![]() Data published to date suggest that aluminium leaching occurs only in the initial period following setting ( Crisp et al., 1980 Wilson and McLean, 1988). Aluminium ion release is particularly important and plays a somewhat controversial role ( Nicholson et al., 1991), particularly following reports of four cases of post-otoneurosurgery aluminium encephalopathy and deaths among patients treated with a glass–ionomer bone cement ( Renard et al., 1994 Reusche et al., 2001). Ion exchange with the tissues of the implant bed has been confirmed to be a significant determinant in the bioactivity of a GIC ( Devlin et al., 1994 Johal et al., 1995). The release of other ions from GIC is less well reported, although it has been proposed that ion release is a major factor in the bioactivity of different GICs ( Brook et al., 1991a, 1992 Doherty, 1991 Nicholson et al., 1991 Hatton and Brook, 1992b Sasanaluckit et al., 1993). It is speculated that this is because fluoride release from GIC during bone formation results in mineralisation containing fluorapatite, which is more resistant to resorption. Studies have reported a greater volume of bone formation associated with GIC than with more inert ceramic bone substitutes and, more recently, related increased fluoride release with bone formation ( Brook et al., 1991b Johal et al., 1995). Fluoride is also used to treat bone resorption in patients with osteoporosis ( Pak et al., 1989 Sogaard et al., 1995), owing to its ability to increase the density of trabecular bone. Although high fluoride concentrations result in enzyme inhibition in vitro, bone-forming cells exhibit increased proliferation and alkaline phosphatise activity in vivo ( Farley et al., 1983 Lundy et al., 1986 Turner et al., 1989 Brook et al., 1991b). The effect of fluoride ions appears to be dose-dependent. Whereas the absence of fluoride has been reported to result in the least in vitro toxicity (although this material contained no phosphate, complicating interpretation of results) ( Brook et al., 1991a), it also produced the lowest osteoconductivity and integration in vivo ( Brook et al., 1991b, Johal et al., 1995). It was originally proposed that fluoride release was the most significant factor affecting biocompatibility of glass-ionomers. Even though caution must be exercised when interpreting the results, due in the main to poor standardisation and incomplete reporting of methods, it is clear that relatively large quantities of fluoride are released from GICs for periods of up to one year. ![]() Glass composition ( Johal et al., 1995) determines ion release, as well as the biochemical environment of the implant bed ( Devlin et al., 1994).įluoride ion release from GIC has been comprehensively reported, although the majority of studies have related to the use of GIC in dental applications ( Wilson and McLean, 1988 El Mallakh and Sarkar, 1990 Forsten, 1991). Studies have reported the presence of such ions in the matrix of the cement ( Hatton and Brook, 1992a) and in adjacent bone ( Hatton and Brook, 1992b), with exchange of ions taking place with the (aqueous) environment ( McLean, 1988 El Mallakh and Sarkar, 1990, Forsten, 1991). As mentioned previously, certain ions released from the glass particles during the gelation process remain mobile once setting is complete. The bulk composition of GIC acts as a reservoir for ion release ( Nicholson et al., 1991 Wood and Hill, 1991b Sasanaluckit et al., 1993 Hill et al., 1995 Johal et al., 1995). These factors, which are believed to play an important role in ontogenesis and the osseointegration of biomaterials ( Weiss and Reddi, 1981 Clark et al., 1982 Mackie et al., 1987 Carter et al., 1991 Bagambisa et al., 1993, 1994) together with the hydrophilic surface of GIC, may explain the osteoconductive properties of implanted GIC ( Jonck et al., 1989a, b Brook et al., 1991a, b, 1992 Doherty, 1991 Nicholson et al., 1991 Hatton and Brook, 1992b Sasanaluckit et al., 1993 Hill et al., 1995 Johal et al., 1995). Immunohistochemical studies of implanted GIC have shown close association of the non-collagenous extracellular matrix proteins of bone (osteopontin, fibronectin and tenascin) with the GIC surface ( Carter et al., 1991 Johal et al., 1996). The ability of the material surface to bind certain biological factors that may recruit and regulate osteogenic cells could also assist the formation of a more stable bone-implant interface and thus improve the potential for clinical success. It has been suggested that this is due to ion exchange with the biological environment ( Brook et al., 1991a, Wood and Hill, 1991a, Hatton and Brook, 1992b, Hatton et al., 2006). The osteoconductivity exhibited by specific GICs is of particular interest. ![]() IM BROOK, in Joint Replacement Technology, 2008 11.3.1 Ion release and bioactivity
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