Color presents experience of visual observation that responds to the light reflected or transmitted from an object (1). Three different factors influence the color perception: light source, the observing object and the observer (1). Tooth color presents the combination of the light reflected from the enamel and the light spread and reflected from both enamel and dentin (1).
Dependent on the type of the procedure and the tools the dentist and the dental technician are using, the tooth color measurement can be divided in two groups: classical (conventional) using shade guides and a digital one (2-5). The use of shade guides to measure tooth color is a subjective process and many factors may affect the results, such as the illumination, the angle of view of the tooth and the tools used
The most important factor influencing the color perception is the nature of the surrounding light in the room, its type, power and the input angle (1). The metamerism, when two objects with different spectral reflectance curves appear different color under different illumination or observer conditions, is the phenomenon correlated with the conventional tooth color assessment (1, 7).
Dental shade matching instruments have been brought to market to decrease deficiencies of the traditional tooth color assessment. They include spectrophotometers, colorimeters and imaging systems (3). Among all, the spectrophotometers are the most precise, flexible and helpful tools for color assessment in dentistry (8, 9). They measure the amount of light energy reflected from an object at 1-25 nm intervals (10, 11). Compared with the eye, or classical techniques, it was found that spectrophotometers offered a 33% increase in accuracy and a more objective match in 93.3% of cases (2). Considering the importance of accurate color matching in esthetic dentistry, some authors suggest that both methods should be used together (12, 13).
The aim of this study was to measure CIE (Commission Internationale de l'Éclairage) color values in maxillary right central incisors in different times of a day and under different illumination conditions.
First null hypothesis was that the measurement in two times of a day under the same light conditions presents no statistically different CIE LCh and L*a*b* values measured in maxillary right central incisors using intraoral spectrophotometer VITA Easyshade Advance 4.0®.
The second null hypothesis was that the type of light conditions presents no statistically different CIE LCh and L*a*b* values measured in maxillary right central incisors using intraoral spectrophotometer VITA Easyshade Advance 4.0®.
MATERIALS AND METHODS
The two observers who participated in this study were well trained in color assessment and handling of the dental shade-matching device under standardized test conditions. Before the clinical measurement, they underwent testing of their color assessment ability and, intra- and inter-observer reliability.
Color assessment ability of two observers
Farnsworth-Munsell 100 HueColor Vision Test was used in order to test the color blindness (14). Both observers were wearing glasses or eye contact lenses. The first observer’s diopter on the right eye was -4.50, on the left eye -4.00, and the second observer’s diopter on the right eye was -4.25, and on the left eye -4.50.
Each observer measured the color of maxillary right central incisors in four patients, two times with an interval of 5 minutes (10.00 am), in the room with dental light and natural light source (dental office)(light temperature 6500 K, illuminance 1000 lux) using intraoral spectrophotometer VITA Easyshade Advance 4.0® (VITA Zahnfabrik, Bad Sackingen, Germany) in “tooth single” mode.
Before measuring, the shade-matching device was calibrated and operated according to the manufacturer’s instructions, the teeth of each of the subjects were cleaned and polished (Proxyt RDA 83; Ivoclar Vivadent, Liechtenstein), the heads of the subjects were placed against the headrest of the treatment chair and their mouths were slightly open during the measurement with the tongue away from the maxillary teeth.
Central region of the labial surfaces of maxillary right central incisors were measured (Figure 1).
Statistical power analysis for investigations using spectrophotometer VITA Easyshade Advance 4.0®
In previous research, supported by University of Zagreb in 2014.-BM1.57 (this study is part of it) we analized the statistical power and confirmed the adequate sample size between 10 and 120 subjects (15).
Ten subjects, the 5th year students at the School of Dental Medicine in Zagreb, participated in the study. The basic inclusion criteria of each subject were the presence of completely healthy and intact upper anterior teeth. Exclusion criteria were the presence of discolorations, white spots, damaged teeth or those with tooth wear, composite fillings, veneers or crowns. The subjects with gingivitis, those with missing maxillary right central incisors and the subjects with implants were also excluded from the study.
Similar to our previous reliability testing, the teeth of each of the subjects were cleaned and polished (Proxyt RDA 83; Ivoclar Vivadent, Liechtenstein), the head of each subject was placed against the headrest of the treatment chair with the mouth slightly open during measurement with the tongue away from the maxillary teeth. In order to avoid dehydration of the teeth, which could influence the results, the subjects were asked to drink water between measurements.
Tooth color measurement
Tooth color measurement of each maxillary right central incisor was performed using intraoral spectrophotometer VITA Easyshade Advance 4.0® (VITA Zahnfabrik, Bad Sackingen, Germany) set in “tooth single” mode. Before any measurement, the shade-matching device was calibrated. It was operated according to the manufacturer’s instructions and the measured values were recorded. During the measurement the devices's probe was set at the right angle, in the central region of the labial surface of maxillary right central incisors (Figure 1). Electronic caliper (VINCA DCLA-0605) was used to measure each tooth in order to assess the central region of the labial surface. The measurement was recorded and used later in the repeated measurements.
