Freshly prepared glass ionomer is ______ cytotoxic, but this effect is _____ over time.

• A. not cytotoxic; unchanged
• B. mildly cytotoxic; reduced
• C. highly cytotoxic; increased
• D. moderately cytotoxic; stable

Answer: (B)

Glass ionomer cement shows a time-dependent biocompatibility shift during setting. When freshly mixed, the acid-base reaction produces a relatively acidic environment and some leaching of components, which can cause mild cytotoxic effects on cells that are in direct contact. As the cement matures and sets, the matrix becomes more crosslinked and the pH tends toward neutral, reducing the release of acidic constituents and thus lowering cytotoxicity. Fluoride release continues but at levels that are not cytotoxic and can be beneficial. So the best description is that fresh glass ionomer is mildly cytotoxic, and this effect diminishes over time.