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Year : 2020  |  Volume : 23  |  Issue : 4  |  Page : 523-533

How are the color parameters of a CAD/CAM feldspathic ceramic of the material affected by its thickness, shade, and color of the substructure?

Department of Prosthodontics, Faculty of Dentistry, Gazi University, Ankara, Turkey

Date of Submission24-Sep-2019
Date of Acceptance07-Dec-2019
Date of Web Publication4-Apr-2020

Correspondence Address:
Dr. E Tamam
Department of Prosthodontics, Faculty of Dentistry, Gazi University, Ankara
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/njcp.njcp_517_19

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Objectives: The purpose of this study was to evaluate the effect of the tooth color, ceramic color, and ceramic thickness on the final color parameters of a feldspathic computer-aided design (CAD)/computer-aided manufacturing (CAM) ceramic material. Materials and Methods: Resin specimens (12 × 14 × 4 mm) were prepared from six shades, namely, 0M1S, 1M1S, 2M3S, 3M2S, 4M3S, and 5M3S, to simulate tooth color. Ceramic slices with thicknesses of 0.3, 0.5, 0.7, and 1 mm were sectioned from Vitablocs Mark II (12 × 14 × 18 mm) in 10 shades—OM1C, 1M1C, 1M2C, 2M1C, 2M2C, 2M3C, 3M1C, 3M2C, 3M3C, and 4M2C. An intraoral spectrophotometer was used and three axes of Commission Internationale de l'Eclairage (CIE) LAB color space (CIE L* a* b*) and chroma (C) and hue (H) values were obtained. Results: The a* and b* values showed a decrease with increasing thickness. Generally, C decreased with the increasing ceramic thickness. The effect of ceramic thickness on H changed depending on the block and substructure color. The change of ceramic thickness resulted in changes in the lightness parameter (L*) of the ceramics. Generally, with an increase in the thickness, the L* value increased. The univariate analysis of variance (ANOVA) indicated a significant interaction between ceramic thickness and substructure color (P <. 005) and ceramic thickness and ceramic color (P <. 005). Conclusion: The final color parameters of a feldspathic CAD/CAM block were significantly affected by the changes in the ceramic thickness and substructure color.

Keywords: Ceramic shade, ceramic thickness, color parameters, feldspathic ceramic, substructure color

How to cite this article:
Tamam E, Güngör M B, Nemli S K. How are the color parameters of a CAD/CAM feldspathic ceramic of the material affected by its thickness, shade, and color of the substructure?. Niger J Clin Pract 2020;23:523-33

How to cite this URL:
Tamam E, Güngör M B, Nemli S K. How are the color parameters of a CAD/CAM feldspathic ceramic of the material affected by its thickness, shade, and color of the substructure?. Niger J Clin Pract [serial online] 2020 [cited 2022 Oct 3];23:523-33. Available from:

   Introductıon Top

Since the introduction of laminate veneers in 1983, they are considered one of the most feasible treatment alternatives because of their biocompatibility, aesthetics, longevity, and their quality of requiring little or no tooth preparation.[1] Over a period, the fabrication techniques of laminate veneers have improved into the computer-assisted design and computer-assisted milling technology (CAD/CAM). In the beginning, the ceramic veneers were fabricated using the layering technique, and it is still used with its highly aesthetic results.[2],[3] Some drawbacks of this technique are refractory die materials used to support the condensed layers of the ceramic slurry, which is difficult to remove from the veneer after firing and a labor-intensive process.[4] Subsequently, pressable ceramics were introduced.[5] Precise production of full-contour restorations and fabricating restorations with minimal flaws are the main benefits of this technique.[2],[3] However, pressed restorations are usually monochromatic and often require superficial surface staining to achieve a more aesthetic appearance.[2] Nowadays, CAD/CAM is increasingly used to design and fabricate porcelain laminate veneers in both the dental office and laboratory.[6] Thereby, more time-efficient, predictable, and accurate restorations may be produced compared with previous methods. In addition, it has been found that the mechanical properties of CAD/CAM materials are excellent because of the advantages of industrially fabricated homogenous blocks.[7],[8] However, the color parameters of the ceramic veneers produced by milling are limited by the color of the preferred block.[7],[9]

