|Year : 2018 | Volume
| Issue : 7 | Page : 925-931
Color relationships of natural anterior teeth: An In vivo study
Sedanur Turgut1, Hamiyet Kilinc1, Gunes Bulut Eyupoglu2, Bora Bagis3
1 Department of Prosthodontics, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey
2 Department of Restorative Dentistry, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey
3 Department of Prosthodontics, Faculty of Dentistry, Izmir Katip Celebi University, Izmir, Turkey
|Date of Acceptance||31-Jan-2018|
|Date of Web Publication||09-Jul-2018|
Dr. Bora Bagis
Department of Prosthodontics, Faculty of Dentistry, Izmir Katip Celebi University, Izmir
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objectives: To investigate the color relationships between the anterior teeth in vivo. Materials and Methods: A total of 640 volunteers (age: 18–22) participated in the study. The color measurements of left maxillary and mandibular central, lateral, and canine were performed using a colorimeter. Color differences were calculated according to the CIE L*a*b* (ΔE*) and CIEDE2000 (ΔE00*) system. The National Bureau of Standards (NBS) ratings were also evaluated. Statistical analyses were performed using two-way ANOVA and Fisher's exact test (P < 0.05). Results: Significant differences were found between the L*, a*, b*, and ΔE* values (P < 0.05), except for mandibular central and lateral. ΔE* values were found between 1.5 ΔE* (mandibular central–mandibular lateral) and 8.1 ΔE* (maxillary central–maxillary canine). While the highest L* (80.5) and the least b* (15.1) values were obtained for mandibular central, the mean L* (73.6) and the mean b* values (21.3) were obtained for the maxillary canine. a* value was found to be highest for the mandibular lateral (1.1) and the least for the maxillary central (−0.2) teeth. NBS values were between 1.3 and 7.4 units, and only mandibular central and mandibular lateral teeth exhibited “almost the same” color values, while the other teeth exhibited “slightly different,” “very different,” or “remarkably different” color values. Conclusion: Anterior maxillary and mandibular teeth exhibited “different” color values. Only mandibular incisors and mandibular laterals showed “almost the same” color. Canines were more dark/red/yellow for both mandible and maxilla. Centrals were more bright/green/yellow for maxilla and bright/green/blue for mandibular. Clinicians should select the color one by one for each tooth and be aware of their color relations for optimal esthetics.
Keywords: Color selection, esthetic, tooth
|How to cite this article:|
Turgut S, Kilinc H, Eyupoglu GB, Bagis B. Color relationships of natural anterior teeth: An In vivo study. Niger J Clin Pract 2018;21:925-31
| Introduction|| |
Color of a tooth is the most prominent factor among optical properties and is influenced by both internal morphology and external texture such as the outline form, size, shape, surface anatomy, and light reflection patterns. Tooth tissues (pulp, dentin, and enamel) have different optical properties, and their natural appearance depends on their thickness, calcification, composition, and translucency, which are ultimately responsible for the polychromatic characteristics of the crown. Enamel has a highly calcified structure and less organic material content, while dentin has less mineral content and higher organic tubular structure. Therefore, enamel displays higher light transmission and is more translucent than dentin. The thickness of dentin and enamel tends to vary according to the different teeth groups and also different parts of the same crown., Enamel thickness is lower in the cervical region and increases toward the incisal edge, whereas the dentin distribution shows the opposite pattern. Accordingly, due to the reflection of the underlying dentin, high density in cervical region decreases toward the incisal., The red and yellow colors of natural teeth increase, and the translucency characteristic decreases toward the cervical portion from the incisal portion of teeth.
Some authors have claimed that the dentin predominately determines tooth color, unlike enamel, which has a minor effect through scattering at wavelengths in the blue range. The volume of the pulp chamber and the vitality of the tooth vary at different stages of the dental development. In general, the pulp chamber is very wide and has greater intensity of red between the ages of 13 and 19 years. With the formation of secondary dentin, the pulp chamber becomes smaller and less red with age.
As the tooth crown is not monochromatic and has various color layers on the crown surface, it seems difficult to replicate these structures using dental materials that have different colors and translucency. For adequate color reproduction, it is valuable to quantify the color distributions of natural teeth accurately, and the color of the restoration should be prepared in accordance with the adjacent and symmetrical teeth.
