Calcium Release.
An increasing amount of Ca21 released from bone cements was observed after incubating the bone cements in all solutions throughout the 21-day study period (Figure 1). There was no statistically significant difference (analysis of variance, P . 0.05) in Ca21 dissolution from cements immersed in 1.0 mol/L Tris buffer solution as compared with both 5% fetal bovine serum solution and tissue fluid substitute.

Inorganic Phosphate Dissolution.
Similar to the calcium release, an increasing amount of P51 dissolution was also observed throughout the 21-day study period (Fig. 2). There was no statistically significant difference in the dissolution properties of P51 between the 1.0 mol/L of Tris buffer (0.370 6 0.02 mg/mm2) and 5% fetal bovine serum solutions (0.247 6 0.06 mg/mm).2 However, for cements that were incubated in tissue fluid substitute, the dissolution of P51 was significantly less (0.03 6 0.002 mg/mm)2 throughout the study period as compared to the cements that were immersed in 1.0 mol/L Tris buffer and 5% fetal bovine serum solution.

Flexural Strength.
There was no significant difference in strength measurements of bars immersed in all media throughout the 21-day period (Fig. 3). However, regardless of solution, the strength increased to an average of 7.78 6 1.82 N in comparison with 3.19 6 0.93 N for non-immersed samples after 21 days.

Fig. 1. Release of Ca ions from bone cements after 21 days in different media.
Solid line: Tris buffer; Broken line: tissue fluid substitute; Dotted line: Tris buffer and fetal bovine serum.



Fig. 2. Release of P ions from bone cements after 21 days in different media.
Solid line: Tris buffer; Broken line: tissue fluid substitute, Dotted line: Tris buffer and fetal bovine serum.



Fig. 3. Flexural strength of the bone cements before and after immersion in different media for 21 days.