Dentin dental applications

The following chapters are devoted to applications of phosphorus-based materials. Thus Chapter 8 by Mozsner and Catel deals with the use of polymerizable phosphonic acids (PAs) and dihydrogen phosphates (DHPs) for dental applications. Several PAs and DHPs were synthesized to notably improve the shear bond strength to dentin and enamel, the stability of the adhesive formulation, and the chemical adhesion to tooth tissues. Some of these monomers are nowadays included in commercial dental adhesives. 

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).

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 Biomineralization section begins with a summary of the current state of research on bone, dentin and enamel phosphates, a topic that crosses disciplines that include mineralogical, medical, and dental research. The following two chapters treat the stable isotope and trace element compositions of modern and fossil biogenic phosphates, with applications to paleontology, paleoclimatology, and paleoecology. 

Acidic monomers could be phosphates as well as carboxylic, sulfonic, or phosphonic acids. Some examples of carboxylic acid monomethactylates are 4-(2-methactyloyloxyethyl)trimellitic acid (4-MET) and 11-methactyloyloxy-1,1-undecanedicarboxylic acid (MAC-10). Among the functionalized monomers, free-radically polymerizable phosphonic acids (PAs) and dihydrogen phosphates (DHPs) have found wide and intensive applications as adhesive components in enamel/dentin adhesives. In this chapter, a review of the various PAs and DHPs prepared for application in dental adhesives is provided. 

Copol5nners of diethyl (methacryloylox5rmethyl)phosphonate have recently been reinvestigated for possible flame-retardant use (87). Various acrylate and methacrylate monomers with phosphonic acid groups, which aid bonding to dentine, have shown promise for dental restoration purposes (88). Various allyl phos-phonates (89) have been proposed for these uses but none appear to have foimd application. 

The most important properties of the dentin and incisal materials are shown in Table 4-19. The coefficient of linear thermal expansion plays an important role in the optimal joining of ious types of apatite-leucite glass-ceramics and the Zr02-rich opaquer, which are applied to the different metals. Therefore, CTE of the opaquer has been included as a comparative value in Table 4-19. A comparison of CTE of glass-ceramics and of the opaquer with that of metals clearly shows that the application of the glass-ceramic to the metal framework systematically builds up compressive strain. As a result, the finished dental product demonstrates surface tension and a controlled increase in strength, ensuring retention on the substructure. 

In terms of quantity, the incisal and dentin materials comprise the largest part of the apatite-leucite glass-ceramics of the IPS d.SIGN system. Their microstructure and properties are described in Section 2.4.6. The main applications of these glass-ceramics include dental crowns and multi-unit bridges. 

The initial results demonstrate that molecular prototype delivery systems are able to harness free radical reactivity within the laboratory. Proof of the concept has also highlighted the importance, as well as plausibility, of innovative development of functional dental restorative materials that have bioactive and bonding properties suitable for use in dentin and enamel that also show beneficial preventative and therapeutic properties [215,216]. Further evaluation is required in the application of these novel drug-delivery systems for the prevention and treatment of disease states mediated by free radicals. 

The need to resume the application many times prevented the commercialization of methyl and ethyl cyanoacrylates for fissure sealing. A reduced capacity to adhere to enamel, the diminished resistance of the material to hydrolysis, and toxicity of products of hydrolysis accounts for the refusal in 1974 of the application of these materials by the Council on Dental Materials and Devices. To this the scarcity of long lasting chemical and biological investigation was added [155]. A reduced resistance to impact is also notable, and in some cases their adherence to dentine has not been satisfactory [156]. 

Glass-ionomer cements have taken a major place in dental treatments as restorative filling materials and also in a range of more adhesive applications due to their ability to bond to both dentine and composite fillers. Acid-etching techniques are well established for the bonding of resins to enamel. 

Adhesion of restorative dental biomaterials to tooth substrates is primarily based on micromechanical interlocking of resin monomers to the components of the hard tissue. In addition to micromechanical retention, chemical bonding can be achieved via functional monomers, which are able to chemically and mechanically bond to the tooth [10, 11]. While commonly classified as generations by industry, the most appropriate way to classify the current adhesive systems is by the dentin surface treatment and application techniques. The application techniques recommended by manufacturers is greatly influenced by the composition of the adhesive polymer [12]. A summary of the current adhesive systems is shown in Table 9.1. 

The clinical technique can also affect the performance of dental adhesive systems. Significant reduction in the degree of conversion and mechanical properties of adhesive systems was observed when solvents were not properly evaporated [23-26]. The application of simplified-step adhesive systems to an excessively wet dentin surface may lead to phase separation and a hydrophobic-poor and hydro-philic-rich zone may be formed, lowering the stability of the adhesive interface [13]. Acidic monomers remain active when poorly polymerized resulting in continuous etching of the underlying dentin [27]. 

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