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Since no specific data on the toxicokinetics of silicocalcium is available, the assessment of the behaviour of silicocalcium in human body will be based on in vitro studies on the release of the different silicocalcium components from silicocalcium particles in different artificial biological fluids. This data will give us information on bioaccessibility, and therefore, also possible bioavailability of the silicocalcium. These dissolution studies have been made with a grade of silicocalcium which have been described in detailed in Chapter 1. Silicon has been the main constituent in the tested silicocalcium material, being present in bulk material at concentration of 61.93 (wt-%, later expressed as 62%). These studies show that silicon is released at similar or slightly lower amounts from CaSi than from pyrogenic silica particles, the fact that justifies read-across from some toxicological properties of amorphous silica Thus, the bioavailability of silicon from silicocalcium is likely to be similar or lower than from amorphous silica.Calcium is another main element released from silicocalcium matrix. No data is available on the chemical form, in which calcium is released inbiologicalfluids..The release of iron from silicocalcium is very low. This can be explained by the surface oxide layer, which restricts the release of elements from silicocalcium matrix. When the results on the release of different elements from CaSi matrix are compared to the results obtained from pyrogenic silica, it can be concluded that:·

CaSi releases similar or somewhat lower levels of silicon than pyrogenic silica. Thus, the bioavailability of silicon from CaSi is similar or lower than from pyrogenic silica. Some of the differences in release rate can be explained by different particle characteristics (pyrogenic silica particles ested were smaller andhad higher particle surface area).

The release of iron from CaSi is very restricted and lower than from pyrogenic silica.

Calcium release was significantly higher from CaSi than from pyrogenic silica.

Aluminium is relesed from silicocalcium only in acidic environment like gastric juice.

The release of other elements from both pyrogenic silica and CaSi is very low.