Evaluation of translucency of monolithic zirconia and framework zirconia materials

Immediate Patient Satisfaction with Dental Esthetics After Endodontic and Prosthodontic Treatment of Dental Dyschromia

Objectives: This study aimed to evaluate patients' satisfaction with the esthetic outcomes of combined endodontic and prosthetic treatments for devitalized or dyschromic teeth, a condition influenced by various intrinsic and extrinsic factors that present a growing concern in modern dentistry. Methods: A total of 104 patients, including 43 men and 61 women, underwent treatment using lithium disilicate restorations for esthetic zones and zirconium oxide restorations for regions with higher occlusal demands. Patient satisfaction was evaluated through a post-treatment questionnaire, classifying responses as either "satisfied" or "dissatisfied". Dissatisfied participants were further asked to specify their concerns. Results: The study revealed a high satisfaction rate of 93%. Dissatisfaction was slightly more prevalent among women than men, but this difference was statistically insignificant. The primary reasons for dissatisfaction included darker restoration color, chipping, and gingival recessions. Conclusions: Combined endodontic and prosthetic treatments, utilizing lithium disilicate and zirconium oxide restorations, achieved high levels of patient satisfaction. Nevertheless, addressing specific issues, such as color matching and gingival health, could enhance outcomes further.

Evaluation of Extra-High Translucent Dental Zirconia: Translucency, Crystalline Phase, Mechanical Properties, and Microstructures

Highly translucent zirconia (TZ) is frequently used in dentistry. The properties of several highly translucent zirconia materials available in the market require an in-depth understanding. In this study, we assessed the translucency, crystalline phase, mechanical properties, and microstructures of three newly developed highly translucent zirconia materials (Zpex 4. m, 4 mol% yttria-stabilized zirconia: 4YSZ; Zpex Smile.m, 5YSZ; ZR Lucent ULTRA, 6YSZ). The translucency parameter (TP) was analyzed using the CIELAB system. X-ray diffraction was conducted for the crystalline phase analysis, followed by Rietveld refinement. A biaxial flexural strength test using the Weibull analysis was performed to evaluate the mechanical properties. Scanning electron microscopy, grain size distribution, and average grain size were used to analyze the microstructures. The TP content of the ZR Lucent ULTRA was the highest among the samples investigated. The Rietveld analysis revealed that the cubic zirconia phase content of the ZR Lucent ULTRA was the highest. The biaxial flexural strength of the ZR Lucent ULTRA was the lowest (622.9 MPa). The average grain size and proportion of large grains (1.0 µm < x) were the highest in ZR Lucent ULTRA. Therefore, extra-high translucent zirconia has the potential for use in anterior monolithic restorations owing to its esthetics and strength.

Effect of simulated intraoral adjustment on the color and translucency of gradient multilayered monolithic zirconia

STATEMENT OF PROBLEM

The use of multilayered monolithic zirconia ceramics is becoming popular because it simplifies the production of esthetic restorations. The effect of clinical adjustment on the optical properties of these ceramics, especially strength-gradient zirconia, remains unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the color and translucency of gradient multilayered zirconia brands after grinding and polishing.

MATERIAL AND METHODS

Sixty 10×10×1-mm monolithic zirconia specimens were milled from 6 zirconia brands (Ceramill Zolid HT White, Ceramill Zolid HT Preshade, Ceramill Zolid FX Multicolor, VITA YZ XT Multicolor, IPS e.max ZirCAD Prime, and KATANA YML). The zirconia specimens were milled to include all layers of A2 preshaded multilayered zirconia blanks (A2 shade) except Ceramill Zolid HT White and Ceramill Zolid HT Preshade. Ceramill Zolid HT White specimens were milled from a white zirconia blank with subsequent shading. The color coordinates and the relative translucency parameter after glazing and after grinding and polishing were determined with a reflectance spectrophotometer, and the relative translucency parameter and contrast ratio were measured. The differences in color and translucency were calculated. The data were analyzed using 2-way ANOVA and 1-way ANOVA tests followed by the post hoc Tukey test (α=.05).

RESULTS

Statistically significant changes (P<.001) in the color coordinates measured before and after grinding and polishing were detected for each zirconia brand except for the KATANA YML that showed no significant difference (P=.686) in lightness. The highest color difference after grinding and polishing was detected in group KATANA YML. The 2-way ANOVA test showed a statistically significant interaction (P<.001) between the zirconia brand and the grinding and polishing regarding the relative translucency parameter. The zirconia brand had a significant impact on the relative translucency parameter before and after grinding and polishing (both P<.001).

CONCLUSIONS

Except for KATANA YML, the color change in multilayered zirconia after clinical adjustment with polishing was not beyond the clinically acceptable limit of the color difference. Although clinical adjustment with polishing reduced the translucency of gradient zirconia, the change in translucency was below the clinically detectable threshold value of the translucency difference.

Impact of liner treatment on the translucency of CAD/CAM multi-colored lithium disilicate and multi-layered zirconia implant-supported crowns, and evaluation of fracture strength of ceramic crowns

This study aimed to evaluate the optical properties of liner-treated CAD/CAM Multi-colored lithium disilicate (Amber Mill Direct; AMD) and multi-layered zirconia (Omega multi; OM) implant-supported crowns, as well as their effect on the fracture strength of Ti or Zr abutments to which they were applied. After sintering AMD and OM ceramic blocks, they were classified into three groups: untreated, liner-treated, and liner-treated with added color. Optical properties were evaluated by analyzing color differences using background materials to assess translucency and the masking ability of liner-treated ceramics. Subsequently, the fracture strength of implant-supported crowns applied to Ti or Zr abutments was measured, and statistical analysis was conducted using Weibull statistics. Untreated AMD exhibited the highest translucency. Liner treatment reduced translucency in both ceramics, while color-added liner treatment increased translucency. Liner-treated AMD showed greater color difference compared to OM, whereas color-added liner treatment reduced the color difference. Fracture strength was highest in Ti abutment-OM crowns (548.03 N) and lowest in Zr abutment-AMD crowns (283.58 N). Additionally, the Weibull coefficient was over twice as high in Ti abutment-AMD crowns (m = 17.500). Color liners can adjust the high translucency of lithium disilicate ceramics to block discoloration, providing natural tooth-like color and enabling the creation of esthetic restorations. Furthermore, lithium disilicate ceramic crowns applied to Ti abutments exhibited high Weibull coefficients and fracture strengths.

The Influence of Thickness on Light Transmission for Pre- and Fully Crystallized Chairside CAD/CAM Lithium Disilicate Ceramics

AIM

This in vitro study aimed to compare the light-transmission properties of two chairside CAD/CAM lithium disilicate (LD) ceramics (a novel fully crystallized and a traditional pre-crystallized) across varying thicknesses.

MATERIALS AND METHODS

One hundred flat specimens were obtained from precrystallized (e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein) and fully crystallized (LiSi GC Block; GC, Tokyo, Japan) LD at five different thicknesses (0.5, 0.75, 1.0, 1.50 and 2.0 mm). All specimens were polished with a polishing system for lithium disilicate restorations following recommendations from the manufacturer. Light transmission was evaluated with a radiometer. The statistical analysis between e.max CAD and LiSi GC Block was performed using a Mann-Whitney test for each thickness at a significance level of 0.05 (p < 0.05), followed by a Kruskal-Wallis test to compare the light transmission between the thicknesses of e.max CAD and LiSi GC Block.

RESULTS

Light transmittance was significantly affected by ceramic thickness. The 0.5 mm thick specimens exhibited the highest transmittance values compared to all other groups, while a light transmittance of 0.00 was observed in the 2.0 mm thick specimens for both e.max CAD and LiSi GC Block. In the comparison between e.max CAD and LiSi GC Block according to thickness, there was a statistically significant difference exclusively between groups with a thickness of 1.50 mm (p = 0.002).

CONCLUSIONS

Light transmission for pre- and fully crystallized CAD/CAM lithium disilicate ceramics only showed a statistical difference at the thickness of 1.50 mm (p = 0.002). E.max CAD demonstrated acceptable light transmission up to a thickness of 1.5 mm.

CLINICAL SIGNIFICANCE

A thickness of 2 mm for chairside CAD/CAM lithium disilicate ceramics, whether pre-crystallized or fully crystallized, necessitates the use of dual-cure resin luting cement due to reduced light transmission.

