Effect of micro-additions of carbon nanotubes to polymethylmethacrylate on reduction in polymerization shrinkage

Carbon nanotubes are used in dentistry, although there are no adequate scientific data to support their use in acrylic resins. The polymerization shrinkage that occurs with polymethylmethacrylate (PMMA) resins is well known. This study compared the polymerization shrinkage of denture base acrylic resin with and without micro-additions of carbon nanotubes.

Two materials were used, PMMA resin and multiwalled carbon nanotubes. Four groups were established of 10 specimens each according to the weight percent of carbon nanotubes dispersed and disintegrated in the monomer: group I (0.5% of carbon nanotubes in monomer), II (0.25%), III (0.125%), and IV (control group, 0%). The polymerization shrinkage of acrylic resin for each group was evaluated based on the distance between the reference points in wax (before polymerization) and in acrylic (after polymerization), measured using a traveling microscope. The data were submitted to Kruskal-Wallis and one-way ANOVA for comparison among the groups, and the results were statistically analyzed.

The Kruskal-Wallis test detected that the different percentages of carbon nanotubes incorporated in the monomer showed significant differences, and the mean ranks of polymerization shrinkage (%) showed differences among all the groups (group IV = 0.126, III = 0.037, II = 0.017, I = 0.006). Hence, the order of severity of polymerization shrinkage was 0% > 0.125% > 0.25% > 0.5% for the amount of carbon nanotubes incorporated in methylmethacrylate.

The present study was done to prove polymerization shrinkage in PMMA resins with micro-additions of carbon nanotubes. The results clearly show reduction in polymerization shrinkage when carbon nanotubes are incorporated into the PMMA resin.