Dental Ceramics Research Articles

Translucent Zirconia in Fixed Prosthodontics-An Integrative Overview.

Over the past two decades, dental ceramics have experienced rapid advances in science and technology, becoming the fastest-growing field of dental materials. This review emphasizes the significant impact of translucent zirconia in fixed prosthodontics, merging aesthetics with strength, and highlights its versatility from single crowns to complex bridgework facilitated by digital manufacturing advancements. The unique light-conducting properties of translucent zirconia offer a natural dental appearance, though with considerations regarding strength trade-offs compared to its traditional, opaque counterpart. The analysis extends to the mechanical attributes of the material, noting its commendable fracture resistance and durability, even under simulated physiological conditions. Various zirconia types (3Y-TZP, 4Y-TZP, 5Y-TZP) display a range of strengths influenced by factors like yttria content and manufacturing processes. The study also explores adhesive strategies, underlining the importance of surface treatments and modern adhesives in achieving long-lasting bonds. In the realm of implant-supported restorations, translucent zirconia stands out for its precision, reliability, and aesthetic adaptability, proving suitable for comprehensive dental restorations. Despite its established benefits, the review calls for ongoing research to further refine the material's properties and adhesive protocols and to solidify its applicability through long-term clinical evaluations, ensuring its sustainable future in dental restorative applications.

Mechanical, low temperature degradation, and biocompatibility of Al-doped dental 3Y-TZP ceramic

3Y-TZP ceramics are widely used in dental restoration materials due to their excellent biocompatibility, mechanical properties, and aesthetics. However, the low temperature aging characteristics seriously affect the service life of 3Y-TZP. This study aimed to investigate the mechanical properties, low temperature degradation properties and biocompatibility of a certain amount of alumina doped dental 3Y-TZP ceramics. The 3Y-TZP powder was produced by co-precipitation and then combined in a predetermined ratio with alumina powder. The fitting results of the Johnson-Mehl-Avramorow-Kolmogorow (JMAK) equation shows that the doping of alumina is beneficial to improve the low temperature degradation resistance of 3Y-TZP. The doped 3Y-TZP exhibited favorable biocompatibility, indicating its potential suitability as a dental restorative material.

Do electronic cigarette devices/vapes impact the colour of dental ceramics?

In vitro primary research study. Five frequently used restorative dental ceramic materials (pressable ceramics (PEmax), pressed and layered ceramics (LEmax), layered zirconia (LZr), monolithic zirconia (MZr) and porcelain fused to metal (PFM)) were selected and manufactured in shade A1. Samples of each material were prepared in discs and kept in water at 37°C for 24 hours then aged via thermocycling. Samples were positioned in a plastic chamber to mimic the intraoral setting and exposed to vape smoke through an artificial lung vacuum system. The procedure was repeated until target exposure puffs were achieved, ranging from 250-1500 puffs. The ECDs/vape device, refill juice and concentration used for puff generation were chosen based on a survey reporting high consumption. A spectrophotometer was used to measure sample colour through L*a*b values (lightness, axes of green, red, blue and yellow). CIELAB formula was used to calculate total colour difference (∆E) at six time intervals. One-way analysis of variance (ANOVA) and Tukey's posthoc testing was used to compare mean ∆E values with 95% confidence intervals for all specimens. Cut off for significance was α < 0.05. All ceramics showed colour variation following exposure to ECD aerosol. With the exception of PEmax, all tested materials lightness values changed following exposure to 250 puffs. At 1500 puff exposures, LEmax, LZr and MZr showed significant colour changes, whereas PEmax and PFM showed clinically acceptable and insignificant change. Colour change of dental ceramics varies depending on the ceramic material used and puff exposure number. Exposure to ECD aerosols can result in aesthetically noticeable colour changes in LEmax, LZr and MZr. Colour changes demonstrated are less than those caused by traditional tobacco smoking.

