An in vitro investigation of a poly (vinyl phosphonic acid) based cement with four conventional glass-ionomer cements: Part 2: maturation in relation to surface hardness

Objective: To investigate the surface hardness of four conventional glass-ionomer cements: Ketac-Molar (KM), HiFi (HF), Vivaglass Fil (VF), Ketac-Fil (KF) and a newly developed glass polyphosphonate based cement, Diamond Carve (DC) at different maturation times in water and to investigate the effects of early water exposure on their surface hardness. Method: Disc specimens (10 mm diameter, 1 mm thick) were prepared and mould stored at 37°C. The effect of different maturation times (15, 30 and 60 min) and storage in water over 24 h after those maturation times on surface hardness was determined using a microindentor with a Vickers diamond indentor. The results of the surface hardness tests were analysed using Mann-Whitney non-parametric statistics (p≤0.05). The working (WT) and setting (ST) times of the cements were also measured using a modified Wilson oscillating rheometer. Results: All the materials became harder after 24 h immersion in water. HF, VF and DC showed initial sensitivity to a short maturation time, but only HF was adversely affected by early moisture exposure. KF and KM were least sensitive to short maturation time or early water exposure. DC had the shortest and HF the longest WT and ST. HF and VF had a high WT:ST ratio of 1:7 and 1:9, respectively. Conclusions: A short maturation time (of 15 min) and early exposure to water did not adversely affect the surface hardness of KF, KM, VF and DC. DC, based on poly(vinyl phosphonic acid), had the shortest WT and ST. Poly(acrylic acid) based HF and VF had a long ST in relation to their WT.