Marginal gap and internal fit of 3D printed versus milled monolithic zirconia crowns

Evaluation of vertical marginal discrepancy and load-to-failure of monolithic zirconia and lithium disilicate laminate veneers manufactured in different thicknesses

OBJECTIVES

This study aimed to evaluate the feasibility of monolithic zirconia laminate veneers (MZLV) compared to lithium disilicate laminate veneers (LDLV).

MATERIALS AND METHODS

Sixty resin replicas, each prepared with depths of 0.5 mm, 0.7 mm, and 1 mm, were produced using a 3D printer from acrylic teeth. Laminate veneers of these thicknesses were milled from pre-sintered monolithic zirconia (3rd generation) and lithium disilicate blocks. The intaglio surface of MZLV was treated with air abrasion using 110 μm diameter silica-modified aluminium oxide particles and ceramic primer, while LDLV was etched with etchant gel and treated with the ceramic primer before cementation with resin cement. Vertical marginal discrepancy (VMD) was assessed using a stereomicroscope, and a load-to-failure test was conducted using a universal testing machine. Failure modes were evaluated macroscopically on fractured surfaces. Data were analysed statistically using Two-way ANOVA and Bonferroni correction (α = 0.05).

RESULTS

LDLV samples exhibited significantly larger VMD compared to MZLV samples across all thicknesses, especially in cervical, palatal, and mean data. Within the LDLV group, load-to-fracture values for 0.7 mm and 1.0 mm thicknesses were similar, whereas for 0.5 mm thickness, it was significantly lower. In the MZLV group, load-to-fracture values were lower for 0.7 mm and 1.0 mm thicknesses compared to LDLV, but higher for 0.5 mm thickness.

CONCLUSIONS

Material choice and restoration thickness significantly influence laminate veneer restorations' success. MZLV generally exhibits superior vertical marginal fit compared to LDLV, with varying load-to-failure values across different thicknesses. Clinical management of debonding in MZLV is simpler compared to restoration fracture in LDLV.

CLINICAL RELEVANCE

Considering clinical factors, MZLV may be a preferable option to LDLV for this restoration with the thickness of 0.5 mm.

The physical-mechanical properties of 3D-printed versus conventional milled zirconia for dental clinical applications: A systematic review with meta-analysis

AIM OF STUDY

This systematic review aimed to compare the physical-mechanical properties of 3D-printed (additively manufactured (AM)) zirconia compared to conventionally milled (subtractive manufactured: SM) zirconia specimens.

MATERIALS AND METHODS

A thorough search of Internet databases was conducted up to September 2023. The search retrieved studies that evaluated AM zirconia specimens and restorations regarding the physical-mechanical properties and mechanical behavior of zirconia. The main topic focused on 3Y-TZP. However, records of 4YSZ and 5YSZ were also included to gather more comprehensive evidence on additively manufactured zirconia ceramic. The quality of studies was assessed using the ROB2 tool, Newcastle Ottawa scale, and the Modified Consort Statement. Of 1736 records, 57 were assessed for eligibility, and 38 records were included in this review, only two clinical trials meet the inclusion criteria and 36 records were laboratory studies. There were no signs of mechanical complications and wear to antagonists with short-term clinical observation. SM thin specimens ≤1.5 mm showed statistically significant higher flexural strength than AM zirconia (p ≤ 0.01), while thicker specimens showed comparable outcomes (p > 0.5). The fracture resistance of dental restorations was dependent on the aging protocol, restoration type, and thickness. The bond strength of veneering ceramic to zirconia core was comparable.

CONCLUSIONS

The results pooled from two short-term clinical trials showed no signs of mechanical or biological complications of additively manufactured 3Y-TZP zirconia crowns. The flexural strength might depend on the specimens' thickness, but it showed promising results to be used in clinical applications, taking into account the printing technique and orientation, material composition (yttria content), solid loading, and sintering parameters. 3D-printed restorations fracture resistance improved when adhered to human teeth. The veneering ceramic bond was comparable to milled zirconia specimens. Long-term RCTs are recommended to confirm the mechanical behavior of 3D-printed restorations.

Advances in zirconia-based dental materials: Properties, classification, applications, and future prospects

OBJECTIVES

Zirconia (ZrO2) ceramics are widely used in dental restorations due to their superior mechanical properties, durability, and ever-improving translucency. This review aims to explore the properties, classification, applications, and recent advancements of zirconia-based dental materials, highlighting their potential to revolutionize dental restoration techniques.

