Try-in Pastes Versus Resin Cements: A Color Comparison

Edenize Cristina Vaz, DDS; Maysa Magalhães Vaz, DDS; Maria Beatriz Rodrigues Gonçalves de Oliveira, DDS; Alfa Emília Takano, DDS; Paula de Carvalho Cardoso, DDS, MS, PhD; Érica Miranda de Torres, DDS, MS, PhD; and Lawrence Gonzaga Lopes, DDS, MS, PhD

As a result of innovation and development in restorative materials, ceramic veneers are currently preferred over other types of restorations because they require only minimally invasive tooth preparation.¹ Additionally, the properties of ceramic veneers, such as color stability, mechanical strength, compatibility with periodontal tissues, clinical longevity, and enamel-like appearance, make them a good choice for esthetic treatments.² However, clinical color reproduction still poses a challenge due to color interaction with the underlying substrate, whether it is tooth structure or an esthetic restorative material.³

Ceramic veneers generally have a thickness from 0.3 mm to 0.7 mm⁴; however, literature data are not conclusive about the influence of this parameter on the final color of ceramic restorations.^3,5 Therefore, a question has been raised: Would different shades of resin cement under various thicknesses of different ceramic veneer materials cause perceptible color differences in ceramic restorations?⁵

Current adhesive systems and resin cements allow effective interaction between ceramic veneer and tooth structure.^6,7 These materials come in several colors, which vary in hue, chroma, and value.⁷ Resin cements exhibit favorable fracture load, good longevity, and satisfactory clinical performance.⁸ The resin cements specifically used for luting ceramic veneers are activated by visible light. These cements present color stability and longer working time compared with chemically cured and dual-cured materials.²

For clinical evaluation, the ceramic material is placed over the substrate prior to cementation; this can be carried out with water, glycerin gel, or try-in pastes.⁹ The try-in pastes, which accompany resin cements, allow dentists to predict the final esthetic result.⁸ Nevertheless, the color agreement between the try-in paste and the resin cement under ceramic restorations is critical, especially when using extremely thin and translucent ceramic materials.^8,10,11

The color selection process is complex due to the different characteristics of the color components, lighting type (natural or artificial), subjectivity of the viewer’s perception and experience, scales, dental shape, gloss, surface texture, translucency, gingival color, adjacent teeth, and tooth position in the arch.^6,12 To reduce this problem, a spectrophotometer can be used for color evaluation. This device makes color measurements based on three coordinates, namely L*, a*, and b* (CIE L*a*b* system), allowing the degree of perceptible color to be evaluated using numerical values.^8,13,14

Objective

The objective of this investigation was to compare the final color of ceramic veneer restorations using different shades of either try-in pastes or resin cements. The null hypothesis was that the ceramic colors obtained with the try-in materials and resin cements tested would present no differences.

Method
Teeth and Discs Preparation

In this in vitro study, 40 bovine teeth were used. The teeth were stored in 0.05% thymol solution. Prior to use, they were kept in deionized water for 24 hours to remove thymol. Crowns were utilized, and the enamel surface was ground flat with wet 180-grit silicon carbide abrasive paper, model 3M-211Q (3M, Brazil, www.3m.com.br), on a polishing machine, model DP-10 (Panambra Struers, Brazil, www.struers.com) (Figure 1).

For discs preparation, 40 ETC0 IPS Empress® Esthetic (Ivoclar Vivadent, Brazil, www.ivoclarvivadent.com) ingots were injected to obtain a ceramic block. The blocks were cut using a low-speed saw (IsoMet® 1000, Buehler, www.buehler.com) at 250 rpm to obtain 1-mm thick discs, which were manually polished with wet 800-grit (medium) and 1200-grit (thin) silicon-carbide abrasive paper (3M, Brazil) to a final thickness of 0.6 mm, measured using a Mitutoyo Absolute 500-196-20 digital electronic caliper (Mitutoyo, Brazil, www.mitutoyo.com.br) (Figure 2).

Try-In Application

After preparation, the ceramic discs were placed on the dental substrates using the try-in materials. A pilot study was conducted prior to the present work to standardize the application of the try-in materials.

Samples were distributed in four groups according to the try-in materials used, as follows: group I, water-soluble gel (K-Y® Jelly, Johnson & Johnson, Brazil, www.jnjbrasil.com.br); groups II, III, and IV, try-in paste (Variolink® Veneer Try-in, Ivoclar Vivadent), values 0, -3 (low value), and +3 (high value), respectively (Figure 3). The thickness of the materials was standardized using a special appliance developed in the pilot study for the present work. To standardize the film thickness and ensure that the restoration was fully seated, a pressure of 1 kg was exerted over the ceramic veneer (Figure 4). Although the film thickness was not measured directly, it was assumed to be relatively homogeneous due to the uniform loading conditions.

