Polymerization dental applications

Other applications of zirconium tetrafluoride are in molten salt reactor experiments as a catalyst for the fluorination of chloroacetone to chlorofluoroacetone (17,18) as a catalyst for olefin polymerization (19) as a catalyst for the conversion of a mixture of formaldehyde, acetaldehyde, and ammonia (in the ratio of 1 1 3 3) to pyridine (20) as an inhibitor for the combustion of NH CIO (21) in rechargeable electrochemical cells (22) and in dental applications (23) (see Dentalmaterials). 

Dimethacrylate monomers were polymerized by free radical chain reactions to yield crosslinked networks which have dental applications. These networks may resemble ones formed by stepwise polymerization reactions, in having a microstructure in which crosslinked particles are embedded in a much more lightly crosslinked matrix. Consistently, polydimethacrylates were found to have very low values of Tg by reference to changes in modulus of elasticity determined by dynamic mechanical analysis. 

As described above, the majority of materials used in dental applications contain multifunctional monomers that polymerize to form highly crosslinked polymer networks. In addition, many of the applications, such as tooth restorations, require that the crosslinked polymer is polymerized intraorally. This restriction can often complicate the cure of the monomers since the material is exposed to oxygen and moisture in the oral environment. Also, depending on the thickness of the restoration, the material might not be uniformly cured because of variations in light intensity with depth in the sample. These problems... 

With the light curing mechanism, there is a limitation to the penetration of the light. The dentist may have to place a restoration that is 6 + mm thick, whereas the light may penetrate only 2 mm [182]. Factors that affect this penetration are the translucence of the material, the color or shade used to match the tooth, the ability to place the light source close to the material being polymerized, and the intensity of the source. Under relatively ideal conditions, the mean depth of cure is approximately 4-5 mm. Thus, the dental application requires that the material be placed in layers. Due to the oxygen inhibition of the outside surface of the resin layers, additional layers can be laminated and cured with the appearance of uniformity of the final restoration. 

Thermal analysis techniques have had only limited use in the study of the various dental materials used for restorative, prosthetic and implant applications. The innovative research by Brantley s group, using conventional and temperature-modulated DSC (TMDSC) to examine the thermal behaviour of several metallic and polymeric dental materials, is described in Chapter 17 and numerous matters requiring additional research are identified. 

A wide variety of dental materials is used in the oral environment for restorative, prosthetic and implant applications, and these materials are described at length in textbooks [1-3]. While their physical and mechanical properties have been studied extensively, there has been relatively little use of thermal analysis techniques to gain insight into dental materials. Our group has performed extensive research on several metallic and polymeric dental materials, principally utilizing conventional DSC and temperature-modulated DSC (TMDSC). These studies and thermal analysis studies of dental materials by other research groups are reviewed in this chapter. Although much novel information has been provided, numerous matters are discussed that require additional research. 

Table 19.1 summarizes some of the existing usage of polymeric biomaterials in a variety of implantable prostheses for cardiovascular, orthopedic, ophthalmologic, and dental applications. 

In recent years, dental research has been focused on dental implants and artificial teeth rooted in a patient s jaw allowing for a permanent denture, as alternatives to bridges or false teeth. A wide array of materials including polymers such as UHMWPE, PTFE, and PET have been used in many types of existing dental implants [54,119]. Porous polymeric surfaces are now designed to facilitate bone integration [54], Other dental applications of polymeric biomaterials have been for the development of a dental bridge, meant as a partial denture or false teeth. In extreme cases, removable dentures fabricated from PMMA are used to overcome the loss of all teeth [203]. 

The low polymerization shrinkage of cycloolefins which is typically <5% (e.g. ca. 4% for DCPD polymerization), compared with >10% for acrylate and methacrylate polymerization, makes PROMP systems attractive for stereolithography or dental applications. Indeed we could formulate stereolithographic resins, which were laser cured by PROMP. However, the lack of an appropriate quenching mechanism (once initiated, the polymerization continues even in the absence of light and leads finally to... 

Dental fields of application of methacrylates are, among others, dental prostheses, composite resins and primers. Methacrylic plastics are formed by polymerization of chemically highly reactive methacrylic monomers. For dental applications, it is most common to use a powder of pre-polymerized (meth)acrylates, which has to be mixed with the right amount of liquid methacrylic monomers. Depending on the polymer-... 

