milled zirconia.

MATERIAL AND METHODS

A metal die was scanned, and a crown was designed using a computer-aided-design program. The computer-aided-manufacturing milling method (conventional technique) was used to produce 10 zirconia crowns, and additive manufacturing was used to produce 10 self-glazed zirconia crowns. Internal and marginal fit measurements were made by using the silicone replica method; marginal fit was also measured by using the direct-view technique. An independent t test was performed to compare both types of crowns and test the null hypothesis (α=.05).

RESULTS

For the occlusal, internal, and total mean distances, significant differences were found between self-glazed and milled zirconia crowns (P<.001). With the direct-view technique, a significant difference (P=.004) between the 2 techniques was found in the marginal area. The accuracy for the axial and occlusal areas combined for self-glazed and milled zirconia was 27 μm and 49 μm, respectively.

CONCLUSIONS

Both techniques produced crowns with clinically acceptable marginal and internal fit. The self-glazed zirconia crowns had higher accuracy of internal fit than milled zirconia crowns.

Clinical outcomes of self-glazed zirconia veneers produced by 3D gel deposition: a retrospective study

BACKGROUND

Self-glazed zirconia (SZ) restorations are made by a novel additive three-dimensional gel deposition approach, which are suitable for a straightforward completely digital workflow. SZ has recently been used as minimally invasive veneer, but its clinical outcomes have not been clarified yet. This study aimed to evaluate the preliminary clinical outcomes of SZ veneers compared with the widely used lithium disilicate glass-ceramic veneers made by either pressing (PG) or milling (MG) process.

METHODS

Fifty-six patients treated with SZ, PG, and MG veneers by 2 specialists between June 2018 and October 2022 were identified. Patients were recalled for follow-up at least 1 year after restoration. Clinical outcomes were assessed by 2 independent evaluators according to the modified United States Public Health Service (USPHS) criteria. Overall patient satisfaction was assessed using visual analogue scale (VAS), and analyzed by one-way ANOVA. Chi-square test was applied to compare the difference in the success and survival rates among the 3 groups.

RESULTS

A total of 51 patients restored with 45 SZ, 40 PG, and 41 MG veneers completed the study, with a patient dropout rate of 8.9%. Mean and standard deviation of follow-up period was 35.0 ± 14.7 months. All restorations performed well at baseline, except for 2 SZ veneers with mismatched color (rated Bravo). During follow-up, marginal discrepancy (rated Bravo) was found in 4 MG veneers and 1 PG veneer, and partially fractured (rated Charlie) was found in another 2 PG veneers. The survival rate of SZ, PG, and MG veneers was 100%, 95%, and 100%, with a success rate of 95.56%, 92.50%, and 90.24%, respectively, none of which were significantly different (p = 0.099 and 0.628, respectively). The mean VAS score of SZ, PG, and MG was 95.00 ± 1.57, 93.93 ± 2.40, and 94.89 ± 2.00 respectively, without significant difference (p > 0.05).

CONCLUSION

SZ veneers exhibited comparable preliminary clinical outcomes to PG and MG veneers, which could be considered as a feasible option for minimally invasive restorative treatment.

Evaluation of Er:YAG laser energy transmitted through novel dental zirconia ceramics

Erbium:yttrium-aluminum-garnet (Er:YAG) laser debonding is a promising removal method in prosthodontics. This study aimed to assess Er:YAG laser energy transmission through novel zirconia ceramics. Five types of ceramic samples: lithium disilicate ceramic (LDC), self-glazed zirconia (SGZ), 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP), 4Y-TZP and 5Y-TZP with 5 thicknesses (0.5, 1.0, 1.5, 2.0, 2.5 mm) and 2 shades (A1, A3), 50 specimens total, were made. Fourier transformation infrared absorption spectra were obtained for each ceramic type, and Er:YAG laser energy transmission tests were conducted for each specimen. The novel zirconia ceramic (SGZ, 4Y-TZP, 5Y-TZP) transmission ranged from 40%-60%. The transmitted laser energy decreased with increasing ceramic thickness, and the differences between different shades were significant (p<0.05). The novel zirconias had a higher translucency than 3Y-TZP at any given thickness and shade, and when the thickness was >1.5 mm, the novel zirconias had a higher translucency than LDC.

