Effect of Clinical Experience on the Shade Matching Accuracy in Different Dental Occupational Groups.

OBJECTIVES: The aim of this study was to evaluate the effect of clinical experience level on the shade matching accuracy in different dental occupational groups.
MATERIALS AND METHODS: A total of 80 participants, assigned to one of four groups depending on the level of their clinical experience in shade matching: dental technicians (DTs), residents in prosthodontics (RPs), specialists in prosthodontics (SPs) and dental students (DSs) took part in the study. They were asked to use Tooth guide Training Box (TTB) and determine 15 standardized shade tabs using VITA 3D-Master shade guide. The number of mistakes in final test for each participant was recorded and accuracy was calculated. Color difference (ΔE) values for each shade were calculated from L*, a* and b* values. Differences in accuracy, mean ΔE values and mean error ΔE values between four different groups were examined.
RESULTS: No statistically significant differences were found between the groups regarding accuracy and mean ΔE values (p>0.05). The accuracy rate in four groups was 0.51±0.20 (DTs), 0,54±0.18 (RPs), 0.49±0.16 (SPs) and 0.55±0.14 (DSs), respectively. Mean ΔE values were 2.10±0.98 (DTs), 2.18±0.97 (RPs), 2.51±0.97 (SPs) and 2.08±0.86 (DSs), respectively. Regarding mean error ΔE values, DTs made errors with significantly less deviations compared to other groups (p<0.05).
CONCLUSIONS: This study has shown that clinical experience is not found to be a significant factor to the shade matching accuracy. With regard to the mean error ΔE values, DTs were more successful in shade matching than other participants.

Introduction

Correct tooth shade assessment is one of the most important components of esthetic dental treatment.

There are a number of different subjective and objective ways for choosing shades, including various shade guides as well as spectrophotometers. Although the instrumental color matching has already been proved more reliable, the selection of matching shade tabs from commercially available shade guides is still the most common method of tooth color assessment ().

Visual color matching is affected by many variables, such as age of the observer, his/her experience, possible color deficiency, condition of the teeth observed and light source (-).

Knowledge about the physical appearance of color is also one of the important factors for visual shade selection. The well-known Munsell’s theory is describing color as a three-dimensional phenomenon consisting of hue, value and chroma, color characteristics necessary to observe while assessing tooth shade (, ).

Therefore, a new shade guide Vita 3D Master has been developed, using the above mentioned Munsell’s terminology (Vita Zahnfabrik, Bad Sackingen, Germany). It utilizes the color perception concept with five levels of values and three levels of chroma and hue and has been proved to be more accurate than other theories (-). In 2007, in order to assess tooth color using 3D Master shade guide as precise as possible and practice the procedure, a system known as the Toothguide Training Box Mark II (TTB)(Vita Zahnfabrik, Bad Sackingen, Germany) was introduced, designed to familiarize the dentists with tooth shade selection (-). It enables the user to systematically select tooth shades by determining all three color characteristics in accordance with human color perception under the standardized artificial daylight with color temperature of 5500 K (, ).

The aim of this study was to evaluate the effect of clinical experience level on the shade matching accuracy in four different dental occupational groups - dental technicians (DTs), residents in prosthodontics (RPs), specialists in prosthodontics (SPs) and dental students (DSs).

The first null hypothesis was that there will be differences in accuracy of the shade tabs selection using TTB between different groups depending on their level of clinical experience in tooth shade assessment. The second null hypothesis was that there will be differences in ΔE values, calculated as a deviation from the correct answers, between four different groups. The third null hypothesis was that there will be differences in error ΔE values in those who selected wrong shades between different groups depending on their level of clinical experience in tooth shade assessment.

Materials and methods

The design of the study was approved by the Ethics Committee of the School of Dental Medicine, University of Zagreb, Croatia.

Sample size

A total of 84 participants, assigned to one of four groups depending on the level of their clinical experience in shade matching:

20 dental technicians (DTs): 5 men, 15 women; average age 30.4±1.5,

21 residents in prosthodontics (RPs); 8 men, 13 women; average age 31.1±2.1,

23 specialists in prosthodontics (SPs) and 10 men, 13 women; average age

43.2±3.4, minimum 10 years of service as the specialist, and

20 dental students (DSs); 7 men, 13 women; average age 22.1±1.5, took part in the study. All of the participants used the Chromascop shade guide (Ivoclar Vivadent, Schaan, Liechtenstein) for the tooth color assessment and did not receive any type of lecture or training about the 3D Master system.

