The potential of additive manufacturing technologies and their processing parameters for the fabrication of all-ceramic crowns: A review

Balancing strength and translucency: The role of microstructure in additive and subtractive dental zirconia

OBJECTIVES

To elucidate the effect of microstructure on the strength and translucency of dental zirconia fabricated using additive (AM) and subtractive manufacturing (SM) technologies.

METHODS

Twelve 3Y-TZP discs were fabricated using AM with two print orientations (0°: group AM0; 90°: group AM90; n = 6), and six via CAD/CAM machining (group SM). Density, composition, roughness, translucency parameter (TP), and biaxial flexural strength (σ) were evaluated. Fractographic analysis was conducted and defect size estimated. Based on the preliminary σ results (n = 6), the optimal print orientation was identified. Nine additional specimens were prepared for each of the AM90 and SM groups for Weibull σ analysis (n = 15). Differences in Weibull modulus were assessed via non-overlapping 95 % confidence intervals. An one-way ANOVA followed by Tukey's post-hoc test and an independent samples t-test were used (α = 0.05).

RESULTS

The relative density was consistent across all groups (>99 %). The tetragonal and cubic phases were comparable among groups, with proportions exceeding 82 wt% and 17 wt%, respectively. Group SM exhibited significantly higher roughness (1.18 µm) than AM0 (0.71 µm) and AM90 (0.51 µm). Group SM exhibited the highest TP values, while groups AM0 and AM90 had statistically similar TP values. AM0 showed the lowest σ value (411.60 ± 73.99 MPa) and larger defects. Groups AM90 and SM (n = 15) possessed comparable σ values (969.85 ± 123.13 MPa and 989.72 ± 107.78 MPa, respectively) (p = 0.6417) and Weibull moduli (9.17 and 10.62, respectively).

SIGNIFICANCE

SM zirconia showed higher translucency and roughness, while defects reduced translucency in AM zirconia. Flexural strength was lower for AM0 due to larger defects, whereas AM90 matched SM strength.

Advanced superimposition method to evaluate the marginal and internal fit of ceramic crowns fabricated using heat pressing techniques

Background

Digital technologies can enhance the success of permanent crowns. The present study aimed to evaluate marginal adaptation and internal fit of permanent crowns fabricated using stereolithography (SLA) and digital light processing (DLP) 3D printing technologies following scans using two different intraoral scanners (IOS) (Medit i700, shape (TRIOS 3)).

Methods

Three typodont #14 teeth were prepared for full veneer all ceramic crowns with three types of margins-chamfer (CFL), rounded shoulder (RSFL) and rounded shoulder with bevel (RSBFL). A total of 360 study models were made and divided into two groups based on the type of intraoral scanner used for digital impressions. Group A in which the intraoral scanner MEDIT i700 was used, and Group B in which intraoral scanner TRIOS 3 was used (n = 360/group). The subgroups were made as Medit i700-SLA, Medit i700-DLP, TRIOS 3-SLA and TRIOS 3-DLP (n = 180/subgroup). These were further divided into three sub-subgroups based on the finish lines: CFL, RSFL, and RSBFL (n = 30 each sub-subgroups). All ceramic crowns were made on models and scanned to assess discrepancies (marginal adaptation and internal fit) at nine zones (Z1-Z9). Three-way analysis of variance and pairwise comparison was done (Tukey HSD test) (α = 0.05).

Results

The mean marginal gap and internal fit values were lowest for Group A-1 with RSBFL in each zone. The intergroup comparison showed values for marginal gap and the internal fit were minimum for Group A-1 for each finish line design, with the lowest for RSBFL at zone Z2 0.04 ±0.001.

Conclusions

Regardless of the IOS and 3D printing techniques, the smallest gap was observed in RSBFL, followed by RSFL and CFL. The all-ceramic crowns fabricated using a Medit intraoral scanner with an SLA 3DPrinter with a rounded shoulder finish line had the best marginal and internal fit.

The impact of customized surface topography and porosity created by additive manufacturing technology on gingival fibroblasts

PURPOSE

The purpose of this study was to analyze gingival fibroblast proliferation on additively manufactured polymethylmethacrylate (PMMA) groups with different surface characteristics namely no treatment group (NTG) and customized 250 µm diameter porosity (AM-250G) group.

MATERIALS AND METHODS

3D-printed NTG was compared for its influence on growth of cells to a additively manufactured surface with porosity (AM-250G). For each group (NTG, AM-250G) 20 samples of material were tested. Fibroblast cells, at a concentration of 2.5 × 104 cells/mL, were seeded into 48 plates separately into two groups (NTG, AM-250G). These were cultured in Dulbecco's Modified Eagle's Medium (DMEM) supplemented with 10% fetal bovine serum (FBS) at 37°C and 5% CO2 atmosphere. For cell proliferation MTT assay was conducted at 24, 48, and 72 h. Cell proliferation was quantified through optical density (OD) measurements of the cell supernatant, and surface analysis was conducted using a scanning electron microscope (SEM). Data normality was confirmed by the Shapiro-Wilk test, with a significance level set at p < 0.05. Statistical analysis was conducted using an independent Student's t-test at each time point.

RESULTS

A significant difference in cell proliferation was observed at 24 h, with the NTG group showing higher cell numbers compared to AM-250G group. Qualitative analysis of cell culture was performed using scanning electron microscopy to compare to the NTG and the porosity (AM-250G) groups after 24, 48, and 72 h of fibroblast tissue attachment. No significant differences were observed between the groups at the 48 and 72-h intervals.

CONCLUSIONS

At 24 h, the NTG surface demonstrated superior cell proliferation compared to the surface with porosity (AM-250G). However, significant differences in cell growth on both materials at 48 and 72 h, suggesting that both surface types eventually support similar levels of cell proliferation, with an increase of extensive spread and elongation of fibroblasts cells proliferation on the surface with porosity.

Shear bond strength of resin cement to additively manufactured zirconia with customized surface texture and porosity: Part 1

STATEMENT OF PROBLEM

The additive manufacturing of zirconia has been reported to present promising mechanical properties. However, studies on bonding to additively manufactured (AM) zirconia are lacking.

PURPOSE

The purpose of this in vitro study was to investigate the effect of customized porosity and surface texture on the shear bond strength (SBS) of resin cement to 3-dimensionally (3D) printed zirconia.

MATERIAL AND METHODS

A total of 60 zirconia disks (Ø12×5 mm) were designed with different surface porosity using a computer-aided design (CAD) software program and manufactured via stereolithography (SLA) 3D printing. The disks were divided into 4 groups (n=15) based on surface texture and porosity: Control (no designed porosities), G1:50 (50×50-µm pores 200 µm apart), G2:100 (100×100-µm pores 400 µm apart), and G3:200 (200×200-µm pores 800 µm apart). The specimens were cleaned, and the binder removed before sintering. The microstructural analysis of the specimen's surface before SBS was performed using a profilometer to determine surface texture (n=5). SBS was measured using a universal testing machine, and thermal cycling was performed to simulate aging (n=10). Data for SBS were analyzed using 2-way ANOVA (α=.05).

RESULTS

Surface texture and porosities were confirmed by profilometry. In all comparisons, the G3:200 group demonstrated the highest mean SBS with 8.78 MPa (P<.001); however, it was similar to the Control group, which had a mean of 8.41 MPa (P=.631). The G1:50 showed significantly lower SBS values at 3.90 MPa (P<.001), followed by the G2:100 group with 5.14 MPa (P<.001). Thermal cycling generally decreased SBS in all groups (P<.001).

CONCLUSIONS

Customized surface textures can improve bond strengths, with larger pores (200×200 µm) providing values comparable with those of traditional mechanical pretreatments surfaces, while smaller pores resulted in lower bond strengths. This approach avoids surface damage and phase transitions caused by traditional treatments. These findings provide a foundation for future research aimed at developing more durable and reliable zirconia restorations, ultimately enhancing clinical outcomes.

An esthetic solution for restoring a labially inclined implant by using an additively manufactured plug-assisted retained zirconia veneer: A dental technique

The facial opening of the screw access channel can lead to esthetic compromises in screw-retained restorations, while the use of cement-retained complete crowns may result in residual cement in the proximal areas, and traditional veneers without proximal coverage often lack adequate retention. To address these issues, a plug-assisted retained veneer was developed. First, the 3-dimensional position of an implant was obtained, and a custom abutment was designed to mimic the contour of a veneer preparation. Subsequently, the abutment was fabricated and positioned on the printed cast. After the acquisition of the scan data, a veneer with a plug was designed and produced. A reference scan was then obtained. Finally, the veneer with the plug was delivered, where a digital protocol was used to verify a good fit. This plug functions as a macro retention form while simultaneously seals the screw access opening, enhancing retention and the esthetic outcomes without compromising the fit.

Light-curing of restorative composite through milled and 3D-printed full-contour zirconia for adhesive luting

OBJECTIVES

To evaluate the effect of different zirconia compositions and manufacturing processes on the light irradiance (LI), to measure the degree of conversion (DC) of solely light-curing restorative composite underneath these zirconia grades and to evaluate the respective zirconia microstructures.

METHODS

Six dental zirconia grades (GC HT, GC UHT [GC]; Katana HT, Katana UTML [Kuraray Noritake]; Lava Esthetic, Lava Plus [3 M Oral Care]) were cut and sintered per manufacturer instructions. One 3D-printed zirconia grade (XJet [XJET]) was prepared according to previous research. Zirconia plates were ground to four thicknesses (0.5, 1.0, 1.5, 3.0 mm). The LI through these zirconias was measured using light spectrometry using two light-curing units (Demi Plus [Kerr], Bluephase G4 [Ivoclar]). Restorative composite (Clearfil AP-X [Kuraray Noritake]) was light-cured through the zirconia plates and the DC was determined by micro-Raman spectrometry 5 min, 24 h and 1 w after light-curing. Statistical analysis of LI and DC data involved linear mixed-effects modelling and multi-way ANOVA. Microstructural analysis of zirconia was performed by scanning electron microscopy.

