HEMA is _____ times less cytotoxic than Bis-GMA.

• A. 2 times
• B. 10 times
• C. 100 times
• D. 1000 times

Answer: (C)

The amount of harm a resin monomer can cause to cells depends on how it behaves once it can escape the polymer: its size, solubility, and reactivity influence how much gets into cells and what it does there. Bis-GMA is a large, rigid, aromatic monomer, which means that when it does release, its interactions with cellular components can be quite disruptive. HEMA, by contrast, is a smaller, more hydrophilic molecule. While it can be cytotoxic, the extent of harm it causes is much less than that of Bis-GMA under comparable exposure. That difference in molecular characteristics translates into a substantially larger harmful potential for Bis-GMA, often estimated around two orders of magnitude (about 100 times) greater. So, HEMA is about 100 times less cytotoxic than Bis-GMA.

The other magnitudes—2x, 10x, or 1000x—don’t align as well with how these monomers behave in cells. A 2x or 10x difference would imply only a small gap in toxicity, which isn’t consistent with the distinct structural and release properties of these materials. A 1000x figure would imply an extreme disparity not typically observed in standard in vitro comparisons.