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 ph ysical properties such as working time, setting time, compressive stre ngth and disintegration rate. The working and setting times were deter mined by an indentation method. The ISO recommended method was used to determine compressive strength. The rate of disintegration in vitro w as evaluated in buffered sodium citrate at pH 4.5, 5.8, buffered phosp hate at pH 7.0 and in bovine serum (pH 6.8), and examined using a repl ica method and scanning electron microscopy. Kalzinol and EBA were use d as control materials for the disintegration experiment. IRM had long er mean working (4 min 43.5 s) and mean setting (6 min 28.5 s) times t han 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 + 1 0% 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 i n buffered phosphate and in bovine serum. In contrast, IRM and EBA sho wed no noticeable signs of disintegration after 6 months in the same m edia. 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.