RESULTS

Zirconia type and thickness, and LCU had a significant effect on LI (p < .0001). DC significantly increased over time (p < .0001) and was not influenced by curing-light attenuation if LI reached at least 40 mW/cm². Increased yttria content resulted in an increased zirconia grain size.

SIGNIFICANCE

Despite significant light attenuation, DC of composite light-cured through zirconia at almost all thicknesses, approached DC measured without zirconia interposition for five out of seven zirconia grades. Additionally, the manufacturing process did not seem to influence LI or DC.

Mechanical Properties of 3D Printed vs. Subtractively Manufactured Composite Resins for Permanent Restorations: A Systematic Review

OBJECTIVE

To conduct a systematic review on the mechanical properties of 3D printed resin-based composites when compared with those of subtractively manufactured resin-based composites.

MATERIALS AND METHODS

In vitro studies comparing the mechanical properties of additively and subtractively manufactured resin-based composites were sought. A systematic search, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), was performed on four databases (PubMed, Embase, Web of Science, and Scopus) for articles published until 23 December 2024. The quality of the studies was assessed with the QUIN tool (risk-of-bias tool for assessing in vitro studies conducted in dentistry) and those assessed with a high risk of bias were excluded.

RESULTS

Of the 1058 screened articles, 13 were included in this review. A noticeable heterogeneity emerged in the methodologies employed, mainly regarding samples' fabrication techniques, materials involved, and parameters analyzed. The most investigated mechanical property was fracture resistance, followed by microhardness, flexural strength, and wear behavior. Among the tested materials, the most used 3D printable resins were VarseoSmile Crown Plus (Bego) and Crowntec (Saremco Dental), whereas for the subtractive groups, the most investigated was Brilliant Crios (Coltène).

CONCLUSIONS

The mechanical properties of 3D printed resins designed for permanent restorations are still lower than those of their subtractively manufactured counterparts. Moreover, in the long term, the degradation processes that inevitably occur might significantly increase their chances of failure.

Accuracy and adaptation of 3D printed zirconia crowns: A review of current methodologies

STATEMENT OF PROBLEM

The 3-dimensional (3D) printing of polymers and metals is a reality in dentistry; however, despite the advances, the printing of ceramic crowns is still in its infancy.

PURPOSE

The purpose of this review was to examine studies that evaluated the accuracy and adaptation of zirconia crowns produced by additive manufacturing with an emphasis on 3D printing.

MATERIAL AND METHODS

Electronic databases (Embase, PubMed, SCOPUS, Web of Science, and Google Scholar) were searched between February and March 2024 using the keywords zirconium, zirconium oxide, crowns, 3D printing, additive manufacturing, stereolithography, vat polymerization, digital light processing, nanoparticle jetting, lithography-based ceramic manufacturing, accuracy, trueness, and precision, augmented by manual searches. The eligibility criteria included articles only in English and published in peer-reviewed journals.

RESULTS

The database search resulted in 136 articles, reduced to 52 after duplicates were eliminated. After abstract reading and the application of the exclusion criteria, 14 articles remained to be read in full. All studies showed a low risk of bias.

CONCLUSIONS

The main printing techniques for zirconia crowns include material jetting and vat polymerization, which generally allow crown manufacture with accuracy and marginal adaptation within the clinically accepted range and close to that of milled crowns.

Additive-manufactured ceramics for dental restorations: a systematic review on mechanical perspective

Background

Additive manufacturing (AM) is rapidly expanding as a substitute for conventional heat-pressing and milling techniques for ceramic restorations. However, experimental and clinical evidence on the mechanical properties and performance of the final ceramic products is yet insufficient. This systematic review aimed to update the latest advances in additive manufacturing of restorative ceramics with a focus on their mechanical properties.

Methods

This systematic review was structured using the 5-step methodology based on the research question: what are the mechanical properties of additive-manufactured restorative ceramics in comparison with subtractive manufacturing? The electronic literature search was performed independently by 2 authors in the following databases: PubMed/MEDLINE, Web of Science, and Scopus. Published articles from 2019 to 2023 were screened, analysed and the relevant papers were selected for inclusion in this review.

Results

A total of 40 studies were included. The available ceramics include zirconia, alumina and alumina-zirconia composites, lithium disilicate, porcelain and fluorapatite glass ceramic. The mechanical properties were summarized according to material and technique: density (15 studies), flexural strength (31 studies), fracture toughness (7 studies), Young's modulus (7 studies), hardness (11 studies) and performance (7 studies). Overall, the properties exhibited an upward trend toward the values of conventional techniques. Typical processing defects, including porosity, agglomerates, cracks, surface roughness, and other defects, were also analyzed.

Conclusions

With significant technological advancements, the mechanical properties of AM ceramics have come close to ceramics by conventional manufacturing, whereas their reliability, the influence of printing layer orientations, and long-term performance still need further investigation.

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.

In vitro fracture and fatigue resistance of monolithic zirconia crowns fabricated by stereolithography

STATEMENT OF PROBLEM

Stereolithography has been used to print zirconia ceramic crowns with acceptable dimensional accuracy and fracture force. However, studies that compared the fatigue resistance of zirconia crowns fabricated by stereolithography are lacking.

PURPOSE

The purpose of this in vitro study was to compare the fracture and fatigue resistance of monolithic zirconia crowns printed by stereolithography apparatus (SLA) and digital light processing (DLP) with those of zirconia crowns milled by computer numerical control (CNC).

MATERIAL AND METHODS

A total of 120 crowns were fabricated (n=40/material) and underwent 0, 104, 105, or 106 dynamic loading cycles of 30 to 300 N in artificial saliva, followed by a static fracture loading test (n=10). After fracture, 1 crown from each group was selected for fractography analysis by scanning electron microscopy (SEM). Data were statistically analyzed through 2-way ANOVA and post hoc analysis for multiple comparisons (α=.05).

RESULTS

The 2-way ANOVA results showed that the mean ±standard deviation force at fracture was the highest for CNC (before fatigue loading: 5154 ±568 N, 104: 5735 ±1231 N, 105: 5523 ±797 N, and 106: 6007 ±1258 N), followed by DLP (before fatigue loading: 3381 ±612 N, 104: 4046 ±1146 N, 105: 2929 ±559 N, and 106: 3223 ±739 N), and the lowest for SLA (before fatigue loading: 2956 ±598 N, 104: 2757 ±421 N, 105: 3326 ±391 N, and 106: 3103 ±246 N) (P<.01). The fracture force of the crowns was not significantly affected by the number of fatigue cycles (P>.05). Fractography analysis showed that the number of arrest lines increased for crowns of all 3 materials. SEM images also showed the steps of SLA and DLP from their layer-by-layer printing and small cracks between layers of SLA after 106 loading cycles.

CONCLUSIONS

The fracture force of monolithic zirconia crowns milled by CNC was significantly higher than that of zirconia crowns printed by stereolithography. Zirconia crowns printed by SLA and DLP could withstand typical clinical conditions, and their fracture and fatigue resistance exceeded the clinically estimated average occlusal forces.

Three-Dimensional-Printed Photopolymer Resin Materials: A Narrative Review on Their Production Techniques and Applications in Dentistry

Additive manufacturing (3D printing) has transformed dentistry by providing solutions with high precision and accuracy achieved through digital workflows, which facilitate the creation of intricate and personalized structures. Additionally, 3D printing promotes cost efficiency by reducing material waste and errors while enabling on-demand production, minimizing the need for extensive inventories. Recent advancements in 3D-printed resin materials have enhanced their clinical applications by improving mechanical strength, biocompatibility, esthetics, and durability. These innovations have facilitated the fabrication of complex and patient-specific structures, such as dental prostheses, surgical guides, and orthodontic appliances, while significantly reducing production time and material waste. Ongoing research and innovation are expected to strengthen resin properties, including strength, translucency, and durability, broadening their clinical applications. The ongoing evolution of 3D printing technology is poised to play a critical role in driving personalized treatments, streamlining clinical workflows, and shaping the future of dental care. This narrative review comprehensively examines the production techniques and clinical applications of 3D-printed photopolymer resins across various dental specialties, including prosthodontics, orthodontics, pediatric dentistry, maxillofacial surgery, periodontology, endodontics, and conservative dentistry. Additionally, the review provides insight into the transformative impact of these technologies on patient care, highlights existing challenges, and suggests future directions for advancing resin properties and their integration into routine dental practice.

Accuracy, fit, and marginal quality of advanced additively manufactured and milled zirconia 3-unit fixed dental prostheses

STATEMENT OF PROBLEM

Advanced additive manufacturing (AM) of zirconia is an emerging technology that can explore the limitations of traditional computer-aided design and computer-aided manufacturing (CAD-CAM) milling techniques. However, a comprehensive evaluation of their differences in producing zirconia restorations, especially multi-unit restorations, is lacking.

PURPOSE

The purpose of this in vitro study was to compare the accuracy, fit, marginal quality, and surface roughness of zirconia 3-unit fixed dental prostheses (FDPs) by using advanced AM and 2 CAD-CAM milling materials.

MATERIAL AND METHODS

Based on the same CAD model, 30 3-unit posterior FDPs (n=10) were manufactured by using AM and 2 CAD-CAM milling materials (VT and UP). The accuracies of the total, intaglio, occlusal, axial, and marginal regions were calculated separately by comparing the scanned model with the design model by using 3-dimensional (3D) deviation analysis. The silicone layer was scanned to evaluate the marginal and intaglio fit in 3 dimensions. A 3D laser microscope was used for surface roughness detection, marginal quality assessment, and marginal defect measurement. The data were analyzed using ANOVA and the Tukey post hoc test (α=.05).