Promoted Abutment-Soft Tissue Integration Around Self-Glazed Zirconia Surfaces with Nanotopography Fabricated by Additive 3D Gel Deposition

Introduction

Improving the biological sealing around dental abutments could promote the long-term success of implants. Although titanium abutments have a wide range of clinical applications, they incur esthetic risks due to their color, especially in the esthetic zone. Currently, zirconia has been applied as an esthetic alternative material for implant abutments; however, zirconia is purported to be an inert biomaterial. How to improve the biological activities of zirconia has thus become a popular research topic. In this study, we presented a novel self-glazed zirconia (SZ) surface with nanotopography fabricated by additive 3D gel deposition and investigated its soft tissue integration capability compared to that of clinically used titanium and polished conventional zirconia surfaces.

Materials and Methods

Three groups of disc samples were prepared for in vitro study and the three groups of abutment samples were prepared for in vivo study. The surface topography, roughness, wettability and chemical composition of the samples were examined. Moreover, we analyzed the effect of the three groups of samples on protein adsorption and on the biological behavior of human gingival keratinocytes (HGKs) and human gingival fibroblasts (HGFs). Furthermore, we conducted an in vivo study in which the bilateral mandibular anterior teeth of rabbits were extracted and replaced with implants and corresponding abutments.

Results

The surface of SZ showed a unique nanotopography with nm range roughness and a greater ability to absorb protein. The promoted expression of adhesion molecules in both HGKs and HGFs was observed on the SZ surface compared to the surfaces of Ti and PCZ, while the cell viability and proliferation of HGKs and the number of HGFs adhesion were not significant among all groups. In vivo results showed that the SZ abutment formed strong biological sealing at the abutment-soft tissue interface and exhibited markedly more hemidesmosomes when observed with a transmission electron microscope.

Conclusion

These results demonstrated that the novel SZ surface with nanotopography promoted soft tissue integration, suggesting its promising application as a zirconia surface for the dental abutment.

Incomplete Polymerization of Dual-Cured Resin Cement Due to Attenuated Light through Zirconia Induces Inflammatory Responses

Zirconia restorations are becoming increasingly common. However, zirconia reduces the polymerization of dual-cured resin cement owing to light attenuation, resulting in residual resin monomers. This study investigated the effects of dual-cured resin cement, with incomplete polymerization owing to attenuated light through zirconia, on the inflammatory response in vitro. The dual-cured resin cement (SA Luting Multi, Kuraray) was light-irradiated through zirconia with three thickness diameters (1.0, 1.5, and 2.0 mm). The light transmittance and the degree of conversion (DC) of the resin cement significantly decreased with increasing zirconia thickness. The dual-cured resin cement in 1.5 mm and 2.0 mm zirconia and no-irradiation groups showed significantly higher amounts of hydroxyethylmethacrylate and triethyleneglycol dimethacrylate elution and upregulated gene expression of proinflammatory cytokines IL-1β and IL-6 from human gingival fibroblasts (hGFs) and TNFα from human monocytic cells, compared with that of the 0 mm group. Dual-cured resin cement with lower DC enhanced intracellular reactive oxygen species (ROS) levels and activated mitogen-activated protein (MAP) kinases in hGFs and monocytic cells. This study suggests that dual-cured resin cement with incomplete polymerization induces inflammatory responses in hGFs and monocytic cells by intracellular ROS generation and MAP kinase activation.

Dimensional accuracy and clinical adaptation of monolithic zirconia crowns fabricated with the nanoparticle jetting technique

STATEMENT OF PROBLEM

The nanoparticle jetting (NPJ) technique is a recently developed additive manufacturing method that may have useful dental applications. The manufacturing accuracy and clinical adaptation of zirconia monolithic crowns fabricated with NPJ are unknown.

PURPOSE

The purpose of this in vitro study was to compare the dimensional accuracy and clinical adaptation of zirconia crowns fabricated with NPJ and those fabricated with subtractive manufacturing (SM) and digital light processing (DLP).

MATERIAL AND METHODS

Five standardized typodont right mandibular first molars were prepared for ceramic complete crowns, and 30 zirconia monolithic crowns were fabricated using SM, DLP, and NPJ (n=10) with a completely digital workflow. The dimensional accuracy at the external, intaglio, and marginal areas was determined by superimposing the scanned data and computer-aided design data of the crowns (n=10). Occlusal, axial, and marginal adaptations were evaluated by using a nondestructive silicone replica and dual scanning method. The 3-dimensional discrepancy was evaluated to determine clinical adaptation. Differences among test groups were analyzed by using a MANOVA and the post hoc least significant difference test for normally distributed data or the Kruskal-Wallis test with Bonferroni correction for nonnormally distributed data (α=.05).