The shade-matching device was tested previously and intraclass correlation coefficients (ICCs) for in vivo measurements ranged from 0.858 to 0.971, for in vitro from 0.992 to 0.994, and the accuracy of the device tested was 93.75% (3).
Tooth color measurement was performed twice during the day, early in the morning at 08.15 AM and later at 10.00 AM under three different lightning conditions:
in the room without any natural light sources (no windows), with fluorescent lighting (4 x 120 cm, 36 W, color 765, Philips, Hamburg, Germany), light temperature of 5080 K and illuminance of 500 lux,
in open space, with natural light source, with light temperature of 5400 K and illuminance of 2100 lux at 08.15 AM, and light temperature of 5600 K and illuminance of 2700 lux at 10.00 AM, and
in dental office, with dental light (24 V, 150 W, KaVo Biberach, Germany) and natural light source (next to the window), with light temperature of 5150 K and illuminance of 1200 lux.
Light temperature and illuminance measurements in different times of the day and under different lightning conditions were performed using colorimeter Chroma-2 (Lisun Electronics, Shangai, China).
Colour quantification was based on the CIE L*a*b* values. Data were imported into statistical program SPSS 19.0 (SPSS, Chicago, IL, USA). To estimate intra-observer reliability in measuring natural tooth colour a paired t-test was used, and to estimate inter-observer reliability a t-test for independant samples was used. In both cases the ICCs were calculated.
To estimate the differences in CIE LCh and L*a*b* values measured under the same lightning conditions in two different times of a day, a t-test for independant samples was used, and to estimate the differences in CIE LCh and L*a*b* values in different lightning conditions one-way, the ANOVA (Bonferroni Post Hoc test) was used. All tests were performed at an alpha of .05.
Color assessment ability of two observers
For the first observer, a total error score (TES) was 20, and for the second 24. The result of testing the color assessment ability using Farnsworth-Munsell 100 HueColor Vision Test showed an excellent ability of color assessment for both observers who participated in this study with error scores within a normal range (total error score 46 upward is considered to be a deviation) (16).
The lowest ICC values were found for the lightness (L) - for the first observer it was 0.71, and for the second 0.87, while the highest ICC values were found for a value (0.99) for the first observer and hue (0.95) for the second one.
The results of t-test for independant samples in this study revealed no statistically significant differences among the measurements between the observers (p<0.05) (Figures 4 and 5). The ICCs were high again - for the first measurement they ranged from 0.57 to 0.97 (Table 3), and for the second one from 0.67 to 0.99 (Table 4). The lowest ICC values were found for the lightness (L) - for the first measurement it was 0.57, and for the second 0.67, while the highest ICC values were found for hue in both measurements (0.97 and 0.99, respectively).
Since it was proved that values of intra- and interobserver reliability of the subjects who participated in this study were high, the mean values for CIE LCh and L*a*b* values measured by both observers were used in the further analysis.
The differences in CIE LCh and L*a*b* values measured under the same lightning conditions in two different times of a day
Mean CIE LCh and L*a*b* values (x) and their standard deviations (SD) measured on maxillary central incisors under the same lightning conditions (three types) in two different times of a day are shown in Figures 6, 7 and 8. The paired t-test revealed no differences in measured values in two times of a day for each type of lightning condition (p>0.05) (Table 5, 6, 7). Since the difference between values measured during two different periods of a day was not found, mean values for both measurements under each lightning condition were used in further analysis.
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The differences in CIE LCh and L*a*b* values measured under different lightning conditions
Mean values (x) and standard deviations (SD) for CIE LCh abd L*a*b* values measured under three different lightning conditions are shown in Figure 9. A statistically significant difference between these measuremenst was not found (p>0.05)(Table 8).
The aim of this study was to measure and compare the CIE LCh and L*a*b* values of maxillary right central incisors in different times of a day and under different lightning conditions. Therefore, two observers and 10 subjects participated in the study and the intraoral spectrophotometer was used. All three beforementioned components were previously tested.
Tooth color measurement was performed by two observers, and their reliability had been previously tested.
Since this study aimed to measure the tooth color, it was necessary to investigate the color assessment ability for both observers, as well as their deviations influencing the measurements. The results of the study revealed no deviations in the color assessment ability in both observers (TES 20 and 24, respectively). Besides, almost the same diopters were found for both of them, and therefore the errors in the color estimation were reduced to a minimum.