RESULTS

Compared with CAD-CAM milling, the AM group had higher accuracy and smaller positive deviations on the axial and intaglio regions (P<.001). Different manufacturing methods showed no statistically significant effect on the mean intaglio fit (P>.05), and all were within the clinically acceptable range (<100 µm). The intaglio gap was significantly higher than the target parameter in the occlusal regions. AM-fabricated FDPs had significantly higher surface roughness than milled ones, yet showed better margin quality with fewer marginal defects CONCLUSIONS: Compared with CAD-CAM milling, the advanced additively manufactured zirconia 3-unit FDPs provided better accuracy, improved margin quality, and clinically acceptable fit, but higher surface roughness, and may be a promising alternative for clinical applications.

Shear bond strength of porcelain to milled and stereolithography additively manufactured zirconia with and without surface treatment: An in vitro study

STATEMENT OF PROBLEM

Delamination of veneering ceramic is one of the most common challenges relating to veneered zirconia restorations. Additive manufacturing (AM) is a fast-expanding technology that has gained widespread acceptance in dentistry and is increasingly being used to produce dental restorations. However, information about bonding of porcelain to AM zirconia is lacking.

PURPOSE

The purpose of this in vitro study was to investigate the shear bond strength (SBS) of porcelain to milled and additively manufactured zirconia, and the effect of surface treatment on bond strength.

MATERIAL AND METHODS

A Ø12×5-mm disk was designed virtually to fabricate all specimens, which were divided into 2 groups according to the manufacturing technique: additively manufactured or milled zirconia. The effect of airborne-particle abrasion and a zirconia liner before porcelain application was investigated in both groups. Veneering porcelain was fired into an alumina ring mold on the zirconia surface. SBS was measured by using a universal testing machine at a crosshead speed of 1 mm/min before and after aging (n=10). SBS data were analyzed with 3-way ANOVA (α=.05) RESULTS: A significant difference was found between milled and AM zirconia. The SBS of porcelain to milled zirconia was significantly higher (1.38 MPa) than to AM zirconia (0.68 MPa) (P<.001). The surface treatment of zirconia had no significant effect on porcelain SBS in either group (P=.254), whereas thermocycling significantly reduced the SBS of porcelain to zirconia in both milled and AM groups (P=.001).

CONCLUSIONS

Porcelain bonding to milled zirconia was better than to AM zirconia. Pretreating the zirconia substrate before porcelain application did not improve the porcelain bond.

Zirconia crowns manufactured using digital light processing: Effects of build angle and layer thickness on the accuracy

OBJECTIVES

This study investigated the effects of build angle and layer thickness on the trueness and precision of zirconia crowns manufactured using digital light processing (DLP) technology.

MATERIALS AND METHODS

Single crowns were fabricated from zirconia using DLP technology. The crowns were manufactured with three different representative build angles (0°, 45°, and 90°) and two different layer thicknesses (30 μm and 50 μm). After printing, the specimens were non-contact-scanned, and their accuracy was assessed using a 3D analysis software. Root mean square (RMS) values were used to determine trueness and precision. Color maps were generated to detect deviations within the specimens. Statistical analyses were conducted using two-way ANOVA.

RESULTS

Build angle and layer thickness significantly affected trueness and precision (p < 0.05). At a 30-μm layer thickness, the crowns printed at angles of 0° (32.2 ± 3.2 μm) and 45° (33.9 ± 2.4 μm) demonstrated the best marginal trueness compared to those in other groups (p < 0.05). Notably, those printed at an angle of 90° exhibited the best intaglio surface trueness (37.4 ± 4.0 μm). At a 50-μm layer thickness, the crowns printed at an angle of 90° exhibited the lowest accuracy concerning marginal and intaglio surface aspects (27.7 ± 8.2 μm).

CONCLUSIONS

Both the build angle and layer thickness significantly affected the dimensional accuracy of DLP-printed zirconia crowns, with the 30-μm layer thickness offering superior trueness. Optimal results were achieved using build angles of 0° and 45° in conjunction with thinner layers, minimizing marginal defects.

CLINICAL SIGNIFICANCE

All zirconia crowns produced at different build angles and layer thicknesses satisfied clinical requirements. Specific combinations of these factors realized the fabrication of single crowns that possessed the highest accuracy.

Influence of 3D printing system, postpolymerization and aging protocols on resin flexural strength and dimensional stability for printing occlusal splints, models and temporary restorations

OBJECTIVES

Investigate the effect of different postpolymerization protocols, aging, and 3D printing systems on the flexural strength (σ), dimensional stability, and roughness of resins used to fabricate occlusal splints, dental models, and temporary restorations.

MATERIAL AND METHODS

180 bars (25 × 2 x 2 mm-ISO 4049) of each type of resin (T-Temporary/Cosmos Temp, Yller; OS-Occlusal splint/Cosmos Splint, Yller; MO - Models/ Cosmos Model, Yller) were printed and divided into 12 groups (n = 15) according to the factors: "Postpolymerization" (Ctr - Control; UV - Ultraviolet oven and MW - Microwave); "Printer" (SLA- stereolithography (Forms 2/Formslab); LCD- liquid crystal display (FlashForge Foto 6.0/FlashForge)) and "Aging" (TC - 10,000 thermocycling cycles and Without). Each bar was measured with a digital caliper at 11 points before and after postpolymerization to evaluate dimensional stability. The samples were subjected to the σ test (100Kgf;1 mm/min). Data was evaluated using Three- and Two-way ANOVA, and Tukey's test (5%). Weibull analysis, Scanning Electron Microscopic and optical profilometry was performed.

RESULTS

LCD printing system and UV oven postpolymerization exhibited the highest σ (P < .05). The groups printed in SLA and post-polymerized in microwave ovens showed the greatest variations in their dimensions, for the occlusal splint resin, the OS-SLA-MW group (-4.29 ± 3.15)A showed a shrinkage of 40.2%. The resins for models (3.31 ± 0.66)A and temporary (-2.06 ± 1.52)A showed a shrinkage of 33% and 20.6%, respectively.

CONCLUSIONS

LCD printing with UV light postpolymerization was the most effective method for resins used in occlusal splints, dental models, and temporary restorations. SLA printing with UV postpolymerization showed the most significant dimensional changes, leading to shrinkage in occlusal splint resins, while model resins and temporary restorations expanded.

CLINICAL RELEVANCE

Resins for 3D printing should ideally be post-polymerized with UV light and printed using LCD technology, as this approach results in better mechanical properties and less dimensional change compared to microwave oven post-polymerization.

3D-printed intracoronal restorations, occlusal and laminate veneers: Clinical relevance, properties, and behavior compared to milled restorations; a systematic review and meta-analysis

OBJECTIVES

To assess the feasibility of producing 3D-printed intracoronal restorations, thin and ultrathin veneers, and to compare their mechanical behavior, accuracy, biological, and stain susceptibility to the currently applied milled restorations.

MATERIALS AND METHODS

The databases were comprehensively searched for relevant records up to January 2024 without language restrictions. All studies that assessed 3D-printed partial coverage restorations including inlays, onlays, laminate, and occlusal veneers were retrieved.

RESULTS

The web search yielded a total of 1142 records, with 8 additional records added from websites at a later stage. Only 17 records were ultimately included in the review. The included records compared 3D-printed; alumina-based- and zirconia ceramics, lithium disilicate ceramics, polymer infiltrated ceramics, polyetheretherketone (PEEK), resin composites, and acrylic resins to their CNC milled analogs. The pooled data indicated that it is possible to produce ultrathin restorations with a thickness of less than 0.2 mm. 3D-printed laminate veneers and intracoronal restorations exhibited superior trueness, as well as better marginal and internal fit compared to milled restorations (p < 0.05). However, it should be noted that the choice of materials and preparation design may influence these outcomes. In terms of cost, the initial investment and production expenses associated with 3D printing were significantly lower than those of CNC milling technology. Additionally, 3D printing was also shown to be more time-efficient.

CONCLUSIONS

Using additive manufacturing technology to produce restorations with a thickness ranging from 0.1 to 0.2 mm is indeed feasible. The high accuracy of these restorations, contributes to their ability to resist caries progression, surpassing the minimum clinical threshold load of failure by a significant margin and reliable adhesion. However, before 3D-printed resin restorations can be widely adopted for clinical applications, further improvements are needed, particularly in terms of reducing their susceptibility to stains.

CLINICAL SIGNIFICANCE

3D-printed intracoronal restorations and veneers are more time and cost-efficient, more accurate, and could provide a considerable alternative to the currently applied CNC milling. Some limitations still accompany the resin materials, but this could be overcome by further development of the materials and printing technology.

Fracture resistance, marginal and internal adaptation of innovative 3D-printed graded structure crown using a 3D jet printing technology

PURPOSE

This in vitro study aimed to create a graded structured dental crown using 3D printing technology and investigate the fracture resistance and the adaptation of this new design.

MATERIALS AND METHODS

A dental crown with a uniform thickness of 1.5 mm was designed, and the exported stereolithography file (STL) was used to manufacture 30 crowns in three groups (n = 10), solid (SC), bilayer (BL), and multilayer (ML) crowns using  3D jet printing technology. Marginal and internal gaps were measured using the silicone replica technique. Crowns were then luted to a resin die using a temporary luting agent and the fracture resistance was measured using a universal testing machine. One-way ANOVA and Tukey post hoc tests were used to compare the fracture resistance and the adaptation of crowns at a significance level of 0.05.

RESULTS

Mean marginal and internal gap of the ML group were 80 and 82 mm, respectively; which were significantly (p < 0.05) smaller than BL (203 and 183 mm) and SC (318 and 221 mm) groups. The SC group showed the highest mean load at fracture (2330 N) which was significantly (p < 0.05) higher than the BL (1716 N) and ML (1516 N) groups.

CONCLUSION

3D jet printing technology provides an opportunity to manufacture crowns in a graded structure with various mechanical properties. This study provided an example of graded structured crowns and presented their fracture resistance. SC group had the highest fracture resistance; however, ML had the best marginal and internal adaptation.

