Objective. To determine the translucency acceptability and perceptibility thresholds for dental resin composites using CIEDE2000 and CIELAB color difference formulas. Methods. A 30-observer panel performed perceptibility and acceptability judgments on 50 pairs of resin composites discs (diameter: 10mm; thickness: 1mm). Disc pair differences for the Translucency Parameter (TP) were calculated using both color difference formulas (TP00 ranged from 0.11 to 7.98, and TPab ranged from 0.01 to 12.79). A Takagi–Sugeno–Kang (TSK) Fuzzy Approximation was used as fitting procedure. From the resultant fitting curves, the 95% confidence intervals were estimated and the 50:50% translucency perceptibility and acceptability thresholds (TPT and TAT) were calculated. Differences between thresholds were statistically analyzed using Student t tests (˛ = ۰٫۰۵). Results. CIEDE2000 50:50% TPT was 0.62 and TAT was 2.62. Corresponding CIELAB values were 1.33 and 4.43, respectively. Translucency perceptibility and acceptability thresholds were significantly different using both color difference formulas (p = 0.01 for TPT and p = 0.005 for TAT). CIEDE2000 color difference formula provided a better data fit than CIELAB formula. Significance. The visual translucency difference thresholds determined with CIEDE2000 color difference formula can serve as reference values in the selection of resin composites and evaluation of its clinical performance.

Introduction

The increased demand of patients for highly esthetic restorations has driven the development of dental materials with suitable optical properties. Translucency is an important property of dental tissues and materials. Thus, an appropri- ate determination and communication of optical properties should include translucency, in addition to more popular parameters such as: lightness (L*), a* and b* (CIELAB coordinates), hue angle (h◦) and chroma (C*). Translucency describes the ability of a material to transmit light [1]. The translucency parameter [2] (TP) has been used to assess the translucency of dental materials [3–۷]. TP is defined as the CIELAB color difference (E*ab) for a material, at a particular thickness, on optical contact with ideal black and white backings [2]. Aiming to improve correction between perceived and computed color differences of CIELAB formula, the Commission Internationale de l’Éclairage (CIE) [8] recommended the use of CIEDE2000 color difference formula. However, at the moment in the majority of translucency studies in dental literature, the TP is still quantified using the CIELAB color space and its associated color formula (E*ab). Thus, determination of TP has shown differences in translucency of different composite resins depending of its shade [9],thickness [10]; matrix composition [11]; filler particle size and content [12,13] and type and amount of the opacifiers used [14]. Perceptibility difference threshold represents the lower perceptual limit, and it is widely applicable, mainly, to develop new color notation systems and their color difference metrics, to study discernible colors by the human visual system [15] and to understand the mechanisms of color vision [16]. However, in many practical situations, differences above the threshold (supra-threshold) are used, passing from perceptibility thresholds or “just noticeable differences” to higher differences, named “acceptable differences” or “tolerances.” The industrial interest on these differences is justified, on one hand, by the high cost required to maintain the industrial production below the limits of the visual threshold (perceptible threshold) and, on the other hand, by the need of maintaining the differences under an admissible limit. The complete absence of control (monitoring) should involves a lack of similarity in the production outcome, with negative implications on the overall quality of the product.