Mechanical and antibacterial properties of polymethyl methacrylate modified with zinc dimethacrylate

Polymethyl methacrylate (PMMA) has been widely used for denture base resin. However, concerns associated with PMMA, such as poor mechanical strength, high roughness, and porosity promoting microbial adhesion have been voiced; appropriate modification of PMMA denture base resin may improve its clinical application.

The purpose of this in vitro study was to investigate the effect of zinc dimethacrylate (ZDMA) modification on the mechanical and antibacterial properties of PMMA.

ZDMA at different mass fractions was mixed into PMMA as the experimental group, and unmodified PMMA was the control group. X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectrometry (SEM-EDS), and the degree of conversion (DC%) were applied for characterization. Mechanical properties were measured with the 3-point bend test (n=10). The Streptococcus mutans biofilm model was used to investigate the antibacterial property by using colony-forming unit counts, metabolic activity, live/dead staining, quantitative real-time PCR (qRT-PCR), and SEM (n=5). The cell counting kit (CCK)-8 test was used to evaluate cytotoxicity. Data were subjected to analysis of variance and the post hoc Tukey honestly significant difference test (α=.05).

SEM-EDS and XRD analysis revealed successful ZDMA incorporation into the PMMA matrix. DC% increased with the mass fraction of ZDMA, and no significant differences in DC% values were found among each tested group (P=.554). ZDMA mass fraction at 1 wt%, 2.5 wt%, and 5 wt% enhanced its mechanical properties, but those at 7.5 wt% and 10 wt% were reduced. The results of antibacterial experiments showed that ZDMA-modified PMMA displayed antibiofilm capabilities. Quantitative real-time PCR indicated that the expression levels of tested genes were significantly suppressed and that CCK-8 test indicated no cytotoxicity.

ZDMA-modified PMMA exhibited antibacterial properties without its mechanical properties being affected. ZDMA is a potential metal crosslinking monomer for the modification of PMMA denture base resin.