| Abstract|| |
Introduction: The aim of this study was to evaluate the influence of metal oxides from investment dies on the color of metal-free VM7 ceramic.
Materials and Methods: Forty circular patterns were made with an elastic gelatin duplicator. These were divided into four groups (n = 10) for pouring the investment: G1, Begoform (Bego); G2, Ducera Lay Superfit (DeguDent GmbH); G3, Duravest (Polidental), and G4, Refrax Magnum (CNG). Refractory dies were subjected to the degassing process for gas and metal oxide elimination, and the testing was done with the application of two layers of VM7 ceramic. These layers were sinterized in accordance with the manufacturer's recommendation and then glazed. For the control group, 10 additional VM7 ceramic discs were made without the use of any investment die. The ceramic's control color and the tested groups were analyzed with the aid of a portable colorimeter (Minolta CR-10) in the CIELab. The color change (ΔE) of the specimens from the tested groups was obtained, and the data were submitted to one-way ANOVA and post-hoc Tukey's test.
Results: All tested groups had a color change from the control group. G1 (5,3) and G2 (5,3) were those that showed the greater color change and did not show statistical differences between themselves; G3 (3,3) and G4 (3,1) were those that showed the least color change from control group and did not show statistical differences between themselves.
Conclusion: Once all investments present a perceptible color change from the control group, color selection should be done with a laboratory-produced color scale.
Keywords: Ceramics, color, investment, metal-free, refractory
|How to cite this article:|
Waldemarin Rd, Pieper CM, Camacho GB. Influence of refractory on the color of VM7 metal free ceramics. Indian J Dent Res 2015;26:2-4
The judicious choice of dental materials and careful execution of clinical and laboratory steps is crucial to achieving satisfactory cosmetic results in restorative dental treatments where aesthetics is a priority. Among the many existing esthetic restorative materials, ceramics is an excellent choice because of their esthetic characteristics, hardness, color, and dimensional stability, which favors the longevity of this type of restoration. According to Zhang et al.  the increasing demand for esthetic ceramic requires a better understanding of the factors that influence the esthetic properties of these. Often, although the laboratory used the ceramic color ordered by the dentist, the final restoration may not achieve the desired results, , presenting a significant difference in color when it is evaluated against what was expected. Thus, the aim of this study was to assess whether there is any kind of change in the color of a ceramic used in the construction of metal-free restorations (Vita VM7), due to their interaction with the investment dies used to build them.
|How to cite this URL:|
Waldemarin Rd, Pieper CM, Camacho GB. Influence of refractory on the color of VM7 metal free ceramics. Indian J Dent Res [serial online] 2015 [cited 2019 Dec 10];26:2-4. Available from: http://www.ijdr.in/text.asp?2015/26/1/2/156786
| Materials and methods|| |
With a matrix, 40 reversible hydrocolloid molds were used to hold the pourings from the 4 groups of 10 investment patterns, known as group G1, Begoform (Bego); group G2, Ducera Lay Superfit (DeguDent GmbH); group G3, Duravest (Polidental) and group G4, Refrax Magnum (CNG). After the final cure, these investment patterns were removed from the mold, and they had the form of a 3.0 cm diameter circular base where, in the middle, there was a 1 mm deep/1 cm diameter circular depression.
The patterns were then subjected to degassing firing in a typical casting furnace.
The Vita VM7 ceramic (transpa-dentine 3M2 color) was then applied to every investment pattern with a camel-hair brush and distilled water, and the patterns were then subjected to the first firing cycle. Then, a second layer of ceramic was applied, and the second firing cycle was performed. The ceramics were removed from within the investment with the aid of a 10 μm-particle aluminum oxide jet; they were washed, dried, and then subjected to the glaze firing cycle. As a control group, 10 ceramics that had no contact with any investment were done with the aid of a metallic pattern. This device had a plunger that allowed the ceramic to be applied to and removed from the metallic pattern to be subjected to the first firing cycle. The ceramics were again put into the device, and the process was repeated for the second firing cycle. Once they were not inside any investment, they were subjected to the glaze firing cycle without any special preparation. All firing cycles of the tested and control groups were performed in accordance with the ceramic's manufacturer recommendations.
