Enamel, interaction with

Food is taken into the buccal cavity, where it is masticated by the teeth and mixed with saliva from three pairs of salivary glands. It moistens the food and dissolves some molecules enabling them to interact with the taste receptors on the tongue. Saliva contains Na% Cl and HCOs ions and a protein, mucin, which is a component of mucus that lubricates the chewed food on its way down the oesophagus. The pH of saliva is about 7.8, which neutralises acid formed by bacteria in the mouth this protects tooth enamel... 

Tributoxyphenylsilane is produced when phenyltrichlorosilane interacts with butyl alcohol in the 1 3.3 mole ratio the synthesis is carried out in enameled apparatus 7. Phenyltrichlorosilane (the 196-202 °C fraction, the chlorine content is 49-50.5%) self-flows from batch box 2 into pre-dried apparatus 1. The agitator is switched on, and anhydrous butyl alcohol is sent from batch box 3 at such speed that the temperature in the reactor does not exceed 30-35 °C. After the whole alcohol has been introduced, the reactive mixture is heated to 90-100 °C (gradually, for 7-8 hours). At this temperature and agitation the mixture is held for 7-10 hours and sampled for the chlorine content, which should not exceed 1.5%. The obtained product is cooled to 80-85 °C by sending water into the jacket of the reactor. The hydrogen chloride released in the reaction is withdrawn into a water-flushed hydroejector and in the form of weak hydrochloric acid sent to biochemical purification. 

Ruan et al. [97] were unable to detect IgA amongst substances adsorbed onto enamel and cementum from saliva in vivo. This is perhaps not surprising since the mode of action of the antibodies is more likely to involve specific interaction with bacteria. 

Enamel mineral has many large hydroxyapatite crystals, whereas bone has many small ones with numerous vacancies and substitutions. These differences increase the elasticity of bone compared with enamel and promote its interactions with the surrounding collagen. Recently, a tightly bound hydration shell that fills a porous collagen-apatite junction was discovered around normal bone crystals. The water-filled pores are normally immobile, but repeated stresses cause the water to leak out from between the mineral and collagen. The drying increases mineralization and crystal formation, which may explain the decreased elasticity of bones with age. 

Saliva - Enamel Interactions. Enamel becomes adsorbed with a bacteria-free film almost instantaneously after contacting saliva. ) and is constantly renewable if... 

Glass-ionomers not only release ions, but are capable of taking them up. Studies have shown that cements exposed to natural saliva take up calcium and phosphate ions, and develop a surface of significantly increased hardness [121]. Also, when used as pit and fissure sealants, they interact with saliva to form a substance with increased content of calcium and phosphate that is considerably more resistant to cutting with a dental drill than the original material. Under these circumstances, the cement had become transformed into a material with enamel-like optical and mechanical properties [122]. This observation is the basis of the development of glass-ionomer type materials with even further enhanced bioactivity, the so-called glass carbomers, which are discussed in Chapter 8. 

There are a certain number of options to control and reduce dental caries, the biggest problem in tooth care. The use of fluoride salts is one of the most effective methods to prevent or slow down demineralization that causes tooth decay [16,17]. The action of fluoride can be explained by its antimicrobial action, its interaction with enamel to form a fluorinated hydroxyapatite compound (hydroxyfluorapa-tite or fluorapatite Ca5(P04)3F) by substitution of an hydroxyl ion in hydroxyapatite Ca5(P04)3(0H), which is more resistant to add than enamel on its own, and its repairing effect by formation of calcium and phosphate, which ranineralize the tiny lesions in which caries begin. 

Kava pyrones are potent, centrally acting skeletal muscle relaxants. They act as hypnotics, antipyretics, sedatives, local anaesthetics, smooth muscle relaxants and antifungal agents. No interaction with benzodiazepine drugs or with moderate consumption of alcohol occurs, nor does kava impair mental alermess. However, continually chewing the root can destroy tooth enamel and eventually becomes habit forming (Bone 1994). 

Figure 34.2 Cell-surface interactions. The total energy of interaction (I) of a negatively charged bacterial cell with a negatively charged pellicle-covered enamel surface is shown as a function of separation distance in an aqueous solvent of moderate ionic strength. The cell is temporarily held in an energy minimum about 10 nm from the surface and is subsequently stabilized in this position by polymers which specifically interact with each surface. The polymers could be an integral component of the cell structure or be produced by bacterial metabolic activity or be a salivary component. They could also promote bacterial cell-cell interactions in the same manner. Key -( -[ specific recognition sites ...

Alloys suitable for castings that ate to be bonded to porcelain must have expansion coefficients matching those of porcelain as well as soHdus temperatures above that at which the ceramic is fired. These ate composed of gold and palladium and small quantities of other constituents silver, calcium, iron, indium, tin, iridium, rhenium, and rhodium. The readily oxidi2able components increase the bond strength with the porcelain by chemical interaction of the oxidi2ed species with the oxide system of the enamel (see Dental materials). 

The precise nature of the adhesion of the polyelectrolyte cements to untreated dental enamel and dentine has yet to be established. The earliest theory was due to Smith (1968) who speculated that the polyacrylate chains of the cement formed a chelate with calcium ions contained in the hydroxyapatite-like mineral in enamel and dentine. Beech (1973) considered this unhkely since it involved the formation of an eight-membered ring. Beech studied the interaction between PAA and hydroxyapatite, identified the formation of polyacrylate and so considered that adsorption was due to ionic attraction. 

Of particular note is the importance of erosion in accelerating tooth wear. The softening of enamel and dentine surfaces by erosive attacks from acid renders the surface extremely susceptible to mechanical attacks [9]. Abfraction is also an example of interaction between wear mechanisms, where abrasion and erosion may act in combination with cyclic loading and unloading to produce an overall wear effect. 

Whilst the use of enamel and dentine as test substrates is widespread, they are complex materials to work with due to the natural variability both within and between specimens. A number of authors have examined alternative materials, which have similar mechanical properties to enamel and dentine, to use as test substrates. Acrylic [19, 20] and synthetic hydroxyapatite [21] have been proposed as suitable materials for abrasion testing, where mechanical effects dominate. These materials have several advantages since they are available as relatively large, smooth samples and exhibit better intra- and inter-sample reproducibility than their natural counterparts. This may, therefore, give better discrimination between test products for formulation development. However, the use of natural enamel and dentine is preferred, particularly for studies that aim to understand interactions between toothpaste products and tooth hard tissues. Other methods for assessing toothpaste abrasivity to hard tissues include gravimetry [22], scanning electron microscopy [23] and laser reflection [24]. 

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