Cytotoxicity of contemporary resin-based dental materials in contact with dentin.

In this study, the cytotoxicity of different combinations of contemporary resin-based restoratives (adhesives, composites, luting agents) against human keratinocytes (HaCaT) was evaluated under two conditions, whether materials were applied to dentin or not. Adhesives (3-step etch-and-rinse/3ER: OptiBond FL; 2-step self-etch/2SE Clearfil SE Bond; Single Bond Universal/UNI), composites (conventional composite resin/CCR: Filtek Z350XT; flowable/FCR: Filtek Z350XT Flow; self-adhesive composite resin/SACR: Dyad Flow), and luting agents (conventional luting agent/CLA: Variolink-II; self-adhesive luting agent/SLA: RelyXU200) were combined according to their clinical use. Eluates from polymerized specimens applied to dentin were placed in contact with cells grown for 1 and 7 d. The controls were defined by cells without material contact. Cell viability was determined using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)] assay. C=C conversion was investigated using Fourier-transform infrared spectroscopy. After 1 d of incubation, when dentin was not present, 2SE yielded the highest cell viability, whereas 3ER, UNI, and SACR showed higher cell viability in the presence of dentin. After 7 d, when dentin was absent, 2SE and CLA achieved significantly higher cell viability. The presence of dentin resulted in a drastically higher cell viability for all materials, except 2SE and CLA. UNI had the lowest C=C conversion. The presence of dentin was a significant factor, which resulted in higher cell viability than what was seen for the material specimens per se. All materials resulted in a lower viability of HaCaT than what was seen under the no-material control conditions, with effects mainly limited to the first 24 h.

Flexural strength and crystalline stability of a monolithic translucent zirconia subjected to grinding, polishing and thermal challenges.

The objective of this study is to investigate the magnitude of structural degradation of a monolithic translucent zirconia caused by clinically relevant grinding and polishing procedures, when associated or not with low temperature degradation (LTD), induced by accelerated hydrothermal aging using autoclave or thermocycling Ninety disks (Ø12 × 1 mm) were prepared from dental zirconia for monolithic restorations (Vipi Block Zirconn Translucent, Vipi). The specimens were divided into 3 groups (n = 30) according to surface treatment: As Sintered (untreated), Grind (diamond bur), Grind + Polish (diamond bur + polish); and then subdivided according to aging method (n = 10): Baseline (no aging), Autoclave (134°C, 2.2 kgf/cm2 pressure for 5 h), and Thermocycling (200,000 cycles, 5°C and 55°C, for 15 s each). Roughness, biaxial flexural strength and percentage of monoclinic phase were evaluated. Regarding surface treatment, the Grind group presented higher roughness and greater flexural strength compared to As Sintered group, while Grind + Polish showed intermediate roughness and flexural strength similar to Grind group. Aging had little effect on roughness, but yielded a significant reduction in flexural strength. Tetragonal to monoclinic phase transformation was observed in all groups, caused by both mechanical stresses (grinding and polishing) and LTD, which was similarly induced by the traditional autoclave method, as well as the thermocycling method The use of diamond burs to grind zirconia surface may result in deleterious effects on the surface quality of monolithic zirconia restorations, yet has a potential toughening effect by phase transformation. However, when zirconia is exposed to LTD, regardless of the surface treatment, degradation of the surface quality and strength are observed.

Speed sintering translucent zirconia for chairside one-visit dental restorations: Optical, mechanical, and wear characteristics.

The fabrication of zirconia dental restorations is a time-consuming process due to traditional slow sintering schemes; zirconia (Y-TZP) produced by these conventional routes are predominantly opaque. Novel speed sintering protocols have been developed to meet the demand for time and cost effective chairside CAD/CAM-produced restorations, as well as to control ceramic microstructures for better translucency. Although the speed sintering protocols have already been used to densify dental Y-TZP, the wear properties of these restorations remain elusive. Fast heating and cooling rates, as well as shorter sintering dwell times are known to affect the microstructure and properties of zirconia. Thus, we hypothesize that speed sintered zirconia dental restorations possess distinct wear and physical characteristics relative to their conventionally sintered counterparts. Glazed monolithic molar crowns of translucent Y-TZP (inCoris TZI, Sirona) were fabricated using three distinct sintering profiles: Super-speed (SS, 1580 °C, dwell time 10 min), Speed (S, 1510 °C, dwell time 25 min), and Long-term (LT, 1510 °C, dwell time 120 min). Microstructural, optical and wear properties were investigated. Crowns that were super-speed sintered possessed higher translucency. Areas of mild and severe wear were observed on the zirconia surface in all groups. Micropits in the wear crater were less frequent for the LT group. Groups S and SS exhibited more surface pits, which caused a scratched steatite surface that is associated with a greater volume loss. Tetragonal to monoclinic phase transformation, resulting from the sliding wear process, was present in all three groups. Although all test groups had withstood thermo-mechanical challenges, the presence of hairline cracks emanating from the occlusal wear facets and extending deep into the restoration indicates their susceptibility to fatigue sliding contact fracture.