Optimized 3D printed zirconia-reinforced leucite with antibacterial coating for dental applications

OBJECTIVES

This study aims to produce by robocasting leucite/zirconia pieces with suitable mechanical and tribological performance, convenient aesthetics, and antibacterial properties to be used in dental crown replacement.

METHODS

Leucite pastes reinforced with 12.5%, 25%, and 37.5% wt. ZrO2 nanoparticles were prepared and used to print samples that after sintering were characterized in terms of density, shrinkage, morphology, porosity, mechanical and tribological properties and translucency. A coating of silver diamine fluoride (SDF) and potassium iodide (KI) was applied over the most promising material. The material's antibacterial activity and cytotoxicity were assessed.

RESULTS

It was found that the increase of ZrO2 reinforcement up to 25% enhanced both microhardness and fracture toughness of the sintered composite. However, for a superior content of ZrO2, the increase of the porosity negatively affected the mechanical behaviour of the composite. Moreover, the composite with 25% ZrO2 exhibited neglectable wear in chewing simulator tests and induced the lowest wear on the antagonist dental cusps. Although this composite exhibited lower translucency than human teeth, it was three times higher than the ZrO2 glazed material. Coating this composite material with SDF+KI conferred antibacterial properties without inducing cytotoxicity.

SIGNIFICANCE

Robocasting of leucite reinforced with 25% ZrO2 led to best results. The obtained material revealed superior optical properties and tribomechanical behaviour compared to glazed ZrO2 (that is a common option in dental practice). Moreover, the application of SDF+KI coating impaired S. aureus proliferation, which anticipates its potential benefit for preventing pathogenic bacterial complications associated with prosthetic crown placement.

Translucency of recent zirconia materials and material-related variables affecting their translucency: a systematic review and meta-analysis

BACKGROUND

Recent forms of translucent zirconia material have been developed, offering a wide range of options and varieties for enhancing aesthetics, making it a preferred choice in the field of prosthetic dentistry. However, there is insufficient understanding regarding the recent types of zirconia materials and their optical behavior. Understanding the variables that influence the translucency of zirconia and identifying strategies to enhance its esthetics are crucial.

PURPOSE

The current systemic review highlights a comprehensive understanding of different zirconia generations in relation to their optical characteristics and evaluates material-related variables affecting their translucency.

METHODS

The present review studied in-vitro studies that evaluated the optical characteristics of different yttria content of yttria stabilized materials. The topics explored were: (1) the different zirconia material generations and their optical behavior; (2) material-related factors that affect their translucency. The research was restricted to online publication in the English language from July 1, 2010, to July 31, 2023, using PubMed, Scopus, and Science Direct resources. The search key terms and their combinations were "zirconia," "translucent zirconia," "cubic zirconia," "highly translucent zirconia," "yttria partially stabilized zirconia," "monolithic zirconia," "translucency," "optical properties," and "light transmission."

RESULTS

The data obtained from fifty-three studies addressed the optical characteristics of various zirconia generations. They reported that changing yttria content had a significant impact on translucency. Different kinds of zirconia ceramics of the same generation have varying translucencies. Achieving optimum aesthetics with monolithic zirconia is challenging due to factors related to material aspects such as the presence of additives, point defects, microstructure, thickness, phase distribution, and sintering conditions.

CONCLUSIONS

Newly developed monolithic dental zirconia ceramics have improved aesthetics and translucency. However, additional research is necessary to evaluate their performance and long-term durability.

TRIAL REGISTRATION

This systematic review was registered in PROSPERO, under number CRD42023474482.

Optical Characteristics of Monochrome and Multilayer Fully Stabilized Zirconia Upon Sintered Cooling Speed

OBJECTIVES

 Firing protocols influence optical properties of dental ceramics. Effects of varying cooling rates of monochrome and multilayer 5 mol% yttria-stabilized tetragonal polycrystalline (5YTZP) on optical properties are subjected for investigation.

MATERIALS AND METHODS

 Ninety specimens (width, length, thickness = 10 × 20 × 2 mm) were prepared from monochrome (Mo: Cercon xt) and multilayer (Mu: Cercon xt ML with cervical (C) and incisal (I) zoning) 5YTZP. Specimens were sintered and randomly treated with three cooling rates (n = 15/group): slow (S: 5°C/min), normal (N: 35°C/min), and fast (F: 70°C/min). Color appearance (∆EW), color appearance difference (∆E diff), translucency parameter (TP), contrast ratio (CR), and opalescence parameter (OP) were evaluated in CIEL*a*b* (Commission International de I'Eclairage) system. ∆E diff was achieved from the coordinate difference of specimen to VITA classic shade A2. Microstructures and compositions were evaluated by scanning electron microscope and energy dispersive spectroscopy. Monoclinic (m), tetragonal (t), and cubic (c) phases were investigated with X-ray diffraction.

STATISTICAL ANALYSIS

 An analysis of variance and Bonferroni multiple comparisons were determined for significant differences (p < 0.05).

RESULTS

 ΔEW of MoF was highest (66.04 ± 1.86), while MuN-I was lowest (62.60 ± 0.86). TP and OP of MoS were highest at 2.85 ± 0.11, and 2.25 ± 0.10, while MuF-I was lowest at 2.16 ± 0.10 and 1.60 ± 0.12. CR of MuF-I was highest (0.948 ± 0.005), while MoS was lowest (0.936 ± 0.005). ΔEdiff of MoF was highest (3.83), while MuN-I was lowest (0.93). Limited grain growth and m-phase composition were indicated upon fast cooling. There were significant differences for all color parameters due to varied materials, cooling rates, and their interactions (p < 0.05) except for interaction in ∆EW and OP.

CONCLUSIONS

 Translucency of monochrome and multilayer 5YTZP were different, possibly due to colorant additives. Incisal layer of multilayer 5YTZP was perfectly matched with VITA shade. Increasing cooling speed resulted in smaller grain size, t-m transformation, and finally lower translucency and opalescence. Therefore, to achieve most favorable optical properties, slow cooling rate is recommended.

Translucency and Strength of Lithium Disilicate for Computer-Aided Design and Manufacturing at Different Thermal Temperatures and Thicknesses: An In Vitro Study

To manufacture dental restorations composed of lithium disilicate (LD) through the computer-aided design and manufacturing (CAD/CAM) process, thermal refinement is an essential process that can affect the optical and mechanical properties of ceramics. In this study, we aimed to evaluate the translucency and flexural strength of lithium disilicate glass-ceramic for CAD/CAM using different thermal refinement schedules and thicknesses by measuring the total transmission of light through the specimen and calculating the peak load of the specimen until fracture in a piston-on-three-ball test, respectively. The results showed that a lower translucency was exhibited in thicker specimens, and the flexural strength decreased in the order of 1.0, 0.5, and 2.0 mm (p < 0.05). The lithium disilicates thermally refined at a heat of 820 degrees were shown to have the highest biaxial flexural strength (p < 0.05). These findings suggest that it is possible to adjust transparency and strength according to the clinical situation by choosing an appropriate thickness and thermal refinement process.

Effect of sintering time on microstructure and optical properties of yttria-partially stabilized monolithic zirconia

OBJECTIVES

To evaluate the impact of speed sintering on the microstructure and optical properties of 3 and 5 mol% yttria-partially stabilized monolithic zirconias.

METHODS

120 plate-shaped zirconia specimens (10x10x 0.4 mm) were prepared from three commercial 5 mol% yttria-partially stabilized zirconia blocks (5Y-PSZs); Katana UTML (Kuraray Noritake), Cercon xtML (Dentsply Sirona), and Zolid FX white (Amann Girrbach), and two commercial 3 mol% yttria-partially stabilized zirconia blocks (3Y-PSZs); Lava Plus (3 M ESPE) and InCoris (Sirona, GmbH). Specimens were either conventional sintered (CS) using a 7-hour program or speed sintered (SS) using a quick 90-minute program. The microstructure was inspected with a scanning electron microscope (SEM), and phase fractions were detected using x-ray diffraction analysis (XRD). Translucency (TP00), and contrast ratio (CR) were obtained using a spectrophotometer (VITA Easyshade V). Color difference (ΔE00) between both sintering processes was calculated with the CIEDE2000 formula. ΔE00 up to 1.8 was set as the acceptability threshold. Data were analyzed using two-way ANOVA, Krusakll-Wallis, and Mann-Whitney U tests. (n = 12, α = .05).

