Year : 2007 | Volume
: 10 | Issue : 3 | Page : 77--82
Evaluation of the color matching ability of three light cure composite materials, in variable thickness with their respective shade guides and the standard vitapan shade guide using CIE Lab spectroscopy - an invitro study
Gurmeet Singh Sachdeva, Suma Ballal, Deivanayagam Kandaswamy
Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Alapakkam Main Road, Maduravoyal, Chennai 600 095, India
Gurmeet Singh Sachdeva
Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Alapakkam Main Road, Maduravoyal, Chennai 600 095
Shade guides continue to be the most widely used method in clinical practice for shade selection of restorative materials. The Vitapan shade guide is the most widely used method in clinical practice for shade selection of restorative materials. The Vitapan shade guide is the universal standard against which shade matching for ceramics is done. The same does not hold good for composites because each manufacturer has their own system for shade matching. This study highlights the discrepancies existing in different shade guide systems.
|How to cite this article:|
Sachdeva GS, Ballal S, Kandaswamy D. Evaluation of the color matching ability of three light cure composite materials, in variable thickness with their respective shade guides and the standard vitapan shade guide using CIE Lab spectroscopy - an invitro study.J Conserv Dent 2007;10:77-82
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Sachdeva GS, Ballal S, Kandaswamy D. Evaluation of the color matching ability of three light cure composite materials, in variable thickness with their respective shade guides and the standard vitapan shade guide using CIE Lab spectroscopy - an invitro study. J Conserv Dent [serial online] 2007 [cited 2022 Jan 20 ];10:77-82
Available from: https://www.jcd.org.in/text.asp?2007/10/3/77/42261
The clinical use of composite resins has increased substantially over the past few years due to increased esthetic demands by patients, improvements in formulation, and simplification of bonding procedures. Composite resins are recommended for restoring cavities in anterior and posterior teeth. Regardless of the cavity size and site, color matching is clinically important, as it determines the esthetics of composite resin restorations.
Shade guides are the main tool for assessing and communicating the color of the teeth in clinical dentistry but, none of the shade guides available today cover the entire dental shade range. Color determination is not consistent among different clinicians and can vary within the same clinician. To improve the reliability of shade selection procedures, the Vitapan tooth Shade System (Vita Zahnfabrik, Bad Sackingen, Germany) was developed. The manufacturer of this system claims that it helps to make shade matching simple, consistent and reproducible  .
The Vita System of shade matching has gained popularity worldwide for shade matching of ceramic restorations. But when it comes to composite resins, it is not the same. Almost every brand of composite resins manufacturers have brought out their own system of shade matching through their individual shade guides.
Many a times the color of a particular shade of composite when cured may not match its corresponding shade tab. Variability in the thickness of the restoration also influences the final color of composite resin restoration.
Color determination in dentistry can be categorized into instrumental and visual. Advanced computerized instruments (CIE Lab system) can precisely quantify color and reduce the subjectivity inherent in visual color perception. In this system the color change (AE) mathematically expresses the amount of difference between the L*a*b* coordinates of different specimens or the same specimen at different instances. The Commission Internationale de Eclairage (CIE) L*a*b* color system, which is related to the color perception of the human eye for 3 coordinates, is an approximately uniform color space, with coordinates for lightness, namely white-black (L*), red-green (a*), and yellow-blue (b*). Various studies have reported different thresholds of +E values above which the color change is perceptible to the human eye. These values ranged from +E equal to 1 , greater than or equal to 3.3 and greater than or equal to 3.7 Values of +E in the range of 2 to 3 were perceptible, values from 3 to 8 were moderately perceptible, and values above 8 were markedly perceptible. +E v alue of 3.7 or less is considered to be clinically acceptable according to Johnston and Kao  . Consequently they are used extensively in dental research.
The aim of this in vitro study was to evaluate the color matching ability of three commonly used light cure composite materials, in variable thickness with their respective shade guides and the standard vitapan shade guide using CIE Lab spectroscopic study.
Materials and Methods
In this study, 3 light polymerized resins (Shade A3) of the following companies were used.
3M ESPE(FiltekZ350)Hereaus kulzer (Charisma)IvoclarVivadent(InTen-S)
The specimens fabricated [Figure 1] from these light polymerized resins were compared with
Their respective shade guides [Figure 2a],[Figure 2b],[Figure 2c] and Standard Vitapan shade guide [Figure 3]
A stainless steel mold was used to prepare the specimens [Figure 4] and color difference was analyzed using a Spectrophotometer (Gretag- Macbeth AG CH-8105 Regensdorf Switzerland).[Figure 5]
Fabrication of the Specimens
A total of 30 specimens using three different light polymerized resins materials measuring 10mm in diameter and 1mm and 3mm in thickness were prepared. The samples were divided into 3 groups of 10 specimens each according to the material used and their thickness.
