Color match of ultra-translucency multilayer zirconia restorations with different designs and backgrounds.

PURPOSE: The purpose of this in vitro study was to assess the color match of ultra-translucency multilayer zirconia restorations with different designs and backgrounds. MATERIALS AND METHODS: Thirty ultra-translucency multilayer zirconia crown specimens were made in VITA classical shade B2 for a prepared maxillary central incisor. The specimens were divided into three groups based on the restoration design: veneered zirconia with a trestle design (VZT), veneered zirconia with a dentin core design (VZD), and full-contour zirconia (FCZ). In the groups VZT and VZD, the zirconia specimens were layered with a feldspathic veneering ceramic. The specimens were seated on five different backgrounds: shade B2 composite resin, shade B2 zirconia, copper-colored metal alloy, silver-colored metal alloy, and the prepared central incisor. CIELab values of the labial middle sections of the crown specimens were measured with a spectrophotometer. Color differences between the specimens and a shade B2 VITA classical tab (as a control) were calculated from the ΔE* ab formula and compared with an acceptability threshold (ΔE* ab = 3.7) to be clinically explicated. RESULTS: Mean ΔE* ab values ranged between 1.17 and 8.48. The restoration design, the background type, and their interaction affected the ΔE* ab (p < 0.001). The mean ΔE* ab values for VZT with all backgrounds and for VZD with the silver-colored metal background were greater than the threshold (p < 0.001), whereas the mean ΔE* ab values for VZD with the other backgrounds and FCZ with all backgrounds were less than the threshold (p = 1). CONCLUSIONS: Restoration design and background type affected the color match of ultra-translucency multilayer zirconia restorations. VZT restorations on all backgrounds and VZD restorations on a silver-colored metal background showed color mismatches. However, VZD restorations on the other backgrounds and FCZ restorations on all backgrounds demonstrated color matches.

Applications, functions, and accuracy of artificial intelligence in restorative dentistry: A literature review.

OBJECTIVE: The applications of artificial intelligence (AI) are increasing in restorative dentistry; however, the AI performance is unclear for dental professionals. The purpose of this narrative review was to evaluate the applications, functions, and accuracy of AI in diverse aspects of restorative dentistry including caries detection, tooth preparation margin detection, tooth restoration design, metal structure casting, dental restoration/implant detection, removable partial denture design, and tooth shade determination. OVERVIEW: An electronic search was performed on Medline/PubMed, Embase, Web of Science, Cochrane, Scopus, and Google Scholar databases. English-language articles, published from January 1, 2000, to March 1, 2022, relevant to the aforementioned aspects were selected using the key terms of artificial intelligence, machine learning, deep learning, artificial neural networks, convolutional neural networks, clustering, soft computing, automated planning, computational learning, computer vision, and automated reasoning as inclusion criteria. A manual search was also performed. Therefore, 157 articles were included, reviewed, and discussed. CONCLUSIONS: Based on the current literature, the AI models have shown promising performance in the mentioned aspects when being compared with traditional approaches in terms of accuracy; however, as these models are still in development, more studies are required to validate their accuracy and apply them to routine clinical practice. CLINICAL SIGNIFICANCE: AI with its specific functions has shown successful applications with acceptable accuracy in diverse aspects of restorative dentistry. The understanding of these functions may lead to novel applications with optimal accuracy for AI in restorative dentistry.

Accuracy and precision of intraoral scanners for shade matching: A systematic review.

STATEMENT OF PROBLEM: The use of intraoral scanners is rising in prosthetic dentistry; however, systematic analysis of their accuracy and precision for shade matching is scarce. PURPOSE: The purpose of this systematic review was to evaluate the accuracy and precision of intraoral scanners for shade matching. MATERIAL AND METHODS: In addition to a manual search, an electronic systematic search was conducted on MEDLINE/PubMed, EMBASE, Web of Science, Cochrane, and Scopus databases. English-language original studies published between January 1, 2010 and March 1, 2022 with intraoral or digital scanners were chosen based on the keywords of tooth color or shade selection or determination, color or shade matching, accuracy, validity, or trueness, and precision, repeatability, or reproducibility as inclusive criteria. Two reviewers independently performed the literature search, selected the studies, collected the data from the studies included, and evaluated the quality of the studies included using a quality assessment method and the Joanna Briggs Institute Critical Appraisal Checklist for Quasi-Experimental Studies. A third reviewer resolved disagreements. RESULTS: A total of 17 articles concerning the shade matching accuracy and precision of intraoral scanners were selected and reviewed. Among them, 4 articles evaluated only accuracy, 4 articles assessed only precision, and 9 articles investigated both accuracy and precision. Ten articles reported low levels of shade matching accuracy for intraoral scanners, while 11 articles reported high levels of shade matching precision for intraoral scanners. CONCLUSIONS: Based on the current literature, intraoral scanners show acceptable precision but unacceptable accuracy for shade matching.