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.

Silver vanadate nanomaterial incorporated into heat-cured resin and coating in printed resin - Antimicrobial activity in two multi-species biofilms and wettability

OBJECTIVES

To incorporate the nanostructured silver vanadate decorated with silver nanoparticles (AgVO3) into denture base materials: heat-cured (HC) and 3D printed (3DP) resins, at concentrations of 2.5 %, 5 %, and 10 %; and to evaluate the antimicrobial activity in two multi-species biofilm: (1) Candida albicans, Candida glabrata, and Streptococcus mutans, (2) Candida albicans, Pseudomonas aeruginosa, and Staphylococcus aureus, and the wettability.

METHODS

The AgVO3 was added to the HC powder, and printed samples were coated with 3DP with AgVO3 incorporated. After biofilm formation, the antimicrobial activity was evaluated by colony forming units per milliliter (CFU/mL), metabolic activity, and epifluorescence microscopy. Wettability was assessed by the contact angles with water and artificial saliva.

RESULTS

In biofilm (1), HC-5 % and HC-10 % showed activity against S. mutans, HC-10 % against C. glabrata, and HC-10 % and 3DP-10 % had higher CFU/mL of C. albicans. 3DP-5 % had lower metabolic activity than the 3DP control. In biofilm (2), HC-10 % reduced S. aureus and P. aeruginosa, and HC-5 %, 3DP-2.5 %, and 3DP-5 % reduced S. aureus. 3DP incorporated with AgVO3, HC-5 %, and HC-10 % reduced biofilm (2) metabolic activity. 3DP-5 % and 3DP-10 % increased wettability with water and saliva.

CONCLUSION

HC-10 % was effective against C. glabrata, S. mutans, P. aeruginosa, and S. aureus, and HC-5 % reduced S. mutans and S. aureus. For 3DP, 2.5 % and 5 % reduced S. aureus. The incorporation of AgVO3 into both resins reduced the metabolic activity of biofilms but had no effect on C. albicans. The wettability of the 3DP with water and saliva increased with the addition of AgVO3.

CLINICAL SIGNIFICANCE

The incorporation of silver vanadate into the denture base materials provides antimicrobial efficacy and can prevent the aggravation of oral and systemic diseases. The incorporation of nanomaterials into printed resins is challenging and the coating is an alternative to obtain the inner denture base with antimicrobial effect.

Trueness, physical properties, and surface characteristics of additive-manufactured zirconia crown

OBJECTIVE

This study aimed to conduct a comparison of trueness and physical and surface properties among five distinct types of additive manufactured (AM) zirconia crowns and zirconia crowns produced using the subtractive manufacturing (SM).

MATERIAL AND METHODS

Zirconia crowns were fabricated using five distinct techniques, each varying in the method of slurry transfer and photocuring source. Each experimental group utilized either one of the four digital light processing (DLP)-based techniques (DLP spreading, DLP spreading gradation, DLP vat and DLP circular spreading) or the stereolithography (SLA)-based technique (SLA spreading). The control (CON) group employed SM. To assess accuracy, trueness was measured between the scan and reference data. To analyze the physical properties, voids were examined using high-energy spiral micro-computed tomography scans, and the crystal structure analysis was performed using X-ray diffraction (XRD). Surface roughness was assessed through laser scanning microscopy.

RESULTS

Differences in the trueness of internal surfaces of crowns were found among the groups (P < 0.05). Trueness varied across the measurement surfaces (occlusal, lateral, and marginal) in all the groups except for the DLP spreading gradation group (P < 0.05). Voids were observed in all AM groups. All groups showed similar XRD patterns. All AM groups showed significantly greater surface roughness compared to the CON group (P < 0.001).

CONCLUSION

The AM zirconia crowns showed bubbles and a rougher surface compared to the SM crowns. All groups exhibited typical zirconia traits and trueness levels within clinically acceptable limits, suggesting that current zirconia AM techniques could be suitable for dental applications.

Bond Strength of Milled and Printed Zirconia to 10-Methacryloyloxydecyl Dihydrogen Phosphate (10-MDP) Resin Cement as a Function of Ceramic Conditioning, Disinfection and Ageing

This study aimed to assess the suitability of printed zirconia (ZrO2) for adhesive cementation compared to milled ZrO2. Surface conditioning protocols and disinfection effects on bond strength were also investigated. ZrO2 discs (n = 14/group) underwent either alumina (Al2O3) airborne particle abrasion (APA; 50 µm, 0.10 MPa) or tribochemical silicatisation (TSC; 110 µm Al2O3, 0.28 MPa and 110 µm silica-modified Al2O3, 0.28 MPa), followed by disinfection (1 min immersion in 70% isopropanol, 15 s water spray, 10 s drying with oil-free air) for half of the discs. A resin cement containing 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) was used for bonding (for TSC specimens after application of a primer containing silane and 10-MDP). Tensile bond strength was measured after storage for 24 h at 100% relative humidity or after 30 days in water, including 7500 thermocycles. Surface conditioning significantly affected bond strength, with higher values for TSC specimens. Ageing and the interaction of conditioning, disinfection and ageing also impacted bond strength. Disinfection combined with APA mitigated ageing-related bond strength decrease but exacerbated it for TSC specimens. Despite these effects, high bond strengths were maintained even after disinfection and ageing. Adhesive cementation of printed ZrO2 restorations exhibited comparable bond strengths to milled ZrO2, highlighting its feasibility in clinical applications.

Effect of Luting Materials on the Accuracy of Fit of Zirconia Copings: A Non-Destructive Digital Analysis Method

The marginal accuracy of fit between prosthetic restorations and abutment teeth represents an essential aspect with regard to long-term clinical success. Since the final gap is also influenced by the luting techniques and materials applied, this study analyzed the accuracy of the fit of single-tooth zirconia copings before and after cementation using different luting materials. Forty plaster dies with a corresponding zirconia coping were manufactured based on a single tooth chamfer preparation. The copings were luted on the plaster dies (n = 10 per luting material) with a zinc phosphate (A), glass-ionomer (B), self-adhesive resin (C), or resin-modified glass-ionomer cement (D). The accuracy of fit for each coping was assessed using a non-destructive digital method. Intragroup statistical analysis was conducted using Wilcoxon signed rank tests and intergroup analysis by Kruskal-Wallis and Mann-Whitney U tests (α = 0.05). Accuracy of fit was significantly different before/after cementation within A (0.033/0.110 µm) and B (0.035/0.118 µm; p = 0.002). A had a significantly increased marginal gap compared to C and D, and B compared to C and D (p ≤ 0.001). Significantly increased vertical discrepancies between A and B versus C and D (p < 0.001) were assessed. Of the materials under investigation, the zinc phosphate cement led to increased vertical marginal discrepancies, whereas the self-adhesive resin cement did not influence the restoration fit.

Bacterial adhesion to composite resins produced by additive and subtractive manufacturing

The aim of this study was to evaluate the surface roughness and contact angle of composite resins produced by CAD/CAM milling and three-dimensional (3D) printing for permanent restorations as well as the adhesion of S. mutans and S. sanguinis bacteria to these composites. Three CAD/CAM milling composite resins (Vita Enamic-VE, Cerasmart-CE, Lava Ultimate-LU) and three 3D printing resins (Varseo Smile Crown plus-VSC, Saremco print Crowntech-SPC, Formlabs 3B Permanent crown-FLP) were selected. Twenty samples were prepared for each group. Using a contact profilometer, the surface roughness was determined, and an optical goniometer was used to quantify the contact angle. To evaluate the bacterial adhesion, composite specimens were immersed in mucin containing artificial saliva. All samples were incubated for 24 h at 37°C in 5% CO2. CFUs were determined by counting colonies after the incubation period. Surface roughness values of test samples were the highest in the Group VSC [0.46 (0.14) µm], whereas the lowest values were found in the Group LU [0.23 (0.05) µm]. There was no statistically significant difference between the groups in contact angle values (p > 0.05). The S. mutans adhesion extent on the Group SPC was statistically higher compared to all other materials with p < 0.05. For S. sanguinis, the lowest bacterial adhesion value was recorded in Group CE (3.00 × 104 CFU/ml) and statistically significant differences were found with Group VE and VSC (p < 0.05). Different digital manufacturing techniques and material compositions can affect the surface roughnesses of composite resins. All composite resin samples have hydrophobic characteristics. Microbial adhesion of the tested composite resins may be varied depending on the bacterial species. S. mutans showed much more adhesion to these materials than S. sanguinis.

Effect of printing layer thickness on the trueness of 3-unit interim fixed partial dentures

STATEMENT OF PROBLEM

Three-dimensional printing has facilitated the fabrication processes in dentistry. However, knowledge on the effect of layer thickness on the trueness of 3D printed fixed partial dentures (FPDs) is lacking.

PURPOSE

The purpose of this in vitro study was to compare the effect of printing layer thickness on the trueness of 3-unit interim FPDs fabricated by using additive manufacturing with that of those fabricated by subtractive manufacturing.

MATERIAL AND METHODS

The right first premolar and first molar teeth of a dentate mandibular model were prepared for a 3-unit restoration and then digitized by using an intraoral scanner. A 3-unit interim FPD was designed to fabricate 40 restorations by using either the additive (NextDent C&B MFH) with layer thicknesses of 20 μm (n=10), 50 μm (n=10), and 100 μm (n=10) or subtractive manufacturing technique (Upcera) (milled, n=10). After fabrication, the interim FPDs were digitized by using the same intraoral scanner and were superimposed over the design data by using a 3D analysis software program. Root mean square (RMS) was used to analyze the trueness of the restorations at 4 different surfaces (external, intaglio, marginal area, and intaglio occlusal) and as a complete unit (overall). Data were analyzed with the Kruskal-Wallis and Wilcoxon tests with Bonferroni correction (α=.05).

