Impact of thio-urethane additive and filler type on light-transmission and depth of polymerization of dental composites

- Addition of synthetized thio-urethane oligomers to methacrylate-based composites.
- Composites filled with inorganic fillers varying refractive index and size.
- Filler content affected the light-transmission and depth of polymerization.
- Effect of thio-urethane on light-transmission was a function of filler.
- Thio-urethane improved the conversion and depth of cure irrespective the filler.

ObjectiveThis study evaluated the effects of filler type and the addition of thio-urethane oligomers on light-transmission, polymerization kinetics and depth of cure of resin composites.MethodsBisGMA:UDMA:TEGMA (5:3:2 wt%) were mixed with 0 (control) or 20 wt% thio-urethane. Fillers with various sizes and refractive indices were included and refractive index (RI) measured. Unfilled resins were used as controls. The RIs of materials were measured before and after polymerization. The irradiance reaching the bottom of 3-mm thick specimens was measured during the polymerization. Degree of conversion to a depth of 5 mm was mapped. An optical bench was used to simultaneously follow conversion and light transmission.ResultsThe addition of thio-urethane increased the RI for all composites. As expected, RI also increased with conversion for all materials. The one exception was for the material filled with OX-50, in which the RI of the composite decreased with conversion. In this case, the irradiance at the bottom of the 3 mm specimen was also the lowest among all groups. The addition of thio-urethanes had only minimal effect on light transmission within a filler type, but led to increased conversion in depth for all groups. The filler type itself had a greater effect on light transmission, and that correlated well with the degree of conversion.SignificanceThe effect of the thio-urethane addition on degree of conversion in depth was dependent on filler type. The additive can be tailored to improve the RI match with the filler to optimize light transmission in dental composites.

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