Cytotoxicity from resin composites is primarily due to release of what material?

• A. Water
• B. Resin components
• C. Filler particles
• D. Oxygen

Answer: (B)

Cytotoxicity from resin composites mainly comes from the resin components that remain unreacted after curing and can leach out into surrounding tissues. During light-activated polymerization, the resin doesn’t reach 100% conversion, leaving residual monomers and short-chain oligomers (the resin components) that can diffuse through dentin and affect pulp cells, causing cellular stress or death. The result is that these resin components are the primary source of cytotoxic effects.

Water isn’t the toxic agent itself; it serves as a solvent and carrier for any leached substances. Filler particles are inorganic and largely inert under normal conditions, so they’re not the main cause of cytotoxicity. Oxygen can influence the curing process by inhibiting polymerization at the surface, which can increase residual monomer and thereby influence toxicity, but the toxic effect still stems from the resin components released.