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ePaper created 2018-02-16, 10:54:19 | version 1.38.0
| technique naturomimetic layering Optical characteristics of anterior teeth As mentioned previously, teeth suffer modifications over the years that directly interfere with their ap pearance and colour. Due to an increase in thickness of dentine and a decrease in thickness of enamel and its surface texture bring changes in translucency and opacity of dentine and enamel. Understating optical properties of dental structures is immensely important as enamel and dentine in teract with natural light differently due to their vari ations in composition and mineralisation. Enamel allows 70.1 per cent average light passage, whereas istics. Enamel translucency may also be attributed to variations in calcification levels, because the more porous and less mineralised the enamel, the larger the dispersion index.51, 52 Optical properties of dentine Dentine can be considered as the dental tissue of higher relevance when concerned with color.46, 53 From an optical point of view, dentine is a low translucency structure with various chroma and saturation variations. Dentine has a special property of producing relative opacity, this is because the dentinal tubule arrangement enables the dentine Fig. 6a Fig. 6b Fig. 6c Figs. 6a–c: Childhood teeth. Figs. 7a–c: Adolescent teeth. Fig. 7a Fig. 7b Fig. 7c 52.6 per cent of light can be transmitted through the dentine structure.43, 44 It can be said that dentine is the colour and enamel is the colour modifier.4547 Optical properties natural enamel While dealing with enamel, clinicians need to keep in mind the orientation of the rods that comprise the basic structure of the enamel. Generally, these rods rise at right angles from the dentinal surface. In cervical areas, the rods divert from their horizontal orientation and lean apically. Near the incisal or cusp tip, the rods change direction gradually, be coming oblique and nearly vertical over the edges.48 Because of this orientation change, less light is transmitted, which decreases the translucency of the enamel.49 Enamel also modifies the chromatic aspects of the teeth because of phenomena such as reflection, transmission, refraction, thickness and surface texture. Moreover, enamel has the ability to attenuate underling colours, which can affect the chromatic aspect of teeth.50 Hence the properties of light reflection, or transmission of enamel depend upon its texture, orientation of enamel rods, and its ability to refract light, in addition to histological character to demonstrate selective light diffraction, as certain rays are reflected, whereas others are absorbed.51 As age increases, primary dentine begins to evolve or change, originating secondary and tertiary den tines, which have different structure and compo sitions, and affect optical properties of tissues.54 In elderly patients, the reduction in the diameter of the dentinal tubules causes progressive dentine sclerosis and high saturation. Basic characteristics of teeth The visual characteristics of teeth modify with age and can be studied under four categories: child hood, adolescent, middleaged and aged teeth. Childhood teeth (Figs. 6a–c) At about the age of 10 years, enamel presents an almost milkwhite hue, the superficial enamel layers are the most opaque and frequently appear as though they have a white frost. Enamel generally shows a clear opalescent effect, the prominent enamel surface with micro and macrotexture has a very low surface lustre; the incisal edges of the dentinal lobes are completely covered by enamel. 16 cosmeticdentistry 1 2017