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

How could mouthwashes affect the color stability and translucency of various types of monolithic zirconia? An in-vitro study

OBJECTIVES

This study aimed to evaluate the color stability and translucency of various types of monolithic zirconia after immersion in chlorhexidine and Listerine mouthwashes.

MATERIALS AND METHODS

This experimental study was performed on 36 disk-shaped specimens fabricated from low-translucent, high-translucent, and multilayered monolithic zirconia (n = 12 per group). Each group was equally divided and immersed in either 2% chlorhexidine (CHX) or Listerine mouthwash for 2 min daily over 7 days. Changes in color (ΔE) and the translucency parameter (ΔTP) were evaluated and compared. The data were analyzed with one-way ANOVA followed by Tukey's post-hoc tests (α = 0.05).

RESULTS

Chlorhexidine caused a significantly lower ΔE and a significantly higher ΔTP in multilayered zirconia compared to the low-translucency (ΔE: P = 0.0027, ΔTP: P<0.001) and the high-translucency zirconia group (ΔE: P<0.001, ΔTP: P = 0.022). Listerine caused a significantly higher ΔE in the high-translucency zirconia group compared to the multilayered zirconia group (P = 0.0165). It also resulted in a significantly higher mean ΔTP in the multilayered zirconia group compared to the low-translucency (P = 0.0003) and high-translucency zirconia groups (P = 0.019).

CONCLUSIONS

In both mouthwashes, multilayered monolithic zirconia exhibited the highest color stability among the tested materials; albeit with the most pronounced changes in translucency. Meanwhile, high-translucency monolithic zirconia was more prone to discoloration when exposed to both mouthwashes.

Instrumental and visual evaluation of the color adjustment potential of a recently introduced single‑shade composite resin versus multishade composite resins

STATEMENT OF PROBLEM

Single-shade composite resins simplify the process of shade selection by providing a narrow range of color but the ability to simulate all shades. However, evidence is limited for the color shifting ability of a newly developed single‑shade composite resin.

PURPOSE

The purpose of this in vitro study was to evaluate the instrumental color adjustment potential (CAP-I) and visual color adjustment potential (CAP-V) of a recently introduced single-shade composite resin compared with conventional multishade composite resins against different background colors.

MATERIAL AND METHODS

Four multishade composite resins (Spectrum TPH3, Beautifil II, Clearfil AP-X, and Gradia Direct) and a single-shade composite resin (Charisma Diamond One) were tested. Four base shades (A1, A2, A3, and A3.5) of the same composite resin (Filtek Z350XT) were selected as different background colors. Dual specimens (an outer base material with an inner hole filled with inner test material) and single specimens of all test and base materials were prepared (n=6 per group). Spectral reflectance values were obtained by using a spectroradiometer. The color difference (ΔE00) and relative translucency parameter (RTP) were calculated by using the CIEDE2000 and RTPCIEDE2000 formula. Visual scoring of color matching was performed by independent observers. The CAP-I and CAP-V values were calculated according to ΔE00 and visual scoring. Analysis of variance (ANOVA) was used for statistical analysis (α=.05).

RESULTS

CAP-I and CAP-V were significantly affected by composite resin type, background color, and their interaction (P<.001). Positive CAP-I and CAP-V values were found for the majority of test materials. Charisma Diamond One exhibited the highest CAP-I value under all background colors, the highest CAP-V value under most background colors, and the significantly highest RTP value (P<.001).

CONCLUSIONS

The color adjustment potential was dependent on the material type and background color. Charisma Diamond One exhibited the highest color adjustment potential and the most pronounced color shifting ability.

Effect of simulated gastric acid on aesthetical restorative CAD-CAM materials' microhardness and flexural strength

Background

Gastric acid, which is among erosive substances, gradually rises to the mouth in individuals with reflux and bulimia nervosa disorders, and this causes various effects on dental restorations.

Aim

The objective of this study is in vitro investigation of gastric acid's effect on flexural strength and hardness on aesthetic restorative computer-aided design and computer-aided manufacturing (CAD-CAM) materials.

