• The Journal of Advanced Prosthodontics
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• v.6 no.6
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• pp.456-461
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• 2014

PURPOSE. Translucency and colour stability are two most important aspects for an aesthetic dental restoration. Glass ceramic restorations are popular amongst clinicians because of their superior aesthetic properties. In the last decade, zirconia has generated tremendous interest due to its favorable mechanical and biological properties. However, zirconia lacks the translucency that lithium disilicate materials possess and therefore has limitations in its use, especially in esthetically demanding situations. There has been a great thrust in research towards developing translucent zirconia materials for dental restorations. The objective of the study was to evaluate and compare the transmittance of a translucent variant of zirconia to lithium disilicate. MATERIALS AND METHODS. Two commercially available zirconia materials (conventional and high translucency) and 2 lithium disilicate materials (conventional and high translucency) with standardized dimensions were fabricated. Transmittance values were measured for all samples followed by a microstructural analysis using a finite element scanning electron microscope. One way analysis of variance combined with a Tukey-post hoc test was used to analyze the data obtained (P=.05). RESULTS. High translucency lithium disilicate showed highest transmittance of all materials studied, followed by conventional lithium disilicate, high translucency zirconia and conventional zirconia. The difference between all groups of materials was statistically significant. The transmittance of the different materials correlated to their microstructure analysis. CONCLUSION. Despite manufacturers' efforts to make zirconia significantly more translucent, the transmittance values of these materials still do not match conventional lithium disilicate. More research is required on zirconia towards making the material more translucent for its potential use as esthetic monolithic restoration.

• The Journal of Advanced Prosthodontics
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• v.15 no.4
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• pp.171-178
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• 2023

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 CoCr 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.

• Journal of the korean academy of Pediatric Dentistry
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• v.46 no.3
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• pp.318-327
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• 2019

The purpose of this study was to identify which combination of zirconia crowns and cements is most similar in color to the maxillary primary incisors by varying the color of zirconia crowns, crown thickness, and shade of cements. Prefabricated zirconia crowns in 3 shades and crowns fabricated using 6 types of zirconia blocks were used in this study. These were filled with A2-shade or translucent-shade resin cement and the $L^*$, $a^*$, and $b^*$ values were calculated using a spectrophotometer. The color differences between the natural teeth and the zirconia crowns were assessed. The shade of the final restoration was more similar to that of the natural teeth using A2-shade than translucent-shade resin cement. Application of A2-shade cement to a 0.5-mm-thick crown fabricated from a smile series 2 zirconia block resulted in the color most similar to that of the natural teeth. A2-shade resin cement is recommended for zirconia crown restoration in anterior primary teeth compared to TR-shade resin cement for more esthetic restoration. Since restorations with Nu-smile zirconia crowns were not esthetically favorable in terms of shade, improvement of the shade characteristics of the product or development of a new kind of zirconia crown is required.

• The Journal of Advanced Prosthodontics
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• v.13 no.4
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• pp.246-257
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• 2021

PURPOSE. This study aimed to investigate the Vickers Hardness Number (VHN) of light- and dual cured resin cements cured through monolithic zirconia specimens (VITA YZ) of various translucencies: translucent (T); high translucent (HT); super translucent (ST); and extra translucent (XT) at 0, 24, and 48 h after curing. MATERIALS AND METHODS. Four zirconia specimens from each translucency were prepared. Two light-cured resin cements (Variolink N LC; VL and RelyX Veneer; RL) and two dual-cured resin cements (Variolink N DC; VD and RelyX U200; RD) were used. The cement was mixed and loaded in a mold and cured for 20 s through the zirconia specimen. The upper surface of cements was tested for VHN using a microhardness tester at 0, 24, and 48 h after curing. The VHN were analyzed using two-way repeated, Brown-Forsythe ANOVA with Games Howell post-hoc analysis and independent t-tests (P < .05). RESULTS. All cements showed significantly higher VHN from 0 h to 24 h (P < .001). At 48 h, the VHN of light-cured cements were significantly lower when cured under the T groups than under XT groups (P = .001 in VL, P = .014 in RL). At each post curing time of each translucency, VD showed higher VHN than VL (P < .05), and RD also showed higher VHN than RL (P < .05). CONCLUSION. The translucency of zirconia has an effect on the VHN for light-cured resin cements, but has no effect on dual-cured resin cements. Dual-cured resin cement exhibited higher VHN than the light-cured resin cement from the same manufacturer. All resin cements showed significantly higher VHN from 0 h to 24 h.

