|Year : 2022 | Volume
| Issue : 3 | Page : 163-169
The effect of thermocycling on the color stability of high translucency monolithic lithium disilicate and cubic zirconia materials
Maha Suliman Mezied
Department of Prosthodontic, College of Dentistry, Riyadh Elm University, Riyadh, Saudi Arabia
|Date of Submission||24-Aug-2022|
|Date of Decision||06-Nov-2022|
|Date of Acceptance||06-Nov-2022|
|Date of Web Publication||31-Dec-2022|
Dr. Maha Suliman Mezied
Department of Prosthodontic, College of Dentistry, Riyadh Elm University, Riyadh
Source of Support: None, Conflict of Interest: None
Introduction: The color stability and esthetic is an important factor of the long-term clinical success of dental ceramic restorations. However, the impact of thermocycling on the color stability of high translucency monolithic lithium disilicate and cubic zirconia materials is not well known.
Aim: To evaluate the effect of thermocycling on the color stability of three types of monolithic cubic zirconia compared with one type of lithium disilicate.
Materials and Methods: A Four groups of 10 disc-shaped specimens (10 mm x 1.2 mm) were made from: One brand of lithium disilicate (IPS e.max CAD® HT (E.max)) as a control, and three brands of cubic zirconia (Katana UTML, Cercon XT, and Ceramill Zolid FX UT) as experimental groups. Color analysis of specimens were performed before and after thermocycling by using a Spectrophotometer (Hunterlab, EasyMatch QC. Ver 4.90). Then, same discs were subjected to thermocycling for 10000 cycles. The data was analyzed with one-way ANOVA, Tukey's post hoc test. Data analyses were evaluated at a significance level of P < 0.05.
Results and Discussion: Parameters L*, a*, and b* were statistically significant differences before and after AAA among groups (P<0.001). The IPS e.max CAD® HT showed the greatest change in color (ΔE= 2.15±0.24), followed by Cercon XT (ΔE= 1.70±0.22), Ceramill Zolid FX UT (ΔE= 1.44±0.25), and least change in color was Katana UTML (ΔE= 1.41±0.41). The Tukey's post hoc test, showed that the IPS e.max CAD® HT had significant changes when compared to the other materials (P<0.05).
Conclusion: The effect of thermocycling on the color stability in this study results were significant effect in the (ΔE) of the four tested materials. The IPS e.max CAD® HT the greatest change in color and the and least change in color was Katana UTML. The color difference was significant within all groups, but changes were not a clinically perceivable.
Keywords: Artificial accelerated aging, color stability, cubic zirconia, lithium disilicate, thermocycling
|How to cite this article:|
Mezied MS. The effect of thermocycling on the color stability of high translucency monolithic lithium disilicate and cubic zirconia materials. Saudi J Oral Sci 2022;9:163-9
|How to cite this URL:|
Mezied MS. The effect of thermocycling on the color stability of high translucency monolithic lithium disilicate and cubic zirconia materials. Saudi J Oral Sci [serial online] 2022 [cited 2023 Feb 6];9:163-9. Available from: https://www.saudijos.org/text.asp?2022/9/3/163/366527
| Introduction|| |
Esthetic and color stability of natural teeth would be one of the prime factors for esthetic dental ceramic restorations. The color stability is one of most important factors as the mechanical properties of a restoration. The lifespan and quality of dental restorations depend partially on the color stability of a restorative material over time., Consequently, restorative material should have a good color stability to be able to resist any stains from solutions, chemical degradation, and surface roughness.,
Lithium disilicate has become suitable for esthetic rehabilitation. Color stability of lithium disilicate is an important factor of the long-term clinical success of dental restorations. It come with several advantages such as high strength, easy construction procedure, adequate bonding to tooth structure, and acceptable esthetic appearance.
Tetragonal partially stabilized Zirconia was developed over a 15 years ago. It has a tiny crystal structure which renders it highly opaque and can be nonaesthetic in many clinical situations. To overcome this disadvantage, the substructure is layered with feldspathic ceramic. This came with its main complications with veneered Zirconia is chipping (delaminating) of the veneering ceramics.