The Effect of Brushing and Aging on the Staining and Smoothness of Resin Composites.

OBJECTIVES: To evaluate the staining and smoothness of resin composites undergoing aging in water or red wine and simulated brushing with or without dentifrice. METHODS: The resin composites (Z250 microfilled and Z350XT nanofilled) were tested according to aging media (deionized water or red wine) and surface treatment (no brushing, brushed with water, or brushed with dentifrice). Specimens (n = 10) were subjected to three aging cycles (5 days) of continuous immersion in the aging media; each followed by simulated brushing (585 strokes). Color coordinates (CIEL*a*b*) were measured with a spectrophotometer (SP60, EX-Rite) and roughness (Ra) measured with a contact profilometer (Surftest SJ-201P, Mitutoyo), in five time points across the experiment. Surface morphology was analyzed using AFM (SPM-9600, Shimadzu) at the end of the experiment. Data for color change (ΔE00 ) and Ra were analyzed by two-way repeated measures ANOVA and Tukey test (p < 0.05). RESULTS: Color change was observed for all groups, and it was always greater for Z350. Surface treatment did not influence the ΔE00 values for the groups aged in water. However, brushing decreased ΔE00 for the groups aged in red wine. In general, ΔE00 increased with time. Little to no differences in smoothness were observed with aging and brushing. The surface morphology analyses showed exposed/lost filler particles for brushed Z250. Such observations were not so clear for Z350. CONCLUSIONS: Within the limitations of the present experiment, short-time simulated toothbrushing with soft-bristle toothbrush and low abrasive dentifrice did not increase roughness and reduced staining for both nanofilled and microfilled materials. CLINICAL SIGNIFICANCE: Staining and surface degradation of the resin composites was reduced, but not prevented by brushing alone. Thus, minimizing the restoration exposure to staining substances is important for maintaining the aesthetic appearance of the restoration. (J Esthet Restor Dent 29:E44-E55, 2017).

Influence of Bleaching Agents on Color and Translucency of Aged Resin Composites.

OBJECTIVES: Evaluate the influence of two bleaching agents (16% carbamide peroxide-CP and 35% hydrogen peroxide-HP) on color and translucency of one resin composite (Filtek Z350 XT) in two opacities (enamel and dentin) previously aged in deionized water or red wine. METHODS: Sixty specimens of each material were divided in two groups (n = 30): aged in water or red wine for 14 days. Then the specimens were divided in three subgroups (n = 10): control/no treatment, treated with 16% carbamide peroxide (Mix Night), treated with 35% hydrogen peroxide (Mix One). Color readings were performed 24 hours after polishing (baseline); after the 14 days of aging; and after bleaching treatment. Color coordinates CIE L*a*b* were measured using a spectrophotometer (SP60 X-Rite). Color change (CIEDE2000) and translucency parameter were calculated. Data were analyzed with repeated measures two-way ANOVA, and Student-Newman-Keuls tests (5%). RESULTS: Bleaching decreased color change in stained resin composites (aged in red wine), whereas increased it in non-stained enamel resin composites (aged in water). CP had better bleaching results with stained resin composites than HP. Translucency of non-stained dentin resin composite decreased with aging, but did not change with bleaching. For stained resin composites, aging caused reduced translucency, whereas bleaching increased it. CLINICAL SIGNIFICANCE: Effective bleaching of discolored resin composites aged in an acidic and alcoholic media rich in staining agents was achieved, improving color and translucency. Carbamide peroxide showed better performance than hydrogen peroxide for the bleaching of stained resin composites. (J Esthet Restor Dent 29:368-377, 2017).