The aesthetics of veneers are among the significant factors affecting the success of such restorations, while color is the most important determinant of aesthetics.[10] Reproducing the final intended or selected tooth color with ceramic laminate veneers is a difficult process, as the optical behavior of a ceramic restoration is determined by the integration of several critical factors, including the translucency of the restorative material, thickness and shade of the ceramic veneer, underlying color of the tooth structure, and shade of the luting cement.[11] Many different materials have been used for ceramic veneers (e.g., feldspathic, leucite, and lithium disilicates).[12] For many years, conventional feldspathic porcelains have been considered the best material to provide optimal aesthetic results for porcelain veneers.[13] In recent years, advances in dental ceramics have introduced higher-strength porcelains, but these materials tend to have reduced translucency.[14] Therefore feldspathic porcelain is still the premier aesthetic material for veneers, which closely mimics the patient's natural dentition.[2] However, the high translucency of feldspathic porcelain can have a negative effect on the resulting color of the restoration.[10]

Underlying tooth structure or restorative substructure material is the primary source of the definitive color of porcelain laminate veneers.[6],[15],[16],[17],[18],[19] If a ceramic restoration is placed on a dark substructure, such as an endodontically treated tooth, discoloration and shadowing of the restoration may be jeopardized.[20] To eliminate this undesirable effect, factors like the thickness of the final veneer restoration and shade and translucency of the ceramic should be considered, as well as the color of the luting cement.[20],[21] The thickness of the laminate veneer restorations is closely related to tooth preparation. Over the years, tooth preparation to receive porcelain veneers has changed. Early concepts suggested minimal or no tooth preparation.[22] Later, the preparation depth within the enamel was recommended to be in the range of 0.4–0.7 mm.[23] Currently, the typical thickness of veneers without tooth preparation is stated to be 0.3 mm—a minimally invasive solution for certain aesthetic situations.[24]

In dentistry, color matching has traditionally been performed by using shade guides. In this method, a visual color determination is performed by comparing the patient's tooth with a shade guide.[25] The dimensions required for identifying a shade are its value (lightness), chroma (C; color saturation), and hue (H).[26],[27] On the other hand, the color of the material is often expressed in Commission Internationale de l'Eclairage (CIE) L*a*b coordinates.[28] The L* (lightness) color coordinate ranges from 0 to 100 and characterizes lightness; the a* color coordinate ranges from 90 to 70 and characterizes greenness on the positive axis and redness on the negative one; and the b* color coordinate ranges from 80 to 100 and characterizes yellowness (positive b*) and blueness (negative b*).[28],[29] All parameters required for color analysis can be obtained from spectrophotometers.

The purpose of this study was to evaluate the cumulative effect of the tooth abutment color, ceramic color, and ceramic thickness on the final color parameters of a feldspathic ceramic material produced by the CAD/CAM technology. The null hypothesis was that the color parameters of a CAD/CAM ceramic material would not be affected relative to the tooth abutment color, ceramic color, and ceramic thickness.

   Materıals and Methods Top

Color of substructure (an underlying tooth or restorative material), ceramic thickness, and ceramic shade were the three variables tested in the study. To simulate the shade of the prepared tooth, resin composite specimens (Vita Simulate; Vident) were prepared from six shades—0M1S, 1M1S, 2M3S, 3M2S, 4M3S, and 5M3S—and abbreviated as—S0, S1, S2, S3, S4, and S5. For the fabrication of the resin composite substructures, a pink baseplate wax (Kerr Manufacturing Co) was prepared (12 × 14 × 4 mm); the dimensions were adjusted according to the dimension of the ceramic specimens. Light-cured urethane dimethacrylate (TRIAD Colorless, Visible Light Cure Material; Dentsply International Inc) was used to fabricate a mold. The materials for the substructures were injected into the mold and cured in a halogen spectral range between 400 and 500 nm (TRIADTM 2000; Dentsply International Inc).[29]

Ceramic slices in thicknesses of 0.3, 0.5, 0.7, and 1 mm were sectioned from Vitablocks Mark II (12 x 14 x 18 mm) (Vitablocks Mark II; Vident) for CEREC CAD/CAM (Sirona Dental) using a low speed diamond disk (Isomet 1000; Buehler) which used a diamond disk 75 mm in diameter and 0.2 mm in thickness (Series 15LC Diamond; Buehler). To avoid the fatigue and overuse of the sawing blades, a new blade was used for every five sections. Each sectioned slice was further measured at four points using an electronic digital micrometer (Powertectools), and the standard deviation (SD) for the four tested thicknesses was 0.03 mm. The ceramic slices were fabricated from 10 shades of Vitablocs Mark II, namely, OM1C, 1M1C, 1M2C, 2M1C, 2M2C, 2M3C, 3M1C, 3M2C, 3M3C, and 4M2C [Figure 1]. The block shades indicate lightness, H, and C dimensions for blocks as described in the Vitapan 3D-Master system.[27] Accordingly, the lightness of the blocks decreases from 0 to 4, all blocks are composed of the same H (M), and C increases from 1 to 3.
Figure 1: Color of the Vitablocs tested in the study