RESULTS

Grain size was significantly decreased after SS for all tested materials (P < .0001). The average grain sizes of 5Y-PSZs were significantly larger than those of 3Y-PSZs. The atomic structure, microstructure, and transparency of CS and SS were all affected by the amount of yttria, the size of the crystals, and tetragonality. SS significantly reduced TP00 (F = 7135.95, P < 0.0001) and increased CR (F = 453.21, P < 0.0001). The CS Katana presented the highest TP00 and lowest CR value. ΔE00 between the CS and SS groups were clinically acceptable except for Lava, which had values above the set threshold (1.89).

SIGNIFICANCE

SS altered the grain size and internal structure of the tested materials, which was reflected in translucency.

Effect of connector configuration on the fracture load in conventional and translucent zirconia three-unit fixed dental prostheses

PURPOSE

The purpose of this study was to determine the effect of the connector configuration on the fracture load in conventional and translucent zirconia of three-unit fixed dental prostheses (FDPs).

MATERIALS AND METHODS

Six different three-unit FDPs were prepared (n = 6) from three types of zirconia (3Y-TZP (Katana ML®), 4Y-TZP (Katana STML®), and 5Y-TZP (Katana UTML®)) in combination with two connector configurations (4 × 2.25, 3 × 3 mm). The Co-Cr master models were scanned, and the FDPs were designed and fabricated using CAD-CAM. The FDPs were cemented on the metal model and then loaded with a UTM at a crosshead speed of 1 mm/min until failure. Two-way ANOVA and Tukey's test were used for statistical analysis (α = .05).

RESULTS

Fracture loads of 3Y-TZP (2740.6 ± 469.2 and 2718.7 ± 339.0 N for size 4 × 2.25 mm and 3 × 3 mm, respectively) were significantly higher than those of 4Y-TZP (1868.3 ± 281.6 and 1663.6 ± 372.7 N, respectively) and 5Y-TZP (1588.0 ± 255.0 and 1559.1 ± 110.0 N, respectively) (P < .05). No significant difference was found between fracture loads of 4Y-TZP and 5Y-TZP (P > .05). The connector configuration within 9 mm2 was found to have no effect on the fracture loads on all three types of zirconia (P > .05).

CONCLUSION

Fracture loads of three-unit FDPs were affected by the type of zirconia. The fracture loads of conventional zirconia were higher than those of translucent zirconia. However, it was not affected by the connector configuration when the connector had a cross-sectional area of 9 mm2.

Optical effect of rapid sintering protocols on different types of zirconia

STATEMENT OF PROBLEM

Rapid sintering protocols are available for the fabrication of zirconia restorations, but whether rapid sintering influences color or translucency is unclear.

PURPOSE

The purpose of this in vitro study was to investigate the effect of different rapid sintering protocols on the color and translucency of cubic and tetragonal zirconias.

MATERIAL AND METHODS

Sixty disk-shaped specimens of 1-mm-thick cubic (DD CubeX2) and tetragonal (DD Bio ZX2) zirconia were investigated. Specimens of each type of zirconia were divided into three groups: conventional, speed, and superspeed sintering protocols. The conventional group of each zirconia type served as the control for calculating color differences. Translucency for each group was assessed by the translucency parameter and contrast ratio. Two-way analysis of variance was used for statistical analysis of the data (α=.05).

RESULTS

The translucency of cubic and tetragonal zirconia decreased after speed and superspeed sintering (P<.001). Superspeed sintering resulted in a greater color change than speed sintering (P<.001).

CONCLUSIONS

Rapid sintering protocols produced a significant effect on the color and translucency of cubic and tetragonal zirconias.

The mechanical properties, tribological behaviors and color stability of a feldspar nanoceramics strengthening extrinsic stain for high-translucent zirconia

The present work is aimed to explore the mechanical properties, tribological behaviors and color stability of nanoceramics and microceramics strengthened extrinsic stain coatings (NS and MS) upon high-translucent zirconia (TZ). The Na-rich feldspar ceramics component, microstructure and particle size of NS and MS were verified. The mechanical properties including elastic modulus and hardness of NS were enhanced compared to MS. Reciprocating wear tests under a ball-on-plate configuration manifested that the reduced coefficient of friction, wear depth and wear volume loss of NS was evaluated after 1 × 10 ⁴ cycles and the wear scar morphology of NS characterized by microcracks while MS featured more delamination and wear debris. Post toothbrushing simulation revealed that the color stability of extrinsic stain coatings was elevated with the addition of feldspar nanoceramics. The feldspar nanoceramics strengthening extrinsic stain exhibited enhanced elastic modulus, hardness, wear resistance and color stability, especially for TZ.

Layer characteristics in strength-gradient multilayered yttria-stabilized zirconia

OBJECTIVES

To investigate crystallography, translucency, phase content, microstructure and flexural strength of two commercial strength-gradient multilayered dental zirconia grades.

METHODS

Two zirconia grades, i.e., KATANA Zirconia YML (Kuraray Noritake; referred to as "YML"; composed of four layers: enamel, body 1-3) and IPS e.max ZirCAD Prime (Ivoclar Vivadent; referred to as "Prime"; composed of three layers: enamel, transition, body) were investigated. Fully sintered square-shaped zirconia specimens from each layer were prepared. Microstructure, chemical composition, translucency parameter and zirconia-phase composition of each layer were characterized. Four-point and biaxial flexural strength of each layer was measured using fully sintered bar- and square-shaped specimens. Square-shaped samples were used to measure strength across the layers.

RESULTS

For both multilayer zirconia grades, the 'enamel' layer contains a higher amount of c-ZrO₂, which resulted in higher translucency but lower flexural strength than the 'body' layers. The characteristic 4-point flexural strength of the YML 'body 2' (923 MPa) and 'body 3' (911 MPa) layers, and of the Prime 'body' (989 MPa) layer were comparable and higher than for the YML 'enamel' (634 MPa), Prime 'transition' (693 MPa) and 'enamel' (535 MPa) layers. The biaxial strength of specimens sectioned across the layers was in-between that of the 'enamel' and 'body' layers for both YML and Prime, implying the interfaces did not form a weak link.

SIGNIFICANCE

The difference in yttria content affects the phase composition and mechanical properties of each layer of the multi-layer zirconia. The strength-gradient approach allowed to integrate monoliths with irreconcilable properties.

Aesthetic and functional rehabilitation of collapsed occlusal vertical dimension using an advanced digital workflow

This report presents a clinical case that follows a comprehensive digital workflow to increase occlusal vertical dimension of a patient presenting with occlusal wear. A 56-year-old patient with aesthetic and functional problems presented to the authors' clinic. An intraoral scanner was used to obtain digital models of the patient's existing maxillary and mandibular arches. Advanced sculpting software and digital tooth libraries were used to design the patient's ideal smile. A three-dimensional (3D) printer was used to fabricate temporary restorations and resin casts. Full-mouth restoration was successfully completed with zirconia crowns using an advanced digital workflow.

An engineering perspective of ceramics applied in dental reconstructions

The demands for dental materials continue to grow, driven by the desire to reach a better performance than currently achieved by the available materials. In the dental restorative ceramic field, the structures evolved from the metal-ceramic systems to highly translucent multilayered zirconia, aiming not only for tailored mechanical properties but also for the aesthetics to mimic natural teeth. Ceramics are widely used in prosthetic dentistry due to their attractive clinical properties, including high strength, biocompatibility, chemical stability, and a good combination of optical properties. Metal-ceramics type has always been the golden standard of dental reconstruction. However, this system lacks aesthetic aspects. For this reason, efforts are made to develop materials that met both the mechanical features necessary for the safe performance of the restoration as well as the aesthetic aspects, aiming for a beautiful smile. In this field, glass and high-strength core ceramics have been highly investigated for applications in dental restoration due to their excellent combination of mechanical properties and translucency. However, since these are recent materials when compared with the metal-ceramic system, many studies are still required to guarantee the quality and longevity of these systems. Therefore, a background on available dental materials properties is a starting point to provoke a discussion on the development of potential alternatives to rehabilitate lost hard and soft tissue structures with ceramic-based tooth and implant-supported reconstructions. This review aims to bring the most recent materials research of the two major categories of ceramic restorations: ceramic-metal system and all-ceramic restorations. The practical aspects are herein presented regarding the evolution and development of materials, technologies applications, strength, color, and aesthetics. A trend was observed to use high-strength core ceramics type due to their ability to be manufactured by CAD/CAM technology. In addition, the impacts of COVID-19 on the market of dental restorative ceramics are presented.

