RESEARCH ARTICLE | https://doi.org/10.5005/jp-journals-10019-1304 |
Color Stability, Translucency, and Wettability of a Lithium Disilicate Dental Ceramics Submitted to Different Surface Treatments
1,2,4,6Department of Dental Materials and Prosthodontics, Ribeirão Preto School of Dentistry, University of São Paulo, Ribeirão Preto, São Paulo, Brazil
3Department of Clinical Pathology and Dental Surgery, School of Dentistry, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais Brazil
5Department of Restorative Dentistry, College of Dentistry, Faculty of Health Sciences University of Manitoba, Winnipeg, Canada
Corresponding Author: Fernanda de CP Pires-de-Souza, Department of Dental Materials and Prosthodontics, Ribeirão Preto School of Dentistry, University of São Paulo, Ribeirão Preto, São Paulo, Brazil, Phone: +55 16 3315 3973, e-mail: ferpanzeri@usp.br
How to cite this article Soares EJ, de Lima Oliveira RF, Jardilino Silame FD, et al. Color Stability, Translucency, and Wettability of a Lithium Disilicate Dental Ceramics Submitted to Different Surface Treatments. Int J Prosthodont Restor Dent 2021;11(1):4–8.
Source of support: Nil
Conflict of interest: None
ABSTRACT
Aim and objective: This study aimed to evaluate the color stability, translucency, and wettability of a lithium disilicate dental ceramic.
Materials and methods: Forty specimens (6 × 1 mm) of lithium disilicate dental ceramic were fabricated. Initial color and translucency readings were measured using a spectrophotometer. Then, the specimens were randomly separated into four groups (n = 10), according to the different types of surface treatment (control: control group; HF + S: hydrofluoric acid gel and silane; Al + HF + S: Al2O3, hydrofluoric acid gel, and silane; Al + S: Al2O3 and silane) and new color and translucency readings were done. The wettability was analyzed using the sessile drop method in all specimens, and the results were statistically analyzed using one-way ANOVA and the Tukey test (p %3C; 0.05).
Results: The results showed higher color and translucency changes to the groups treated (HF + S, Al + HF + S, and Al + S), different (p < 0.05) from the control group, and without significance between them. All groups demonstrated different wettability (p < 0.05), lower for the control group.
Conclusion: It is possible to conclude that the surface treatment can influence the color, translucency, and wettability of lithium disilicate dental ceramics.
Keywords: Ceramic bonding, Color stability, Lithium disilicate, Translucency, Wettability.
INTRODUCTION
Currently, cosmetic treatments are common due to the esthetic appeal in modern society. Dental ceramics are the first-choice material for prosthetic restorations of anterior teeth because of its translucency and optical properties, which are similar to those of the teeth.1–3
Besides having a pleasant esthetic, dental ceramic is an inert material and has excellent mechanical properties, like elastic modulus of 900 GPa, flexural strength of 900 MPa, and fracture strength of 3–7 MPa when submitted to static forces.4–7 The same properties evaluated in resin composites showed values of 8–15 GPa, 70–130 MPa, and 0.7–1.5 MPa, respectively.6,8,9 Thus, dental ceramic has been demonstrated to have superior mechanical properties and could be the material of choice for esthetic treatments.
The success of ceramic veneers depends on different aspects like the adhesion between the resin cement and substrate (enamel or dentin), between the resin cement and the internal surface of the dental ceramic,10 and also on the esthetic outcome.
The esthetics of ceramic veneers can be influenced by many factors. One of them is the resin cement shade which can improve or jeopardize the final color of the restoration.11–14 The shade selection of resin cement is a challenging procedure, and the correct choice can reduce the color change of the final restoration. However, the thickness of the resin cement can also influence the esthetic restoration.11 According to Vichi et al.,11 the thicker the resin cement, the higher is the alteration of the ceramics’ optical properties when associated with a lower dental ceramic thickness.
The dental ceramic surface treatment is essential to the fixation of the restoration and when it is performed, creates microporosity that improves the micromechanical retention and adhesion of resin cement.15,16 Thus, the interaction between the resin cement and the dental ceramic surface is also improved, causing a better flow and penetration of the luting agent, and consequently a smaller thickness of the resin cement.13 Nevertheless, the factual results of the interaction between ceramics’ wettability and resin cement thickness are still not known.
