Biomimetic calcium-silicate cements aged in simulated body solutions. Osteoblast response and analyses of apatite coating

Calcium-silicate cements have been recently proposed for application in dentistry as root-end filling and root-perforation repair materials. The aim of this study was to investigate the effect of ageing of experimental calcium-silicate cements on the chemistry, morphology and in vitro bioactivity of the surface, as well as on osteoblast viability and proliferation.

Two experimental cements (wTC-Bi, containing bismuth oxide and wTC), mainly based on dicalcium-silicate and tricalcium-silicate, were prepared and tested for their bioactivity after soaking in Dulbecco's phosphate buffered saline (DPBS), used as simulated body fluid. Human marrow stromal cells (HMSC) were seeded on the cements maintained in DPBS for 5 hr (non-aged group), 14 and 28 days (aged group). Cell viability was assessed by the Alamar blueTM test and morphology by scanning electron microscopy (SEM) at different time endpoints. The surface of the soaked cements was analyzed by environmental scanning electron microscopy or SEM coupled with energy dispersive X-ray microanalysis (ESEM/EDX or SEM/EDX respectively) and the micro-Raman technique.

The ESEM/EDX results showed a uniform surface composed of CSH hydrogel (mainly derived from the hydration of belite and alite) on both non-aged cements. Micro-Raman spectroscopy revealed the presence of calcium carbonate, anhydrite, ettringite, alite and belite. The SEM/EDX data showed an irregular calcium-phosphate multi-layered biocoating with many sharp and protruding crystals on both the aged cements. Micro-Raman spectroscopy revealed crystalline apatite and calcite. The osteoblast response results showed that both the experimental cements exerted no acute toxicity in the cell assay systems. The non-aged samples promoted greater cell growth. SEM showed cells well spread and adherent to the non-aged materials. A reduced number of attached cells was noticed on the aged cements. Bismuth oxide-containing cement allowed a reduced cell viability suggesting some cytotoxic effects. However, the thick biocoating formed on the 28-day aged samples lowered the deleterious effect of bismuth oxide on cell growth. Actually, micro-Raman spectroscopy revealed progressive bismuth oxide depletion on the wTC-Bi surface, due to the increased thickness of the apatite deposit.

The study demonstrated that (1) these materials support osteogenic cells growth and may induce early bone formation, (2) the ageing in DPBS reduced the growth of HMSC, but eliminated the deleterious effect of the bismuth oxide on cell growth. In conclusion, the experimental cements have adequate biological properties to be used as root-end/root repair filling materials or pulp capping materials.