Dental materials thermal properties

In the late 1940s a reaction against this idea of a dental material took place. Increasing attention was paid to problems of compatibility between the restoration and the tooth. We now believe that a restorative should be at one with the tooth material in all respects. It should possess identical properties. Its thermal characteristics should be the same as those of the tooth and its appearance should match that of the enamel. It should provide some therapeutic action. In fact, a restorative material should no longer be regarded as a filling but as an enamel or dentine substitute . 

Polymers used as dental materials must meet several stringent requirements. Dental restorative materials must be nontoxic, have aesthetic appearance, and good adhesive and mechanical properties. In addition, these materials must exhibit long term stability in the presence of water, enzymes, and various oral fluids, and withstand thermal and load cycles. Finally, a desirable dental restorative materia] should be convenient to work with at the time of application. 

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. 

The preceding research on the model maxillofacial material was followed by TMDSC study of several representative elastomeric impression materials, which are extensively used in dentistry for the accurate fabrication of inlays and crowns from dental alloys, metal-ceramic restorations, and fixed and removable partial dentures [1-3]. There have been numerous studies reporting the clinically relevant properties of these impression materials (viscosity before setting by polymerization, strain in compression after setting, permanent deformation for simulated in vivo removal of the impressions, and tear strength of the thin impressions). However, only minimal research has been reported [44] on some thermal properties of impression materials obtained by conventional DSC. Our pioneering TMDSC study [45] was designed to obtain fundamental information about impression materials and seek correlations with their relevant properties. 

Uses Polymerization/copolymerization thermally crosslinkable paint resin adhesion promoter binder for textiles, paper adhesives floor care prods. dental prods. base material for other methacrylates Properties Pt-Co 25 max. clear liq. pungent odor misc. with water ( > 24 C) m.w. 86.1 sp.gr. 1.015 vise. 1.38 mPa s (20 C) vapor pressure 0.8 mbar b.p. 161 C solid, pt. 15.8 C flash pt. 65 C ref. index 1.432 99.5% min. purity 0.02% max. water... 

Complete and uniform dispersibility of fillers in a matrix is a prerequisite for a con )osite to have optimum properties. Regardless of conq>osition, shape or size of the particles, less than optimum distribution in, for exanq)le, ceramic, metal or polymer material can result in lower mechanical strength, random discoloration or decreased electrical or thermal conductivity. For these and other reasons much effort has been and continues to be devoted to understanding fundamental reasons why some powders readily disperse in a medium and others do not. It is clear from many historic studies (1-4) that the surface chemistry of a particle, which dictates relative hydrophilicity-hydrophobicity and zeta potential, is the dominant factor. Benefit of perfected filler dispemibility are found in dental resins (5), personal body armor (6), cosmetics and sunscreens (7), rubber products (5), latex paint (P), metal matrix conq)osites (10), inks and gels (11), many foods, and in abrasive slurries used for chemical mechanical planarization (CMP of wafers during con )uter chip manufacture (12),... 

A further direction of advancement was originated by the progress being made in research and surgery and by the demand for materials with special properties for special applications. For these cases the materials, which are often composite materials, had to be tailored to the intended application. One example is the development of the alloy TiTa30 which in its thermal expansion coefficient is very similar to alumina and can therefore be crackfree bonded with the ceramic. This material is used as a dental implant. The metallic biomaterial which can resist bending stresses is inserted into the jaw. The upper part of the implant consisting of alumina, which shows a smaller deposition of plaque than the metallic materials. 

Co-based surgical implant alloys (see Table 3.1-88 for compositions) are used to fabricate a variety of implant parts and devices. These are predominantly implants for hip and knee joint replacements, implants that fix bone fractures such as bone screws, staples, plates, support structures for heart valves, and dental implants. The mechanical properties (shown in Table 3.1-89) depend sensitively on the thermal and thermomechanical treatments of the materials. 

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. 

Multicomponent hybrids containing zirconium propoxide, tetraethoxysilane and dimethyl-diethoxysilane, intended for dental restorative or adhesive materials, were successfully obtained by the dual-cure [272]. Zirconium-containing species proved to be highly effective in catalyzing the epoxy polymerization/crosslinking reactions, as compared to those containing Ti, and enhanced mechanical properties, as well as thermal stability of nanocomposites. 

Silicate ceramics are generally alumino-silicate based materials obtained from natural raw materials. They exhibit a set of fundamental properties, such as chemical inertia, thermal stability and mechanical strength, which explain why they are widely used in construction products (sanitary articles, floor and wall tiles, bricks, tiles) and domestic articles (crockery, decorative objects, pottery). They are often complex materials, whose usage properties depend at least as much on microstructure and aesthetics as on composition. Silicate products with an exclusively technical application (refractory materials, insulators or certain dental implants) will not be explicitly discussed in this chapter. 

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