Exclusion criteria

The respondents who have previously participated in similar research or have been practicing color determination had some previous shade selection experience or training using 3D Master shade guide were excluded from this study. One female resident and 3 female specialists in prosthodontics were therefore excluded.

Since the TTB curriculum includes a color vision test all the participants were given the Ishihara test of 24 plates and those participants who had more than two errors are excluded (). The evaluation of the Ishihara test did not reveal color vision deficiency in participants.

Therefore, the sample group finally consisted of 80 participants, 20 in each of the four investigated groups.

TTB

The TTB was used for the purpose of the study. Each participant was asked to sit in front of the device, in the upright position and received instructions regarding the functioning of the device and training steps.

The electro mechanic device was connected to a software system and consisted of 52 teeth from the 3D Master shade guide, radially arranged. The visualization of the tested teeth and the selected group from the color key was performed trough an opening in the center of the device. The selection was performed using arrow buttons positioning the key in accordance with the ones assortment (Figure 1).

Figure 1

TTB system

The TTB worked under daylight lamp conditions (Dialite Color System) with diffused light from two angled 5 W lamps of 5500 K and 1000 lux. The approximate distance of the participants’ eye during the observation was 25 cm.

The TTB training was structured in three exercises and a final test that measured knowledge and color assessment capacity in shade matching. During the period of three exercises the participants had to correctly select the lightness, lightness and chroma and lightness, chroma and hue of the tested teeth, respectively. After completion of exercises, the participants had to undergo a final test in which all three parameters needed to be assessed for 15 tested teeth.

Observed parameters

Accuracy

The number of correct answers from the final test of each participant was collected and accuracy calculated as the ratio of correct and total number of attempts (x: 15).

Mean ΔE

The distance in the color space (ΔE) was determined for each shade tab and color difference between the task tab and selected tab was calculated using equation

ΔE=((ΔL)2+(Δa)2+(Δb)2)1/2 (). On the basis of L*a*b* values provided by the manufacturer it was possible to calculate the differences in ΔL*, Δa* and Δb*. In calculation, the correct answers were recorded as ΔE=0.

Mean error ΔE

In order to get information about the range of ΔE values when wrong shade tab was selected, mean error ΔE only for wrong answers was calculated as mentioned above.

All the observed parameters were calculated in the four aforementioned study groups.

Statistical analysis

The collected data were entered into Excel database and statically analyzed, imported into statistical program SPSS 19.0 (SPSS, Chicago, IL, USA).

The differences in accuracy, ΔE and error ΔE values between the four study groups were analyzed using the one-way ANOVA and Bonferoni corrections.

Results

Out of a total of 84 participants, 80 participated in the study (96%). Four participants were excluded because they had previous training and shade selection experience with the 3D Master shade guide (1 RP and 3 SPs).

The evaluation of the Ishihara test did not reveal any color perception deficiencies in participants.

Mean accuracy, ΔE and error ΔE values from the results of the final test with the TTB system were calculated in all groups (Figures 2-4).

Figure 2

Mean (x), minimum (min) and maximum (max) accuracy among four dental occupational groups

Figure 3

Mean (x), minimum (min) and maximum (max) ΔE values among four dental occupational groups

Figure 4

Mean (x), minimum (min) and maximum (max) error ΔE values among four dental occupational groups

Mean accuracy ranged from 0.49 to 0.55, of which DSs have reached the highest, and SPs the lowest values (Figure 2). A statistically significant difference in accuracy between four groups was not recorded (p>0.05; Table 1).

Table 1

Difference in accuracy, mean ΔE and mean error ΔE among four dental occupational groups

	F	df	p
accuracy	0,48	3	0,70
mean dE	0,88	3	0,45
mean errof dE	3,15	3	0,03

Mean ΔE ranged from 2.08 to 2.51, with DSs who reached the lowest, and SPs the highest values (Figure 3). A statistically significant difference in ΔE between four groups was not recorded (p>0.05; Table 1).

Mean error ΔE ranged from 4.05 to 4.84, with DTs reaching the lowest, and SPs the highest values (Figure 4). DTs’ mean error ΔE statistically differed from the other three groups (p<0.05; Table 1).

Discussion

The purpose of this study was to evaluate the effect of clinical experience level on the shade matching accuracy in different dental occupational groups using the TTB and applying the 3D Master protocol.