Materials and Methods

For this study, four materials have been used, namely Enamic (Vita), Superfect Zir (Aidite) Zirconia, IPS e.max CAD (Ivoclar Vivadent), and Mark II (Vita). From these four different materials, 24 samples with 14 × 4 × 1 dimensions in rectangular prism form are used, which makes a total of 96 samples. One group was separated as the control group, while the rest was allowed to wait at 37°C, 5 ml gastric acid for 96 hours. Hardness value and flexural strengths were measured as pre-exposure and post-exposure to gastric acid.

Results

There is a statistically significant difference between the groups in terms of the amount of decrease in the mean hardness after exposure to gastric acid compared to pre-exposure values (p: 0,000; P < 0,05). There was no statistically significant difference between the groups in terms of the amount of decrease in the post-exposure average flexural strength compared to the pre-exposure value (p: 0.063; P > 0.05). There is a statistically significant difference between the groups in terms of the average flexural strength after exposure to the acid.

Conclusions

According to the data obtained, it was concluded that exposure to gastric acid affects the hardness and flexural strength properties of dental restorative ceramic materials.

Influence of coloring techniques on the surface characteristics and color stability of a monolithic zirconia ceramic

STATEMENT OF PROBLEM

The color of monolithic zirconia restorations is obtained by presintering or postsintering coloring techniques. However, studies on the differences in surface characteristics and their influence on color stability are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of shading and staining techniques for a zirconia ceramic on the surface characteristics and colorimetric parameters (color difference, translucency, and whiteness index) after exposure to coffee or red wine and then polishing.

MATERIAL AND METHODS

Ceramic disks (N=30; Ø10×1mm) were allocated into 3 groups: preshaded-shaded by the manufacturer (IPS e.max ZirCAD MT, shade A2); manually shaded-unshaded zirconia (IPS e.max ZirCAD MT, bleaching shade-BL) colored by the brushing technique, before sintering; stained-unshaded zirconia (IPS e.max ZirCAD MT BL) colored by the staining technique, after sintering. Spectrophotometric color assessments ensured the same initial perceived color (Vita Classical A2) for specimens included in the study (∆E00<1.77 acceptability threshold). Surface characteristics were assessed by scanning electron microscopy and atomic force microscopy. The specimens were immersed in coffee (n=5) or red wine (n=5) for 12 and 24 days and subsequently polished. The data were statistically and descriptively analyzed for color differences (∆E00), translucency parameters (TP00), and whiteness indexes for dentistry (WID), considering acceptability and perceptibility thresholds.

RESULTS

The shaded groups found an irregular ceramic surface with uniformly sized zirconia crystals. The stained group found a glass-covered smoother surface. Significant alterations in color parameters (∆E00, TP00, WID) were observed with immersion in pigmenting beverages (P<.001) both after 12 days, and after 24 days. The shaded specimens had greater color alterations after immersion but benefited from the polishing procedure, which reduced color differences below an acceptable threshold in comparison with the baseline. Stained specimens had lower color alterations after immersion, but the polishing protocol was detrimental as it whitened the ceramic by subsurface exposure.

CONCLUSIONS

The coloring technique influences the surface characteristics of zirconia ceramic and also the color parameters after exposure to colored beverages and polishing.

Effect of thickness of externally characterized stains on optical properties of high-translucency zirconia

OBJECTIVES

There is insufficient information about the effects of the thickness of externally characterized stains or glazes on CIELAB color parameters and the translucency parameter (TP) of 5 mol% yttria partially stabilized zirconia (5Y-PSZ). The present study evaluated the effect of a thickness reduction of the externally characterized or glazed layer on its CIE2000 color parameters and TP₀₀ of 5Y-PSZ.

