BAZOS/MAGNE
ENAMEL +
DENTIN +++
Fig 12 A submerged maxillary premolar was photographed with reflected long wavelength UV illumina- tion (365 nm), enabling the visualization of dentin exhibiting three times the fluorescence intensity than that of enamel. Note that the DEC also exhibits pronounced fluorescence. 39-41
of that material either on a white or black background, defines its infinite optical thickness (IOT). Although light transmission in enamel at 1 mm has been tentatively measured to be 66% ± 11%, while that of dentin at 1 mm is 44% ± 12%, 47 one must con- sider the significance of sample loca- tion, the relative thickness distribution of both tissues as well as stage of tissue maturation. 48 With regards to dynamic aging on the macrostructural level, enamel inad- vertently goes through a volumetric re- duction via functional wear, mechanical abrasion and chemical erosion, result- ing externally in a hyperpolished sur- face. Conversely, internally the dentin volume increases via secondary and tertiary dentin deposition. On a microstructural level, a signifi- cant reduction in the porosity of the enamel is due to posteruptive matura- tion via hypermineralization 49–51 and homogenization leading to HAp crys-
lagen-rich, highly cross-linked composi- tion, with primary intrinsic (endogenous) fluorophores being the aromatic amino acid tryptophan 36,37 and the collagen cross-linking agent hydroxypyridium (Fig 12). 38 Dynamic infinite optical thickness Perceived color can be considered a combination of the reflected color of the translucent enamel layer plus the color reflected from the underlying relatively opacified dentin layer. As the enamel and dentin layers vary inversely in rela- tive thickness from cervical to incisal, the amount of color contribution from the two tissues will be reciprocal (vice versa) (Figs 13 and 14). 44–46 The thickness of a given translucent material at which any further material ad- dition does not alter the transmission of light, nor the perceived reflected color
343 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY VOLUME 9 • NUMBER 3 • AUTUMN 2014
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