Composite formulations, dental

As discussed in Section 5.5, the formulation and use of bio-derived epoxy resins will represent one of the most important challenges both for the academic world and for industry in the next few years. In particular, all industrial fields where composite materials find application will aim to increase the use of epoxy matrices to reduce the environmental impact and CO2 emissions. A further future development of epoxy resins is related to their use as matrices in composites for dental applications, substituting for methacrylate ones, thanks to their lower shrinkage. 

PE gCjgT fiber-reinforced composite formulations have been developed to be used as structural components for various dental appliances such as prosthodontic frameworks, retainers and splints. PE gCgpT reinforced with continuous glass fibers were pultruded continuously in profiles with small rectangular cross sections. The microstructure was evaluated with SEM and optical microscopy, and fiber content and flexure properties were measured. These composites can be molded into individualized devices so the free fibers do not need to be manipulated by the operator. The attractive properties and handling of these composites deserved further study as possible structural dental materials (154). 

SCH 12] Schneider L.F.J., Cavalcante L.M., Prahl S.A. et al, Curing efficiency of dental resin composites formulated with camphorquinone or trimethylbenzoyl-diphenyl-phosphine oxide . Dental Materials, vol. 28, no. 4, pp. 392-397, 2012. 

Voelker (1916a) reported three early dental silicate cements which appeared in 1895, 1897 and 1902 all proved inadequate. The first successful material was developed by Steenbock (1903,1904) who explicitly sought and formulated a translucent cement (Voelker, 1916a,b). It was marketed by Ascher in 1904 as New Enamel Richters Harvadid cement followed in the same year. Thereafter development was rapid and eight varieties were reported by Morgenstem in 1905. However, from their chemical composition we doubt whether they were sufficiently translucent. 

Cowan Teeter (1944) reported a new class of resinous substances based on the zinc salts of dimerized unsaturated fatty acids such as linoleic and oleic acid. The latter is referred to as dimer acid. Later, Pellico (1974) described a dental composition based on the reaction between zinc oxide and either dimer or trimer acid. In an attempt to formulate calcium hydroxide cements which would be hydrolytically stable, Wilson et al. (1981) examined cement formation between calciimi hydroxide and dimer acid. They found it necessary to incorporate an accelerator, alimiiniiun acetate hydrate, Al2(OH)2(CHgCOO)4.3H2O, into the cement powder. 

In the first portion of this section, we will focus on the materials and processes used to form polymer dental composites. This section will be followed by a discussion of the problems associated with polymer composite materials. An overview of the photopolymerization behavior and the polymer structure of these highly crosslinked materials is presented in Sects. 3 and 4. Lastly, some of the properties of current composite resin formulations are presented. 

A US patent was granted to Bindan Corp. on a Ceramicrete-based composition [5]. This patent emphasizes the importance of recent Mg-based CBPC formulations for dental cements and bioceramics. 

MPa, compressive strength 245-303 MPa, water sorption 0.5-0.7/cm ) considerably exceeded the minimum requirement of the specification for dental composite resins (37). If low concentrations are employed in the formulations especially with DEAPAA as accelerator, the cured composites are nearly colorless. No perceptible change occurs in the color of the specimens containing a UV absorber after 24 hours exposure to a UV light source. Because of the excellent overall physical properties, nearly colorless appearance and the potentially better biocompatibility, compositions using these accelerators should yield improved restoratives. 

The extent of polymerization can be quantified by comparing the proportion of double bonds in the set material with those in the composite paste as formulated initially [21]. This is typically expressed as a percentage, and called the degree of polymerization (DP), or DC. Values vary widely in practical dental composites, ranging from 35% to 77% [23]. 

To formulate a successful composite material, and in particnlar to ensnre that there is adequate stress transfer from matrix to filler phase, a conpling agent is deployed at the matrix-filler interface. The type of silane nsed for conventional dental composite resins effectively forms a mono-molecnlar hydrophobic layer on the snrface of the inorganic filler particles. In silanating the reactive ionomer glass in this way, the chemical reactivity of the glass is affected. It is no longer quite so hydrophilic, and hence is less susceptible to acid attack in the presence of moisture. 

