Translucency can be defined as the ratio of the intensity of the transmitted light to that of the incident light. The general equation of the Lambert-Beer law is given by T = C e− αd, where T is the transmission coefficient, C the constant related to the reflection material, e the Naperian number, α the coefficient of absorption, and d the sample thickness. The absorption coefficient ( α) and the constant value related to the reflection (C) of the samples are obtained from the relationship of the natural logarithm ( ln) of the transmission coefficient ( T) to the specimen’s thickness. The Lambert-Beer law relates the attenuation of light to the properties of the material through which the light is traveling. While the term translucency is used to describe the optical property, the corresponding term transmission is a physical term which represents the ability of a medium to permit light to pass through it. Translucency is the relative amount of light transmission or diffuse reflection from a substrate surface through a turbid medium. The advantage of this system over the Munsell color system composed of hue, chroma and value attributes is that the CIELAB coordinates are evenly spaced in terms of visual perception, so that the spectral readings can be correlated with subjective observations. Chroma is calculated as C * ab = ( a * 2 + b * 2) 1/2, and the color difference is calculated as ∆ E * ab = (∆ L * 2 + ∆ a * 2 + ∆ b * 2) 1/2. The CIE L * coordinate ranges from 0 to 100 and represents the luminosity, the a * coordinate ranges from −90 to 70 and represents greenness (positive a *) and redness (negative a *), and the b * coordinate ranges from –80 to 100 and represents yellowness (positive b *) and blueness (negative b *), and the CIE standard illuminants are generally used. In the evaluation of optical properties, the Commission Internationale de l’Eclairage (CIE) LAB system is generally used. As to the optimization of the translucency of dental ceramics, the biomimetic simulation of natural tooth microstructure might be a promising method. All-ceramic restorations have been advocated for superior esthetics. Considering the translucency and the mechanical strength of dental ceramics simultaneously, high-translucency ceramics should be used when high-level esthetics are required, since high-strength ceramics tend to be more opaque and pose a challenge when trying to match tooth color. Īs dental ceramics evolve and patients’ demands for esthetic restorations increase, guidance in selecting an appropriate ceramic system when faced with different esthetic demands was offered. In addition, translucency of dental ceramics is closely related to the light transmission and light-curing efficiency of underlying resin-based luting agents. Requirements for dental esthetic materials are contradictory since translucency of restorative materials influences the masking ability and color blending effect. Translucency is emphasized as one of the primary factors in controlling the esthetic outcome because it makes restorations appear more natural. Since human tooth enamel is highly translucent, translucency is a desirable characteristic of dental ceramic materials.
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