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 vitro' bioactiv ity of pseudowollastonite was further assessed in human parotid saliva. The main objective was to compare behaviour of the material in a natural mediu m of high protein content (human parotid saliva) with its behaviour in an a cellular protein-free solution (simulated body fluid). Methods: Samples of polycrystalline pseudowollastonite were immersed for on e month in human parotid saliva at 37(degrees)C. Changes in ionic concentra tions in the human parotid saliva and the pH right at the interface of pseu dowollastonite/human parotid saliva were determined. The products of the in terfacial reactions were studied by thin-film X-ray diffraction, scanning a nd 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 hydro xyapatite-like layer formation in saliva was similar to that showed in simu lated body fluid. Conclusions: The hydroxyapatite-like layer formed at the interface was foun d to be compact, continuous and composed of many small crystallites with ul trastructure similar to that of natural cortical bone and dentine. The stud y also concluded that the high pH conditions (10.32) existing right at the pseudowollastonite/human parotid saliva interface promoted hydroxyapatite-l ike precipitation. At this stage of the study, similarities of the material behaviour in saliva and acellular simulated body fluid suggest that the ps eudowollastonite could be of interest in specific periodontal applications for bone restorative purposes. (C) 1999 Elsevier Science Ltd. All rights re served.