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The outer surfaces of the sectioned blocks were polished mechanically using a ceramic surface polishing kit (Easy Polishing System; Vident). After polishing, the dimensions were confirmed by measurement with a digital micrometer. All specimens were ultrasonically (Euronda; Erosonic Energy) cleaned in distilled water for 10 min to remove debris. Then, the polished surfaces of the specimens were glazed (VITA Akzent glaze; Vident) according to the manufacturer's instructions. Two hundred and forty groups (n = 10) were derived as shown in [Table 1].
Table 1: Mean L*, a*, and b* values and SD of ceramic specimens when measured on different colored substructures

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An intraoral dental spectrophotometer (VITA Easyshade Advanced 4.0; Vident), which has a large terminal detecting head with a diameter of 6 mm, was used to measure the color of the ceramic slices on different substructures. Color measurements were performed under standardized lighting conditions (CIE D65 illumination). Each specimen, along with the tested substructure, was placed on a white plate. As the specimens were combined, a droplet of distilled water was positioned between each one (refraction index close to 1.7).[29] This addition of the distilled water was performed to enhance the optical contact during the color measurement, which served to minimize the loss of light through the margins of the specimens (known as edge loss).[29] In addition, before each measurement, the spectrophotometer was recalibrated with the calibration plate. An average of three measurements per specimen on each background was recorded. Three axes of CIELAB color space (L*, a*, b*) and C and H values were obtained.

Descriptive statistical analysis was performed for the CIE L*a* b*, C, and H values, including the mean, SD, and 95% confidence limits by using the Statistical Package for the Social Sciences (SPSS) software, version 18 (SPSS Inc). Univariate analysis of variance (ANOVA) was used to determine the differences by means of each color parameter for the ceramic shades, ceramic thickness, and composite substructures. The level of significance was set at α = 0.05. Dunnett T3 post hoc test was used whenever a statistically significant interaction was found.

   Results Top

The means and SDs of the L*a*b* values in each of the combinations of the test groups are presented in [Table 1]. The change of ceramic thickness resulted in changes in the lightness parameter (L*) of ceramics. The L* value increased with increasing thickness for color 1M1C; this is true when the colors 1M2C and 2M1C are placed on 2 dark substructures (S3 and S4), and for 2M2C and 2M3C colors are placed on the darkest substructure (S5). Apart from these, a 0.3 mm ceramic thickness revealed a higher L* value than 0.5 mm thickness. The highest L* value for 0M1C was 1 mm thick, followed by a thickness of 0.7 mm to 0.3 mm. The same order applies to 3M3C colored ceramics. The same result was achieved when the 1M2C and 2M1C ceramics were placed on the S1 and S4 infrastructures and the 2M2C and 2M3C ceramics were placed on the S1 and S4 infrastructures. The lightness of 4M2C-colored ceramic generally showed the highest value in the thickness of 0.7 mm. The a* and b* values showed a decrease with increasing thickness [Table 1].

The substructure color affected the color parameters of feldspathic ceramics differently, depending on the ceramic thickness. The highest L* value was found when ceramics were placed on the S1 (1M1S) substructure for all-ceramic thicknesses, regardless of the ceramic color. For all ceramic colors, the L* values of 0.3, 0.7, and 1 mm ceramics revealed a decrease from S1 to S5 substructures. For 0.5 mm ceramics, L* value showed a similar change in 0M1C and 1M1C ceramic colors, while in other ceramic colors, the lowest L* value was observed when they were placed on an S4 (4M3S) substructure. For all ceramic colors, a* value increased from S0 to S4 substructures while b* value revealed different measurements when they were placed on each of the six substrates.

