Discussion.
Acidic, basic, and buffered physiological salt solutions have been used as electrolytes for evaluating the dissolution of CaP implant materials. Furthermore, in recent studies, the success of CaP implants was suggested to be dependent on their ability to resorb or degrade; thereby allowing cellular penetration. However, irrespective of the degree of crystallinity, all CaP implants will degrade or dissolve to some degree. Because the amorphous phases are expected to dissolve first, it is possible that they control the initial biological response at the ceramic surface.
Protein content of the microenvironment has also been shown to affect dissolution properties of both hydroxyapatite and CaP test samples. It has been speculated that the anionic nature of proteins causes the attraction of Ca ions. However, the influence of proteins did not have a significant effect on the dissolution quantities of calcium in comparison with media without proteins. This could be the result of the fact that calcium dissolution has been shown to be strongly dependent on the microenvironment of the surrounding media. Therefore, because the media was removed and replaced daily, it was never allowed to become supersaturated with calcium in any of the three media tested. For this reason, the solutions in which the CaP cement bars were immersed were always undersaturated with respect to Ca, subsequently causing the release of Ca from the bars into the microenvironment.

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