Bioactivity of pseudowollastonite in human saliva

Objectives: Pseudowollastonite (CaO·SiO2) was found to be bioactive in a simulated body fluid environment. In the present study, ‘in vitroʹ bioactivity of pseudowollastonite was further assessed in human parotid saliva. The main objective was to compare behaviour of the material in a natural medium of high protein content (human parotid saliva) with its behaviour in an acellular protein-free solution (simulated body fluid). Methods: Samples of polycrystalline pseudowollastonite were immersed for one month in human parotid saliva at 37°C. Changes in ionic concentrations in the human parotid saliva and the pH right at the interface of pseudowollastonite/human parotid saliva were determined. The products of the interfacial reactions were studied by thin-film X-ray diffraction, scanning and transmission electron microscopy. Results: The results confirmed formation of a hydroxyapatite-like layer on the surface of the material, and also suggested that the mechanism of hydroxyapatite-like layer formation in saliva was similar to that showed in simulated body fluid. Conclusions: The hydroxyapatite-like layer formed at the interface was found to be compact, continuous and composed of many small crystallites with ultrastructure similar to that of natural cortical bone and dentine. The study also concluded that the high pH conditions (10.32) existing right at the pseudowollastonite/human parotid saliva interface promoted hydroxyapatite-like precipitation. At this stage of the study, similarities of the material behaviour in saliva and acellular simulated body fluid suggest that the pseudowollastonite could be of interest in specific periodontal applications for bone restorative purposes.