RESULTS

The 100-μm-layer thickness interim FPDs showed the greatest overall (P≤.015), external (P≤.021), and intaglio occlusal (P≤.021) deviations, whereas the milled interim FPDs showed the lowest (P=.001). No significant differences were found among the test groups for marginal RMS (P≥.108). The differences between the 50-μm-layer thickness and 100-μm-layer thickness interim FPDs for the intaglio surface deviations (P=.064) and between the 20-μm-layer thickness and 50-μm-layer thickness interim FPDs for each surface tested were not statistically significant (P≥.108).

CONCLUSIONS

The printing layer thickness had a significant effect on the trueness of the additively manufactured interim FPDs. However, subtractively manufactured interim FPDs presented higher trueness than those additively manufactured, regardless of the printing layer thickness.

Effect of firing time and wall thickness on the biaxial flexural strength of 3D-printed zirconia

OBJECTIVES

To evaluate the effect of accelerated firing on 3D-printed zirconia.

METHODS

To check if formulae provided by ISO 6872 can be extended to thin samples, finite element analyses were carried out in advance of fabricating 3-mol% yttria-stabilized tetragonal zirconia polycrystal discs by milling and by 3D-printing. Four groups (n = 38 each) of 3D-printed specimens were produced with two nominal thicknesses (0.6 mm and 1.2 mm) and two firing strategies (long: 51 h, accelerated: 14.5 h). In the milled group (thickness 1.2 mm, n = 30), a standard firing program (9.8 h) was selected. Biaxial flexural strength tests were applied and mean strength, characteristic strength, and Weibull modulus were calculated for each group. Differences were analyzed using Welch ANOVA and Dunnett-T3 post-hoc tests.

RESULTS

Maximum tensile stresses occurring during biaxial strength testing can be calculated according to ISO 6872 for thin samples with b > 0.3 mm. Variability of measured strengths values was smaller for milled zirconia compared with 3D-printed zirconia. The 1.2-mm-thick 3D-printed samples had significantly decreased strength after accelerated firing than after long firing. However, for the 0.6-mm-thick samples, comparable mean biaxial strength values of about 1000 MPa were measured for both firing protocols.

SIGNIFICANCE

At the moment, long fabrication time for zirconia restorations is a major drawback of 3D-printing when compared with milling technology. This investigation showed that the strength of 0.6-mm-thick zirconia discs fabricated by 3D-printing was not impaired by accelerated firing. Thus, overnight firing of thin-walled 3D-printed zirconia restorations could be possible.

Comparative analysis of flexural strength of 3D printed and milled 4Y-TZP and 3Y-TZP zirconia

STATEMENT OF PROBLEM

The mechanical properties of 3 dimensionally (3D) printed zirconia have been reported to be comparable with those of milled zirconia, except for the flexural strength. However, most previous studies tested 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP), making it necessary to study 3D printed zirconia with 4 mol% yttria content (4Y-TZP).

PURPOSE

The purpose of this in vitro study was to compare the flexural strength of 3D printed 4Y-TZP with 3Y-TZP materials and milled 4Y-TZP.

MATERIAL AND METHODS

A total of 80 disk specimens (Ø15×1.5 mm) were fabricated and divided into 4 groups (n=20) using the fabrication method and yttria content: milled 3Y-TZP (Katana HT; Kuraray Noritake), 3D printed 3Y-TZP (TZ-3Y-E; Tosoh), milled 4Y-TZP (Katana STML; Kuraray Noritake), and 3D printed 4Y-TZP (3DMAT; Genoss). The biaxial flexural strength was determined with a piston-on-3-ball test (n=15). The flexural strength of each specimen was measured, and the Weibull modulus (m) and characteristic strength (σ0) were estimated from the fracture load distribution. Two intact and fractured specimens were examined with scanning electron microscopy (SEM). The crystalline phase of the specimens in each group was identified through X-ray diffraction (XRD) analysis (n=5). A 1-way ANOVA was used to compare the flexural strength among different groups. Subsequently, pairwise comparisons were conducted with the Tukey post hoc method (α=.05).

RESULTS

The flexural strength of 3D printed 4Y-TZP was significantly higher than that of milled 4Y-TZP (P<.001). In contrast, the flexural strength of 3D printed 3Y-TZP was significantly lower than that of milled 3Y-TZP (P<.001). X-ray diffraction (XRD) analysis revealed that the tetragonal phase was the dominant phase in all groups, with the identification of some cubic phase peaks.

CONCLUSIONS

Three dimensionally printed 4Y-TZP showed significantly higher flexural strength than milled 4Y-TZP and exhibited a clinically acceptable flexural strength exceeding 800 MPa.

Effect of a new support design on the marginal and internal gap of additively manufactured interim crowns using direct light deposition technology

PURPOSE

To investigate the design and location of supporting structures on the marginal and internal gap of interim restorations.

MATERIALS AND METHODS

A mandibular right first molar resin tooth was prepared for a full coverage crown and scanned using a laboratory scanner (3Shape D900). The scanned data were converted into standard tessellation language (STL) format and an indirect prosthesis was designed using computer-aided design (CAD) software (exocad DentalCAD). The STL file was used to fabricate a total of 60 crowns with a 3D printer (EnvisionTEC Vida HD). The crowns were printed using E-Dent C&B MH resin and divided into 4 groups based on four different support structure designs, including supports on the occlusal (0° group), buccal and occlusal (45° group), buccal (90° group), and a new design consisting of horizontal bars placed on all surfaces and line angles (Bar) (n = 15). The silicone replica technique was used to determine the gap discrepancy. Fifty measurements were obtained for each specimen to examine the marginal and internal gaps by using a digital microscope (Olympus SZX16) at ×70 magnification. Additionally, the marginal discrepancy at different locations of the tested crowns, including buccal (B), lingual (L), mesial (M), and distal (D), as well as the maximum and minimum marginal gap intervals among groups, were analyzed. The collected data were analyzed using factorial ANOVA, followed by the Tukey HSD test for multiple comparisons (a = 0.05).

RESULTS

There was a significant difference in marginal and internal gaps among the groups (p < 0.001). The buccal placement supports (90° group) had the least marginal and internal discrepancies (p < 0.001). The new design group showed the highest marginal and internal gap. The marginal discrepancy in different locations of the tested crowns (B, L, M, D) was found to be significantly different among the groups (p < 0.001). The mesial margin of the Bar group had the largest marginal gap, whereas the buccal margin of the 90° group had the lowest marginal gap. The new design had a significantly smaller difference between the maximum and minimum marginal gap intervals than other groups (p < 0.001).

CONCLUSION

The location and design of the supporting structures affected the marginal and internal gaps of an interim crown. The buccal placement of supporting bars (90° printing orientation) showed the smallest mean internal and marginal discrepancies.

Comparative evaluation of gingival fibroblast growth on 3D-printed and milled zirconia: An in vitro study

PURPOSE

The purpose of this study was to analyze the fibroblast growth and proliferation on 3D-printed zirconia in presence and absence of porosities.

MATERIAL AND METHODS

A total of 40 bars (8 × 4 × 3) were included in this study. Thirty 3D-printed and 10 milled zirconia samples were prepared. The 3D-printed samples had different porosities, 0% (PZ0), 20% (PZ20), and 40% (PZ40) with 10 specimens in each group. Milled zirconia samples were used as the control (MZ). Rat gingival fibroblasts were cultured for 48 h, and the proliferation of fibroblasts on each sample in each group (n = 10) was determined by MTT assays. The differences among the four groups were compared by one-way ANOVA. To test the significance of the observed differences between two groups, an unpaired Student's t-test was applied. The significance level was set at p < 0.05. Qualitative analysis for the cell culture was performed using scanning electron microscopy.

RESULTS

One-way ANOVA showed that the numbers of the fibroblasts among the four groups had a statistical difference. Post hoc Bonferroni test revealed that there was no significant difference between PZ0 and MZ; however, all other groups and among groups were significantly different.

CONCLUSIONS

Fibroblasts had a better affinity toward the MZ and PZ0 in a short period of cell culture time.

Accuracy of zirconia crowns manufactured by stereolithography with an occlusal full-supporting structure: An in vitro study

STATEMENT OF PROBLEM

Additive manufacturing is emerging as an alternative method of fabricating dental restorations, but the support design needs to be optimized.

PURPOSE

The purpose of this in vitro study was to evaluate the 3-dimensional trueness and adaptations of zirconia crowns manufactured by stereolithography (SLA) with an occlusal full-supporting structure, compared with those SLA-printed with pillar supports, and those made by milling.

MATERIAL AND METHODS

A zirconia abutment was prepared, and an anatomic contour crown was designed. The crowns were manufactured by SLA and milling (n=6). For SLA manufacturing, a full-supporting base and pillar supports were designed. The 3-dimensional (3D) trueness of the fabricated crowns was characterized by 3D deviation analysis. The adaptations of crowns in the SLA-base and milling groups were measured by using a triple-scan method. Color-difference maps and the root mean square (RMS) values were used to characterize the 3D trueness. One-way analysis of variance (ANOVA) and Tukey post hoc test were used to analyze the difference in RMS values among the 3 groups, and Student t test was used to analyze the difference in cement-gap width between the milling group and the SLA group with the full-supporting base (α=.05).

RESULTS

The 3D deviation analysis showed that in the external area, the RMS value of the SLA-pillar group was significantly higher than that of the SLA-base and the milling groups (P<.05). In the intaglio area, the milling group showed a lower RMS value than the 2 SLA groups (P<.05). The color-difference maps showed the SLA-base group had smaller positive errors at the cusp inclines than the SLA-pillar group. No statistically significant difference was found in adaptations between the SLA-base and milling groups (P>.05).

CONCLUSIONS

The occlusal full-supporting base provided improved support in fabricating the crowns, and no remnants were left after removal. The zirconia crowns manufactured by SLA with an occlusal full-supporting structure had good external 3D trueness and clinically acceptable adaptation.

