Water sorption and colour stability of composites containing the antibacterial monomer MDPB

Objectives: Previously, we have reported that composites incorporating the newly developed antibacterial monomer methacryloyloxydodecylpyridinium bromide (MDPB) inhibited bacterial growth and plaque accumulation on their surfaces without releasing antibacterial components, and that the antibacterial effect was not lost even after ageing in a wet environment for a long period. The purpose of this study was to investigate the influence of the incorporation of MDPB on the water sorption characteristic and colour stability of Bis-GMA based composites. Methods: Cured disc-shaped specimens of composites containing 0.4% or 0.5% MDPB were fabricated, and water uptake, the diffusion coefficient and the surface contact angle for water were determined. Discoloration of MDPB-containing composites was evaluated after immersion in water at 37°C and 60°C for 4 weeks and compared with that of the control composite without MDPB. Results: There were no significant differences in water uptake, diffusion coefficient and contact angle between the control and MDPB-containing composites. Although composites incorporating MDPB showed greater discoloration than the control when maintained at 37°C, no difference was found after 4 weeks of immersion in water at 60°C. Conclusions: Incorporation of small amounts of the antibacterial monomer MDPB showed no influence on the water sorption characteristic and affected a little the colour stability of the Bis-GMA based composite, causing rapid discoloration.