Mineralization dentin

Mclnroy et al. 1985). Americium radioactivity can be measured in the teeth of rats, where it accumulates in the dental pulp of developing teeth and eventually is incorporated into the mineralized dentin (Hammerstrom and Nilsson 1970). 

The relationship between the degradation of organic matrix and dentin lesion formation has been studied both in vitro and in situ. Several authors employed matrix destruction to assess the role of the matrix in de-and remineralization. For example, Apostolopoulos and Buonocore (1966) reported facilitated demineralization of dentin at pFl<5.5 after treatment with ethylene diamine. Inaba and coworkers (1996) found that removal of matrix from dentin lesions by hypochlorite promotes remineralization, consistent with a larger crystal surface available for mineral deposition after ashing (McCann and Fath, 1958). Flypochlorite-mediat-ed destruction also increases the permeability of mineralized dentin (Barbosa et ah, 1994). 

In an in situ study, specimens combining demineralized and mineralized dentin were exposed intraorally (Van Strijp et al., 1997). No correlation was found between demineralization of the mineralized dentin and collagen degradation in the demineralized dentin. 

Affer incubafion wifh collagenase, various changes were seen. In incipienf erosive lesions formed in HAc af pH 5.0, fhree differently stained layers were observed (fig. 9A). When fhe secfions were taken from slices demineralized affer fixafion, the layer on the bottom of the lesion (1) could not be distinguished from the underlying mineralized dentin and was apparently unaffected. It was covered by a narrow and faintly stained layer of irregular thickness (2). Tubules surrounded by more intensely stained material were present in this area. The top layer (3) consisted of intensely stained material and had a uniform appearance, with a few tubules still discernible. Erosive lesions formed in HAc at pH 5.5 resembled those formed in HAc at pH 5.0, except that the top layer was absent. The depth of the lesions could be measured accurately only in buffer-treated lesions and was approximately 90 pm (pH 5.0) and 50 pm (pH 5.5). 

Fluorine is an essential element involved in several enzymatic reactions in various organs, it is present as a trace element in bone mineral, dentine and tooth enamel and is considered as one of the most efficient elements for the prophylaxis and treatment of dental caries. In addition to their direct effect on cell biology, fluoride ions can also modify the physico-chemical properties of materials (solubility, structure and microstructure, surface properties), resulting in indirect biological effects. The biological and physico-chemical roles of fluoride ions are the main reasons for their incorporation in biomaterials, with a pre-eminence for the biological role and often both in conjunction. This chapter focuses on fluoridated bioceramics and related materials, including cements. The specific role of fluorinated polymers and molecules will not be reviewed here. 

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... 

Fibrils of this latter substance within the dentine act as a scaffold for the mineral crystalhtes. These crystallites reinforce the dentine matrix and the whole structure acts as a support for the enamel. The mineralized dentine has the important biomechanical function of preventing cracks propagating from the enamel, which is very brittle, through the dentino-enamel junction into the dentine [34]. This prevents the enamel crown from fracturing when loaded. 

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... 

Zhang K, Kim YK, Cadenaro M, Bryan TE, Sidow SJ, Loushine RJ, Ling JQ, Pashley DH, Tay FR. Effects of different exposure times and concentrations of sodium hypochlorite/ethylenediaminetetraa-cetic add on the structural integrity of mineralized dentin. J Endod 2010 36(1) 105-9. 

When freshly mixed, the carboxyHc acid groups convert to carboxjiates, which seems to signify chemical adhesion mainly via the calcium of the hydroxyapatite phase of tooth stmcture (32,34—39). The adhesion to dentin is reduced because there is less mineral available in this substrate, but bonding can be enhanced by the use of minerali2ing solutions (35—38). Polycarboxylate cement also adheres to stainless steel and clean alloys based on multivalent metals, but not to dental porcelain, resin-based materials, or gold alloys (28,40). It has been shown that basic calcium phosphate powders, eg, tetracalcium phosphate [1306-01-0], Ca4(P0 20, can be substituted for 2inc oxide to form strong, hydrolytically stable cements from aqueous solution of polyacids (41,42). 

