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

Abstract

Objectives This 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. Methods BisGMA: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. Results The 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-utethanes 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. Significance The 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.

Impact of thiourethane filler surface functionalization on composite properties

“…The refractive index of the specific thiourethane used has been determined in a previous study to be 1.53. The addition of this oligomer to the same organic matrix (BisGMA/UDMA/TEGDMA 50/30/20 mass %) led to a statistically significant increase in the material's refractive index, and that translated in a better match with the filled composite in the unpolymerized and polymerized states, using the same fillers used in the present study . Therefore, a better match in refractive indices was expected between the organic matrix and the thiourethane functionalized fillers in this study, leading to greater depths of cure.…”

“…2,2‐dimethoxy‐2‐phenylacetophenone at 0.1 mass %, and 2,6‐di‐tert‐butyl‐4‐methylphenol at 0.5 mass % (Sigma‐Aldrich) were used as the initiator and inhibitor, respectively. This formulation was similar to prior studies evaluating the addition of thiourethane to composite . YBF fillers with average size of 0.11 μm (YBF100) and 0.05 μm (YBF402) and radiopaque barium glass fillers with 0.80 μm were used in the study, and all fillers (Sukgyung AT.…”

“…One additional advantage demonstrated with the use of thiourethanes was the increase of the depth of cure . Thiourethanes present higher refractive index than methacrylates, commonly used for filler silanization, due to the presence of thiol and/or phenyl groups, depending on the structures of the starting materials used to produce the oligomer .…”

“…Thiourethanes present higher refractive index than methacrylates, commonly used for filler silanization, due to the presence of thiol and/or phenyl groups, depending on the structures of the starting materials used to produce the oligomer . When the oligomers are added to the matrix, this means the refractive index of the resin increases and better matches that of the filler, so light transmission is improved throughout the polymerization reaction . The match between the refractive indices of fillers and resin matrix is essential to increase the light transmission through the composite thickness, and may facilitate insertion in bulk .…”

“…One additional advantage demonstrated with the use of thiourethanes was the increase of the depth of cure. 5 Thiourethanes present higher refractive index than methacrylates, commonly used for filler silanization, due to the presence of thiol and/or phenyl groups, depending on the structures of the starting materials used to produce the oligomer. 6 When the oligomers are added to the matrix, this means the refractive index of the resin increases and better matches that of the filler, so light transmission is improved throughout the polymerization reaction.…”