Development of a detoxified polymethyl methacrylate-based resin for cells

Polymethyl methacrylate (PMMA)-based dental resin is often directly loaded on the prepared teeth in fabricating temporary crown, under which situation cytotoxicity of PMMA chemicals on dental pulp cells through the dental tubules has been concerned. N-acetyl cysteine (NAC), an anti-oxidant amino-acid, potentially erases major factors of its toxicity. Objective: This study determined whether PMMA extracts adversely effects on the viability and function of dental pulp cells and whether the cytotoxicity, if there is, can be detoxified by NAC. Methods: Commercial self-curing PMMA-based dental resin (Unifast II, GC, Tokyo, Japan) was polymerized and extracted into culture medium with various mol concentrations of NAC (0mM, 0.5mM, 5.0mM and 7.5mM). Dental pulp-derived cells extracted from rat upper central incisors were cultured with osteoblastic media, following exposure of cells to PMMA extracts with or without NAC for 1 hour. Results: Annexin-based flowcytometry showed that only 20% of cells after exposure to the extracts were viable, which was rescued by the addition of NAC. The degree of rescue was NAC-dose dependent, elevating a percentage of viable cells up to 70%. Alkaline phosphatase (ALP) activity at day 5 and von Kossa-stained mineral deposition area at day 14 was significantly suppressed in the cells once exposed to PMMA extract down to 35% or 60% of that in the control polystyrene culture, which was microscopically confirmed as weak and sparse staining on the matrix. In contrast, this early- or late-stage odontblastic function was improved by the addition of NAC into extracts up to the level equivalent to that seen in the control culture. Conclusion: The viability and odontblastic functions of dental pulp cells were significantly suppressed after exposure to PMMA extracts, which was nearly completely recovered by the addition of NAC into the extracts.