Determination of Castability of Novel Canasite-based Glass-Ceramics

Objectives: Miller et al. showed that the addition of excess CaO and P2O5 to the stoichiometric fluorcanasite glass-ceramic composition induced the early formation of an apatite layer in simulated body fluid, and commented that these materials might be useful for use as bone substitutes. While it was also suggested that these materials could be cast to shape via the lost wax process (due to their relatively low liquidus), no quantitative data has been published to date. The aim of this study was therefore to determine the relative castability of modified canasite-based glass-ceramics. Methods: Glass A was a commercial canasite composition, Glass B had reduced sodium content, Glass C had an increased calcium concentration while Glass D contained P2O5. Glass S was a stoichiometric fluorcanasite composition. Castability was determined using the lost wax method and a graduated spiral cast (as reported previously). Gypsum and phosphate bonded investments were both used to observe their effect on the casting process and cast surfaces. Results: The stoichiometric composition had the greatest castability (Glass S = 29 mm), while increasing calcium concentration relative to sodium did not have as great an effect on castability as anticipated. Fluorcanasite glasses could also be cast to reproduce complex shapes using the lost wax method. X-ray diffraction showed similar bulk crystallisation for each glass irrespective of the investment material. However, some differences in surface crystallisation in the presence of different investment materials were detected. Gypsum bonded investment was superior to phosphate bonded investment under the conditions used in this study. Conclusion: Modified fluorcanasite glasses had excellent castability compared to control materials, confirming that they may be useful for fabrication of custom prostheses via the lost wax technique. While there was a relationship with glass soda content, this was not the sole factor that determined castability.