The effects of low-dose 2-hydroxyethyl methacrylate on apoptosis and survival in human dental pulp cells

Background/Purpose: 2-hydroxyethyl methacrylate (HEMA) is one of the most major components in dentin bonding systems. Uncured HEMA is eluted through the dentin and harmful to pulp cells. The study aimed to investigate the death pattern, morphological change and factors of human dental pulp cells (HDPCs) cultured with low-dose HEMA. Methods: HDPCs were cultured with low-dose concentration of HEMA at 0 mM (control), 0.125 mM, 0.25 mM, 1 mM, 2 mM and 4 mM on Day 3 and 5. The cell morphology was observed with F-actin immunocytochemical staining. The flow cytometry was used to analyze the death pattern. NF-kB and Trx-1 were measured using ELISA kits. Results: The major death pattern was early apoptosis and late apoptosis. The morphological characteristics of apoptosis were observed clearly at 4 mM on Day 3 and Day 5. The phosphorylated NF-kB normalized to total NF-kB protein was significantly higher at 2 mM and 4 mM on Day 5. There was no difference of Trx-1 on Day 3, but significantly higher at 0.25 mM and 1 mM on Day 5. The trend line of phosphorylated NF-kB and Trx-1 showed highly positive correlations with HEMA concentration. Conclusion: The significant cellular morphology characteristics of apoptosis can be observed at higher dose and longer period after exposed to uncured HEMA. The expression of NF-kB was following the ratio of late apoptosis at longer exposure period. Clinically, the remaining dentin thickness should be enough to decrease HEMA concentration and thus to protect pulp cells free from harm.