The color distributions of teeth have been evaluated before either visually or using spectrophotometers, colorimeters, or digital cameras.,, The color distributions were reported in the CIE L*a*b* system. The system enabled the evaluation of the degree of color change (ΔE*) based on three coordinates. L* color coordinate represents lightness or brightness, a* represents greenness (positive) and redness (negative), and b* represents yellowness (positive) and blueness (negative).,, Numeric description of color permits precise definition of the magnitude of the color difference between objects. The critical level of ΔE* values can be quantified by the National Bureau of Standards (NBS) rates, which is the way that a color change is evaluated by the human eye. The CIEDE2000 color difference (ΔE00*) was found considerably more sophisticated and computationally involved than the equations for CIE L*a*b* difference., Perceptibility threshold (PT) and acceptability threshold (AT) have been introduced as two major thresholds for assessing color differences and serve as a control to evaluate the dental structures clinical success and interpret visual and instrumental findings. The ΔE00*values were compared with 50:50% PT and 50:50% AT values reported in the previous studies., Several studies ,,, determined that 50:50% PT ranged from 0.80 to 1.30 ΔE00* units and that 50:50% AT ranged from 1.80 to 2.25 ΔE00*. Paravina et al. found that 50:50% PT and ATs were significantly different. CIEDE2000 50:50% PT was 0.8 ΔE00*, whereas 50:50% AT was 1.8 ΔE00*.
The factors affecting the color of a tooth have been examined earlier; however, searching the literature, there was no adequate knowledge of the color relationship between the anterior teeth. As the age of the patient and the morphology and thickness of both enamel and dentin of teeth differ, the color values of teeth may also differ. If the color values for anterior teeth are different, the shade of the restoration should not be selected based on the existing neighbor teeth, and clinicians should select the color for each tooth individually, especially when two or more teeth are absent. The purpose of this study was to investigate the color relationship between both the maxillary and mandibular central, and the lateral and canine teeth in vivo. By doing this, it would be possible to predict the proper color of the missing anterior tooth from the color of another existing tooth in the anterior region.
The hypothesis of the present study was that there would be differences between the color values of anterior teeth.
| Materials and Methods|| |
A total of 640 volunteer dentistry students (320 females and 320 males) with ages between 18 and 22 years (average age = 20.8) participated in this study. Written information was obtained from all participants and they signed informed consent form which was approved by the Ethical Board of the Karadeniz Technical University (no: 2015/58). The criteria of the evaluated participants are given in [Table 1]. Participants were clinically examined, and only the teeth that met the inclusion criteria were included for the study, while others were excluded from the study. A single operator performed the color measurements in the same time period (at 11:00–12:00 noon hours) and at the same dental unit.
Before the color measurements, each tooth (left maxillary and mandibular central, lateral, and canine) was cleaned using a soft polishing brush and polishing paste by one clinician. After the cleaning procedure, the teeth surfaces were wiped with clean paper for saliva and moisture, and the color values were immediately measured. Before the measurements, the colorimeter (ShadeEye NCC, Shofu, Japan) was calibrated with its own special calibration tool and positioned in the center side (middle third) of the facial surface of the teeth. The measurements were carried out according to the CIE L*a*b* system three times for each tooth, and the average was recorded.
Color differences (ΔE*) between the teeth of the same individual were calculated using the following formula: ΔE (L*a*b) = ([ΔL*]2 + [Δa*]2 + [Δb*]2)1/2
ΔL*: The difference between the L* values
Δa*: The difference between the a* values
Δb*: The difference between the b* values
ΔE* values of the evaluated teeth were multiplied by a factor of 0.92 to obtain the NBS values. NBS ratings of how a color change is evaluated by the human eye are given in [Table 2].
|Table 2: National Bureau of Standards units and their critical remarks of color differences|
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The ΔE00* values were also calculated from the CIE L*a*b* color space. Given a pair of color values in CIE L*a*b* color space, L0*, a0*, b0* and L1*, a1*, b1* and color differences were calculated with the following formula;
ΔC' and ΔH' are the differences in chroma and hue for a pair of specimens. SL, SC, and SH are the weighting functions for the lightness, chroma, and hue, respectively, and kL,kC, and kH are the parametric weighting factors for variations in experimental conditions. RT, a rotation function, is applied to account for the interaction between chroma and hue differences in the blue region., The parametric factors were set to 1. The ΔE*00 values were then compared with 50:50% PT and 50:50% AT values.
