Effect of aging on bioactive of modified Portland cements.

Objectives: To evaluate the effect of aging in phosphate solution on biological behaviour of modified Portland cements for endodontics. Methods: Experimental cements were designed: wTC (modified Portland cement), wTC-Bi (plus bismuth oxide), wTC-alphaTCP (plus alpha-tricalciumphosphate). Sample discs were prepared and the biological behaviour of cements was tested on fresh cement (t0) and on samples aged for 14 (t14) or 28 (t28) days in DPBS at 37°C. The surface morphology and chemistry of fresh and aged cements was studied by SEM-EDX and micro-Raman. Materials were sterilized with 1% antibiotic/antimycotic solution (2 h) and pre-wetted with culture medium plus 10% fetal calf serum at 37°C (16 h). Human MSC were seeded on cements, and MSC on TCPS provided the controls. MSC were cultured up to 28 days, and cell adhesion, viability and growth, alkaline phosphatase (ALP) activity and collagen release were measured at different time endpoints. Results: All tested cements were not toxic for MSC. Cell adhesion and proliferation were higher on unaged cements (Fig.1). Differentiation of MSC to osteoblasts was confirmed by ALP expression in all samples, even if with high variability (data not shown). Collagen too increased with time, confirming the proper secretory activity of cells on the cements (Fig.2). A thick Ca-P coating layer was detected by SEM-EDX after 28 days of aging in DPBS (Fig.3 - Magnification 3100x). Raman analysis showed the presence of phosphate bands (965, 590 and 435 cm-1) and calcite bands (1088, 713, 280 cm-1) after both aging times (14 and 28 days) in DPBS. Conclusions: A thick apatite-calcite coating layer (biocoating) formed on surface of the experimental Portland-based cements aged for 14 and 28 days in phosphate solution. However fresh cements showed higher cell viability. WTC-alphaTCP demonstrated better biological behaviour. Bismuth oxide reduced cell viability and collagen release.