Cement functions

Solvent cements and dope cements function by attacking the surfaces of the adherends so that they soften and, on evaporation of the solvent, will join together. The dope cements, or bodies cements, differ from the straight solvents in that they contain, in solution, quantity of the same plastic which is being bonded. On drying, these cements leave a film of plastic that contributes to the bond between the surfaces to be joined. 

Bone cement functions as a grouting material consequently, its anchoring power depends on its ability to penetrate between bone trabeculae during the insertion of the prosthesis [Charnley, 1979]. Being a viscoelastic polymer, it has the ability to function as a shock absorber. It allows loads to be transmitted uniformly between the implant and bone, reducing locahzed high-contact stress. 

In cemented total joint arthroplasties, acrylic bone cement functions as the piima ry load bearing material used to transfer loads from the implant to the bone. Bone cement Is formed from an exothermic reaction of benzoyl peroxide initiator present In polymethylmethacrylate powder (PMMA) and AI,AI-dimethyl-p-tolui-dene In methylmethacrylate monomer liquid (MMA), resulting in polymerization of PMMA to form a solid cement matrix. The in vivo integrity and performance of bone cement Is necessary for longevity of orthopedic implants, because it is believed that mechanical failure of the bone cement layer can lead to aseptic loosening of the Implant [101]. 

Figure 8 Impedance variation in function of the cementation thicknesses (f=700Hz).

Epichlorohydnn is the common name of an industrial chemical used as a component in epoxy cement The molecular formula of epichlorohydnn is C3H5CIO Epichlorohydnn has an epoxide functional group it does not have a methyl group Write a structural formula for epichloro hydrin... 

Tannins occur in many plants and are separated by extraction. At present, only quebracho extract is used as a mud thinner in significant quantity in the United States. Quebracho is an acidic material and performs best at high pH. It is an excellent thinner for lime-treated and cement-contaminated muds. However, it is not effective at high salt concentrations. Sulfomethylated tannin products are functional over a wide range of pH and salinity and have either been treated with chromium for good thermal stabiUty (58) or are chrome free. Concentrations of tannin additives are ca 1.5—18 kg/m (0.5—6 lb/bbl). 

The materials used in a total joint replacement ate designed to enable the joint to function normally. The artificial components ate generally composed of a metal piece that fits closely into bone tissue. The metals ate varied and include stainless steel or alloys of cobalt, chrome, and titanium. The plastic material used in implants is a polyethylene that is extremely durable and wear-resistant. Also, a bone cement, a methacrylate, is often used to anchor the artificial joint materials into the bone. Cementiess joint replacements have mote tecentiy been developed. In these replacements, the prosthesis and the bone ate made to fit together without the need for bone cement. The implants ate press-fit into the bone. 

The material in use as of the mid-1990s in these components is HDPE, a linear polymer which is tough, resiUent, ductile, wear resistant, and has low friction (see Olefin polymers, polyethylene). Polymers are prone to both creep and fatigue (stress) cracking. Moreover, HDPE has a modulus of elasticity that is only one-tenth that of the bone, thus it increases the level of stress transmitted to the cement, thereby increasing the potential for cement mantle failure. When the acetabular HDPE cup is backed by metal, it stiffens the HDPE cup. This results in function similar to that of natural subchondral bone. Metal backing has become standard on acetabular cups. 

Once a metal surface has been conditioned by one of the above methods, a coupling agent composed of a bifimctional acid—methacrylate similar to a dentin adhesive is appHed. This coupling material is usually suppHed as a solvent solution that is painted over the conditioned metal surface. The acidic functional group of the coupling molecule interacts with the metal oxide surface while the methacrylate functional group of the molecule copolymerizes with the resin cement or restorative material placed over it (266,267). 