In 2012–2013, the second generation was introduced. The main goal of this generation is to fabricate more translucent material with good mechanical properties by reducing the amount of alumina Oxide and re-positioning the alumina in the Zirconia framework. However, the second generation can be used monolithically as posterior restoration only and cannot be used in patients replacing teeth in the highly esthetic demanding anterior area.
In 2015, the third generation of Zirconia was introduced to the market. This Zirconia is meta-stabilized in the tetragonal phase and contains up to 53% cubic phase with a mixture of cubic/tetragonal structure. It is a porous substance due to the large particle volume of the cubic phase, which leads to less light scattering at the borders and therefore more translucency of the material. Besides, it has been stated that the third-generation cubic crowns are more translucent than lithium disilicate crowns.
In the presence of water or humid environment, tetragonal to monoclinic phase transformation occurs which is known as low-temperature degradation (LTD). Imbalanced state, as in greater particle size, low Yttrium oxide content or presence of residual stress or even presence of cubic Zirconia, leads to the transformation of some particles., This in turn results in particle size enlargement that causes stress and crack propagation, allowing water to infiltrate inside the material. The recurrent growth process depends on porosity, stresses, and size of the particles. To simulate the oral environment extra-orally, accelerated artificial aging (AAA) is used. Nowadays production of Zirconia with higher cubic crystal content is less liable to LTD since that phase does not undergo transformation. Furthermore, cubic crystals have a higher volume to decrease residual porosity and also have higher light scattering at the grain outlines. This, in effect, is expected to better the clinical life span and color stability of third-generation Zirconia.
Dikicier et al. 2014 studied the effect of various core thicknesses (0.5 mm, 0.8 mm and 1.0 mm) and aging on the color stability of Zirconia, which were layered by three different ceramic systems (In-Ceram Alumina, IPS™ E. max Press and Katana™). Aging was done by exposing ceramic to ultraviolet light and water spray by using weathering machine for 200 h. The conclusion was that aging and varying core thicknesses affected the color stability of the three types of all-ceramic systems that were tested.
This study is motivated by the fact that, to date, only limited data are available regarding the effect of thermocycling on the color stability of high translucency monolithic lithium disilicate and cubic zirconia materials.
The null hypothesis of the study was that no effect of AAA on color stability of cubic zirconia and lithium disilicate materials.
| Materials and Methods|| |
One brand of lithium disilicate (IPS e.max CAD® HT [E.max]) as a control, and three brands of cubic zirconia (Katana UTML, Cercon XT, and Ceramill Zolid FX UT) as experimental groups were selected and used in this study, as shown in [Table 1].
Four groups of 10 disc-shaped specimens (10 mm × 1.2 mm) were made using the 3D software (Dental Wings, Canada), according to ISO 6872, and a Stereolithography file was generated.
The lithium disilicate blocks were sectioned into the required thicknesses, whereas the cubic zirconia blocks were prepared from partially sintered blocks into disks slightly larger than the final thickness to compensate for the sintering shrinkage of 20%–25% according to the manufacturer's instructions.
For cubic zirconia, the specimens were sintered in the furnace according to the manufacturer's instructions at 1500°C for 5 h in a Nabertherm sintering furnace (Nabertherm GmbH. Lilienthal, Germany) used for Katana UTML system, Tabeo furnace (Tabeo, Mihm-Vogt, Stutensee, Germany) for 5 h at 1450°C used for Cercon XT specimens, and Ceramill Therm furnace (Ceramill Therm, Amann Girrbach, Koblach, Austria) for 2 h at 1550°C used for Ceramill Zolid FX UT and thereafter finished by fine cross-cut tungsten carbide bur. For lithium disilicate, the specimens were polished with (OptraFine® diamond polishing system, Ivoclar Vivadent). Glazing was performed according to the manufacturer's instruction in Ivoclar Dental Programat EP 3010 ceramic furnace. The diameter and thickness were checked using a digital caliper.
