Reaction between CSH and Phosphate Buffered Saline Solution

Objective: The aim was to characterize the nature of reaction between a calcium silicate hydrate (CSH) and a phosphated buffer saline solution (PBS). CSH is the major hydration product of bioactive portland cement based endodontic materials.

Methods: CSH powder (CaO/ SiO2 = 2.0) was synthesized, and immersed in PBS (pH = 7.2) at 370C for 2 m. The powder exposed to PBS, following washing and drying, was characterized by SEM, EDXA, XRD and FTIR. Untreated powder served as reference control.

Results: The solution remained clear and the particle free flowing during the study period. Microscopic examination indicated the deposition of globular products on each original particle during exposure to PBS. The deposits contained mainly Ca, P, and O, and were identified to be crystalline carbonated hydroxyapatite (HA).

Conclusions: (1) CSH is sparingly soluble in PBS. Its conversion to HA is surface nucleated, and not the result of a dissolution – precipitation type reaction within the solution.

(2) In addition to calcium hydroxide, a minor hydration product and a known dentinogenic material (2007 IADR Abst. # 2022), CSH is likely to contribute significantly to the favorable biological properties of portland cement based materials through its transformation to HA (Sarkar, et al, JOE, 31, 2, 2005).