Providing an esthetically pleasant smile is one of the main concerns in esthetic dentistry and the patients' demands for an improved dental appearance have prompted the industry to continuously raise the bar with regard to materials, techniques and technology.
Recent studies have shown that the tooth color is one of the most important parameters determining the patients' satisfaction with their dental appearance (1-3). On the other hand, clinical assessment and the patient's evaluation of esthetic parameters, including teeth or restorations’ color, may also differ (4). Samorodnitzky-Naveh et al. have proven that laypeople evaluate their teeth darker in comparison to the professionals, and that women assessed tooth shades more accurately than men (5).
In order to avoid the differences arising from both the clinicians and patients’ subjective visual color determination affected by the surrounding illumination, the angle of view of the tooth and the tab, clothing, make-up and the chromatic perception of the dentist such as previous eye exposure and metamerism, fatigue, ageing and emotions, dental shade matching instruments have been brought to the market to reduce or overcome imperfections and inconsistencies of traditional shade matching (6-11).
They encompass different instruments and software. Spectrophotometers are amongst the most accurate, useful and flexible instruments for color matching in dentistry (10, 12). They measure the amount of light energy reflected from an object at 1-25 nm intervals along the visible spectrum (13, 14). Compared with observations by the human eye, or conventional techniques, it was found that spectrophotometers offered a 33% increase in accuracy and a more objective match in 93.3% of cases (8). Some authors suggest that instrumental and visual color matching methods should be used together since they complement each other (15, 16).
The aim of this study was to evaluate the inter-observer reliability of dental shade-matching device (VITA Easyshade® Advance 4.0) using an in vivo model. The null hypothesis was that the color assessment tested shows no difference between four observers using the same dental shade-matching device.
Materials and methods
Ten patients with completely healthy and intact maxillary anterior teeth participated in this study. Those with discolorations, stains, evidence of visible tooth wear, composite fillings, veneers of crowns on investigated teeth were excluded. The patients were instructed to place their heads against the headrest of the dental chair and to keep their mouths slightly open during measurement. They were instructed to keep the tongue in a relaxed position away from the maxillary teeth during measurement to prevent false measurements. The central region of the labial surface of each patient's right maxillary central incisor was measured twice by each observer with an interval of 1 hour, and the average value was considered. Patients were provided with water after each sequence to prevent dehydration of the teeth. The following colors were measured: B1, A1, A2, A3, C1 and C3. An intraoral spectrophotometer VITA Easyshade® Advance 4.0 (VITA Zahnfabrik, Bad Sackingen, Germany) was used (Figures 1 and 2). The shade-matching device was operated according to the manufacturer's instructions.
All operators in this study were well trained in color assessment and handling of the dental shade-matching device under standardized test conditions. Before any measurement, the device was calibrated on its own white ceramic block and it was used in ‘tooth single’ mode.
Light test conditions
According to the CIE standard, the daylight illumination conditions (Just Normlicht, Weilheim an der Teck, Germany) were set at 6500 K and 1000 Lux, of 93 foot-candles. Natural daylight was excluded using an optical opaque louver.
Color quantification was based on CIE L*a*b* values. Color differences (E) were calculated. Data were imported into statistical program SPSS 19.0; SPSS, Chicago, IL, USA). To estimate the in vivo inter-observer reliability in measuring and matching tooth colors, one-way ANOVA (Bonferroni Post Hoc test) and intraclass correlation coefficients (ICCs) were calculated. All tests were performed at an alpha of .05.
The mean L*a*b* values for measurements of 10 right maxillary central incisors measured in an in vivo model by four different observers are shown graphically in Figure 3. One-way ANOVA showed no statistically significant differences in color measurement of four observers in all the measured values (p>0.05).
The mean color differences for the same measurements are shown graphically in Figure 4. Delta E values in this study ranged from 3.018 to 5.234. Although some small differences existed, a statistically significant difference between the observers was not found (p>0.05).
In modern dentistry today it is very important to correctly assess the color of the teeth in order to produce the same color effect of the future restoration.
In our previous study we already tested the intra-device repeatability and accuracy of dental shade-matching device (VITA Easyshade® Advance 4.0) using both in vitro and in vivo models (17). The results revealed higher L* and lower a* and b* values in the in vivo than the in vitro model, with mean differences of 3.51 and 1.25 delta E units, respectively (p<.001). The device repeatability ICCs for in vivo measurements ranged from 0.858 to 0.971 and for in vitro from 0.992 to 0.994, and the accuracy of the device tested was 93.75% (17).
Before starting color measurements, it is important not only to test the device but to test the potential independent observers to see if two or more of them watching the same events agree on what they observe. In that way, if an adequate level of inter-observer reliability is obtained, each of the observers can observe independently, perhaps at different times and/or in different locations, and their observations can be combined into one data set for analysis.
In the present study, the null hypothesis was that the color assessment tested shows no difference between four observers using the same dental shade-matching device. Although some small differences existed, our results revealed no statistically significant differences in color measurement of four observers in all the measured values (p>0.05) (Figure 3), delta E values ranged from 3.018 to 5.234 (p>0.05) (Figure 4) and observers' ICCs were very high (Table 1). Therefore, the hypothesis was confirmed.
In Lab measurements the values for all four observers were consistent, but delta E values showed wider ranges - exceeded the 50% of perceptibility threshold for a clinical mismatch in the in vivo model (2.6 E units) but still remained below the 50% acceptability level of 5.5 E units (8, 18-21). The highest delta E value was found in the fourth observer (5.234) which almost reached the upper acceptability level and his ICC for L values was the lowest (65%) and therefore we have decided to exclude him from the further measurements (Figure 4, Table 1). Since all four observers in this study were trained and well experienced in color measurements with the tested device and we achieved the standardized conditions and illumination, this finding may be attributed to the tooth variance in surface morphology and the observer's selection of device tip position in the middle third of each tooth.
It has already been reported that there were some differences in the inter-observer reliability dependent on the type of the teeth. Lasserre et al. showed more regular inter-observer measurements on canines than those made on central incisors explaining it with more errors in measurements on the incisors mostly because of their high translucency (22). In the present study we only measured the color of the central incisors and the sample size was small (only 6 shades) and therefore it is difficult to compare the results.
The second explanation for the errors observed in the fourth observer is the device tip position that could have been avoided using the positioning jig. In some studies, the authors mentioned positioning the jig to accurately reposition the measuring unit for each shade measurement due to the smaller diameter of VITA Easyshade® Advance 4.0 (3-5 mm) (8, 23).
Further research should be performed to determine whether a higher number of observers with different levels of experience in color measurement, participating subjects and groups of teeth with different shades would change the repeatability. The positioning jig is highly recommended, too.
The inter-examiner reliability of measurements using VITA Easyshade® Advance 4.0 shade-matching device was acceptable. The mean color differences ranged from 3.018 to 5.234, which was within the clinical acceptability level. Apart from the digital equipment, a well-trained observer is needed in order to achieve accurate dental color measurement.