Initiator-dependent effects of thiourethane on resin cement curing under light attenuation conditions

Thiourethanes (TU) improve mechanical properties and depth of cure in dental materials. This study investigated whether these benefits are maintained under light attenuation conditions, when TUs are combined with different photoinitiators, and used in cements cured under different ceramic thicknesses.

BisGMA/UDMA/TEGDMA (50/30/20 wt%) were combined with 0 or 20 wt% TU. Camphorquinone/amine (CQ/EDMAB), BAPO, or Ivocerin were used as photoinitiators. Polymerization kinetics and light transmission were monitored by near-IR spectroscopy during photoactivation (320-500 nm, 1580 mW/cm², 300 s, n = 3) through 0, 0.5, and 1.5 mm ceramic. Irradiance and photoinitiator consumption were evaluated by UV-Vis. Data were analyzed by three-way ANOVA/Tukey's test (α=0.05).

Conversion increased with TU under most conditions (p < 0.001), but decreased as a function of ceramic thickness (p < 0.001), due to reduced irradiance. TU only reduced Rp_max when combined with CQ (p < 0.05). Ivocerin achieved the highest conversion at the clinically relevant 40-s exposure, while CQ produced the highest final DC at 300 s. Shorter wavelengths were more attenuated with increasing ceramic thickness (p < 0.001). Photoinitiator consumption was highest for Ivocerin (88%), followed by BAPO (74%) and CQ (60%).

TU improved conversion under all conditions, and led to at least partial recovery of the loss in conversion observed under light attenuation conditions under different ceramic thickness, compared with non-TU controls. That recovery was greater when TU was combined with alpha-cleavage type initiators.

Combining TU with alternative photoinitiators improves curing under light attenuation.