Grain size, crystalline phase and fracture toughness of the monolithic zirconia

PURPOSE

This study evaluated the relationship among translucency, crystalline phase, grain size, and fracture toughness of zirconia.

MATERIALS AND METHODS

Four commercial zirconia - Prettau®Anterior® (PA), Prettau® (P), InCorisZI (ZI), and InCorisTZI (TZI)- were selected for this study. The bar specimens were prepared to determine fracture toughness by using chevron notched beam method with four-point bending test. The grain size was evaluated by a mean linear intercept method using a scanning electron microscope. X-ray diffraction and Rietveld refinement were performed to evaluate the amount of tetragonal and cubic phases of zirconia. Contrast ratio (CR) was measured to investigate the level of translucency.

RESULTS

PA had the lowest fracture toughness among other groups (P < .05). In addition, the mean fracture toughness of P was significantly less than that of ZI, but there was no difference compared with TZI. Regarding grain size measurement, PA had the largest average grain size among the groups. P obtained larger grain size than ZI and TZI (P < .05). However, there was no significant difference between ZI and TZI. Moreover, PA had the lowest CR value compared with the other groups (P < .05). This means PA was the most translucent material in this study. Rietveld refinement found that PA presented the greatest percentage of cubic phase, followed by TZI, ZI, and P, respectively.

CONCLUSION

The different approaches are used by manufacturers to fabricate various types of translucent zirconia with different levels of translucency and mechanical properties, which should be concerned for material selection for successful clinical outcome.

Effect of Different Shading Techniques on the Color of Zirconia Ceramic Restoration (An In vivo Study)

BACKGROUND: The color of all ceramic restorations has a significant effect on the final appearance of the restoration. AIM: This study aimed to evaluate the effect of different shading techniques on the color stability of monolithic zirconia crowns cemented on the upper anterior teeth. METHODS: In this study, there were nine patients. Each patient has undergone a reduction for the upper six anterior teeth. Fifty-four zirconia jacket crowns were constructed using CAD/CAM technique. According to the shading technique, the crowns were categorized into two groups (pre-shaded and liquid shaded), where the upper right reduced teeth received pre-shaded zirconia crowns while the upper left reduced teeth received liquid-shaded zirconia crowns according to the selected shade. The color was assessed using easy shade after cementation and 1 year follow-up period. Data were collected, tabulated, and statistically analyzed. RESULTS: Color change (ΔE) of the cemented pre-shaded zirconia crowns on the upper right central incisors, lateral incisors, and canines was 2.37, 2.84, and 1.92, respectively, while color change (ΔE) of the cemented liquid-shaded zirconia crowns on the upper left central incisors, lateral incisors, and canines was 2.52, 2.88, and 2.77, respectively. Color change of both pre-shaded and liquid-shaded zirconia crowns after 1 year follow-up was within the clinically acceptable range 1>E>3.7, and there was no significant difference between them. CONCLUSIONS: The aging and technique of shading had no significant effect on the color of zirconia ceramic.

Biomechanical comparison of different prosthetic materials and posterior implant angles in all-on-4 treatment concept by three-dimensional finite element analysis

The study aimed to evaluate the biomechanical behaviors of different prosthetic materials and posterior implant angles in All-on-4 implant-supported fixed maxillary prostheses with three-dimensional (3D) finite element analysis. The model of complete edentulous maxilla was created using the Rhinoceros and VRMesh Studio programs. Anterior vertical and 17°- and 30°-angled posterior implants were positioned with All-on-4 design. Straigth and angled multi-unit abutments scanned using a 3D scanner. Two different prosthetic superstructures (monolithic zirconia framework and lithium disilicate veneer (ZL) and monolithic zirconia-reinforced lithium silicate (ZLS)) were modeled. Four models designed according to the prosthetic structure and posterior implant angles. Posterior vertical bilateral loading and frontal oblique loading was performed. The principal stresses (bone tissues-Pmax and Pmin) and von Mises equivalent stresses (implant and prosthetic structures) were analyzed. In all models, the highest Pmax stress values were calculated under posterior bilateral loading in cortical bone. The highest von Mises stress levels occured in the posterior implants under posterior bilateral load (260.33 and 219.50 MPa) in the ZL-17 and ZL-30 models, respectively. Under both loads, higher stress levels in prosthetic structures were shown in the ZLS models compared with ZL models. There was no difference between posterior implant angles on stress distribution occurred in implant material and alveolar bone tissue. ZLS and ZL prosthetic structures can be reliably used in maxillary All-on-4 rehabilitation.

An In Vitro Study to Evaluate the Effect of Artificial Aging on Translucency, Contrast Ratio, and Color of Zirconia Dental Ceramic at Different Sintering Levels

Increasing demands for aesthetically pleasing dental restorations have promoted the use of materials that display superior optical properties. Zirconia-based all-ceramic systems have good optical properties, thus providing the desired esthetics for dental restorations. The altered oral conditions impact the physical properties of these materials. Multiple studies have been conducted to evaluate the effect of aging on the mechanical properties of computerized-aided design and computerized-aided manufacturing (CAD/CAM)-based zirconia; however, there is a scarcity of literature discussing the effect of aging on change in translucency, contrast ratio, and color. Therefore, this research aimed to evaluate the effect of accelerated artificial aging on translucency parameter (TP), contrast ratio (CR), and color of CAD/CAM zirconia at different sintering temperatures. Twenty-eight rectangular-shaped specimens were obtained by CAD/CAM milling of zirconia blank. Sintering of the samples was carried out at four different temperatures 1350 °C, 1400 °C, 1450 °C, and 1500 °C, respectively. Thermocycling of the samples was performed in a thermocycler. TP, CR, and color evaluation of all the samples was done again using a Spectrophotometer. Data acquired were statistically evaluated by one-way ANOVA and Post Hoc test. The highest amount of change in TP was recorded for specimens sintered at 1400 °C (1.86), whereas the least change was attributed to 1350 °C (0.51). The highest change in CR was observed in specimens sintered at 1500 °C (0.0971), and the least change in CR was observed at 1450 °C (0.0086). The highest ΔE values were recorded for 1400 °C against both white (1.86) and black background (2.17), whereas the least change was attributed to 1350 °C against white (0.86) and against a black background (1.41). The changes in TP were significant, but CR did not show any significant change. ΔE values for all the experimental groups were significant, but were below the clinically perceptible range. An increase in sintering temperature increased the translucency.

Effect of grinding on the optical properties of monolithic zirconia

OBJECTIVES

The purpose of this study was to analyze the color infiltration in monolithic zirconia after grinding, which plays an essential role in the color stability of restorations after occlusal adjustment.

METHODS

One hundred and eight white zirconia plates (36 Dentsply Sirona-Cercon high translucency [C], 36 Zirkonzahn-Prettau [P], 36 Zirkonzahn-Prettau anterior [Pa]) were stained by infiltration with target colors Vita A2, A3.5, and A4. In a standardized experimental setup, all plates were grinded in nine successive steps (from baseline to 500 μm), and color was measured with a spectroradiometer at each grinding step. Color differences ΔE₀₀ between initial color and after each grinding step were calculated. The data was analyzed using regression, Kruskal-Wallis test, inverse prediction, and simultaneous 95%-confidence intervals.

RESULTS

Grinding had a significant effect on color stability across all zirconia types and target colors (p < 0.001). At each cut level and target color, ΔE₀₀ means for groups C, P, and Pa were statistically different (p < 0.05). Among the three zirconia types, Pa had the lowest ΔE₀₀ mean score for cut levels 20-100 μm for A2 and between 50 and 300 μm for A3.5 and A4. For all other cut levels, differences between Pa and P were not significant (α = 0.05). C had the largest mean ΔE₀₀ except for A4 until 100 μm, where it was second best.

CONCLUSION

Zirconia type had a significant effect on the color infiltration depth across all target colors. Pa showed the best color stability until 150 μm material reduction, whereas C presented significantly less color stability than the other two zirconia materials.

CLINICAL SIGNIFICANCE

Color stability is important for minimizing the risk of restoration failure due to unacceptable color changes after grinding. Pa is less susceptible to color change and has an additional buffer of 60 μm until exceeding the color acceptability threshold. When higher flexural strength is needed, P is to be preferred.

