Cements, bioactive

Tamura J, Kitsugi T, lida H, Fujita H, Nakamura T, Kokubo T, Yoshihara S. Bone bonding ability of bioactive cements. Clin Orthop... 

Shinzato, S., Nakamura, T., Kokubo, T., and Kitamura, Y., 2002, PMMA-based bioactive cement effect of glass bead filler content and histological change with time. J. Biomed. Mater. Res. 59 225-232. 

Zinc phosphate, Zn2(P0 2> forms the basis of a group of dental cements. Chromium and zinc phosphates are utilized in some metal-treating appHcations to provide corrosion protection and improved paint adhesion. Cobalt(II) phosphate octahydrate [10294-50-5] Co2(P0 2 8H20, is a lavender-colored substance used as a pigment in certain paints and ceramics. Copper phosphates exhibit bioactivity and are used as insecticides and fungicides. Zinc, lead, and silver phosphates are utilized in the production of specialty glasses. The phosphate salts of heavy metals such as Pb, Cr, and Cu, are extremely water insoluble. 

A current area of interest is the use of AB cements as devices for the controlled release of biologically active species (Allen et al, 1984). AB cements can be formulated to be degradable and to release bioactive elements when placed in appropriate environments. These elements can be incorporated into the cement matrix as either the cation or the anion cement former. Special copper/cobalt phosphates/selenates have been prepared which, when placed as boluses in the rumens of cattle and sheep, have the ability to decompose and release the essential trace elements copper, cobalt and selenium in a sustained fashion over many months (Chapter 6). Although practical examples are confined to phosphate cements, others are known which are based on a variety of anions polyacrylate (Chapter 5), oxychlorides and oxysulphates (Chapter 7) and a variety of organic chelating anions (Chapter 9). The number of cements available for this purpose is very great. 

A recent development has been the incorporation of a bioactive organic component into the AB cement during preparation. Since AB cements are prepared at room temperature, this can be done without causing degradation of the organic compound. In this case, the AB cement may merely act as a carrier for the sustained release of the added bioactive compound. 

Ohtsuki, C., Miyazaki, T., Kyomoto, M., Tanihara, M. and Osaka, A. (2001) Development of bioactive PMMA-based cement by modification with alkoxysilane and calcium salt. Journal of Materials Science-Materials in Medicine, 12, 895-899. 

Bioactive PMMA bone cement prepared by modification with methacryloxypropyltrimethoxy silane and calcium chloride. Journal of Biomedical Materials Research, 67A, 1417-1423. 

Shinzato, S., Kobayashi, M., Mousa, W.F., Kamimura, M., Neo, M., Kitamura, Y., Kokubo, T. and Nakamura, T. (2000) Bioactive polymethyl methacrylate-based bone cement Comparison of glass beads,... 

T. Yamamuro, T. Nakamura, H. lida, K. Kawanabe, Y. Matsuda, K. Ido, J. Tamura, Y. Seneba, Development of bioactive bone cement and its clinical applications. Biomaterials 19 (1998) 1479-1482. 

H. Fujita, T. Nakamura, J. Tamura, M. Kobayashi, Y. Katsura, T. Kokubo, T. Kikutani, Bioactive bone cement Effect of the amount of glass-ceramic pow/der on bonebonding strength, J. Biomed. Mater. Res. 40 (1998) 145-152. 

In a recent article [Shinzato, S., et al., A new bioactive bone cement Effect of glass bead filler content on mechanical and biological properties, J. Biomed. 

Figure 15.23 shows that an increased amount of glass filler increases the affinity index of bioactive bone cement. Because fillers are relatively inert they have the potential to improve biocompatibility of artificially produced materials. Figure... 

Kazemzadeh, A. (2012) Development of strong and bioactive calcium phosphate cement as a light-cure organic-inorganic hybrid. /. Mater Sci. Mater Med., 23 (7), 1569-1581. 

Osaka A, Mima Y, Takeuchi K, Asada M, Takahashi K (1991) Calcium apatite prepared from calcium hydroxide and orthophosphoric acid. J Mater Sci Mater in Med 2 51-55 Osaka A, Tsura K, lida H, Ohtsnki C, Hayakawa S, Miura Y (1997) Spray pyrolysis preparation of apatite-composite particles for biological application. J Sol-Gel Sci Technol 8 655-61 Otsuka M, Matsuda Y, Suwa Y, Fox JL, Higuchi W1 (1995) Effect of particle size of metastable calcium phosphates on mechanical strength of a novel self-setting bioactive calcium phosphate cement. J Biomed Mater Res 29 25-32... 