MATERIALS AND METHODS

Twenty-eight specimens were sectioned from 5Y-PSZ blanks. Three brands of powdered stains (namely VI, SH, and IV) and a glaze (GL) were used to extrinsically stain the specimen surfaces (n = 7 per group). After measuring the final thickness and color, specimens of each group were carefully ground and finally polished. The reduced thickness was carefully controlled in decrements of 0.02 mm on the characterized stains or glazed layers at each reduction cycle until the surface of the un-stained zirconia was exposed. The CIELAB color parameters of specimens were measured using a spectrophotometer. Subsequently, differences in lightness (∆L'), chroma (∆C'), and hue (∆H'), and TP₀₀ values and color differences (ΔE₀₀) were calculated using the CIEDE2000 formula to determine differences between the specimen and the un-stained zirconia at each reduction cycle. A paired-samples t-test, two-way mixed-design analysis of variance, and Pearson correlation coefficient were used to analyze the data (α = 0.05).

RESULTS

There were no significant differences in lightness, chroma, hue, or TP₀₀ values before or after glazing or after each reduction cycle of the glazed layer. Mean ΔE₀₀ values ranged between 20.94 and 33.55 after applying the externally characterized stains. With a decreased thickness of the characterized stain layer, there were observed that significant decreases in ∆L', ∆H', ∆C', and ΔE₀₀, and significant increases in TP₀₀.

CONCLUSIONS

Increasing the thickness of externally characterized stains decreased the lightness and caused the alternation of chroma and hue, whereas these phenomena were not observed in the glazed group. There was a slight change of CIE2000 color parameters and TP₀₀ when the thickness of the characterized layer exceeded 0.06 mm.

CLINICAL RELEVANCE

The application and thickness of externally characterized stains can sensitively affect CIE2000 color parameters and translucency of 5Y-PSZ.

Effect of thermocycling on the mechanical properties, inorganic particle release and low temperature degradation of glazed high translucent monolithic 3Y-TZP dental restorations

The influence of thermocycling on the surface deterioration of glazed monolithic high translucent 3Y-TZP dental restorations is still unclear. The purpose of this study therefore was to evaluate low temperature degradation (LTD), elemental release and surface degradation pattern after five years of simulated clinical time. A total of 123 specimens were prepared from second-generation high translucent 3Y-TZP as per ISO 6872:2015 standards (3 mm × 4 mm × 30 mm). They were classified as per glazing and thermocycling protocol; group CPT, DGT and IGT. Glaze materials were applied on one surface of the specimen and subjected to a thermocycling in artificial saliva, four-point bending test, inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and x-ray diffraction (XRD). Flexural strength, characteristic strength and Weibull modulus values were derived from four-point bending test. Descriptive fractographic analysis of surfaces was conducted to observe the surface degradation characteristics and point of failure. Control/no glaze with thermocycling (CPT = 621.5, 1σ = 117.0 MPa) presented higher flexural strength values compared to glaze I with thermocycling (442.4, 1σ = 45.4 MPa) and glaze II with thermocycling (534.3, 1σ = 46.3 MPa). Characteristic strength from Weibull analysis also observed higher values (669.2 MPa) for the control specimens. XRD analysis showed that monoclinic volume fraction (Vm = 11.0, 1σ = 0.7%) was highest in control specimens. Fractographic analysis suggested that there was no correlation between the point of failure initiation and mean flexural strength values. Glazing protected the high translucent 3Y-TZP surface against LTD during thermocycling but negatively impacted on the flexural strength.

Masking Ability of Monolithic and Layered Zirconia Crowns on Discolored Substrates