• The Journal of Advanced Prosthodontics
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• v.14 no.5
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• pp.324-333
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• 2022

PURPOSE. The purpose of this study is to evaluate translucency and masking ability of translucent zirconia compared to conventional zirconia and lithium disilicate materials. MATERIALS AND METHODS. Three types of zirconia blocks with different yttria contents (3Y, 4Y, 5.5Y) and LS blocks (Rosetta SM) were used. Ten specimens for each group were fabricated with 10 mm diameter, with both 0.8 mm and 1.5 mm thicknesses (± 0.02 mm). All groups of zirconia specimens were sintered and polished according to the manufacturer's instructions. To calculate the translucency parameter (TP), CIELAB value was measured with a spectrophotometer on black and white backgrounds. To investigate the color masking abilities, background shades of A2, normal dentin, discolored dentin, and titanium were used. The color difference (ΔE) was calculated with the CIELAB values of A2 shade background as a reference compared with the values in the various backgrounds. One-way ANOVA and Bonferroni tests were conducted (P < .05). RESULTS. The TP values of zirconia specimens increased as the yttria content increased. All materials used in the study were able to adequately mask normal dentin shade (ΔE < 5.5), but were incapable of masking severely discolored dentin (ΔE > 5.5). On the titanium background, all materials of 1.5 mm thickness were able to mask the background shade, but with a thickness of 0.8 mm, only 3Y-TZP and 4Y-PSZ were able to mask titanium background. CONCLUSION. All zirconia materials and lithium disilicate specimens used in this study were unable to adequately mask the shade of severely discolored dentin. It is recommended to use 3Y-TZP or 4Y-PSZ with a sufficient thickness of 0.8 mm or more to mask titanium.

• The Journal of Advanced Prosthodontics
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• v.6 no.5
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• pp.415-422
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• 2014

PURPOSE. The purpose of this study was to evaluate and compare the translucency of shaded zirconia allceramic systems. MATERIALS AND METHODS. Translucency of 3 different zirconia all-ceramic systems colored by different techniques was compared with a lithium disilicate glass-ceramic (IPS e.max Press). Square-shaped specimens with 0.5 mm thickness were fabricated from In-Ceram YZ, ICE Zirkon and Katana systems in A1, A2 and A3.5 shades according to Vitapan Classical shade tab (n=11). Specimens were then veneered and glazed with corresponding veneer ceramic recommended by each zirconia system manufacturer and the total thickness was set to 1.5 mm. Translucency measurements were performed with VITA Easyshade Compact spectrophotometer after each stage and translucency parameter was calculated. Data were statistically analyzed with repeated measures ANOVA and Tukey multiple comparison test. RESULTS. The control group was significantly more translucent than the zirconia systems (P<.05). ICE Zirkon cores showed the least translucency; neither In-Ceram YZ nor Katana systems were superior to each other in terms of translucency. Translucency of all specimens was decreased after veneering, and the translucency rankings were changed. CONCLUSION. Coloring technique did not have a significant effect on translucency of zirconia cores. Although zirconia systems were less translucent than lithium disilicate glass ceramic, they had partial translucency and there were translucency differences among the zirconia systems. Chroma affected the translucency of precolored zirconia cores.

• The Journal of Advanced Prosthodontics
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• v.11 no.6
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• pp.324-330
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• 2019

PURPOSE. The aim of the study was to evaluate and compare the fracture resistance and modes of fracture of monolithic zirconia crowns with two preparation designs. MATERIALS AND METHODS. Forty human maxillary first premolar teeth were extracted for orthodontic purposes and divided into two main groups (n=20): Group A: monolithic traditional zirconia; Group B: monolithic translucent zirconia. The groups were further subdivided into two subgroups (n=10): (A1, B1) shoulder margin design; (A2, B2) feather-edge margin design. Teeth were prepared with either a 1 mm shoulder margin design or a feather-edge margin design. The prepared teeth were scanned using a digital intraoral scanner. The crowns were cemented using self-adhesive resin cement. All cemented teeth were stored in water for 7 days and thermocycling was done before testing. All samples were subjected to compressive axial loading until fracture. The fractographic analysis was done to assess the modes of fracture of the tested samples. RESULTS. The highest mean values of fracture resistance were recorded in kilo-newton and were in the order of subgroup A1 (2.903); subgroup A2 (2.3); subgroup B1 (1.854) and subgroup B2 (1.523). One-way ANOVA showed a statistically significant difference among the 4 subgroups. Concerning modes of fracture, the majority of samples in subgroups A1 and B1 were fracture of restoration and/or tooth, while in subgroups A2 and B2, the majority of samples fractured through the central fossa. CONCLUSION. Even though all the tested crowns fractured at a higher level than the maximum occlusal forces, the shoulder margin design was better than the feather-edge margin design and the monolithic traditional zirconia was better than the monolithic translucent zirconia in terms of fracture strength.