Evaluation of robocasting process in the layering of dental feldspathic porcelain in metal‐ceramic restorations

AbstractThe objective of the present in vitro study was to evaluate the robocasting process for the fabrication of metal‐ceramic dental restorations, according to ISO 9693. In this work, the rheological properties of dental porcelain pastes doped with organic additives and the parameters of robocasting process were determined, and the microstructural and physical‐mechanical characterization of the sintered material were performed. Subsequently, the suitability of the robocasting process for the production of metal‐ceramic dental restorations was evaluated. Results revealed that the dental feldspathic porcelain specimens, prepared by robocasting process, exhibited a homogeneous and dense microstructure with little or no microporosity, and the measured mechanical properties point towards good performance in oral cavity. The metal‐ceramic bonds produced by the robocasting process have markedly higher strength values than the minimum value of 25 MPa, required by ISO 9693, with a cohesive failure mode.

Ceramic Bond Strength of Various Metal Substrate Using Traditional and Digital Methods

Purpose: The aim of this study was to investigate the bond strength of cobalt-chromium (Co-Cr) metal frameworks prepared with three different production techniques with dental porcelain. Methods: In this study, a total of thirty disc samples divided to Three groups (n = 10/group) of metal cylinders (10 mm diameter x 4mm thickness with ring base (12 mm diameter x 1mm thickness) were fabricated by casting (Co–Cr), CAD CAM milling blank(Co–Cr) and by selective laser sintering SLM (Co–Cr) and abraded with airborne-particles then feldespathic porcelain was applied for all discs (10mm diameter x 2mm thickness), before the shear bond strength (SBS) test, the Surface characteristics of the dental alloys were observed by scanning electron microscopy (SEM) to determine the thickness of the oxide layer then surface roughness tester using TR220 portable roughness tester The average surface roughness (Ra) was determined for each group. SBS test-values and failure modes were recorded. Data were analyzed using ANOVA, Tukey’s HSD (a = 0.05). Result: no statistically significant difference of the metal-ceramic bond strength of the test roughness used between casting, milling, and laser no statistically significant difference of the metal-ceramic bond strength of the SBS test between casting compare with milling, and laser groups SBS test statistically significant difference of the metal-ceramic bond strength of the test between milling, and laser technique. The mode of failure shows was mainly cohesive and mixed for all specimens. Conclusion: Within the scope of this research, the CAD/CAM milling Co-Cr alloy has a shear bond strength comparable to the castable alloy. For metal-ceramic restorations, the CAD/CAM milling Co-Cr alloy is an alternative to the castable alloy. Co-

Investigation of mechanical properties and low-temperature degradation of dental 3Y-TZP ceramics fabricated by stereolithography in combination with microwave sintering

The purpose of this study was to obtain dental ceramic materials with excellent mechanical properties and high resistance to low temperature degradation (LTD) via stereolithography (SLA) in combination with microwave sintering (MWS). The results have shown that the unaged MWS-1425 °C 3Y-TZP ceramics with uniform microstructure have high density up to 99.04% and excellent mechanical properties (Vickers hardness 14.07 GPa, fracture toughness 4.32 MPa m1/2, flexural strength 947.87 MPa). After 50 h of LTD, the m-phase content of MWS 3Y-TZP ceramics accounts for only 10.3%. In addition, the surface roughness increases by only 1.3 nm, the degraded depth is less than 5 μm, and the flexural strength exceeds 900 MPa. This exhibits the high resistance to LTD and excellent mechanical properties of dental 3Y-TZP ceramics can be obtained.

The Effect of Various Lasers on the Bond Strength Between Orthodontic Brackets and Dental Ceramics: A Systematic Review and Meta-Analysis.

Background/objective: This systematic review and meta-analysis aimed to assess how laser conditioning affected brackets bonded to dental ceramics' shear bond strength (SBS). Materials and methods: The study was conducted by searching Pubmed/Medline, Scopus, Embase, Web of Science, the Cochrane Library, and Google Scholar up to September 14, 2022. In addition, the reference lists of the relevant articles were checked manually. Articles that compared SBS of laser-treated feldspathic, lithium disilicate, or zirconia surfaces with other standard techniques for bonding metal or ceramic orthodontic brackets were considered. Using a random-effects model, data pooling was carried out as the weighted mean difference (WMD). Results: This study initially contained 1717 reports, and following review, 32 articles were deemed suitable for our meta-analysis. The pooling results showed that the treatments with lasers such as "Er:YAG" [WMD = -1.12 MPa; 95% confidence interval (CI): -1.93 to -0.31], "Er:YAG + Silane" (WMD = -3.08 MPa; 95% CI: -4.77 to -1.40), and "Nd: YAG + Silane" (WMD = -2.58 MPa; 95% CI: -3.76 to -1.40) had statistically significant lower adhesion values compared with controls. Contrarily, "Ti:Sapphire femtosecond" demonstrated significantly higher bonding values (WMD = 0.94 MPa; 95% CI: 0.29-1.60). In contrast, other interventions obtained no statistically significant difference in SBS. Conclusions: Most of the laser groups showed results comparable with those of conventional approaches. Although more research is necessary for definitive conclusions, laser treatment may be an effective option for treating the surfaces of ceramic materials.

