Colour parameters and shade correspondence of CAD–CAM ceramic systems

Comparing the color match of monolithic CAD-CAM dental ceramics with the VITA Classical shade guide

STATEMENT OF PROBLEM

Matching the shade selected and the final color of a ceramic restoration is challenging, and studies on matching monolithic ceramics to the shade selected are lacking.

PURPOSE

The purpose of this in vitro study was to compare the color match of monolithic lithium disilicate (LDS), zirconia-reinforced lithium silicate (ZLS), presintered zirconia-reinforced lithium silicate (PS-ZLS), polymer-infiltrated ceramic network (PICN), and multilayer zirconia with the 3 modes of the VITA Classical shade guide.

MATERIAL AND METHODS

This study was performed on 50 rectangular plates (14×12×1 mm) of 5 types of ceramics with A2 shade (n=10). Zirconia specimens were evaluated in 3 locations: incisal, medial, and cervical thirds. The color coordinates of the specimens of all 7 groups were measured on #3 and #8 Ivoclar Natural Die Color material by using a reflective spectrophotometer. The color coordinates of A2 VITA shade were measured in 5 modes: without backing placed in specimen holder, shade tab on the backgrounds #3 and #8, and 1-mm-thick shade tab on the backgrounds #3 and #8. The color difference of each specimen with 3 modes of A2 shade (without backing and on similar backgrounds) was calculated by using the ΔE00 formula, and comparison among groups was performed by using 2-way ANOVA and Tamhane post hoc tests. The comparison of ΔE00 between the values obtained from backgrounds #3 and #8 was performed by using the independent t test (α=.05).

RESULTS

In both backgrounds, statistically significant differences were found between the studied groups and VITA shade (P<.001). In most situations, the amount of color difference was lowest for the "shade tab on the backgrounds" mode. On background #3, the highest color difference was related to ZLS (6.48 ±0.23), and the lowest values were observed in the PICN group (1.02 ±0.31). On background #8, the highest color difference was related to ZLS compared with the "without backing" mode (8.62 ±0.27), and the lowest values were reported for ZLS compared with the "shade tab on the backgrounds" mode (1.27 ±0.44). The independent t test showed a statistically significant color difference on the 2 different backgrounds for all situations (P<.001).

CONCLUSIONS

Color selection of monolithic ceramics with the VITA Classical shade guide is improved by placing the VITA tabs on a similar background. Background color has a significant effect on the final shade of the monolithic ceramics. Choosing the correct color for LDS, ZLS, and PS-ZLS requires more care than for PICN and zirconia.

Effect of simulated gastric acid exposure on the hardness, topographic, and colorimetric properties of machinable and pressable zirconia-reinforced lithium silicate glass-ceramics

STATEMENT OF PROBLEM

The effects of gastric acid on the hardness, topographic, and colorimetric properties of zirconia-reinforced lithium silicate glass-ceramics (ZLSs) for dental restorations remain unknown.

PURPOSE

The purpose of this in vitro study was to investigate the effect of simulated gastric acid exposure on the microhardness, surface roughness, color stability, and relative translucency of ZLSs.

MATERIAL AND METHODS

Two pressable ZLSs (VITA AMBRIA, VA and Celtra Press, CP) and 2 machinable ZLSs (VITA Suprinity, VS and Celtra Duo, CD)(n=64) were randomly allocated to artificial saliva (control) or gastric juice immersion groups simulating 10 and 20 years of clinical exposure. Microhardness (Hv) was measured with a Vickers hardness device, and surface roughness (Sa) was recorded with an optical profilometer. The color stability (ΔE00) and relative translucency parameter (RTP) were measured with a spectrophotometer. Data for Hv, Sa, and RTP were analyzed by repeated 2-way ANOVA, and data for ΔE00 were analyzed by 2-way ANOVA. Post hoc comparisons were obtained from Tukey HSD and Student t tests (α=.05).

RESULTS

Machinable ZLSs exhibited greater Hv after the simulated gastric acid challenge than pressable ZLSs. Sa was significantly impacted by material type (P=.001), storage media (P=.050), and their interaction (P<.001). ΔE00 was significantly affected by the type of simulated aging media (P<.001). After 20 years of simulated gastric acid aging, all ZLS materials surpassed the ΔE00 perceptibility threshold but did not exceed the ΔE00 acceptability threshold. VS displayed significantly lower RTP than other ZLS materials at all time points (P<.001).

CONCLUSIONS

The topographic and colorimetric characteristics of ZLS were significantly altered by exposure to simulated gastric acid.

The impact of Streptococcus mutans biofilms on the color stability and topographical features of three lithium disilicate ceramics

PURPOSE

Secondary caries around ceramic restorations is the most common reason for the replacement of fixed dental prostheses (FDPs). Therefore, it is important to examine the susceptibility of different ceramic materials to biofilm formation. This study aimed to evaluate biofilm development and associated roughness and color alterations in three lithium disilicate ceramics: Emax CAD (EC), Emax Press (EP), and LiSi Press (LP).

MATERIALS AND METHODS

Streptococcus mutans biofilms were grown on the three ceramics (n = 10 per group) for 7 days. Surface roughness values and color alteration were assessed before and after the biofilm using a non-contact profilometer and spectrophotometer, respectively. Biofilm growth was evaluated using colony-forming units (CFUs) and scanning electron microscope (SEM) images. The data were analyzed using one-way ANOVA and Tukey tests.

RESULTS

There was a significant (p ≤ 0.001) growth of S. mutans colonies on EC (6.75 ± 0.56) and EP (6.72 ± 0.54) specimens compared to LP, which showed no biofilm growth. The change in average surface roughness (∆Ra, nm) was significantly lower (p < 0.001) in the EC specimens (0.029 ± 0.003) compared to the EP (0.055 ± 0.012) and LP (0.041 ± 0.010). When the changes in the Rv and Rt values were investigated, no significant difference was observed among the groups. Following the biofilm challenge, the change in color (∆E00) was significantly lower (p = 0.005) in the LP group (1.68 ± 1.45) compared to the EC group (3.89 ± 1.50) and no significant difference was observed between the EP group (2.74 ± 1.01) and the other two ceramics (p ≥ 0.05).

CONCLUSION

LP ceramics exhibited superior resistance to S. mutans biofilm formation and associated changes in surface roughness and color compared to the Emax CAD and Emax Press ceramics. These findings suggest that the LiSi Press material may be more favorable to mitigate the risk of secondary caries.

Randomized clinical trial of zirconia laminate veneers sintered by using conventional versus speed process: 1-year follow-up

STATEMENT OF PROBLEM

The application of highly translucent multilayered zirconia ceramic in minimally invasive esthetic dentistry allows the achievement of both esthetics and strength with minimal thickness. Clinical studies that have assessed the performance of zirconia ultrathin veneers sintered with the conventional and speed procedure are lacking.

PURPOSE

The purpose of this clinical study was to evaluate the effect of speed sintering processes on the translucency and clinical performance of zirconia laminate veneers.

MATERIAL AND METHODS

Four participants had their teeth restored with 32 ultratranslucent zirconia laminate veneers. Based on the zirconia sintering procedure, the participants were randomly allocated into 2 groups. The teeth were prepared by selective reduction over trial restorations. Zirconia veneers were milled from multilayer zirconia blanks and sintered either by speed sintering or conventional sintering as specified by the manufacturer's recommendations. The intaglio surface of the veneers were airborne-particle abraded with 50-μm aluminum-oxide, and the veneers were then adhesively bonded to the teeth with translucent light-polymerizing resin cement. The modified California Dental Association (CDA)/Ryge criteria were used to assess participants at baseline and every 3 months for 12 months. The translucency and the color difference of the tooth before and after veneer restoration were evaluated. For statistical analysis, the Pearson chi squared test, independent t test, and paired t test were used (α=.05).

RESULTS

Translucency and color differences were significantly higher in the conventionally sintered group (P<.05). No restorations were lost. No significant differences were found between the 2 groups in the CDA/Ryge criteria or color parameter after follow-up intervals (P>.05). The primary qualitative changes observed at the final recall were marginal integrity and marginal discoloration. The color match and zirconia surface were rated Alfa.

CONCLUSIONS

After 1 year of follow-up, both conventional and speed sintered ultrathin zirconia laminates showed satisfactory functional, esthetic, and color stability outcomes.

Staining and bleaching susceptibility of zirconia-reinforced lithium silicate glass-ceramics with different thicknesses, translucencies, and fabrication methods

STATEMENT OF PROBLEM

The influence of different thicknesses, translucencies, and fabrication methods on the spectrophotometric and topographical properties of zirconia-reinforced lithium silicate glass-ceramics (ZLSs) for dental restorations remains unclear.

PURPOSE

The purpose of this in vitro study was to investigate the effect of thicknesses, translucencies, and fabrication methods on the color stability, translucency parameter, opalescence parameter, whiteness stability, transmitted irradiance, light transmittance, opacity, gloss, and roughness of ZLSs exposed to coffee staining and bleaching treatments.

