Enamels crystal

C. Robinson, K. Yamamoto, S.D. Connell, J. Kirkham, H. Nakagaki, A.D. Smith, The effect of fluoride on the nanostructure and surface pK of enamel crystals An atomic force microscopy study of human and rat enamel, Eur. J. Oral Sci. 114 (2006) 99-104. E.D. Eanes, A.W. Mailer, The effect of fluoride on the size and morphology of apatite crystals grown from physiological solutions, Calcif. Tissue Int. 63 (1998) 250-257. 

Hydroxyapatite (with some carbonate inclusions) is the most stable of the possible calcium phosphate salts that can be formed under physiological conditions. However, it is not the most rapid one to form. Instead, octacalcium phosphate (OCP) will precipitate more readily than hydroxyapatite. This led Brown in 1987 to propose that, as the kinetically favoured compound, OCP precipitates first, and then undergoes irreversible hydrolysis to a transition product OCP hydrolyzate [68]. This hypothesis is consistent with the observation that enamel comprises hydroxyapatite crystals that have the long, plate-like morphology that is generally considered characteristic of OCP crystals [69]. Overall, it seems that enamel crystals, with their elongated form, result from early precipitation of OCP, which forms a template on which hydroxyapatite units grow epitaxially [70,71]. This leads to enamel mineralisation with the observed thin, ribbon-like structure of crystals. 

T. Yanagisawa, S. Takuma, FI. Tohda, O. Fejerskov, R.W. Fearnhead, Fligh resolution electron microscopy of enamel crystals in cases of human dental fluorosis, J. Electron Microsc. 38 (1989) 441-448. 

The dimensions of bone crystallites can be as small as 96 10 A, with the order of magnitude even a factor of two or three smaller56. The mean size of the apatite crystals in dentine and cementum is of the same order as that found in bone. Enamel crystals, however, are at least an order of magnitude larger in all dimensions. There appears to be good agreement that the smallest dimension of the bone apatite crystal is about 50 A. On the other hand, there is a discrepancy in the reported size of the... 

Teeth are composed of different parts enamel at the outer surface, then mainly dentine, cementum and pulp. Dentine has basically the same composition as bone, in contrast to enamel, which is composed of 96wt.% of well crystalline carb. HAP. The enamel crystals can reach up to 1 p.m length. 

Finally, the ameloblasts secrete an unusual basal lamina, which partially mineralizes into the surface enamel crystals, the enamel cuticle. By this time, the enamel organ has shrunk so that its outer layers have merged with the ameloblast layer at the completed enamel surface postmaturation stage). This reduced enamel epithelium is rubbed off as the teeth erupt, but the enamel cuticle is abraded more slowly and gradually replaced by proteins from saliva, the acquired pellicle (Sect. 12.1.3). 

Fluoride is both incorporated into enamel crystals and also affects the enzymes involved in enamel formation (Sect. 16.2.2), causing mottled enamel, a severe example of enamel fluorosis. Enamel fluorosis is evident as specks or white flecks on the enamel surface (Fig. 16.2b). In 1941, the public water supply of Aurora (IL) contained 1.2 ppm of fluoride (F), but only 5% of teeth exhibited fluorosis, mostly premolars and second molars. A sensitive index of... 

Aoba T (1996) Recent observations on enamel crystal formation dnring mammalian amelogenesis. Anatomical Record 245 208-18... 

Bres EF, Chems D, Vincent R, Momiroli J-P (1993a) Space group determination of htrman tooth-enamel crystals. Acta (irystallogrB49 56-62... 

Bres EF, Steuer P, Voegel J-C, Frank RM, Cuisinier FJG (1993b) Observation of the loss of the hydroxyapatite six-fold symmetry in a human fetal tooth enamel crystal. J Micros 170 147-154 Brown WE (1966) Crystal growth of bone mineral. Clin Orthopaedics 44 205-220 Brown WE, Eidelman N, Tomazic B (1987) Octacalcium phosphate as a prectrrsor in biomineral formation. Adv Dent Res 1 306-313... 

Daculsi G, Mentanteau J, Kerebel LM, Mitre D (1984) Length and shape of enamel crystals. Calcif Tissue Inti 36 550-555... 

Elliott JC, Feamhead RW (1962) Electron microscope and electron diffraction study of developing enamel crystals. J Dent Res 41 1266... 

In fi"eshly secreted enamel, crystals first appear near the ameloblasts and, as soon as they do so, the enamel takes on the pattern of its final form, an intricate beautifully arranged two-phase system which may not only last throughout life, but may survive in fossil form for millions of years. 

Tohda, H., Yamada, M., Yamagudri, Y. and Yanagisawa, T. (1997) High-resolution electron microscopical observations of initial enamel crystals. Journal of Electron Microscopy, 46, 97-101. 

The model states that there are three reactions to be considered in the treatment of the reaction kinetics of the firing of a Ti02-opacified porcelain enamel crystallization of anatase, crystallization of rutile, and inversion of anatase to rutile. Our task is to find kinetic expressions for each of these reactions and then combine them to derive overall equations for the anatase and rutile concentrations. Our previous work C) had indicated that a simple first-order kinetic expression is an excellent description for the inversion reaction ... 

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