Color Stability of Resin Hybrid Ceramic Materials in Comparison to Zirconia-Reinforced Lithium Silicate Ceramic.

Objectives: This in vitro study aimed to compare the effect of external staining agents (black tea and grape juice) on the color change of three hybrid ceramics including a new material in comparison to zirconia-reinforced lithium silicate. Materials and Methods: Ten samples of two hybrid dental ceramics including Vita Enamic (Vita Zahnfabrik) and Crystal Ultra (Digital Dental) in addition to a resin nanoceramic, Lava Ultimate (3M ESPE); and a zirconia-reinforced lithium silicate glass ceramic, Vita Suprinity (Vita Zahnfabrik) were prepared and immersed in black tea or grape juice for 30 days. A spectrophotometer was used to evaluate color change. All samples were carefully chosen in A3 shades or their equivalent. Two-way ANOVA and Bonferroni tests were used to analyze the color differences (ΔE00) among the materials and the staining solutions at a significant level of 0.05. Results: Significant color changes were observed in Vita Enamic and Lava Ultimate groups after immersion in both solutions (P<0.001). The least color changes (ΔE00) belonged to the Vita Suprinity (1.34) and Crystal Ultra (1.92) groups, respectively. Conclusion: The color changes of Vita Enamic and Lava Ultimate materials were beyond clinical acceptability. However, the mean color changes of Vita Suprinity and Crystal Ultra groups were clinically acceptable.

TiO2 coatings on titanium obtained by anodising in a 2% Na2SiO3 solution at various voltages

Commercially pure titanium is recognised as one of the most biocompatible materials used in everyday medicine, particularly in prosthodontics. However, its high reactivity with oxygen and low thermal expansion makes titanium difficult to process, making it less popular as a material for porcelain fused to metal substructures. Analysing the available literature studies, both positive and negative effects of the oxide layer on the titanium-ceramic bond have been found. The given work attempted to anodically create oxide coatings in a 2% Na2SiO3 solution on commercially pure titanium, which could serve as substructures for crowns and dental bridges.Grade 2 titanium discs (diameter 20 mm, height 5 mm) were ground and polished. The alloy composition was determined by X-ray fluorescence analysis. The samples were divided into six groups and subjected to anodic oxidation in a 2% Na2SiO3 solution at constant voltages: 230 V, 270 V, 300 V, 350 V, 400 V, and a time of t = 1 min. The obtained oxide layers were examined by X-ray diffraction, chemical composition analysis, and SEM observation.Coating thicknesses ranging from 0.65 μm to 13.2 μm were obtained. Besides titanium oxide, an amorphous phase is present in the anodised layer.It is crucial to provide the ideal voltage directly related to the employed solution to maintain the useable thickness of the oxide layers. Variations in oxide layer thickness beyond optimal value may lead to exfoliating if it exceeds 1 μm or present fractures if it subceeds 1 μm.Titanium oxide layers obtained by anodic oxidation are mainly tested on their biocompatibility and tissue integration so important in implantology. However, the given paper focuses on creating oxide layers that may strengthen the bond between titanium and dental ceramics.