There is scarce information on the colorimetric behavior of monolithic and layered zirconia crowns in combination with various abutment colors. This study evaluated the masking ability on discolored substrates of monolithic and layered zirconia crowns. Anterior crowns were fabricated using 3Y-TZP zirconia and layering ceramic and divided into three groups: monolithic (ML), bi-layer (BL), and tri-layer (TL). The crowns were placed over eleven substrates (ND1-ND9, zirconia, metal), and CIE L*, a*, b*, C*, and h° color coordinates were measured in the cervical, middle, and incisal areas with a spectrophotometer. Masking ability was calculated using the color difference formula, and values were interpreted according to the perceptibility and acceptability thresholds. Data were analyzed statistically (α = 0.001). The L* coordinate was not significantly different between BL and TL crowns, regardless of the measurement area or substrate (p ≥ 0.001). In the middle area, the L* coordinate of the ML group was statistically different from the BL and TL groups only for zirconia and metal substrates, while in the incisal area, only for ND7 and metal substrates. The a* coordinate was significantly different between the ML and layered crowns for all measurement areas and substrates (except zirconia). The b* and C* coordinates differed significantly between the groups only in the cervical area (p < 0.001). The ML crown had better masking ability than the BL and TL crowns. However, the color differences for ML crowns were below the acceptability threshold for ND2, ND3, and ND7 substrates in the cervical and middle areas and below perceptibility threshold only for the incisal area. The lowest masking ability of the crowns was found for ND9 and metal substrates in all measurement areas.

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.

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

Aim

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

Settings and Design

This was a comparative in vitro study.

Materials and Methods

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

Statistical Analysis Used

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

Results

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

Conclusions

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

Repair Bond Strength of Composite Resin to Aged Resin and Glass-Matrix CAD/CAM Ceramic Materials Using Two Different Repair Systems

This study evaluates the repair bond strength of resin-matrix and glass-matrix CAD/CAM ceramic materials based on two repair systems. Thirty specimens measuring 2.5 mm in thickness were prepared from Crystal Ultra (CU), Vita Enamic (EN), Lava Ultimate (LU), Cerasmart (CS), and Vitablocs Mark II (VM2) materials and aged for 5000 thermal cycles. Specimens were randomly allocated into three groups: control, Monobond-S (MS) primer, and Monobond Etch & Prime (MEP). Composite resin (Tetric N Ceram) (5 mm in diameter and 2 mm thick) was packed and light-cured onto treated specimen surfaces. Subsequently, the specimens’ shear bond strength (SBS) was evaluated, and failure modes was recorded. Statistical analysis was performed using factorial ANOVA and Tukey’s post hoc tests (a = 0.05). The factorial ANOVA revealed significant interactions between the material type and repair system, which was significant (p < 0.01). The highest and lowest SBS were obtained for CU (27.09 ± 1.11) and VM2 (4.30 ± 0.59) in MS and control groups, respectively. In all the groups, CU demonstrated higher SBS, whereas VM2 demonstrated lower SBS. There were no significant differences in SBS between EN and LU, and CS and CU in all the study groups (p > 0.05). The Monobond-S repair system provided non-significantly higher SBS compared to the MEP systems, except for VM2 and LU materials. The new resin-matrix CAD/CAM material demonstrated the highest SBS compared to the other materials for both conventional and MEP repair systems. Both repair systems showed clinically acceptable bond strength and allowed for successful repair of the resin-matrix ceramic materials.

Surface roughness and color measurements of glazed or polished hybrid, feldspathic, and Zirconia CAD/CAM restorative materials after hot and cold coffee immersion

Background

The purpose of this study evaluates and compares the effect of surface roughness (Ra) and color stability on computer-aided design/computer-aided manufacturing (CAD/CAM) hybrid resin (Vita Enamic), feldspathic (Vitablocs® Mark II), and lithium disilicate Zirconia (Vita Suprinity) glazed or polished ceramics immersed in hot Arabic Qahwa and cold coffee.

Methods

A total of 96 standardized samples were prepared from CAD/CAM restorative materials. Half of the samples were polished as per the manufacturer’s instructions using a porcelain polishing kit, and the other half were glazed. Samples were distributed and immersed in hot Arabian Qahwa and cold coffee followed by thermocycling. Ra measurements and color changes were conducted before and after immersion. SEM images were captured from each type of glazed or polished ceramic. One-way ANOVA paired Student’s t-test, and Bonferroni test were conducted to detect significant difference between the groups. P > 0.05 was a significant level.