Cementation

The distribution in groups according to the colors of the resin cement used is described in Figure 3. In groups I and II, Variolink Veneer value 0 was used. In groups III and IV, Variolink Veneer values -3 and +3 were applied, respectively.

The teeth and veneers were cleaned and dried before cementation. Tooth surfaces were etched using 37% phosphoric acid (Total Etch, Ivoclar Vivadent) for 30 seconds, cleaned for 30 seconds, and dried. The bond system (Excite® F, Ivoclar Vivadent) was applied for 10 seconds. The resin cement was cured using a Radii Plus cordless LED curing light (SDI Limited, www.sdi.com.au) for 60 seconds according to the manufacturer’s instructions. The standardization of the resin cement thickness (set tooth–resin cement–ceramic disc) was performed employing the same appliance used for the try-in materials (set tooth–try-in material–ceramic disc).

Color Measurements

Color measurements of the specimens were performed using an Easyshade® spectrophotometer (VITA Zahnfabrik, www.vita-zahnfabrik.com). Data were expressed using the CIE L*a*b* system parameters: L* indicates the lightness; a* and b* indicate the hue (a* = red-green axis, b* = blue-yellow axis).¹⁴

Three measurements were performed for each of these coordinates at three different moments, and the mean of each coordinate was considered for statistics: straight in the tooth substrate (L₀*, a₀*, and b₀*); with the ceramic veneer in position over the substrate for the trial, using try-in pastes (L₁*, a₁*, and b₁*); and after cementation (L₂*, a₂*, and b₂*).

Color change (ΔE*) is commonly used to represent the difference in color between two measurements. This parameter can be calculated using the formula:
ΔE* = [(ΔL*)2 + (Δa*)2 + (Δb*)²]^0.5
where: ΔL* is the variation of L*, Δa* is the variation of a*, and Δb* is the variation of b*.

For this study, three values of ΔE* were calculated:
1. ΔE₁* (in the trial): using L₁*, a₁*, and b₁*, to trial; and L₀*, a₀*, and b₀*, to substrate
2. ΔE₂* (after cementation): using L₂*, a₂*, and b₂*, to after cementation; and L₀*, a₀*, and b₀*, to substrate
3. ΔE₃* (difference between trial and after cementation): using L₂*, a₂* and b₂*, to after cementation; and L₁*, a₁*, and b₁*, to trial

Statistical Analysis

The statistical analysis was performed using IBM SPSS Statistics for Windows Version 21.0 (IBM Corp., www.ibm.com) and a significance level of 0.05. Shapiro-Wilk test was used to evaluate the normality of data distribution. Kruskall-Wallis test (P < .05) was used to make comparisons of ΔE₁* and ΔE₂* among groups. Wilcoxon test (P < .05) was applied to compare the values of ΔE₁* and ΔE₂* for all the groups. To evaluate the variance of the color among groups in the trial and after cementation (ΔE₃*), one-way ANOVA (P < .05) was employed.

Results

The median and percentiles of the values obtained for ΔE₁* in the groups tested are presented in Figure 5. No statistical differences were observed among ΔE* found for all the groups tested (P = .701).

Similarly, the median and percentiles of the values obtained for ΔE₂* in the groups tested are presented in Figure 6. No statistical differences were observed among ΔE* found for all the groups tested (P = .704). When comparing the values of ΔE* obtained for each group in pairs (ΔE₁* and ΔE₂*), no statistically significant differences were found (P = .646, P = .169, P = .508, and P = .05, respectively, for groups I, II, III, and IV).

The means and standard deviation for ΔE₃* are shown in Figure 7. No statistically significant differences were observed among groups (P = .312).

