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Corresponding author: Dr Cristina Gómez-Polo, Department of Dentistry, School of Medicine, University of Salamanca, Campus Miguel de Unamuno s/n 37007, SPAIN
How pink gingival porcelain color is perceived by participants classified according to profession and sex is unclear.
Purpose
The purpose of this in vitro study was to evaluate the degree of correlation between the ordering of color tabs by participants classified according to profession, years of dental work experience, and sex and the ideal chromatic order based on the color coordinate L∗ (lightness).
Material and methods
Twenty-one colored specimens made of Heraceram pink gingival porcelain were used. A group of 352 participants (118 men and 234 women) comprised of dental students (n=126), dentists (n=54), dental assistants (n=56), and laypersons (n=116) were enrolled. They were asked to order the specimens starting from the lightest to the darkest. The Kendall coefficients of concordance W and correlation T were used to determine whether the individuals in each experimental group rating the specimens were consistent and accurate.
Results
The degree of agreement between the ideal ordering and that carried out by the participants within the different professional categories was greater than 0.8 in all assessments. No statistically significant differences were found among the groups in relation to professional category, work experience, or sex (P>.05). The Kendall coefficients were higher in the ranking of the darker specimens for all groups of participants.
Conclusions
No statistically significant differences were found among dentists, dental assistants, dental students, and laypersons in the arrangement of pink porcelain specimens according to their lightness. In addition, in all groups, the darker gingival specimens were ordered significantly better according to their lightness than the lighter specimens.
Clinical Implications
Making a correct color selection is more likely for darker gingivae, regardless of sex, professional category, or years of dental work experience.
Chromatic perception is a subjective and individual process.
Outcome evaluation of early placed maxillary anterior single-tooth implants using objective esthetic criteria: a cross-sectional, retrospective study in 45 patients with a 2- to 4-year follow-up using pink and white esthetic scores.
although gingival color is often included in removable dentures and implant-supported prostheses, particularly in patients with large defects, or anterior bone resorption.
but a standard gingival color guide is lacking. The lack of a reference guide impedes gingival color selection and communication with the dental laboratory technician. Therefore, studies that analyze the perception of gingival specimens among different population groups are needed because color selection is a critical factor for the success of esthetic restorations.
Spectrophotometric assessment of peri-implant mucosa after restoration with zirconia abutments veneered with fluorescent ceramic: a controlled, retrospective clinical study.
Randomized-controlled clinical trial of customized zirconia and titanium implant abutments for single-tooth implants in canine and posterior regions: 3-year results.
In the CIELab space, lightness (L∗ coordinate) quantifies the amount of black and white, where pure black is L∗=0 and pure white is L∗=100; a∗ coordinate represents the amount of red-green, where positive a∗ indicates the amount of red and negative a∗ indicates the amount of green; b∗ coordinate is the yellow-blue measurement axis, where positive b∗ indicates the amount of yellow and negative b∗ indicates the amount of blue.
However, the CIELab color space is not a uniform space, and the perception of teeth is not necessarily identical to the perception of gingival space color.
The objective of the present study was to determine whether the professional category (students, dentists, dental assistants, laypersons), the sex, and the years of dental professional experience (0 years, 1-10 years, more than 10 years) influence the ability to correctly sort pink ceramic specimens according to their degree of lightness. The null hypotheses were that none of the 3 variables would significantly influence the accuracy level of participants in the arrangement of pink ceramic specimens and that the participants would be as accurate when ordering lighter specimens as when doing so with darker ones.
Material and methods
A total of 21 different colored specimens made of pink gingiva Heraceram porcelain (Heraceram; Kulzer GmbH) were used in this study. The specimens were made from a 10.6×61.6×33.2-mm silicone template (New Architect wax-up assistant anterior Form B Large; SmileLine Europe GmbH), obtained from Kulzer GmbH. The 21 specimens comprised the 6 basic gingival colors of the Heraceram gingiva system and an additional 15 specimens by mixing the basic colors, as shown in Table 1. Porcelain dispensers (dosifiers; Renfert) were used to ensure the accuracy of the mixtures (Fig. 1).
