An in vitro investigation of a poly(vinyl phosphonic acid) based cement with four conventional glass-ionomer cements. Part 1: flexural strength and fluoride release

Objective: To investigate the flexural strength and fluoride release of four conventional glass-ionomer cements: Ketac-Molar (KM), HiFi (HF), Vivaglass Fil (VF), Ketac-Fil (KF) and a newly developed glass polyphosphonate cement, Diamond Carve (DC). Method: Disc specimens (10 mm diameter, 1 mm thick) were prepared and mould stored at 37°C. After one hour, the specimens were removed from their mould and immersed in 20 ml of deionised water until required for testing. Biaxial flexural strength was determined at 1 hour and at 1, 7, 30 and 90 days after the start of mixing. Measurements of fluoride release from the specimens were carried out at 2 hours and at 1, 3, 7, 14, 30, 60 and 90 days after the start of mixing using a fluoride ion selective electrode. The results were analysed using ANOVA and student ‘tʹ tests. Results: All the materials displayed different flexural strength patterns. KM and DC became stronger whilst KF and VF plateaued in strength with time. HF peaked in strength and then became weaker. At 90 days, the mean flexural strengths in decreasing order was as follows: KM≥VF≥DC≥HF>KF. An initial fast rate of fluoride release followed by a slower but steady release of fluoride was observed in each of the materials. The mean cumulative fluoride release in decreasing order was as follows: VF>KF≥HF>DC>KM. VF released significantly higher level and KM significantly lower level of fluoride than the other materials. Conclusions: The acid used to form the cement could not be used to predict changes in cement strength behaviour with respect to time. DC increased in strength with time and its flexural strength at 90 days was comparable to that of HF and VF. The cumulative and rate of fluoride release varied for the materials. DC had a low fluoride release consistent with a fast setting material with good early resistance to water.