The color was then measured with a CR-10 Konica-Minolta portable colorimeter with 0.8 cm measurement aperture in CIELab. The data were mounted on a table to calculate the color variation (ΔE, CIE L* a* b* system) and then submitted to statistical analyses using GMC freeware.
| Results|| |
In order to quantify ΔE, the L* a* b* values of the tested group's ceramics were compared with the means values of L* a* b* obtained in the control group ceramics.
The statistical analyses showed that the data had normal distribution and homogeneity, after which the data were subjected to one-way ANOVA. This test showed a statistical difference with 5% significance. Next, the data were subjected to a post-hoc Tukey's test, also with 5% significance. The means (and standard deviation) of tested groups are shown in [Table 1].
The post-hoc Tukey's test showed that all tested groups had a statistically significant color change from the control group; among these, groups 1 and 2 had the highest values with no statistical difference between themselves, despite being higher than all the others. Similarly, groups 3 and 4 also had intermediate values with no statistical difference between them.
| Discussion|| |
In this study, we used the CIELab scale, where (L) represents luminescence and varies from black to white; (a) values represent the green-red axis while (b) values represent the blue-yellow axis. Distances between two points (ΔE) in this scale may be calculated with the equation ΔE = (ΔL 2 + Δa 2 + Δb 2 ) 0],[5 , which represents the hypotenuse of a right triangle in a three dimensional space. The colorimetric technique used in our study has been validated previously by others, ,,,, and it shows that aesthetic and final ceramic color used to be a concern in dentistry.
The VM7 ceramic's color was altered by all the tested investments, as found previously for other investments and ceramics.  The "L" alteration, when compared with the means values of control groups, always turned to a lighter value when an investment was used. Furthermore, in the red-green axis, the color had a tendency to change to red in all groups tested, despite groups 2 and 3 having had some individual values with different behavior. Groups G1 and G4 showed a yellowish tendency while G2 and G3 had no alteration in the blue-yellow axis. Yellowish and reddish tendency on color change had been not found in other studies that analyzed investment effect on ceramic color,  however, it may be explained by the ceramic used, because previous authors had not used VM7 and had presented some ceramics with increases in their a* values.
Some authors showed that investment material can affect surface and shrinkage crystallization of ceramics , as well its surface roughness and biaxial flexural strength. , It was also demonstrated that the color of ceramics may be modified by its surface roughness or texture, ,, and that investment may change the color of ceramics.  Once ceramics and investments have an intimate contact under high temperatures, it may not discard the hypothesis that, to some degree, the color alteration may be due to different interactions between ceramics and the investment die, causing different surface roughness among tested groups.
In this study, all tested groups showed color alteration when compared to the control group. In a previous study,  it was concluded that a color change >2.0 points may be distinguishable by professionals and anyone may perceive an alteration >3.0 points. This way, all tested groups showed a perceptible color alteration when compared to the control group, as found for some investments before,  despite the fact that G3 and G4 were only slightly above the limit of 3.0 points. It was shown, in addition, that the investments used presented statistical differences among themselves (groups G1 and G2 being equal and more distinct from the control group than groups G3 and G4).
It is important to note that some authors  also showed that ceramics from different manufacturers may present different color, despite having the same shade. Considering this information allied with the present and former  observations that all investment used may change the color of ceramics and the different behavior of ceramics when submitted to the investments, one may not be allowed to indicate or contraindicate specific investments. Rather, this implies that the better way to perform color selection is to determine it using a scale made with the same ceramic and investment used by the laboratory that will produce the restoration. This way, dentist, and technicians may work to improve their communications in order to achieve better results.
Future studies are needed in order to know whether or not the patient perceives the difference between diverse investments used, as well understands how the investment composition, the ceramics/investment thermal expansion, and the surface treatment may affect the color of metal-free restorations.
| Conclusion|| |
Within the limitations of the methodology used, we may conclude that:
- The color selection should be done with a color scale that is produced with the ceramic/investment used by the laboratory.
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Renato Fabricio de Andrade Waldemarin
Department of Restorative Dentistry, Federal University of Pelotas, Pelotas, RS
Source of Support: We strongly thanks the support partially provided by
FAPERGS. (Foment Research Foundation from Rio Grande do Sul), Conflict of Interest: None