Functionalized pink Al2O3:Mn pigments applied in prosthetic dentistry.

STATEMENT OF PROBLEM: The color of dental poly(methyl methacrylate) (PMMA) is conventionally rendered by organic and inorganic pigments, which are usually not bonded to the polymer network. Functionalized ceramic pigments can be used to color PMMA, allowing improved chemical interaction with the resin matrix. PURPOSE: The purpose of this in vitro study was to synthesize, functionalize, and characterize pink manganese-doped alumina ceramic pigments. The hypothesis tested was that functionalized ceramic pigments would render pink coloration to a translucent PMMA without jeopardizing its mechanical properties. MATERIAL AND METHODS: Pink alumina powders doped with 1 or 2 mol% of manganese (Al2O3:Mn) were prepared by means of a polymeric precursor method. Pigment (Pig.) particles were functionalized with a silica coating method followed by silanation before preparation of PMMA-based composite resins (5 wt% pigment). The color of composite resins (Pig.1% and Pig.2%) and PMMA controls (Pink and translucent [Trans]) was evaluated (CIELab color coordinates), and their mechanical properties were tested (3-point bending). RESULTS: The microstructure of the pigment particles showed approximately 55-nm nanocrystals of manganese-doped α-alumina clustered into irregular porous particles up to 60 µm. The composite resins and pink PMMA showed similar color parameters (CIE a* pink=20.1, Pig.1%=14.6, Pig.2%=16.0, Trans=0.19, P<.001; CIE b* Pink=17.0, Pig.1%=18.6, Pig.2%=19.0, Trans=2.52, P<.001). No statistical differences were observed in mechanical properties among groups (σf pink=98.4, Pig.1%=98.1, Pig.2%=98.8, trans=89.1, P=.136). CONCLUSIONS: The addition of the functionalized pink ceramic pigments to a translucent PMMA yielded similar coloration to that of the regular pink PMMA used in dentistry and did not jeopardize its mechanical properties.

Shade of Resin-Based Luting Agents and Final Color of Porcelain Veneers.

OBJECTIVES: This study evaluated the influence of different shades of flowable resin composite used as luting agent on the final shade of porcelain veneers of different opacities over A2 and B1 simulated dental substrate. MATERIALS AND METHODS: One millimeter monolithic (enamel E1.0 or dentin D1.0) and bilayer (E0.5D0.5) porcelain discs shade A2 were paired with flowable resin composite disks (0.1 mm thick) of different shades (A1, A2, B1, white opaque - WO or IL - translucent), as veneer + luting agent (n = 10). The CIE L*a*b* color coordinates were measured with a spectrophotometer over white and black standard background, as well as over A2 and B1 simulated dental substrates. Translucency of all specimens and the shade matching of the pairs over the A2 and B1 substrates (ΔE*00 ) were calculated by Translucency Parameter and CIEDE2000 methods. Data were statistically analyzed by 95% confidence interval. RESULTS: Porcelain veneer E1.0 groups were the most translucent, while the pairs veneer + luting agent WO showed the lowest translucency, and A1, A2, B1, and IL yielded little to no differences in translucency of the pairs. The overall best shade matching with A2 substrate was observed for D1.0 veneer + WO luting agent. CONCLUSION: The opacity of the porcelain veneer paired with luting agents of different shades affected the final appearance of the restorations over distinct simulated tooth substrates. CLINICAL SIGNIFICANCE: Distinct shades of flowable resin composites used as luting agent might yield clinically visible color differences on porcelain veneers facilitating an excellent shade match with adjacent teeth. (J Esthet Restor Dent 28:295-303, 2016).

Influence of whitening and regular dentifrices on orthodontic clear ligature color stability.

