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Research

Author:Dr.Arjun Balakrishnan, Dr.Chethan Hegde, Dr.Krishna Prasad D.

Abstract:

Background & Objectives:
With the advent of newer restorative materials, the stress on esthetic restorations has increased. Shade matching is an important aspect in esthetic dentistry. Two methods have been largely followed, viz. Visual Shade Matching Techniques and Instrumental Shade matching techniques. Shade matching by visual comparison is a subjective method and is prone to inconsistencies.
This study aims at checking the reliability of shade matching by visual comparison with that of Digital Shade Analysis.

Methods:
100 subjects were examined for both Visual Shade Matching as well as Digital Shade Matching under the similar conditions. The shade of three regions (viz. Cervical, Middle and Incisal) each of the maxillary central incisors, lateral incisors and canines were analysed visually by 2 observers. The digital analysis done using photographs taken on a digital camera, which were analysed for CIELab coordinates L, a and b using Adobe® Photoshop® and compared with the same values derived from that of photographs of the shade tabs. The closest colour match was considered as the shade match, and was compared to that of the two observers visual shade matches to check the correlation.

Results:
There was only 48.2% reliability of the Visual Shade Matching with Digital Shade Analysis. Amongst the three teeth, the lateral incisor showed best agreement. The three regions (viz. Cervical Incisors, Lateral Incisors and Canine) of the teeth were perceived equally. Interobserver variability was negligible with upto 99.92% of agreement. The hue of the teeth was identified visually as compared with digital with very high value of significance.

Interpretation & Conclusion:
The Visual shade matching showed definite inconsistency with that of digital shade matching, and the reliability was found to be only 48.2 %.

Keywords: Visual Shade Matching, Digital Shade Matching, Shade guide, Colour

Introduction
Tooth colour matching is an important aspect in esthetic dentistry.1 Colour is complex and encompasses both subjective and objective phenomena.2 Colour is dependent on three factors, namely, the observer, the object and the light source. Each one of these is a variable and when any one is altered, the perception of colour changes.3 Colour matching, however is a challenge to a restorative dentist because teeth encompass a wide range of light-yellow colours among patients.4 Two methods commonly used to analyse the colour of natural teeth and shade guides are visual comparison and instrumental measurement.5

Visual colour determination by comparison of the tooth colour standards is the most frequently applied method in dentistry. Colour evaluation by visual comparison is a subjective method using commercially manufactured shade guides as the colour standard to which the colour of the tooth is matched.6

Colour is perceived visually or measured with photometric instruments, the usefulness of a measurement system becomes dependent on the ability of a colour-difference formula to generate values that correlate with the visual responses.7,8

Digital analysis method of shade determination has been shown to be in accordance with those of spectrophotometric evaluations, with respect to a* and b* values and has been suggested as a more practical and consistent method to determine the colour in dental clinics and to transmit this information to dental laboratories.9

Shade matching by visual comparison is a subjective method and is prone to inconsistencies. This study aims at checking the reliability of shade matching by visual comparison with that of Digital Shade Analysis.

Methodology
100 subjects were chosen randomly from the student population and the students reporting at the department of Prosthodontics. Male and female subjects in the age group 18 – 50 years were considered for the study and it was ensured that the operators were free of any refractory errors. Subjects with Discoloured and Stained teeth, Mal-aligned teeth, Restored teeth, Carious teeth and Subjects with Heavy Make up and Lip Colour were excluded from the study.
For Visual Shade Matching
The shades of the maxillary central incisors, lateral incisors and canines were observed at three aspects, viz. cervical, middle and incisal thirds, by 2 observers separately to account for observer variability. Both observers were examined for refractive errors and were subjected to the ‘Ishihara test’ to eliminate Colour blindness and found to be free of any visual inadequacies. Observer 1 was subjected to online training for colour matching using the ‘Dental Color Matcher’ by the Vita Zahnfabrik. Observer 2 was not subjected to the training programme.
Verbal consent was obtained from the subjects for the study. VITAPAN® Classical Shade Guide was used for the study. All Visual Shade Matching was done between 1100 hrs and 1400 hrs in daylight on a clear day. A distance of 25 to 35 cm was maintained between the observer and the subject during visual shade matching, it was ensured that there were no bright sources of light behind the observer. A neutral grey coloured backdrop was used to prevent visual fatigue.10 The light intensity in the environment was ensured between 18 and 28 Lux10 using a Luxmeter (Digital Lux Meter, Sigma Instruments, India). A neutral coloured cheek retractor was placed to ensure complete isolation of the six anterior teeth, viz. canines, lateral incisors and central incisors.

The shade selection was done in accordance with the training recommended by the ‘Dental Color Matcher’ for VITAPAN CLASSICAL Shade Guide as provided by Vita Zahnfabrik (figure 1).
 