MATERIAL AND METHODS

Two pressable ZLSs (VITA AMBRIA, VA and Celtra Press, CP) and 2 machinable ZLSs (VITA Suprinity, VS and Celtra Duo, CD) were examined at high translucency (HT) and low translucency (LT) levels in 2 thicknesses (n=160). The specimens were evaluated at baseline, after coffee staining, and after bleaching. The color stability (ΔE2000), translucency parameter (TP), opalescence parameter (OP), whiteness index (WID), and whiteness stability (ΔWID) were measured with a spectrophotometer. Transmitted irradiance (It), light transmission (T), and opacity (O) were obtained from a light-polymerizing unit and a polymerization light collection device. Roughness stability (ΔSa%) was determined with an optical profilometer, and gloss stability (ΔGU%) was recorded with a gloss meter. Data of ΔCIE2000, ΔWID, ΔSa%, and ΔGU% were analyzed by 4-way ANOVA, and data of the TP, OP, WID, It, T, and O were analyzed by repeated 4-way ANOVA (α=.05).

RESULTS

VS-HT exceeded the ΔCIE2000 acceptability threshold after coffee staining and bleaching protocols. Pressable ZLSs exhibited greater color stability than machinable ZLSs. The 1-mm-thick VA, CP, and CD materials exceeded the ΔWID perceptibility threshold after bleaching. The highest TP and OP was displayed by the 1-mm-thick CP after bleaching. ΔGU increased after water storage and decreased after coffee staining and bleaching. ΔSa% significantly increased after bleaching (P<.05).

CONCLUSIONS

The color stability and other spectrophotometric properties of ZLSs depended on material thickness. The effects of ZLS fabrication methods and translucency levels on their measured properties were inconsistent. Subjecting 1-mm-thick ZLS materials to acidic media adversely impacted their stainability and surface texture.

Quantitative analysis of the color in six CAD-CAM dental materials of varied thickness and surface roughness: An in vitro study

STATEMENT OF PROBLEM

Computer-aided design and computer-aided manufacturing (CAD-CAM) monochromatic restorative materials are gaining popularity because of their convenience and efficiency. However, studies that quantitatively analyzed color change associated with thickness and surface roughness are sparse.

PURPOSE

The purpose of this in vitro study was to quantitatively evaluate the color of 6 CAD-CAM monochromatic materials of different thickness and surface roughness using the CIELab color system.

MATERIAL AND METHODS

A total of 150 12×12-mm square specimens of 6 different CAD-CAM monochromatic materials (VITA Enamic HT [VE], IPS e.max CAD HT [LS], LAVA Ultimate HT [LU], Telio CAD HT [TE], VITA Suprinity HT [VS], and Celtra Duo HT [CD]) in shade A2 and 5 different thicknesses (from 0.5 mm to 2.5 mm, with 0.5-mm increments) were fabricated (n=5). After 3 different surface treatments (polished, roughened by SiC P800-grit, and P300-grit), CIELab color parameters (L*, a* and b*) were measured using a spectrophotometer (VITA Easyshade V), and surface roughness was measured with a profilometer (VK-X200). Color variation was quantified by ΔE00 and 50:50% acceptability and perceptibly thresholds. Data analyses were performed using MANOVA, 2-way ANOVA, post hoc Tukey-Kramer test, and the 1-sample t test (α=.05).

RESULTS

The L*, a*, and b* of the monochromatic specimens were significantly influenced by material type, thickness, and surface roughness (P<.001). An overall increase in the L* (from 61.90 to 82.2), a* (from -4.22 to 1.16), and b* (from 5.48 to 43.22) of the specimens was observed with increased thickness. The roughened specimens exhibited lower L* and higher a* and b* than the polished ones (P<.001). The use of P300-grit for roughening resulted in greater ΔE00 compared with P800-grit (P<.001). As thickness decreased or surface roughness increased, the ΔE00 increased and exceeded the acceptability and perceptibly thresholds for color difference.

CONCLUSIONS

Material type, thickness, and surface roughness were major factors affecting the color of CAD-CAM monochromatic materials. Variations in thickness of 0.5 mm or more, as well as roughening treatments, may lead to clinically unacceptable color changes.

An investigation on fatigue, fracture resistance, and color properties of aesthetic CAD/CAM monolithic ceramics

OBJECTIVES

To evaluate and compare fracture resistance, translucency, and color reproducibility, as well as the effect of aging on the fracture load and color stability of novel monolithic CAD/CAM ceramics.

MATERIALS AND METHODS

One hundred crowns of uniform thickness were milled from five ceramic blocks (n = 20): partially crystallized lithium disilicate (PLD) and fully crystallized lithium disilicate (FLD), lithium metasilicate (LMS), 4Y-TZP (SMZ), and 5Y-TZP (UMZ) monolithic zirconia. PLD crowns were glazed, LMS was fired, and FLD was polished. SMZ and UMZ crowns were sintered and polished. Crowns were adhesively cemented to epoxy dies. Half of the crowns (n = 10) were subjected to 1.200.000 load cycles with thermal cycling. Color space values L, a, b defined by the Commission Internationale de l´Eclairage (CIELAB) were measured before and after aging, and (∆E) was calculated. Both aged and non-aged specimens were loaded until fracture in a universal testing machine and the fracture load was recorded. X-ray diffraction (XRD) and scanning electron microscope (SEM) fractographic analysis were carried out on fractured fragments of representative samples. For translucency and color reproducibility, 50 rectangular-shaped specimens were fabricated and processed as described previously. Color values were measured over black and white backgrounds, and the translucency parameter (TP) was computed. Using the shade verification mode, (∆E) to shade A3 was calculated. Data were statistically analyzed using one-way and two-way ANOVA, and t-test.

RESULTS

Aging did not affect fracture resistance significantly (p > 0.05). The highest mean fracture load was obtained for the SMZ and UMZ. A significant color change was observed after aging in all groups. The highest TP was noted for FLD. SMZ and UMZ had the best shade match.

CONCLUSIONS

Zirconia showed higher fracture resistance and color stability than lithium silicate ceramics. Lithium silicate ceramics were more translucent. The experimental FLD demonstrated high translucency.

CLINICAL RELEVANCE

Tested ceramics showed sufficient stability to withstand masticatory forces. Characterization of final restorations might be mandatory for better color match.

The Toothbrushing Effects on Surface Properties and Color Stability of CAD/CAM and Pressable Ceramic Fixed Restorations-An In Vitro Study

Pressable ceramic restorations have been introduced and investigated, and found comparable to CAD/CAM ceramic in terms of mechanical properties; however, the effect of toothbrushing on the pressable ceramic has not been thoroughly investigated. The objective of the current study was to assess the effect of artificial toothbrushing simulation on the surface roughness, microhardness, and color stability of different ceramic materials. Three lithium disilicate-based ceramics (IPS Emax CAD [EC], IPS Emax Press [EP]; (Ivoclar Vivadent AG), and LiSi Press [LP] (GC Corp, Tokyo, Japan)) were examined. For each ceramic material, eight bar-shaped specimens were prepared and subjected to 10,000 brushing cycles. Surface roughness, microhardness, and color stability (∆E) were measured before and after brushing. Scanning electron microscopy (SEM) was used for surface profile analysis. The results were analyzed using one-way ANOVA, Tukey's post hoc test, and paired sample t-test α = 0.05. The findings revealed a non-significant decrease in the surface roughness of EC, EP, and LP groups (p > 0.05), and both LP and EP have the lowest surface roughness values (0.64 ± 0.13, 0.64 ± 0.08 µm) after brushing, respectively. Toothbrushing showed a decrease in the microhardness of the three groups: EC and LP, p < 0.001; EP, p = 0.012). EP showed the lowest hardness value after brushing (862.45 ± 273.83). No significant changes (∆E) were observed in all groups (p > 0.05); however, the EC group was found to be considerably affected by color changes, in comparison to the EC and LP groups. Toothbrushing had no effect on surface roughness and color stability of all tested materials, but it decreased the microhardness. Material type, surface treatments, and glazing of ceramic materials contributed to the surface changes in the ceramic materials, necessitating further investigations in terms of the toothbrushing effect with different glazing as variables.

3D Printing of CNT- and YSZ-Added Dental Resin-Based Composites by Digital Light Processing and Their Mechanical Properties

This study demonstrates the successful 3D printing of dental resin-based composites (DRCs) containing ceramic particles using the digital light processing (DLP) technique. The mechanical properties and oral rinsing stability of the printed composites were evaluated. DRCs have been extensively studied for restorative and prosthetic dentistry due to their clinical performance and aesthetic quality. They are often subjected to periodic environmental stress, and thus can easily undergo undesirable premature failure. Here, we investigated the effects of two different high-strength and biocompatible ceramic additives, carbon nanotube (CNT) and yttria-stabilized zirconia (YSZ), on the mechanical properties and oral rinsing stabilities of DRCs. Dental resin matrices containing different wt.% of CNT or YSZ were printed using the DLP technique after analyzing the rheological behavior of slurries. Mechanical properties such as Rockwell hardness and flexural strength, as well as the oral rinsing stability of the 3D-printed composites, were systematically investigated. The results indicated that a DRC with 0.5 wt.% YSZ exhibits the highest hardness of 19.8 ± 0.6 HRB and a flexural strength flexural strength of 50.6 ± 6 MPa, as well as reasonable oral rinsing steadiness. This study provides a fundamental perspective for designing advanced dental materials containing biocompatible ceramic particles.