Effect of surface treatment and surface region on the color stainability of a cemented high-translucency monolithic zirconia ceramic after coffee thermocycling.

STATEMENT OF PROBLEM: Restorations should show low color stainability after clinical and laboratory procedures; however, the impacts of surface treatment and surface region on the color stainability of zirconia restorations are unclear. PURPOSE: The purpose of this in vitro study was to evaluate the effect of surface treatment and surface region on the color stainability of a cemented high-translucency monolithic zirconia ceramic after coffee thermocycling. MATERIAL AND METHODS: Thirty high-translucency Ø10×0.5-mm monolithic zirconia disk specimens were divided into 3 groups based on the surface treatment applied: adjusting (A), polishing (P), and glazing (G). Specimens were cemented to composite resin backings and given 10 000 thermocycles in a coffee solution. CIELab values were measured with a spectrophotometer before and after thermocycling in central and marginal surface regions. ΔE00 values were calculated and compared with perceptibility (ΔE00=0.8) and acceptability (ΔE00=1.8) thresholds to interpret the color changes due to coffee thermocycling. Repeated measures ANOVA and Bonferroni tests were used for data analysis (α=.05). RESULTS: Mean ΔE00 values ranged between 0.72 and 1.26. The surface treatment significantly affected the ΔE00 (P=.005); however, the surface region (P=.499) and the interaction of surface treatment and surface region (P=.998) did not affect the ΔE00. The mean ΔE00 values were less than 0.8 for group G, but greater than 0.8 and less than 1.8 for groups A and P. CONCLUSIONS: Glazing provides the lowest color stainability for cemented high-translucency monolithic zirconia, inducing imperceptible color changes after coffee thermocycling.

Are there any color match and color correlation between maxillary anterior teeth?

OBJECTIVE: To evaluate the color match and color correlation between maxillary anterior teeth. MATERIALS AND METHODS: CIELab values of 1182 intact maxillary anterior teeth in 197 human specimens were measured through spectrophotometry. ∆E00 color differences between similar regions of the same and different type teeth were calculated and compared with perceptibility and acceptability thresholds using 1-sample t test to evaluate color matches. Regression analyses assessed linear relationships between the color coordinates of similar regions of different type teeth. Percentages of different modes of the color match between the same specimen's teeth (2-tooth/3-tooth color match or color mismatch) were determined. RESULTS: Mean ∆E00 values for the same type teeth were less than 1.8 (p = 1). Mean ∆E00 values for different type teeth were mostly greater than 1.8 (p < 0.001), except for central and lateral teeth in middle (p = 0.29) and incisal (p = 0.75) regions and for lateral and canine teeth in cervical regions (p = 0.33). The 2-tooth color match showed the highest percentage (>50%). CONCLUSIONS: The same type teeth indicated color matches. Central and lateral teeth showed color matches in middle and incisal regions, while lateral and canine teeth disclosed color matches in cervical regions. The corresponding color coordinates of mismatched regions were linearly correlated. CLINICAL SIGNIFICANCE: In order to predict and determine the shade of maxillary anterior teeth and create natural colors for corresponding restorations, some tooth color relationships and equations are presented in this study.

Visual and digital tooth shade selection methods, related effective factors and conditions, and their accuracy and precision: A literature review.