The Influence of Alumina Airborne-Particle Abrasion on the Properties of Zirconia-Based Dental Ceramics (3Y-TZP)

The objective of this study was to assess the effect of airborne-particle abrasion with alumina particles of various sizes (50 μm, 110 μm, 250 μm) on the surface properties of 3Y-TZP (3 mol% yttria-stabilized tetragonal zirconia polycrystals). The analysis comprised the Vickers hardness test (HV1kp), a surface roughness evaluation (Ra, Rq, Rz, Rsk, Rsm, Rt, Vo, profile displays), and SEM–EDS microanalysis (scanning electron microscopy–energy-dispersive X-ray spectroscopy). Any statistical relationships were assessed using the Kruskal–Wallis one-way analysis-of-variance-by-rank test (p = 0.05). While airborne-particle abrasion with 50 µm alumina significantly increases the Vickers hardness of 3Y-TZP (1678.8 HV1kp), 110 μm and 250 μm alumina particles do not appear to have any such effect. The surface roughness of 3Y-TZP increases with the size of the alumina particles (Ra, Rq, Rz, Rt, Vo: vertical plane and retention volume assessment); a higher Rsm (horizontal plane assessment) was noted for specimens air-abraded with 250 µm alumina particles; air abrasion with 50 μm alumina particles yielded a symmetrical surface roughness profile (Rsk). The major topographic pattern of the surface of 3Y-TZP is altered by alumina airborne-particle abrasion, with larger alumina particles causing more severe changes. Aluminum traces on the 3Y-TZP surface are observed. The shape of the alumina particles is irregular, with rough edges; the size of the alumina particles plays a significant role in the air abrasion of zirconia-based dental ceramics, affecting their morphology and properties.

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

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

Crack Propagation and Fatigue Performance of Partial Posterior Indirect Restorations: An Extended Finite Element Method Study.

Dental ceramics are susceptible to slow, progressive crack growth after cyclic loading. The purpose of this study was to investigate the progressive patterns of cracks in two different types of CAD/CAM ceramic materials used with three different partial posterior indirect restoration (PPIR) designs and to determine the materials' failure risk using a fatigue test. Standard initial cracks were formed in Standard Tessellation Language (STL) files prepared for three different PPIRs. The materials chosen were monolithic lithium disilicate (LS) and polymer-infiltrated ceramic networks (PICNs). The extended finite element method (XFEM) was applied, and the fatigue performance was examined by applying a 600 N axial load. The cracks propagated the most in onlay restorations, where the highest displacement was observed. In contrast, the most successful results were observed in overlay restorations. Overlay restorations also showed better fatigue performance. LS materials exhibited more successful results than PICN materials. LS materials, which can be used in PPIRs, yield better results compared to PICN materials. While inlay restorations demonstrated relatively successful results, overlay and onlay restorations can be specified as the most and the least successful PPIR types, respectively.

Investigation of Spark Plasma Sintering on Microstructure-Properties of Zirconia Reinforced Fluormica Glass for Dental Restorations.

Conventional sintering methods of dental ceramics have limitations of high temperature and slow cooling rates with requirements of additional heat treatment for crystallization. Spark plasma sintering (SPS) is an emerging technique that has the potential to process dental restorations with dense microstructures and tailor-made clinically relevant properties with optimized processing parameters. This study explored the potential of the SPS of zirconia-reinforced fluormica glass (FM) for dental restorative materials. FM glass frit was obtained through the melt-quench technique (44.5 SiO2-16.7 Al2O3-9.5 K2O-14.5 MgO-8.5 B2O3-6.3 F (wt.%)). The glass frit was ball-milled with 20 wt.% of 3 mol% yttria-stabilized zirconia (FMZ) for enhanced fracture toughness. The mixtures were SPS sintered at a pressure of 50 MPa and a heating rate of 100 °C/min for 5 min with an increase in temperature from 650-750 °C-850 °C-950 °C. Phase analysis was carried out using XRD and microstructural characterization with SEM. Micro-hardness, nano-indentation, porosity, density, indentation fracture toughness, and genotoxicity were assessed. The increase in the SPS temperature of FMZ influenced its microstructure and resulted in reduced porosity, improved density, and optimal mechanical properties with the absence of genotoxicity on human gingival fibroblast cells.

Flexural strength and translucency of barium-silicate-filled resin nanoceramics for additive manufacturing.