RESULTS

Significant differences were found in the dimensional accuracy and clinical adaptation among the groups (P<.001). The NPJ group had a lower overall root mean square (RMS) value for dimensional accuracy (22.9 ±1.4 μm) than the SM (27.3 ±5.0 μm) and DLP (36.4 ±5.9 μm) groups (P<.001). The NPJ group had a lower external RMS value (23.0 ±3.0 μm) than the SM group (28.9 ±5.4 μm) (P<.001) and equivalent marginal and intaglio RMS values than the SM group. The DLP group had larger external (33.3 ±4.3 μm), intaglio (36.1 ±10.7 μm), and marginal (79.4 ±12.9 μm) deviations than the NPJ and SM groups (P<.001). With regard to clinical adaptation, the marginal discrepancy was smaller in the NPJ group (63.9 ±27.3 μm) than in the SM group (70.8 ±27.5 μm) (P<.001). No significant differences were found between the SM and NPJ groups in terms of the occlusal (87.2 ±25.5 and 80.5 ±24.2 μm, respectively) and axial (39.1 ±19.7 and 38.4 ±13.7 μm, respectively) discrepancies. The DLP group had larger occlusal (239.0 ±60.1 μm), axial (84.9 ±29.1 μm), and marginal (140.4 ±84.3 μm) discrepancies than the NPJ and SM groups (P<.001).

CONCLUSIONS

Monolithic zirconia crowns fabricated using NPJ have higher dimensional accuracy and clinical adaptation than those fabricated using SM or DLP.

Trueness of stereolithography ZrO2 crowns with different build directions

This study aims to measure the trueness of zirconia crowns with different build directions of materials fabricated using the stereolithography (SLA) method. The anatomic contour crown of prepped maxillary right first molar was designed using CAD software to obtain the standard tessellation language (STL) file. Two different build directions were set for the crowns using Materialize Magics software. One group was built with a margin base platform, while the other group was built in the direction opposite to the occlusal surface base platform. The 20 crown-shaped parts were printed. The STL files of scanned printing zirconia crowns were superimposed each segment by the 3D analysis software. The two groups were statistically analyzed using t-tests. Significant differences were found in the marginal and internal discrepancies between the groups. The build direction had a significant influence on the accuracy of the zirconia crown. The results indicate the most effective build direction for manufacturing SLA 3D-printed crowns.

Marginal and Internal Fit of Monolithic Zirconia Crowns Fabricated by Using Two Different CAD-CAM Workflows: An In Vitro Study

Objectives: Few studies have evaluated the marginal fit of computer-aided design—computer-aided manufacturing (CAD-CAM) monolithic zirconia crowns fabricated through completely digital workflow; however, the internal fit of these restorations is not well known. The purpose of this in vitro study was to evaluate the marginal and internal fit of monolithic zirconia crowns fabricated by using digital workflow, including intraoral scanner (IOS) scans, and compare the results to those of a semi-digital workflow, which combined conventional impressions, poured casts, and extraoral scanner (EOS) scanning. Materials and methods: A typodont right mandibular first molar was prepared for a complete-coverage ceramic crown and scanned using an IOS. The conventional impressions of the preparation were also made, and stone casts were poured and scanned by using an EOS. Virtual models were generated for both workflows, and identical virtual anatomic contour crowns were designed using CAD software. Monolithic zirconia crowns were fabricated for both IOS (ZI; n = 10) and EOS (ZE; n = 10) groups. The silicon replica technique was used to evaluate the marginal and internal fit of the crowns. Measurements were made at 13 points on buccolingual and mesiodistal cross-sections per specimen with a ×6.5 to ×50 zoom stereo microscope. The results from both groups were statistically compared using the Independent Samples t-tests and the Mann–Whitney U test (α = 0.05). Results: Mean gap values at all measurement locations for ZE were significantly higher than those for ZI (p ≤ 0.002). Overall mean values ranged between 29 and 43 µm (median: 28–42 µm) for ZI and 42 and 75 µm (median: 43–77 µm) for ZE. Conclusion: Completely digital workflow through intraoral scans provided significantly better marginal and internal fit for CAD-CAM monolithic zirconia crowns compared with the semi-digital workflow, where stone casts obtained from conventional impressions were scanned with an EOS. Yet, both workflows provided an acceptable marginal and internal fit for CAD-CAM monolithic zirconia molar crowns (<120 µm). Clinical Relevance: Completely digital workflow using IOS scans may be advantageous for the fabrication of CAD-CAM monolithic zirconia crowns as favorable results can be obtained with less material waste and potentially shortened overall treatment time as the impression files can be transferred to the production facility electronically. The results need to be corroborated with clinical studies.