Results

Of all the tested samples, Ra increased without any significant difference; however, mean color changes (ΔE*) showed significant differences. An increase in Ra was noted for all the glazed and polished samples after immersion and thermocycling. However, differences were significant only in VM II. In addition, ΔE* was significant only in Vita Suprinity (VS) samples. For immersion groups, significant Ra changes were noticed in glazed samples, only in Vita Enamic (VE) with no ΔE*. In polished samples, mean Ra changes were observed in VM II and VS samples. Significant differences were also noticed in polished VE and VS subgroups of ΔE*.

Conclusions

Ra affects all the tested samples, providing higher values on the polished specimens. The ΔE* caused by hot Arabic Qahwa and cold coffee on glazed or polished CAD/CAM restorative materials were clinically acceptable.

Patient Satisfaction with Implant-Supported Monolithic and Partially Veneered Zirconia Restorations

The digital workflow and the application of Computer-Aided Manufacturing (CAM) to prosthodontics present the clinician with the possibility of adopting new materials that confer several advantages. Especially in the case of zirconia, these innovations have profoundly changed daily practice. This paper compares the satisfaction and perception of patients who received implant-supported single crowns (SC) and fixed partial dentures (FPD) made from zirconia, either monolithic or partially veneered, after 3 years of follow-up; the success and survival rate of these restorations were also measured. Forty patients, who had been previously treated with implant-supported SC or FPD, either monolithic or partially veneered, and submitted to a yearly maintenance program, were recalled 3 years after their treatment and requested to complete an 8-question questionnaire regarding their perceptions of the treatment. Any mechanical or biological complication that had occurred from the time of delivery was also recorded. Patients that experienced ≥1 complication were less likely to be prone to repeat the treatment. The 3-year success rate was 92.6% for monolithic restoration and 92.3% for partially veneered restoration, while the survival rate was 100% for both restorations. The 3-year follow-up found that monolithic and partially veneered zirconia restorations are both well-accepted treatment options, and patients preferred the veneered restorations (0.76, p < 0.05) from an aesthetic point of view. According to our results, monolithic and veneered zirconia restorations are both reliable treatment options and are both equally accepted by patients.

Influence of coloring liquid immersion on flexural strength, Vickers hardness, and color of zirconia

STATEMENT OF PROBLEM

Zirconia is a widely used restorative material, yet its white color does not meet esthetic requirements and coloring is needed. However, the effects of different durations of coloring have not been thoroughly investigated.

PURPOSE

The purpose of this in vitro study was to evaluate the effects of coloring liquid immersion of different durations on the flexural strength, Vickers hardness, and color of zirconia.

MATERIAL AND METHODS

Fifty bar-shaped and 60 disk-shaped zirconia specimens were milled from nonshaded (Copran Zri) and preshaded (Copran Zri Precoloured Medium) disks by using a computer-aided design and computer-aided manufacturing (CAD-CAM) system. Preshaded specimens were assigned to the group PS and received no further immersion. Nonshaded specimens were divided into 4 subgroups as per immersion time in coloring liquid (Copran Color A2 Shade): control (C; no immersion), G45 (45 seconds of immersion), G90 (90 seconds of immersion), and G135 (135 seconds of immersion). Bar-shaped specimens were subjected to a 3-point flexural strength test by using a universal testing machine (Lloyd LRX), following the International Organization for Standardization (ISO) 6872:2015 specification. Color coordinates of disk-shaped specimens were measured with a spectrophotometer (VITA Easyshade Advance 4.0) over a gray background. Color differences were calculated by using both CIE76 and CIEDE2000 formulas, followed by a comparison of obtained values with perceptibility (CIE76: 3.7, CIEDE2000: 0.8) and acceptability (CIE76: 6.8, CIEDE2000: 1.8) thresholds of each formula. Subsequently, Vickers hardness measurements were conducted. The data were statistically analyzed by using the Shapiro-Wilk test, 1-way ANOVA, and the Tukey HSD test (α=.05).