The means and SDs of the C and H values in each combination of test groups are presented in [Table 2]. Generally, C decreased with the increasing ceramic thickness for OM1C, 1M1C, 1M2C, and 2M1C-colored ceramics. It should be noted that this decrease is more prominent when they placed on S0 and S1-colored substructures. On the other hand, the effect of thickness on the C values of 2M2C, 2M3C, and 4M2C ceramics was differed according to the substructure color [Table 2]. The C value of 3M1C ceramic generally decreased when the thickness increased, while a notable change was observed in 3M2C and 3M3C ceramics with increasing thickness. The effect of ceramic thickness on the H value was changed depending on the block and substructure color [Table 2]. For OM1C, H decreased with increasing thickness. For 1M1C and 1M2C ceramic color, H value did not change with the thickness when they placed S0-S3 substructures, but it increased when they placed S4 and S5 substructures. Other ceramics (2M1C, 2M2C, 2M3C, 3M1C, and 4M2C) showed increased H value with the increasing thickness. However, this increase was more notable when they were placed on S4 and S5 substructures.
Table 2: Mean C and H values and SD of ceramic specimens when measured on different colored substructures

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For 0.3, 0.5, 0.7, and 1 mm ceramic thickness, the highest C values were obtained from ceramics placed on S2 and S5 substructures. On the other hand, the H value decreased from S0 to S4 substructures [Table 2].

The ANOVA indicated a significant interaction between ceramic thickness and substructure color (P<. 005) and ceramic thickness and ceramic color (P <. 005), as shown in [Table 3].
Table 3: ANOVA interactions between variables

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   Dıscussıon Top

This in vitro study measured the color parameters of feldspathic ceramic specimens of different thicknesses on different colored substructures. The null hypotheses were rejected as there was a significant interaction between ceramic thickness and substructure color and ceramic thickness and ceramic color with regard to L* (lightness or value), a*, b*, C, and H parameters. The findings of the study are in agreement with previous reports in the literature.[10],[20],[30],[31],[32],[33],[34] However, it should be taken into consideration that color parameters were evaluated in this study, while the change in color (ΔE) was the evaluation criteria of most studies in the literature.[10],[20],[30],[31],[32],[33] Therefore, the findings of this study cannot be directly compared with previous research. Evaluating color parameters of ceramics when they are set in different thicknesses and placed on various substructures was the primary aim of this research. With this purpose, C and H dimensions of the color, required for the identification, comparison, and selection of shades, were determined in addition to CIE L*a*b* values.[26],[34] Instead of calculating color differences, the final values of measured color parameters (L*, a*, b*, C, and H) were presented for all combinations, including ceramic thickness, ceramic color, or substructure color. According to the authors, resulting color parameters of 240 combinations [Table 1] and [Table 2] may represent as a guide for clinicians. These resulting parameters may help clinicians choose translucency and shade of the ceramic block by considering the thickness of the ceramic material and underlying tooth color. However, it should not be forgotten that the color and thickness of the selected luting cement might alter the results. In this study, the variables of thickness and color of cement were not taken into consideration.

Assessing and optimally matching the color of dental ceramics for aesthetic restorations is a significant challenge in practice.[34],[35],[36] Achieving the final intended color is determined by multiple factors. Besides the inherent features of the ceramic system used, the thickness of the ceramic layers, underlying tooth substrate color, and resin luting agent are important factors affecting the final restoration color.[15],[16],[17],[18],[19] All ceramic materials have various compositions with different crystalline contents, such as lithium disilicate, fluorapatite, or leucite, which may affect the optical properties of these materials. An increase in the crystalline content to achieve greater strength generally results in reduced translucency.[37] While ceramics that are more translucent allow more light to enter and scatter, they provide natural-looking all-ceramic restorations. However, the reduced masking ability of these restorations and significant influence of underlying tooth or core build-up material should be taken into careful consideration. Various commercially available ceramic systems were evaluated with respect to optical properties and clinical factors affecting the final color of a restoration.[7],[16] Feldspathic porcelains have been reported to be the most translucent among all the ceramic materials.[2],[16],[38] However, the literature search revealed only a few studies that have addressed the optical properties of machinable feldspathic ceramics.[10],[11],[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23],[24],[25],[26],[27],[28],[29],[30],[31],[32],[33],[34],[35],[36],[37],[38] In the present study, color parameters of a machinable feldspathic ceramic, including 10 different block shades were assessed when they were cut in different thicknesses and placed on different substructures.