Optical properties of monolithic zirconia crowns: In vitro and In vivo evaluation

Background/Aim: The aim of this study was to compare the monolithic and layered zirconia crowns by their optical property of translucency, using in vitro and in vivo evaluation methods. Material and Methods: One upper incisor and one canine were prepared to receive 6 monolithic Lava Plus HT and 6 layered Lava crowns using the CAD/CAM technology. The translucency in the vitro evaluation, was determined using a digital photoradiometer to measure the light reflected by the crowns in two different conditions, natural and metal plated abutment tooth. A provisional complete prosthesis of an edentulous patient, with the abutment teeth mounted in their anatomical position, was used for the in vivo evaluation. The crowns were randomly placed and evaluated by two independent operators in the oral cavity conditions. Results: In vitro results showed that monolithic crowns were not significantly less translucent than layered ones in both incisor (p=0.098) and canine (p=0.340): contrast ratio 0.978 vs. 0.956 and 0.941 vs. 0.929, respectively (Student -t test; a=0.05). In vivo evaluation results showed that the difference in the luminance was not statistically significant between Lava Plus HT and layered Lava crowns according to Mann Whitney Test, p=0.089 (a=0.01). Conclusions: The difference in translucency between monolithic and layered zirconia crowns was not statistically significant both in vitro and in vivo evaluation. Monolithic zirconia had a good masking ability of the abutment tooth.

Influence of zirconia/glass veneer thickness and implant abutment material on the final shade of implant restorations

Aim

The aim of this study was to investigate the combined effect of ceramic material, ceramic thickness, and implant abutment background to the final color of restorations.

Settings and Design

This was a comparative in vitro study.

Materials and Methods

Three different types of monolithic and porcelain-veneered zirconia disc-shaped specimens (Prettau Anterior, VITA YZ ST, and VITA YZ HT) were prepared in A3 shade with two different thicknesses (1 mm and 1.5 mm) (n = 10). Each zirconia material was made of 4-mm thickness as a control specimen of each monolithic zirconia type, and 4-mm thick veneering ceramic (VITA VM9 Base Dentine) was made as a control for veneered zirconia groups. Three simulated implant abutments were fabricated from titanium, white-shaded and yellow-shaded zirconia. The zirconia specimens were placed on different abutment backgrounds, and the color difference (ΔE) between experimental and control specimens was measured.

Statistical Analysis Used

The three-way ANOVA and the Scheffé test were used for data analysis (α = 0.05).

Results

The mean ΔE values between two thicknesses were significantly different in every background for all zirconia materials. The ΔE values of zirconia specimens on yellow zirconia were lower than those of other abutments. The clinically acceptable ΔE value (ΔE <3) was found in some monolithic zirconia specimens on white-shaded and yellow-shaded abutments, while the ΔE value is approximately 3 or less in all 1.5-mm thick porcelain-veneered zirconia groups.

Conclusions

Different zirconia materials on implant abutments affected the final color of restorations. To achieve satisfactory color, the minimum thickness of zirconia restorations should be at least 1.5 mm on yellow zirconia abutment.

Effect of different zirconia surface pretreatments on the flexural strength of veneered Y-TZP ceramic before and after in vitro aging

PURPOSE

The investigation of zirconia core surface pretreatments on the flexural strength of bilayered zirconia ceramics before and after artificial accelerating aging.

METHODS

Ninety bar-shaped specimens were manufactured from Yttria Stabilized Tetragonal Zirconia Polycrystal (Y-TZP) and divided in three groups depending on zirconia surface pretreatment before veneering: layering with liner, pretreatment with silane-containing gas flame (SGF) with the Silano-Pen device and alumina air-abrasion. Half of the veneered specimens in each group (n=15) underwent artificial accelerating aging. A 4-point bending test was performed to determine flexural strength. Three specimens from each group were further analyzed using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) before veneering and after fracture (aged and non-aged subgroups).

RESULTS

Alumina air-abrasion was correlated to increased phase transformation from tetragonal to monoclinic zirconia phase. Qualitative analysis revealed that with the majority of the specimens pretreated with the silane-containing gas flame, areas of the veneering material remained firmly attached to the zirconia core after flexural strength testing. There was no statistically significant difference on the flexural strength among the groups before or after aging. Artificial accelerating aging resulted in statistically significant higher flexural strength of the specimens after aging.

CONCLUSION

SGF pretreatment can be an acceptable and feasible alternative method before the veneering of Y-TZP zirconia as it presented slightly higher bond strength compared with alumina air-abrasion which was associated with higher tetragonal to monoclinic (t→m) phase transformation. Accelerating aging leads to an increase of the mechanical properties under in vitro conditions.

Spectrophotometric study determining staining tendency in different restorative materials (longitudinal in vitro study)

Aim

Our aim was to measure the discolouration degrees in a packable composite, zircon, ceramic, a flowable composite, and GIC (glass isomer cement) and to determine their tendencies to discolour to provide guidance to dentists and prosthodontist for choosing proper materials for cases in which aesthetics is the main treatment goal.

Materials and methods

Sixty discs were fabricated from the composite, zircon, ceramic, the flowable composite, and GIC, and natural teeth were the control group. The shades were recorded using the Ivoclar Vivadent Shade Guide, and readings were recorded from a Vita Easyshade 4.0 spectrophotometer before immersion, after 1 week, 2 weeks, 3 weeks, and 24 weeks of immersion in coffee. The analysis was performed using a SPSS paired t-test and CIE 76 formula.

Results

The ceramic had a starting shade of B1 and kept the same colour throughout the testing period. Zircon had a starting shade of A3 and transitioned to B3 by the second week. The composite had a shade of A1, and after the first week, it was A4; in the second week and afterwards, it was C4. The flowable composite had a starting shade of A1, and after one week, the shade was B3, and then after one more week A3.5; after five months, it was A4.

Conclusion

The ceramic showed no change, making it ideal for aesthetic regions and anterior replacements. Zircon had the second-highest colour stability, whereas all the other materials showed variable degrees of colour and surface changes, making them not ideal choices for anterior restorations. Thus, this information can aid choices for aesthetic regions to provide the highest longevity.

Step-by-Step Esthetic Rehabilitation with Chairside System

In modern dentistry, Computer-Aided Design and Manufacturing (CAD/CAM) is a promising technology that allows fabrication of prosthetic restorations through milling procedures. Over years, with the continuous improvement of technology, direct CAD/CAM or “chairside” technology is becoming a widespread approach which offers immediate rehabilitation with long-term rates reported by several studies compared to conventional techniques. All steps are generally carried out in the dental office during the same treatment session. The present paper is about a healthy female patient with a decayed 36 tooth which was restored by ceramic onlay using Planmeca's PlanCAD system. Through the present clinical case, a detailed protocol of chairside technology would be presented from the digital impression to the milling process. It would detail impression steps. It would also highlight especially the virtual design confection of prosthetic restoration using a biogeneric model included in the software. It also illustrated tools which could be used by the dentist to perform the design. Also, some useful tips would be presented in order to perform the confection. On this subject, various studies showed the viability of such technology. To summarize, referring to previous studies, this promising technology allows especially time-saving and patient's comfort compared to the indirect one.

High bonding strength between zirconia and composite resin based on combined surface treatment for dental restorations

Zirconia is the preferred material for dental restorations; however, dental restorations are usually affected by zirconia fractures due to chipping and delamination of the veneer ceramic. One effective solution for repairing chemically inert zirconia frameworks is to strongly chemically bond them with the composite resin via surface modification. Thus, the bonding strength between the zirconia and composite resin determines the performance of dental restoration. Herein, we investigate the shear bond strength between zirconia ceramic and two ceramic repair systems before and after thermal cycling based on different surface pretreatments, including air-abrasion and a novel silane coupling agent. When treated with combined sandblasting, novel silane and 10-methacryloyloxydecyl hydrogen phosphate act as a bonding agent for the zirconia surface, and the maximum shear bond strength achieves 27.5 MPa, as measured by a universal testing machine through the average of 16 separate measurements. The results show that the combined treatment resists the interface damage caused by expansion and contraction during thermal cycling. The long-term bond durability is due to the micro-mechanical bond force formed by resin and ceramic, and the chemical bonds of Zr-O-Si at the interface. Results indicate that selective pretreating the surface results in high bond strength between the zirconia and the composite resin, which is meaningful to optimize dental restoration.