Using artificial intelligence to predict the final color of leucite-reinforced ceramic restorations

OBJECTIVES

The aim of this study was to evaluate the accuracy of machine learning regression models in predicting the final color of leucite-reinforced glass CAD/CAM ceramic veneer restorations based on substrate shade, ceramic shade, thickness and translucency.

METHODS

Leucite-reinforced glass ceramics in four different shades were sectioned in thicknesses of 0.3, 0.5, 0.7, and 1.2 mm. The CIELab coordinates of each specimen were obtained over four different backgrounds (black, white, A1, and A3) interposed with an experimental translucent resin cement using a calibrated spectrophotometer. The color change (CIEDE2000) values, as well as all the CIELab values for each one of the experimental groups, were submitted to 28 different regression models. Each regression model was adjusted according to the weights of each dependent variable to achieve the best-fitting model.

RESULTS

Different substrates, ceramic shades, and thicknesses influenced the L, a, and b of the final restoration. Of all variables, the substrate influenced the final ceramic shade most, followed by the ceramic thickness and the L, a, and b of the ceramic. The decision tree regression model had the lowest mean absolute error and highest accuracy to predict the shade of the ceramic restoration according to the substrate shade, ceramic shade and thickness.

CLINICAL SIGNIFICANCE

The machine learning regression model developed in the study can help clinicians predict the final color of the ceramic veneers made with leucite-reinforced glass CAD/CAM ceramic HT and LT when cemented with translucent cements, based on the color of the substrate and ceramic thicknesses.

Effect of multiple firings on surface roughness and flexural strength of CAD-CAM ceramics

STATEMENT OF PROBLEM

Knowledge on the effect of multiple firings on surface roughness and the flexural strength of different types of monolithic computer-aided design and computer-aided manufacturing (CAD-CAM) ceramics is limited.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of multiple firings on the surface roughness and flexural strength of 4 different CAD-CAM ceramics after thermocycling.

MATERIAL AND METHODS

Four different CAD-CAM ceramics (Lava All Zirconia 3-mol yttria tetragonal zirconia polycrystal [3-YTZP] [Z], VITA SUPRINITY [S], IPS e.max CAD [EX], IPS Empress CAD [E]) (n=33) were wet-sectioned to form rectangular 18×4×1.2-mm specimens. After glaze application, the specimens were divided into 3 subgroups according to the number of firings (1, 2, and 4) (n=11). The specimens were thermocycled (10 000 cycles), and surface roughness and flexural strength values were measured (n=10). One additional specimen from each group was analyzed by using scanning electron microscopy (SEM). Data were analyzed by 2-way analysis of variance (ANOVA) and the Tukey honestly significance difference (HSD) test (α=.05).

RESULTS

According to the 2-way ANOVA, the material, number of firings, and the interaction between the material and number of firings affected the surface roughness (P<.001). For flexural strength, material (P<.001) and number of firings (P<.039) were found significant. Multiple firings (2 or 4 firings) affected the surface roughness of E (P<.001). Regardless of the number of firings, the Z material had the highest flexural strength (P<.001). Four firings affected the flexural strength values only for the Z material (P≤.005).

CONCLUSIONS

CAD-CAM ceramic type affected the surface roughness and flexural strength values. The surface roughness of E was lower when fired 2 or 4 times than when fired once. The flexural strength of Z was lower when fired 4 times than when fired once.

Color prediction of layered dental resin composites with varying thickness

OBJECTIVE

The aim of this study was to assess the accuracy of a Principal Components Analysis (PCA)-based method for reflectance reconstruction and color estimation of layered dental resin-based composites with different thicknesses.

METHOD

Bi-layered samples of different clinically relevant thicknesses were created using shades of VITAPAN Excell (VE), VITAPAN Dentine (VD) and VITA Physiodens (VP), combined with their corresponding enamel shades. Spectral reflectance of all samples was measured over a black background using a non-contact spectroradiometer with CIE 45^∘∕0^∘ geometry. Two different PCA-based models, built from two different configurations of known samples, were proposed to reconstruct the spectral data and color of unknown layered samples. Root Mean Square Error (RMSE), Goodness of Fit (GFC), as well as ΔE₀₀ with corresponding 50:50% acceptability and perceptibly thresholds (AT and PT) were used as performance assessment.

RESULTS

The 5-samples training set approach provided an average RMSE < 0.015 and GFC > 0.999 when measured and predicted spectral reflectances were compared, while for the 9-samples training set, RMSE < 0.0098 and GFC > 0.9999 were obtained. The overall mean color differences obtained with the 5-samples training set approach were ΔE₀₀ = 0.99 (AT% = 96.25% and PT% = 32.50%), while using the 9-samples training set resulted in lower overall mean color differences: ΔE₀₀ = 0.50 (AT% = 99.22% and PT% = 83.87%).

SIGNIFICANCE

Within the framework of this study, the two proposed PCA-based configurations allow the prediction of the spectral reflectance of layered dental resin-based composites of different shades and thicknesses, with a high degree of accuracy.

In Vitro Evaluation of the Shading Effect of Various Zirconia Surface Stains on Porcelain Crowns

Human teeth display various colors under natural light. Dental restorations, such as zirconia crowns, are generally used to rehabilitate the oral function of patients with tooth loss due to trauma or natural tooth falls. However, significant improvements in the color and translucency of zirconia are required to meet the clinical needs for dental restoration. In the past, a large amount of ceramic powder has been used to improve the appearance of zirconia. However, the interface between the ceramic powder and zirconia makes them prone to falling off. Therefore, the aesthetics of zirconia crowns remains a major challenge. Recently, substantial advances have been made in the field of dental materials, as special staining agents for zirconia have been introduced as alternatives to ceramic powders. Therefore, this study tested zirconia-specific staining agents that were used to produce zirconia samples with A1 and A3 colors. A dental colorimetric plate was used as the control group to assess the staining effects of the different brands of staining agents. Meanwhile, two hypotheses were proposed: that the staining effects of these special staining agents for zirconia met the criteria for clinical application and that there was no significant difference between the different staining agents for zirconia. The results showed that the coatings of different brands of staining agents were ultrathin, with a thickness of approximately 27–78 µm. In addition, the coloring effects of the zirconia staining agents were not significantly different from those of the colorimetric plates. After staining, the zirconia samples had decreased surface roughness and contact angle values, which improved surface smoothness and cleanliness. In summary, the results support the hypothesis of this study that zirconia stains can be used as an alternative to the current fabrication methods for clinical dental restorations. We sought to identify the clinical techniques that are easier to perform and to overcome the current problem of dental technicians requiring considerable dentin space for staining. It is expected that the results of this study will be useful in clinical dental restorations.

Quantitative analysis of color accuracy and bias in 4 dental CAD-CAM monolithic restorative materials with different thicknesses: An in vitro study

STATEMENT OF PROBLEM

Computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic restorative materials have become a popular option because of advantages such as convenience and efficiency. However, studies that quantitatively analyzed their color accuracy and bias are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the color accuracy and bias of 4 CAD-CAM monolithic restorative materials with different thicknesses by using the CIELab color space.

MATERIAL AND METHODS

Four types of dental CAD-CAM monolithic restorative materials in shade A2, lithium disilicate glass-ceramic (IPS e.max CAD), infiltrated ceramic (VITA Enamic), resin-nano ceramic (LAVA Ultimate), and polymethyl methacrylate (Telio CAD), were prepared as 12×12-mm specimens of 10 different thicknesses (from 0.5 to 5.0 mm) (N=200, n=5). After polishing with SiC P1500-grit, CIELab color coordinate parameters of the specimens were measured with a spectrophotometer (VITA Easyshade V). The color accuracy and bias were described by ΔE₀₀, ΔL∗, Δa∗, and Δb∗ in the CIELab color space, and the data were analyzed by using a 2-way ANOVA, post hoc Tukey-Kramer test, and the t test (α=.05).

RESULTS

The ΔE₀₀, ΔL∗, Δa∗, and Δb∗ were significantly influenced by material type and thickness (P<.001). Specimens at a thickness of 0.5 mm represented the maximum ΔE₀₀. The minimum ΔE₀₀ was observed at a thickness of 2.0 mm for LAVA Ultimate, 1.5 mm for VITA Enamic and Telio CAD, and 4.0 mm for IPS e.max CAD. The ΔE₀₀ of all specimens significantly exceeded the 50:50% acceptability threshold (1.8 unit) (P<.001). LU exhibited higher ΔE₀₀, Δa∗, and Δb∗ than the other 3 materials in all thickness expect for 0.5 mm. For color bias, the ΔE₀₀ was more influenced by Δb∗ and ΔL∗ than Δa∗.