OBJECTIVES: This study evaluated the effect of brushing orthodontic clear ligatures with a whitening dentifrice containing a blue pigment (Close Up White Now, Unilever, London, UK) on their color stability, when exposed to a staining agent. MATERIALS AND METHODS: Ligatures from 3M Unitek (Monrovia, CA, USA) and Morelli (Sorocaba, SP, Brazil) were tested. Baseline color measurements were performed and nonstained groups (control) were stored in distilled water whereas test groups were exposed for 1 hour daily to red wine. Specimens were brushed daily using regular or whitening dentifrice. Color measurements were repeated after 7, 14, 21, and 28 days using a spectrophotometer based on the CIE L*a*b* system. RESULTS: Decreased luminosity (CIE L*), increased red discoloration (CIE a* axis), and increased yellow discoloration (CIE b* axis) were generally observed for ligatures exposed to the staining agent. Color variation was generally lower in specimens brushed with regular dentifrice, but ligatures brushed with whitening dentifrice were generally less red and less yellow than regular dentifrice. The whitening dentifrice led to blue discoloration trend, with visually detectable differences particularly apparent according to storage condition and ligature brand. CONCLUSIONS: The whitening dentifrice containing blue pigment did not improve the ligature color stability, but it decreased yellow discoloration and increased a blue coloration. CLINICAL SIGNIFICANCE: The use of a whitening dentifrice containing blue pigment during orthodontic treatment might decrease the yellow discoloration of elastic ligatures.

Resin-based luting agents and color stability of bonded ceramic veneers.

STATEMENT OF PROBLEM: The type of resin-based luting agent might influence the color stability of ceramic veneers. PURPOSE: The purpose of this study was to investigate the effects of resin-based agents and aging on the color stability of ceramic veneers bonded to enamel. MATERIAL AND METHODS: Ceramic disks were cemented to bovine enamel disks with 4 resin-based luting agents (n=10): dual-polymerizing cement (RelyX ARC), light-polymerizing cement (RelyX Veneer), flowable composite resin (Filtek Z350 Flow), or composite resin preheated for 30 minutes at 60°C (Filtek Z350 XT). CIE L*, a*, and b* color coordinates were measured 24 hours after cementation (baseline) with a color spectrophotometer and reevaluated after 10,000 and 20,000 thermal cycles. Color variation was calculated by using CIELab (ΔE*(ab)) and CIEDE2000 (ΔE00) methods. Then 95% confidence intervals were calculated for color variation means between baseline and 10,000 thermal cycles and between 10,000 and 20,000 thermal cycles. The 95% confidence intervals were also calculated for the means of individual color coordinates (L*, a*, and b*). RESULTS: The dual-polymerizing cement had the highest color variation among all luting agents. No significant differences were found in color variation among the light-polymerizing materials. All agents showed ΔE*(ab)>3.46 and ΔE00>2.25 after 20,000 thermal cycles. Variations in L*, a*, and b* coordinates were material dependent. The dual-polymerizing agent was yellowish and reddish after aging. CONCLUSIONS: The dual-polymerizing cement had higher color variation than the light-polymerized materials when used for bonding ceramic veneers to enamel. Flowable and preheated composite resins had similar color stability to that of light-polymerizing resin-based cement.

High-viscosity glass-ionomer cement or composite resin for restorations in posterior permanent teeth? A systematic review and meta-analyses.

OBJECTIVES: Answer the PICO question: Do class I and II posterior restorations in permanent teeth placed with high-viscosity glass-ionomer cement (HV-GIC) fail more than composite resin (CR) restorations? DATA: The study was registered in the PROSPERO database (CRD42020138290). Randomized and controlled clinical trials, comparing the performance of HV-GIC and CR in load bearing cavities of posterior permanent teeth were included. Cochrane risk of bias tool and GRADE were used to assess the quality and certainty of the evidence. Meta-analyses were performed for clinical outcomes on USPHS and FDI criteria for 12-, 24- and 36-months follow-ups. SOURCES: PubMed, Scopus and Web of Science were last searched on April 2, 2022, without language or date restrictions. Reference lists of primary studies and their related article link in PubMed were manually searched. STUDY SELECTION: Ten studies were included, while data from 8 were used for the meta-analyses. A total of 849 HV-GIC and 800 CR restorations were followed. The primary outcome was the fracture/retention of the restoration, with a comparable performance for both materials on all follow-ups. The 36 months follow-up for class I restorations (longest) showed risk difference of -0,00 (95%CI -0,03 to 0,03; p = 0,98) and no heterogeneity (p = 0,98, I2=0%). The certainty of the evidence is moderate, as all included studies were at an uncertain risk of bias. CONCLUSIONS: HV-GIC and CR presented comparable clinical performance in posterior permanent teeth up to 36 months. HV-GIV wear in class I restorations followed by 24 months was the only poorer result compared to CR. CLINICAL SIGNIFICANCE: Conservative load bearing cavities in permanent posterior teeth can be restored with HV-GIC with comparable clinical performance to CR expected at least up to 3 years. HV-GIC is a valuable direct restorative option for posterior teeth in high caries risk patients, in which CR is frequently associated with failure.

