Faria–e–Silva AL, et al. – The prime focus of this research was to assess the effects of filler type and the addition of thio–urethane oligomers on light–transmission, polymerization kinetics and depth of cure of resin composites. The present data indicated that the effect of the thio–urethane addition on degree of conversion in depth was dependent on filler type. The outcomes suggested that the additive can be tailored to improve the refractive index (RI) match with the filler to optimize light transmission in dental composites.