CONCLUSIONS

The color accuracy and bias were significantly affected by material type and thickness. The color inaccuracy of the tested materials was statistically significant and clinically perceptible. Improved clinical outcomes may be expected from the 1.5-mm- to 2.0-mm-thick restorations.

Influence of manufacturing technique on the color of zirconia restorations: Monolithic versus layered crowns

OBJECTIVES

The study aimed to compare the color of monolithic and layered zirconia crowns fabricated using different brands in the cervical, middle, and incisal areas.

MATERIALS AND METHODS

A total of 45 crowns were fabricated from three brands (Katana, Nacera, Cercon) using three methods (monolithic = ML (n=5), cut-back + enamel = BL (n=5), cut-back + dentin + enamel = TL (n=5)). CIE L*, a* b*, C*, h° color coordinates were recorded with a dental spectrophotometer in cervical, middle, and incisal areas. Color differences between manufacturing techniques, tooth areas, and brands were calculated using the CIEDE2000(1:1:1) formula, and the values were compared to the perceptibility (PT₀₀ ) and acceptability thresholds (AT₀₀ ). Comparisons between color coordinates were analyzed statistically (Kruskal-Wallis and Mann-Whitney U tests, p < 0.001).

RESULTS

Significant differences were found between CIE L*, a*, b*, C*, h° coordinates of the zirconia crowns (p < 0.001), generally. The lowest color differences were obtained between BL and TL crowns in cervical and middle areas. Color differences between cervical and middle areas were mostly below PT₀₀ . An acceptable color difference was found between Katana and Cercon crowns.

CONCLUSIONS

The manufacturing technique and the brand influenced the color of zirconia crowns. Also, the color of the crowns varied from cervical to incisal.

CLINICAL SIGNIFICANCE

Reproducing the optical properties of teeth with ceramic crowns might be challenging, given the differences in the internal configuration of the enamel and dentine, as well as their complex behavior when interacting with light. When deciding whether to fabricate a monolithic crown in translucent zirconia or improve its appearance by layering with more translucent glass-ceramic, the clinicians and dental technicians must be aware of these procedures' effect on the final color of the restorations.

Masking Abilities of Dental Cad/Cam Resin Composite Materials Related to Substrate and Luting Material

An outstanding treatment challenge related to aesthetic monolithic materials is to mask discolored substrates in aesthetic areas. The purpose of the study is to evaluate the substrate masking ability of different resin composite materials and the influence of their association with luting agents and substrates. Five types of 2M2 HT (high translucency) resin composite materials were selected: Vita Enamic [E] and four types of nanoparticle-filled composites Lava Ultimate [L], Cerasmart [C], Shofu HC [S], and Hyramic [H]. Resin composite Vita VM LC with different shades was used for the substrates: 2M2, 3M2, and CP2. Variolink Esthetic Try-inpastes neutral, light+, and warm+ colors were chosen to simulate the luting agent color. Optical parameters (TP (translucency), CR (contrast ratio), and OP (opalesce)) and color differences ΔE (chromatic difference) were calculated. Statistical analyses were performed to evaluate the comparisons between the groups and establish correlations. TP average values for all materials were in the range of 21.49–24.53. OP average values were in the rage of 6.31–7.85. OP is moderate positive correlated to TP and CR is negative and strong correlated to TP. Related to materials, average color changes decrease as following: E > H > C > L > S. Referring to the tryin material, warm colors induce marked color changes of the restoration. The differences of the color changes determined by all studied substrates are significant. For the final aesthetic aspect of the restoration, it is essential to consider the underlying dental structure, luting agent, and restoration material as a whole unit. The masking ability of the investigated resin matrix ceramic materials materials shows differences, the best behavior demonstrated Shofu HC and Lava Ultimate. Marked color changes are related to high chroma substrates. For substrates with a darker color, the association with warm try-in pastes lead to marked color changes, but with neutral and light try-in pastes at most perceivable.

Applications of artificial intelligence in dentistry: A comprehensive review

OBJECTIVE

To perform a comprehensive review of the use of artificial intelligence (AI) and machine learning (ML) in dentistry, providing the community with a broad insight on the different advances that these technologies and tools have produced, paying special attention to the area of esthetic dentistry and color research.

MATERIALS AND METHODS

The comprehensive review was conducted in MEDLINE/PubMed, Web of Science, and Scopus databases, for papers published in English language in the last 20 years.

RESULTS

Out of 3871 eligible papers, 120 were included for final appraisal. Study methodologies included deep learning (DL; n = 76), fuzzy logic (FL; n = 12), and other ML techniques (n = 32), which were mainly applied to disease identification, image segmentation, image correction, and biomimetic color analysis and modeling.

CONCLUSIONS

The insight provided by the present work has reported outstanding results in the design of high-performance decision support systems for the aforementioned areas. The future of digital dentistry goes through the design of integrated approaches providing personalized treatments to patients. In addition, esthetic dentistry can benefit from those advances by developing models allowing a complete characterization of tooth color, enhancing the accuracy of dental restorations.

CLINICAL SIGNIFICANCE

The use of AI and ML has an increasing impact on the dental profession and is complementing the development of digital technologies and tools, with a wide application in treatment planning and esthetic dentistry procedures.

The Effects of a coffee beverage and whitening systems on surface roughness and gloss of CAD/CAM lithium disilicate glass ceramics

OBJECTIVES

To investigate the effects of a coffee beverage and two whitening systems on the surface roughness and gloss of glazed Lithium Disilicate Glass-Ceramics (LDGC) for computer-aided design/computer-aided manufacturing (CAD/CAM) systems.

METHODS

Sixty-eight LDGC disks (12 × 10 × 2 mm) were prepared from blocks of CAD/CAM systems (IPS e.max CAD ceramic). Baseline measurements for surface roughness (Ra) and gloss (GU) were taken using a 3-D optical profilometer and a glossmeter, respectively; then specimens were randomized into four groups (n = 17). All specimens were immersed in a coffee solution (24 h × 12 days) then subjected to two whitening systems. G1-negative control (kept moist × 7 days); G2-positive control (brushed with distilled water, 200 g/load, 2 min twice daily × 7 days); G3-whitening toothpaste (Colgate optic white; relative dentin abrasivity (RDA) = 100, 200 g/load, 2 min twice daily × 7 days); and G4-simulated at-home bleaching protocol (Opalescence,15% carbamide peroxide (CP), 6 h/day × 7 days). The study outcomes were measured at baseline and after the treatments. Data were analyzed using paired T-test and one-way ANOVA (α = 0.05).

RESULTS

The mean surface roughness significantly increased (p ⩽ 0.002) for all groups after the designated treatment protocols. Among groups, the mean surface roughness of G2 and G3 were significantly higher (p ⩽ 0.001) (Ra: 0.51 and 0.57 μm, respectively) compared to the control group (Ra: 0.23 μm), and were not significantly different from G4 (Ra: 0.46 μm). Surface gloss decreased with no significant change within or among groups after treatment.

CONCLUSION

All glazed LDGC had a significant increase in surface roughness after being subjected to simulated 1 year of coffee drinking and whitening systems (15% CP and whitening toothpaste), and the greatest change was associated with brushing (simulating 8 months). However, coffee beverages and whitening systems had no significant effect on the surface gloss.

Effects of abutment tooth and luting agent colors on final color of high-translucent zirconia crowns

PURPOSE

This study aimed to evaluate the effects of the tooth portion evaluated and the colors of the abutment tooth and resin luting agent on the final color of monolithic zirconia crowns.

METHODS

Monolithic zirconia crowns were fabricated for left maxillary central incisors using two shades (A2 and A3) of highly translucent monolithic zirconia disks. A model of the abutment tooth was fabricated using resin core materials (white: W; dentin: D). The color of the crowns was measured with try-in pastes (clear: C; brown: B) as a resin-luting agent substitute. The measurement was performed after placing the crown on the model with the attached abutment tooth with try-in paste. The color of three labial portions (cervical, body, and incisal) was evaluated using a dental spectrophotometer. The color difference (ΔE) between the CIELab values of the zirconia disks and the final me asurement of zirconia crowns was calculated.

RESULTS

The ΔE between the crown of the A2 shade and the zirconia disk of the A2 shade had the highest ΔE value in the body portion with W-B (ΔE=3.92). Similarly, the A3 shade had the highest ΔE value in the cervical portion, with W-B (ΔE=4.27). The results of three-way ANOVA showed that the ΔE values were influenced by the tooth portion evaluated and the color of the abutment tooth.

CONCLUSIONS

The final color of the monolithic zirconia crowns was significantly in fluenced by the tooth portion evaluated and the color of the abutment tooth.

Effect of CAD-CAM ceramic materials on the color match of veneer restorations

STATEMENT OF PROBLEM

With the different translucency levels and types of computer-aided design and computer-aided manufacturing (CAD-CAM) ceramic materials, choosing the most appropriate CAD-CAM ceramic materials to better reproduce the color appearance of natural teeth can be challenging.

