Dentine composition

Figure 5.21 The laminate restoration, showing the glass polyalkenoate cement as a dentine substitute and a composite resin as an enamel substitute.

McLean, J. W., Powis, D. R., Prosser, H. J. Wilson, A. D. (1985). The use of the glass-ionomer cement in bonding composite resins to dentine. British Dental Journal, 158, 410-14. 

Good bonding was obtained to several substrates under aqueous conditions. Values obtained were 41 to 10-3 MPa to composite resins, and 9-8 to 15-6 MPa to stainless steel (Table 9.6). They were also reported as adhering to porcelain. No adhesion was obtained to untreated dentine or enamel. The cements could be bonded to enamel etched with add (3-5 MPa) and to dentine conditioned with poly(acrylic acid) (10 MPa). 

The mechanism of adhesion to various substrates has not been fully explained. Brauer Stansbury (1984b) consider that bonding to composite resins occurs by the diffusion of methacrylate polymer chains into the resin. Bonding to base metals is, perhaps, by salt or chelate bridges. Here it is significant that ZOE cements do not bond, so perhaps bonding is due to the action of free EBA on the substrate. The adhesion to porcelain is surprising. Porcelain is inert so that the attachment can hardly be chemical. Also, it would be expected that if a cement adheres to porcelain then it should adhere to untreated enamel and dentine, but this is not so. 

Teeth, the hard conical structures embedded in their jaws that vertebrate animals use to chew food, consist of two layers of compact matter surrounding a core of soft, living tissue. The inner layer is composed of dentine, also known as ivory, whose composition is similar, but not identical, to that of bone it contains less collagen and is harder than bone. The thin outer layer of the teeth, the teeth s enamel, includes even less collagen and other organic matter than dentine and is the hardest substance produced by animals (Hilson 1986a Kurten 1986b 1982). 

Preliminary bonding studies [11] to dentin treated with 3-methoxy-PIDAA or 2-carboxy-PIDAA (0.1 mol/L in aqueous acetone 1 1 mass) yielded composite to dentin mean shear bond strength values of 26.4 MPa ( 4.5 MPa) and 21.0 MPa ( 5.4 MPa), respectively, similar to the PIDAA control value of 24.2 MPa ( 6.7 MPa), where represents standard uncertainity in these measurements. 

Linde A (1989) Dentin matrix proteins composition and possible functions in calcification. Anat Rec 224, 154-166. 

In both types of lesion, the peritubular matrix appeared to be more resistant to proteolytic activity than the intertubular matrix, which may be due to a compositional difference between the matrices. In this respect, it is interesting to note that Takagi et al. (1990) found the calcification of dentin to be accompanied by the degradation of proteoglycans throughout the intertubular matrix, but not in the peritubular matrix. However, there is no evidence that there is less degradation of the peritubular than the intertubular matrix, when demineralized dentin specimens are exposed to the oral environment (Van Strijp et al., 1992). This discrepancy can be explained by the assumption that a wide variety of enzymes participates in the degradation of the dentin matrix in vivo. 

Armstrong WG (1964) Modification of the properties and composition of the dentin matrix caused by dental caries. Advances Oral Biol 1, 309-332. 

Nkhumeleni FS, Raubenheimer EJ, Dauth J, Van Heerden WFP, Smith PD and Pitout MJ (1992) Amino acid composition of dentin in permanent human teeth. Arch Oral Biol 37, 157-158. 

Crosslinked polymers are widely used as dental materials (1-31. Perhaps the most challenging application is in the restoration of teeth (4). The monomers must be non-toxic and capable of rapid polymerization in the presence of oxygen and water. The products should have properties comparable to tooth enamel and dentin and a service life of more than a few years. In current restorative materials such properties are sought using so-called "dental composites" which contain high volume fractions of particulate Inorganic fillers (5-71. However in the present article attention is concentrated on one commonly used crosslinked polymeric component, and on the way in which some of its properties are influenced by low volume fractions of fillers. 

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. 

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. 

Table 1.35 Composition and Selected Properties of Inorganic Phases in Adult Human Enamel, Dentine, and Bone...

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