Figure 8 shows the values of ΔE₃* obtained for each specimen and allows the visualization of their relationship with the values indicated by the horizontal lines, which express the cutoff points for the color variation imperceptible to the human eye accepted by different authors (ΔE = 2.0, ΔE = 3.3, and ΔE = 5.5).^8,10 Considering that 3.3 is the most accepted value of ΔE in the literature for visible color changes, 45% of the specimens tested showed color variance higher than this value (ΔE* > 3.3).^2,8,9,15

Discussion

The final shade of the veneer depends not only on the color, opacity, and thickness of the ceramic, but also on the color of the underlying tooth and the color and thickness of the resin cement.^5,16 The type of illuminant and substrate, as well as the thickness of the material, should always be considered, because they all influence the final color of ceramic restorations.¹⁷

The results of the present study revealed that the colors obtained with the ceramic in position were similar for all try-in materials (P = .701) and resin cements (P = .704) tested (Figure 5 and Figure 6, respectively). Therefore, using 0.6-mm-thick ceramic veneers, no differences in the final color were observed for any shades of try-in material or resin cement assessed. Two possible reasons for this are: (1) the cement and try-in paste layer thickness employed; (2) the thickness of the ceramic discs (0.6 mm) used. However, new studies are necessary to investigate the magnitude of color alterations with different thicknesses of ceramic veneers, as well as with different resin cements and try-in materials.

Comparing the groups in pairs (trial × cementation), no statistically significant differences were found for the optical behavior at these two moments (P = .646, P = .169, P = .508, and P = .05 for groups I, II, III, and IV, respectively). These results indicated similarity between colors generated by use of different resin cements’ shades and correspondent try-in pastes’ shades. Similarly, Xing et al¹⁰ reported that the color of resin cements and their corresponding try-in pastes had high agreement.

Analyzing the values found for ΔE₃* (Figure 7), no statistically significant differences in color change were observed between the try-in materials and the corresponding shades of cured resin cements among groups (P = .312). These results disagree with those reported by Alghazali et al,⁸ who found statistically significant difference between the color achieved using the try-in paste and the same shade of cured resin cement. Further studies involving different brands of resin cements and ceramic veneers are indicated.

The cutoff to visible color change should be considered when using ΔE* to evaluate this parameter. Xing et al¹⁰ affirmed that ΔE* values higher than 2.0 may be considered as perceptible color change, whereas Chang et al¹⁸ considered this value as the gold standard. Ruyter et al¹⁵ found that 3.3 units of color difference have been considered unacceptable by 50% of observers. However, more recently, another in vivo study has presented the clinically acceptable threshold to be ΔE* 5.5 units.¹⁹ Nevertheless, the most widely accepted value for ΔE* in the literature is 3.3 units for visible color change.^{2,8,9,15,16,20}

Considering that in the present study the results found for ΔE₃* represent the color change, in numeric values, between the results obtained for the trial and after cementation, and acknowledging each cutoff point, the following situation has resulted: 70% of specimens presented ΔE₃* values higher than 2.0; 45% presented ΔE₃* values higher than 3.3; and 5% presented ΔE₃* values higher than 5.5 (Figure 8). Although no statistically significant differences were observed between the results found for the trial and after cementation for any of the groups, a difference in color may be noticeable to the human eye. This aspect should be considered in decision making during routine clinical practice.

Conclusions and Clinical Implications

No differences were found in the shades of the ceramic veneers used when tested with water-soluble gel or try-in pastes values 0, -3, and +3. Also, the different resin cements (values 0, -3, and +3) produced similar effects on the color of ceramic restorations.

No statistically significant differences were found in the values of color change among three shades of try-in paste placed underneath the ceramic discs. Considering the parameters for color change perceptible to the human eye, 45% of the ceramic restorations presented visible changes (ΔE > 3.3).

This study has important clinical implications. It shows indifference to using different shades of try-in or resin cement materials, in numeric values. However, it calls attention to the color concordance between try-in materials and resin cements, in regard to color perception by the human eye.

About the Authors

Edenize Cristina Vaz, DDS
Master Student
Department of Prevention and Oral Rehabilitation
School of Dentistry
Federal University of Goiás
Goiânia, Brazil

Maysa Magalhães Vaz, DDS
Master Student
Department of Prevention and Oral Rehabilitation
School of Dentistry
Federal University of Goiás
Goiânia, Brazil

Maria Beatriz Rodrigues Gonçalves de Oliveira, DDS
Professor
Department of Operative Dentistry
Training School Dentists
Goiânia, Brazil

Alfa Emília Takano, DDS
Professor
Department of Operative Dentistry
Training School Dentists
Goiânia, Brazil

Paula de Carvalho Cardoso, DDS, MS, PhD
Professor
Department of Operative Dentistry
Brazilian Association of Dentistry-Goiás
Goiânia, Brazil

Érica Miranda de Torres, DDS, MS, PhD
Professor
Department of Prevention and Oral Rehabilitation
School of Dentistry
Federal University of Goiás
Goiânia, Brazil

Lawrence Gonzaga Lopes, DDS, MS, PhD
Professor
Department of Prevention and Oral Rehabilitation
School of Dentistry
Federal University of Goiás
Goiânia, Brazil

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