RESULTS

Immersing zirconia specimens in coloring liquid decreased the flexural strength and hardness values, as group C presented the highest values for both parameters. In addition, prolonged duration had a negative effect on mechanical properties. The flexural strength of groups PS and G45 (P=.993) and groups G90 and G135 (P=.999) was statistically similar. For Vickers hardness, group G135 presented the lowest values with the difference between groups G90 and G135 being statistically similar (P=.061). Color differences among groups varied from 2.49 to 27.33 for ΔE∗, whereas ΔE₀₀ values ranged from 0.58 to 8.26. Compared with group C, ΔE∗ values of all shaded specimens exceeded the acceptability threshold of 6.8. The color difference between each group was higher than the acceptability threshold values of both ΔE∗ and ΔE₀₀ except for groups G45 and PS.

CONCLUSIONS

Colored zirconia specimens had lower flexural strength and Vickers hardness values than nonshaded specimens, regardless of the immersion time or coloring technique.

Effect of surface finishing and polishing procedures on color properties and translucency of monolithic zirconia restorations at varying thickness

OBJECTIVE

This study aimed to assess the impact of monolithic zirconia thickness on its color properties after different surface finishing and polishing procedures, and following aging in coffee solution.

MATERIALS AND METHODS

Two types of monolithic zirconia brands [Prettau Anterior (PA) and DD Cubex2 (DDC)] with three different thicknesses: 0.5, 1, and 1.5, and 10 mm diameter were tested. The color properties were evaluated after various surface finishing procedures (glazing, adjusting with burs + glaze, polishing, adjusting with burs + polishing) and after 5,000 cycles in a coffee solution were evaluated. The differences in color (ΔE) and translucency, were calculated and statistically analyzed by three-way ANOVA and pairwise comparison (α = 0.05).

RESULTS

The brand, material thickness, and surface finishing protocol before and after coffee thermocycling had significant effect on color variations (p < 0.001). For translucency, 3-way ANOVA revealed a significant interaction between the material thickness and surface finishing protocol following aging in coffee solution (p < 0.001), however no significant interaction was observed following the surface finishing protocols (p = 0.247).

CONCLUSIONS

The optical properties of monolithic zirconia ceramics can be influenced by the material brand, material thickness and the procedure of surface finishing and polishing.

CLINICAL SIGNIFICANCE

Clinicians should take into consideration the potential change of the color properties of monolithic zirconia restorations following both contouring and occlusal adjustment procedures and coffee intake.

Effect of surface finishing treatments on the color stability of CAD/CAM materials

PURPOSE

The aim of this study was to evaluate the effect of different surface finishing processes on the color stabilities of lithium disilicate glass-ceramics, zirconia-reinforced lithium silicate ceramics, and resin nanoceramics after artificial ageing.

MATERIALS AND METHODS

216 samples were prepared from 3 different CAD/CAM materials (LAVA Ultimate, IPS e.max CAD, VITA Suprinity) with A1 HT color at a size of 14 × 12 mm and a thickness of 0.5 ± 0.05 mm. Color measurements of the samples were performed with a spectrophotometer using color parameters and CIE Lab color system on a gray backing between baseline color and after 5000 cycles of artificial ageing in 4 stages (i.e. the first measurement before the treatment, the second measurement after polishing, the third measurement after cement application, and the fourth measurement after artificial ageing). The results were evaluated using the Variance analysis and Fisher's LSD test.

RESULTS

Resin nanoceramics (LU) exhibited higher color change values than zirconia-reinforced lithium silicate (VS) and lithium disilicate (EC) ceramics after artificial ageing. Manual polishing and glazing resulted in similar color change for LU and VS (P>.05). In the EC group, glazing provided statistically different results as compared to the manual polishing and control groups (P<.05). Among the ceramic groups, color change values of the subgroup, which was treated by glazing, of the zirconia-reinforced lithium silicate (VS) and lithium disilicate (EC) samples were below the clinically acceptable level (ΔE < 3.5).

CONCLUSION

The lowest color change for all stages was observed in Vita Suprinity.

