Evaluation of novel glass-ionomer cements for hard tissue repair using in vitro and in vivo methods

Ionomeric cements (ICs) have a successful history as restorative materials in dentistry where they are called glass-ionomer cements (GICs). More recently they have potential for use as bone substitutes and cements in orthopaedic, otolaryngology and maxillofacial surgery. The influence of glass composition on IC properties such as biocompatibility has not been adequately studied. The broad aim of this research was to characterise a series of ICs of defined composition and evaluate their biocompatibility in vitro and in vivo. The hypothesis was that ICs could be optimised through their glass composition for clinical use as bone substitutes or cements.

ICs are formed by the neutralisation reaction of an inorganic basic glass and organic polyelectrolyte acid. In vitro studies involved the determination of ions eluted from set cement discs and evaluation of the toxicology and biocompatibility of the ICs using cell culture techniques. In vivo studies involved the implantation of set and wet ICs into the midshaft of the rat femur. The osteoconduction and osseointegration of specified ICs were determined by histomorphometric analysis. Additionally, the role of noncollagenous extracellular matrix bone proteins were studied as they play an important role in the interactions of the healing of hard tissues with implants.

The response of bone was dependent upon IC formulation with increase in fluoride and phosphate stimulating bone cell response. Bone response was negatively correlated with aluminium. It was concluded that the IC from the apatite stoichiometric series (designated LG26) had the most promising formulation for biomedical applications. This study confirmed that ICs have some potential clinical use as a bone substitute and cement. However, in vitro studies suggested that aluminium ions released from set ICs were responsible for some cytotoxicity and further work might usefully be directed at reducing the release of this ion from the cement.