STUDY SELECTION, DATA AND SOURCES

The most recent literature available in scientific databases (PubMed and Web of Science) reporting advances of zirconia-based materials within the dental field is thoroughly examined and summarized, covering the major keywords "dental zirconia, classification, aesthetic, LTD, applications, manufacturing, surface treatments".

CONCLUSIONS

An exhaustive overview of the properties, classifications, and applications of dental zirconia was presented, alongside an exploration of future prospects and potential advances. This review highlighted the importance of addressing challenges such as low-temperature degradation resistance and optimizing the balance between mechanical strength and translucency. Also, innovative approaches to improve the performances of zirconia as dental material was discussed.

CLINICAL SIGNIFICANCE

This review provides a better understanding of zirconia-based dental biomaterials for dentists, helping them to make better choice when choosing a specific material to fabricate the restorations or to place the implant. Moreover, new generations of zirconia are still expected to make progress on key issues such as the long-term applications in dental materials while maintaining both damage resistance and aesthetic appeal, defining the directions for future research.

Accuracy, adaptation and margin quality of monolithic zirconia crowns fabricated by 3D printing versus subtractive manufacturing technique: A systematic review and meta-analysis of in vitro studies

OBJECTIVE

The purpose of this systematic review and meta-analysis was to evaluate the accuracy (trueness and precision), marginal and internal adaptation, and margin quality of zirconia crowns made by additive manufacturing compared to subtractive manufacturing technology.

METHODS

The investigation adhered to the PRISMA-ScR guidelines for systematic reviews and was registered at the Prospero database (n°CRD42023452927). Four electronic databases, including PubMed, Scopus, Embase, and Web of Science and manual search was conducted to find relevant studies published until September 2023. In vitro studies that assessed the trueness and precision, marginal and internal adaptation, and margin quality of printed crowns compared to milled ones were included. Studies on crowns over implants, pontics, temporary restorations, laminates, or exclusively experimental materials were excluded.

RESULTS

A total of 9 studies were included in the descriptive reporting and 7 for meta-analysis. The global meta-analysis of the trueness (P<0.74,I2=90 %) and the margin quality (P<0.61,I2=0 %) indicated no significant difference between the root mean square of printed and milled zirconia crowns. The subgroup analysis for the printing system showed a significant effect (P<0.01). The meta-analysis of the crown areas indicated no significant difference in most of the areas, except for the marginal (favoring milled crowns) and axial (favoring printed crowns) areas. For precision and adaptation, both methods showed a clinically acceptable level.

CONCLUSIONS

Additive manufacturing technology produces crowns with trueness and margin quality comparable to subtractive manufacturing. Both techniques have demonstrated the ability to produce crowns with precision levels, internal discrepancy, and marginal fit within clinically acceptable limits.

CLINICAL SIGNIFICANCE

3D printing emerges as a promising and potentially applicable alternative method for manufacturing zirconia crowns, as it shows trueness and margin quality comparable to restorations produced by the subtractive method.

The application of 3D printing in dentistry: A bibliometric analysis from 2012 to 2023

STATEMENT OF PROBLEM

Three-dimensional (3D) printing has had extensive applications across dentistry, but a comprehensive bibliometric analysis relating to the application of 3D printing in dentistry is lacking.

PURPOSE

The purpose of this study was to conduct a comprehensive bibliometric analysis of the scientific literature concerning the application of 3D printing in dentistry from 2012 to 2023.

MATERIAL AND METHODS

The literature search was conducted in the Web of Science Core Collection Database. The retrieved literature data were downloaded as plain text file in "full record and cited references" format, with software programs (VOSviewer, CiteSpace, Biblioshiny, RStudio, Carrot2, and Microsoft Excel) used for bibliometric analysis and quantitative assessment.

RESULTS

The bibliometric analysis incorporated 1911 publications. Revilla-León, Marta was the most productive author. Zurich University had the highest number of publications and citations. The United States dominated the research landscape with the highest publication volume and H-index. The Journal of Prosthetic Dentistry was the leading journal in both publication volume and citation frequency. Co-occurrence analysis of keyword and co-cited analysis of reference indicated a robust research environment, characterized by a strong focus on the pursuit of accuracy in dental restorative solutions, biocompatibility of materials, and clinical applications.