Damage sensitivity of dental zirconias to simulated occlusal contact.

OBJECTIVE: Mechanical damages can occur from dental restoration processing and fitting, or while it is in-service. This study evaluates the damage sensitivity of translucent zirconia (5Y-PSZ) relative to conventional 3Y-PSZ following mouth-motion simulations at various loads. METHODS: 5Y-PSZ and 3Y-PSZ discs were adhesively bonded to a dentin-like substrate and divided into groups according to the load (50 N or 200 N) and number of cycles (up to 106) used in the chewing simulation. Specimens were mounted with 30° inclination in an electrodynamic mouth-motion simulator, and subjected to contact-slide-liftoff cyclic loading in water. Surface and sub-surface damages were analyzed using a sectioning technique. After the simulation, specimens were removed from the substrate and loaded with the damaged surface in tension for biaxial strength testing to assess their damage tolerance. RESULTS: The strength of both ceramics underwent significant degradation after mouth-motion simulations. For 5Y-PSZ, the strength degradation was greater (∼60%) and occurred at a lower number of cycles than 3Y-PSZ. Herringbone cracks emerged on 3Y-PSZ and 5Y-PSZ surfaces under a 200-N load after 50 and 10 cycles, respectively. Meanwhile at a 50-N load, cracks formed at ∼1000 cycles in both ceramics. Further increasing the number of cycles only had moderate effects on the strength of both ceramics, despite an increase in surface and sub-surface damage. More significantly, a 50-N occlusal load can debase the zirconia strengths as much as a 200-N load. SIGNIFICANCE: Surface flaws produced during the chewing simulation are capable of significant strength degradation in zirconia, even after a small number of low-load cycles.

Wear behavior and microstructural characterization of translucent multilayer zirconia.

OBJECTIVE: To characterize the composition, microstructure and wear properties of a multilayer translucent zirconia relative to the conventional 3Y-TZP. METHODS: Two types of ceramics were evaluated: a multilayer zirconia (MULTI, IPS e.max ZirCAD Multi, Ivoclar Vivadent) and a control 3Y-TZP (IPS e.max ZirCAD LT, Ivoclar Vivadent). Pre-sintered CAD-CAM blocks were cut, ground, sintered and polished to 1 µm finish. The phase fraction and grain size were measured using XRD and FE-SEM. For wear testing (n = 12), square-shaped specimens (16 × 16 × 1 mm) were adhesively bonded to a dentin analog. Sliding wear tests were performed using a spherical zirconia antagonist (r = 3.15 mm), with 30 N load at 1.5 Hz for 500,000 cycles in water. Optical and scanning electron microscopes and 3D laser scanner were used for quantitative wear analyses. Data were analyzed using Student's t-test (α = 0.05). RESULTS: For MULTI, the enamel layer had the highest cubic content and the largest grain size, followed by the two transition layers, and the dentin layer. 3Y-TZP showed the smallest grain size and cubic content. A significant amount of wear was observed in both materials up to 50,000 cycles until it reached a plateau. MULTI showed higher volume loss and greater wear depth than 3Y-TZP (p < 0.01). The higher volume loss was associated with extensive lateral fracture, leading to material spalling from the surface of cubic-containing zirconias. SIGNIFICANCE: The wear pattern in multi-layered zirconia was more severe than 3Y-TZP. Additionally, the different layers of the multi-layered zirconia had similar wear behavior.

Probing the interfacial strength of novel multi-layer zirconias.

