Dental enamel, hardness

Cement, dentin, and enamel are bone-like substances. The high proportion of inorganic matter they contain (about 97% in the dental enamel) gives them their characteristic hardness. The organic components of cement, dentin, and enamel mainly consist of collagens and proteoglycans their most important mineral component is apatite, as in bone (see above). 

Decoction. A preparation made by boiling a plant part in water a boiled extract. Dental enamel. A hard, thin, transcluent layer of calcified substance that envelops and protects the dentin of the crown of the tooth. It is the hardest substance in the body and is almost entirely composed of calcium salts. 

Flard tissue engineering can include structures such as bone, and several examples of bone tissue engineering are presented in the sections above, other hard tissues that can potentially be repaired by self-assembling peptides include human dental enamel. Kirkhan and colleagues (2007) used self-assembling anionic peptides named Pn-4 to promote... 

Phosphates are found in soft organic tissues as phosphate esters, and in hard tissues, notably bones and teeth, as solid calcium orthophosphates see Biomineralization). Hard tissues are composites of Apatite and an organic matrix collagen in bone, dentin, and dental cement, and keratin in dental enamel. The Apatite phases are defective with Ca/P ratios of 1.6-1.8 and can incorporate other cations (Na+, K+, Mg +) or anions (F , d , COs ", citrate). 

Polycrystalline hydroxyapatite has a high elastic modulus (40 to 117 GPa). Hard tissue such as bone, dentin, and dental enamel are natural composites which contain hydroxyapatite (or a similar mineral), as well as protein, other organic materials, and water. Enamel is the stiffest hard tissue, with an elastic modulus of 74 GPa, and contains the most mineral. Dentin ( = 21 GPa) and compact bone E = 12 to... 

Nixon and others (652,653,654,655,657,659) have investigated the concentrations of Mn, Sb, Hg, Cu and other elemental species in the enamel from human teeth. As a result of some of this work, Nixon and Smith (658) have shown that submicrogram amounts of Hg could be a hazard in dental surgery. Hadjimarkos (369) indicates that the selenium content of human milk could have a possible effect on dental caries. In another study Sairenji et al. (795) investigated the effect of arsenic on the hard tissues of arsenic devitalized teeth. Stubbins and Fremlin (923) used charged-particle activation analysis to estimate the distribution of C, Ca, and P in dental enamel. 

The biomaterials will be in contact with different tissue - enamel, dentine and hard bone tissue and soft tissue - as well as other biomaterials contact surfaces. The actual contact zone developed depends on a combination of the discussed mechanisms and the surtoimding tissue. The latter varies from a ceUular-free high content apatite tissue in the case of a dental enamel, via dentine to a bone structure with cellular and body liquid contact. Both a pure nanostructural, mechanically controlled integration, and a chemically induced integration seem plausible. The figirtes 4-5 below show the nanostmeture of phases and porosity formed. 

Dental enamel is a unique biological system that provides a hard surface for the teeth, and enables them to reduce food to particles sufficiently small for effective attack by the digestive enzymes. Provided that it remains free from disease, human enamel can withstand a lifetime of crushing work without becoming fractured or completely worn away. Enamel is capable of performing this function only because of its most abundant constituent, hydroxyapatite, which gives it a hardness intermediate between that of iron and carbon steel. 

Human teeth are also composed primarily of biological apatite. The outer two layers of a human tooth consist of enamel on the outside and dentine underneath that. Dentine and bones are very similar in composition and mechanical properties, but enamel is almost pure hydroxyapatite, Ca5(P04)30H. Dental enamel is the hardest part of the human body. In addition, the hardness of dental enamel is enhanced by the presence of fluoride ions in place of the hydroxides. (Thus we see... 

Human studies and rodent experiments demonstrating the potential for CCM to reduce the risk of tooth enamel erosion are included in the patent of Andon et ah (1992). One experiment assessed rats provided with soft drink, soft drink with added CCM, or water as their only source of fluids for 21 days. Based on a predefined erosion scale, the average extent of dental erosion compared to the unfortified soft drink was 4.5 and sixfold less in water and soft drink + CCM, respectively. Another study used the Vickers hardness measurement to assess the mean ( SEM) reduction in surface hardness of human enamel specimens (n = 8 per group) immersed for 60 min in 15 ml of OJ (-101 8.7), OJ + CCM (0.9 5.8), grapefruit juice (-130 12.7), grapefruit juice + CCM (2.8 6.4), or... 

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. 

For testing dental restorative materials, many regimes exist that use similar principles to those described for assessing toothpaste abrasivity. These tests may be conducted under conditions of two-body or three-body wear [25], i.e. focussing either on attrition or abrasion. Two-body tests for restorative materials either use human enamel [26] or a hard material, such as alumina [27] or steatite [28], as the abrader. For three-body tests, an abrasive medium, such as toothpaste slurry [29, 30], or an abrasive food, such as rice or millet seeds [31,32], is typically used. These test methods are usually not truly representative of the oral environment rather, they are designed to assess the wear resistance of restorative materials under extreme conditions. 

Willems G, Celis JP, Lambrechts P, Braem M, Vanherle G Hardness and Young s modulus determined by nanoindentation technique of filler particles of dental restorative materials compared with human enamel. J Biomed Mater Res 1993 27 747-755. 

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. 

Teeth consist of three kinds of hard tissues (enamel, dentin, and cementum) and they attach to the alveolar bone through the periodontal ligament The dental pulp, the only vascularized tissue containing nerves, is encased in mineralized dentin. The structural integrity of tooth and periodontal tissue is a prerequisite for chewing and... 

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