This in vitro study aimed to evaluate the flexural strength (FS) and translucency parameter (TP) of resin nanoceramics (RNCs) with barium silicate for additive manufacturing. An RNC slurry was prepared by mixing a barium silicate filler and resin monomer. For the FS tests, specimens with three filler contents (0, 50, and 63 wt%) were designed according to ISO6872 for dental ceramics and ISO10477 for dental polymers. These specimens were then formed into discs with thicknesses of 1 and 2 mm for TP measurement. In the specimens prepared according to ISO6872, the FS increased significantly depending on the filler content. However, in the case of ISO10477, there was no significant difference between the FSs of the specimens with 0 and 50 wt% filler contents. The increase in thickness affected translucency, and the lowest translucency was obtained at a filler content of 63 wt%. The filler distribution was dense in the specimen with 63 wt% filler and uniform but relatively sparse in the specimen with 50 wt% filler. More voids were observed in the specimen with 63 wt% filler. The thickness and filler content of the specimen affected its TP. The TP of the specimen with 63 wt% filler was similar to that of human enamel. The FS was significantly higher at a filler content of 63 wt%. The lowest translucency was obtained at a filler content of 63 wt% for all tested thicknesses. Increasing the filler content was advantageous for the mechanical properties of the RNCs. A high filler content led to low translucency in the RNCs. Therefore, the esthetics of human teeth can be reproduced if layering according to the filler content is performed in areas where esthetic characteristics are required.

Shade selection for natural tooth color replication on porcelain laminate veneers

The final color of dental ceramics depends on different factors such as light source, substrate, and selected material (thickness, contour, and texture). Objective: To report a clinical case in which a predictable protocol is used to optimize the final color of porcelain laminate veneers. Case report: A male patient attended the dental clinic dissatisfied with the composite resin restorations made on his upper anterior teeth. After anamnesis and clinical examination, it was suggested that the resin restorations be replaced by laminated porcelain veneers. A diagnostic wax-up was performed. The mock[1]up was also used to evaluate the aesthetic length for replicating the details of the incisal edge and the shape and size of the embrasures. The shade was selected before composite resin removal to avoid dehydration of the dental substrate. A photograph was taken to guide the selection of colors in different thirds. After removing the restorations, another photograph was taken to evaluate the color of the substrate. The impression was taken with 000 retractor wire and addition silicone. The laminates were made with pressed ceramic and feldspathic porcelain veneers were subsequently applied by layering the layers of dentin, incisal edge and enamel based on the waxing diagnosis. After approval by the patient, a conventional cementation technique was performed. The occlusal adjustment was made with rubber polishing cups and the anterior and lateral guides were checked. Conclusion: The protocol recommended for successful selection of the color of a porcelain laminate relies on the combination of knowledge of concepts, resources such as shade guides, spectrophotometers, and photographs, and porcelain application and characterization techniques performed by the technician and luting techniques by the dentist.

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

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

Optimized Erbium-Doped Yttrium Aluminum Garnet (Er:YAG) Laser Parameters for the Removal of Dental Ceramic Restorations.

The use of lasers for debonding adhesively luted ceramic restorations is a rather recent oral laser application in dentistry. The removal of all-ceramic restorations in the mouth can often be a troublesome task. A novel method for the debonding of ceramic restorations without damaging the restorations is Er:YAG laser irradiation. The aim of this study was to evaluate the Er:YAG laser for debonding procedures of different dental ceramics and to identify appropriate laser settings. Lithium disilicate, zirconium-reinforced lithium silicate, feldspatic ceramic, and zirconium dioxide were investigated. Ten ceramic rectangular-shaped specimens with 1 and 2 mm thickness were produced from each material. All specimens were irradiated with four different power settings 1.5; 2.5; 3.5; 4.5 W, pulse duration 50 μs, laser repetition rate 10 Hz, time of irradiation 10 s. The transmitted energy was measured with a powermeter. Additionally the suitability of the Er:YAG laser to remove the adhesively bonded ceramic and the time until loss of retention was evaluated. The transmission rate for 1 and 2 mm platelets was determined for zirconium-reinforced lithium silicate at 54.6%/35.6%, lithium disilicate at 53.2%/35.7%, zirconium dioxide at 40.6%/32.4%, and for the feldspathic ceramic at 19.4%/10.1%. For zirconium-reinforced lithium silicate and zirconium dioxide 2.5 W (250 mJ/10 Hz) was an appropriate energy level for effective debonding. Whereas for lithium disilicate and for feldspathic ceramic, 4.5 W (450 mJ/10 Hz) is required for efficient debonding. There are differences regarding transmission rates between ceramic types for the Er:YAG laser light and additionally depending on the type of ceramic different energy settings should be used for adequate debonding. Based on our in-vitro experiments we recommend 2.5 W for zirconium-reinforced lithium silicate and zirconium dioxide and 4.5 W for lithium disilicate and feldspatic ceramic. Transmission rates of different ceramic types and varying influences of thicknesses and bonding materials should be considered to adjust the laser parameters during laser debonding of adhesively luted all-ceramic restorations.