OBJECTIVE: Despite developments of dental shade selection methods, shade selection is still a challenge affecting esthetic outcomes. The purpose of this review was to discuss visual and digital shade taking methods, related effective factors and conditions, and their accuracy and precision to find out the most accurate, precise shade selection method available in dentistry. OVERVIEW: The key terms of accuracy, background, ceramic, color, colorimeter, color analysis, color science, color measurement, color measuring instrument, color matching, composite resin, dental/tooth shade guide, digital camera, esthetics, imaging, imaging application/program/ software, intraoral scanner, light source, photography, precision, shade, shade matching/ determination/prediction/reproduction/selection, shade taking device, spectrophotometer, spectrophotometry, tooth color measurement, tooth color/shade, and visual perception were used separately and jointly to detect related English-language articles published between January 1, 1985, and January 1, 2021. Electronic/non-electronic searches of Google Scholar/PubMed/Scopus/Web of Science were accomplished. Consequently, 249 articles were considered. Accordingly, the digital methods show higher accuracy and precision compared to the visual methods while requiring to be enhanced regarding accuracy to achieve ideal shade taking results. CONCLUSIONS: Dental spectrophotometers provide the highest overall accuracy and precision among different shade selection methods while needing clinical setting to control related effective factors/conditions and technological improvement to perform optimally. CLINICAL SIGNIFICANCE: Different factors can affect the accuracy and precision of tooth shade selection methods and devices. The understanding of these effective factors may lead to a standard shade taking protocol using accurate, precise methods and devices.

Can identical dental shade guides be used interchangeably?

OBJECTIVE: To determine if identical dental shade guides can be used interchangeably considering their precision. MATERIALS AND METHODS: Twenty Vita classical (VC) and Vita 3D-Master (VM) shade guides were subjected to spectrophotometric measurements and their CIELab values were measured in three shade tab regions: incisal, middle, and cervical and also in total. The mean L*, a*, and b* values for analogous shade tabs were calculated to identify CIELab values for typical shades. ∆E00 color differences between a typical shade and its analogous shade tabs were measured. ∆E00 values were compared with perceptibility (∆E00  = 0.8) and acceptability (∆E00  = 1.8) thresholds using one-sample t test (α = 0.05). An error was considered when the ∆E00 value was greater than the threshold. Subsequently, the shade guides' precision scores were calculated. RESULTS: Mean ∆E00 values ranged between 0.3 and 0.5 for VC tabs and between 0.3 and 0.6 for VM tabs. Precision scores for both shade guides ranged from 83.3% to 100%, considering the perceptibility threshold. Regarding the acceptability threshold, precision scores for VC ranged from 93.3% to 100%, while the precision scores for VM were 100%. CONCLUSIONS: Owing to high precision of VC and VM, identical dental shade guides can be used interchangeably. CLINICAL SIGNIFICANCE: Using identical dental shade guides interchangeably may affect the color results of restorative treatments. This study identified high levels of precision for identical shade tabs of Vita classical and Vita 3D-Master across different batches. Thus, similar dental shade guides can be used interchangeably.

Effect of Ceramic Thickness and Cement Type on the Color Match of High-Translucency Monolithic Zirconia Restorations.

PURPOSE: To find proper ceramic thickness-cement combinations for color matching of high-translucency monolithic zirconia restorations. MATERIALS AND METHODS: A total of 300 A2-shade high-translucency zirconia disk specimens of six different thicknesses (0.7, 0.9, 1.1, 1.4, 1.6, and 1.8 mm) were cemented to A3.5-shade composite resin backgrounds with five different cements: Temp-Bond, Zinc Phosphate, RelyX Unicem 2, PANAVIA SA Cement Plus, and GC Gold Label 1. Color measurements were conducted before and after cementation to determine the specimens' CIE L*a*b* values. ΔE00 values were calculated for specimens to assess color differences between before cementation and after cementation (ΔE1), between the A2 VITA classical shade (target) and specimens before cementation (ΔE2), and between the target and specimens after cementation (ΔE3). The ΔE3 values were compared with an acceptability threshold (ΔE00 = 1.8) to evaluate color matches. Data were analyzed using two-way analysis of variance, Bonferroni, and one-sample t tests (P < .05). RESULTS: Mean ΔE3 values ranged between 1.0 and 3.4. Ceramic thickness, cement type, and their interaction affected the ΔE3 (P < .001). Temp-Bond with ceramic thickness of ≥ 1.1 mm and Zinc Phosphate with ceramic thickness of ≥ 0.9 showed color matches, but RelyX, PANAVIA SA, and GC did not show color matches with any tested ceramic thickness. CONCLUSION: Opaque cements with sufficient ceramic thicknesses created color matches for high-translucency monolithic zirconia restorations on A3.5-shade backgrounds.

