Coefficient of thermal expansion of bioactive glasses: available literature data and analytical equation estimates

Bioactive glasses are able to develop a tenacious bond with human bone tissues and therefore they are largely used in orthopaedic and dental implants. However, due to their brittleness, they are mainly applied as coatings on tough substrates, such as titanium, alumina and zirconia. The reliability of bioactive glass coatings is deeply influenced by their thermodilatometric compatibility with the substrate, which may govern the development of dangerous thermal stresses at the interface. In spite of the technological relevance of the coefficient of thermal expansion (CTE) of bioactive glasses, few papers are specifically dedicated to such topic. In the present contribution, more than 70 bioactive glasses were reviewed in the literature, in order to investigate the relation existing between their composition and their CTE. Then four analytical models were applied to estimate the CTE of the same glasses and the calculated values were compared to the experimental results, in order to assess the reliability of the models and define an effective tool to predict the CTE. In particular, on the basis of the literature data and calculated values, the effect of modifier oxides and intermediate oxides, such as KO and MgO, on the CTE was discussed.