• The Journal of Advanced Prosthodontics
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• v.14 no.2
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• pp.96-107
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• 2022

PURPOSE. Microstructural and physico-mechanical characterization of highly translucent zirconia, prepared by milling technology (CAD-CAM) and repeated firing cycles, was the main aim of this in vitro study. MATERIALS AND METHODS. Two groups of samples of two commercial highly-translucent yttria-stabilized dental zirconia, VITA YZ-HT^White (Group A) and Zolid HT + White (Group B), with dimensions according to the ISO 6872 "Dentistry - Ceramic materials", were prepared. The specimens of each group were divided into two subgroups. The specimens of the first subgroups (Group A₁ and Group B₁) were merely the sintered specimens. The specimens of the second subgroups (Group A₂ and Group B₂) were subjected to 4 heat treatment cycles. The microstructural features (microstructure, density, grain size, crystalline phases, and crystallite size) and four mechanical properties (flexural strength, modulus of elasticity, Vickers hardness, and fracture toughness) of the subgroups (i.e. before and after heat treatment) were compared. The statistical significance between the subgroups (A₁/A₂, and B₁/B₂) was evaluated by the t-test. In all tests, P values smaller than 5% were considered statistically significant. RESULTS. A homogenous microstructure, with no residual porosity and grains sized between 500 and 450 nm for group A and B, respectively, was observed. Crystalline yttria-stabilized tetragonal zirconia was exclusively registered in the X-ray diffractograms. The mechanical properties decreased after the heat treatment procedure, but the differences were not statistically significant. CONCLUSION. The produced zirconia ceramic materials can be safely (i.e., according to the ISO 6872) used in extensive fixed prosthetic restorations, such as substructure ceramics for three-unit prostheses involving the molar restoration and substructure ceramics for prostheses involving four or more units. Consequently, milling technology is an effective manufacturing technology for producing zirconia substructures for dental fixed all-ceramic prosthetic restorations.

• Journal of Dental Rehabilitation and Applied Science
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• v.36 no.1
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• pp.41-47
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• 2020

Purpose: The purpose of this study was to evaluate the flexural strength and reliability of highly translucent colored zirconia for all ceramic restoration. Materials and Methods: Bar-shaped specimens (25 × 4 × 2.5 mm) were prepared from highly translucent monolithic zirconia. Three experimental groups were set up according to color (shade A0, A1, and A3). For each group, 20 specimens were prepared. Flexural strength was determined using a 3-point flexural test and results were analyzed with one-way ANOVA test. Weibull statistical analysis provided 2 parameter estimates: Weibull modulus and characteristic strength. X-ray diffraction (XRD) analysis was performed. Results: There was statistically significant difference between uncolored (Shade A0) and colored (shade A1 and A3) (P < 0.05), but there was no difference between colored groups (P > 0.05). The uncolored group had higher reliability compared with colored study groups. On x-ray diffraction analysis of each group, typical peaks of tetragonal phase appeared in all groups. Conclusion: Within the limitations of this in vitro study, coloring highly translucent zirconia had significant effect on flexural strength and reliability. Therefore, clinicians should be careful when using highly translucent colored zirconia to prevent breakage of veneering ceramic and enhance aesthetics.

• Journal of Dental Rehabilitation and Applied Science
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• v.38 no.2
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• pp.71-80
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• 2022

Although low translucency 3 mol% yttria stabilized tetragonal zirconia polycrystal has excellent mechanical properties, it has limited application as a monolithic prosthesis. To improve these optical limitations, translucent zirconia has improved esthetics due to an increase in the cubic phase; however, it is accompanied by a decrease in mechanical properties simultaneously. Lithium disilicate has improved its mechanical properties through crystal size reduction and various heat treatment methods; therefore, its clinical application range is continuously increasing. Translucent zirconia shows a wide distribution of physical properties depending on the yttria content and lithium disilicate according to the size and density of crystal grains. As a result, the indications for translucent zirconia and lithium disilicate are increasing. Therefore, in this literature review, we intend to examine the rationale behind the material selection criteria in clinical situations and considerations for designing fixed dental prostheses including pontic, in particular, by summarizing recent studies.