OBJECTIVES: The rapidly increasing use of zirconia-based CAD/CAM multi-layer structures in dentistry calls for a thorough evaluation of their mechanical integrity. This work examines the effect of the multi-layering architecture as well as variations in composition and inclusion of pigments among the layers on the flexural strength of multi-layer zirconias. METHODS: A modified 4-point bending test, aided by a Finite Element Analysis (FEA), was used to probe the interfacial strength of 3 classes of yttria-partially-stabilized zirconia: Ultra Translucent Multi-Layer (UTML-5Y-PSZ), Super Translucent Multi-Layer (STML-4Y-PSZ), Multi-Layer (ML-3Y-PSZ). In accord with the size limitation (22-mm height) of CAD/CAM pucks, test samples were prepared in the form of "long" (25×2×3mm) and "short" (17.8×1.5×2mm) beams. Homogeneous beams (both long and short) were produced from either the Enamel (the lightest shade) or Dentin (the darkest shade) layer, whereas multi-layer beams (short beam only) were obtained by cutting the pucks along their thickness direction, where the material components of various shades were stacked. RESULTS: The Enamel and Dentin layers exhibited similar flexural strength for a given material class, with ML amassing the highest strength (800-900MPa) followed by STML (560-650MPa) and UTML (470-500MPa). The 3 classes of multi-layer zirconia showed a trade-off between strength and translucency, reflecting different yttria contents in these materials. The failure stress of the cross-sectional multi-layer beams was, however, ∼30% lower than that of their Enamel or Dentin layer counterparts, regardless of material tested. SIGNIFICANCE: The weakness of interfaces is a drawback in these materials. Additionally, when measuring strength using short beam flexure, friction between the specimen and supporting pins and accuracy in determining loading span distances may lead to major errors.

Non-silicate nanoparticles for improved nanohybrid resin composites.

OBJECTIVE: Zirconia and alumina nanoparticles were coated with a silica-rich layer (ALSI and ZRSI) and used to prepare experimental nanohybrid resin composites, which were characterized and compared to a control commercial resin composite (Filtek Z350 XT). METHODS: Silica nanoparticles with sizes compatible to ALSI (Aerosil 150) and ZRSI (Aerosil OX 50) were tested as references. The volume of nanoparticles was equivalent across the composites, which also had consistent content of glass microparticles. CC conversion, viscosity, depth of cure, surface topography, hardness, opacity, radio-opacity, and edge chipping resistance (ReA) were tested after 24 h. Flexural strength (σf) and fracture toughness (KIC) were also tested after 15 K thermal cycles. Data were analyzed using one-way or two-way ANOVA and Tukey's test (α = 0.05). RESULTS: ALSI and ZRSI yielded resin composites with lower viscosity and more irregular nanoagglomerates compared to nanosilica-based composites. CC conversion and depth of cure were lower for ZRSI composite, which had higher opacity, radio-opacity, and hardness. ReA was higher for ALSI composite. Composites with ALSI and ZRSI showed stable σf after aging, whereas the control and Aerosil 150 resin composites showed significant degradation. The commercial and nanosilica-based composites showed up to 42% reduction in KIC after aging, whereas resin composites with ZRSI and ALSI showed a more stable KIC. SIGNIFICANCE: ALSI and ZRSI generated nanohybrid resin composites with improved and/or more stable physical properties compared with nanosilica-based and commercial composites. This study suggests that changing the composition of nanofillers is a simple method to enhance the performance of nanohybrid composites.

New multi-layered zirconias: Composition, microstructure and translucency.

OBJECTIVES: To fully realize the range of indication and clinical advantages of the new multi-layered zirconias, a comprehensive understanding of their chemical composition, microstructure, low temperature degradation (LTD) resistance, and translucency properties is paramount. METHODS: A zirconia system (Katana, Kuraray Noritake), including 3 distinct grades of multi-layered zirconias, was selected for study: Ultra Translucent Multi-layered zirconia (UTML), Super Translucent Multi-layered zirconia (STML), and Multi-layered zirconia (ML). For different materials and their individual layers, the chemical composition, zirconia phase fractions, and microstructure were determined by X-ray fluorescence (XRF), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). Also, their resistance to LTD and translucency properties were characterized. RESULTS: Our findings revealed no major differences amongst layers, but the 3 materials were very distinct-UTML: 5Y-PSZ (5 mol% yttria-partially-stabilized zirconia) with ˜75 wt% cubic content and a 4.05 (±0.85) µm average grain size, STML: 4Y-PSZ with ˜65 wt% cubic content and a 2.81 (±0.17) µm average grain size, and ML: 3Y-PSZ with <50 wt% cubic content and a 0.63 (±0.03) µm average grain size. After water aging at 120 °C for 12 h, greater monoclinic content was found in ML. UTML and STML did not show detectable monoclinic phase. The translucency was similar among layers, and also between UTML and STML, which were superior to ML. SIGNIFICANCE: For each multi-layered zirconia grades, the layers are only differed in pigment types and contents, which yield remarkably natural shade gradients. Also, despite the significant compositional difference between STML and UTML, both materials showed similar translucencies.