Color match of high translucency monolithic zirconia restorations with different thicknesses and backgrounds.

OBJECTIVE: To assess the effects of ceramic thickness and background type on the color match of high translucency monolithic zirconia restorations. MATERIALS AND METHODS: Fifty A2 shade high translucency zirconia disk specimens with five different thicknesses (0.7, 0.9, 1.1, 1.4, 1.6 mm) were placed on 12 backgrounds: A1, A2, A3, A3.5, B1, and B2 shade composite resin, A3 shade zirconia, nonprecious gold-colored alloy, nickel-chromium alloy, amalgam, and A2 and A3 shade tooth. Color measurements were performed to determine the specimens' CIELab values. CIEDE2000 formula was used to determine ΔE00 color differences between specimens and A2 VITA classical shade (target). The ΔE00 values were compared with perceptibility (0.8) and acceptability (1.8) thresholds to assess color matches. Data were analyzed using repeated measures ANOVA, Bonferroni, and 1-sample t tests (P < .05). RESULTS: Mean ΔE00 values ranged between 1.3 and 5.7. Ceramic thickness, background type, and their interaction significantly affected the ΔE00 (P < .001). Ceramic thicknesses of ≥1.1 mm with the A2 or A3 shade tooth background showed 0.8 < ΔE00 ≤ 1.8 producing acceptable color matches. CONCLUSIONS: High translucency monolithic zirconia restorations with a minimum thickness of 1.1 mm on tooth backgrounds could create acceptable color matches; however, with other backgrounds tested, they could not. CLINICAL SIGNIFICANCE: Ceramic thickness and background type affect the color of high translucency monolithic zirconia restorations. A minimum zirconia thickness of 1.1 mm and normal color tooth structures, as a background, are essential for achieving the acceptable color match of these restorations.

Effect of Resin Cement Brand on the Color of Zirconia-Based Restorations.

PURPOSE: The purpose of this in vitro study was to evaluate the effect of resin cement brand on the color of zirconia-based restorations. MATERIALS AND METHODS: Ninety A2 shade veneered zirconia disc specimens (0.5 mm zirconia thickness, 1 mm veneer thickness, 10 mm diameter) and 90 A3.5 shade composite resin background specimens (10 mm height, 10 mm diameter) with a superficial cement space (0.1 mm depth, 8 mm diameter) were fabricated. The zirconia specimens were cemented to the background specimens using universal resin cements: RelyX Unicem 2 (RU), PANAVIA SA Cement Plus (PS), and NX3 Nexus (NN). CIELab values were measured with a spectrophotometer before and after cementation. ∆E values were calculated to determine the color differences between before and after cementation of specimens (∆E1 ), and between the A2 VITA classical shade tab and specimens before cementation (∆E2 ) and after cementation (∆E3 ). The ΔE values were compared with an acceptability threshold (ΔE = 3.7) to evaluate color changes/matches. Welch, 1-way ANOVA, Games-Howell, Tukey HSD, and 1-sample t test were used to analyze data (p < 0.05). RESULTS: Mean ΔE1 values were 0.6 ± 0.3 for RU, 0.8 ± 0.4 for PS, and 0.6 ± 0.2 for NN. Resin cement brand significantly affected the ΔE1 (p = 0.029) and the ΔE3 (p < 0.001). Mean ΔE3 values were 3.6 ± 0.3 for RU, 3.5 ± 0.3 for PS, and 3.9 ± 0.3 for NN. RU (p = 0.960) and PS (p = 0.999) showed a color match, but NN did not (p < 0.001). CONCLUSIONS: The resin cement brand affected the color match of zirconia-based restorations. Although the tested cements created minor color changes, RU and PS were better than NN for color match. The use of resin cements with the corresponding shade to the target shade is indicated.

