Cytotoxicity is caused by ______ released from the composite.

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

Answer: (C)

Cytotoxicity in a composite primarily comes from the resin components that can leach out as unpolymerized monomers or degradation products. Even after curing, there are residual monomers such as Bis-GMA, UDMA, TEGDMA, and HEMA that may diffuse through dentin or surrounding tissues and interact with cells, potentially reducing cell viability, altering metabolism, or triggering apoptosis. This leaching is more likely when the degree of conversion is low, which can happen if curing is insufficient, if the material is thick or shaded, or if the light source isn’t optimal.

Filler particles themselves are largely inert and don’t typically release toxic substances that cause cytotoxicity, so they’re not the primary source of cytotoxic effects. Oxygen at the curing surface can inhibit polymerization and thereby increase residual monomer content, which indirectly elevates cytotoxic risk, but the root cause remains the resin components. In practice, maximizing the degree of conversion through adequate curing minimizes these leachable resin monomers and reduces cytotoxic potential.