Translucency of Monolithic Zirconia after Hydrothermal Aging: A Review of In Vitro Studies

PURPOSE

Recent modifications in composition, structure, and fabrication methods have led to monolithic zirconia ceramics of superior translucency. However, during aging, intrinsic microstructural features, such as grain boundaries and pores, may affect light scattering and consequently the translucency of zirconia. The aim of this study was to systematically review if hydrothermal aging affects the translucency of monolithic zirconia.

MATERIALS AND METHODS

An electronic search in Medline and Scopus was conducted to identify the effect of hydrothermal aging on the translucency of zirconia. The search was limited to English-language publications and in vitro studies. The following search terms were used alone or in combination: "monolithic zirconia," "full contour zirconia," "Y-TZP zirconia," "tetragonal zirconia," "cubic zirconia," "aging," "hydrothermal aging," "steam autoclave," "translucency," "translucency parameter," and "contrast ratio." From the titles found after searching the electronic databases, only 10 articles met the inclusion criteria and were included in this review. The translucency parameter or total transmittance was used to extract data from the studies.

RESULTS

Aging reduced the translucency of monolithic zirconia in most of the studies; however, the differences varied according to the brand tested and the microstructure and thickness of the specimens. The thinner specimens presented higher translucency alterations. Although in all studies a change in translucency was recorded, its mean values suggest that the differences are within the acceptability threshold in most cases, independent of the color system used to calculate translucent parameter, so they are clinically undetectable. For longer aging times, beyond the perspective clinical life of the restorations, the change in translucency is higher than the acceptability threshold.

CONCLUSIONS

There is a controversy regarding how aging affects the translucency of monolithic zirconia ceramics; however, this may not be clinically important, as in most cases, changes (either decrease or increase) in translucency were within the acceptability thresholds.

Influence of resin cement shade on the color and translucency of zirconia crowns

Background

Zirconia crowns are highly attractive for clinicians, although have poor translucency when used as single restorations, in addition to unknown effect of resin cement shade on final cemented crown shade. This study aimed to assess effect of resin cement opacity on color replication potential of different zirconia frameworks with target tooth color, in addition to different zirconia crowns translucency evaluation.

Material and Methods

Twenty-four zirconia crown restorations were fabricated to restore single central maxillary incisor for 8 patients, divided into 3 groups according to color and type of zirconia used (white Zr core, colored Zr core and monolithic HT Zrcowns). Each group was further subdivided into 2 subgroups according to resin cement shade. Using Easyshade spectrophotometer, Delta E color difference was calculated between each crown parameters using 2 different resin luting cement shades and adjacent target tooth. Translucency parameters (TP) were tested for finished crowns. ΔEs obtained were assessed based on ΔEof 1.6 which represented color difference that could not be detected by human eye and considered clinically acceptable.

Results

No statistically significant values were found between subgroups related to different resin cement shade. Translucency parameters showed statistically significant different values. Monolithic crowns showed highest translucency parameters followed by Zr crowns on white cores then Zr crowns on colored cores.

Conclusions

Resin cement shade didn’t affect final color perception. Monolithic high translucency crowns usage gained advantages of high translucency and delamination prevention. Zirconia crowns could be cemented by opaque or transparent cement without affecting final color.

Key words:Zirconia, resin cement, monolithic, translucency, spectrophotometer, Delta E.

The effects of repetitive firing processes on the optical, thermal, and phase formation changes of zirconia

PURPOSE

The aim of this study was to investigate the effect of different numbers of heat treatments applied to superstructure porcelain on optical, thermal, and phase formation properties of zirconia.

MATERIALS AND METHODS

Forty zirconia specimens were prepared in the form of rectangular prism. Specimens were divided into four groups (n = 10) according to the number of firing at heating values of porcelain. Color differences and translucency parameter were measured, and X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC) were performed. Data were analyzed with analysis of variance (ANOVA).

RESULTS

There were no statistically significant differences in ΔE, TP, L, a, and b value changes of the zirconia specimens as a result of repetitive firing processes (P>.05).

CONCLUSION

Although additional firing processes up to 4 increase peak density in thermal analysis, additional firing processes up to 4 times can be applied safely as they do not result in a change in color and phase character of zircon frameworks.

Effect of different cement systems and aging on the bond strength of chairside CAD-CAM ceramics

STATEMENT OF PROBLEM

The bond strength of different chairside computer-aided design and computer-aided manufacturing (CAD-CAM) restorative materials to dentin with different resin cements needs to be evaluated.

PURPOSE

The purpose of this in vitro study was to investigate the effect of 3 different cementation systems after thermal aging on the shear bond strength of different CAD-CAM materials.

MATERIAL AND METHODS

The occlusal surfaces of 63 molar teeth of similar size were removed, and 21 zirconia-reinforced lithium disilicate (Vita Suprinity-VS), 21 polymer infiltrated ceramic (Vita Enamic-VE), and 21 resin nanoceramic (GC Cerasmart-GC) rectangular specimens of 2.5 mm in thickness were obtained. The ceramics were cemented using total etch (TE), self-etch (SE), and self-adhesive (SA) cement systems. Half of the specimens were subjected to thermal aging with 5000 cycles. The shear bond strength test of all the specimens was measured. Fractured ceramic surfaces were examined by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) analysis. The Shapiro-Wilk test, 3-way analysis of variance (ANOVA), and Fisher Least Significant Difference (LSD) tests were used to analyze the shear bond strength test data (α=.05).

RESULTS

The highest bond strength value was found in the nonthermal aged VS-TE and the lowest in the thermal aged VE-TE. Significant interaction was found between TE and SE cemented ceramics (P<.001). For specimens cemented with the SA system, significant interaction was found among ceramics with thermal aged specimens (P<.001). Thermal aging significantly decreased the mean bond strength (P<.05).

CONCLUSIONS

Differences in bond strength were observed in chairside CAD-CAM ceramics when cemented with TE, SE, and SA systems. Additionally, thermal aging significantly reduced the bond strength values of all the ceramic materials, regardless of the cementation procedure. Clinicians should consider these variables and choose the most suitable cementation systems for the material used.

Influence of core color on final shade reproduction of zirconia crown in single central incisor situation - An in vivo study

Background

A lot of shaded zirconia blocks are being introduced into the market. Their effect on the final shade of the restoration is yet uncertain.

Material and Methods

Twenty-four zirconia crowns were fabricated for 8 patients who needed to restore a single maxillary central incisor, and divided into 3 groups according to the color and type of the zirconia (Zr) used (white Zr core, colored Zr core, and monolithic high translucency (ht) Zr crowns). Using Easyshade spectrophotometer, delta E color difference was calculated between fabricated crown and adjacent tooth. The ΔEs obtained were assessed based on 1.6 ΔE which represented the color difference that could not be detected by the human eye and considered clinically acceptable.

Results

No statistically significant values were found between the 3 groups related to different Zr color and type.

Conclusions

Within the limitations of this study, it could be concluded that the shade of the zirconia blank had no significant effect on the final color of the crown. This raises reasonable doubt about the necessity to use colored zirconia blanks or use of dip-in solutions. The clinical implications were that, there was no need to use colored zirconia cores to get more esthetically pleasing restorations with respect to color perception. The use of monolithic high translucent zirconia crowns gained the advantages of high translucency and color reproduction. Key words:Zirconia, easyshade, monolithic, spectrophotometer, delta E.

Zirconia toughened mica glass ceramics for dental restorations: Wear, thermal, optical and cytocompatibility properties

BACKGROUND

In an effort to design novel zirconia reinforced mica glass ceramics for dental restorations, clinically relevant properties such as wear, coefficient of thermal expansion, optical transmittance, and cytocompatibility with human gingival fibroblast cell lines were investigated in the present study.

MATERIALS & METHODS

Microstructure analysis of two body wear of heat treated mica glass ceramic ceramics (47.2 SiO2-16.7 Al2O3-9.5 K2O-14.5 MgO-8.5 B2O3-6.3F wt.%) reinforced with 20wt.% YSZ, were evaluated against a steatite antagonist in a chewing simulator following Willytec Munich method. In addition, Coefficient of thermal expansion (CTE), total transmittance, scattering coefficient and cytocompatibility on human gingival fibroblast cell lines were performed and compared to the commercially available dental ceramic systems.

RESULTS

The experimental mica glass ceramic demonstrate micro-ploughing, pull out and debris formation along the cutting surface, indicating abrasive wear mechanism. Thermal expansion of mica glass ceramic composite was recorded as 5×10-6/°C, which is lower than the thermal expansion of commercially available core and veneering ceramics. Further, significant differences of transmittance and scattering coefficient of mica glass ceramics with 20wt.% YSZ with commercial dental ceramics was found and extensive fibroblast cell spreading with filopodial extension, cell-to-cell bridges and proliferation with human gingival fibroblast cell lines.

