Influence of Initiators and Co-initiators on Cure of Experimental Resins

Objectives: The purpose of this investigation was to evaluate the cure of an experimental resin composite with an LED light by monomer conversion and hardness tests when the type and concentration of initiators and co-initiators were varied. Methods: Seven experimental resin composites were produced with 26% wt resin and 74% wt silanized glass. The composition of the monomer resin was constant: 60-mol % Bis-GMA (bisphenol a diglycidyl ether dimethacrylate) and 40-mol % TEDGMA (tri-ethylene glycol dimethacrylate), but the content and nature of initiators and amine co-initiators varied. The resins were dispensed into a black nylotron cylindrical mould, 4mm diameter and 2mm deep. The specimens were irradiated for 40s with a commercial LED light, (Freelight 1) at standard setting. Diffuse reflectance FTIR for degree of conversion and Wallace hardness tests were then carried out on them following dry specimen storage for 2days and 2months post-cure. Statistical significance was determined using two-way ANOVA and Tukey’s tests for multiple comparisons at a 0.05 confidence level. Results: Degree of conversion at 2 days post-cure for 0.2% CQ +0.3% CEMA, 0.2% CQ +0.3% DEPT, 0.2% CQ +0.3% DABE, 0.2% CQ +0.1% DABE, 0.2% CQ +0 % DABE, 0.2% PPD +0.3% DABE and 0.2% BZ +0.3% DABE were: 68.15+2.31, 61.36+2.97, 68.88%+1.24, 66.85+2.13, 55.25%+5.25, 62.72%+2.48, 54.15%+0.78, whilst the Wallace hardness were: 75.73+0.21, 91.53+2.22, 77.87+3.19, 80.70+0.66, 106.40+2.86, 81.50+0.98 and 105.00+1.25 respectively. Degree of conversion at 2 months post-cure were: 71.80%+0.38, 63.41%+3.12, 71.46%+3.86, 68.34%+1.10, 63.95%+3.66, 69.24%+1.40, 59.40%+1.01,whilst the Wallace hardness were: 74.83+1.36, 90.43+1.53, 78.20+1.01, 82.93+0.64, 106.57+4.10, 81.67+1.29 and 112.67+3.93 respectively. Conclusion: The degree of conversion and hardness were influenced by the type of the initiators and co-initiators in the experimental resin composite.