PURPOSE

The purpose of this in vitro study was to analyze the color differences between natural teeth and milled veneers fabricated with the different types of CAD-CAM ceramic materials.

MATERIAL AND METHODS

Ten extracted maxillary central incisor teeth with the A2 shade in the body region were prepared for ceramic veneers. The veneer restorations were designed by using the duplicating method and fabricated from 9 milling blocks (IPS e.max CAD HT/LT, Lava Ultimate CAD HT/LT, VITA SUPRINITY HT/T, IPS Empress CAD HT/LT/Multi) in a dental milling unit (n=10). The bonding surface of the abutment tooth was coated with a thin layer of a separating agent, and the veneer specimen with resin cement was then bonded to the corresponding abutment tooth. A clinical spectrophotometer was used to measure the Commission Internationale de l'Eclairage Lab values of natural teeth, abutment teeth, and milled veneers in the cervical, body, and incisal regions. Color differences between the natural tooth and A2 shade tab (ΔE₁) and between the milled veneer and natural tooth (ΔE₂) were calculated. The ΔE₂ values were compared with the perceptibility threshold (ΔE=2.6) and acceptability threshold (ΔE=5.5). The paired-samples t test, 1-way analysis of covariance, and 2-way ANOVA were used to analyze data (α=.05).

RESULTS

The results of 1-way analysis of covariance showed that ceramic materials significantly affected the a∗ and b∗ values of the milled veneers (P<.001) but did not affect the L∗ values of the milled veneers (P>.05). The results of 2-way ANOVA indicated that the ΔE₂ values were not significantly affected by different CAD-CAM ceramic materials (F=1.560, P=.138), while statistically significant differences were found in the veneer regions (F=6.588, P=.002). The ΔE₂ values ranged from 2.41 to 5.36, less than the clinically acceptable color threshold of 5.5.

CONCLUSIONS

The color parameters of milled veneers were affected by the different types of CAD-CAM ceramic materials. The color of the veneer restoration was able to match that of the natural tooth.

Computer-aided indirect bonding versus traditional direct bonding of orthodontic brackets: bonding time, immediate bonding failures, and cost-minimization. A randomized controlled trial

INTRODUCTION

The primary aim of this randomized controlled trial was to compare the time for bracket bonding using either direct or computer-aided indirect bonding; a secondary aim was to assess immediate bracket debondings and cost minimization.

METHODS

Consecutive patients were randomly allocated to two groups (blocks of four, online-generated sequence) using a split-mouth design with a direct and a computer-aided indirect bonding method: group 1 (upper right and lower left quadrants: indirect bonding; upper left and lower right quadrants: direct bonding) or group 2 (opposite situation). The primary outcome was difference in time spent for bonding brackets. The secondary outcome was immediate bracket debondings (at the bonding appointment). Time for indirect bonding was recorded in two steps: digital bracket placement and clinical bonding procedure. Outcome assessment was blinded. Friedman's ANOVA test was used to assess differences in bonding time. Chi-square test was used to compare immediate debondings. A cost-minimization analysis was undertaken.

RESULTS

Thirty-seven patients were randomized to group 1 or 2. Ten patients were excluded: 15 patients were analyzed in group 1 and 12 in group 2. Clinical chair time for bonding half a mouth was significantly shorter for computer-aided indirect bonding (12 minutes 52 seconds) than for direct bonding (16 minutes 47 seconds) (P < 0.001). When adding the time for digital bracket placement, the total bonding time (28 minutes 14 seconds) was longer for indirect bonding than for direct bonding (P < 0.001). There was no single immediate debonding with the direct bonding method, while 14 brackets were lost with the indirect bonding method (5.1 per cent) (P = 0.0001). Cost-minimization analysis showed that computer-aided indirect bonding was more expensive than direct bonding.

CONCLUSIONS

The clinical chair time was significantly shorter for computer-aided indirect bonding than for direct bonding. However, the total bonding time for computer-aided indirect, including digital bracket placement, was longer than for direct bonding. There were significantly more immediate debondings with computer-aided indirect bonding than with direct bonding. Under these conditions, computer-aided indirect bonding was more expensive than direct bonding.

REGISTRATION

This trial was retrospectively registered on ClinicalTrials.gov (University of Aarhus Protocol Record 10101).

PROTOCOL

The protocol was not published before trial commencement.

Influence of background color on color perception in dentistry

OBJECTIVE

To evaluate the influence of neutral color backgrounds on the perception of color differences in dentistry.

METHODS

A software was developed for this study that calculated the perceptibility (PT) and acceptability (AT) thresholds of color differences between a pair of computer-simulated incisor samples (n = 60 pairs) over three neutral color (white, gray and black) backgrounds. CIELAB and CIEDE2000 color difference formulas were used. Five groups of volunteer observers (N = 100) participated in the psychophysical experiment (n = 20): Dentists; Dental students; Dental auxiliaries; Dental technicians; and Laypersons. The psychophysical experiment was performed in a dark environment on a calibrated high-resolution screen. To determine PT and AT values, the 60 pairs of samples were randomly presented to each observer over the different backgrounds. The data were adjusted (TSK Fuzzy) and analyzed statistically using Student t-test and ANOVA (α = 0.05).

RESULTS

Regardless of the metric and the background used, the PT values showed no difference among different observers (p > 0.05). Dentists showed the lowest PT values. Dental technicians showed the lowest AT (p ≤ 0.05) and similar values for the three backgrounds (p > 0.05), regardless of the metric used. The other groups of observers showed the lowest and the highest AT values when using black and white backgrounds, respectively (p ≤ 0.05).

CONCLUSIONS

The lowest AT values using a black background indicates that the use of this background allows for the evaluation of slight color differences, and should be used for challenging color differences in esthetic dentistry. This study showed the influence of the observer experience on color evaluation in dentistry.

CLINICAL SIGNIFICANCE

There was no influence of the background color on the perceptibility threshold. However, dentists and dental technicians showed greater ability to perceive slight color differences compared to other groups of observers.

Color compatibility between dental structures and three different types of ceramic systems

BACKGROUND

To assess color compatibility between dental structures (human enamel and dentine) and three different types of ceramic systems.

METHODS

Samples (1 and 2 mm-thick) of extracted tooth (containing dentine and enamel areas) and three ceramic systems with different shades and opacities (HT-High Translucent, T-Translucent) were prepared for this study: Vita Suprinity-VS (HT, T; A1, A2, A3, A3.5, B2, C2, D2) (Vita Zahnfabrik); Vita Enamic-VE (HT, T; 1M1, 1M2, 2M2, 3M2) (Vita Zahnfabrik) and Noritake Super Porcelain EX-3-NKT (A1, A2, A3, A3.5, B2, C2, D2) (Kuraray Noritake Dental). Reflectance measurements of all samples were performed over black backgrounds using a non-contact spectroradiometer (SpectraScan PR-670, Photo Research) under a CIE 45°/0° geometry. CIE L*a*b* color parameters were measured and CIELAB/CIEDE2000 color differences (ΔE₀₀/ΔE^*_ab) and corresponding Coverage Error (CE) of ceramic system for dentine or enamel samples were calculated. Color data was analyzed using one-way ANOVA and post-hoc multiple comparisons tests. CE values were interpreted by comparisons with available 50:50% acceptability color threshold (AT) for dentistry.

RESULTS

Statistically significant differences in lightness were found among all ceramic systems and human dentine (p < 0.001), while no significant differences were registered between enamel and VSHT, T and VEHT. 1 mm dentine showed no statistical differences with VST and VSHT for a* coordinate, while 2 mm dentine showed no significant differences (p > 0.05) with VEHT. Thin samples (1 mm) of dentine and enamel showed significant statistical differences (p < 0.05) for b* coordinate with less translucent materials (NKT, VET and VST). For dentine samples, none of the ceramic materials provided a CE lower than AT. VSHT provided the best CE for 1 mm-thick (CE₀₀ = 1.7, CE_ab = 1.9) and for 2 mm-thick (CE₀₀ = 2.3; CE_ab = 2.5) enamel samples.

CONCLUSIONS

Color coordinates of evaluated esthetic ceramic systems were statistically different from those of human dentine in almost all cases. The evaluated ZrO₂ lithium silicate glass-ceramic (VS), with its two levels of translucency, provided lower CE values with human enamel samples while conventional feldspathic ceramic (NKT) and hybrid ceramic systems (VE) demonstrated a better color compatibility with dentin samples.

Impact of short-term dental dehydration on in-vivo dental color and whiteness

OBJECTIVE

To determine in-vivo chromatic and whiteness changes produced by short-term dental dehydration.

METHODS

Spectral reflectance of 452 upper incisors (226 centrals and 226 laterals) of 113 participants were measured using a spectroradiometer at baseline and after short-term dehydration (minutes 2, 4, 6, 8 and 10). CIE L*a*b* color coordinates (L*, a*, b*, C*_ab and h_ab) and whiteness index for dentistry (WI_D) were calculated. Color differences (ΔE₀₀, ΔE_ab^*) and whiteness differences (ΔWI_D) were computed and interpreted based on their respective 50:50% perceptibility (PT) and acceptability thresholds (AT). Statistical analysis was performed using the related samples Wilcoxon signed-rank test.