Fitha, J. Polymeric drugs effects of polyvinyl analogs of nucleic acids on cells, animals and their viral infections, in Biomedical and Dental Applications of Polymers, (eds.) Gebelein, C. G., Koblitz, F. K., p. 203, New York, Plenum 1981 Maack, T. et sd. Kidney Int. 16, 251 (1979)... 

Note the presence of two double bonds, leading to dense cross-linking. From a chemical point of view, the hw-GMA exhibits low shrinkage on polymerization (cure), so as to reduce the probability of unwanted bacteria, and so on, entering between the filling and the remaining natural tooth material (115). [Unfortunately, an effective expanding polymerization for dental applications has yet to be developed see (116).]... 

Given that the structural building blocks of the tooth are essentially composed of polymeric constituents, it is no surprise that the progress of dentistry and dental biomaterials would seek to approximate the polymeric composition of the natural tooth [7], Interestingly, however, it was not until the mid 1900s that polymeric materials emerged as an alternative material for dental applications [8],... 

Nowadays, polymers are largely used for restorative applications as a treatment for decayed teeth, as materials for prosthetic applications in the fabrication of partial and complete dentures, in different laboratorial methods for molding and modeling, and more recently for controlled remineralization of teeth and tissue engineering, amongst other applications. In this chapter, we will discuss the applications of polymers in the wide field of clinical dentistry, with particular emphasis in restorative procedures and emerging smart polymeric materials with potential dental applications. 

GC alone can be a valuable monomer for the synthesis of hyperbranched poly(hydroxyether)s (Scheme 25). In case of polymerization, GC, containing a l,3-dioxolan-2-one ring and hydroxyl group in a single molecule, is considered a latent cyclic AB2-type monomer. The anionic ROP of the GC, which proceeds with CO2 liberation, leads to a branched polyether. l,l,l-Tris(hydroxymethyl)propane or other multihydroxyl molecules are usually used as a initiator-starter and central core of the polyether. The hyperbranched polyglycerol structure is obtained by slow addition of the cyclic carbonate monomer at above 150 °C. Such polymers are characterized by a flexible polyether core and a multihydroxyl outer sphere. They are suitable for preparation of acrylic resins for dental applications or additives for polyurethane foams. Hyperbranched poly (hydroxyether)s from biscyclic carbonate with phenol group (2, Scheme 24) were also reported. 

Amines, such as dimethylaniline and triethylamine, are also used as coinitiators for free-radical polymerizations [154,155]. In these cases, initiating radicals are supposedly generated through exciplex formation, followed by proton transfer. The low order of toxicity of camphor quinone and its curability by visible light makes such systems particularly useful for dental applications [152,156,157]. Noteworthy is that the reactivity is relatively low, owing to a comparably low efficiency in hydrogen-abstraction reactions. This circumstance has prevented the use of quinones in other applications. 

In most medical and paramedical applications of plastics, the materials used are those already produced by the manufacturers in a polymerized or formulated form. Certain surgical and dental applications, however, require that the material be polymerized or formulated just prior to use. Surgical cements and adhesives, a host of dental filling materials, materials for dentures, cavity liners, and protective coatings for tooth surfaces are in this category. 

Acrylic resins, because of their desirable esthetics, ease of processing, optical clarity that can duplicate in appearance the oral tissues it replaces, satisfactory mechanical properties and excellent biocompatibility, are the materials of choice wherever plastics have found applications in dental practice. The ready acceptability of these materials is the result of the ease with which they can be converted into their final state even under clinical conditions. In practically all dental applications a liquid monomer-solid mixture is cured by a free radical initiated polymerization that is generated by heat, light, an initiator, or a redox initiator-accelerator system adapted to the constraints imposed by the oral environment. 

Colorless composites with good mechanical properties can be obtained with either -butyl perbenzoate, cumene- or -butyl hydroperoxide and ascorbic acid or ascorbyl palmitate systems (50). Mechanisms for the free radical formation are given in Fig. 4. Addition of trace amounts of transition metals in their higher oxidation state (Cu", Fe" ) to the perester component further speeds up the polymerization. On admixture with the ascorbic acid derivative the metal cation is reduced to its lower oxidation state which, because it is a potent one electron reductant and will rapidly activate the free radical decomposition of the perester, which it in turn is reoxidized to its higher oxidation state. Means for prevention of oxidation of ascorbic acid or its derivatives on prolonged storage must be developed for these formulations to be suitable for dental application. 

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