Dental materials made from

The increased use of plastics in dentistry and medical implants calls for materials that can be detected and analyzed by rapid, nondestructive methods [1,2]. For example, ingested dentures or restorative dental materials made from radiolucent plastics cannot be easily detected by common radiographic diagnostic techniques. The difficulty to detect plastic fireweapons by current screening devices could be cited as another reason for the need of X-ray contrast or radiopaque resins. 

Plasters made from hemiliydrate also find applications in many orthopedic and dental materials and sanitary wares. 

For much of the last century, scientists attempted to make useful plastics from hydroxy adds such as glycolic and lactic acids. Poly(glycolic acid) was first prepared in 1954, but was not commercially developed because of its poor thermal stability and ease of hydrolysis. It did not seem like a useful polymer. Approximately 20 years later it found use in medicine as the first synthetic suture material, useful because of its tendency to undergo hydrolysis. After the suture has served its function, the polymer biodegrades and the products are assimilated (Li and Vert 1995). Since then, suture materials, prosthetics, artificial skin, dental implants, and other surgical devices made from polymers and copolymers of hydroxy carboxylic acids have been commercialized (Edlund and Albertsson 2002). 

One of the primary uses of indium is in making alloys. An alloy is made by melting and mixing two or more metals. The mixmre has properties different from those of the individual metals. Indium has been called a metal vitamin in alloys. That means that very small amounts of indium can make big changes in an alloy. For example, very small amounts of indium are sometimes added to gold and platinum alloys to make them much harder. Such alloys are used in electronic devices and dental materials. 

Dental Polymers. Every year nearly a half billion dental fillings are done, and over a million dentures are constructed. Most of the materials used in each of these cases are polymeric. In addition, over 300,000 dental implants are made each year with either ceramics or polymers (1). The majority of the dental fillings and dentures are made from various copolymers of methyl methacrylate with other acrylics, although some other polymers, such as polyurethanes, vinyl chloride-vinyl acetate-methacrylate copolymers, vulcanized rubber, and epoxies, have been used to some extent. One major problem is aesthetics—the prosthesis must look natural and not discolor (by photoinduction or staining) to any great extent. 

Around 1870, John Wesley Hyatt, an American printer, attempted to win a 10000 prize by developing a substitute material for ivory billiard balls. Hyatt mixed cellulose nitrate with camphor, heated it under pressure and shaped it The product, known as celluloid, could be used to form boxes, wipe-clean linen shirt collars and cuffs, ping-pong balk, dolls and dental plates, which were made from ebonite in the early nineteenth century (Figure 2.1). Because cellulose nitrate softens on warming (thermoplasticity) it was not an ideal material for fake teeth, which curfed when the wearer drank hot coffee. Its... 

Solution polymerization (in ketones, aromatic solvents, esters) is used for lacquer resins, which are physically air drying (copolymers with, e.g., lauryl methacrylate) or stoving (with glycidyl methacrylate or glycol dimethacrylate) lacquers. Water-soluble resins from copolymers of methyl methacrylate with a little methacrylic acid are made in this way, being later neutralized with ammonia. The viscosity improvers (see below) are also synthesized in solution (mineral oil). Suspension-polymtnztA polymer is used for injection-molded, extruded, and dental materials (palate or dental plates, teeth fillings). 

These are typically built on a polyester base membrane (PETP, 35 pm, copper-laminated) with a polyester spacer membrane, safety chamber and front membrane. The snap disc being gold plated stainless steel. Other designs use electrical contacts made from silver, silver on carbon or carbon only. Keypads may also be made from conductive silicone rubber. Conventional computer keyboards made from ABS, polyester or other polymers, may be covered by a polymer overlay to protect it against dirt, dust, water or other substance present in a hostile environment. Polyester and PVC overlays are used in a wide variety of applications with computer and instrumentation equipment in dental and medical healthcare and other areas. Typical casing materials include PC and polychloroprene. 

The past 10 years have been characterized by an explosion in the field of materials science. It cannot be denied that scientists all over the world exdted by the development of smart polymers, composites, and systems invest effort in studying them in potential biomedical appUcations. The term Smart defines a material or system having the ability of adapting itself to external stimulus by a number of ways, for example, shape shifting. The most known nonpolymer biomaterial is the shape memory alloys, such as NiTinol, with many dental applications [111]. Smart polymers are still under development [112, 113], some are already commercially available as in the case of smart polyurethanes (DiAPLEX ) by Mitsui Polymers. Recently, a cardiology product has been released in the market featuring smart characteristics. The discussion is about a cardiology stent dilated with the help of a balloon made from smart shape memory polyurethane as described in a 2002 US patent, and placed inside the blocked arteries of a patient [114]. 

Current inventions show improvements in solvent utilization, as follows. PVC-based adhesive for PVC pipes, typically containing solution of PVC in tetrahydrofuran, was replaced by solution of chlorinated PVC in 1,3-dioxolane and/or its derivatives whieh are far less toxic than THF. Ethanol is used in polyimide adhesive and dental adhesive. Monomer solvent mixture is used in crosslinkable acrylate adhesive, which permits formulation of VOC-free composition. Polyurethane hot-melt adhesive produced from polyacrylates and polyesters does not need solvents for its production and cure which occurs under the effect of moisture. Similar observations can be made for sealants. For example, sealing agent for semiconductor light emitting elements have been made from acrylic monomers without application of solvent. Material for production of printed wiring board was produced and cured without solvent from polymethacrylate. It is clear from these examples that new processes are consciously directed towards less toxic solutions. 

Dental silicate cement was once the most favoured of all anterior (front) tooth filling materials. Indeed, it was the only material available for the important task of aesthetic restoration from the early 1900s to the mid 1950s, when the not very successful simple acrylic resins made their appearance (Phillips, 1975). In the mid sixties there were some 40 brands available (Wilson, 1969) and Wilson et al. (1972) examined some 17 of these. Since that time the use of the cement has declined sharply. It is rarely used and today only two or three major brands are on the market. The reason for this dramatic decline after some 50 years of dominance is closely linked with the coming of modern aesthetic materials the composite resin from the mid 1960s onwards (Bowen, 1962), and the glass-ionomer cement (Wilson Kent, 1971) from the mid 1970s. 

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