FIG. 17-73 Normal (perpendicular) rapping efficiency for various precipitated dust layers having about 0.03 g diist/cm (0.2 g diist/in ) as a function of maximum acceleration in multiples of g, Curve 1, fly ash, 200 or 300°F, power off. Curve 2, fly ash, 70°F, power off also 200 or 300°F, power on. Curve 3, fly ash, 70°F, power on. Curve 4, cement-ldln feed, 300°F, power off. Curve 5, cement dust, 300°F, power off. Curve 6, same as 5, except power on. Curve 7, cement-ldln feed, 300°F, power on. Curve 8, cement dust, 200°F, power off. Curve 9, same as 8, except power on. Curve 10, cement-ldln feed, 200°F, power off. Curve 11, same as 10, except at 70°F. Curve 12, cement-ldln feed, 200°F, power on. Curve L3, cement-ldln feed, 70°F, power on. °C = (°F — 32) x %. [Spioull, Air Polliit. Control Assoc. J., i.5, 50 (1965).]... 

Organic peroxide-aromatic tertiary amine system is a well-known organic redox system 1]. The typical examples are benzoyl peroxide(BPO)-N,N-dimethylani-line(DMA) and BPO-DMT(N,N-dimethyl-p-toluidine) systems. The binary initiation system has been used in vinyl polymerization in dental acrylic resins and composite resins [2] and in bone cement [3]. Many papers have reported the initiation reaction of these systems for several decades, but the initiation mechanism is still not unified and in controversy [4,5]. Another kind of organic redox system consists of organic hydroperoxide and an aromatic tertiary amine system such as cumene hydroperoxide(CHP)-DMT is used in anaerobic adhesives [6]. Much less attention has been paid to this redox system and its initiation mechanism. A water-soluble peroxide such as persulfate and amine systems have been used in industrial aqueous solution and emulsion polymerization [7-10], yet the initiation mechanism has not been proposed in detail until recently [5]. In order to clarify the structural effect of peroxides and amines including functional monomers containing an amino group, a polymerizable amine, on the redox-initiated polymerization of vinyl monomers and its initiation mechanism, a series of studies have been carried out in our laboratory. 

It functions as a water-reducing plasticizer, producing a flooring composition with good workability at low water/cement ratios. 

Pontieri FE, Tanda G, Orzi F, et al Effects of nicotine on the nucleus accumbens and similarity to those of addictive drugs. Nature 382 235-237, 1996 Pontieri FE, Zocchi A, Orzi F Mapping of functional changes associated with administration of substances of abuse in the rat. Funct Neurol 13 311-326, 1998 Preble E, Laury GV Plastic cement the ten cent hallucinogen. Int J Addict 2 271— 272, 1967... 

Collagenases and hyaluronidases are produced by most of the aggressive invaders. These are able to dissolve eollagen fibres and hyaluronie aeids which function as intracellular cements. Their loss causes the tissues to breakup and produce oedematous lesions. 

Figure 5.18 This figure shows how the properties of a glass polyalkenoate cement change as it ages. S is the compressive strength, E the modulus, a a stress-relaxation function, and c a strain-conversion function from elastic to plastic strain (Paddon Wilson, 1976).

By contrast, the acidity of the metal salts used in these cements has a less clear origin. All of the salts dissolve quite readily in water and give rise to free ions, of which the metal ions are acids in the Lewis sense. These ions form donor-acceptor complexes with a variety of other molecules, including water, so that the species which exists in aqueous solution is a well-characterized hexaquo ion, either Mg(OH2)g or Zn(OH2)g. However, zinc chloride at least has a ternary rather than binary relationship with water and quite readily forms mixtures of Zn0-HCl-H20 (Sorrell, 1977). Hence it is quite probable that in aqueous solution the metal salts involved in forming oxysalt cements dissolve to generate a certain amount of mineral acid, which means that these aqueous solutions function as acids in the Bronsted-Lowry sense. 

In a similar way there has been a passing reference to a cobalt oxychloride cement (Prosser et ai, 1986). No explicit details of the fabrication or chemical behaviour of this material were provided, but the ingredients were listed among series of acids and bases for forming cements as agents for the sustained release of trace elements to grazing animals. The implication of this paper was that cobalt oxide would function as the base... 

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