The incorporation of hydroxyapatite into glass-polyalkenoate (“glass-ionomer”) cements: a preliminary study

The effect of adding finely divided hydroxyapatite (HAp) powder to glass-polyalkenoate cements has been studied. Two different glasses were used in cement formation, an oxide and a fluoride glass. Cements were prepared at a powder: liquid ratio of 2:1, higher ratios being unattainable because of the low bulk density (hence large volume fraction per unit mass) of HAp powder. For the oxide glass there was a steady reduction in compressive strength and an increase in working and setting times with increased loadings of HAp. By contrast, for the fluoride glass, there was a plateau region from 2.5 to 40% by mass HAp in the glass powder in which the compressive strengths and the working and setting times remained approximately constant. At HAp levels above 40%, as for the oxide glass, there was a significant reduction in strength and an increase in working and setting times. The presence of HAp in the cement was not found to inhibit the development of compressive strength with time for cements prepared from the fluoride-containing glass. Cements prepared from the oxide glass, by contrast, did not increase in strength with time and this feature was also not changed by the presence of HAp.