Figure 1: Visual shade matching



The Visual Shade Matches thus collected were manually entered in a tabulated performa, this data was later transferred to Microsoft® Excel Sheets for ease of calculations.
Photography for Digital Shade Analysis

The subjects were comfortably seated on a dental chair with their head positioned parallel to the floor. The subject was made to face a digital camera mounted on a tripod at a distance of 40 cm11, such that the facial surfaces of the central incisors were perpendicular to the long axis of the lens of the camera (figure 2). A neutral coloured cheek retractor was placed to ensure complete isolation of the six anterior teeth, viz. canines, lateral incisors and central incisors. And photographs were clicked without the use of any digital zoom or flash.
 

Figure 2: Setup for photographs of subjects for Digital shade analysis



The photographs were taken in a similar environment as that for the visual shade match. Photographs of the shade guide was also taken in a similar environment using a similar setup.
All images were saved in JPEG format. The images were then resolved on a 32-bit resolution screen, and analysed by using a standard imaging software (Adobe Photoshop®).

Digital Colour Analysis of the Shade Tabs
During the analysis, the three zones, viz. cervical, middle and incisal zones of each of the shade tabs were considered. The tooth was divided into equal thirds, along the long axis of the tooth, circular areas of 74 pixels in diameter were chosen in the middle of each third of the shade tab. The CIE Lab colour coordinates (L, a* and b*) for each of these zones were noted using the colour picking tool of Adobe Photoshop software® and recorded using MS Excel Sheets.

Digital Shade Analysis of the Photograph
a. Digital Colour Analysis of the Photograph (figure 3)

During the analysis, the three zones, viz. cervical, middle and incisal zones of each of the three teeth viz. Central Incisor, Lateral Incisor and Canine of the first quadrant were considered. The tooth was divided into equal thirds, along the long axis of the tooth, circular areas of 74 pixels in diameter were chosen in the middle of each third of the tooth. The CIE Lab colour coordinates (L, a* and b*) for each of these zones were noted using the colour picking tool of Adobe Photshop software®.
 

Figure 3: Photographs processed using Adobe® Photoshop® Software



b. Analysis of the Digital Shade (figure 4) The colour coordinates derived from the photograph, of the three zones of the three teeth were then compared to those derived from similarly analysed three zones from photographs of the shade tabs.
 

Figure 4: Photograph of shade tabs processed using Adobe® Photoshop® Software



The difference in shade was calculated using the following equation which gives the colour difference between the Colour coordinates of the shade tab and the tooth.

∆E= [(L*t – L*s)2 + (a*t – a*s)2 + (b*t – b*s)2] ½

L*t a*t b*t indicate the colour coordinates derived from each of the zone of the tooth.

L*s a*s b*s indicate the colour coordinates derived from each of the corresponding zone of the shade tab.

The shade that showed the least ∆E value (calculated between the Colour coordinates from the tooth and those derived from the 16 shade tabs) for the particular zone of the tooth was considered the closest match for that zone of the particular tooth. The shade match thus derived was denoted as the Digital Shade Match.

The calculation for ∆E values was done using Microsoft® Excel sheet, the lowest values were manually observed and retabulated in an Excel sheet along with the Visual Shade Matches. This data was then analysed statistically using the SPSS® 15 Software.

Discussion
The aim of an aesthetic restoration is to replicate the natural tooth and achieve morphologic, optical and biological acceptance. However, patient satisfaction of an aesthetic restoration is primarily associated with surface and outline form, translucency and colour of the artificial teeth. Whereas meticulous preparation and laboratory techniques help to achieve the form of the restoration, the colour matching remains a dilemma for the dentist.9
The criteria dentists use to determine an exact shade match vary considerably depending on the dentist’s skill, type of shade guide used and lighting conditions. Although many studies have evaluated shade guides, lighting conditions and tooth colour12, few studies have examined the reliability of the shade matching. Shade analysis and selection requires the accurate and objective evaluation of hue, chroma, value, characterization, and translucency. Conventional shade analysis techniques using shade tabs often result in the subjective analysis and miscommunication of color. Digital shade analysis systems have been designed to eliminate the subjectivity of color analysis and provide exact information for laboratory buildup and fabrication. The advent of digital shade analysis can facilitate the precise and uniform fabrication of aesthetic restorations by technicians at all levels of color expertise.9 In medical and dental diagnosis, various computer-assisted image analyses were performed on the colour of the digital images, and the applicability and accuracy of computer analyses have already been established. Digital shade analysis systems have been introduced in an attempt to eliminate the subjectivity of visual colour analysis, miscommunication of colour, and provide precise and uniform fabrication of aesthetic restorations.9

Colour differences upto 2∆E units cannot be differentiated by the naked human eye, and colour variations in this range is accepted clinically tolerable by the ADA.13 This Parameter has been incorporated within the Digital Shade Analysis and a range of ±2∆E units have also been considered for the correlations to achieve clinically comparable results.

