Tooth structure

Mammalian teeth are Nature s well-designed functional gradient composites (FGC) consisting of a top layer of hard and inert enamel, underlain by dentin, a less mineralised but more resilient and vital hard connective tissue formed from 

Property Cortical bone Cancellous bone Articular cartilage Tendon 

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Select a bit with enough gage tooth structure so that the gage structure will not round off before the inner-tooth structure is gone. 

The lack of adhesion of available filling materials to tooth structure is considered as one of their shortcomings. A solution to this problem would indeed represent a milestone in dentistry. 

Figure 5.20 The effect of a citric acid solution on tooth structure (a) enamel surface before application, (b) enamel surface after application showing etching, (c) dentine surface before application, (d) dentine surface after application showing the opening-up of the dental tubules (Powis et al, 1982).

Smith, D. C. (1975). Approaches to adhesion to tooth structure. In Silverstone, L. M. Dogson, I. L. (eds.) The Acid Etch Technique, pp. 119-38. St Paul, Minnesota North Central Publishing Company. 

R.L. Erickson, E.A. Glasspole, Bonding to tooth structure A comparison of glass-ionomer composite resin systems, J. Esthet. Dent. 6 (1994) 227-244. 

Caries involves the actual demineralization and destruction of tooth structure. 

The most common oral condition and dental emergency is dental caries, which is a destructive disease of the hard tissues of the teeth due to bacterial infection with Streptococcus mutans and other bacteria. It is characterized by destruction of enamel and dentine. Dental decay presents as opaque white areas of enamel with grey undertones and in more advanced cases, brownish discoloured cavitations. Dental caries is initially asymptomatic and pain does not occur until the decay impinges on the pulp, and an inflammation develops. Treatment of caries involves removal of the softened and infected hard tissues, sealing of exposed dentines and restoration of the lost tooth structure with porcelain, silver, amalgam, composite plastic, gold etc. 

Lack of adhesion of a dental restoration to tooth structure results in microleakage at tooth-restoration interface. This occurrence can result in discoloration at the margin of the restoration, or in the formation of caries. Occlusal forces on the restoration and differences between the coeffidents of thermal expansion of the cement and tooth material can lead to leakage. In addition, oral fluids and moisture may affect the adhesion. Microleakage of composite resin restorations has been reviewed by Ben-Amar [233]. Microleakage is not as serious a problem with glass-ionomer cements as it is with resin-based restorative materials, due to reduced polymerization shrinkage [234]. 

Finally, amalgam approximates many of the properties required for replacement of tooth structure. 

Amalgam is aesthetically unattractive compared to new materials. It has a metallic color that does not reproduce the natural appearance of the ce-ramo-organic tooth structure. The release of metallic ions from the amalgam restoration also can discolor the neighboring tooth structure [19]. 

The demand for aesthetic dental restorative materials continues to increase and may be the most important criterion for the promising future of the aesthetic polymeric composite resins. As the physical, mechanical, and wear properties of these materials improve, their use in dentistry will expand. The acid-etching of dental enamel [20] and dentin bonding procedures [21] will allow for conservative cavity preparation and the preservation of healthy tooth structure. 

A number of mechanical properties have been studied that may affect the clinical success of dental composite restorative materials. Among these are diametral tensile strength (DTS), flexural strength, fracture toughness, elastic modulus, hardness, and fatigue resistance. The mechanical properties should approximate those of tooth structure [183], but correlation of clinical success to any of these properties is limited. 

Thermal expansion differences exist between the tooth and the polymer as well as between the polymer and the filler. The tooth has a thermal expansion coefficient of 11 x 10-6/°C while conventional filled composites are 2-4 times greater [63, 252], Stresses arise as a result of these differences, and a breakdown between the junction of the restoration and the cavity margin may result. The breakdown leads to subsequent leakage of oral fluids down the resulting marginal gap and the potential for further decay. Ideal materials would have nearly identical thermal expansion of resin, filler, and tooth structure. Presently, the coefficients of thermal expansion in dental restorative resins are controlled and reduced by the amount and size of the ceramic filler particles in the resin. The microfilled composites with the lower filler loading have greater coefficient of thermal expansions that can be 5-7 times that of tooth structure. Acrylic resin systems without ceramic filler have coefficients of thermal expansion that are 9 times that of tooth structure [202-204, 253],... 

An additional thermal property of interest is thermal diffusivity. The dental pulp sensory system is extremely sensitive to changes in temperature. These sensory inputs are interpreted only as pain. Metallic restorations of deep carious lesions of the tooth frequently need to have a low thermal conductor placed beneath them to avoid causing pulpal pain. The thermal diffusivity of composite varies from approximately that of tooth structure (0.183 mm2/s) to twice that value [204, 254], Metallic restorations of concern have diffusivities at least an... 

Dental composites containing thermally labile components, (IV) and (V), were prepared by Kalgutkar et al. (5) and used for reducing bond strength of orthodontic appliances that were adhered to tooth structures. 

Trauma. Accidental or deliberate damage to the tooth structure. 

Teeth fulfill very specific functions and it can be safely assumed that the tooth structure is finely tuned for this purpose. The dentin structure is clearly anisotropic, with all the mineralized fibrils being located on one plane, and all the tubules oriented perpendicular to this plane. It is therefore most surprising that in terms of microhardness, dentin is isotropic. This has recently been confirmed in a careful study in which root dentin microhardness was measured at the same precise location in three orthogonal directions [33],... 

Odontoblasts more or less columnar cells on the outer surface of the pulp of a tooth specialized cells that contribute to many aspects of tooth structure and function. They give rise to the dentine matrix that underlies the enamel of a tooth Otoliths earstones, are small calcareous structures found in the head of all bony fishes (other than sharks, rays, and lampreys)... 

A cavity surface from which decayed material has been removed and which has been rinsed and dried resembles a loosely held brush-heap of debris held electrostatically to sound tooth structure. 

Acrylic resins are the materials of choice for almost all dental applications wherever synthetic plastics are favored for the restoration of missing teeth or tooth structures. This is not surprising because polymers derived from methacrylate esters fulfill most requisites of a restorative adequate strength, resilience and abrasion resistance dimensional stability during processing and subsequent use translucency or transparency simulating the visual appearance of the oral tissue that it replaces satisfactory color stability after fabrication resistance to oral fluids, food or other substances with which it may come Into contact satisfactory tissue tolerance low toxicity, and ease of fabrication into a dental appliance. 

Radioactive Strontium. Osteonecrosis was reported for 2-day-old rats that were injected intraperitoneally with 2 mCi 90Sr/kg of body weight (Hopkins and Casarett 1972). In weanling rabbits, injection of 600 pCi 90Sr/kg resulted in increasing cell death of differentiating odontoblasts and pulp cells of immature teeth and disordered tooth structure (Rushton 1963). Mature teeth in the same animal, or teeth in adults injected at the age of 3 years or older, were not affected as severely. 

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