CONCLUSIONS

Research on 3D printing in the field of dentistry continues to grow. Collaborations with leading organizations and countries have been established, with Revilla-León, Marta et al playing a pivotal role. Top journals represented included the Journal of Prosthetic Dentistry and Dental Materials. Main research domain resided in prosthodontics and implantology. Hot research topics included improvements in accuracy, dental materials, and clinical applications centered on implant guide design.

Trueness and precision of digital light processing fabricated 3D printed monolithic zirconia crowns

OBJECTIVES

The present study aimed to evaluate the trueness and precision of monolithic zirconia crowns (MZCs) fabricated by 3D printing and milling techniques.

METHODS

A premolar crown was designed after scanning a prepared typodont. Twenty MZCs were fabricated using milling and 3D-printing techniques (n = 10). All the specimens were scanned with an industrial scanner, and the scanned data were analyzed using 3D measurement software to evaluate the trueness and precision of each group. Root mean square (RMS) deviations were measured and statistically analyzed (One-way ANOVA, Tukey's, p ≤ 0.05).

RESULTS

The trueness of the printed MZC group (140 ± 14 μm) showed a significantly higher RMS value compared to the milled MZCs (96 ± 27 μm,p < 0.001). At the same time, the precision of the milled MZCs (61 ± 17 μm) showed a significantly higher RMS value compared to that of the printed MZCs (31 ± 5 μm,p < 0.001).

CONCLUSIONS

The Fabrication techniques had a significant impact on the accuracy of the MZCs. Milled MZCs showed the highest trueness, while printed MZCs showed the highest precision. All the results were within the clinically acceptable error values.

CLINICAL SIGNIFICANCE

Although the trueness of the milled MZCs is higher, the manufacturing accuracy of the 3D-printed MZCs showed clinically acceptable results in terms of trueness and precision. However, additional clinical studies are recommended. Furthermore, the volumetric changes of the material should be considered.

Do 3D-printed and milled tooth-supported complete monolithic zirconia crowns differ in accuracy and fit? A systematic review and meta-analysis of in vitro studies

STATEMENT OF PROBLEM

Additive (3-dimensional printing) and subtractive (milling) methods are digital approaches to fabricating zirconia restorations. Comparisons of their resultant fabrication accuracy and restoration fit are lacking.

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate the accuracy and fit of monolithic zirconia crowns fabricated by 3-dimensional printing and milling.

MATERIAL AND METHODS

The PubMed (Medline), Scopus, Embase, Web of Science, Cochrane Library, and Google Scholar databases were searched up to August 2023. Eligible records were included, and the standardized mean difference (SMD) analyzed 4 outcomes: marginal fit, intaglio fit, trueness, and precision. Publication bias was analyzed with Trim-and-fill, the Egger regression test, and Begg funnel plot. Methodological quality was rated using the QUIN tool.

RESULTS

A total of 15 publications were found eligible out of the initial 6539 records. The 3-dimensional printing group demonstrated a lower marginal fit (SMD=1.46, 95% CI=[0.67, 2.26], P<.001; I2=83%, P<.001) and trueness (SMD=0.69, 95% CI=[0.20, 1.18], P=.006; I2=88%, P<.001) and a significantly higher precision (SMD=-2.19, 95% CI=[-2.90, -1.48], P<.001; I2=56%, P=.045). The intaglio fit did not differ significantly across the study groups (SMD=0.77, 95% CI=[-0.22, 1.77], P=.127; I2=87%, P<.001).

CONCLUSIONS

Given the high degree of heterogeneity, it can be cautiously concluded that while 3-dimensional printing led to greater precision, the outcomes of the 2 accuracy and adaptation parameters most crucial to the longevity of the restorations-trueness and marginal fit-showed the superiority of the milling technique.

3D-printed versus conventionally milled zirconia for dental clinical applications: Trueness, precision, accuracy, biological and esthetic aspects

OBJECTIVES

This systematic review aimed to compare the clinical outcome, internal gap, trueness, precision, and biocompatibility of 3D-printed (AM) compared to milled (SM) zirconia restorations.

DATA SOURCE

A thorough search of Internet databases was conducted up to September 2023. The search retrieved studies compared AM zirconia to SM zirconia restorations regarding clinical outcome, fit, trueness, precision, and biocompatibility.

STUDY SELECTION

Of 1736 records, only 59 were screened for eligibility, and 22 records were included in this review. The quality of studies was assessed using the revised Cochrane risk-of-bias tool (ROB2), and the Modified Consort Statement. One clinical study exhibited a low risk of bias. All laboratory studies revealed some bias concerns. Short-term observation showed 100 % survival with no signs of periodontal complications. 3D-printed zirconia crowns showed statistically significant lower ΔE and a better match to adjacent teeth (p ≤ 0.5). The fit, trueness, and precision vary with the printing technique and the tooth surface.