The forty specimens were subjected to color measurements before thermocycling aging, which was performed using a spectrophotometer (Hunterlab, EasyMatch QC. Ver 4.90) with a standard illuminant D65 (white background). The head of the spectrophotometer was placed to record measurement in the disc center of each specimen. The average value of three readings were recorded for each specimen was used as the L* a*b* values for the corresponding specimen. The specimens were then subjected to thermocycling aging to 10,000 cycles correspond to the usage period about 1 year in the oral cavity at 5°C and 55°C. Each cycle lasted 60s: 20 s in 5°C bath, 10s transfer time to the 55°C bath, 20s in 55°C bath and 10 s transfer time back to the 5°C bath. After thermocycling, the specimens were subjected to color parameters following the same way as described before to the aging process.
Color change was calculated using the following formula:
ΔE = ([ΔL*]2+ [Δa*]2 + [Δb*]2)1/2.
Where L* value represents the brightness of an object on y-axis.
a* value represents red (positive x-axis) or green (negative x-axis).
b* value represents yellow (positive z-axis) or blue (negative z-axis).
Descriptive statistics were used to determine the mean L*, a*, b* values of the ceramic material before and after AAA and found to be normally distributed (Kurtosis <+/-3, Skew between ± 0.5). The one-way analysis of variance (ANOVA) and Tukey's post hoc test were used to compare the color characteristics among the four different materials used.
Permission for the study was obtained from the institutional ethical committee. The study proposal was submitted to the research center of Riyadh elm university ethical approval was obtained from institutional review Borad FPGRP/43832001/283 on November 20, 2018.
| Results|| |
One-way ANOVA revealed a statistically significant difference between the groups and it was observed that the IPS e.max CAD® HT showed the greatest L* value while the Ceramill Zolid FX UT showed the lowest L* value and there were significant differences among the different materials tested (P < 0.001). The Ceramill Zolid FX UT showed the greatest a* value while IPS e.max CAD® HT showed the lowest a* value with significant differences among groups (P < 0.001). Regarding the b* values the Cercon XT showed the highest b* value while Katana UTML showed the lowest b* value with significant differences among groups (P < 0.001, [Table 2]]. Then, Tukey's post hoc test was performed to compare the mean color change between the tested all-ceramic restorative materials. The L*, a*, and b* values showed a statistical difference in the mean among the groups.
|Table 2: Values of the one-way analysis of variance test for the L*, a* and b* before accelerated artificial aging|
Click here to view
After AAA, one-way ANOVA was used and revealed a statistically significant difference between the groups and it was observed that the IPS e.max CAD® HT showed the greatest L* value while Ceramill Zolid FX UT showed the lowest L* value and there were significant differences among the different materials tested (P < 0.001). The Ceramill Zolid FX UT showed the greatest a* value while IPS e.max CAD® HT showed the lowest a* value with significant differences among groups (P < 0.001). Regarding the b* values, the Cercon XT showed the highest b* value while Katana UTML showed the lowest b* value with significant differences among groups [P < 0.001, [Table 3]]. Then, Tukey's post hoc test was performed, and it was observed that the L*, a*, and b* value showed a significantly different when compared to the other.
|Table 3: Values of the one-way analysis of variance test for the L*, a*, and b* after accelerated artificial aging|
Click here to view
One-way ANOVA was used and showed a statistically significant differences among groups (P < 0.001). The IPS e.max CAD® HT showed the greatest change in color (ΔE = 2.15 ± 0.24), followed by Cercon XT (ΔE = 1.70 ± 0.22), Ceramill Zolid FX UT (ΔE = 1.44 ± 0.25), and least change in color was Katana UTML (ΔE = 1.41 ± 0.41) [Table 4]. The Tukey's post hoc test showed that the IPS e.max CAD® HT had significantly greater color change when compared to the other three materials [P < 0.05, [Graph 1]].