The properties described above have important consequences for the way in which these skeletal tissues are subsequently preserved, and hence their usefulness or otherwise as recorders of dietary signals. Several points from the discussion above are relevant here. It is useful to ask what are the most important mechanisms or routes for change in buried bones and teeth One could divide these processes into those with simple addition of new non-apatitic material (various minerals such as pyrites, silicates and simple carbonates) in pores and spaces (Hassan and Ortner 1977), and those related to change within the apatite crystals, usually in the form of recrystallization and crystal growth. The first kind of process has severe implications for alteration of bone and dentine, partly because they are porous materials with high surface area initially and because the approximately 20-30% by volume occupied by collagen is subsequently lost by hydrolysis and/or consumption by bacteria and the void filled by new minerals. Enamel is much denser and contains no pores or Haversian canals and there is very, little organic material to lose and replace with extraneous material. Cracks are the only interstices available for deposition of material. 

The precise nature of the adhesion of the polyelectrolyte cements to untreated dental enamel and dentine has yet to be established. The earliest theory was due to Smith (1968) who speculated that the polyacrylate chains of the cement formed a chelate with calcium ions contained in the hydroxyapatite-like mineral in enamel and dentine. Beech (1973) considered this unhkely since it involved the formation of an eight-membered ring. Beech studied the interaction between PAA and hydroxyapatite, identified the formation of polyacrylate and so considered that adsorption was due to ionic attraction. 

Although adsorbed carbonates on bone mineral and dentine can be easily removed by routine cleaning pre-treatment, the diagenetic fraction has proved more difficult and controversial. Attempts have been made to use sequential acid washing and density separation for bone, as described above, but, at present, the results are rather ambiguous. The carbonate fraction of dental enamel, however, has proved much more amenable, and significant progress... 

Bone and teeth in mammals and bony fishes all rely on calcium phosphates in the form of hydroxyapatite [Ca5(P04)30H]2, usually associated with around 5% carbonate (and referred to as carbonated apatite). The bones of the endoskeleton and the dentin and enamel of teeth have a high mineral content of carbonated apatite, and represent an extraordinary variety of structures with physical and mechanical properties exquisitely adapted to their particular function in the tissue where they are produced. We begin by discussing the formation of bone and then examine the biomineralization process leading to the hardest mineralized tissue known, the enamel of mammalian teeth. 

Body fluids have a very high supersaturation with respect to hydroxyapatite, which cannot be explained by the small particle size of bone mineral. In fact, they behave as agueous solutions which are in metastable eguilibrium with DOHA. However, the minerals in bone, dentin, dental enamel and dental calculus contain considerable amounts of Na, Mg and CO3, in addition to calcium and phosphate which are the major components. Therefore, the phases mentioned above which all show a solubility comparable to that of DOHA, all come into consideration as components of these minerals. 

The major non-collagenous components of the dentin matrix are highly-phosphorylated proteins, phosphoryns, with many phosphoserine and aspartate residues (Butler et al., 1992). Dentin contains fewer proteoglycans than predentin. The proteoglycans from predentin are degraded upon mineralization, while small proteoglycans and phosphoryns are excreted by odontoblasts and incorporated into dentin (Goldberg et al., 1987 Linde, 1989). 

In root surface caries, the root is affected after it has become exposed by gingival recession. The cement is damaged first with sequential destruction of laminated cementum layers. When the caries reaches the dentin, the lesion becomes wedge-shaped (Nyvad and Fejerskov, 1990 Schiipbach et ah, 1989). The histochemical changes of root surface caries correspond with those of dentin caries (Frank, 1990). Mineralized surface layers have been reported for both dentin and root surface caries (Mellberg, 1986). 

Van Strijp AJP, Van Steenbergen TJM and Ten Cate JM (1997) Bacterial colonization of mineralized and completely demineralized dentine in situ. Caries Res (in press). 

Root caries can occur when tooth roots are exposed to the oral environment, for example after periodontal surgery or gingival recession. Two stages are distinguished microscopically. First, the dentin mineral is dissolved and bacteria penetrate the tubules. Second, the demineralized dentin matrix is degraded, and bacteria infiltrate the intertubular area (Frank et al., 1989 Frank, 1990 Schiipbach et al., 1989). This sequence of events may indicate that the degradation of the dentin matrix occurs after it has become accessible by the removal of mineral. In an in vitro study, Klont and Ten Cate (1991) confirmed that the dentin matrix cannot be degraded unless it is demineralized. 

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