CONCLUSION

With acceptable cytocompatibility with human gingival fibroblast cells and better wear properties with respect to commercial IPS emax Press, the mica glass ceramic composites (47.2 SiO2-16.7Al2O3-9.5 K2O-14.5 MgO-8.5 B2O3-6.3F wt.%) with 20wt.% YSZ have the potential for dental restorative applications as machinable veneering ceramics.

Does the application of surface treatments in different sintering stages affect flexural strength and optical properties of zirconia?

OBJECTIVE

To investigate the influence of surface treatments conducted in presintering and postsintering stages on flexural strength and optical properties of zirconia.

MATERIALS AND METHODS

Specimens were milled from partially sintered zirconia blocks in different geometries and divided into three main groups as presintered, postsintered, and control groups. Test groups were further divided into three subgroups (n = 10) according to the surface treatments conducted (grinding, Er,Cr:YSGG laser irradiation, air-borne particle abrasion [APA]). Four-point flexural strength (σ) test and Weibull analysis were conducted. Color differences (ΔE₀₀ ) and translucency parameter (TP_ab ) were calculated with a spectrophotometer. Surfaces of specimens were scrutinized under FESEM. Data were statistically analyzed.

RESULTS

Postsintered groups exhibited higher σ values (P < .05). Within all groups, highest and lowest σ values were detected at postsintered and presintered APA groups, respectively (P < .05). All ΔE₀₀ values were above the perceptibility threshold (ΔE₀₀  > 0.8). Higher TP_ab values were obtained and deeper scratches were observed in presintered groups.

CONCLUSIONS

Surface treatments performed at postsintering stage had a favorable effect on the flexural strength of all specimens. Surface treatments performed before sintering increased translucency and caused higher ΔE₀₀ values.

CLINICAL SIGNIFICANCE

Surface treatments performed at different sintering stages can alter mechanical and optical properties of zirconia.

Influence of thermal tempering processes on color characteristics of different monolithic computer-assisted design and computer-assisted manufacturing ceramic materials

Background

The optical properties of dental restoration were influenced by the sintering parameters. This study investigated the effects of different tempering processes on optical properties of three monolithic Cad-Cam ceramics.

Material and Methods

135 monolithic material bars (4 mm width, 14 mm length, 1.2 mm thickness) were prepared from yttria-stabilized tetragonal zirconia polycrystalline (inCoris TZI, I), zirconia-reinforced lithium silicate (Vita Suprinity, V), and lithium disilicate glass (e.max CAD, E) ceramics, with different tempering processes through slow (S), normal (N), and fast (F) cooling (n=15). The color appearance (∆EW), translucency parameter (TP), contrast ratio (CR), and opalescence parameter (OP) were determined. ANOVA and Bonferroni's multiple comparisons were determined for significant difference (α=0.05). The grain sizes were microscopically examined by scanning electron microscope. The phase transformation of zirconia was determined using X ray diffraction.

Results

The mean±sd of ΔEW, TP, CR, OP were 74.15±0.46, 1.26±0.15, 0.977±0.006, 1.02±0.12 for IS; 74.00±0.83, 1.27±0.19, 0.977±0.007, 1.02±0.12 for IN; 74.44±0.64, 1.70±0.08, 0.965±0.003, 1.30±0.07 for IF; 73.35±1.32, 2.44±0.24, 0.958±0.006, 2.10±0.20 for VS; 66.37±0.88, 4.05±0.3, 0.911±0.010, 3.18±0.20 for VN; 67.02±0.65, 3.79±0.17, 0.919±0.006, 3.01±0.13 for VF; 60.01±0.30, 5.53±0.17, 0.821±0.006, 2.71±0.06 for ES; 60.18±0.23, 5.49±0.17, 0.822±0.006, 2.66±0.05 for EN; and 59.82±0.26, 5.36±0.06, 0.826±0.002, 2.64±0.07 for EF. The color parameters were significantly affected by type of materials, tempering processes, and their interactions (p<0.05). Phase transformation from t→m related with tempering procedure for zirconia.

Conclusions

Rapid thermal tempering process of Y-TZP resulted in larger grain size and t→m phase transformation leading to higher translucency. To achieve optimum translucency, a fast thermal tempering process was suggested for inCoris TZI and IPS e.max CAD, whilst a normal tempering process was recommended for Vita Suprinity. Key words:Color, cooling process, contrast, opalescence, thermal tempering, translucency.

Monolithic Zirconia: An Update to Current Knowledge. Optical Properties, Wear, and Clinical Performance

The purpose of this paper was to update the knowledge concerning the wear, translucency, as well as clinical performance of monolithic zirconia ceramics, aiming at highlighting their advantages and weaknesses through data presented in recent literature. New ultra-translucent and multicolor monolithic zirconia ceramics present considerably improved aesthetics and translucency, which, according to the literature reviewed, is similar to those of the more translucent lithium disilicate ceramics. A profound advantage is their high strength at thin geometries preserving their mechanical integrity. Based on the reviewed articles, monolithic zirconia ceramics cause minimal wear of antagonists, especially if appropriately polished, although no evidence still exists regarding the ultra-translucent compositions. Concerning the survival of monolithic zirconia restorations, the present review demonstrates the findings of the existing short-term studies, which reveal promising results after evaluating their performance for up to 5 or 7 years. Although a significant increase in translucency has been achieved, new translucent monolithic zirconia ceramics have to be further evaluated both in vitro and in vivo for their long-term potential to preserve their outstanding properties. Due to limited studies evaluating the wear properties of ultra-translucent material, no sound conclusions can be made, whereas well-designed clinical studies are urgently needed to enlighten issues of prognosis and long-term survival.

Effects of veneering porcelain thickness and background shade on the shade match of zirconia-based restorations

Background. Effects of veneering porcelain thickness and background shade on the shade match of zirconia-based restorations are unclear. The aim of this study was to evaluate the impacts of veneering porcelain thickness and background shade on the shade match of zirconia-based restorations.

Methods. Forty A2 shade veneered zirconia disk specimens (10 mm in diameter) were fabricated, with veneering porcelain thicknesses of 1.6, 1.8, 2.0 and 2.2 mm. Three backgrounds were made of A2 shade composite resin (A2), nickel-chromium alloy (NC) and amalgam (AM). The veneered zirconia specimens were placed on the backgrounds. CIELab values were measured with a spectrophotometer. ΔE values were measured to determine color differences between the specimens and the A2 VITA classical shade (target shade). ΔE values were compared with an acceptability threshold (ΔE=3.7). Repeated measures ANOVA, Bonferroni, and 1-sample t-test were used to analyze data (P<0.05).

Results. Mean ΔE values ranged between 1.9 and 5.0. The veneering porcelain thickness, the background shade and their interaction affected the ΔE (P<0.0001). The minimum veneering porcelain thickness for the shade match was 2 mm for NC and 1.8 mm for AM.

Conclusion. Veneering porcelain thickness and background shade affected the shade match of zirconia-based restorations. With dark-shaded backgrounds, the amount of veneering porcelain thickness needed for the shade match might be beyond acceptable clinical limits. Tooth-shaded backgrounds are esthetically advocated rather than dark-shaded backgrounds in zirconia-based restorations.

Optical and colorimetric evaluation of a multi-color polymer-infiltrated ceramic-network material

OBJECTIVE

To evaluate color, translucency parameter and optical properties (scattering (S), absorption (K) and transmittance (T)) of a multi-color polymer-infiltrated ceramic-network (PICN) material.

METHODS

Samples of shades 1M1-HT, 1M2-HT, 2M2-HT, 3M2-HT, and 4M2-HT from VITA ENAMIC^® multiColor (E-MC) High Translucent were fabricated (n = 3). CAD-CAM blocks were cut and polished to 1.00 ± 0.01 mm of thickness. Diffuse reflectance and color coordinates were measured against white and black backgrounds, using a calibrated spectroradiometer, CIE D65 illuminant and the CIE 45°/0° geometry. Color and translucency differences were evaluated using 50:50% perceptibility (PT and TPT) and 50:50% acceptability (AT and TAT) thresholds. S and K coefficients and T were calculated using Kubelka-Munk's equations. Data was statistically analyzed using Kruskal-Wallis, Mann-Whitney tests, and VAF coefficient.