The effect of low-temperature degradation and building directions on the mechanical properties of additive-manufactured zirconia

This study aimed to investigate the effect of low-temperature degradation (LTD) on the mechanical properties of additive-manufactured zirconia. In addition, the mechanical properties of additive-manufactured were compared with those before aging under similar experimental conditions. This study prepared stereolithography apparatus fabricated zirconia specimens with flexural strength, modulus of elasticity, Vickers hardness, and fracture toughness. The specimen position data were set as parallel (0°), diagonal (45°), and perpendicular (90°) to the direction of the building. The LTD condition was 5 h under 134ºC and 0.2 MPa in an autoclave. It was found that the 0° direction differed significantly from all other conditions before and after aging, and the highest flexural strength was obtained when the additive specimen was manufactured perpendicular to the building direction. However, the results indicate that there is a negligible effect of aging on the mechanical properties of additive-manufactured zirconia.

Effect of exposure energy dose on lateral resolution and flexural strength of three-dimensionally printed dental zirconia

PURPOSE

This study aims to evaluate the effects of exposure energy on the lateral resolution and mechanical strength of dental zirconia manufactured using digital light processing (DLP).

MATERIALS AND METHODS

A zirconia suspension and a custom top-down DLP printer were used for in-office manufacturing. The viscosity of the suspension and uniformity of the exposed light intensity were controlled. Based on the exposure energy dose delivered to each layer, the specimens were classified into three groups: low-energy (LE), medium-energy (ME), and high-energy (HE). For each energy group, a simplified molar cube was used to measure the widths of the outline (Xo and Yo) and isthmus (Xi and Yi), and a bar-shaped specimen of the sintered body was tested. A Kruskal-Wallis test for the lateral resolution and one-way analysis of variance for the mechanical strength were performed (α = .05).

RESULTS

The zirconia green bodies of the ME group showed better lateral resolution than those of the LE and HE groups (both P < .001). Regarding the flexural strength of the sintered bodies, the ME group had the highest mean value, whereas the LE group had the lowest mean value (both P < .05). The ME group exhibited fewer agglomerates than the LE group, with no distinctive interlayer pores or surface defects.

CONCLUSION

Based on these findings, the lateral resolution of the green body and flexural strength of the sintered body of dental zirconia could be affected by the exposure energy dose during DLP. The exposure energy should be optimized when fabricating DLP-based dental zirconia.

Effect of build angle on the dimensional accuracy of monolithic zirconia crowns fabricated with the nanoparticle jetting technique

STATEMENT OF PROBLEM

The build angle is an essential parameter in additive manufacturing. Its effect on the dimensional accuracy of zirconia restorations fabricated using the nanoparticle jetting (NPJ) technique is unknown.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of the build angle on the dimensional accuracy of monolithic zirconia complete crowns fabricated by using NPJ.

MATERIAL AND METHODS

Standardized artificial right maxillary incisors and mandibular first molars were prepared for ceramic complete crowns. In total, 100 monolithic zirconia crowns were fabricated using NPJ at build angles of 0, 45, 90, 135, and 180 degrees (n=10/angle for incisors and molars). The dimensional accuracies in the external, marginal, and intaglio regions were determined by superimposing the scanned data and computer-aided design data on the crowns. Root mean square (RMS) values were used to analyze the accuracy of the zirconia crowns overall and at the external, marginal, and intaglio surfaces. The Shapiro-Wilk test was used to examine the normality of data distribution. Differences among test groups were assessed using a 1-way analysis of variance and the post hoc least significant difference test (α=.05).

RESULTS

Significant differences were found in the accuracy of monolithic zirconia incisor and molar complete crowns in the external, marginal, and intaglio regions among the 5 build angles (P<.05). For incisors, the external RMS value was lowest for a build angle of 45 degrees (18.2 ±3.0 µm), the marginal and intaglio RMS values were lowest for a build angle of 135 degrees (47.4 ±10.7 and 26.5 ±6.1 µm, respectively), and the overall RMS values did not differ significantly among the 5 build angles (P>.05). For molars, build angles of 0 degrees and 180 degrees yielded the lowest RMS values overall (22.3 ±1.5 and 21.8 ±3.2 µm, respectively) and in the external (23.2 ±2.9 and 22.3 ±2.5 µm, respectively) and intaglio (22.2 ±3.7 and 21.2 ±4.6 µm, respectively) regions. No significant difference was observed in the marginal area among the 5 build angles (P>.05). The overall RMS values reflecting dimensional accuracy for the 5 build angles were between 23.5 and 26.7 µm for incisors and 21.8 and 26.2 µm for molars.

CONCLUSIONS

The dimensional accuracy of monolithic zirconia crowns fabricated by using NPJ was affected by the build angle and was within clinically acceptable limits.

Additively and subtractively manufactured implant-supported fixed dental prostheses: A systematic review

AIM

To compare and report on the performance of implant-supported fixed dental prostheses (iFDPs) fabricated using additive (AM) or subtractive (SM) manufacturing.

METHODS

An electronic search was conducted (Medline, Embase, Cochrane Central, Epistemonikos, clinical trials registries) with a focused PICO question: In partially edentulous patients with missing single (or multiple) teeth undergoing dental implant therapy (P), do AM iFDPs (I) compared to SM iFDPs (C) result in improved clinical performance (O)? Included were studies comparing AM to SM iFDPs (randomized clinical trials, prospective/retrospective clinical studies, case series, in vitro studies).

RESULTS

Of 2'184 citations, no clinical study met the inclusion criteria, whereas six in vitro studies proved to be eligible. Due to the lack of clinical studies and considerable heterogeneity across the studies, no meta-analysis could be performed. AM iFDPs were made of zirconia and polymers. For SM iFDPs, zirconia, lithium disilicate, resin-modified ceramics and different types of polymer-based materials were used. Performance was evaluated by assessing marginal and internal discrepancies and mechanical properties (fracture loads, bending moments). Three of the included studies examined the marginal and internal discrepancies of interim or definitive iFDPs, while four examined mechanical properties. Based on marginal and internal discrepancies as well as the mechanical properties of AM and SM iFDPs, the studies revealed inconclusive results.

CONCLUSION

Despite the development of AM and the comprehensive search, there is very limited data available on the performance of AM iFDPs and their comparison to SM techniques. Therefore, the clinical performance of iFDPs by AM remains to be elucidated.

Clinical Effectiveness of 3D-Milled and 3D-Printed Zirconia Prosthesis-A Systematic Review and Meta-Analysis

BACKGROUND

Additive manufacturing (three-dimensional (3D) printing) has become a leading manufacturing technique in dentistry due to its various advantages. However, its potential applications for dental ceramics are still being explored. Zirconia, among ceramics, has increasing popularity and applications in dentistry mostly due to its excellent properties. Although subtractive manufacturing (3D milling) is considered the most advanced technology for the fabrication of zirconia restorations, certain disadvantages are associated with it.

METHODS

A systematic review was piloted to compare the clinical performance of zirconium crowns that were fabricated using three-dimensional (3D) milling and 3D printing. A meta-analysis was performed, and studies published up to November 2022 were identified. The terms searched were "Zirconium crowns", "3D printing", "CAD/CAM" (Computer-Aided Design and Computer-Aided Manufacturing), "Milling", "dental crowns", and "3D milling". The characteristics that were compared were the year in which the study was published, study design, age of the patient, country, the number of crowns, the type of crown fabrication, marginal integrity, caries status, and outcomes. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used to structure this systematic review. Out of eleven hundred and fifty titles identified after a primary search, nine articles were included in the quantitative analysis. The research question based on PICO/PECO (Participant, Intervention/exposure, Comparison, and Outcome) was "Do 3D-printed and milled (P) zirconia crowns and FDPs (I) have a better survival rate (O) when conventional prosthesis is also an option (C)"? The data collected were tabulated and compared, and the risk of bias and meta-analysis were later performed. Only nine articles (clinical research) were selected for the study. Since there were no clinical studies on the 3D printing of zirconium crowns, six in vitro studies were considered for the comparison. Zirconium crowns in the milling group had an average minimum follow-up of 6 months.

RESULTS

A moderate risk of bias was found, and survival was significant. A high heterogeneity level was noted among the studies. Marginal integrity, periodontal status, and survival rate were high. Linear regression depicted no statistical correlation between the type of cement used and the survival rate.

CONCLUSIONS

It can be concluded that the milled crowns had a higher performance and satisfactory clinical survival.

Mechanical and surface properties of additive manufactured zirconia under the different building directions

PURPOSE

This study investigates the mechanical and surface properties of zirconia manufactured using additive manufacturing (AM) technology and the effect of the building direction on the mechanical and surface properties.

METHODS

Specimens were prepared using ZrO₂ paste (3DMix ZrO₂; 3DCeram) and a three-dimensional printing system (CeraMaker 900; 3DCeram) based on the principles of stereolithography (SLA). The mechanical properties (flexural strength, Vickers hardness, fracture toughness, elastic modulus, and Poisson's ratio) and surface properties (chemical composition and surface observation) were evaluated for three building directions (parallel, diagonal, and perpendicular) to investigate the relationship between the building directions and the anisotropy of the mechanical and surface properties of SLA-manufactured zirconia. Statistical analysis was performed using a one-way analysis of variance and Tukey's honestly significant difference test.

RESULTS

The highest flexural strength was obtained for a perpendicular building direction. The flexural strength was significantly higher in the perpendicular direction than in the parallel and diagonal directions; it was also significantly higher in the diagonal direction than in the parallel direction (P<0.05). The Vickers hardness, fracture toughness, elastic modulus, Poisson's ratio, and chemical composition did not differ significantly. Microstructural observations revealed that the layers, large crystals, and pores were more prominent in the parallel direction.

CONCLUSIONS

The flexural strength and surface structure of the tested SLA-manufactured zirconia were influenced by the building direction; however, other mechanical properties remained unaffected. The layer boundaries affected the anisotropic behavior of the builds to a certain extent, owing to the layer-by-layer production method.