RESULTS

L* showed an increasing trend with dehydration, while a*, b*, C*_ab and h_ab have a decreasing tendency. All chromatic coordinates showed statistically significant differences (p < 0.003) at each interval of dehydration compared with baseline, except a* for all teeth. For ΔE₀₀ and ΔE_ab^* values were higher than PT after 2 min of teeth dehydration and higher than AT after 6 and 8 min, respectively. The percentage of teeth exceeding corresponding PT was higher than 50% after 2 min. WI_D index increased with dehydration time, while whiteness differences were clinically perceptible after 4 min. Statistically significant differences were found for WI_D between all dehydration intervals (except 8-10 min). The percentage of teeth exceeding whiteness PT was higher than 50% after 6 min of teeth dehydration.

CONCLUSIONS

Short-term dental dehydration produces clinically unacceptable changes in tooth color and clinically perceptible increase in tooth whiteness level.

CLINICAL SIGNIFICANCE

Clinical shade matching must be done within the first two minutes of any clinical procedure that requires precise chromatic determination but implies a risk of tooth dehydration.

Effect of fabrication techniques on the optical properties of zirconia-based systems

STATEMENT OF PROBLEM

How the optical properties of zirconia restorations are affected by their differing processing techniques is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the effects of 5 different fabrication techniques on the optical properties of zirconia-based systems, including the color difference between the corresponding shades (ΔE∗_ab, ΔE₀₀), translucency parameter, opalescence parameter, and fluorescence (ΔE∗_ab-FL).

MATERIAL AND METHODS

Sixty zirconia disks (IPS e.max ZirCAD) were prepared (0.5 ±0.01mm thick) and veneered by using different techniques (n=15): Group L - layering with fluorapatite ceramic; Group P - pressing with fluorapatite ceramic; Group CB - veneered with pressing followed by layering technique; Group CO - digitally veneered with lithium disilicate glass-ceramic; and Group FZ - prepared from monolithic zirconia (inCoris TZI) (n=15). All the specimens were set to 1.5 ±0.02 mm in thickness. Color measurements were made with a spectrophotometer. Data were statistically analyzed with 1-way ANOVA and the Tukey honestly significant difference, Kruskal-Wallis, Bonferroni (α=.05), Pearson, and Spearman correlation tests (α=.01).

RESULTS

Significant differences were found among the groups for all the optical parameters (P<.05). All the groups showed color differences higher than the perceptibility and acceptability thresholds for ΔE∗_ab and ΔE₀₀, except the P and FZ groups that showed values lower than the acceptability threshold (ΔE∗_ab<2.7). Translucency parameter, opalescence parameter, and ΔE∗_ab-FL values ranged between 5.77 and 9.95, between 4.72 and 7.07, and between 1.93 and 3.14, respectively. Strong positive correlations were found between ΔE∗_ab and ΔE₀₀, as well as between translucency parameter and opalescence parameter (P<.001).

CONCLUSIONS

The optical properties of the zirconia-based systems were significantly affected by the fabrication techniques even when the same nominal shade was used. Therefore, the color reproduction, translucence, opalescence, and fluorescence of the selected materials should be considered for acceptable color matching.

Accuracy and repeatability of different intraoral scanners on shade determination

OBJECTIVE

To evaluate the accuracy and repeatability of different intraoral scanners on shade determination.

MATERIALS AND METHODS

Ten different shades of Vita Mark II blocks were used. A disc-shape specimen (10 mm in diameter and 1 mm thick) per ceramic block was fabricated. Ten color measurements per specimen were performed by each instrument (Vita Easyshade V [control], 3shape Trios, Cerec Omnicam, Cerec Primescan) and recorded in Vita Classic color system. The number of correct shade match per instrument for each shade was recorded. Instrumental accuracy was compared using Cochran Q test and repeatability was analyzed using Cronbach's alpha.

RESULTS

There was a significant difference in the instrumental accuracy for shade determination (p < 0.001). There was no statistical difference between the Easyshade V (78%) and the 3Shape Trios (66%) (p > 0.05), with the latter being similar to the other scanners Primescan(63%) and Omnicam (57%) (p > 0.05). No significant difference was found (p > 0.05) when different shades were evaluated by the same instrument. Similar repeatability was found for the different devices, ranging from 44.3% for Easyshade to 51.9% for Omnicam.

CONCLUSION

The evaluated instruments showed less than expected repeatability and accuracy on measuring different dental shades. Therefore, caution should be exercised when using instrumental shade determination, which should be accompanied by experienced human visual assessment.

CLINICAL SIGNIFICANCE

The outcome of this study might help clinicians evaluate the performance of intraoral scanners as a shade matching tool.

Evaluation of shade correspondence between current monolithic CAD/CAM blocks and target shade tab by considering the influence of cement shade and restorative material thickness

It was aimed to evaluate shade matching between novel CAD/CAM blocks and the A2 target shade tab by considering the influence of cement shade and restorative material thickness on the chromatic background. A total number of 120 rectangular-shaped specimens were subtracted from four different prefabricated CAD/CAM blocks [Vita Enamic (VE), Lava Ultimate (LU), GC Cerasmart (GC), and Vita Mark II (VMII)]. These specimens had thicknesses of 0.5 mm and 1.0 mm. Three different shades (A2, opaque, and translucent) of dual-polymerized resin cement were chosen. The dentin shade (A3.5) restorative composite foundation was incrementally fabricated in a silicon mold. For control group, the A2 shade tab of the Vitapan classical shade guide was used. Different restorative material-cement-foundation assemblies were generated with optic gel. Color readings were performed by using a clinical spectrophotometer, and CIEDE2000 (ΔE₀₀) formula was used to assess color differences. Data were statistically analyzed (α = 0.05). With increasing thickness, color difference values decreased. Higher mean ΔE₀₀ units were observed in all restorative material sub-groups for 0.5 mm thickness. In TR shade, no statistically significant difference was detected among the mean ΔE₀₀ values of 0.5 mm-thick restorative materials. Color differences in groups 1.0 mm-opaque-LU and 1.0 mm-opaque-GC indicated perceptible but clinically acceptable values (0.8˂ΔE₀₀ ≤ 1.8). The highest and lowest ΔE₀₀ units were observed in the 0.5 mm-A2-VE group (ΔE₀₀ = 7.07) and 1 mm-opaque-GC group (ΔE₀₀ = 1.46), respectively. Luting cement shade, restorative material type, and thickness significantly influenced the resultant color of restoration. Opaque cement on dentin foundation exhibited lower color differences.

Effect of substrate and cement on the final color of zirconia-based all-ceramic crowns

OBJECTIVE

To evaluate the influence of the substrate and the cement on the final color of ceramic crowns.

METHODS

Prosthetic crowns (framework + porcelain) were fabricated using two all-ceramic systems (YZ, 3 mol% yttria-stabilized tetragonal zirconia; IZ, alumina-based zirconia-reinforced glass-infiltrated ceramic) and a metal-ceramic system (MC; n = 8). Metal (M) and resin (R) were used as substrate abutments. For R substrate, crowns were evaluated as seated (R) and after cementation (R-C). CIELAB color coordinates were obtained using a dental spectrophotometer with D65 light illumination. CIELAB, CIEDE2000 (1:1:1) and CIEDE2000 (2:1:1) color difference metrics were used. Data were analyzed using 95% confidence intervals and compared to perceptibility (PT) and acceptability (AT) thresholds.

RESULTS

The ∆ E ab * , ∆E₀₀ (1 : 1 : 1), and ∆E₀₀ (2 : 1 : 1) values of the restorative systems evaluated using different substrates (M.R) were similar to the AT values of each metric. When non-cemented and cemented crowns were evaluated (R.R-C), MC had color difference values at PT and below AT; while YZ and IZ showed similar values to AT, for ∆ E ab * and ∆E₀₀ (1 : 1 : 1) metrics.

CONCLUSION

The substrate and cement affected the final color of zirconia-based all-ceramic crowns, but the color differences corresponded to an acceptable match.

CLINICAL SIGNIFICANCE

As both substrate and cement influence the final color of multi-layered ceramic prosthesis, dentists and dental technicians should understand the optical properties of dental ceramics to reproduce the natural appearance of dental structures and maximize the chance for excellent color matches.

Acid Effects on the Physical Properties of Different CAD/CAM Ceramic Materials: An in Vitro Analysis

PURPOSE

To evaluate the flexural strength, elastic modulus, microhardness, and surface roughness of monolithic zirconia, lithium disilicate ceramics, and feldspathic ceramics after being exposed to different acidic solutions.