There are different ceramic surface treatments like air abrasion with aluminum oxide and silane or hydrofluoric acid etching and silane, or the combination of air abrasion with aluminum oxide, hydrofluoric acid etching, and silane. All these treatments aim to improve the contact area between the resin cement and the dental ceramic.17,18
There are many techniques and fixation protocols, which generates doubt among dentists about which technique to choose. Despite much research and advances in this area, there is still not enough evidence to provide theoretical, practical, and scientific knowledge for dentists to affirm which technique is best.19 Cosmetic treatments require a lot of skill and knowledge from dentists, to be able to understand the patients’ needs and choose the best technique for each situation.
Researchers have investigated the influence of different types of surface treatments and bond strength.19–22 The variation of roughness can change the ceramics’ optical properties. Although the translucency and color change of dental ceramics have been evaluated in the literature, the influence of different kinds of surface treatments on the ceramics’ optical properties should be better clarified.
This study aimed to investigate the influence of different types of surface treatments on the color change, translucency, and wettability of a lithium disilicate dental ceramic. The null hypothesis of the study was that there would be no difference in color change, translucency, and wettability regardless of the type of surface treatment of dental ceramics.
MATERIALS AND METHODS
In this study, 40 samples of lithium disilicate-based dental ceramic (IPS e.max Press, Ivoclar Vivadent, Schaan, Liechtenstein) were used to test three different types of surface treatments which are hydrofluoric acid and silane; aluminum oxide abrasion, hydrofluoric acid, and silane; aluminum oxide abrasion and silane. Alterations in color, translucency, and wettability were measured before and after the treatments.
Sample Preparation
Lithium disilicate-based dental ceramic (IPS e.max Press; Ivoclar Vivadent, Schaan, Liechtenstein) was used to fabricate 40 samples (6 mm diameter × 1 mm thickness) using the lost wax casting method. The 1 mm thickness was chosen because this would be the greater thickness possible to a ceramic laminate, according to the recommendation of this kind of restoration. For this purpose, melted wax (Ceras Rainbow Ltda; Porto Ferreira, Brazil) was placed in a Teflon mold. After cooling, the wax patterns were placed inside the silicon rings (IPS Silicon Ring; Ivoclar Vivadent, Schaan, Liechtenstein) following the manufacturer’s guidelines. The investment material (IPS PressVest; Ivoclar Vivadent, Schaan, Liechtenstein) was measured, mixed with the proper liquids, and poured into the silicon rings.
After the material set, the silicon rings were removed, and the investment cylinder was processed (3000-3P EDG, EDG Equipamentos e Controles; São Carlos, Brazil) at 850°C to burn out the wax. The dental ceramic was heat pressed (Programat EP 5000; Ivoclar Vivadent, Schaan, Liechtenstein) according to the manufacturer’s recommendations (Technical Manual IPS e.max Press, 2009).
After cooling, the specimens were separated, finished with microsphere abrasion (Renfert; Hilzingen, Germany), and polished using abrasive stones, diamond burs, and specific rubber discs (EVE; Ernst Vetter GmbH; Pforzheim, Germany). The samples were cleaned ultrasonically for 1 minute and 30 seconds (Cuba de Ultrassom, Cristófoli Equipamentos de Biossegurança LTDA; Campo Mourão, Brazil) using 10 mL of Invex liquid (Ivoclar Vivadent, Schaan, Liechtenstein), rinsed under running water, dried with air, and air abraded with spherical aluminum oxide particles at 1–2 bar pressure.
Each sample was polished (Polipan-U, Panambra; São Paulo, Brazil) with abrasive papers (Norton 600, 1000, and 1200 grits), and the final thickness was measured with a digital caliper (Digimess, Instruments Precision LTDA; São Paulo, Brazil). The dental ceramic specimens were cleaned ultrasonically with 90% ethanol for 4 minutes and glazed at 403°C for 6 minutes and 770°C for 1 minute and 30 seconds.
Surface Treatments
The samples were randomly separated into four groups (Control, HF + S, Al + HF + S, and Al + S) according to the surface treatment received (n = 10). The power mean (92.94%) was calculated by the comparison of means with a confidence interval of 95% (openepi.com/power/powermean.htm).
Control (Control Group)
No surface treatment was performed.
HF + S
The dental ceramic samples were etched with 5% hydrofluoric acid (HF) gel (Condicionador de Porcelanas, Dentsply; Petrópolis, Brazil) for 20 seconds, rinsed, and dried with air. Silane was applied for 1 minute (Monobond S, Ivoclar Vivadent; Schaan, Liechtenstein).
Al + HF + S
The dental ceramic surfaces were air-abraded with aluminum oxide particles at 10 mm of distance at 1 bar pressure (15 psi). Then, the samples were etched with 5% hydrofluoric acid gel (Condicionador de Porcelanas, Dentsply; Petrópolis, Brazil) for 20 seconds, rinsed, dried with air, and silane was applied for 1 minute (Monobond S; Ivoclar Vivadent; Schaan, Liechtenstein).
