Teeth, demineralization

The principal commercial use of stannous fluoride is in toothpaste formulations and other dental preparations, eg, topical solutions, mouthwash, chewing gum, etc, for preventing demineralization of teeth (21—23) (see Dentifrices). 

In the course of dentin caries, both demineralization and reactions with the organic matrix take place. Matrix reactions include proteolysis and covalent modifications. From the introduction (Chapter 2) and the review on discoloration in caries (Chapter 3), it becomes clear that there are still few reports on the effect of matrix modifications on dentin caries. In Chapters 2, 4, and 5, the investigations were aimed at filling the information gap concerning the effect of reactions of dentin matrix on caries. To this end, degradation and modification of dentin were studied in demineralized specimens in vitro. In addition, specimens placed in dentures in situ and caries lesions in extracted teeth were analysed for modifications. 

Recently, Yekkala et al. [144,145] have proposed an HPLC method with fluorescence detection. The method involves a rather laborious sample preparation due to the peculiar nature of the substrate involved (teeth), including pulverization, demineralization, hydrolysis of dentin and derivati-zation with o-phthaldialdehyde and A-acetyl-L-cysteine in order to obtain the enantioseparation of aspartic acid. Using a similar procedure, Benesova et al. [146] found that, in comparison with GC, HPLC provides shorter analysis time and higher sensitivity. 

Calcium is critical to your diet as you grow older. It may be too late for it to do much for your teeth, but you should do what you can to maintain strong bones. If you don t get enough calcium, the body secretes a hormone that causes the needed calcium to be taken from your bones. This process, called demineralization, causes bones to become porous. The medical word for this is osteoporosis. 

The amino acid composition of the protein portion of a 2-hour pellicle acquired in vivo on human teeth was the subject of a communication by Sonju and Rolla (13). Their data (Table I) are significant because, unlike previous studies in which pellicle films were obtained by acid demineralization of tooth enamel, their pellicle preparation was removed by careful scaling only. No significant differences were observed in findings for various teeth, an observation that supports selective adsorption... 

Because these products offset mineralization, there has been concern over demineralization of teeth. All manufacturers have addressed this issue and have reported that this has not been a problem, probably because of the positive effect of fluoride on remineralization of dentin and enamel. 

Dental caries is a common chronic disease in which contact between teeth, food, and bacteria is involved. The major bacteria involved are believed to be Streptococcus mutans and S. sobrinus, although several Other types of bacteria are involved. Three stages have been outlined in caries adherence of bacteria to the teeth, formation of glycocalyx due to synthesis of a sticky glucan by the action of the bacterial enzyme glucosyl transferase on sucrose, and accumulation of plaque, which is a biofilm. In the dental plaque, there is continuing acid production by the bacteria, which are able to metabolize carbohydrates in acid medium, and the acid demineralizes the enamel of the teeth. 

White DJ The application of in vitro models to research on demineralization and remineralization of the teeth. Adv Dent Res 1995 3 175-193. 

To make the white spot lesions, human premolars were coated with nail polish except for a 5-mm square on their buccal surfaces. This ensured that demineralization always occurred at a specific location. The samples were then immersed in 200 ml methyl cellulose gel with 200 ml lactic acid solution (pH 4.6) poured on top, but separated by a sheet of filter paper. The teeth were stored in this solution at 3 7°C for 14 days to allow the lesions to develop. After removal from the gel, the teeth were washed and sectioned through the center of the lesions to enable the cross-section of each lesion to be viewed. The two cross-sections created for each lesion were then mounted in a low temperature cure epoxy and polished to an optical finish using 1/4-micron grit (diamond paste). 

Salivary a-amylase is a protein that contributes to the enamel pellicle (Sect. 12.1.3). More importantly, it attaches bacteria, especially streptococci, to teeth surfaces. Thus, following a meal rich in carbohydrates, amylopectin, amylase, and glycogen are digested to maltose at the surface of many oral bacteria. The maltose is taken into the cytosol by a phosphoenolpyruvate transporter homologous to the fructose transporter of S. mutans. Within these bacteria, the maltose is digested to two molecules of glucose 6-phosphate and metabolized to lactic acid. Thus, twice as much acid is produced per mole maltose than per mole sucrose and it contributes to tooth demineralization even if less sucrose is consumed. 

