Elsevier

Dental Materials

Volume 35, Issue 6, June 2019, Pages e122-e130
Dental Materials

Masking ability of indirect restorative systems on tooth-colored resin substrates

https://doi.org/10.1016/j.dental.2019.03.001Get rights and content

Abstract

Objective

To evaluate the masking ability of different indirect restorative systems (IRS) on tooth-colored resin substrates.

Methods

A1-shaded specimens from 5 IRS (LDC–IPS e.max® CAD; YZW-Zenostar Zr Translucent; PICN-Enamic; YLD-T-IPS e.max® ZirCAD + IPS e.max Ceram; CAD-on-Zenostar Zr Translucent + Crystall./Connect + IPS e.max® CAD) were fabricated. Specimens (n = 5) were cemented with a resin luting agent (Variolink® N; shade White) on three different shades (ND3, ND8 and ND9) of a tooth-colored resin substrate (IPS Natural Die Material). Spectral reflectance and color coordinates were measured using a spectroradiometer under standardized lighting conditions (CIE D65 illumination) and optical geometry 0/45°. Color differences (ΔEab* and ΔE00) from cemented specimens and CIELAB- and CIEDE2000-based translucency parameter (TP and TP00) from non-cemented specimens were calculated. Data was statistically analyzed using one-way ANOVA and Tukey’s tests (α = 0.05). ΔE values were also analyzed using perceptibility (PT = 1.22 ΔEab* units; 0.81 ΔE00 units) and acceptability (AT = 2.66 ΔEab* units; 1.77 ΔE00 units) thresholds.

Results

The cemented specimens of CAD-on, LDC, YZW and PICN on different substrates (ND3–ND8, ND3–ND9 and ND8–ND9) showed different ΔEab* and ΔE00 values (p ≤ 0.05), which were above AT. YLD-T showed ΔEab* and ΔE00 values below AT for all comparisons. Lowest and highest TP and TP00 values were obtained for YLD-T and PICN, respectively (p ≤ 0.05).

Significance

Resin-cemented YLD-T on different tooth-colored substrates showed less translucency as well as smaller color differences (below acceptability threshold), indicating the best masking ability among evaluated systems.

Introduction

Considering dental color appearance, natural-looking restorations require adequate shade matching and blending optical properties from adjacent natural teeth [1,2]. The final appearance of esthetic indirect restorations is influenced by factors such as composition and microstructure [2,3] optical properties [4] and layering of the ceramic systems [5], surface texture and material thickness [6,7], and color and opacity of luting agents [6,7]. In addition, the tooth preparation (substrate) color is major factor influencing on final color and appearance of indirect restorations [1,8].

In clinical situations requiring restoration of non-vital discolored teeth or metal abutment structures, dentists are confronted to choose materials to mask the underlying color producing an adequate esthetic restoration. That is one of the greatest challenges in esthetic dentistry [8,9]. Additionally, the ceramic framework translucency was recognized as a key factor determining the optical characteristics of all-ceramic restorations [10].

There are many CAD–CAM ceramic systems combining strength and esthetics to cover different clinical situations. Lithium disilicate-based glass-ceramic has generated considerable interest for restorative dentistry mostly because of adequate strength (350–450 MPa) [8] and optical properties [4]. Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) is still the strongest and toughness ceramic ever used in dentistry [8,11] but its limited translucency [12] and the veneer porcelain chipping [11] are major disadvantages for veneered Y-TZP systems [13]. To avoid such problems, monolithic zirconia restorations using highly-translucent Y-TZP were introduced to dentistry as an alternative to porcelain-fused-to-zirconia restorations [[14], [15], [16]]. In addition, in 2011, a new technique was developed (CAD-on) to produce multilayered all-ceramic restorations (zirconia framework and lithium disilicate-based veneer fused together using a glass-ceramic) manufactured using the CAD–CAM technology [17,18]. A polymer-infiltrated ceramic-network (PICN) material with a dominant ceramic-network interconnected to a polymer-based matrix was introduced as an attempt to combine good material properties from polymers and ceramics [19,20].

Different parameters have been used to evaluate the masking ability of restorative materials, such as: contrast ratio (CR) [21,22] and translucency parameter (TP) [9,10,[21], [22], [23], [24], [25]]. In addition, CIELAB color space and its associated CIELAB (ΔEab*) and CIEDE2000 (ΔE00) total color difference formulas have been extensively used for color research in dentistry and, as a consequence, ΔEab* [7,9,10,24,[26], [27], [28], [29]] or ΔE00 [23,25] have been also used to evaluate the masking ability of restorative materials cemented on colored substrates. Yet, the International Organization for Standardization (ISO/TR 28642:2016) [30] states that color differences should be assessed on the basis of 50:50% acceptability (AT: ΔEab* = 2.66 and ΔE00 = 1.77) and 50:50% perceptibility (PT: ΔEab* = 1.22 and ΔE00 = 0.81) thresholds [31]. Thus, if the color difference between two specimens is at or below PT, it represents an excellent match; if the difference is between PT and AT, it represents an acceptable match; and if the difference is above AT, it represents an unacceptable match.

As the masking ability of indirect restorative systems (IRS) is critical for acceptable esthetic restorations on discolored substrates, the objective of this study was to evaluate the masking ability of IRS on different tooth-colored resin substrates using CIELAB (ΔEab*) and CIEDE2000 (ΔE00) metrics for color differences and the translucency parameters (CIELAB-based TP and CIEDE2000-based TP00) for measuring the translucency of non-cemented IRS specimens. The hypotheses tested were that (1) color differences from same IRS cemented on different color of substrate are not acceptable (above AT), and (2) translucency varies with structural characteristics.

Section snippets

Material and methods

This in-vitro study used five indirect restorative systems (Table 1) being three monolithic structures (LDC, YZW and PICN), one bilayer structure (YLD-T) and one trilayer structure (CAD-on).

Results

CIELAB color coordinates of IRS are shown in Fig. 1. Fig. 2(a and b) show mean and standard deviation values of translucency parameter (TP and TP00) for different indirect restorative systems. The behavior of all systems was similar for both translucency parameters. PICN and YLD-T showed, respectively, the greatest and the lowest TP values (p ≤ 0.05). In addition, LDC and CAD-on showed similar TP values (p > 0.05) (Fig. 2(a and b)).

Table 2 shows mean and standard deviation values of color

Discussion

The present study was designed to evaluate the masking ability of indirect restorative systems manufactured by CAD–CAM technology, except for the veneer layer of YLD-T structure. Therefore, monolithic (LDC — lithium disilicate-based glass-ceramics, YZW — zirconia, and PICN — polymer-infiltrated ceramic-network), bilayer (YLD-T — zirconia framework veneered with feldspathic ceramic) and trilayer (CAD-on — zirconia framework and lithium disilicate-based veneer fused with a glass-ceramic)

Conclusions

Within the above mentioned limitations of the present in-vitro study, it can be stated that resin-cemented YLD-T on different tooth-colored substrates showed less translucency and color differences below acceptability threshold, indicating the best masking ability among the evaluated systems.

Acknowledgments

This work was partially supported by CNPq do Brasil [grant #302587/2017-9]; CAPES do Brasil [grants PNPD 42009014007P4 and PROSUC 88887.147565/2017-00]; “Junta de Andalucía” (Spain) [grant number JA TEP-1136] and Spanish Ministry of Economy and Competitiveness and European Regional Development Fund (ERDF) [grant number MAT2013-43946R]. The authors thank Dr. Dileta Cecchetti for the support in the statistical analysis and the dental laboratory “Coral”.

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