Effect of addition of hydroxyapatite on the physical properties of IRM

The aim of this study was to evaluate the effect of adding 10% and 20% hydroxyapatite (HAP) to Intermediate Restorative Material (IRM) on physical properties such as working time, setting time, compressive strength and disintegration rate. The working and setting times were determined by an indentation method. The ISO recommended method was used to determine compressive strength. The rate of disintegration in vitro was evaluated in buffered sodium citrate at pH 4.5, 5.8, buffered phosphate at pH 7.0 and in bovine serum (pH 6.8), and examined using a replica method and scanning electron microscopy. Kalzinol and EBA were used as control materials for the disintegration experiment. IRM had longer mean working (4 min 43.5 s) and mean setting (6 min 28.5 s) times than IRM + 10 or 20% HAP (P < 0.001), the mean reductions being 16% and 9% for IRM + 10% HAP, and 29% and 19% for IRM + 20% HAP, respectively. IRM had a greater compressive strength (68.5 MPa, P < 0.01) than IRM + 10% HAP (65.0 MPa) or IRM + 20% HAP (60.0 MPa, P < 0.001). Kalzinol, IRM + 10% HAP and IRM + 20% HAP were found to disintegrate after 8 weeks in buffered phosphate and in bovine serum. In contrast, IRM and EBA showed no noticeable signs of disintegration after 6 months in the same media. The physical properties of IRM + 10% HAP and IRM + 20% HAP were reduced compared with IRM but the reductions were not considered to be of clinical significance.