Dentine

When freshly mixed, the carboxyHc acid groups convert to carboxjiates, which seems to signify chemical adhesion mainly via the calcium of the hydroxyapatite phase of tooth stmcture (32,34—39). The adhesion to dentin is reduced because there is less mineral available in this substrate, but bonding can be enhanced by the use of minerali2ing solutions (35—38). Polycarboxylate cement also adheres to stainless steel and clean alloys based on multivalent metals, but not to dental porcelain, resin-based materials, or gold alloys (28,40). It has been shown that basic calcium phosphate powders, eg, tetracalcium phosphate [1306-01-0], Ca4(P0 20, can be substituted for 2inc oxide to form strong, hydrolytically stable cements from aqueous solution of polyacids (41,42). 

Calcium Chelates (Salicylates). Several successhil dental cements which use the formation of a calcium chelate system (96) were developed based on the reaction of calcium hydroxide [1305-62-0] and various phenohc esters of sahcyhc acid [69-72-7]. The calcium sahcylate [824-35-1] system offers certain advantages over the more widely used zinc oxide—eugenol system. These products are completely bland, antibacterial (97), facihtate the formation of reparative dentin, and do not retard the free-radical polymerization reaction of acryhc monomer systems. The principal deficiencies of this type of cement are its relatively high solubihty, relatively low strength, and low modulus. Less soluble and higher strength calcium-based cements based on dimer and trimer acid have been reported (82). 

The calcium chelate cements are limited to the use of a cavity liner. They may be placed directly over an exposed tooth pulp to protect the pulp and stimulate the growth of secondary dentin, or used as a therapeutic insulating base under permanent restorations. The high alkalinity and high solubihty of these materials prohibits use in close proximity to soft tissues or in contact with oral fluids. 

Once a metal surface has been conditioned by one of the above methods, a coupling agent composed of a bifimctional acid—methacrylate similar to a dentin adhesive is appHed. This coupling material is usually suppHed as a solvent solution that is painted over the conditioned metal surface. The acidic functional group of the coupling molecule interacts with the metal oxide surface while the methacrylate functional group of the molecule copolymerizes with the resin cement or restorative material placed over it (266,267). 

Dentifrices are also vehicles for agents that alleviate dentinal hypersensitivity. Among the materials that have given positive results in clinical tests are potassium nitrate [7757-79-1] (5%) and strontium chloride [10476-85-4] (10%). 

Zatm-bein, n. dentine, -blei, n. (Bot.) lead-wort. -biirete, /. tooth brush,... 

Resorption The loss of substance through physiological or patholigical means, such as loss of dentin and cementum of a tooth. 

Horton MA, Taylor ML, Arnett TR et al (1991) Arg-Gly-Asp (RGD) peptides and the anti-vitronectin receptor antibody 23C6 inhibit dentine resorption and cell spreading by osteoclasts. Exp Cell Res 195 368-375... 

But potassium nitrate is also used in toothpastes that are formulated to make teeth less sensitive to pain. As gums recede and the tooth root dentin becomes exposed, teeth can become hypersensitive to hot or cold foods. Potassium nitrate interferes with the transmission of pain signals in the nerves of the teeth. 

The 5 C values of bone and dentine collagen extracted from a mandible and a lower first molar from a Siberian wolf are identical (Table 4.2). On the contrary, the 5 N value of bone collagen is clearly lower (8.2%o) than the 8 N value of dentine collagen (9.8%o). 

The 5 N enrichment in dentine collagen relative to bone collagen in species with definite tooth growth is observed in samples from Marillac, Kent s Cavern, Aldene and Mialet caves (Fig. 4.10). The highest 8 N values are measured for deciduous teeth in fossil samples (Bocherens et al. 1994 Fizet et al. 1995). No enrichment is observed between dentine and bone collagen in horses (Bocherens et al. 1995b Fizet et al. 1995). 

Figure 4.10. Differences in 6 N values between bone and dentine collagen from Pleistocene and recent mammals. Isotopic abundances are from Bocherens et al. (1994, 1995b) and this paper.

The properties described above have important consequences for the way in which these skeletal tissues are subsequently preserved, and hence their usefulness or otherwise as recorders of dietary signals. Several points from the discussion above are relevant here. It is useful to ask what are the most important mechanisms or routes for change in buried bones and teeth One could divide these processes into those with simple addition of new non-apatitic material (various minerals such as pyrites, silicates and simple carbonates) in pores and spaces (Hassan and Ortner 1977), and those related to change within the apatite crystals, usually in the form of recrystallization and crystal growth. The first kind of process has severe implications for alteration of bone and dentine, partly because they are porous materials with high surface area initially and because the approximately 20-30% by volume occupied by collagen is subsequently lost by hydrolysis and/or consumption by bacteria and the void filled by new minerals. Enamel is much denser and contains no pores or Haversian canals and there is very, little organic material to lose and replace with extraneous material. Cracks are the only interstices available for deposition of material. 

One further difference between the tissues should be noted briefly—that of turnover—which holds implications for the nature of the isotopic signal recorded and its interpretation. Bone is constantly resorbed and reformed during life, i.e., it turns over , whereas enamel and dentine do not, although secondary dentine can be later accreted. Enamel and dentine form during a discrete period in the individual s life. This means that carbon isotope dietary signals in bone, for both collagen and apatite, reflect diet integrated over years, whereas those in enamel and dentine increments reflect diet at time of formation. 

G. Dentine, K. Edwards, M. Jackson, D. Kantor, M. Kelley, K. Murphy, D. Valley, M. Valley, and M. Wilhite for donating or helping obtain teeth for analysis. 

Stuart-Williams, H.L.Q. and Schwarcz, HP. 1997 Oxygen isotopic determination of climatic variation using phosphate from beaver bone, tooth enamel, and dentine. Geochimica et Cosmochimica Acta (iV. 2539-2550. 

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