Non-thermal Plasmas Induced Polymerization of Model Self-etching Adhesives

Objective: To determine effectiveness of non-thermal plasmas on polymerization of model self-etching adhesives. Methods: The monomer mixtures used were bis[2- methacryloyloxy)ethyl] phosphate (2MP) and 2-hydroxyethyl methacrylate (HEMA) with mass ratios of 70/30, 50/50 and 30/70. 10-30 wt% water was added to the above formulations. These adhesive/water mixtures were cast on the glass slices evenly to form very thin liquid films, and then each was treated steadily under an atmospheric cold plasma brush for 40 s. For comparison, the photo-initiators such as camphorquinone and ethyl 4-dimethylaminobenzoate were also added to the above formulations for photo-polymerization studies, which were light-cured for 40 s. The degree of conversion (DC) of both the plasmas and light-cured groups was measured by using a Perkin-Elmer infrared spectrometer with an ATR attachment. Results: The experimental data indicated that the plasma brush was effective in inducing polymerization of model adhesives. The presence of water did not negatively affect the DC under the plasmas brush. Indeed, the DC slightly increased with increasing water content in adhesives. For example, the DC increased from 58.3% to 68.7% when water content increased from 10% to 30% in the adhesive with a 50/50 (2MP/HEMA) ratio. The DCs of the plasma group were higher than those of the light-cured group. Conclusion: The free radicals and other active species provided by the non-thermal plasma brush could induce polymerization of adhesive under clinical settings. This plasma brush could become a promising technique in various dental composite restoration applications for improved performance. This study was supported by US National Science Foundation.