Acid Neutralization Capacity of Calcium Phosphate Cements

Acid Neutralization Capacity of Calcium Phosphate Cements

A calcium phosphate cement (CPC) was shown to have the necessary attributes for good endodontic materials except adequate basicity needed for antimicrobial properties. To enhance its basicity, Ca₃Si₂O₅ , a highly alkaline compound,  was added to CPC.  Objectives: To investigate the acid neutralizing capacity of the CPC-Ca₃Si₂O₅ composites.  Methods: The powders were prepared by combining CPC with a mass fraction of 0 (CPC), 0.25 (CPC-1), 0.5 (CPC-2) or 0.75 (CPC-3) of Ca₃Si₂O₅ . The liquid was 0.5M Na₃PO₄.  A P/L = 2.65 was used for preparing the CPC-Ca₃Si₂O₅  pastes. Mineral trioxide aggregate (MTA), used as the control, was prepared following manufacturers' instructions. After 24 h, the set sample (unexposed to water) was dried and ground. 0.2g of the sample was placed in 10 mL of 150 mM NaCl solution under a N₂ atmosphere and the pH of the solution was monitored. After the maximum pH was recorded, a 0.2 M HCl in 150 mM NaCl solution was added to reduced the pH to predetermined levels (9.0, and 7.4), and the amount of acid consumed was recorded. Results: The setting time (in min by Gilmore needle method) for CPC, CPC-1, CPC-2 and CPC-3 were (mean±s.d.; n=3) 30±3, 30±3, 30±3 and 50±5  respectively. The highest obtainable pH for CPC, CPC-1_, CPC-2_, CPC-3 and MTA were (mean±s.d.; n=3) 9.40±0.16, 11.53±0.07, 12.07±0.06, 12.23±0.14, 12.13±0.09  respectively. The amounts of HCl consumed (in mEq/g of sample) were (1) to pH 9: 0.13±0.03, 1.64±0.30, 6.29±0.60, 9.01±1.02, 11.43±0.96, and (2) to pH 7.4: 0.79±0.04, 4.11±0.26, 9.40±0.96, 13.42±0.86, 15.20±1.03, respectively. Conclusion: Acid neutralizing capacity depends strongly (p<0.05) on Ca₃Si₂O₅  content. CPC-3 can neutralize as much acid as MTA (p>0.1), but it has a shorter setting time than that of MTA (> 4 hr) and excellent handling properties. Supported by NIH grant DE-11789, ADAF, and NIST.