The progressive wear and abrasiveness of novel graded glass/zirconia materials relative to their dental ceramic counterparts.

OBJECTIVE: To investigate the wear behavior of novel graded glass/zirconia materials and their abrasiveness to the antagonist relative to homogeneous zirconias (polished or glazed) and a glass-ceramic. METHODS: Graded glass/zirconia specimens were prepared by sintering with concurrent glass-infiltration of pre-sintered zirconia (3Y-TZP) with a polished or as-machined surface. Monolithic zirconia samples were sintered and their surfaces were polished or glazed (as-machined). Glass-ceramic samples were obtained and the surface polished. All specimens were subjected to chewing simulations with a steatite antagonist (r = 3 mm) and a cyclic load of 50 N. Quantitative measurements of wear and roughness were performed on ceramics and antagonists for prescribed number of cycles. Damage sustained in ceramics and antagonists was analyzed by SEM. RESULTS: The polished zirconia presented little to no variation in wear depth (2 µm) and roughness (0.06 µm). Graded and glazed zirconia experienced a rapid increase in wear depth while the superficial glass layer was present (until 1000 cycles), but showed little variations afterwards - at 450k cycles ∼15 µm for graded and 78 µm for glazed zirconia. The glass-ceramic presented the greatest wear depth (463 µm) and roughness (1.48 µm). Polished zirconia, polished graded zirconia and glazed zirconia yielded significantly lower volumetric wear (∼3 mm3) of the antagonist than as-machined graded zirconia and glass-ceramic (∼5 mm3). SIGNIFICANCE: Polished graded zirconia and polished zirconia presented little wear and roughness, as well as yielded reduced antagonist wear. Glassy materials are both more susceptible to wear and more abrasive to the antagonist relative to zirconia.

Load-bearing capacity of lithium disilicate and ultra-translucent zirconias.

OBJECTIVE: The aim of this study was to evaluate the load-bearing capacity of monolithic lithium disilicate (LiDi - IPS e.max CAD) and novel ultra-translucent zirconia restorative systems of various compositions: 5Y-PSZ (5 mol% yttria-partially-stabilized zirconia) and 4Y-PSZ (4 mol% yttria-partially-stabilized zirconia); relative to a 3Y-TZP (3 mol% yttria-stabilized zirconia) control. MATERIALS AND METHODS: Experiments were carried out with 10 disc specimens (Ø12 ×1 mm) per ceramic material. The zirconia intaglio surface (as machined) was sandblasted (50 µm Al2O3 at 2 bar), while LiDi was etched with 5% HF for 20 s. The ceramic discs were then adhesively bonded onto a dentin-like substrate (G10, a high-pressure fiberglass material) using Multilink Automix cement and Monobond Plus primer, producing a ceramic/cement/dentin-like substrate trilayer structure. The bonded specimens were stored in water for 3 days at 37 °C prior to a Hertzian indentation flexural radial fracture test. The plate-on-foundation theory was used to validate the load-bearing capacity of the trilayer systems based on the flexural tensile stress at the ceramic intaglio (cementation) surface-a cause for bulk fracture of ceramic onlays. RESULTS: The experiment data showed that, when bonded to and supported by a dentin-like substrate, the load-bearing capacity of LiDi (872 N) is superior to the 5Y-PSZ (715 N) and can even reach that of 4Y-PSZ (864 N), while 3Y-TZP still holds the highest load-bearing capacity (1195 N). Theoretical analyses agree with experimental observations. The translucency of 5Y-PSZ approaches that of LiDi, which are superior to both 4Y-PSZ and 3Y-TZP. CONCLUSIONS: When adhesively bonded to and supported by dentin, lithium disilicate exhibits similar load-bearing properties to 4Y-PSZ but much better than 5Y-PSZ.

Viscoelastic finite element analysis of residual stresses in porcelain-veneered zirconia dental crowns.

