Comparison of mechanical properties of polymethyl methacrylate of different mixing ratios

To investigate mechanical properties of polymethyl methacrylate (PMMA) of different mixing ratios.

At 25°C, self-curing denture acrylic and liquid dental base acrylic resin are mixed at mass-volume ratios of 1.5:1, 1:1, 1:1.25, 1:1.5, 1:1.75, 1:2 (g:ml) respectively, and stirred uniformly with a stirring speed of 60 revolutions per minute. A mould of 13 mm diameter and 100 mm length is filled with the mixture, and after it solidifies it is polished. The size of the model is accurate to 0.01 mm. A compression test, tensile test and three-point bending test are conducted.

The difference of compressive strength between groups with mixing ratios of 1.5:1 and 1:1 was not significant (p = 0.326). However, the value of compressive strength of each of the first two groups was remarkably higher than that of the latter four groups (p < 0.01). The difference of tensile strength among the first three groups was not significant (p > 0.05), but the value of each groups was significantly higher than in the latter three groups (p < 0.01). Deflection increased with the decrease of mixing ratio. For the first five groups, the value of elastic modulus decreased with the decrease of mixing ratio, which indicated that the rigidity of the test sample decreased accordingly (p < 0.01).

It can be concluded that PMMAs made from different mixing ratios of powdery polymer and liquid monomer has different mechanical properties. Therefore, during the preparation of PMMA, the mass-volume ratio of the reactants must be taken into precise consideration in order for the result to have optimum performance suitable for making bone substitutes and other applications in orthopaedic surgery.