MATERIALS AND METHODS

Rectangular specimens (n = 180) were prepared from three different ceramic materials: lithium disilicate, monolithic zirconia, and feldspathic porcelain. Initial Surface roughness of ninety specimens (n = 30/material) was evaluated using an optical noncontact profilometer. Thirty specimens of each material were immersed in one of the following solutions (n = 10/group): citric acid; acidic beverage; and artificial saliva, which served as the control. Post immersion surface roughness, flexural strength, and elastic modulus were determined using an optical noncontact profilometer and three-point bending test. Another thirty specimens of each material were immersed in the aqueous solutions (n = 10/group) following the same protocol and subjected to microhardness test using a Vickers diamond microhardness tester. A scanning electron microscope (SEM) was used to examine the surface characteristics changes. ANOVA and Post-hoc Tukey's Kramer tests were used for data analysis (α = 0.05).

RESULTS

Immersion in different solutions did not affect the flexural strength and elastic modulus of lithium disilicate or zirconia. Microhardness and surface roughness were significantly affected in all groups (p < 0.05). For feldspathic porcelain groups, the flexural strength and elastic modulus were significantly decreased in the citric acid group (p = 0.045 and p = 0.019). Also, there were significant differences among all feldspathic porcelain groups (p = 0.001) in terms of microhardness and surface roughness values.

CONCLUSIONS

The tested acidic agents significantly affected the flexural strength, elastic modulus, surface roughness, and microhardness of feldspathic porcelain. However, the flexural strength and elastic modulus of evaluated lithium disilicate and zirconia did not change significantly.

Bond Strength of Metal and Ceramic Brackets on Resin Nanoceramic Material With Different Surface Treatments

Objective

This study aimed to evaluate the effects of different surface conditoning methods on surface texture and shear bond strength (SBS) of brackets bonded to resin nanoceramic material.

Methods

Ceramic specimens were divided into two groups as metal brackets and ceramic brackets. In each group, the following five subgroups were conditoned with orthophosphoric acid (OPA), hydrofluoric acid (HFA), silica coating with Cojet, Nd: Yag laser, and Femtosecond (Fs) laser. Extra samples were used for scanning electron microscopy and 3D profilometer evaluation.

Results

All surface conditioning methods caused optimum or higher SBS. Metal brackets had higher SBS than porcelain brackets, but this difference reached statistical significance only in Fs laser group. OPA caused surface modification comparable to HFA because of polymer content of resin nanoceramic. Although Fs laser and Cojet conditioning caused optimum or higher SBS, surface damage of these methods to the resin nanoceramic specimens clearly seen on 3D profilometer.

Conclusion

HFA and Nd: Yag laser are effective surface conditioning methods for resin nanoceramics. OPA combined with silane application caused optimum SBS and can be used as an alternative to HFA. Surface texture changes should be considered to determine surface damage while deciding the optimum surface conditioning method for ceramics other than SBS.

Knowledge and Attitudes of Dental Interns and Dentists on Implants and Implant-Retained Restorations in Jeddah, Saudi Arabia

Objectives:

This cross-sectional study aimed to assess the knowledge and attitudes of dental interns and dentists in Jeddah, Saudi Arabia, about Cement-Retained Restoration (CRR), Screw Retained Restoration (SRR), and implant restoration.

Methods:

A total of 530 dentists and students participated in the study. Data were collected using a self-administrated questionnaire modified from previous studies. The collected data were analyzed using SPSS software for t-test, linear regression, and ANOVA.

Results:

Participants had a mean score of 5.01 (SD = 1.50) for a total of nine implant-retained restoration (IRR)knowledge questions (lowest score = 0, highest score = 9), and general implant knowledge had a mean score of 3.12 (SD = 1.25) for five questions with scores of 0 to 5. The participants’ knowledge about implants significantly differed in relation to gender, place of work, and work status. Also, participant knowledge about IRR showed significant differences in relation to participants' knowledge, age, gender and place of work. The dental interns and dentists were in agreement in considering SRR to be better than CRR for six out of nine factors. Those factors were cost effectiveness, expertise required for provision, retrievability, retention, fracture resistance, and passivity of fit.

Conclusion:

The overall knowledge of dental interns and dentists regarding implants and IRR was fair and needs to be improved, given the tendency of general dentists to engage in implant dentistry. Both dentists and interns considered CRR to be aesthetically superior, easier to fabricate, and requiring comparatively less expertise in comparison to SRR.

Dentists’ Self-perception on Teledentistry: The Changing Landscape Driven by Technological Booming in the 21stCentury

Aim:

Teledentistry has gained popularity worldwide because it is cost-effective and increase accessibility to dental healthcare. This study assessed the self-perceptions of teledentistry among dental practitioners in Saudi Arabia and examinedany gender-related differences.

Methods:

This cross-sectional study was conducted between January and December 2017 and recruited a convenience sample of dental practitioners, whose self-perceptions of the practice-related use of teledentistry were assessed viaateledentistry survey (TDS). The TDS consisted off our sections:efficiency in patient care, cost reduction,capabilities forimproving practice, and security and confidentiality.Data analyseswere conducted throughdescriptive statistics,internalreliability tests(Cronbach’s alpha), andchi-squaredtests of the TDS.

Results:

The response rate was 620/800(78%). Most respondents were female (62%), and 58% of themworked in the public sector. The internal reliability of the TDS was 0.85 for the whole sampleand 0.85 and 0.90 for males and females, respectively. Among the entire sample, 51% agreed that teledentistry reduced potential cost, and 65% reported shortened waitlists. More females (42%, p<0.001) than males (22%) agreed that teledentistry could help monitor a patient’s condition.More females (35%) than males (13%, p<0.001) considered that teledentistry would require additional appointments for imaging. More females(29%, p=0.0001) than males (22%) expressed great concern aboutpotential violations of confidentiality.

Conclusion:

These findings suggest thatteledentistry in dental practiceis well perceived by practitioners in Saudi Arabia. Gender differences in perceptions are linked to certain aspects of teledentistry.

Prolonged UV-C Irradiation is a Double-Edged Sword on the Zirconia Surface

Zirconia has become an excellent choice of dental implants because of its excellent mechanical strength, aesthetic, and biocompatibility. Although some studies have shown ultraviolet (UV) irradiation is effective to photofunctionalize dental zirconia that can improve osteoblastic function, the scattered information has not identified the most effective exposure time and wavelength of UV. Herein, this study has investigated the effects of UV irradiation on zirconia after UV-A (365 nm) or UV-C (243 nm) photofunctionalization for different times (15 min, 3 and 24 h). After irradiation, the zirconia surface was analyzed by color spectrophotometry, scanned electron microscopy (SEM), energy-dispersive X-ray spectrometry, water contact angle (WCA) with goniometer, and X-ray diffraction. Osteoblastic (MC3T3-E1) cells were cultured on zirconia discs and evaluated with a CCK-8 test kit for cell proliferation (3 h and 1 day) and with alkaline phosphatase (ALP) activity (14 days). Significant color change (ΔE) was observed by irradiating with UV-C for 15 min (1.99), 3 h (1.92), and 24 h (3.35), whereas only minute changes were observed with UV-A (respectively, ΔE: 0.18, 0.14, 0.57). No surface textural changes were observed nor a monoclinic phase was detected on both the UV-A and UV-C irradiated samples. UV-C significantly decreased the C/Zr ratios and WCA, with irradiating for 24 h presenting the lowest values, and it was the only condition to give significantly higher ALP activity at 14 days (p < 0.05) and CCK-8 values for 1 day culture (p < 0.05). It is concluded that UV-C (but not UV-A) irradiation can significantly change the aesthetic in color, and only prolonged 24 h UV-C irradiation can enhance MC3T3-E1 cell adhesion on zirconia by photofunctionalization.

Influence of Bleaching and Aging Procedures on Color and Whiteness of Dental Composites

Bleaching can cause perceptible color changes on resin-based composite (RBC) restorations that may not be stable with aging. The objective of this study was to evaluate color stability and whiteness variations of RBCs after bleaching and aging procedures. Discs (10 mm in diameter and 1 mm thick) of shades A2 and A3 were fabricated from two RBCs (Filtek Z250 and Filtek Z350 XT) and divided into three subgroups (for each composite and shade) (n=5) as follows: control (no bleaching), at-home bleaching, and in-office bleaching. All specimens underwent an accelerated artificial aging up to 450 KJ/m2 and 900 KJ/m2 in an aging chamber (Suntest XXL+). A spectroradiometer (SpectraScan PR-670) was used to obtain CIE L*a*b* coordinates. CIEDE2000 color difference (ΔE00) and whiteness index for dentistry (WID) were used to evaluate color stability. Color and whiteness differences data were analyzed considering the 50:50% visual color difference thresholds (perceptibility [PT] and acceptability [AT]) and 50:50% whiteness thresholds (whiteness perceptibility [WPT] and whiteness acceptability [WAT]). Analysis of variance and Tukey tests (α=0.05) were used to statistically analyze the data. After bleaching, all specimens showed ΔE00 and ΔWID values below their corresponding acceptability thresholds (AT and WAT, respectively). After aging, L* and WID values decreased while b* values increased (p≤0.05), resulting in ΔE00 and ΔWID values above AT and WAT, respectively. Color changes after bleaching RBCs were clinically acceptable, while aging provoked clinically perceptible color changes.