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.

Effect of Thickness of Zirconia Ceramic on Its Masking Ability: An In Vitro Study.

PURPOSE: Color-masking ability of zirconia ceramics as coping materials has not been clearly understood in zirconia-based restorations. This in vitro study aimed to evaluate the effect of zirconia ceramic thickness on its masking ability, and to define a thickness cutoff for the tested ceramic. MATERIALS AND METHODS: Ninety zirconia disc specimens, in nine thickness groups including 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, and 2 mm were fabricated. A white substrate and a black substrate were prepared. The disc specimens were placed onto the substrates for spectrophotometric measurements. A spectrophotometer measured L* , a* , and b* color attributes for the specimens. ΔE value was calculated to determine the color difference of specimens on the white and black substrate. Then the ΔE values were compared with an acceptable clinical threshold (ΔE = 5.5) and an ideal threshold (ΔE = 2.6). Welch test, Games-Howell Post Hoc, one-sample t-test, and a regression analysis were performed (p < 0.05). RESULTS: The means of ΔE values for the thickness groups of 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, and 2 mm were 13.0, 11.9, 9.7, 5.0, 4.2, 3.9, 2.2, 1.9, and 1.5, respectively. A significant difference was found in the ΔE value among the groups (p < 0.0001). An exponential relation was detected between the thickness and the ΔE by the regression analysis (∆E = 25.68e-1.45 (thickness) ). CONCLUSIONS: The masking ability increased as the zirconia ceramic thickness increased. The tested zirconia ceramic had an acceptable clinical masking ability with a minimum thickness of 1 mm, and an ideal masking ability with a minimum thickness of 1.6 mm.

Color Aspect of Monolithic Zirconia Restorations: A Review of the Literature.

Monolithic zirconia restoration is an acceptable treatment option in restorative dentistry and a developing trend in esthetic dentistry. Digital dentistry has simplified fabrication of monolithic zirconia restorations. Zirconia ceramic has introduced an opportunity to achieve both esthetic and mechanical requirements for restorations. This is rarely found for a ceramic in dentistry. Monolithic zirconia restorations represent an acceptable durability, comparable to metal-ceramic restorations, while they are superior to metal-ceramic restorations esthetically; however, difficulties to gain an optimal shade reproduction and a color match with monolithic zirconia restorations still remain. The color of these restorations may be influenced by manufacturing processes, laboratory procedures, and clinical factors. Manufacturing processes determine basic optical properties of zirconia ceramics. Different laboratory procedures may create optical changes in zirconia ceramics. Also clinical factors such as dental background, cement, and zirconia restoration features may affect the resulting color. This literature review aimed to discuss potent factors in the color of monolithic zirconia restorations. An electronic search of the PubMed/Google Scholar database was performed to find related English-language articles published between January 1, 2000, and October 31, 2017. The key terms of background, cement, ceramic, color, esthetics, shade, spectrophotometry, thickness, translucency, and zirconia were used both individually and simultaneously. Also, a manual search was conducted, and five classic articles of color science were added. Thus 192 articles were included. In the last decade, shade reproduction of monolithic zirconia restorations has been highly regarded; however, further improvements are required in the manufacturing process to produce tooth-like zirconia ceramics. An esthetic guideline named background-cement-ceramic color harmony was suggested in this study; however, more clinical practice guidelines should be established for monolithic zirconia restorations on esthetics, and therefore, more studies are required.

Influence of coping and veneer thickness on the color of zirconia-based restorations on different implant abutment backgrounds.

