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

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Abstract

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.

Introduction

v alue of 3.7 or less is considered to be clinically acceptable according to Johnston and Kao ^[11] . 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 )^½

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 < 0.05 was considered as the level of significance.

Results

Our results showed that the ΔE value for 3M composite resin restorative materials (1 mm specimens) was 2.07 + 3.130 (mean + SD) which was just perceptible but within the clinically acceptable limit.

ΔE value for 3M composite resin restorative materials (3 mm specimens) was 1.85 ± 2.074 (mean+ SD) which was in the imperceptible range.

The ΔE value for Ivoclar vivadent composite resin restorative materials (I mm specimens) was 3.0920 + 1.924 (mean + SD) which was moderately perceptible but within the clinically acceptable limit.

ΔE value for Ivoclar vivadent composite resin restorative materials (3 mm specimens) was 2.9720± 2.287 (mean + SD) which was in the just perceptible range.

The ΔE value for Hereaus kulzer composite resin restorative material (1 mm specimens) was 4.0340+ 1.342 (mean + SD) which was moderately perceptible and not within the clinically acceptable limit.

ΔE value for Hereaus kulzer composite resin restorative materials (3 mm specimens) was 4.022 ± 1.095 (mean + SD) which was moderately perceptible and not within the clinically acceptable limit.

Discussions

Increase in demand for esthetics has gone up considerably in the past few years and hence the use of composite resins as direct resin restorative materials has also significantly increased. One of the most challenging aspects of esthetic dentistry is color assessment and its reproduction.

There are two well-accepted international color order systems that are currently being used to communicate color data. They are the CIE (International Commission on Illumination) system and the Munsell system. The CIE system involves the collection of reflectance data in the visible region of the spectrum, and, by means of tristimulus colorimetry, the data are converted to a set of numerical coordinates which define the color of the object being measured. The Munsell system is a visual comparison system in which colors are ordered by the principle of equal visual perception of color difference.

Color evaluation by visual comparison has been shown to be unreliable as a result of inconsistencies in color perception specifications among observers. Visual color assessment is dependent on the observer's physiologic and psychologic responses to radiant energy stimulation. Inconsistencies may result from uncontrolled factors such as fatigue, aging, emotions, lighting conditions, previous eye exposure, object and illuminant position and metamerism. Since instrumental measurements eliminate the subjective interpretation of visual color comparison, 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 ^[16] . 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 ^[16] . 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 ^[6],[7] , between 2 and 3, greater than or equal to 3.3 ^[19] and greater than or equal to 3.7 ^[17] . 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 ^[19] . A E value of 3.7 or less is considered to be clinically acceptable ^[17],[11].

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.

Conclusion

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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Correspondence Address:
Gurmeet Singh Sachdeva
Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Alapakkam Main Road, Maduravoyal, Chennai 600 095
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/0972-0707.42261

Figures

  [Figure 1], [Figure 2a], [Figure 2b], [Figure 2c], [Figure 3], [Figure 4], [Figure 5], [Figure 6]