Statistical analyses were performed with two-way ANOVA and Fisher's exact test to evaluate the mean values of the L*, a*, b*, and ΔE* values of anterior teeth for both maxilla and mandible with a significance level of 5%.
| Results|| |
The data obtained from the variables L*, a*, b*, and ΔE* were analyzed to predict the color relations for both maxillary and mandibular anterior teeth. The mean values of the L*, a*, and b* values are given in [Table 3].
|Table 3: Mean values of L*, a*, and b* for anterior maxillary and mandibular teeth|
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Evaluating the L* values, significant differences were found between all the maxillary anterior teeth (P < 0.05); the mandibular central and lateral teeth, on the other hand, exhibited no significant differences (P = 0.25).
Evaluating the a* values, significant differences were found for all anterior maxillary teeth (P < 0.05). No significant difference was found between the maxillary lateral, mandibular central, and mandibular lateral (P > 0.05). There were also no significant differences between the maxillary canine and mandibular canine (P = 0.553).
Evaluating b* values, significant differences were found between all the anterior teeth (P < 0.05). The mandibular central and mandibular lateral teeth exhibited no significant difference (P = 0.63).
While the highest L* (80.5) and the least b* (15.1) values were obtained with the mandibular central, the Mean L* (73.6) and the Mean b* values (21.3) were obtained with the maxillary canine. a* value was found to be the highest for the mandibular lateral (1.1) and was found to be the least for the maxillary central (−0.2) teeth.
The color change values of the evaluated teeth and their relations are given in [Table 4]. ΔE* values were found between the 1.5 ΔE* unit (mandibular central– mandibular lateral) and the 8.1 ΔE* unit (maxillary central–maxillary canine) for the anterior teeth. Perception of color differences according to NBS is also given in [Table 5]. Only the mandibular central and the mandibular lateral teeth showed “almost the same” color in terms of human perception. According to CIEDE2000 system, all of the color differences between the evaluated teeth were above the 50:50% PT. The highest ΔE00* was found between maxillary central and mandibular canine (ΔE00* = 5.4); it was above 50:50% AT. The color difference thresholds according to ΔE00* values are given in [Table 6].
|Table 5: Perception of color differences according to National Bureau of Standards|
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| Discussion|| |
The hypothesis of the present study that there would be color value differences between anterior teeth was partially accepted. Significant color differences were found between the teeth except for the mandibular central and mandibular lateral teeth at three CIE L*a*b coordinates. Evaluating the L*, a*, and b* values of maxillary teeth, the central, lateral, and canine teeth exhibited significantly different colors. For mandibular anterior teeth, the canine exhibited significantly different color values at the L*, a*, and b* coordinates compared to the central and lateral, as the canine was darker, redder, and yellower.
In the present study, color variation values were between 1.5 and 8.1 ΔE* units. As the variations perceived by the human eye are limited to a certain degree,, the acceptability and PTs of color differences have been the subject of debate in the dental literature. Several authors have determined that the clinical PTs ranged from ΔE* = 1.0–3.7. The NBS ratings, which are quantified by ΔE* values, are commonly used to evaluate color changes according to the human eye. According to NBS, only mandibular central and mandibular lateral teeth exhibited “almost the same” color values, while the other teeth exhibited “slightly different,” “very different,” or “remarkably different” color values. Currently, the CIEDE2000 system was considered as a better indicator of human perceptibility and acceptability of color differences between tooth colors., The ΔE00* values were between 1.0 and 5.4 units for the present study. According to the Paravina et al., evaluating the present study findings, maxillary central/maxillary lateral, maxillary central/maxillary canine, maxillary lateral/maxillary canine, mandibular central/mandibular canine, and mandibular lateral/mandibular canine showed 50:50% AT; whereas, the other comparisons were 50:50% PT. Previous studies , have shown that the amount of reflected and absorbed light through the tooth depends on the thickness and translucency of the dentin and enamel. The authors have reported that the exact thickness of the enamel and dentin in all tooth types differs. Oguro et al. reported that the enamel thickness of the human anterior tooth affected the color and that it was a statistically significant predictor of tooth color change. In that study, Δb* changes were widely distributed in the range of 6.6–9.15 with a decrease in enamel thickness, whereas Δa* hardly showed any changes as the enamel thinned. These results indicate that tooth color change with a decrease in enamel thickness was most dependent on changes in b* values. Different color values obtained in the present study may be attributed to the different enamel or dentin thickness of each tooth. Mandibular central and lateral teeth are known to be the smallest human adult teeth, and possessing approximately the same enamel and dentin thickness could be the reason for the fact that their color values were found to be “almost the same.”
