Optical properties and colorimetric evaluation of resin cements formulated with thio-urethane oligomers

The aim of this study was to evaluate the color parameters and optical properties of resin cements (RCs) formulated with thio-urethanes (TUs).

Six TUs were synthesized by combining thiols (pentaerythritol tetra-3-mercaptopropionate [PETMP] or trimethylol-tris-3-mercaptopropionate [TMP]) with di-functional isocyanates (1,6-Hexanediol-diissocyante [HDDI] [aliphatic-AL] or 1,3-bis(1-isocyanato-1-methylethyl) benzene [BDI] [aromatic-AR] or Dicyclohexylmethane 4,4'-Diisocyanate [HMDI] [cyclic-CC]). TUs (20 wt%) were added to a BisGMA/UDMA/TEGDMA matrix. Filler was introduced at 60 wt%. Fluorescence was evaluated through an UV-light emitting equipment. Coordinates L*, a*, and b* were obtained in the black and white reflectance to evaluate the contrast ratio (CR) and translucency parameter (TP₀₀ ). The coordinates obtained from transmittance were used to evaluate lightness (L*), chroma (C*), color difference (ΔE₀₀ ) after 6 month, and whiteness index for Dentistry (WI_D ).

RCs formulated with TUs presented significantly higher CR, and fluorescence (with T_AR). Significantly lower C*, L*, and TP₀₀ (except for P_AR and T_AL) were also observed in RCs containing TUs. ΔE₀₀ were not significant among the materials. WI_D was not influenced.

RCs composed by TU oligomers present higher CR and lower translucency. The material also present higher fluorescence depending on the oligomer used.

The use of thio-urethanes to formulate resin cements can ensure a luting material with improved potential to mask colored substrates due to the higher contrast ratio and lower translucency obtained. A final higher fluorescence of restoration is also expected with the use of specific oligomer.