The main problem of porcelain-veneered zirconia (PVZ) dental restorations is chipping and delamination of veneering porcelain owing to the development of deleterious residual stresses during the cooling phase of veneer firing. The aim of this study is to elucidate the effects of cooling rate, thermal contraction coefficient and elastic modulus on residual stresses developed in PVZ dental crowns using viscoelastic finite element methods (VFEM). A three-dimensional VFEM model has been developed to predict residual stresses in PVZ structures using ABAQUS finite element software and user subroutines. First, the newly established model was validated with experimentally measured residual stress profiles using Vickers indentation on flat PVZ specimens. An excellent agreement between the model prediction and experimental data was found. Then, the model was used to predict residual stresses in more complex anatomically-correct crown systems. Two PVZ crown systems with different thermal contraction coefficients and porcelain moduli were studied: VM9/Y-TZP and LAVA/Y-TZP. A sequential dual-step finite element analysis was performed: heat transfer analysis and viscoelastic stress analysis. Controlled and bench convection cooling rates were simulated by applying different convective heat transfer coefficients 1.7E-5 W/mm2 °C (controlled cooling) and 0.6E-4 W/mm2 °C (bench cooling) on the crown surfaces exposed to the air. Rigorous viscoelastic finite element analysis revealed that controlled cooling results in lower maximum stresses in both veneer and core layers for the two PVZ systems relative to bench cooling. Better compatibility of thermal contraction coefficients between porcelain and zirconia and a lower porcelain modulus reduce residual stresses in both layers.

Influence of light-cured luting agents and associated factors on the color of ceramic laminate veneers: A systematic review of in vitro studies.

OBJECTIVE: The luting agent plays a significant role in the appearance of ceramic laminate veneers (CLV), allowing improved/stable shade matching with adjacent teeth. A systematic review was conducted to investigate the influence of light-cured luting agents and color-associated factors aiming to draw guidelines for stable shade matching of CLV. The paper has also given an overview of the compositional characteristics of all luting agents and ceramic systems whose performance was presented herein. METHODS: A search of in vitro studies that quantitatively investigated the influence of light-cured luting agents on the color of CLV was conducted. PubMed/MedLine, Cochrane Library, SciVerse Scopus and Web of Science databases were explored until December 2017 with no year limit. Data regarding the effect of light-cured luting agent, ceramic systems, effect of background, accelerated aging and surface treatments on color change were collected. A meta-analysis was not possible due to heterogeneity of data. RESULTS: After duplicates' removal, 3630 studies were identified, 48 were selected for full-text analysis, and 21 remaining papers met the inclusion criteria and were included in this systematic review. SIGNIFICANCE: Considering the shade aspects of luting agents, translucency and value showed the greatest visible color differences for CLVs. The effect of luting agent shade on the color of veneers is greatly affected by ceramic thickness and opacity.

Polymer infiltrated ceramic network structures for resistance to fatigue fracture and wear.

OBJECTIVE: To investigate fatigue fracture resistance and wear behavior of a polymer infiltrated ceramic network (PICN) material (ENAMIC, Vita Zahnfabrik). METHODS: Anatomically shaped ENAMIC monolithic crowns were milled using a CAD/CAM system. The crowns were cemented on aged dentin-like composite abutments (Z100, 3M ESPE) with resin-based cement (Vita DUO Cement, Vita). The specimens were subjected to 2 types of fatigue and wear tests: (1) accelerated sliding-contact mouth-motion step-stress fatigue test (n=24) in water; and (2) long-term sliding-contact mouth-motion fatigue/wear test using a clinically relevant load (P=200N, n=8) in water. Failure was designated as chip-off or bulk fracture. Optical and scanning electron microscopes were used to examine the occlusal surface and subsurface damage, as well as to reveal the material's microstructure. In addition, wear volume and depth were measured by X-ray micro-computed tomography. RESULTS: For accelerated mouth-motion step-stress fatigue testing, 3 out of the 24 ENAMIC crowns fractured following cyclic loading up to 1700N. Minor occlusal damage and contact-induced cone cracks were observed in all surviving specimens, but no flexural radial cracks were seen. For long-term mouth-motion fatigue/wear testing under a 200N load in water, a small wear scar without significant cracks was observed in all 8 tested ENAMIC crowns. SIGNIFICANCE: Monolithic CAD/CAM ENAMIC crowns showed superior resistance to sliding-contact fatigue fracture and wear.