Influence of Tooth Thickness on Degree of Conversion of Photo-Activated Resin Composite Irradiated Through the Tooth

Objective: To investigate the influence of trans-dental photo-curing on the degree of conversion (DC) of a resin composite irradiated by a light curing unit operating in different curing modes. Methods: A curing lamp having six different curing modes was used for indirect photo-activation of a Nanocomposite through different thicknesses of tooth tissues. Fourier transformation infrared (FTIR) spectroscopy was used to determine DC. Three main experimental groups were formed in accordance with the 0.5mm, 1mm and 1.3mm, tooth thicknesses which were further subdivided into six minor groups formed according to irradiation modes. Control groups employed direct irradiation. Results: For each of the six light curing modes, the average DC decreased with increase in intervening tooth thickness. Among the groups, 0.5mm had the highest DC mean values, 21.5mm group had the lowest mean values (P<0.05). The composite resin showed lower DC mean values when irradiated indirectly compared to control direct curing (P<0.05). DC mean values for turbo and high light modes were statistically significantly higher compared to Normal, Soft Start, Pulse and Pulse Soft light modes. Conclusions: A Nano-composite resin cured through different tooth thickness has lower DC compared to direct curing. DC decreases with increasing intervening tooth thickness. DC mean values for turbo and high light modes were statistically higher compared to normal, soft start, pulse and pulse soft light modes.