Chang H‐H, Chang M‐C, Huang G‐F, Wang Y‐L, Chan C‐P, Wang T‐M, Lin P‐S, Jeng J‐H. Effect of triethylene glycol dimethacrylate on the cytotoxicity, cyclooxygenase‐2 expression and prostanoids production in human dental pulp cells. International Endodontic Journal, 45, 848–858, 2012. Aim  To evaluate the effect of TEGDMA on cell cycle progression as well as alterations of cell cycle‐related gene and protein expression. Methodology  Human dental pulp cells were exposed to 0–5 mmol L−1 TEGDMA for 24 h. Cytotoxicity was evaluated by 3‐(4, 5‐dimethyl‐ thiazol‐2‐yl)‐2,5‐diphenyl ‐tetrazolium bromide assay. Cell cycle progression was analysed by propidium iodide (PI) flow cytometry. Cell death pathway was surveyed by annexin V/PI dual‐staining flow cytometry. The mRNA expression of cell cycle‐related genes (cdc2, cyclinB1 and p21) and COX‐2 was evaluated by reverse transcriptase‐polymerase chain reaction, and their protein expression was evaluated by Western blotting. The production of PGE2 and PGF2α in the culture medium was determined by enzyme‐linked immunosorbent assay. Results  Triethylene glycol dimethacrylate inhibited cellular growth and induced cell cycle deregulation in dental pulp cells. High‐dose exposure provoked both necrotic and apoptotic cell death. The gene and protein expression of cdc2, cyclin B1 and cdc25C declined obviously whilst cells treated with 2.5 mmol L−1 TEGDMA concurrent with the elevated expression of p21. The mRNA and protein expression of COX‐2, along with production of PGE2 and PGF2α, are drastically raised by 2.5–5 mmol L−1 TEGDMA. Conclusions  Triethylene glycol dimethacrylate induced cytotoxicity, cell cycle arrest and apoptosis in dental pulp cells, which was associated with the decline of cdc2, cyclin B1, cdc25C expression and elevation of p21 expression. Concomitantly, COX‐2 expression, PGE2 and PGF2α production increased. These effects may contribute to explain the pulpal damage and inflammation induced by TEGDMA after operative procedures.