Methacrylate resin-based dentin adhesives and root canal sealers used for bonding of filling materials inside the root canal system are cytotoxic and result in reduction in cell proliferation to a variable extent. An in vitro study to examine the detoxifying effects of N-acetylcysteine (NAC) on four commercial adhesive systems on adhesive-induced cytotoxicity and cell survival was conducted so that the use of methacrylate resin-based materials for filling root canals could be optimized. The finding that NAC co-treatment protected the cells from adhesive-induced toxicity by increasing cellular proliferation, attenuating cell cycle arrest, and reducing cell death suggests the null hypothesis that NAC has no effect on dentin adhesive-induced cell death and cell cycle arrest should be rejected.