STATEMENT OF PROBLEM: The effects of coping and veneer thickness on the color of zirconia-based restorations are unknown. PURPOSE: The purpose of this in vitro study was to evaluate the influence of coping and veneer thickness on the color of zirconia-based restorations on different implant abutment backgrounds and to define minimum coping and veneer thicknesses for the backgrounds investigated to achieve a target color. MATERIAL AND METHODS: Thirty zirconia disk specimens with thicknesses of 0.4, 0.6, and 0.8 mm and 30 veneering ceramic disk specimens with thicknesses of 0.8, 1.0, and 1.2 mm were fabricated. Three backgrounds were prepared: titanium alloy, zirconia ceramic, and base metal alloy. The zirconia specimens were placed on the backgrounds, and the veneering ceramic specimens were located on the zirconia specimens. Spectrophotometric measurements were made to determine CIELab values. Color difference (ΔE) values were calculated to measure color differences between the specimens and the A2 VITA classical shade tab. ΔE values were compared with a perceptibility threshold (ΔE=2.6). Repeated measures ANOVA, Bonferroni test, and 1-sample t test were used to analyze data (α=.05). RESULTS: Mean ΔE values ranged from 2.0 to 9.8. Coping thickness, veneer thickness, and their combination significantly affected ΔE (P<.001). CONCLUSIONS: To achieve the target color with zirconia-based restorations, regardless of the backgrounds tested, the minimum thickness of zirconia coping should be 0.6 mm, and the minimum thickness of veneering ceramic should be 1.2 mm.

Effect of screw access hole design on the fracture resistance of implant-supported zirconia-based restorations.

OBJECTIVE: To evaluate the effect of screw access hole design on the fracture resistance of cement-retained implant-supported zirconia-based restorations with screw access holes. MATERIALS AND METHODS: Thirty cement-retained implant-supported zirconia-based molar crown specimens were fabricated. The specimens were divided into 3 groups of 10: without access holes (C), with screw access holes (S), and with screw access holes accompanied with a surrounding zirconia wall (W). The veneering ceramic thickness was 0.8 mm in all groups. Implants were vertically mounted in a metal block. Abutments were screwed on the implants and the specimens were cemented to the abutments. A universal testing machine applied compressive forces to the specimens until fracture. Fracture resistance values of the specimens were measured. One-way analysis of variance (ANOVA) and Tukey HSD tests were used to analyze data (P < .05). RESULTS: The mean fracture resistance values were 5794.85 N for C, 2691.48 N for S, and 3878.06 N for W. The screw access hole design significantly affected the fracture resistance (P < .0001). Significant differences were found between C and S (P < .001), C and W (P < .001), and S and W (P = .026). CONCLUSIONS: The screw access hole decreased the fracture resistance. A surrounding zirconia wall for the screw access hole increased the fracture resistance. CLINICAL SIGNIFICANCE: Screw access hole design may affect the fracture resistance of cement-retained implant-supported zirconia-based restorations with screw access holes. This study introduced a screw access hole design to improve the fracture resistance of these restorations.

Effect of thickness of monolithic zirconia ceramic on final color.

STATEMENT OF PROBLEM: Achieving excellent esthetics with monolithic zirconia restorations is challenging, and the impact of monolithic zirconia thickness on the final color is unclear. PURPOSE: The purpose of this in vitro study was to assess the effect of thickness of monolithic zirconia ceramic on its final color and to define the minimum thickness needed to gain an acceptable final color. MATERIAL AND METHODS: Sixty monolithic zirconia disk specimens with a 10-mm diameter and 3 different thicknesses (0.7, 0.9, and 1.1 mm) were fabricated from 2 zirconia brands. The specimens were divided into 6 groups of 10 based on the thickness and brand. All the specimens were colored with an A2 shade liquid. The specimens were placed on an A4 shade substrate, and their CIELab values were measured with a spectrophotometer. ΔE values were calculated to determine color differences between the specimens and the A2 VITA classical shade tab. The ΔE values were compared with an acceptability threshold (ΔE=3.3). Two-way ANOVA, the Bonferroni test, and 1-sample t test were used to analyze data (α=.05). RESULTS: Mean ΔE values ranged between 2.4 and 4.1. The zirconia thickness affected the ΔE (P<.001); however, the zirconia brand did not affect the ΔE (P=.059). The mean ΔE values for the zirconia thickness of 0.7 mm for both brands were more than the threshold (P<.05). CONCLUSIONS: The thickness of monolithic zirconia ceramic affected its final color. The minimum thickness of a monolithic zirconia ceramic should be 0.9 mm to gain the acceptable final color.

Color in Zirconia-Based Restorations and Related Factors: A Literature Review.

