Tooth wear abrasion

Moreover, it has been speculated that the pellicle layer protects the tooth surface against abrasive damage and excessive tooth wear [86, 87], However, systematic investigations on the effect and influence of the salivary pellicle on tooth wear are lacking. 

The term tooth wear is commonly used to describe the loss of tooth hard tissue due to non-carious causes [1], This encompasses a variety of both chemical and mechanical causes of both intrinsic and extrinsic origin. The term tooth wear is preferred over some of the more precise definitions of individual hard tissue loss mechanisms, because it acknowledges the fact that wear is usually a multifactorial process one mechanism may dominate, but the overall wear is commonly due to the interaction between two or more wear mechanisms. In dentistry, the terms erosion, abrasion, attrition and abfraction are widely used to describe particular mechanisms of hard tissue loss. 

The mechanisms of tooth wear fall into two distinct types those of chemical origin (e.g. erosion) and those of physical origin (e.g. abrasion, attrition). In any individual, both chemical and physical insults to the tooth hard tissue will be present in some form or other, so tooth wear is the combined effect of these insults. Despite the clear definition of a number of distinct tooth wear mechanisms, it is uncommon to find a single wear mechanism present in the... 

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. 

A topic of increasing interest is tooth wear. Chapter 4 describes recent research on the influence of dental product use, diet and other natural factors, and the inter-relationship between abrasive wear and chemical erosion. After describing the various physical and chemical mechanisms implicated in tooth wear, the author discusses the laboratory, in situ, and clinical approaches used to investigate the condition, illustrated with selected examples. 

Dental abrasives range in fineness from those that do not damage tooth stmcture to those that cut tooth enamel. Abrasive particles should be irregular and jagged so that they always present a sharp edge, and should be harder than the material abraded. Another property of an abrasive is its impact strength, ie, if the particle shatters on impact it is ineffective if it never fractures, the edge becomes dull. Other desirable characteristics include the abiUty to resist wear and solvation. 

A property not listed in Table 5.14, but which is of paramount importance to this application, is wear rate. Wear rate was described briefly in Section 8.2.2, and those concepts apply here as well. As it applies to tooth enamel, abrasive wear occurs by fracture or chipping of the enamel, chemical erosion, which may arise due to acidic medications or drinks, dietary oxalate, or high oral hydrogen ion concentrations as a result of disease, physical erosion, or abrasion, which arises due to idiopathic mechanisms, dentrifices, toothbrushes, or abrasive diets. For example, the wear rate of enamel has been measured at about 10 ttm/hour due to brushing with a toothbrush and toothpaste for 86,400 strokes [7],... 

Attrition is the mechanical removal of hard tissue by direct contacts between teeth (either natural or restored) with no foreign substance intervening [5]. This mechanism causes wear by tooth-tooth contacts as well as by tooth-restoration, and indeed restoration-restoration contacts. The action of mastication and bruxism are known causes of attrition. In the field of tribology, the term abrasion refers to the loss of material from a surface by sliding, rubbing or scratching. Two-body abrasion refers to abrasion caused by two contacting surfaces in relative motion, i.e. the mechanism in dentistry that is described as attrition. Three-body abrasion refers to abrasion caused by surfaces in... 

Several studies report the use of replica techniques to assess abrasion in situ [45, 48], This methodology has also been successfully applied in vivo (see previous section). In this case, the wear is assessed using optical or interference microscopy. A drawback of this approach is that the production of replicas and positive copies inevitably provides a source of error and reduces the ability to measure small changes in tooth surface profile. 

However, this view has been challenged. For example, Lee and Eakle [77] suggested that they arise from a combination of factors, of which occlusal stress is one, but with abrasion and erosion also playing a part. Similarly, Spranger [78] has proposed a combination of factors in the development of cervical lesions, and that the phenomenon is related to the tooth anatomy, occlusion and parafunction, all of which contribute to elastic deformation forces at the neck of the tooth and which are augmented by wear phenomena [78],... 

The rapid wear of the edges which occurs with straight-faced hammer mills when used at low gap settings is avoided by the circular shapes of the hammers (alternately toothed and plain) that are free to move around on their retaining pins. The mills are best suited for friable coals otherwise, excessive abrasive wear occurs,... 

The biomaterial must also demonstrate special abrasion properties that stand up to the oral environment. The most favorable properties are those demonstrated by natural teeth. If the surface of a glass-ceramic is too hard for example, it could dam e the antagonist tooth. However, if the biomaterial is too soft compared with natural dentition, it would wear too easily. Comprehensive tests simulating the actual oral conditions have been conducted in a mastication simulator. Heinzmann et al. (1990) and Krecji et al. (1993) were the first to show that the IPS EMPRESS glass-ceramic demonstrates favorable abrasion properties corresponding to those of natural teeth. Subsequent studies have confirmed these findings. It is very likely that this... 

Wear characteristics are a particularly important property of dental materials, as these materials should not damage natural teeth. Some dental ceramics have been shown to be highly abrasive to antagonist natural tooth structure. Sorensen et al. (1999) examined this issue in the course of a six-month clinical study. Eight three-unit premolar bridges (of pressed glass-... 

Other tool wear problems include heat, deflection, and abrasion. High cutting temperatures sofl en chips, which tend to dog and load milling cutters. Deflection of thin parts and slender milling cutters promotes rubbing and adds heat. Abrasive oxide sxirfaces on titanium can notch the cutter at the depth-of-cut line. When forging scale is present, the nose of each tooth must be kept below the scale to avoid rapid tool wear. 

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