Teeth are subjected to a continuous demineralization/mineralization process and, therefore, the apatite in enamel is modified in response to the microenvironment around the teeth. Applications of fluoride through toothpaste and drinking water result in the exchange of F for OIT in hydroxylapatite to form the more stable and acid resistant fluorapatite. Also, development of caries lesions is decelerated as dissolution removes carbonate and magnesium from the outer enamel layer, which further stabilizes the enamel apatite (Le Geros 1999). 

The removal of caries is essential when repairing a tooth damaged by decay. However, when caries is deep this may present a problem, as continued caries removal to prepare the cavity fully may lead to exposure of the pulp. Rather than exposing the pulp in this way, with the risks involved in such a procedure, an alternative approach is to leave the caries-affected demineralized dentine in the region directly adjacent to the pulp and to cover the whole of the affected zone with a cavity liner. This procedure is termed indirect pulp capping [1], and it has been shown to be as successful as restoring teeth conventionally with complete caries removal [26-28]. 

Hydroxylapatite is the mineral in teeth and bone that crystallizes between the collagen fibers and gives strength. When a fluoride ion displaces hydroxyl ions, it becomes fluorapatite. Fluorapatite is even stronger and prevents tooth decay by slowing demineralization and speeding remineralization. 

Teeth enamel is hydroxyapatite [Ca3(P04)30H]. When it dissolves in wate (a process called demineralization), it dissociates as follows ... 

Unfortunately, bacteria in plaque (resulting from not brushing) shift the equilibrium toward demineralization (shown in the figure), and a cavity can begin to form. Scientists realized that fluoride encourages remineralization in teeth by replacing hydroxyl ions in nature s calcium phosphate (hydroxyapatite). The substitution changes the hydroxyapatite to fluorapatite, which is more acid resistant. 

Teeth EDTA has been used to irrigate root canals in dentistry and can cause canal wall erosion, but only after prolonged use of 5.25% sodium hypochlorite (NaOCl) as the initial irrigant the associated reduction in dentine flexural strength and increased tooth surface strain might make teeth more susceptible to vertical fracture [33 ,34 ]. The effects are not attributable to demineralization [35 ]. 

Experiments have shown that the presence of food or food residues in the oral cavity is not necessary for plaque formation since the amount of plaque deposited on the teeth of rats, dogs and monkeys, fed by stomach-tube was about the same as in normally fed animals. Furthermore, it was found that animals fed a cariogenic diet by stomach-tube failed to develop caries. It appears therefore that a carious attack on the teeth must result from interaction between the oral bacteria and the food, and only those bacteria which (1) can adhere effectively to the tooth surface and (2) produce appreciable amounts of acid will cause demineralization and the types of the bacteria present and their metabolic activities depend on the properties of plaque. 

Teeth are protected by a hard enamel layer about 2 mm thick that is composed of a mineral called hydroxyapatite fCasfP04)30H]. Demineralization is the process by which hydroxyapatite dissolves in the saliva. Because phosphates of alkaline earth metals such as calcium are insoluble [W Section 4.2, Table 4.3], this process happens only to a veiy small extent ... 

Calcification proceeds in the adult as well as during growth, and an adequate supply of calcium and phosphorus is thus essential throughout life to a healthy skeletal structure, including teeth in which mineral turnover proceeds after growth at a reduced rate. Certain factors, therefore, which influence absorption or retention of these elements can bring about demineralization of bone in some conditions. Their effects are discussed in the following sections. 

A loss of calcium from the bones and teeth which may occur when (1) the diet contains too little calcium to replace the daily losses of the mineral in the urine and the stool, or (2) overactivity of the parathyroid glands causes demineralization. 

Fiuoride. Fluoride is the most effective agent available for strengthening tooth resistance to acid demineralization. The mechanism by which fluorine increases caries resistance of the teeth is not fully understood. However, it appears that crystals of fluoroapatite can replace some of the calcium phosphate crystals of hydroxyapatite that are normally deposited during tooth formation, and that it may also replace some of the carbonate normally found in the tooth. Apparently these fluoride substances are more resistant to mouth acids. Fluorine may also inactivate oral bacterial enzymes which create acids from carbohydrates. 

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