Mechanical properties of additively manufactured zirconia with alumina air abrasion surface treatment

This study aimed to evaluate the mechanical properties of zirconia fabricated using additive manufacturing technology and compare them to those of zirconia fabricated using subtractive manufacturing technology. Sixty disc-shaped specimens were fabricated for the additive (n = 30) and subtractive manufacturing groups (n = 30), and each group was divided into two subgroups according to their air-abrasion surface treatment: control (n = 15) and air-abrasion groups (n = 15). Mechanical properties including the flexural strength (FS), Vickers hardness, and surface roughness were determined, and the values were analyzed by one-way ANOVA and Tukey's post hoc test (α = 0.05). X-ray diffraction and scanning electron microscopy were used for phase analysis and surface topography evaluation, respectively. The SMA group exhibited the highest FS (1144.97 ± 168.1 MPa), followed by the SMC (944.58 ± 141.38 MPa), AMA (905.02 ± 111.38 MPa), and AMC groups (763.55 ± 68.69 MPa). The Weibull distribution showed the highest scale value (1213.55 MPa) in the SMA group, with the highest shape value in the AMA group (11.69). A monoclinic peak was not detected in both the AMC and SMC groups, but after air abrasion, the monoclinic phase content ([Formula: see text]) reached 9% in the AMA group, exceeding that in the SMA group (7%). The AM groups exhibited statistically lower FS values than those of the SM groups under the same surface treatment (p < 0.05). Air-abrasion surface treatment increased the monoclinic phase content and FS (p < 0.05) in both the additive and subtractive groups, while it increased the surface roughness (p < 0.05) only in the additive group and did not affect the Vickers hardness in either group. For zirconia manufactured using additive technology, the mechanical properties are comparable to those of zirconia manufactured using subtractive technology.

Microfabrication approaches for oral research and clinical dentistry

Currently, a variety of laboratory tools and strategies have been developed to investigate in vivo processes using in vitro models. Amongst these, microfabrication represents a disruptive technology that is currently enabling next-generation biomedical research through the development of complex laboratory approaches (e.g., microfluidics), engineering of micrometer scale sensors and actuators (micropillars for traction force microscopy), and the creation of environments mimicking cell, tissue, and organ-specific contexts. Although microfabrication has been around for some time, its application in dental and oral research is still incipient. Nevertheless, in recent years multiple lines of research have emerged that use microfabrication-based approaches for the study of oral diseases and conditions with micro- and nano-scale sensitivities. Furthermore, many investigations are aiming to develop clinically relevant microfabrication-based applications for diagnostics, screening, and oral biomaterial manufacturing. Therefore, the objective of this review is to summarize the current application of microfabrication techniques in oral sciences, both in research and clinics, and to discuss possible future applications of these technologies for in vitro studies and practical patient care. Initially, this review provides an overview of the most employed microfabrication methods utilized in biomedicine and dentistry. Subsequently, the use of micro- and nano-fabrication approaches in relevant fields of dental research such as endodontic and periodontal regeneration, biomaterials research, dental implantology, oral pathology, and biofilms was discussed. Finally, the current and future uses of microfabrication technology for clinical dentistry and how these approaches may soon be widely available in clinics for the diagnosis, prevention, and treatment of relevant pathologies are presented.

In-vitro performance of subtractively and additively manufactured resin-based molar crowns

PURPOSE

To compare the in-vitro performance and wear behavior of additively or subtractively fabricated resin-based composite molar crowns for temporary and permanent application.

MATERIALS AND METHODS

Identical molar crowns (n = 8 per group) were manufactured from materials for temporary or permanent application (3x temporary additive fabrication, 3x additive permanent fabrication, 1x temporary subtractive fabrication, 1x permanent subtractive fabrication). All crowns were adhesively bonded (Calibra Universal, Dentsply Sirona, USA) on standardized resin-based composite molars (FDI 46, P Pro temporary Crown & Bridge). Thermal cycling and mechanical loading (2 × 3000 × 5°C/55 °C, 2min, H₂0 dist., 1.2 × 10⁶ force 50N) were performed and fracture force was determined (v = 1 mm/min, Z010, Zwick, Germany). Mean wear, maximum wear, and roughness were investigated on polished (P1200) specimens (n = 8 per group, d = 8 mm) in a pin-on-block test (50N; 120000 cycles; 1.6Hz; H₂O). Statistics were performed by using one-way ANOVA, Bonferroni post-hoc-tests, and Pearson-correlation (α = 0.05).

RESULTS

All crowns survived TCML without failures. Fracture forces ranged from 1362.4 ± 182.4N to 2354.1 ± 373.3N for the additive temporary crowns, from 1680.4.4 ± 525.1N to 2601.6 ± 403.7N for the additive permanent crowns, and reached values of 2988.5 ± 604.7N for subtractive temporary crowns and 3092.0 ± 307.6 N for subtractive permanent crowns. Significant (p < 0.001) differences were identified between the various additively manufactured systems, but not for the subtractively fabricated systems (p = 0.673). Mean wear of the additive temporary crowns ranged between 114.5 ± 25.8 μm and 163.8 ± 21.4 μm without significant differences (p = 0.061). Mean wear of the additive permanent crowns ranged between 120.0 ± 27.5 μm and 171.3 ± 31.8 μm with significant differences (p = 0.004). No statistically significant differences were identified between temporary and permanent subtractively manufactured specimens, with mean wear ranging between 140.5 ± 51.1 μm and 176.6 ± 26.8 μm (p = 0.673). Maximum wear of additive temporary specimens ranged between 221.4.5 ± 53.3 μm and 322.1 ± 50.6 μm; significant differences were identified between the groups (p = 0.016). Maximum wear of additive permanent specimens ranged between 246.3 ± 47.3 μm and 337.4 ± 61.4 μm, and significant differences were identified between the groups (p = 0.006). Mean wear of the subtractive group (permanent and temporary) showed no differences in maximum wear from 277.9 ± 79.7.1 μm to 316.4 ± 58.1 μm (p = 0.288). Ra roughness ranged from 0.7 ± 0.2 μm to 3.6 ± 1.3 μm with significant differences (p < 0.001) and Rz reference between 65.9 ± 26.2 μm and 16.8 ± 6.3 μm.

CONCLUSION

Temporary and permanent molar crowns provided at least acceptable in-vitro performance and fracture force for clinical mid-term application. Laboratory wear stability of the resin-based materials appeared sufficient, but should be verified under clinical conditions.

Fit of anterior restorations made of 3D-printed and milled zirconia: An in-vitro study

OBJECTIVES

To evaluate the fit of zirconia veneers made by either 3D printing or milling.

METHODS

A typodont maxillary central incisor was prepared for a 0.5-mm-thick veneer and was reproduced 36 times from resin. Restorations were designed with a 20-µm-wide marginal and a 60-µm-wide internal cement gap, and were made from 3D-printed zirconia (LithaCon 3Y 210, Lithoz, n = 24) and milled zirconia (Cercon ht, DentsplySirona, n = 12). For milled zirconia, a drill compensation was needed to give the milling bur access to the intaglio surface. The restorations were cemented, cross-sectioned, and the cement gap size was analyzed by two raters. Inter-rater reliability was studied at 12 3D-printed veneers (intraclass correlation coefficient, ICC, mixed model, absolute agreement). Twelve remaining 3D-printed restorations were compared with 12 milled restorations regarding fit at three locations: marginally, labially, and at the incisal edge (Mann-Whitney U-tests, α<0.05).

RESULTS

Inter-rater reliability was excellent, with an ICC single-measure coefficient of 0.944 (95%-confidence interval: [0.907; 0.966]). Gap sizes (mean ± SD / maximum) were 55 ± 9 / 143 µm at the margins, 68 ± 14 / 130 µm labially, and 78 ± 19 / 176 µm at the incisor edge for 3D-printed veneers. For milled veneers, gap sizes were 44 ± 11 / 141 µm at the margins, 85 ± 19 / 171 µm labially, and 391 ± 26 / 477 µm at the incisor edge. At the margins, the milled veneers outperformed the 3D-printed restorations (p = 0.011). The cement gap at the incisor edge was significantly smaller after 3D printing (p < 0.001).

CONCLUSIONS

3D-printed zirconia restorations showed clinically acceptable mean marginal gaps below 100 µm. Because drill compensation could be omitted with 3D printing, the fit at the sharp incisal edge was significantly tighter than with milling.

CLINICAL SIGNIFICANCE

The fit of 3D-printed ceramic anterior restorations meets clinical standards. In addition, 3D printing is associated with a greater geometrical freedom than milling. With regard to fit this feature allows tighter adaptation even after minimally invasive preparation.

The Effect of a Digital Manufacturing Technique, Preparation Taper, and Finish Line Design on the Marginal Fit of Temporary Molar Crowns: An In-Vitro Study

The aim of this study is to investigate the combined effect of a digital manufacturing technique (subtractive vs. additive), preparation taper (10° vs. 20° TOC), and finish line (chamfer vs. shoulder) on the marginal adaptation of temporary crowns following cementation with a compatible temporary cement. Four mandibular first molar typodont teeth were prepared for full coverage crowns with standard 4 mm preparation height as follows: 10° TOC with the chamfer finish line, 10° TOC with the shoulder finish line, 20° TOC with the chamfer finish line and 20° TOC with the shoulder finish line. Each of the four preparation designs were subdivided into two subgroups to receive CAD/CAM milled and 3D-printed crowns (n = 10). A total of 80 temporary crowns (40 CAD/CAM milled and 40 3D-printed) were cemented to their respective die using clear temporary recement in the standard cementation technique. The samples were examined under a stereomicroscope at ×100 magnification following calibration. Linear measurements were performed at seven equidistant points on each axial surface and five equidistant points on each proximal surface. One-way ANOVA analysis and Tukey HSD (Honestly Significance Difference) were performed. The best marginal fit was seen in group 8, while the poorest fit was noted in group 2. Shoulder finish lines and 10° TOC resulted in higher marginal gaps, especially in CAD/CAM milled group. The selection of 3D-printed crowns may provide a better marginal fit within the range of clinical acceptability. Marginal gaps were within clinical acceptability (50 and 120 µm) in all groups except group 2.