Table 1CIELab color coordinates of 21 pink porcelain specimens
Pink Gingival Specimens (CIELab Color Coordinates)
A spectrometer (SpectroShade Micro; MHT OpticResearch AG) with a configuration of 45 degrees illumination and 0 degrees observation was used for the color measurements and was tested for reliability and precision. The 21 pink porcelain specimens were measured 3 times with the spectrophotometer in a neutral gray environment after calibration and following the manufacturer's instructions. The mean color coordinates were recorded.
Dental students with previous training in the theory and practice in gingival shade matching were in charge of collecting the data. Each of the students sampled a minimum of 15 participants (without alterations in color perception and without cognitive impairment) in one or more of the professional groups of study (dentists, dental assistants, dental students, or laypersons). Each participant was shown 21 pink specimens on a gray cardboard backing and asked to sort from lighter to darker. The participants were allowed to carry out the task with no time restriction and under standardized conditions in the treatment room of the Department of Prosthodontics, School of Odontology. The ambient lighting was calibrated by using a Philips TLD 95 fluorescent daylight that provided an illumination of 5000 to 5500 K.
The study included 352 participants (118 men and 234 women). The participants included dental students (n=126), dentists (n=54), dental assistants (n=56), and laypersons (n=116). In addition, the individuals were further divided into 3 subgroups based on dental work experience: those with no experience (n=116), those with 1 to 10 years of experience (n=186), and those with more than 10 years of experience (n=50). The study was evaluated by the Bioethics Committee of the University, and a consent form was provided and signed by all the participants.
The Kendall coefficient of concordance W was used to evaluate the extent of agreement among the rankings of the 21 tabs by each experimental group of raters, based on lightness. Kendall W varied from 0 to 1, with 0 representing total lack of agreement and 1 representing total agreement. Thus, the association becomes stronger as the value of Kendall W increases.
A Kendall coefficient of 0.9 or greater is considered as a high level of agreement; a high Kendall coefficient W means that the raters were applying essentially the same standard when assessing the shade tabs. Moreover, the Kendall correlation coefficient T was used to determine whether the raters of each experimental group were accurate. This coefficient, ranging from -1 to 1, was estimated by calculating the average of the Kendall tau coefficients of the rankings given by each rater and the known standard (the ranking of the 21 disks obtained using the L∗ coordinate). A positive value indicated a positive association and a negative value indicated a negative association, and the higher the magnitude, the stronger the association.
To compare the Kendall correlation coefficients among the groups of each category of the variables sex, professional category, and work experience, Mann-Whitney, Wilcoxon, and Kruskal-Wallis tests were applied (α=.05).
Results
The 21 specimens of pink porcelain used in this study showed maximum and minimum color differences according to the Euclidean formula of ΔE∗=33.34 units and ΔE∗=0.41 units. In terms of lightness, the maximum and minimum differences between these specimens were ΔL∗=27.04 and ΔL∗=0.03.
All the W values were greater than 0.9, which indicated high levels of interrater agreement with respect to the assessment of the lightness of the 21 shade tabs (Table 2). Men were slightly less consistent than women, and the dentists were slightly less consistent than the dental students, dental assistants, and laypersons. The W values of the 3 subgroups based on work experience in dentistry were also similar. Table 3 lists the values calculated by using the Kendall correlation coefficient (T) on the results of the rankings obtained by the experimental groups and the rankings obtained objectively using the L∗ coordinates. Table 3 also includes the P values obtained when comparing the correlation coefficients among the groups of each category.
Table 2Kendall W concordance coefficients to assess degree of coincidence of arrangements of all specimens in each group of participants
Table 3Kendall T correlation coefficients to assess, in each group of participants, degree of coincidence of arrangements of all specimens with ideal arrangement
Variable
Experimental Group
n
T
P
Sex
—
—
—
.047
Men
118
0.839
—
Women
234
0.851
—
Professional category
—
—
—
.871
Students
126
0.849
—
Dentists
54
0.839
—
Dental assistants
56
0.847
—
Laypersons
116
0.847
—
Dental work experience
—
—
—
.763
0 years
116
0.847
—
From 1 to 10 years
186
0.848
—
More of 10 years
50
0.841
—
All participants
352
0.847
—
P values of intergroup comparisons of correlation coefficients T.