Takadama H, Kim HM, Koknbo T, Nakamma T (2001a) An X-ray photoelectron spectroscopy stndy of the process of apatite formation on bioactive titanium metal. J Biomed Mater Res 55 185-193 Takadama H, Kim HM, Kokubo T, Nakamttra T (2001b) TEM-EDX study of mechanism of bonelike apatite formation on bioactive titanirrm metal in simulated body flttid. J Biomed Mater Res 57 441-448 Takagi S, Chow LC (2001) Formation of macropores in calcium phosphate cement implants. J Biomed Mater Res 12 135-139... 

The alternative tooth-coloured material, the glass-ionomer cement, has also been widely studied, especially in terms of its bioactivity. This arises from its ability to exchange ions with its surroundings when placed in the mouth. Typical conventional glass-ionomers have been shown to release sodium, silicon and phosphorus under neutral conditions, and also calcium and aluminium under acidic conditions [48]. The non-metals are assumed to be released as sihcate, Si03 ", and phosphate, PO/, respectively. In addition, they release fluoride [49], a process that is capable of continuing for several years [50]. 

As is described in Chapter 10, several different materials have been considered as sealants. These include zinc oxide-eugenol cements, epoxy resins and glass-ionomer cements [73,74]. In addition, calcium hydroxide paste has been used, though this material appears to be susceptible to leakage and may not be entirely satisfactory in forming a durable seal. However, its bioactivity is able to promote the physiological closure of the apex with dentine and cementum via stimulation of the odontoblast and cementoblast cells present [75]. 

Glass-ionomer cements have a degree of natural bioactivity. They release certain key ions into surrounding aqueous media, not only fluoride, but also sodium, aluminium, phosphate and silicate [103]. Under mildly acidic conditions, they release aU of these ions in larger quantities than in neutral conditions, and also release calcium (or strontium), ionic species which are insoluble in neutral solutions but which... 

Glass-ionomers not only release ions, but are capable of taking them up. Studies have shown that cements exposed to natural saliva take up calcium and phosphate ions, and develop a surface of significantly increased hardness [121]. Also, when used as pit and fissure sealants, they interact with saliva to form a substance with increased content of calcium and phosphate that is considerably more resistant to cutting with a dental drill than the original material. Under these circumstances, the cement had become transformed into a material with enamel-like optical and mechanical properties [122]. This observation is the basis of the development of glass-ionomer type materials with even further enhanced bioactivity, the so-called glass carbomers, which are discussed in Chapter 8. 

Despite these observations, both the speed of any ion-exchange processes and the amount of exchangeable ions could be improved. In searching for methods of doing this, there is a difficulty which presents itself immediately, namely that adding substances such as hydroxyapatite, that would improve the bioactivity, slow down the setting reaction and weaken the set cement. The reason for the reduced speed of setting is that candidate additives do not themselves react sufficiently quickly with the polyadd component, if they react at all. Therefore they effectively dilute the proportion of reactive powder in the cement. 

Studies have been made of the inclusion of two possible substances to enhance the bioactivity of conventional glass-ionomer cements, hydroxyapatite [7] and bioglass powder [8]. Both were found to reduce the speed of the setting reaction of the cement, with the reduction being greater with larger proportions of additive. In all cases, the set cements were consistently weaker than those with no additive (Table 8.1). This result has also been found with completely inert powders, such as borax [9]. 

In recent years, a new type of glass-ionomer material has become available that overcomes this problem of the weakening effect of additional fillers designed to enhance the bioactivity of the cement. Known as the glass carbomer , it overcomes the problem of slow setting by specifying the need to cure with the aid of heat from dental cure lamps. 

Enhanced bioactivity conventional glass-ionomer cement... 

H. Yli-Urpo, L.V.J. Lassila, T. Harhi, P.K. Vallittu, Compressive strength and surface characterization of glass ionomer cements modified by bioactive glass. Dent. Mater. 21... 

Physical and chemical properties of Biodentine are shown in Table 9.8. The material can be seen to set rapidly, and to have a reasonable compressive strength and Vicker s Hardness Number at 24h [85,86]. It shows a snbstantial wash out (solubility) in Hank s balanced salt solution (HBSS), which is presumably at least matched in deionized water. However, the pH of deionized water following storage of set Biodentine is only around 9 at 24h, rather than the 11-12.5 of traditional calcium hydroxide chelate cements or supersaturated solution. This may suggest that Biodentine is less bioactive than such materials, and hence less effective at promoting the growth of reparative dentine. 

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