Group l - 10 specimens (3M)
5 specimens 10mm X 1 mm
5 specimens 10mm X 3 mm
Group II - 10 specimens (Hereaus kulzer)
5 specimens l Omm X 1 mm
5 specimens 10mmX 3 mm
Group III - 10 specimens (Ivoclar Vivadent)
5 specimens 1OmmX 1 mm
5 specimens 10mmX 3 mm
After polymerization the specimens were grossly trimmed using the tungsten carbide and polished with sof-lex discs.
Assessment of Color Change
Before each measurement session the spectrophotometer was calibrated according to manufacturer recommendations by using the supplied white calibration standard. After this procedure, the color measurements of the specimens were made and the CIE Lab values were recorded.
Color difference ΔE was calculated from the mean ΔL*,Δa*, Δb* values for each specimen with the formula:
ΔE= (ΔL* 2 +Δa* 2 +Δb* 2 )˝
Where ΔL*, Δa*, Δb* are the differences in L*,a* and b* values between that of the specimens and their respective shade guides and specimens and the standard Vitapan shade guides.
The mean and standard deviation estimated from the specimens for each subgroup was statistically analyzed. Mean values were compared by ONE-WAY analysis of variance (ANOVA). Multiple range test by Tukey-HSD procedure was employed to identify the significant groups at 5% level. 1n the present study, p Colorimeters and Spectrophotometers have been most commonly used to measure color change in dental materials.
Spectrophotometers have been shown to be more accurate in measuring the color change than Colorimeters. Colorimeter generally uses three to four silicon photodiodes that have spectral correction filters that closely simulate the standard observer functions. These filters act as analog function generators that limit the spectral characteristics of the light that strikes the detector surface. They cannot exactly match the standard observer functions with filters while retaining adequate sensitivity for low light levels  . Thus, the absolute accuracy of filter calorimeters is considered inferior to scanning devices such as Spectrophotometer. Spectrophotometers contain monochromators and photodiodes that measure the reflectance curve of a product's color every l0nm or less  . In short, a Colorimeter provides an over all measure of the light absorbed, while a Spectrophotometer measures the light absorbed at varying wavelengths. Because of the apparent advantages of Spectrophotometer over Colorimeter and visual method, color change in this study was measured using spectrophotometer.
In the present study, the CIELab system was used for color measurement. According to Okubo S. and Kanawati A R . the use of CIELab system is recommended for dental purposes. The CIELAB color system characterizes color based on human perception. It is a method developed in 1978 by the Commission Internationale del'Eclairage for characterizing color. It designates color according to 3 spatial coordinates, L*, a* and b* where L represents the brightness (value) of a shade, a* represents the amount of red-green color and b* represents the amount of yellow blue color. L* coordinate are located along a vertical axis that ranges from a value of 0 (blackest) to 100 (whitest). The a* and b* coordinates revolve on axes around L*. As a* becomes more positive in value, the color is more red and as a* becomes more negative in value, the color becomes more green. As b* becomes more positive in value, the color becomes more yellow and as b* becomes more negative in value, the color becomes more blue. Absolute measurements are made in L* a* b* coordinate and color change is calculated as E (L*a*b*). In principle, if a material is completely color stable, no color difference will be detected after its exposure to the testing environment (ΔE = 0) [Figure 6]
Various studies have reported different thresholds of color difference values above which the color change is perceptible to the human eye. These values ranged from E equal to 1 , , between 2 and 3, greater than or equal to 3.3  and greater than or equal to 3.7  . Values of E between 0 and 2 were imperceptible, values of E in the range of 2 to 3 were just perceptible, values from 3 to 8 were moderately perceptible and the values above 8 were markedly perceptible  . A E value of 3.7 or less is considered to be clinically acceptable ,.
The results of the present study showed that statistically significant color difference was present between 1mm and 3mm specimens (p value <0.05), specimens and their respective shade guides (p value <0.05) and specimens and standard Vitapan shade guides. 3M resembled most closely to their corresponding shade tabs followed by Ivoclar and Hereaus kulzer.
Also the ΔE values for the 3mm specimens were less as compared to 1mm specimens which showed that thicker specimens resembled more closely to their shade guides as compared to the thinner specimens. This reveals that a definite bulk of the composite resin restorative material is needed so as to closely resemble its corresponding shade tab.
As dentists we blindly follow the shade guides but CIE Lab system conclusively proved that composite shade guides do not accurately match either with their respective shade guides or the standard Vitapan shade guides. With the increase in demand for esthetic composite resin restorations world wide, the need of the hour is to bring out a universal standard shade guide for composite resins parallel to the one being used for ceramic restorations.
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