Difference in the translucency of all-ceramics by the illuminant
Introduction
Color and its elements such as Hue, Value and Chroma, and translucency/opacity influence the esthetics of dental restoration; therefore, creating a natural-looking ceramic restoration, which blends harmoniously with the surrounding teeth, is not always achieved [1], [2]. Judgments of appearance matching by means of the visual criteria and the CIE (Commission Internationale de l’Eclairage) LAB color difference were determined based on resin composites and teeth [3]. As a result, the overlap in ranges of the color differences for those comparisons rated matches and mismatches indicates the importance of other factors, such as translucency, in appearance matching.
All-ceramic restorations have been advocated for superior esthetics [4]. Modern all-ceramic restorative systems offer the possibility to closely match the natural optical characteristics of tooth structure [5]. When selecting an all-ceramic system, there are several factors to consider, including the translucency of the ceramic material and of the adjacent teeth, the color of the prepared tooth and the forces anticipated in that region [6].
Translucency of esthetic restorative materials has usually been determined with the translucency parameter (TP) or the contrast ratio [7]. There have been varied studies on the translucency of dental ceramics [4], [8], [9]. It was reported that variability in translucency of veneer ceramic may affect their ability to match natural teeth [4]. All-ceramic core materials have a range of translucencies, and a range of translucency was identified in the veneered all-ceramic systems; therefore, such variability may affect their ability to match natural teeth [8]. Correlation between the translucency and the thickness of core and veneering ceramics was determined [9]. Difference in the color and translucency of dental laboratory resin composites and an all-ceramic material was determined [10]. Changes in translucency of enamel porcelain after repeated external staining procedures were also determined [11].
Color and translucency of dental substances are correlated. Changes in the translucency of dental enamel due to illumination alter the overall color of the tooth [12]. Based on a study on the influence of additives on the color and translucency of glass-ceramics, it was reported that certain colorants affect opacity as well as Hue and Chroma [13]. Blending effect of layered resin composites related to material, shade and differences in color and translucency between compared materials was evaluated [14], and it was concluded that blending effect was material, shade and translucency dependent.
Color of an object is identified by the visible light that it reflects or transmits. Accurate estimation of the location, form and color of objects is challenging because the light arriving at the eyes depends not only on object properties, but also on the spectra and spatial layout of the light sources [15]. Although sunlight is the most common standard for lighting, it should be used carefully for shade determination because of its extreme variability. Several standard illuminants have been used to measure the color of dental substances [16], [17], [18]. CIE standard illuminant D65 represents a phase of daylight with a correlated color temperature of approximately 6500 K, illuminant A represents light from the full radiator at absolute temperature 2856 K (incandescent lamp) and illuminant F2 represents light from fluorescent lamp of medium color temperature of 4230 K [19], [20]. Several reports on the color rendering index, color temperature of illuminants and distribution/intensity of illuminations were made [21], [22].
Based on studies of differences in the color of resin composites and shade guides caused by the change of illuminants, it was reported that the color coordinates varied by the illuminant [16], [17]. Changes of the standard illuminants resulted in prominent differences in Hue angle of esthetic restorative materials [18].
Since the spectral power distributions of light from different illuminations differ, translucency of restorative materials under different lights varies by the kind of material. As to the changes of translucency by the illuminant, the difference in TP values relative to the illuminants of ceramic for metal-ceramic restoration and ceramic repairing resin composites was determined [23], and it was concluded that the difference in translucency by the illuminant of ceramic and ceramic repairing resin composites should be considered when matching shade of ceramic and ceramic repairing resin composites.
Therefore, an understanding of interactions between translucency and illuminant is needed to enhance the shade matching of restorations under varied lighting conditions. Although the importance of translucency change by the illuminant on the color of teeth was proposed more than 20 years ago [12], there have been few studies on the influence of changes in illuminants on the translucency of all-ceramic materials. The null hypothesis assumed in the present study was that differences in TP values by the illuminant were not influenced by the type of ceramics (core ceramic, veneering ceramic, A2- or A3-layered ceramics), the brand/thickness combination within each type and the combination of illuminants compared. The objectives of this study were to measure the difference in TP by the CIE standard illuminants D65, A and F2 based on all-ceramic core, veneer and layered specimens.
Section snippets
Specimen preparation
Seven all-ceramic core materials were fabricated, 11 mm in diameter, following the manufacturers’ instructions (Table 1). A VITA Lumin A2 (VITA Zahnfabrik, Bad Sackingen, Germany) corresponding shade was selected for all core ceramics. Thickness of specimens was controlled by grinding with a polishing machine (AM Technology, Kyunggi-Do, Korea), using a series of silicon carbide papers (Buehler Ltd., Lake Bluff, IL, USA) from #600 to #2000, to the manufacturers’ recommended thickness required for
Results
Translucency differences (ΔTP) by the illuminant for core ceramics are presented in Fig. 1, for veneer ceramics in Fig. 2, for A2-layered ceramics in Fig. 3 and for A3-layered ceramics in Fig. 4. For core ceramics, ΔTP value for TP(A) − TP(D65) ranged from 0.05 to 1.02, that for TP(F2) − TP(D65) ranged from 0.04 to 1.01 and that for TP(F2) − TP(A) ranged from −0.12 to 0.01. For veneer ceramics, ΔTP value for TP(A) − TP(D65) ranged from 0.65 to 1.31, that for TP(F2) − TP(D65) ranged from 0.54 to 1.03 and
Discussion
The null hypothesis that the differences in TP values by the illuminant were not influenced by the type of ceramics, the brand/thickness of ceramics and the combination of illuminants was rejected because ΔTP values were influenced by the three fixed factors and there were significant interactions between the factors (p < 0.05).
Comparing by the type of ceramics, ΔTP values for layered specimens were lower than that of core ceramic, both of which were lower than that of veneer ceramic, which
Conclusion
Within the limitations of the present study, translucency was influenced by the standard illuminant used to measure the TP value. TP value relative to the illuminant D65 was lower than those to A and F2. Therefore, in daylight condition, translucency of all-ceramic materials was lower than those of incandescent or fluorescent lamp. Further study on the clinical implication of this result should be performed.
Acknowledgement
Supported by grant (R01-2006-000-10421-0) from the Basic Research Program of the Korea Science & Engineering Foundation, Republic of Korea.
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