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

PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Effect of Thermocycling, Surface Treatments and Microstructure on the Optical Properties and Roughness of CAD-CAM and Heat-Pressed Glass Ceramics

Dental ceramic restorations are widely spread nowadays due to their aesthetics and biocompatibility. In time, the colour and structure of these ceramic materials can be altered by aging processes. How does artificial aging affect the optical and surface roughness of ceramics? This study aims to assess the effect of thermocycling, surface treatments and microstructure upon translucency, opalescence and surface roughness on CAD-CAM and heat-pressed glass-ceramic. Forty-eight samples (1.5 mm thickness) were fabricated from six types of A2 MT ceramic: heat-pressed and milled glass-ceramic (feldspathic, lithium disilicate and zirconia reinforced lithium silicate). The samples were obtained respecting the manufacturer’s instructions. The resulted surfaces (n = 96) were half glazed and half polished. The samples were subjected to thermocycling (10,000 cycles) and roughness values (Ra and Rz), colour coordinates (L*, a*, b*) and microstructural analyses were assessed before and after thermocycling. Translucency (TP) and opalescence (OP) were calculated. Values were statistically analysed using ANOVA test (one way). TP and OP values were significantly different between heat-pressed and milled ceramics before and also after thermocycling (p < 0.001). Surface treatments (glazing and polishing) had a significant effect on TP and OP and surface roughness (p < 0.05). The heat-pressed and milled zirconia reinforced lithium silicate glass-ceramic experienced a loss in TP and OP. Ra and Rz increased for the glazed samples, TP and OP decreased for all the samples after thermocycling. Microstructural analyse revealed that glazed surfaces were more affected by the thermocycling and especially for the zirconia reinforced lithium silicate ceramic. Optical properties and surface roughness of the chosen ceramic materials were affected by thermocycling, surface treatments and microstructural differences. The least affected of the ceramics was the lithium disilicate ceramic heat-pressed polished and glazed.

Optical properties of currently used zirconia-based esthetic restorations fabricated with different techniques

OBJECTIVE

The aim was to evaluate the effects of different types of monolithic zirconia (MZ) and fabrication techniques on the optical properties of newly generated zirconia-based materials after aging.

MATERIAL AND METHODS

Sixty specimens (n = 10) were prepared. For the groups layering-veneering (LV), overpressing (OP), porcelain fused to zirconia (PFZ), and cutback (CB), 3Y-TZP, IPS e.max ZirCAD was prepared as the core material (0.5 ± 0.01 mm). For full-contour (FC) technique, 3Y-TZP was used for MZ-LT (low translucency) and 4Y-TZP was used for MZ-MT (medium translucency). L*, a*, b*, chroma (C), and relative translucency (RTP) were measured before (L₁ *, a₁ *, b₁ *, C₁ , RTP₁ ) and after (L₂ *, a₂ *, b₂ *, C₂ , RTP₂ ) UV aging. Statistical analyses were performed by one-way ANOVA with Tukey's test and paired sample t tests (P = .05).

RESULTS

Fabrication techniques significantly affected the L*, a*, b*, C, RTP, and ΔE₀₀ values (P ˂ .01). The highest L₁ * value was found in MZ-LT; followed, in order, by OP, PFZ, LV, CB, and MZ-MT. The highest b₁ * and C₁ values were found in OP, while MZ-MT had the lowest values (P ˂ .05). FC had the highest RTP values for MZ-MT (13 ± 0.9 RTP_1; 11.2 ± 0.9 RTP₂ ), and the lowest RTP values were found for MZ-LT (8.5 ± 0.9 RTP_1; 8.3 ± 1.2 RTP₂ ) (P ˂ .01). Aging caused significant differences in the L*, a*, b*, C, and RTP values (P < .05). The color changes were between 0.9 and 2.1 ΔE₀₀ .

CONCLUSIONS

The fabrication technique significantly affected the optical properties. UV aging caused zirconia-based restorations to become darker and more yellow, red, saturated, and opaque.

CLINICAL IMPLICATIONS

Fabrication techniques with different zirconia structures affected the optical properties of the restoration, even when the same shades were chosen. If more translucent restorations are needed, choosing 4-YTZP with the FC technique is better than veneering with 3-YTZP. Choosing 3-YTZP with the FC technique produces more esthetic results if brighter and more opaque restorations are needed.