Color could also differ among various types of teeth, locations, and ages. In general, teeth in older people appear darker and yellower, as the enamel hydroxyapatite crystals become larger. It was demonstrated that teeth composed of large enamel hydroxyapatite crystals appeared to be darker than teeth composed of smaller crystals. Increase in the mean size of these crystals might be one of the reasons for tooth shade darkening in older individuals., Furthermore, it has already been shown that concerns about dental esthetics are increasing in priority in younger patients (<35 years of age). As the different age groups could have affected the color distributions, only individuals aged between 18 and 22 years participated in the present study. In this way, the age-dependent changes, which could affect the optical properties of teeth, were avoided.
In this study, a colorimeter was used to analyze the color values of the vital teeth. These devices have become popular because they offer accuracy, standardization, and numerical expression. As shade selection and color matching of restorations with natural dentition continue to be most confusing problems in esthetic dentistry, both instrumental and visual color matching methods should be used whenever possible so that predictable esthetic outcomes can be achieved. Several studies have evaluated the proper choice of colors using various shade-matching devices in the literature, and these were found to be successful.,,
Some authors suggested that color values were different at the cervical, middle, and incisal tooth segments., These results are important as the existing tooth segment provides the possibility to predict the color of the missing tooth segment. The authors also investigated the relationship between the thickness of dentin and enamel and the color distributions along the tooth. In one study, the relation in color of maxillary incisors and canines for each segment (cervical, middle, and incisal) was evaluated, and the researchers found a stronger relation with the cervical than with the middle and incisal segments. As the knowledge of tooth color distributions is critical in replicating pleasing anterior restorations, knowing the color relations among anterior teeth would be useful for clinicians. If the missing natural teeth are to be reproduced with dental materials, differences between ages, quadrants, sex, and locations, in terms of shade and pattern of translucency, should be taken into consideration., The present study demonstrated all anterior teeth color value relations [Table 4]. As giving a patient a natural esthetic appearance with the dental restorations is very important, it can be said that clinicians should select the color for each individual tooth related to the results present in the study.
Dental clinicians generally select only one shade for full-mouth restorations, and the technicians perform color variations. Therefore, the fabricated restoration appearances are usually associated with the dental technicians' talents and performances; however, if relation of the color values of anterior teeth would be known theoretically, the results of the present study might be useful for both dentists and technicians for giving natural esthetics to the patients. Evaluating the color difference thresholds, all the comparisons (except mandibular central/mandibular lateral) showed %50:50 AT with the neighbor teeth; while the comparisons of the same teeth with maxillary and mandibular showed %50:50 PT. Hence, it seems more sensible to select the color of a tooth from the same type of tooth from the opposite denture instead of the neighbor, if exists.
Among the other optical properties, translucency can also affect the esthetics of a restoration. In this study, this was not investigated because the measurements were made with a colorimeter under in vivo conditions. The other limitation of the study was when measuring the inclined surface of a dental structure with the colorimeter, some problems may occur due to the curved facial surfaces of the teeth. The probe tip of the instrument cannot be in direct contact with these surfaces, which cause edge-loss errors, leading to reduced L* values recorded for these types of teeth. Several previous studies reported that edge-loss appears when translucent materials such as tooth structures are measured. Another limitation of this study concerns just comparing the middle third buccal surfaces of anterior teeth. Lower and upper buccal surfaces might also be compared for all anterior teeth in further studies. Further evaluations of color and translucency in different human populations of different ages may provide more useful information and comparisons that can be made with the results of the present study.
| Conclusion|| |
Within the limitations of this study, it was concluded that both maxillary and mandibular anterior teeth exhibited different color values. Only mandibular incisors and mandibular laterals showed “almost the same” color. Canines were more dark/red/yellow for both mandible and maxilla. Maxillary centrals were more bright/green/yellow and mandibular centrals were more bright/green/blue. As the color relationships were different for each anterior tooth, clinicians should select the color one by one for each tooth carefully for the color harmony for optimal esthetics.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]