Elsevier

Dental Materials

Volume 32, Issue 5, May 2016, Pages e105-e112
Dental Materials

Relevant optical properties for direct restorative materials

https://doi.org/10.1016/j.dental.2016.02.008Get rights and content

Abstract

Objectives

To evaluate relevant optical properties of esthetic direct restorative materials focusing on whitened and translucent shades.

Methods

Enamel (E), body (B), dentin (D), translucent (T) and whitened (Wh) shades for E (WhE) and B (WhB) from a restorative system (Filtek Supreme XTE, 3M ESPE) were evaluated. Samples (1 mm thick) were prepared. Spectral reflectance (R%) and color coordinates (L*, a*, b*, C* and h°) were measured against black and white backgrounds, using a spectroradiometer, in a viewing booth, with CIE D65 illuminant and d/0° geometry. Scattering (S) and absorption (K) coefficients and transmittance (T%) were calculated using Kubelka–Munk's equations. Translucency (TP) and opalescence (OP) parameters and whiteness index (W*) were obtained from differences of CIELAB color coordinates. R%, S, K and T% curves from all shades were compared using VAF (Variance Accounting For) coefficient with Cauchy–Schwarz inequality. Color coordinates and optical parameters were statistically analyzed using one-way ANOVA, Tukey's test with Bonferroni correction (α = 0.0007).

Results

Spectral behavior of R% and S were different for T shades. In addition, T shades showed the lowest R%, S and K values, as well as the highest T%, TP an OP values. In most cases, WhB shades showed different color and optical properties (including TP and W*) than their corresponding B shades. WhE shades showed similar mean W* values and higher mean T% and TP values than E shades.

Significance

When using whitened or translucent composites, the final color is influenced not only by the intraoral background but also by the color and optical properties of multilayers used in the esthetic restoration.

Introduction

Traditionally, composites are designed to support masticatory load (posterior teeth) or to produce esthetically beautiful (anterior teeth) restorations [1]. Manufacturers of restorative resin-based composites may manipulate the resin matrix and, mainly, the particle size and shape to improve material properties [1], [2], [3], [4], [5], [6].

With the development of nanotechnology, dental nanocomposites have become available, allowing for significant improvements [2]. Nanofillers range from 1 to 100 nm2, which is below the wavelength of visible light (380–780 nm). This characteristic allows the fabrication of materials unable to scatter or absorb the visible light, named highly translucent materials [2], [7]. To obtain these nanocomposites, two types of nanofillers have been synthesized: nanometric particles (nanomers) and nanoclusters. The former are mainly monodisperse, non-aggregated and non-agglomerated zirconia (2–20 nm) or silica particles (2–75 nm) [2], [7]. Due to reduced particle size, dental nanocomposites exhibit very good resistance to wear and fracture, along with good sculptability [2]. Nanofillers also offer advantages in optical properties. They can provide low opacity in low staining dental composites, allowing for a wide range of shades and opacities [2].

When light strikes a semi-translucent object, four phenomena can result from this interaction: (1) specular light reflection and (2) diffuse light reflection at the object surface, (3) absorption and scattering of light within the object structure, and (4) transmission of the light flux through object structure [6], [8], [9]. The light resulting from the interaction of these phenomena will reach the observer eyes with the object color information [6].

Previous studies reported that background color affects the perceived color of dental composites [10], [11], suggesting that translucency should not be ignore in esthetic dentistry. Highly translucent and low staining composites, which usually have nanoparticles, allow the perception of the background color through the material [2].

Scattering changes with the wavelength of incident light and it is mostly determined by particle size. Absorption and reflectance also vary with the wavelength of incident light and the nature of colorant pigments [8]. Different esthetic restorative resin systems work with different color and translucency effects and these characteristics should be considered when selecting the restorative material.

Actually, most direct restorative materials offer whitened shades, suggesting they are brighter and more opaque than the classic dental shades [11]. Opalescent materials, such as dental enamel, are able to scatter shorter wavelengths of light. Under reflected light, they appear blue, whereas under transmitted light, they appear brown/yellow [2], [12], [13].

CIELAB color space is mostly used in dental color research. This space consists of three axes: L* (lightness), a* (red-green axis) and b* (yellow-blue axis). Chromatic attributes related to visual perception, such as chroma (C*) and hue (h°), are obtained from a* and b* coordinates [14]. Therefore, managing the optical properties of esthetic restorative materials is essential to fabricate natural-looking esthetic restorations. Thus, the purpose of this study was to evaluate the color and optical properties of translucent and whitened shades in relation to their original E and B shades. The study tested the hypotheses that (1) direct restorative composite shades present the optical properties suggested by the manufacturer, and (2) there is a significant difference in color and optical properties between the whitened shades and the corresponding original (E and B) shades from a direct restorative composite system.

Section snippets

Samples

An esthetic resin composite restorative system (FS-Filtek™ Supreme XTE, 3M ESPE, St. Paul, MN, USA), based on layering technique [15], [16], was evaluated (Table 1).

Specimens (10 mm in diameter and 1 mm in thickness) were fabricated (n = 3) with all composite shades. Composite material was packed into an adaptable micrometer metal mold (Smile Line, St-Imier, Switzerland) pressed with a mylar strip and a glass slide. All samples were light activated (Bluephase®, Ivoclar Vivadent, Schaan,

Spectral reflectance and color

Fig. 1 shows spectral distribution of reflectance for a single shade (A2) of different translucency (E, B and D shades) and one representative shade from WhE, WhB and T shades. All shades were not included because they showed overlapped values. T shades showed different spectral behavior from other shades (84.41%  VAF  93.95%). The remaining shades showed similar spectral behavior (VAF values from 97.46% to 99.92%).

Mean values and standard deviation for the color coordinates L*, a*, b*, C* and h°

Discussion

This study evaluated color and optical properties of different shade classes used for direct restorative resin-based composites. It has been reported that the majority of teeth matches to shade A from Vita Classical shade system [28], therefore the present study evaluate this group of shade from the composite system (FS).

Optical properties such as reflectance, transmittance, scattering and absorption coefficients depend on the wavelength of light [20]. Previous studies performed on dental

Conclusions

Within the limitations of the present study, results suggest that the optical behavior of T shades is different from other shades. Considering the whitened shades, WhB shades showed different color and optical properties (including TP and W*) than their corresponding B shades. WhE shades showed similar mean W* values but higher mean T% and TP values than E shades.

Acknowledgments

The authors acknowledge funding support from research projects JA TEP-1136 from “Junta de Andalucía”, Spain, MAT2013-43946R from the Spanish Ministry of Economy and Competitiveness, CNPq do Brasil (304995/2013-4) and CAPES do Brasil (PNPD 42009014007P4). The authors also acknowledge 3M ESPE for providing the resin-based composite used in this study.

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