Optical behavior of one-shaded resin-based composites
Introduction
Resin-based composites are widely used in restorative dentistry. Structural and optical harmonization of the composite restoration within the tooth structure and with the adjacent teeth is a critical factor for the patient acceptance and satisfaction with the dental esthetic treatment. Multilayering techniques [1,2] using resin-based composites of different opacity and shades have been reported to mimic the tooth appearance [[3], [4], [5], [6]]. Yet, this restorative treatment requires a precise shade determination and high technical skills, which often increase dental chair time and cost [7]. There is a trend to reduce treatment complexity, which has a great chance to reduce technical sensitivity and to increase efficiency.
In restorative dentistry, the term 'chameleon effect' (blending effect) describes the ability of a material to acquire a color similar to the surrounding tooth structure [[8], [9], [10], [11]]. This property has enabled the introduction of new dental composites that simplify shade selection and reproduction. An initial approach was the so-called “group-shaded” composites [12] that included a very narrow shade range, where each shade covered a recommended group of VITA classical shades. Recently, the concept of “one shade” or, “single shade” composite resins was introduced [7] to describe resin-based composites designed to esthetically simulate all shades with only one nominal shade. These materials, formulated on this wide color matching concept, supposedly blend seamlessly into the surrounding dentition, regardless of the tooth shade.
The wavelengths reflected from an object determine its perceived color [12]. In the esthetically restorative materials, e.g. resin-based composites and ceramics, this selective reflection of wavelengths is due to pigments included in their composition. However, innovative technological approaches have developed the one-shaded resin-based composites. According to the manufacturer (Tokuyama Dental) [13], Omnichroma (an one shade universal resin-based composite) does not contain pigments, and its optical properties are based on structural color, a “smart chromatic technology” where the resin-based composite responds to light waves at a given frequency by perfectly reflecting a specific wavelength inside the tooth color space [13]. Also, recent studies [[14], [15], [16]] showed that the main advantage of Omnichroma relies on an enhanced Color Adjustment Potential [11]. Another technology, used to develop Venus Pearl One and Venus Diamond One (Kulzer) is based on “the adaptive light matching” concept, where the restoration shade is achieved by absorbing the wavelengths that are reflected by the surrounding tooth shade [17].
The esthetic success of resin-based composite restorations depends, to a great extent, on their optical properties that should mimic those of the natural teeth. Thus, to discuss the color behavior of resin-based composites it is important to consider several optical properties, such as: light reflection, scattering, absorption and transmittance [11,12]. Small changes in the relative amounts of each wavelength band from a light beam significantly influence on color and appearance [11,12]. For instance, light scattering of the shorter wavelengths of the visible spectrum produces a bluish appearance under reflected light and an orange/brown appearance under transmitted light [12]. This optical phenomenon, known as opalescence, varied by brand and shade of the resin-based composites [18].
Translucency is one of primary factors in controlling esthetics and it is critical for materials selection. Translucency directly influences on the material lightness (value) [19], which is the most relevant color dimension, since human eye is more sensitive to value variations than to chroma and hue changes [12].
Further, previous studies [9,10] reported that a decrease in restoration thickness should lead to an increase in the blending effect, which instigates the investigation of the material thickness effect on the optical properties, translucency and opalescence of these new one-shaded restorative materials.
However, as the information on this new class of resin-based restorative material [[14], [15], [16]] is insufficient and incipient, it justifies the need for further studies. Thus, the purpose of this study was to evaluate the optical properties, translucency and opalescence parameters of one-shaded resin-based composites compared to a group-shaded resin-based restorative material. The hypotheses tested were: (1) there are no significant differences in optical properties, translucency and opalescence parameters among the resin-based composites evaluated, and (2) the optical properties, translucency and opalescence parameters of the evaluated one-shaded resin-based composites are not influenced by the material thickness.
Section snippets
Preparation of samples
The information on the materials used in this study are shown in Table 1. Three resin-based composite discs were prepared for each material and each thickness (0.5, 1.0 and 2.0 mm (± 0.05 mm)) using a 10-mm diameter, height-adjustable mold (SmileLine, Switzerland). The resin-based composite was inserted into the mold, covered with a translucent Mylar strip and pressed with a thin glass slide. Light-activation (Bluephase Style, Ivoclar-Vivadent, 1100 mW/cm2, for 20 s) of the resin-based
Translucency and opalescence parameters
Table 2 shows the mean and standard deviation values of TPab, TP00, and OP for the three thickness and four dental materials evaluated. As might be expected, for all materials, translucency decreases as thickness increases with statistically significant differences (p < 0.005). Omnichroma (OM) and Filtek Universal (FU) showed, respectively, the greatest and the lowest translucency values, with significant differences (p < 0.005) for same thickness. The translucency of VD and VP were similar,
Discussion
The results of present study showed significant differences in optical properties, translucency and opalescence parameters among the resin-based composites and the thicknesses evaluated. Therefore, both experimental hypotheses were rejected.
Translucency is one of the primary factors in evaluating dental esthetics. Recently, the CIEDE2000 color difference formula was recommended to calculate the TP00 [24]. In this study, TPab and TP00 formulas and their 50:50% perceptibility and acceptability
Conclusions
Understanding the optical behavior of one-shaded resin-based composites is essential to optimize their clinical performance. Although the spectral optical behavior of one-shaded resin-based composites is similar to the group-shaded resin-based composite evaluated, the values for the optical properties (S, K, and T%), translucency and opalescence significantly vary among both types of materials.
Acknowledgements
The authors acknowledge funding support from the Spanish Ministry of Science, Innovation and Universities (PGC2018-101904-A-100 and EQC2019-005920), from the University of Granada, Spain (A.TEP.280.UGR18) and from CNPq do Brasil (302587/2017-9).
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