On the robustness of the Single-Edge-Precracked-Beam (SEPB) method for fracture toughness testing of ceramic materials

The Single-Edge-Precracked-Beam (SEPB) method for the testing of fracture toughness (KIc) of ceramic materials is a variation of the Single-Edge-Cracked-Beam (SEPB) method for the test of metallic materials that creates a sharp precrack not by fatigue, but by a “bridge indentation” technique that induces a crack to pop-in under compression loading. This precrack is sharp and overcomes the issue of blunt notch-root radii resulting from the Single-Edge-V-Notched-Beam (SEVNB) method, which overestimates the KIc of ceramics with submicrometric microstructures. However, the difficulties in obtaining a valid precrack and measurement make of the SEPB a low-yield, time- and cost-intensive method. Here we evaluate the SEPB method using large datasets of two fine dental grade ceramics to assess the sensitivity of the validity criteria in ISO 15732 and ASTM C 1421 and the effect of their violations in the obtained KIc. We compile datasets including or excluding validity criteria and combine those of the two standards to establish their effect on the mean and scatter of the data. We discuss the appropriateness of the validity ranges and of some criteria as a whole, while arguing for tightening the criterion precrack frontline asymmetry and for the dropping of criteria regulating the extent of stable crack extension.

The Influence of Alumina Airborne-Particle Abrasion with Various Sizes of Alumina Particles on the Phase Transformation and Fracture Resistance of Zirconia-Based Dental Ceramics.

The surface of zirconia-based dental ceramic restorations require preparation prior to adhesive cementation. The purpose of this study was to assess the influence of airborne-particle abrasion with different sizes of alumina particles (50 μm, 110 μm, or 250 μm) on the mechanical strength of zirconia-based ceramics' frameworks and on the extent of phase transformations. A fracture resistance test was performed. The central surface of the frameworks was subjected to a load [N]. The identification and quantitative determination of the crystalline phase present in the zirconia specimens was assessed using X-ray diffraction. The Kruskal-Wallis one-way analysis of variance was used to establish significance (α = 0.05). The fracture resistance of zirconia-based frameworks significantly increases with an increase in the size of alumina particles used for air abrasion: 715.5 N for 250 μm alumina particles, 661.1 N for 110 μm, 608.7 N for 50 μm and the lowest for the untreated specimens (364.2 N). The X-ray diffraction analysis showed an increase in the monoclinic phase content after air abrasion: 50 μm alumina particles-26%, 110 μm-40%, 250 μm-56%, and no treatment-none. Air abrasion of the zirconia-based dental ceramics' surface with alumina particles increases the fracture resistance of zirconia copings and the monoclinic phase volume. This increase is strongly related to the alumina particle size.

Edge damage prediction and analysis of ceramic restorations in ultrasonic-assisted dental grinding based on a multi-grit finite element model

Abrasive machining is heavily used to fabricate ceramic restorations in dentistry. The machining-induced edge damage on ceramic surfaces has been a persistent challenge for reliable restorations. This paper presents a new three-dimensional (3D) finite element analysis (FEA) modeling to visually evaluate and quantitatively predict edge chipping damage of ceramic restorations. In this model, a randomly distributed multi-grit model was built instead of most single-grit or uniform models widely used in the past. Meanwhile, axial ultrasonic vibration was first added to the model to investigate the effects of rotary ultrasonic on surface quality. Dental grinding testing was carried out using a robot arm and a high-speed dental handpiece with and without ultrasonic assistance. The experimentally measured results were in agreement with the FEA predictions. The results indicate that the reasonable rotary-ultrasonic assistance could achieve a clear reduction of edge chipping damage in the brittle dental ceramics, especially at high cutting depths without compromising cutting efficiency, compared with conventional dental grinding. This research has first proved the feasibility of applying the rotary ultrasonic technique to dental high-speed grinding for improving the surface quality of ceramic restorations. Furthermore, the proposed multi-grit FEA model for edge damage prediction is applicable not only to dental grinding but also to other abrasive machining in engineering.