Real-time curing characteristics of experimental resin composites containing amorphous calcium phosphate

The real-time polymerization of light-curable experimental resin composites filled with amorphous calcium phosphate (ACP) was monitored. Experimental composites were based on a 2,2-bis[4-(2-ethoxy-3-methacryloyloxy propoxy)phenyl]propane (Bis-EMA)/triethyleneglycol dimethacrylate (TEGDMA)/2-hydroxyethyl methacrylate (HEMA) resin photoactivated by a camphorquinone/tertiary amine system. Four ACP composites were prepared, containing 40 wt% ACP and 0/10 wt% reinforcing fillers (barium glass and silica). Additionally, two control composites were prepared which contained only reinforcing fillers (40-50 wt%). The degree of conversion (DC) was monitored in real time using a Fourier-transform infrared (FTIR) spectrometer with an attenuated total reflectance accessory. During the light curing (1,219 mW cm^-2 ) for either 20 or 40 s, infrared spectra were collected from the bottom of 2-mm-thick composite specimens at the rate of two spectra per second over 5 min. When cured for 40 s, the ACP composites attained a high DC (89.1%-92.4%), while the DC of control composites was significantly lower (53.5%-68.4%). All materials showed a lower DC for the shorter curing time (20 s) and various extents of 5-min postcure polymerization: 12.9%-21.5% for the ACP composites and 2.7%-5.2% for the control composites. The control composites reached the maximum reaction rate much earlier (4.1-4.3 s) and at lower DC (9.9%-10.4%) than did the ACP composites (17.4-22.0 s and 43.5%-49.3%, respectively).