Tooth enamel crystals

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... 

M. lizima and Y. Moriwaki, In vitro study of the formation mechanism of tooth enamel apatite crystals - Effects of organic matrices on crystal growth of octacalcium phosphate(OCP),/.Japan. Assoc. Crystal Growth, 26,1999,175-83 (in Japanese with English abstract)... 

When studying a complex material such as tooth enamel it is invaluable to have accurate data on single crystals of the apatite of which it comprised. Figure 9.16(a) is a V(z) curve measured using a line-focus-beam microscope at 225 MHz, on the biggest crystal of hydroxyapatite in the world At least 12... 

Because of its mineral composition, the large size of its phosphate crystals and the small amount of pore space, mature tooth enamel is rarely affected by diagenetic contamination (40-42). This has been supported by experimental data that show that enamel reliably retains biogenic strontium isotope signatures (30, 43-48). 

Arends J, ten Cate JM Tooth enamel remineralisation. J Crystal Growth 1981 53 135-147. 

From a mechanistic viewpoint it is reasonable to anticipate an inverse clinical relationship between calculus and caries. Calculus formation is essentially a mineralisation process. The development of a caries lesion is the result of the net demineralisation of tooth enamel by plaque acid. These processes both involve crystalline calcium phosphate phases in contact with liquid, saliva and/or plaque fluid, containing their constituent ions. The oral environment also contains other salivary constituents and bacteria, which either inhibit or promote crystal growth or dissolution. 

Takahashi M, Uematsu K, Ye ZG, Sato M (1998) Single-crystal growth and structure determination of a new oxide apatite, NaLa9(Ge04)602. J Solid State Chem 139 304-309 Terpstra RA, Driessens FCM (1986) Magnesium in tooth enamel and synthetic apatites. Calcif Tissue Inti 39 348-354... 

Fowler BO (1977) I. Polarized Raman spectra of apatites. II. Raman bands of carbonate ions in human tooth enamel. Mineralized Tissue Research Communications Vol 3, no. 68 Fratzl P, Fratzl-Zelman N, Klaushofer K, Vogl G, Roller K (1991) Nucleation and growth of mineral crystals in bone studied by small-angle X-ray scattering. Calcif Tissue Inti 48 407-413 Fratzl P, Schreiber S, Boyde A (1996) Characterization of bone mineral crystals in horse radius by small-angle X-ray scattering. Calcif Tissue Inti 58 341-346... 

Bres EF, Barry JC, Hutchison JL (1984) A stractural basis for the curious dissolution of the apatite crystals of human tooth enamel. Ultramicroscopy 12 367-372... 

Properties Colorless translucent crystals or powd., odorless, strongly acidic tart taste very sol. in water, alcohol, and ether very si. sol. in ether m.w. 192.43 dens. 1.542 m.p. 153 C flash pt. 212 F Toxtology LD50 (oral, rat) 6730 mg/kg poison by IV mod. toxic by subcut. and IP routes poison by IV route mildly toxic by ingestion primary irritant severe eye, mod. skin irritant some allergenic props. erodes tooth enamel TSCA listed... 

A potential use of this monomer Is In the area of dental fillings In which a slurry containing 20% of very fine crystals of the unsaturated splro ortho carbonate VI In 60% of the adduct of methacrylic acid to blsphenol-A diglycidyl ether (Bls-GMA) plus 20% trimethylolpropane trimethacrylate produces on polymerization a material with essentially no change In volume. An Investigation of a bubble test on tooth enamel showed that this copolymer had nearly double the adhesion to the tooth structure that the base resin had without the addition of the unsaturated splro ortho carbonate. The copolymer also had improved impact strength but yet essentially the same modulus, and filled composites appeared to have somewhat improved abrasion resistance. 

The fluoride ion can replace the hydroxide ion in a crystal without significantly altering its structure, an isomorphous ion replacement. Fluoride also affects the enzymes involved in enamel formation, causing mottled enamel, a severe example of enamel fluorosis. White opaque patches on the normally translucent enamel indicate mild fluorosis. Fluorosis is measured on a grade of 0-5 where 1 through 3 indicate an increased cover of opaque white patches on the tooth surface, and 4 and 5 indicate an increased mottling. The two worst affected teeth make up an individual s score. The community s index of fluoridation is the mean score for all individuals. As the natural or artificial fluoride concentration of the water supply increases to 1 ppm, the mean number of cavities in 10-12 year-old children decreases from 7 to 3. Above 1 ppm fluoride, caries does not decrease much more, but the index of fluorosis increases markedly. This is the reason why public water supplies are fluoridated to only 1 ppm and not more or less. 

The presence of even one fluoride ion in the crystal slows the transformation to amorphous calcium monohydrogen phosphate. Thus, in the presence of fluoride (e.g., after using fluoridated toothpastes), fluoroapatite forms at the tooth surface and reduces the rate of caries development. The increased fluoride concentration at the tooth surface also inhibits lactate production. These observations explain why cleaning the teeth with fluoridated toothpaste prevent caries. Cleaning the teeth exposes the apatite at the enamel surface. In the absence of fluoride, there is no protection because the biofilm forms within a few... 

Its topography reveals the unique structure consisting of aligned prisms or rods with 5pm diameter that extent approximately perpendicular from the dentin-enamel junction towards the tooth surface. Each rod consists of tightly packed carbonated hydroxyapatite crystals with very high aspect ratio. Nano-indentation studies revealed a pronounced anisotropy as the stiffness differs parallel and perpendicular to the rod extension. Even so, different fibre orientation on a micro level as shown in Figure 3.4b account for a quasi-isotropic behaviour. 

X-ray diffraction patterns from enamel sections cut in the longitudinal direction of a tooth show that the c-axes (the hexagonal axes) of the apatite crystals (also their long direction) are highly oriented in the direction of the enamel rods (sometimes called prisms) (Miles 1967). The rods run from the enamel surface (to which they are nearly normal) to the enamel-dentin junction and are about 4-7 pm in diameter. 

Substitutions in the HA structure are possible. Substitutions for Ca, PO4, and OH groups result in changes in the lattice parameter as well as changes in some of the properties of the crystal, such as solubility. If the OH" groups in HA are replaced by F" the anions are closer to the neighboring Ca " ions. This substitution helps to further stabilize the structure and is proposed as one of the reasons that fluoridation helps reduce tooth decay as shown by the study of the incorporation of F into HA and its effect on solubility. Biological apatites, which are the mineral phases of bone, enamel, and dentin, are usually referred to as HA. Actually, they differ from pme HA in stoichiometry, composition, and crystallinity, as well as in other physical and mechanical properties, as shown in Table 35.7. Biological apatites are usually Ca deficient and are always carbonate substituted (COs) " for (P04). For... 

Plaque that is not removed from the teeth becomes calcified from minerals in the saliva. The calcified plaque is known as tartar. It is possible to control tartar buildup by using toothpastes containing sodium pyrophosphate (Na P20y), which interferes with the mineral crystallization that causes tartar buildup. Beneath the gum line, tartar is a special problem because its presence makes it easier for plaque to grow, which irritates gum tissue and allows the gum to become diseased. Only a dentist or oral hygienist can remove tartar from beneath the gum line. By keeping teeth free from plaque and from prolonged contact with the acids produced by plaque bacteria, we can preserve the hard, stonelike enamel of the tooth. 

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