An in vitro evaluation of the effect of polishing on the stainability of different CAD/CAM ceramic materials

Purpose

To determine the effect of coffee on the stainability of CAD/CAM ceramics after different surface treatment protocols.

Methods

Ninety specimens (2 mm × 10 mm) of CAD/CAM ceramic materials (Vitablocs Mark II, VITA Enamic, and VITA Suprinity) were prepared. The specimens were subdivided (n = 10) into three groups: G1: Glazed (control group), G2: Subjected to finishing and polishing, and G3: Re-glazed after finishing and polishing. The surface treatment was performed using a diamond polishing system for porcelain (Diapol) followed by applying a diamond polishing paste (Diapolisher). The specimens were immersed in distilled water for 24 h, and the baseline color measurement after finishing and polishing was recorded. Each group was then immersed in a staining solution (coffee) for one week, and the second color measurement was recorded.

Results

The color of the CAD/CAM ceramic materials in the finishing and polishing groups changed significantly after staining (P < 0.05). Statistically significant differences were noticed after staining in the polished groups of Vita Enamic and Vita Suprinity compared with the glazed group (control). However, the color change between the re-glazed and control groups was insignificant for all the materials (P > 0.05). Although the color change values of the three CAD/CAM materials increased, these changes were within the clinically acceptable value (ΔE < 3.3).

Conclusion

Staining of the tested CAD/CAM ceramic materials increased the color change values within the clinically acceptable range in all the groups, with the highest values found after finishing and polishing. Re-glazing is recommended after surface adjustment for all the tested materials to increase their resistance to staining.

Recent Advances in Color and Whiteness Evaluations in Dentistry

Background:

The final goal of color measurement or shade specification in dentistry is the reproduction by prosthetic materials of all important appearance characteristics of natural oral structures. The application of color science in dentistry is an objective way to measure and evaluate such structures and dental materials in clinical practice and dental research.

Methods:

Literature on color science was reviewed to present new metrics to evaluate color differences of dental materials and dental structures. Visual acceptability and perceptibility values of color differences are reviewed and new whiteness indexes to describe whiteness in dentistry are presented.

Results:

In the last decade, the CIELAB 50:50% perceptibility and acceptability thresholds were set to 1.2 and 2.7, respectively, and the CIEDE2000 50:50% perceptibility and acceptability thresholds were set to 0.8 and 1.8. The CIEDE2000 color-difference formula became increasingly popular in dentistry. Developments in color science have led to the description of tooth whiteness and changes in tooth whiteness based on whiteness indexes, with the most relevant being the WID whiteness index, which is a customized index based in CIELAB color space.

Conclusion:

The application of color science in dentistry has allowed the precise description of tooth color and whiteness. The revised and new CIEDE2000 color-difference formula is expected to fully replace the outdated CIELAB formula in almost all dental applications. Recent psychophysical studies have reported values of visual thresholds and new whiteness indexes, which can serve as quality control tools to guide the selection of esthetic dental materials, evaluate clinical performance, and interpret visual and instrumental findings in clinical dentistry, dental research, and subsequent standardization.

The Effect of Ceramic Type and Background Color on Shade Reproducibility of All-Ceramic Restorations

PURPOSE

To investigate the effects of background color on shade reproduction using CAD/CAM zirconia and lithium disilicate ceramics.

MATERIALS AND METHODS

A plastic tooth was prepared for an all-ceramic crown and scanned. Tooth-shaped light background dies were manufactured. Full-contour crowns were milled from translucent zirconia (ZT) and low translucency lithium disilicates (E [LT]). Copings from opaque zirconia (Z) and medium opacity lithium disilicate (E[MO]) ceramics were milled and layered with veneering porcelain to full contour. Metal copings were used to produce a dark background. Specimens were divided into 8 groups with 3 variables: background color, ceramic type, and translucency. Crowns were cemented using composite resin cement. Color was measured with a spectrophotometer. Color difference (∆E) was calculated using the CIEDE2000 formula between the specimens and the target shade, A1. Statistical analysis was performed using a nested design 3-way ANOVA and Tukey multiple comparisons.

RESULTS

The closest ∆E to target shade was produced by E (LT) (2.13 ± 0.19) on the dark background. This increased significantly to 2.90 ± 0.19 on the light background (p = 0.03). The e.max (MO) groups significantly increased (p = 0.001) to 4.40 ± 0.22 and 4.47 ± 0.4, (p = 1.00) for the dark and light backgrounds, respectively. ∆E for the zirconia groups were higher and ranged from 4.85 ± 0.48 to 5.60 ± 0.48 in the ZT groups (p = 0.04) and 6.5 ± 0.82 to 7.75 ± 0.53 (p = 0.001) for Z groups from dark to light backgrounds. There was an overall lack of chromaticity between the specimens and the target shade A1 CONCLUSIONS: Ceramic color was affected by ceramic type, background, and translucency. Lithium disilicate appeared to be better than zirconia in shade reproduction. Less-opaque materials matched the target shade better, while opaque materials and low translucencies were more suitable for dark backgrounds.

Effects of core and veneer thicknesses on the color of CAD-CAM lithium disilicate ceramics

STATEMENT OF PROBLEM

The color of dental ceramics is important for achieving successful esthetic restorations. However, insufficient studies are available of the color of recently introduced computer-aided design-computer-aided manufacturing (CAD-CAM) lithium disilicate ceramics as functions of the core and veneer thicknesses.

PURPOSE

The purpose of this in vitro study was to evaluate the effects of the thickness of different core and veneer thicknesses on the color of CAD-CAM lithium disilicate ceramics.

MATERIAL AND METHODS

A total of 42 specimens from 2 groups of 7 ceramic cores at 3 thicknesses (0.8, 1.0, and 1.2 mm) were fabricated. The veneer was fabricated at 3 thicknesses (0.3, 0.5, and 0.7 mm). The group name was based on the name of the ceramic core (IPS e.max CAD; lithium disilicate [LD], IPS Empress CAD; leucite-reinforced glass-ceramic [LR]), and the associated number was determined by the combined thicknesses of the core and the veneer: 1=0.8+0.7; 2=1.0+0.5; and 3=1.2+0.3. The color coordinates and the color differences were calculated using a spectrophotometer. The color difference was analyzed using the CIEDE2000 chrominance and the acceptability threshold. Two-way ANOVA was used to identify the color difference based on the core/veneer thicknesses, and the Tukey honest significant differences and Games-Howell tests were conducted to verify the ΔE₀₀ differences of the group (α=.05). In addition, regression analysis was carried out to estimate the causal relationship between the independent variables and the chrominance.

RESULTS

At a certain thickness, the color differences of LD1, LR1, and LR2 were not clinically acceptable based on the thicknesses of the core and the veneer. Results of 2-way ANOVA demonstrated that the different thicknesses of core/veneer combination significantly affected the color difference (P<.05). A significant interaction was present between the thickness and the material (P<.05). The results of multiple regression analyses showed that the average color difference of LR increased by 0.019 as the thickness of the core decreased by 0.2 mm.

CONCLUSIONS

The color is influenced by the thicknesses of the core and the veneer. With a certain thickness, the color differences increased as the thickness of the core decreased, and lithium disilicate ceramics were less vulnerable to standard deviation of color difference compared with the leucite-reinforced ceramics.

Masking Colored Substrates Using Monolithic and Bilayer CAD-CAM Ceramic Structures

Objective: To evaluate the masking ability and translucency of monolithic and bilayer CAD-CAM ceramic structures.

Methods: Discs of high translucency (HT) and low translucency (LT) lithium disilicate–based ceramic (IPS e.max CAD) with different thicknesses (0.7, 1, 1.5, and 2 mm) were evaluated as a monolithic structure or combined (bilayer) with a 0.5-mm-thick zirconia framework (IPS e.max ZirCAD). The masking ability and translucency were calculated based on CIE L*a*b* color coordinates measured with a spectrophotometer (SP60, X-Rite). The translucency parameter (TP) was calculated using color coordinates measured over standard white-and-black backgrounds. The masking ability was calculated by CIEDE2000 color difference metric (ΔE00) for each specimen measured over a tooth-colored substrate (shade A2) compared to three darker backgrounds (shade C4 and two metal substrates). Confidence intervals (CI) for the means (95% CI) were calculated for TP and ΔE00. The Pearson correlation between ΔE00 and TP was investigated for monolithic and bilayer structures over all backgrounds.

Results: The thinner the lithium disilicate layer, the greater the translucency and the higher the ΔE00 values. The effect of ceramic thickness on both translucency and masking ability was more pronounced for the monolithic structures. In addition, monolayers always presented a greater color variation than their bilayer counterparts. The metallic background produced greater ΔE00 than the C4-shaded substrate.

Conclusion: Monolithic veneers were able to mask C4-shaded background but did not mask metallic backgrounds. Bilayer structures showed greater shade masking ability than monolithic structures.