Tooth surface

Gear tooth surface deterioration Low oil viscosity and/or excessive... 

Gear tooth surface deterioration Misalignment, high sliding velocity... 

Dental plaque Mass of microorganisms attached to a tooth surface. 

It is generally tme to say that, as speed increases, the oil viscosity decreases, that is, if hydrodynamic conditions exist. Relatively low viscosity oil will allow the oil to spread rapidly over the tooth surfaces before meshing and, in the case of forced lubrication, ease circulation. In the case of bath lubrication, it will eliminate the oil drag effect. 

The elements of gear teeth common to all gears are tooth surface and profile, flank, top and bottom land, crown, root and pitch circle, gear center, line of centers, pitch point, line of action, line of contact, and point of contact. Figure 57.27 labels many of the common gear tooth elements. Figure 57.28 labels the common rack tooth elements. 

Stephan, R. M. (1940). Changes in the hydrogen-ion concentration on tooth surfaces and in carious lesions. Journal of the American Dental Association,... 

Salivary flow is extremely important in the removal of many agents from the oral cavity. Human sahva has a diurnal flow that varies between 500 and 1,500 mL in the daytime to less than 10 mL of secretion at night. The rate of clearance of a drug from the oral cavity therefore is profoundly important in determining the amount of time a drug is in contact with the tooth surface. 

Chlorhexidtne is a symmetrical cationic molecule that is most stable as a salt the highly water-soluble digluconate is the most commonly used preparation. Because of its cationic properties, it binds strongly to hydroxyapatite (the mineral component of tooth enamel), the organic pellicle on the tooth surface, salivary proteins, and bacteria. Much of the chlorhexidine binding in the mouth occurs on the mucous membranes, such as the alveolar and gingival mucosa, from which sites it is slowly released in active form. 

Although chlorhexidine affects virtually all bacteria, gram-positive bacteria are more susceptible than are gram-negative organisms. Furthermore, Streptococcus mutans and Antinomies viscosus seem to be particularly sensitive. S. mutans has been associated with the formation of carious lesions in fissures and on interproximal tooth surfaces and has been identified in large numbers in plaque and saliva samples of subjects with high caries activity. 

The most conspicuous side effect of chlorhexidine is the development of a yellow to brownish extrinsic stain on the teeth and soft tissues of some patients. The discoloration on tooth surfaces is extremely tenacious, and a professional tooth cleaning using abrasives is necessary to remove it completely. The staining is dose dependent, and variation in severity is pronounced between individuals. This side effect is attributed to the cationic na-... 

D. It is due to the ability of this cation to strongly bind to tooth surfaces, requiring strong abrasives to... 

It is now known that teeth undergo a continuous process of demineralisation and remineralisation (see Table 2), which is driven by changes in the plaque composition [29]. In the presence of fermentable carbohydrates plaque microorganisms generate characteristic organic acids, that is, lactic and acetic [17], and these diffuse through the pellicle to the tooth surface and cause demineralisation [30]. Ions are then liberated from the mineral phase into this low pH liquid [31], and they diffuse outwards and re-precipitate at the surface layer of the demineralised lesion [32,33]. If this process is sufficiently rapid, there is a net loss of tooth mineral and irreversible cavity formation. 

Clinical outcome Carious lesion Healthy tooth surface... 

Fluorosis affects the enamel of the tooth, causing it to become hypominera-lised. This is detected as visual changes in the opacity, and it is only in extreme cases that this leads to an adverse appearance as mottling of the tooth surface [86]. The severity of the discolouration depends on the dose of fluoride, its duration and timing of consumption. 

More recently, it has been shown that topical fluoride preparations do not lead to fluoridation of the hydroxyapatite crystal [181]. Rather they form a calcium fluoride-like substance that is deposited onto the tooth surface and dissolves when the local pH is lowered [182]. The resulting dissolution adjacent to the tooth surface provides a source of soluble fluoride that can be incorporated into the mineral structure, and thus augment remineralisation. 

Fluoride-containing varnishes are designed to be painted onto the teeth and retained for a few hours at least, during which they release fluoride close to the tooth surface [188], Like fluoride gels, they are intended for use by dental professionals, but have the advantage that they are considered to be easy to apply. They have an acceptable taste and contain lower amounts of fluoride than gels. They contain either sodium fluoride or difluorosilane as the active ingredient. 

Several methods have been developed for quantifying dental fluorosis. The most commonly used method is Dean s index [49], which classifies fluorosis on a scale of 0 to 4 as follows class 0, no fluorosis class 1, very mild fluorosis (opaque white areas irregularly covering <25% of the tooth surface) class 2, mild fluorosis (white areas covering 25-50% of the tooth surface) class 3, moderate fluorosis (all surfaces affected, with some brown spots and marked wear on surfaces subject to attrition) and class 4, severe fluorosis (widespread brown stains and pitting). The average score of the two most severely affected teeth is used to derive the classification. Other commonly used methods to rate dental fluorosis include the Thylstrup-Fejerskov Index (TFI) [50] and the tooth surface... 

H.S. Horowitz, W.S. Driscoll, R.J. Meyers, S.B. Heifetz, A. Kingman, A new method for assessing the prevalence of dental fluorosis—the tooth surface index of fluorosis, J. Am. Dent. Assoc. 109 (1984) 37-41. 

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