The T values were all above 0.80, which indicated that the raters were moderately accurate. The T value calculated for the men was smaller than the value calculated for the women, and the difference was significant (P =.047). The T values calculated for the dental students, dentists, dental assistants, and laypersons lacked statistical significance (P>.05). Finally, no significant differences were observed for the T values of the 3 subgroups of participants divided according to dental work experience (Table 3) because those values were almost identical.
The same analysis was repeated by using the 10 lighter specimens which had maximum and minimum color differences, according to the Euclidean formula, of ΔE∗=17.98 units and ΔE∗=0.41 units; the lightness (L∗ coordinate) of these 10 specimens had maximum and minimum differences of ΔL∗=7.14 units and ΔL∗=0.07 units, respectively. The T values obtained from the partial rankings of these 10 tabs (L∗, from 56.73 to 63.87) are shown in Table 4.
Table 4Kendall T correlation coefficients to assess, in each group of participants, degree of coincidence of lighter specimens’ arrangements with ideal arrangement.
Variable
Experimental Group
n
T
P
Sex
—
—
—
.009
Men
118
0.585
—
Women
234
0.638
—
Professional category
—
—
—
.278
Students
126
0.642
—
Dentists
54
0.573
—
Dental assistants
56
0.629
—
Laypersons
116
0.615
—
Dental work experience
—
—
—
.431
0 years
116
0.615
—
From 1 to 10 years
186
0.627
—
More of 10 years
50
0.607
—
All participants
352
0.620
—
Pvalues of intergroup comparisons of correlation coefficients T.
All the T values in Table 4 were significantly smaller than those in Table 3. In addition, the values calculated for male and female participants were significantly different (P=.009), with smaller values recorded for men. The values for the 4 professional categories were statistically similar, as were the groups in terms of dental work experience (I>0.05) (Table 4).
The 10 darker specimens had maximum and minimum color differences, according to the Euclidean formula, of ΔE∗=12.70 units and ΔE∗=1.30 units, respectively; the lightness (L∗ coordinate) of these specimens had maximum and minimum differences of ΔL∗=12.10 and ΔL∗=∗0.03, respectively. The values T obtained from the rankings of these shade tabs (L∗, from 36.83 to 48.93) are shown in Table 5.
Table 5Kendall T correlation coefficients to assess, in each group of participants, degree of coincidence of darker specimens’ arrangements with ideal arrangement
Variable
Experimental Group
n
T
P
Sex
—
—
—
.813
Men
118
0.762
—
Women
234
0.754
—
Professional category
—
—
—
.763
Students
126
0.754
—
Dentists
54
0.774
—
Dental assistants
56
0.754
—
Laypersons
116
0.755
—
Dental work experience
—
—
—
.939
0 years
116
0.755
—
From 1 to 10 years
186
0.759
—
More of 10 years
50
0.755
—
All participants
352
0.757
—
P values of intergroup comparisons of correlation coefficients T.
The T values in Table 5 were found to be slightly smaller than those of Table 3 and greater than those of Table 4. This indicated that the raters were more accurate in ranking the darker tabs than the lighter ones. In Table 5, all the values were found to be similar and showed no statistically significant differences (P>.05).
Figure 2 shows the comparison of the Kendall correlation coefficient (T) values calculated from the rankings of the 10 lighter shade tabs to the 10 darker shade tabs by the different experimental groups associated with the 3 variables: sex, work experience, and professional category. All the T values were greater for the darker tabs than those for the lighter ones in every experimental group. All the differences were statistically significant (P<.05).
Figure 2Comparison of the T coefficients obtained when the lighter and darker specimens were ranked. A, By men and women. B, By participants with different levels of dental work experience. C, By participants of different professional categories.
Figure 2Comparison of the T coefficients obtained when the lighter and darker specimens were ranked. A, By men and women. B, By participants with different levels of dental work experience. C, By participants of different professional categories.
Figure 2Comparison of the T coefficients obtained when the lighter and darker specimens were ranked. A, By men and women. B, By participants with different levels of dental work experience. C, By participants of different professional categories.
This study assessed the ability to perceive different degrees of lightness in custom-made pink ceramics shade tabs by a group of participants with different professional profiles and clinical work experience. Limitations of this study included that both the participants and specimens were convenience samples, indicating that the results obtained cannot be generalized to the global population. The 21 specimens of pink porcelain used offered a wide chromatic range, although these shade tabs may not fully represent the true chromatic range of the natural gingival tissue, whose chromatic space has not yet been documented.
making it difficult for dental laboratory technicians to imitate the natural gingival tissue color with pink porcelain. Therefore, on many occasions, the available dental porcelain systems constitute the reference used as a gingival color guide.