There is consensus in the literature regarding the fact that ceramic thickness and the color of the substrate affect the value, C, and H of a ceramic restoration.[6],[10],[20],[33] In general, the thickness of a typical porcelain veneer is in the range of 0.5–0.7 mm and gradually may increase to 2 mm near the incisal edge.[23] The thickness of no-preparation veneers is typically stated to be 0.3 mm.[24] Evaluating color parameters by thickness revealed that lightness increased with increasing ceramic thickness, regardless of the ceramic shade, which is in line with a previous report.[38] This can be attributed to the fact that increasing L* indicates changing the color from black to white, which also means decreasing translucency. Depending on this finding, we may conclude that the lightness or value of restoration increases with the thickness of a restoration, regardless of the color of the material. H is the last determined color parameter, following the determination of the value and C, when matching a tooth shade to the shade tabs. In the literature, the difference in H angle between the three shades has been considered small.[39] In the present study, H value differences can be considered as small between different thicknesses of each ceramic block that measured on each of the substructures. However, great H differences were observed when a ceramic specimen was measured on different substructures. This finding may be interpreted as substructure color is an important factor affecting the H value of a ceramic restoration.

The supporting tooth structure or aesthetic restorative foundation has been stated as the primary source for restoration color.[15-19,34] Particularly, when the ceramic thickness is less than 1.0 mm, substrate color differences were readily detectable by the human eye.[15],[40] This study confirmed findings of previous studies that changing the underlying color of the abutment tooth influenced the final color parameters of the ceramic restoration.[6],[20],[34] The lower lightness of ceramics when they were placed on dark substructures compared with light substructures indicates the effectiveness of the underlying color used in the present study. Furthermore, for all the ceramic thicknesses, the highest C values were obtained from ceramics placed on S2 and S5 substructures. This finding indicates that substructures with the highest C have the most prominent effect on ceramic color. Therefore, knowing the shade of the preparation is imperative to achieve an intended color. To evaluate the effect of supporting tooth color on the final color of the restoration, fabricating a tooth-colored die is recommended. Thereby, achieving an optimum match of the restoration shade to the given clinical situation may be ensured and aesthetic expectations can be met, especially when thin translucent veneers are used and/or tooth discolorations are masked. In the present study, six different colors of a tooth-colored composite resin die material, which can simulate a wide range of clinical situation, was used to support ceramic specimens with different thickness and color. For reliable clinical comparisons with previous investigations[21],[41] and standardization purposes, the thickness of the composite resin specimens was to be 4.0 mm.

In the present study, all commercially available shades of a CAD/CAM feldspathic ceramic block were prepared in four different thicknesses. Furthermore, six different colors of a tooth-colored composite resin die material, which can simulate a wide range of clinical situations, were used to support ceramic specimens with different thicknesses and colors. However, there were limitations in this study, including the in vitro use of only one color measuring device to evaluate color parameters. In addition, the roughness and glossiness can also affect the color measurement of an object. Further studies are necessary to investigate the effects of variables, such as cement shade, color measuring device variations, and roughness and glossiness of ceramic surface, on the color parameters of ceramics. In addition, composite substructures were used to stimulate the different colors of abutment tooth; however, the optical properties of a natural tooth may be different from those of the composites. As the optical properties are related to several factors besides the shade, it was difficult to standardize the tooth's optical properties; such properties can differ among natural teeth, even if they are the same shade. Another limitation of the study includes that the batch differences between the ceramic blocks were not considered in specimen preparation. On the other hand, as the color of cement used for cementation of the ceramic veneers affects the final color of the restoration, further studies should be performed to address the effect of resin cement on the definitive color parameters of feldspathic ceramics.

   Conclusıon Top

Within the limitations of the present study, the following conclusions can be drawn:

  1. The change of ceramic thickness resulted in differences in the lightness parameter (L*) of ceramics depending on the ceramic shade. The a* and b* values showed a decrease with increasing thickness.
  2. Increasing ceramic thickness generally led to a decrease in C value. The effect of ceramic thickness on the H value changed depending on block and substructure color.
  3. The substructure color affected the color parameters of feldspathic ceramics, depending on ceramic thickness. For all ceramic thicknesses, regardless of ceramic color, the highest L* value was found when ceramics were placed on S1 (1M1S) substructure, a* value increased from light to dark substructures, while b* value revealed different measurement when they placed on each of six substrates.
  4. For all ceramic thicknesses, the highest C values were obtained from ceramics placed on S2 (2M3S) and S5 (5M3S) substructures, which have a higher C. The H value decreased from light to dark substructures.

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  [Figure 1]

  [Table 1], [Table 2], [Table 3]


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