| Discussion|| |
Four ceramic brands that are currently popular in the market were selected to be tested, namely, IPS e.max CAD® HT, Katana UTML, Cercon XT, and Ceramill Zolid FX UT. The aim of this study was to evaluate the effect of thermocycling on the color stability cubic zirconia and lithium disilicate ceramics. The null hypothesis that no effect of AAA on color stability of cubic zirconia and lithium disilicate materials was rejected. One-way ANOVA was used and showed a statistically significant difference among groups (P < 0.001). The IPS e.max CAD® HT showed the greatest change in color (ΔE = 2.15 ± 0.24), followed by Cercon XT (ΔE = 1.70 ± 0.22), Ceramill Zolid FX UT (ΔE = 1.44 ± 0.25), and least change in color was Katana UTML (ΔE = 1.41 ± 0.41).
Several machines have been invented to measure the color of dental materials, in the current study, the spectrophotometer utilized. It has been stated that the most useful instruments are Spectrophotometers as they are accurate and have the flexibility to be used for the overall color scheme,, by measuring the amount of light reflected from an object at 1 to 25 nm intervals along the visible spectrum.,, One study showed that the accuracy of spectrophotometers was 33% more than other devices and 93.3% matching objective of the cases as compared with human interpretation of color.,
A color change of dental ceramics as result of aging was reported in many studies.,,,, In general, there are several factors affect the color of ceramic material such as, ceramic stain, thickness, surface crack, roughness, and method of sintering.,, Therefore, when increased the temperature time, the increase in grain size, and a decrease in porosity, thus forming a highly ordered crystalline structure that allows light reflection, which may be the main factor affecting the color difference.,
The proposed reason for the high ΔE of lithium disilicate was it had a undergoes water sorption due to aging. However, cubic zirconia could relatively be low ΔE due to the increase in yttria content as it has electrical neutrality which is achieved by the creation of O2 vacancies which stabilize in cubic phase. T → M transformation in cubic zirconia will take higher temperature and more time than conventional zirconia, since cubic zirconia is less susceptible to aging., Even though color difference after aging was still significant due to T-M transformation and thus presence of tetragonal phase could take place.
To provide a simplistic description of the color changes in the four tested ceramics after AAA, they became darker (decrease in L* values), redder (increase regarding the a* value) with the exception of IPS e.max CAD® HT, which became greener (decrease in a* value), and more bluish (decrease in b* value). A similar study was conducted by, to evaluate the effect of hydrothermal aging on the optical properties of monolithic Zirconia ceramics (Katana ML) compared to IPS e.max CAD lithium disilicate glass-ceramic. They concluded that hydrothermal aging significantly affected the optical properties and aged yttria-tetragonal zirconia polycrystal (Y-TZP) displayed a brighter, redder and more bluish appearance than nonaged Y-TZP specimens regardless of aging time.
Kim et al. analyzed the color and translucency of currently marketed precolored monolithic cubic Zirconia and compared them with those of layered Zirconia, lithium disilicate glass-ceramic, and noncolored Zirconia by using a spectrophotometer. Results showed that there was a significant change in color and translucency among precolored monolithic Zirconia ceramics beyond the acceptability threshold. Due to the high L* values and low a* and b* values, precolored monolithic Zirconia ceramics can be used with additional staining to match neighboring restorations or natural teeth. These results might have been expected due to the isotropic refractive index of cubic phase with high yttrium oxide content and consequently, the reduced scattering from birefringent grain boundaries.
An observation made in the present study is that the four materials that were tested had the same shade (B1), yet the different manufacturers used varying shading techniques and therefore different mixtures of L*, a* and b* to arrive at the same shade.
| Conclusion|| |
Based on the finding of this study, the following conclusions were drawn:
- The small color differences detected in this study can be considered appreciable by skilled operators, but clinically acceptable, rendering monolithic cubic zirconia an esthetically stable material under the thermal variations commonly encountered in the oral cavity
- Regarding color stability of cubic Zirconia, Katana UTML showed the least change in color, hence most color stable.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]