Effect of Acrylic Polymerization on Cytotoxicity, Residual Monomer Content and Mechanical Properties

The aim of this study was to test and find connection between three different parameters of acrylic resins: cytotoxicity, residual monomer content in the material and flexural strength.

Superacryl Plus (SpofaDental, Czech Rep.) acrylic material has been polymerized in three different ways, short-time polymerization (45 minutes), normal time (90 minutes) and long-time (7 hours 30 minutes). Flexural strength was tested in compressive instrument Shimadzu for 65 × 10 × 3.3 mm samples. Then after 24 hours the samples were broken. In 50 mm diameter and 1 mm thick samples, residual monomer was determined by gas chromatography (according to ISO standard), and the last series of the sample was used to perform cytotoxicity tests (5 mm diameter). Statistical analysis: Data were analyzed by two-way ANOVA (in GraphPad Software Inc., San Diego, CA, USA), with p-value < 0.05 as statistically significant.

The results from the tests show that the greatest inhibition in the development of cell cultures (VERO CCL-81) by MTT assay), was observed for the sample polymerized in the first short-time method (73.49±10%). The material also had the largest content of residual monomer 2.02±0.08% (p-value < 0.01) and lowest flexural strength 71.53±2.26 MPa. Hardened acrylic resins over 60 minutes do not adversely affect cell cultures (undisturbed growth 83.18±10.72%). The residual monomer content was below 1% (p-value < 0.01) and the mechanical resistance to fracture was over 80 MPa (p-value < 0.01).

The use of a short polymerization method of acrylic materials can adversely affect both the mechanical properties of the prosthesis itself and its biocompatibility. From a clinical point of view, it is important to take care about the polymerization times of acrylic. Dentures for allergic patients should be carried out in long-term polymerization when the content of residual monomer is as low as possible.