This system was primarily designed to introduce university students to tooth shade selection and several studies investigated the effect of the TTB on training dental students in color identification (, , ). Later on its use was extended to other groups - from dentists, technicians, dental staff members and laypeople (-). In this study, we have decided to assess the ability to accurately assess shade tabs according to the 3D Master shade guide in dental occupational groups, who assess the color mostly on their everyday basis but in different protocols using different shade guides, therefore, we decided to exclude laypeople. Capa et al. have already shown that dental care professionals who routinely performed restorative procedures matched the shades better than other dental occupational groups together with laypeople (). Similar results were obtained by Della Bona et al. who also shown significantly higher visual-instrumental shade agreement where both the VITA Classical and 3D Master shade guides were used by clinically experienced dentists compared to non-dental observers ().

There is still no agreement in the literature about the role of previous knowledge and experience in dental shade matching. Some experts have emphasized the need for training, color teaching and experience proving their impact on color matching ability (, , , ). The others claim that previous experience does not improve ability in color selection or has a minimal impact on tooth-shade matching (, , ).

Since the main purpose of this study was to explore the impact of value-based protocol of the 3D Master shade guide on the ability to match shade tabs using the TTB on participants assessing the color previously using hue-based shade guides, we have excluded four participants who reported earlier training and shade selection experience with the 3D Master shade guide. Therefore, the participants in this study did not receive any type of lecture or training, not even basic information about dental color parameters or determination methods using color keys before they started. The first touch with the new value-based protocol was three exercises they had to pass before the final test on the TTB.

It was also important to exclude the participants with any types of color vision impairments because it had already been proved that color vision deficiency may result in significantly worse color matching quality compared to normal color vision (). None of our participants discovered any color vision deficiencies.

The results of this study revealed that the DSs achieved the highest level of accuracy and the SPs the lowest one, 0.55 and 0.49 respectively (p>0.05; Figure 2). These results are very interesting because the SPs, who determine the tooth color on their daily basis were expected to be the most accurate group and the DSs with the least experience the least accurate. However, we have to take into account that all the participants in the study used Chromascop shade guide (hue-based) in their everyday practice and no one was familiar with the protocol of 3D Master shade guide. Therefore, the results of this study showed that those who used shade guides arranged according to hue over a longer period of time (SPs in this study had been using it for more than 10 years) found it more difficult to assess the color according to value. At the same time, DSs who were still novices in the process of learning how to accurately evaluate the color of the tooth found it easy to assess it according to value.

Sinmazisik et al. used the mistake ratio and scores from the final test to evaluate the ability to match tooth color between dental technician students and graduate dentists and they found students to be more successful in shade matching than dentists, which is in accordance with our results (). In another study, dental technician students, those who still learn how to assess the color, made more mistakes in the h parameter, and dentists made more mistakes in the L parameter ().

The same was with ΔE values in our study. The DSs revealed the lowest shade difference values in the assessment and SPs the highest one, 2.08 and 2.51, respectively (p>0.05; Figure 3). These results are within the accepted perceptibility (PT) and acceptability thresholds (AT), although there is no consensus regarding the values that should be used. Khashayar et al. found that more than half of the studies they investigated defined PT as ΔE=1, and one third of the studies referred to ΔE=3.7 as the threshold at which 50% of observers accepted the color difference (AT) ().

In Sinmazisik et al. study, dental technician students revealed lower ΔE values (1.72) and proved to be even closer to accepted PT than our dental students, but in general dentists group the value was even higher (2.92), but still within AT ().

What is also very important in this study is the fact that DTs were the second best in accuracy and shade difference with ΔE value of 2.1, and one of the participants from this study group even achieved the perfect matching with no errors (ΔE=0; Figure 3). Considering error ΔE, calculated as shade difference only in the case of errors, DTs even revealed significantly lower value in comparison to other three observed groups in the study, meaning that when they made a mistake, its discrepancy was lower (p<0.05; Picture 4; Table 1).These findings regarding more accurate assessment with less difference in shade matching can be attributed to the fact that DTs are focused on colors during their laboratory work even when they are not familiar with value-based protocol, thus having less chance of an error in tooth color assessment.

Haddad et al. also reported that females in their study achieved significantly better shade matching results than males, indicating that gender plays an important role in shade matching (). In our study, we have tried to achieve homogenous subgroups of men and women in each investigated group but have not fully succeeded because we had more women (55%-75%) in all four groups and this probably affected our results. An equal number of men and women, larger number of participants as well as longer periods of training time and scores obtained from the TTB system are needed for pursuing further study.

Conclusions

The students achieved the highest accuracy and the lowest ΔE values in the study. With regard to the mean error ΔE values, DTs were more successful in shade matching than other participants.

This study shows clinical experience is not found to be a significant factor to the shade matching accuracy.