Effect of dimensional variations on the manufacturing process and the 3D shrinkage ratio of stereolithographic dental alumina ceramics

The purpose of the present study was to evaluate the influence of height and length variations of alumina ceramics manufactured by stereolithography on deformations caused by the manufacturing process and on the 3D shrinkage ratio to control the final dimensions and improve the adaptation of stereolithographic ceramic dental prostheses. Two different U-shaped models were designed with variable heights or lengths. The specimens were manufactured by stereolithography and were scanned using a microtomographic device before and after the heat treatment. Dimensional variations were measured using inspection software. The number and surface of layers of alumina ceramic influenced the reliability of the stereolithography manufacturing but did not influence the 3D shrinkage ratio. The larger the layer surface, the larger the deformation of the ceramic. Dental ceramics manufactured by stereolithography with smallest layer surface are the most reliable. This helps in the selection of the build orientation.

Knife-edged crown fabricated by 3-dimensional gel deposition and soft milling

STATEMENT OF PROBLEM

Restorations with knife-edge margins are more prone to margin chipping during the manufacturing process. Three-dimensional gel deposition shows potential for fabricating zirconia restorations with good margin quality, but studies on its performance in fabricating knife-edged crowns are lacking.

PURPOSE

The purpose of this in vitro study was to compare the 3-dimensional trueness, surface morphology, and margin quality of self-glazed zirconia and soft-milled zirconia crowns with knife-edge margins.

MATERIAL AND METHODS

An abutment with a knife-edge finish line design was prepared and scanned with a laboratory scanner. Anatomic contour crowns were designed and fabricated by 3-dimensional gel deposition and soft milling (n=5). The crowns were digitalized, and the scan data were superimposed on the computer-aided design (CAD) data for 3-dimensional deviation analysis. Surface morphology and margin quality were characterized with microscopic examination.

RESULTS

The self-glazed zirconia crowns showed a smooth and glossy appearance. The soft-milled crowns showed traces left by the removal of support bars and numerous micropits of various sizes. In internal areas, no significant difference was found in root mean square values between the 2 groups (P＞.05). For the external surface, self-glazed zirconia showed statistically lower root mean square values than the soft-milled crowns (P＜.05). When observed at ×5 magnification, all the self-glazed zirconia crowns showed smooth edges with no defects, whereas small or large margin defects were found in the soft-milled crowns. When characterized at ×200 magnification, minor margin flaws were observed in the self-glazed zirconia crowns. More and larger margin defects were found in the soft-milled crowns.

CONCLUSIONS

Three-dimensional gel deposition forms a smoother and more homogeneous surface than soft milling. Knife-edged self-glazed zirconia crowns have good dimensional accuracy and margin quality.

[Manufacturing of zirconia restorations by means of additive fabrication. Part 2]

Additive fabrication (AF) or layer-by-layer synthesis technologies is one of the most dynamically developing areas of digital production. Modern additive technologies can be used to fabricate zirconia-based restorations. The second part of this article will present the fabrication of zirconia restorations using additive technologies such as selective laser sintering (SLS), selective laser melting (SLM), binder jetting (BJ), robocasting (fusion deposition modeling, FDM), as well as the advantages and disadvantages of the mentioned technologies. The analysis of the presented works indicates the need for further research aimed at optimizing 3D printing of zirconia restorations.

Indirect restorative systems-A narrative review

OBJECTIVE

The background and clinical understanding of the properties of currently available indirect restorative systems and fabrication methods is, along with manufacturer and evidence-based literature, an important starting point to guide the clinical selection of materials for tooth and/or implant supported reconstructions. Therefore, this review explores most indirect restorative systems available in the market, especially all-ceramic, along with aspects of manufacturing process, clinical survival rates, and esthetic outcomes.

OVERVIEW

Progressive incorporation of new technologies in the dental field and advancements in materials science have enabled the development/improvement of indirect restorative systems and treatment concepts in oral rehabilitation, resulting in reliable and predictable workflows and successful esthetic and functional outcomes. Indirect restorative systems have evolved from metal ceramics and polymers to glass ceramics, polycrystalline ceramics, and resin-matrix ceramics, aiming to improve not only biological and mechanical properties, but especially the optical properties and esthetic quality of the reconstructions, in attempt to mimic natural teeth.

CONCLUSIONS

Based on several clinical research, materials, and patient-related parameters, a decision tree for the selection of indirect restorative materials was suggested to guide clinicians in the rehabilitation process.

CLINICAL SIGNIFICANCE

The pace of materials development is faster than that of clinical research aimed to support their use. Since no single material provides an ideal solution to every case, professionals must continuously seek information from well designed, long-term clinical trials in order to incorporate or not new materials and technological advancements.

Chemical Composition and Flexural Strength Discrepancies Between Milled and Lithography-Based Additively Manufactured Zirconia

PURPOSE

To evaluate the chemical composition, flexural strength, and Weibull characteristics of milled and lithography-based additively manufactured (AM) zirconia.

MATERIALS AND METHODS

A virtual design of a bar (25×4×2 mm) was completed using a software program. The standard tessellation language file was used to manufacture all the specimens: 3Y-TZP zirconia (Priti multidisc ZrO₂ monochrome) milled (M group) and 3Y-TZP zirconia (LithaCon 3Y 210) lithography-based AM (CeraFab System S65 Medical) (AM group) bar specimens (n = 20). The chemical composition of the specimens was determined by using energy dispersive X-ray (EDAX) elemental analysis in a scanning electron microscope. Flexural strength was measured in all specimens using 3-point bend test according to ISO/CD 6872.2 with a universal testing machine (Instron Model 8501). Two-parameter Weibull distribution values were calculated. The Shapiro-Wilk test revealed that the data were normally distributed (p < 0.05). Flexural strength values were analyzed using independent Student's t-test (α = 0.05).

RESULTS

There were no major chemical composition differences observed between M and AM groups. The AM specimens (1518.9 ± 253.9 MPa) exhibited a significantly higher flexural strength mean value compared to the milled (980.5 ± 130.3 MPa) specimens (DF = 13, T-value = -5.97, p < 0.001). The Weibull distribution presented the highest shape for M specimens (11.49) compared to those of AM specimens (6.95).

CONCLUSIONS

There was no significant difference in the chemical composition of milled and AM zirconia material tested. AM zirconia tested exhibited significantly higher flexural strength compared with the milled zirconia evaluated.

Fit, Precision, and Trueness of 3D-Printed Zirconia Crowns Compared to Milled Counterparts

Precise fit of a crown and accurate reproduction of the digital design are paramount for successful treatment outcomes and preservation of clinician and technician time. The study aimed to compare the internal fit, marginal adaptation, precision, and trueness of 3D-printed zirconia crowns compared to their milled counterpart. A total of 20 monolithic 3 mol% yttria stabilized-zirconia crowns (n = 10) were made using computer-assisted design (CAD) followed by additive (3D-printed) and subtractive (milled) manufacturing. Digital scanning of the master die with and without a fit checker followed by image superimposition, and analysis was performed to evaluate internal and marginal adaptation in four areas (occlusal, axial, marginal, and overall). ISO 12836:2015 standard was followed for precision and trueness evaluation. Statistical analysis was achieved using a t-test at α = 0.05. Internal fit and marginal adaptation revealed no significant difference between the two test groups (p > 0.05). The significant difference in trueness (p < 0.05) was found between the two groups in three areas (occlusal, axial, and internal). The best and worst trueness values were seen with 3D-printed crowns at occlusal (8.77 ± 0.89 µm) and Intaglio (23.90 ± 1.60 µm), respectively. The overall precision was statistically better (p < 0.05) in the 3D-printed crowns (9.59 ± 0.75 µm) than the milled (17.31 ± 3.39 µm). 3D-printed and milled zirconia crowns were comparable to each other in terms of internal fit and marginal adaptation. The trueness of the occlusal and axial surfaces of 3D-printed crowns was better, whereas the trueness of fitting surface of milled crowns was better. 3D-printed crowns provided a higher level of precision than milled crowns. Although the internal and marginal fit of both production techniques were comparable, 3D printing of zirconia produced more precise crowns.

Clinical evaluation of 3D-printed zirconia crowns fabricated by selective laser melting (SLM) for posterior teeth restorations: Short-term pilot study

Background/purpose

Zirconia crowns (ZrC) without veneering porcelain have become an effective alternative in clinical practice. Monolithic zirconia restorations fabricated by the dry milling method do not have acceptable clinical properties. This study evaluated the periodontal qualities of three-dimensional printed ZrC using the modified United States Public Health Service (USPHS) criteria.

Materials and methods

A total of 15 patients who required dental crowns were recruited, and all 15 teeth were restored with digital 3D-printed ZrC. All crowns were assessed at the time of crown placement and 2, 6, and 24 weeks post-placement. Clinical parameters, including plaque index, gingival index, probing depth, crown marginal integrity, and attrition of the antagonist's teeth, were evaluated and recorded.

Results

According to the Modified California Dental Association quality evaluation system, 100% of the crowns received satisfactory grades. Despite the significant increase in plaque index and gingival index at two weeks post-ZrC placement, there was no deterioration in probing depth. Moreover, there was discard usage of ZrC on the antagonist's teeth at 24 weeks posttreatment. Of the 15 crowns, one tooth had to be extracted due to a vertical root fracture. Overall, the digital 3D-printed crowns showed no adverse effects on periodontal tissues after 24 weeks of follow-up.

Conclusion

The 3D-printed ZrC showed no periodontal problems. It can serve as an alternative for patients, particularly those with high esthetic expectations.