The main null hypothesis was accepted because none of the 3 variables (age, sex, and professional category) significantly influenced the degree of concordance between the arrangements proposed by the participants and the ideal arrangement of the pink ceramic specimens, in terms of lightness. However, the secondary null hypothesis was rejected because the darkest pink porcelain specimens were arranged significantly better according to their lightness than the lightest specimens.
The decision to study lightness was based on a protocol through which dental color is often selected in clinical practice, where lightness is determined first, followed by chroma and hue.
The Kendall correlation coefficient T evaluated the degree of agreement of the specimen orderings, sorted by the participants according to their lightness (which was influenced not only by the L∗ coordinate but also by the coordinates a∗ and b∗), with the ordering obtained based solely on the L∗ coordinate (the ideal arrangement). Therefore, the coefficient T assessed the influence that the coordinates a∗ and b∗ had on the perception of the lightness of the specimens. Future studies should quantify the influence of the coordinates a∗ and b∗ on the selection of gingival color. The thresholds of gingival chromatic perception and acceptance should also be studied to be able to design gingival guides with a comprehensive mathematical criterion. Although there are no spectrophotometers marketed to measure gingival color, the SpectroShade Micro was used as it has been used in tooth color studies.
Spectrophotometric assessment of peri-implant mucosa after restoration with zirconia abutments veneered with fluorescent ceramic: a controlled, retrospective clinical study.
Randomized-controlled clinical trial of customized zirconia and titanium implant abutments for single-tooth implants in canine and posterior regions: 3-year results.
The results of this study suggest that all the participants were able to order pink specimens correctly and consistently according to lightness (Tables 2 and 3). In addition, it was found that specific training in dental color matching did not necessarily improve the ability to distinguish among the varying degrees of lightness of gingival ceramics. In fact, experienced dentists tended to be less consistent when identifying a range of light colors (Table 4). The T values in Table 5 were slightly smaller than those in Table 3 but greater than those in Table 4, which indicates that the raters were more accurate in ranking the darker shade tabs than the lighter ones. This may occur because the differences in lightness among the 10 darker tabs were larger than the differences in lightness among the 10 lighter tabs.
Other authors have also pointed out that dental work experience does not influence color matching abilities.
This relatively unexpected result may be explained by the fact that continued exposure of dentists to LEDs may cause them to be insensitive to the detection of subtle differences in lightness, due to potential damage to the retina or fatigue of the retinal photoreceptor cells.
Additional studies of this type are needed, as wider knowledge regarding the perception of the gingival chromatic space will help to optimize the subjective selection of gingival color.
Conclusions
Based on the findings of this in vitro study, the following conclusions were drawn:
1.
There were no statistically significant differences among dentists, dental assistants, dental students, and laypersons with respect to the ranking of colors in the gingival chromatic space based on lightness.
2.
The ranking of the darker gingival specimens was significantly more accurate than that of the lighter gingival specimens, irrespective of sex, dental work experience, or professional category.
Acknowledgments
The authors thank the research group named Avances en Salud Oral of Department of Surgery at the University of Salamanca for the institutional support provided for this research project and Elena P. Hernández Rivero (Central Language Service-USAL) for translation and linguistic review. The authors would also like to thank the work of the dental laboratory Dentislab for the design of the gingival porcelain specimens.
References
Gómez-Polo C.
Gómez-Polo M.
Celemin-Viñuela A.
Martínez Vázquez De Parga J.
Differences between the human eye and the spectrophotometer in the shade matching of tooth colour.
Outcome evaluation of early placed maxillary anterior single-tooth implants using objective esthetic criteria: a cross-sectional, retrospective study in 45 patients with a 2- to 4-year follow-up using pink and white esthetic scores.
Spectrophotometric assessment of peri-implant mucosa after restoration with zirconia abutments veneered with fluorescent ceramic: a controlled, retrospective clinical study.
Randomized-controlled clinical trial of customized zirconia and titanium implant abutments for single-tooth implants in canine and posterior regions: 3-year results.
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