Al + S
The specimens were air-abraded with aluminum oxide particles at 10 mm of distance at 1 bar pressure (15 psi). Then, silane was applied for one minute (Monobond S; Ivoclar Vivadent; Schaan, Liechtenstein).
Color and Translucency Alteration
Figure 1 summarizes all the methods applied on the study. Color measurements were performed in all samples on the polished surface (Vita Easyshade, VITA Zahnfabrik; Bad Säckingen, Germany), on a black and white background (BYK, Mast; Santo André, Brazil). The equipment has a 6 mm diameter digital pointer, with 19 individual optical fibers that illuminate the restorative material and two spectrophotometric sensors able to read color numerically. For color readings, the pointer was centralized and placed on the specimen and occupied its entire diameter, allowing the readings to be done in the same position every time.
The optical geometry of color measurement of this device is circular, with the specular component excluded, which simulates a 45/0 measurement. The standard illuminant used was D65 and a standard observer of 20°. The excluded specular component is related to the color measurement on the sample surface to prevent the interference of surface brightness.23,24
Fig. 1: Flow diagram shows how the study was conducted
Color measurements (before and after treatments) were made in a standardized lightbox (Gester International; Fujian Province, China) with a neutral-grey (Munsell N-7) background and under primary standard illuminant D65, which simulates the light spectrum of the day.
For color analysis, the observation standard followed the CIEDE 2000 system, defined by the following formula: ΔE00 = (ΔL/KL. SL) + (ΔC/KC. SC)2 + (ΔH/KH. SH)2 + RT. (ΔC/KC. SC) × (ΔH/KH. SH)0.5, where ΔL′, ΔC′, and ΔH′ are the differences in lightness, chroma, and hue between two specimens, respectively, and RT (rotation function) is a function that accounts for the interaction between chroma and hue differences in the blue region. SL, SC, and SH are the weighting functions for the lightness, chroma, and hue components, respectively. KL, KC, and KH are the parametric factors according to different viewing parameters that were set to one. For clinical relevance, 50:50% perceptibility and acceptability thresholds used were 0.8 and 1.8, respectively.25
The translucency was calculated by the translucency parameter (TP). This calculation is obtained by the color difference between the sample over the white background and then over the black background using the following formula:2
Where “w” refers to the color coordinates over the white background and “b” refers to the color coordinates over the black background. The adopted perceptibility threshold (PT) was 0.62, and the acceptability threshold (AT) was 2.62.26
The color and translucency change data were statistically analyzed by one-way ANOVA and the Tukey test (α = 0.05).
Wettability
The evaluation of the influence of different ceramic surface treatments on wettability was performed by measuring the contact angle (CA) using the sessile drop method. This method consists of measuring the angle between the tangent plane, the liquid surface, and the horizontal plane.
A droplet of distilled water (1 μL) was placed on the treated surface of the dental ceramic samples, and the CA was measured, before and after the treatments, using a goniometer (CAM200, KSV Instruments; Helsinki, Finland). Then, the CA was calculated using the ImageJ software (Research Services Branch, National Institute of Mental Health; Bethesda, MD, USA).
| Groups | CIEDE 2000 | Translucency | Contact angle |
|---|---|---|---|
| Control | 0.31 ± 0.2B | 1.10 ± 0.7B | 59.86 ± 0.5A |
| HF + S | 0.96 ± 0.4A | 4.93 ± 2.6A | 21.25 ± 3.1B |
| Al +HF+ S | 1.42 ± 0.7A | 3.09 ± 1.8AB | 34.77 ± 7.8C |
| Al + S | 1.22 ± 0.5A | 1.43 ± 0.7B | 11.97 ± 3.1D |
Means followed by different superscript capital letters in columns represent statistically significant differences (one-way ANOVA, the Tukey test, p < 0.05)
The data were analyzed according to its normality (Shapiro–Wilk) and the data did not meet the assumption of the equality of variance across groups (Levene’s test, p < 0.05). One variation factor was analyzed (surface treatment), the data were submitted to variance analysis (one-way ANOVA), followed by post hoc Tukey’s test (a = 0.05).
RESULTS
The mean comparisons (one-way ANOVA, the Tukey test, p < 0.05) for all results are presented in Table 1. For color change, the smaller alteration occurred for control (control group), statistically different (p < 0.05) from the other groups that showed similar results (p %3E; 0.05) to each other. All color change values were below the AT, but all the treatments showed color change above the PT.