For light-cured materials, the initiator system can be based on camphorquinone, so that cements can be cured with a conventional dental cure lamp emitting at a maximum wavelength around 470nm. Unlike formulations of composite resin, these materials cannot deploy amines as activators, because they would react with the carboxylic acid groups on the polymer, forming salts. Instead, a substance such as sodium p-toluene sulfinide is used as the activator. In addition, a photo-accelerator such as ethyl 4-NJ -dimethylamino benzoate is included [10]. 

The maximum value of Rp (between 10% and 30% conversion) is one of the reliable parameters to measure the reactivity of the formulation. FTIR profiles also provide the amount of unreacted functional groups remaining in the cured system, which is a parameter that strongly affects the final properties of the polymer. Real-time FTIR is also well suited for dark polymerization reactions that occur immediately after light exposure. One of the disadvantages of this technique appears in composite systems, in which the presence of additives may interfere with the transmission of the light by the polymer system, such as in dental composites. ... 

Bis-GMA is a well-known crosslinking monomer, which is incorporated in many dental composites and adhesives. It is added in various formulations in order to significantly increase the mechanical properties. In this context, Mou et al. undertook the synthesis of PA-6, an analog of Bis-GMA bearing two PA groups on the aromatic moieties (Scheme 8.4). ... 

Poly(ether ether ketone) (PEEK), in various formulations, is found in a wide variety of applications as an alternative biomaterial to ceramic, metal and other polymer implants (such as UHMWPE). These applications include trauma fixation, as well as dental, orthopaedic and spinal implants and, as a result of ongoing research, the uses of PERK as a biomaterial continue to grow (Toth et al. 2006). Research conducted by Morrison et al. (1995) emphasised the biocompatibility of PEEK and its composites. This may mean that the probability of adverse tissue reactions induced by wear debris may be minimised through the use of PEEK as an implant material. 

Dental Took. Many common dental tools are available for home use as part of a daily oral care routine. The most basic of dental tools is the toothbrush. Toothbrushes come in a variety of sizes, shapes, and stiffness. Patient age and oral condition determine the best toothbrush for each individual. Toothbrushes usually consist of a plastic handle with nylon brisdes that remove food, bacteria, and plaque that can lead to tartar and dental caries. Toothpaste is usually added to a toothbrush to aid in cleaning the teeth and freshening the mouth. Toothpaste is available in a variety of flavors and compositions and may contain polishing or bleaching agents. Dental floss is another basic tool used to remove food and debris from between the teeth. Floss is available in waxed and unwaxed formulations and in a variety of widths and thicknesses. Mouthwash is a rinse that prevents gum disease. Mouthwash is available in many flavors, but all types reduce the number of germs in the mouth that cause gingivitis. 

Dental Composite Restoratives. Polymeric restoratives have three major components an organic resin matrix, an inorganic filler modified with a coupling agent, and a suitable polymerization initiator system. The formulation used to produce the organic matrix, or continuous phase, is made up of free-radical polymerizable monomers. The monomer mostly used in the formulations for both anterior and posterior resins is BisGMA (Fig. 7), or alternatively formulated with... 

Dental Cements. Polymeric matrices used in formulating cements are similar to those used in methacrylate-based composites and sealants. BisGMA or some other dimethacrylate is blended with monomers snch as MMA, along with fillers and other additives, to make the formulated adhesive useful in the oral cavity. They may be of the VLC type and/or chemically cnred type. They may also contain additives such as inorganic fluoride salts, which may result in redncing recurrent decay. 

All phenol polymers having free vinyl groups in the side chain (50, 56, and 57) could be furthermore subjected to thermal ciu ing due to cross-linking through the methacryhc groups [47,48]. A multi-methacrylate ohgomer was also prepared by polymer-analogous fimctionahzation of a poly(isopropylidenediphenol) (BPA) resin. Such materials could be of potential interest for the formulation of dental composites as direct esthetic restorative materials [15]. 

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