Evaluation of Depth of Cure and Degree of Conversion of a Photo-Active Composite Resin Irradiated Through Tooth Substance

Abstract

Aims: The study investigated the influence of trans-dental photo-curing on the depth of cure (DoC) and degree of conversion (DC) of resin composite irradiated by different curing modes. Methods: A curing lamp having six different curing modes was used for indirect photo-activation of a nano-composite through six different thicknesses of tooth tissues ranging from 0.5 to 3 mm. The DoC was evaluated by means of an ISO 4049 standard technique and Fourier transformation infrared (FTIR) spectroscopy was used to determine the DC. Results: The composite resin DoC and DC mean values decreased with increasing intervening tooth thickness for each of the six light curing modes. Lower DoC and DC mean values were recorded when indirect irradiation was used compared to control direct curing (P<0.01). The DoC and DC mean values for turbo and high light modes were significantly higher than normal, soft-start, pulse and pulse-soft light modes (P<0.01). Conclusions: Curing composite resin through tooth structures lowers DoC and DC. Turbo and High light curing modes through tooth structures achieve significantly higher DoC and DC mean values than other radiation modes. Keywords: Indirect Curing; Depth of Cure; Degree of Conversion; Irradiation Modes; Photosensitive Composite Resin; Ftir Abbreviations: DOC: Depth of cure; DC: Degree of conversion; FTIR: Fourier transformation infrared; QTH: Quartz-Tungsten Halogen Bulbs; PAC: Plasma-Arc Lamps; LED: Light Emitting Diodes; CQ: Camphor Quinone The required energy (joules) for complete cure is a function of power (mW/cm2) and duration of curing light that may vary by the type and shade of composite material. The delivered amount of energy is also dependent on distance of the light tip from the resin material, movement of light tip during curing, condition of the light curing unit, indirect or direct curing as well as thickness of the resin being cured [5-7]. Even the most powerful curing light will not cure