The treatment with HF + silane produced higher translucency of the dental ceramic, differently (p < 0.05) from Control, which showed less translucency, and Al + S, with no difference between them. The ceramic translucency after treatment with Al2O3 + HF + silane was similar to all other treatments (p > 0.05). All groups showed translucency above the PT, but only HF + S and Al + S showed greater than the AT. For wettability, there were differences between all groups (p < 0.05). Thus, the wettability was higher for Al + S > HF + S > Al + HF + S > Control (greater CA).
DISCUSSION
This study analyzed the influence of different types of surface treatments on the color change, translucency, and wettability of a lithium disilicate dental ceramic. The null hypothesis proposed was rejected, as there were statistical differences among the results.
Color measurement was made by a spectrophotometer because this equipment can detect minor color differences in a spectrum not detected by the human eye.27 The color change can be calculated by CIELAB metric or CIEDE 2000, but in this study, the authors used the CIEDE 2000 equation because recent studies proved this method is more efficient and should be the first option in dentistry.27,28
It is common knowledge that surface treatments affect the roughness and bond strength of dental ceramics,16,19–22 and that the success of ceramic restorations depends on many factors, including its color stability and optical properties29 which can be influenced by the ceramics surface roughness.29–31 However, few studies have reported the interaction of surface treatment with color change and translucency.17,32 All the different surface treatments used in this study were able to perceptibly change the color of the dental ceramic but within the acceptability threshold.25,33 This can be explained because the surface treatment changes the ceramics’ surface roughness.
The etching and air-abrasion with aluminum oxide procedures remove the vitreous matrix and increases the crystalline phase of the ceramic34 which produces a rougher surface in vitreous ceramics. These findings agree with the literature, which affirms that rough surfaces present more color changes than smooth ones.29–31,35 So, all the treated groups demonstrated higher ∆E than the control group. However, the type of surface treatment was not significant for color change. The surface treatment, however, affects other properties. HF + S resulted in higher translucency than Al + S, which resulted in a lower ceramic translucency, similar to the control group, with no treatment. Thus, it was found that the aluminum oxide produces higher ceramic surface alteration than the hydrofluoric acid, which cannot be hidden with silane. When all treatments are associated, the translucency levels are similar to the control and HF + S groups.
Another study found translucency alteration due to surface treatment,32 the authors tested three different types of surface treatments (hydrofluoric acid etching, sandblasting with aluminum oxide, and Er:YAG laser irradiation), and found that the groups treated with aluminum oxide and Er:YAG laser had the lower TP values in comparison to the control group and the HF acid etching group. These results corroborate the ones found in the present study, where the aluminum oxide caused lower translucency than the acid etching. This can be justified because the removal of the vitreous phase of the ceramic after the acid etching is more regular than the one caused by the aluminum oxide air abrasion, due to the force of the aluminum oxide application associated with the process.36,37 Still, according to different studies the ceramics microstructure like type, size, amount of crystal, and porosity can influence its optical properties such as light transmission and scattering changing the material translucency,38–40 which also justifies the higher translucency caused by the acid etching.
When the treatments were associated, the acid etching possibly removed additional vitreous parts, after the removal by the air abrasion. As this acid removal is more homogeneous than the first treatment, the surface energy will be higher and there will be greater penetration of the silane on the ceramic surface41,42 which will allow better penetration and smaller thickness of the resin cement,43 resulting in higher translucency.13
The dental ceramic surface should present enough wettability to produce maximum contact with the adhesive materials applied to the surface. The wettability depends on the roughness and energy of the surface,18 because irregular surfaces possess higher surface energy, and consequently a higher wettability (lower contact angle) improving the contact between the coupling agents and the dental ceramic surface.42,44,45 Thus, in the present study, the surface treatment of ceramic interfered in the wettability at different levels, according to the roughness produced by each kind of surface treatment. Surfaces with a more homogeneous roughness, as when the HF is used,18,36 presented a lower wettability than the ones that were air-abraded with aluminum oxide, which produced more irregular surfaces, resulting in a lower contact angle. Therefore, air abrasion with aluminum oxide produced an irregular surface that increased the superficial area and improved wettability, and these results are in accordance with the ones found in different studies.18,36
The use of only one kind and one shade of dental ceramic is a limiting factor of this study. Therefore, other studies are needed to verify the optical behavior of different dental ceramics and shades when submitted to surface treatment.
CONCLUSION
Despite the limitations of this study, it is possible to conclude that the surface treatments used produced color and translucency changes in a lithium disilicate-based dental ceramic and influenced its surface’s wettability.
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