A cement system for forming an implant comprises a reactive glass ionomer cement (GIC) powder, a polycarboxylic acid or salt, and a filler. The polycarboxylic acid or salt is included to initially provide a paste having a pH less than 7 when the cement system is mixed with water. In one embodiment, the filler is substantially inert when mixed with water and is selected from (CaO)(AI2O3)6, (CaO)(AI2O3)2, calcium silicate (CaOSiO2), and mixtures thereof. In another embodiment, the filler is substantially reactive when mixed with water and is selected from (CaO)2(SiO2), (CaO)3(SiO2), and mixtures thereof, and the cement system includes an additional acid to maintain the paste at a pH less than 7 for at least one hour after the cement system is mixed with water.