Antimicrobial potency of alkali ion substituted calcium phosphate cements

Potassium and sodium containing nanoapatite cements were produced by the reaction of mechanically activated CaNaPO4 (CSP), CaKPO4 (CPP) and Ca2KNa(PO4)2 (CPCP) with a 2.5% Na2HPO4 solution. The cements exhibited clinically acceptable setting times of approximately 5 min and compressive strengths of 5–10 MPa. The antimicrobial properties of the cements were tested with the agar diffusion test using Streptococcus salvarius, Staphylococcus epidermis and Candida albicans. All types of alkali ion containing cements showed a significantly higher antimicrobial potency with inhibition zones of approx. 4–11 mm than a commercial calcium hydroxide cement which resulted in small inhibition zones around the cement samples of a maximum of 1.5 mm. The antimicrobial properties of all the cements were not found to diminish even after longer incubation times. This behaviour was attributed to the formation of soluble alkaline metal phosphates during setting which increased the pH value in the agar gel around the alkali containing calcium phosphate cement to 8.5–10.7 compared to 6.5–8.0 for the Ca(OH)2 product. The high antimicrobial potency of alkali–calcium phosphate cements may find an application in dentistry as pulp capping agents, root fillers or cavity liners.