Elter et al in their study to check the reliability of digital cameras for colour selection compared colours determined using a spectrophotometer, digital cameras and visual shade matching, the values obtained using visual shade matching only reached 26.6% and 46.6% in agreement with the spectrophotometeric values, and also recommended that to achieve a 100% colour match using digital analysis an overall camera resolution of 13.2 megapixels is indicated.14
The present study aimed at investigating the reliability and to check the correlation of visual shade matching technique used in dentistry and the digital analysis technique. No standard was used in the tests, as the purpose was not to determine which technique resulted in more accurate results; rather it was to investigate the presence of a correlation between the performance of the observer and the digital analysis.
The study revealed that there was inconsistency in reliability of visual shade matches when compared to the digitally analysed shades with only 48.2% of agreement (Table I). This was found to be consistent with various previous studies that state there is a significant disagreement between the shades selected by human perception and the shade obtained with computer-aided instrumenation.14,15
The maximum correlation between the Visual Shade Match and Digital Shade Analysis was seen in the middle and incisal third regions of the Lateral Incisors at 46% and 44% respectively, and the least was seen in relation with the cervical thirds regions of the Canines and Central Incisors at 22% and 28% respectively. And a statistically significant difference (χ2= 7.73, P<0.02) in the accuracy of matching the Visually matched shades and the Digital Shade Analysis was seen between the Central Incisors, Lateral Incisors and the Canines (Table I).
A correlation analysis between the data observed and digitally derived revealed a wide range of correlation between different shades, the maximum correlation between the Visual Shade Match and the Digital Shade Match was found to be 50.7% for the shade A1, closely followed by shades A2 and A3, with 45% and 42.1% respectively. The least correlation was found to be with shades A4 and C1 at 10%, closely followed by the shade A3.5 at 14.9%. Studies in the past have not shown a correlation for any particular shade (Table II).
 

Table II: Correlation of Visual Shade Matches and Digital Shade Analysis



Oh et al in their study to check for interobserver agreement found about 85 % agreement for common shade.22 Results of the present study were in agreement with the established data and revealed a good correlation between the two observers with 99.92%. Pearsons Chi Square test revealed a very high significance (P<0.001) between the observations of the two observers (Graph I). Hence, for all correlations observations from only one observer were considered.
 

Graph I: The graph depicts the Correlation between the Visual Shade Matching values of the two observers



Hue of the anterior teeth were identified with a high level of accuracy. A similar analysis has not been done in the past. The Hue of the middle and incisal zones of the central and lateral incisors, and all three zones (viz. cervical, middle, incisal) of the canine were identified with a very high value of significance (Graph II).
 

Graph II: Accuracy of selection of Hue of the Central Incisors, Lateral Incisors and Canines by the Observer and Digital Shade Analysis



However, a variation in the shade correlation was seen. A non uniform distribution of shades chosen may have lead to the variations in correlations of the shade matches for a particular shade, and further studies with equal distribution of shades may allow better correlation.
Oh et al in their study evaluating the visual shade matching errors with 2 shade guides found that the Vitapan 3D Master shade guide gave a better agreement than did the Vitapan Classical shade guide.16 Cal et al have described that the digital colour analysis of shade guides in the same environment are different from each other and that they were not identical to each other.
The use of a 12.1 Megapixels Camera, a popularly used camera configuration at the time of the study may be attributed as a limitation of the study, and further studies using a higher configuration may reveal a better results.
No specifications on the camera angulations and position of the camera for a similar analysis have been documented; however a similar setup was chosen for both the Visual Shade matching and the Digital Shade Analysis for standardisation of the test. These factors may act as limitations to the accuracy of the study and may lead to sources of error during establishing reliability between the two shade matching techniques. Nevertheless, this study confirms that there is a problem of inconsistency in the observations made by Visual Shade matching with the Digital Shade Analysis. However, further studies that compare Visual Shade Matching, Digital Shade Matching and Spectrophotometeric Analysis are required to reveal more conclusive results.

Conclusions:

Within the limitations of the study, 1. There is inconsistency in reliability of shade matching between Visual Shade Matching technique and Digital Shade Analysis.
2. There was only 48.2% reliability found between the Visual Shade Matching and Digital Shade Analysis.
3. Amongst the three teeth, lateral incisor showed the best reliable shade match between the Visual Shade Match and Digital Shade Analysis.
4. Reliability between the Visual Shade Matching and Digital Shade Analysis for the three regions of the teeth (viz. Cervical, Middle and Incisal third regions) was not found to be statistically significant.
5. A1, A2, B1 and B2 were the most commonly observed shades amongst both Visual as well as Digital Shade Matching.
6. There was a high level of reliability found correlating the hue of the teeth identified using Visual Shade Matching and Digital Shade Analysis.

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