CONCLUSIONS

3D-printed zirconia crowns provide better aesthetic color and contour match to adjacent natural teeth than milled crowns. Both 3D printing and milling result in crowns within the clinically acceptable internal and marginal fit. Except for nanoparticle jetting, the marginal gap of SM crowns was smaller than AM crowns, however, both were clinically acceptable. Laminate veneers might be more accurately produced by 3D printing. 3D-printed axial surface trueness was better than milled axial surfaces. Long-term RCTs are recommended to confirm the clinical applicability of 3D-printed restorations.

CLINICAL SIGNIFICANCE

Internal fit and gap, precision, and trueness are fundamental requirements for successful dental restorations. Both techniques produce restorations with clinically acceptable marginal and internal fit. Axial surfaces and narrow or constricted areas favored 3D-printed than conventionally milled zirconia.

Influence of glazing and aging on the marginal, axial, axio-occlusal, and occlusal fit of 3-unit monolithic zirconia restorations fabricated using additive and subtractive techniques

STATEMENT OF PROBLEM

Studies are sparse on how glazing and aging influence the fit of additively fabricated monolithic zirconia restorations.

PURPOSE

The purpose of this in vitro study was to assess the effect of glazing and aging on the fit of 3-unit monolithic zirconia restorations fabricated using different techniques.

MATERIAL AND METHODS

A total of 32 monolithic zirconia restorations were fabricated for a typodont model by using 4 distinct techniques (subtractive fabrication [SF], stereolithography [SLA], digital light processing [DLP], and lithography-based ceramic manufacturing [LCM]). The silicone replica approach was adopted to measure the discrepancy values for premolar and molar abutments after sintering, glazing, and 1 year of aging. The silicone replicas were sliced into mesiodistal and buccopalatal cross-sections, and digital micrographs of the cross-sections were made with a ×80 stereomicroscope. An inherent measuring program was run to record the discrepancy values (µm). Repeated-measures 2-way ANOVAs with the Bonferroni post hoc test were used to statistically analyze the acquired data. (α=.05).

RESULTS

From the repeated measures 2-way ANOVAs, both the glazing×fabrication technique and the aging×fabrication technique interactions were not statistically significant (P>.05). Glazing significantly influenced premolar abutment marginal (P=.022) and occlusal (P=.007) discrepancy values, as well as molar abutment marginal discrepancy values (P=.047). Aging had a statistically significant effect on premolar abutment marginal (P=.008) and occlusal (P=.011) discrepancy values, as well as molar abutment occlusal discrepancy values (P=.039). In both the glazing and aging data, for all areas of interest, statistically significant differences were detected among the fabrication techniques (P<.05). The LCM group had the lowest discrepancy values, followed by the SLA, SF, and DLP groups.

CONCLUSIONS

The LCM and SLA groups outperformed the other groups in terms of fit accuracy. The glazing and aging procedures altered the discrepancy values. The marginal discrepancy values of all groups were below the threshold of clinical acceptability (<120 µm).

Feasibility of images acquired using smartphone camera for marginal and internal fit of fixed dental prosthesis: comparison and correlation study

This study aimed to measure marginal and internal fit using images captured with both an optical microscope and a smartphone camera, comparing the fit measurement performance of these devices and analyzing their correlation. Working casts (with 10 posterior and 10 anterior teeth) created to fabricate fixed dental prostheses were used. These working casts were scanned using a desktop scanner (E1) to design an interim crown, and the designed interim crown was fabricated using a three-dimensional (3D) printer. Utilizing the silicone replica technique, the fabricated interim crown replicated the fit, which was then captured using both an optical microscope and a smartphone camera. The captured images were used to measure the marginal and internal fit according to the imaging device. Intraclass correlation coefficients (ICC) were used for reliability analysis according to the imaging device. Furthermore, the Wilcoxon signed-rank test was adopted for the comparative evaluation of the marginal and internal fit between the imaging devices (α = 0.05). The measurement results of the marginal and internal fit according to the optical microscope and smartphone camera did exhibit a significant difference (P < 0.05). The ICC between the two devices showed an "excellent" agreement of over 0.9 at all measurement points (P < 0.001). A smartphone camera could be used to obtain images for evaluating the marginal and internal fit.