RESULT

Mean C* and b* values increased from incisal to cervical layers with statistically significant differences (p < 0.05). In general, ΔE₀₀ between sequential layers were above PT for all shades. In addition, translucency parameter (TP) increased from cervical to incisal and ΔTP₀₀ values were greater than TPT₀₀ and lower than TAT₀₀ between all sequential layers. Layers from all shades showed similar spectral behavior for S (97.4% ≤ VAF), K (85.0% ≤ VAF) coefficients and T (95.3% ≤ VAF). However, these values presented significant differences (p < 0.05) from cervical to incisal layers.

SIGNIFICANCE

The gradient in color and translucency of this novel CAD-CAM multi-color PICN material can assist dental technicians and dentists to reach greater esthetics than the pre-existing CAD-CAM monolithicmaterials.

Zirconia Use in Dentistry - Manufacturing and Properties

Several types of metal-free ceramics have been developed to meet the patients demand for natural looking appearance restorations. Owing to their biocompatibility and good mechanical properties zirconia has been successfully used in recent years as a dental biomaterial. Due to its high opacity zirconia cores are generally covered with ceramic veneers that provide a more natural appearance but have frequent incidence of chipping. As an alternative to veneered zirconia full-contour zirconia restorations become more widely used nowadays. The paper reviews the current knowledge and scientific data of the zirconia use in dentistry in order to compare the zirconia based dental restorations with the metal-ceramic ones and also the two types of dental restoration based on zirconia, veneered or monolithic zirconia.

Evaluation of the color and translucency of glass-infiltrated zirconia based on the concept of functionally graded materials

STATEMENT OF PROBLEM

Infiltrated zirconia has promising mechanical properties. However, information about its optical behavior is scarce.

PURPOSE

The purpose of this in vitro study was to evaluate the color and translucency of zirconia submitted to infiltration and aging.

MATERIAL AND METHODS

Sixty zirconia disks were machined. Ten disks received no treatment (NT group), 10 disks were immersed in a coloring liquid (A2 group), and 10 disks were immersed in a fluorescent liquid (F group). The other 30 disks were submitted to the same treatments plus glass infiltration (NT+I, A2+I, and F+I groups). The coordinates L*, a*, and b* and the Y tristimulus values were obtained to calculate the color (ΔE₀₀), lightness, chroma, and hue differences; the translucency parameter (TP); and the contrast ratio (CR) associated with the specimens. After aging in an autoclave for 4 hours (T1), new measurements were made. Two- and 3-way ANOVAs were used to analyze color differences, TP, and CR. The lightness, chroma, and hue differences were evaluated by a repeated measures ANOVA. Multiple comparisons were made with the Tukey honestly significant difference (HSD) test (α=.05).

RESULTS

The greatest color differences were observed in the A2+I group (11.23 ΔE₀₀) (P<.001). Aging affected the chroma of the colored groups (P=.013 and P=.001) but did not affect their translucency (P=.347 for TP and P=.132 for CR). The greatest TP values were found in the NT and NT+I groups (2.54 and 2.34, respectively), whereas the CR was equal to or close to 1 in all groups.

CONCLUSIONS

Color differences were observed in the glass-infiltrated groups. The TP and CR were affected by infiltration. Aging did not influence the optical behavior of the specimens.

Effects of fabrication and shading technique on the color and translucency of new-generation translucent zirconia after coffee thermocycling

STATEMENT OF PROBLEM

The color stability and translucency of preshaded and externally shaded monolithic and veneered new generation translucent zirconia are not well known.

PURPOSE

The purpose of this in vitro study was to investigate the effect of fabrication (veneered or monolithic) and shading (preshaded or externally shaded) techniques on the color and relative translucency of translucent zirconia after coffee thermocycling.

MATERIAL AND METHODS

Specimens of different thicknesses (0.5 mm for veneered and 1.5 mm for monolithic) were sectioned from preshaded and externally shaded translucent zirconia. Externally shaded specimens were colored by using the dipping technique. Externally shaded (Ext Mono) and preshaded (Pre Mono) monolithic zirconia specimens were sintered and glazed. Externally shaded (Ext Vene) and preshaded (Pre Vene) 0.5-mm-thick specimens were sintered, veneered with feldspathic porcelain (1 mm), and glazed. The color coordinates of specimens were measured with a spectroradiometer before and after 10 000 thermocycles in coffee solution. Color differences were calculated using CIEDE2000, and relative translucency parameter (RTP) values were calculated using the RTP_CIEDE2000 formula. Analysis of variance (ANOVA) was used to analyze the CIEDE2000 color differences and RTP values (α=.05).

RESULTS

Shading technique had a significant effect on the color difference values (P=.018). For the translucency data, the 3-way ANOVA revealed a significant interaction between the fabrication technique and shading technique (P=.002). Each pair of material subgroups within each combination of fabrication technique and shading technique was found to have a significantly different RTP, except between Ext Vene and Pre Vene (P=.115).

CONCLUSIONS

Externally shaded translucent zirconia had a greater color change in coffee than the preshaded translucent zirconia, either in monolithic or veneered form. Fabrication technique significantly affected the RTP, and the monolithic zirconia was more translucent than the veneered zirconia.

Effect of shading technique and thickness on color stability and translucency of new generation translucent zirconia

OBJECTIVE

To evaluate the effect of shading technique and thickness on the color stability and translucency of translucent zirconia after coffee thermocycling.

METHODS

Specimens in different thicknesses (1; 1.5; 2 mm) (n = 4 for each thickness) were sectioned from translucent preshaded zirconia (Pre) and externally shaded zirconia (Ext). After sintering, specimens were glazed and subjected to 10,000 thermocycling in coffee solution. The color coordinates of specimens were measured with a spectroradiometer before and after coffee thermocyling. Color differences and relative translucency parameter (RTP) values were calculated with CIEDE2000 color difference and TP_CIEDE2000 formulas. ANOVA was used to analyze the CIEDE2000 color difference and RTP values (α = 0.05).

RESULTS

According to 2-way ANOVA, no significant effect of shading technique and thickness on the color difference values was found (P > .05). According to 3-way ANOVA, a significant interaction between the shading technique and thickness (P < .0001) was found for RTP. The RTP parameter decreased with the increase in the thickness. Ext specimens presented significantly higher RTP than Pre specimens (P < .0001), except for between Ext 1 mm and Pre 1 mm (P = .179).

CONCLUSIONS

Neither shading technique nor tested thicknesses affected the color of translucent zirconia. Shading technique and thickness affected the RTP of translucent zirconia. The RTP was inversely affected with the thickness of the material. Externally shaded zirconia presented higher RTP than preshaded zirconia for specimens thicker than 1 mm.

CLINICAL SIGNIFICANCE

Discoloration with coffee was insignificant for the tested translucent zirconia in tested thicknesses (1, 1.5, 2 mm). When a translucent restoration is intended, thinner externally shaded translucent zirconia restorations should be preferred instead of preshaded translucent zirconia.

The color masking ability of a zirconia ceramic on the substrates with different values

Background. The color masking ability of a restoration plays a significant role in coveringa discolored substructure; however, this optical property of zirconia ceramics has not been clearly determined yet. The aim of this in vitro study was to evaluate the color masking ability of a zirconia ceramic on substrates with different values.

Methods. Ten zirconia disk specimens,0.5 mm in thickness and 10 mm in diameter, were fabricated by a CAD/CAM system. Four substrates with different values were prepared, including: white (control), light grey, dark grey, and black. The disk specimens were placed over the substratesfor spectrophotometric measurements. A spectrophotometer measured the L^*, a^*, and b^* color attributes of the specimens. Additionally, ΔE values were calculated to determine the color differences between each group and the control,and were then compared with the perceptional threshold of ΔE=2.6. Repeated-measures ANOVA, Bonferroni, and one-sample t-test were used to analyze data. All the tests were carried out at 0.05 level of significance.

Results. The means and standard deviations of ΔE values for the three groups of light grey, dark grey and black were 9.94±2.11, 10.40±2.09, and 13.34±1.77 units, respectively.Significant differences were detected between the groups in the ΔE values (P<0.0001).The ΔE values in all the groups were more than the predetermined perceptional threshold(ΔE>2.6) (P<0.0001).

Conclusion. Within the limitations of this study, it was concluded that the tested zirconia ceramic did not exhibit sufficient color masking ability to hide the grey and black substrates.