Furthermore, it was necessary to investigate their reliability and compare the values they measured on the same tooth. The results revealed no statistically significant differences in the measurements for each observer, as well as between them (p>0.05)(Figures 2-5; Tables 1-4). However, the ICCs within and between the observers were lowest for the color lightness, and highest for hue (p>0.05)(Figures 2-5; Tables 1-4). This result showed that the tooth lightness is probably the most sensitive value during the measurement, and, also, that hue is the most constant value.
As it has been mentioned before, this study is part of a larger project supported by University of Zagreb. The statistical power analysis has been previously performed and the results revaled that the adequate sample size for the study using intraoral spectrophotometer ranges between 10 and 120 (15). Therefore, we have decided to include 10 subjects in this pilot study.
It is also of great importance to carry out the research using the device previously tested for its repeatability and accuracy (3).
The majority of the dentists have been using different shade-guides during the tooth color assessment and many errors still occur due to the light source, the angle of the view of the object, ageing and eye fatigue (19, 20). On one hand, digital device manufacturers claim that shade-matching devices are more reliable because they do depend on light sources or their changes, hence we aimed to prove it. On the other hand, Sarafianou et al. found that the effects of different illuminants seemed less pronounced for Easyshade compared to Spectroshade (21).
Therefore, the first part of this research consisted of the tooth color measurement early in the morning (at 8.15 AM) and at 10 AM. These hours of a day were chosen because we usually measure the color of the tooth prior to prosthetic procedure (before the reduction), and the majority of our dentists start to work at 08.00 AM or at 09.00 AM. At that precise time, it is already daylight and natural light sources are present in all seasons.
The results of tooth color measurements at 08.15 AM and at 10.00 AM revealed no difference in the CIE LCh and L*a*b* values (p>0.05)(Figures 6-8)(Table 5). This result was expected for the room without any natural light source as the lightning conditions are constant there, but the difference was not found in dental office with certain amount of natural light source nor at open space where the lightning conditions are changeable (p>0.05)(Figures 6-8)(Table 5). Therefore, the first hypothesis, according to which there was no difference in the CIE LCh and L*a*b* values measured in maxillary right central incisors under the same lightning conditions but different times of a day using intraoral spectrophotometer VITA Easyshade Advance 4.0® was confirmed.
In the second part of the research, the difference in measured CIE LCh and L*a*b* values under different lightning conditions was tested. First room had fluorescent lightning and no natural light sources in order to observe the differences that occur in the measurement under the conditions where no lightning changes caused by natural light appears, with lower light temperature and illuminance. According to the color characteristics, it is colder white color with a touch of blue. Regarding open space, between the measurements, an increase of light temperature and illuminance occurred - from 5400 K to 5600 K, which is considered to be a standard natural light at noon. The obtained values were higher from those in the room without natural light sources (22). In dental office, the light temperature was 5150 K, slightly higher than in the room without natural light sources, probably because of the small impact of the natural light source accompanied with the dental light. Illuminance of the dental office was higher in comparison with the room without the natural light source. At the same time, the illuminance characteristics in dental office were lower than those in open space, suggesting that illuminance in dental office is slightly warmer.
Wee et al. reported the light temperatures in dental offices being approximately 4153 K, much lower than the standard, and found it difficult to assess the tooth color under those conditions (22). The light temperature in our dental office was higher and close to the standard. As for illumination, the ideal value for the working space is from 500 to 1000 lux, which again best suits the dentist’s office characteristics (23). In the room without the natural light source the illuminance was on the lower level, and in open space it was too high.
Scientific studies have proven that the light source, meaning the temperature characteristics and the illuminance, can influence the tooth color assessment when using standard shade-guides (24, 25). Hence, the aim of this study was to investigate the impact of different light conditions on the color measurement using intraoral spectrophotometer.
The results revealed no statistically significant difference in the CIE LCh and L*a*b* values measured under different light conditions, proving that the surrounding lightning have no impact on the results of the tooth color measurement using intraoral spectrophotometer (p>0.05)(Figure 9; Table 8). Therefore, the second hypothesis, according to which there was no difference in the CIE LCh and L*a*b* values measured in maxillary right central incisors under different lightning conditions using intraoral spectrophotometer VITA Easyshade Advance 4.0® was confirmed.
The limitation of this study is a too small sample size (pilot study), which needs to be increased in further studies and include more measurements during different periods within the working time (noon, afternoon, evening). In this way, the results obtained in this study need to be compared with those obtained by other researchers.
The results of the study revealed that the measurments performed in different times of a morning and the lighning conditions during the tooth color measurement using intraoral spectrophotometer VITA Easyshade Advance 4.0® do not have any influence on the CIE LCh and L*a*b* values. Therefore, this shade-matching device presents a valuable tool in everyday dental clinical practice. The utilization of a correct device during tooth shade matching will contribute to the final esthetic outcome of the restoration.