Zirconia ceramic is a popular trend in esthetic and restorative dentistry. Computer-aided design/computer-aided manufacturing (CAD/CAM) systems have been well developed to fabricate zirconia frameworks and restorations with acceptable mechanical properties. Zirconia ceramics have excellent optical characteristics; however, achieving optimal esthetic outcomes with zirconia-based restorations is still challenging due to multiple effective factors on the final color. These factors are different layers of a zirconia-based restoration and its underlying structures including: dental substrate, cement, zirconia coping, veneering ceramic, and glaze. Moreover, the laboratory procedure of these restorations' fabrication is another effective factor on the resultant color. Unpredictable esthetic results may be obtained without estimation of the role of each factor and its effect on the final color. This review discussed the color aspect of zirconia-based restorations according to these factors and based on the literature. In the past decade, investigators have been concerned with the shade reproduction with zirconia-based restorations; however, there are no sufficient clinical guidelines on how to reproduce the appearance of natural teeth with these restorations. Zirconia-based restorations have presented a new chance for accomplishing optimum esthetics. Nonetheless further investigations are needed on these restorations to establish clinical guidelines on esthetics.

Effect of coping thickness and background type on the masking ability of a zirconia ceramic.

STATEMENT OF PROBLEM: The masking ability of zirconia ceramics as copings is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the effect of coping thickness and background type on the masking ability of a zirconia ceramic and to determine zirconia coping thickness cut offs for masking the backgrounds investigated. MATERIAL AND METHODS: Thirty zirconia disks in 3 thickness groups of 0.4, 0.6, and 0.8 mm were placed on 9 backgrounds to measure CIELab color attributes using a spectrophotometer. The backgrounds included A1, A2, and A3.5 shade composite resin, A3 shade zirconia, nickel-chromium alloy, nonprecious gold-colored alloy, amalgam, black, and white. ΔE values were measured to determine color differences between the specimens on the A2 shade composite resin background and the same specimens on the other backgrounds. The color change (ΔE) values were compared with threshold values for acceptability (ΔE=5.5) and perceptibility (ΔE=2.6). Repeated measures ANOVA, the Bonferroni test, and 1-sample t tests were used to analyze data (α=.05). RESULTS: Mean ΔE values ranged between 1.44 and 7.88. The zirconia coping thickness, the background type, and their interaction affected the CIELab and ΔE values (P<.001). CONCLUSIONS: To achieve ideal masking, the minimum thickness of a zirconia coping should be 0.4 mm for A1 and A3.5 shade composite resin, A3 shade zirconia, and nonprecious gold-colored alloy, 0.6 mm for amalgam, and 0.8 mm for nickel-chromium alloy.

Masking ability of a zirconia ceramic on composite resin substrate shades.

BACKGROUND: Masking ability of a restorative material plays an important role to cover discolored tooth structure; however, this ability has not yet been well understood in zirconia-based restorations. This study assessed the masking ability of a zirconia ceramic on composite resin substrates with different shades. MATERIALS AND METHODS: Ten zirconia disc specimens, with 0.5 mm thickness and 10 mm diameter, were fabricated by a computer-aided design/computer-aided manufacturing system. A white substrate (control) and six composite resin substrates with different shades including A1, A2, A3, B2, C2, and D3 were prepared. The substrates had a cylindrical shape with 10 mm diameter and height. The specimens were placed onto the substrates for spectrophotometric evaluation. A spectrophotometer measured the L*, a*, and b* values for the specimens. ΔE values were calculated to determine the color differences between the groups and the control and then were compared with a perceptional threshold (ΔE = 2.6). Repeated measures ANOVA and Bonferroni tests were used for data analysis (P < 0.05). RESULTS: The mean and standard deviation of ΔE values for A1, A2, A3, B2, C2, and D3 groups were 6.78 ± 1.59, 8.13 ± 1.66, 9.81 ± 2.64, 9.61 ± 1.38, 9.59 ± 2.63, and 8.13 ± 1.89, respectively. A significant difference was found among the groups in the ΔE values (P = 0.006). The ΔE values were more than the perceptional threshold in all the groups (P < 0.0001). CONCLUSION: Within the limitations of this study, it can be concluded that the tested zirconia ceramic could not thoroughly mask different shades of the composite resin substrates. Moreover, color masking of zirconia depends on the shade of substrate.

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.