Characterization of methacrylate-based composites containing thio-urethane oligomers

Abstract

Objective To evaluate the ability of thio-urethane oligomers to improve the properties of restorative composite resins. Materials and methods Oligomers were synthesized by combining 1,6-hexanediol-diissocyante (aliphatic) with pentaerythritol tetra-3-mercaptopropionate (PETMP) or 1,3-bis(1-isocyanato-1-methylethyl)benzene (aromatic) with trimethylol-tris-3-mercaptopropionate (TMP), at 1:2 isocyanate:thiol, leaving pendant thiols. Oligomers were added at 0–20 wt% to BisGMA-TEGDMA (70–30 wt%). Silanated inorganic fillers were added (70 wt%). Materials were photoactivated at 800 mW/cm2 filtered to 320–500 nm. Near-IR was used to follow degree of methacrylate conversion (DC). Mechanical properties were evaluated in three-point bending with 2 mm × 2 mm × 25 mm bars for flexural strength/modulus and toughness (FS/E, and T) according to ISO 4049, and 2 mm × 5 mm × 25 mm notched specimens for fracture toughness (KIC). Polymerization stress (PS) was measured on the Bioman. Results were analyzed with ANOVA/Tukey’s test (α = 5%). Results Significant increase in DC was observed in thio-urethane-containing materials especially for the group with 20 wt% of aliphatic version. Materials composed by oligomers also promoted higher FS, E, and KIC in comparison to controls irrespective of thio-urethane type. A significant increase in toughness was detected by ANOVA, but not distinguished in the groups. The PS was significantly reduced by the presence of thio-urethane for almost all groups. Conclusions The use of thio-urethane oligomer to compose methacrylate-based restorative composite promote increase in DC, FS, E and KIC while significant reduces PS.

Rheological and mechanical properties and interfacial stress development of composite cements modified with thio-urethane oligomers

“…In this study, the conversion of specimens of similar thickness polymerized with similar irradiance and final dose was followed separately, and the time to reach the crossover between storage and loss modulus in shear was used to estimate the conversion at which the crossover took place. The chain-transfer reactions from the pendant thiols on the thio-urethane backbone to the surrounding methacrylate matrix delayed gelation (G’/G”) to a higher degree of conversion in all TU-based materials (more markedly for PETMP-AL and PETMP-AR, the highest among the oligomer groups), avoiding early-stage diffusion limitations to polymerization, delaying stress development [30, 31], and ultimately reducing overall polymerization stress [16, 32]. In addition, the final shear storage modulus obtained from rheometer has shown a significant increase in cements composed by selected groups of oligomers (except for PETMP-AL and PETMP-CC).…”

3D printed versus conventionally cured provisional crown and bridge dental materials

“…Bars having the same dimensions as the 3D printed samples (25 × 2 × 2 mm) were fabricated by dispensing the materials in a silicon mold covered with a glass slide on top and bottom, and allowing the materials to cure following the manufacturer’s recommendations. Samples were then stored at ambient temperature for 24 hours, had their respective length, width and thickness measured, and the mechanical properties were determined using 3-point bending method, as previously described 21 . The elastic modulus was determined from the slope of the initial linear part of the load-deformation curve according to the ISO 4049 standard.…”

Effect of thiourethane filler surface functionalization on stress, conversion and mechanical properties of restorative dental composites

“…Clinical studies have demonstrated that this is not always the case [5,10]. In this context, thiourethane oligomers have been proposed as an alternative stress reducing additive, allying the higher molecular weight of the oligomer with thiol chemistry, which affords lower stress through delayed gelation and vitrification [16–19]. The rationale is that the thiol functional groups work as chain transfer agents to promote a radically assisted step-growth polymerization of methacrylates [18,19].…”

“…In this context, thiourethane oligomers have been proposed as an alternative stress reducing additive, allying the higher molecular weight of the oligomer with thiol chemistry, which affords lower stress through delayed gelation and vitrification [16–19]. The rationale is that the thiol functional groups work as chain transfer agents to promote a radically assisted step-growth polymerization of methacrylates [18,19]. In fact, several prior studies demonstrated the effectiveness of the addition of thiourethane oligomers on polymerization stress reduction and depth of polymerization increase, which in turn relates to the high refractive index of these oligomers [20–23].…”

“…However, it has also been demonstrated that the effect of thiourethane depends on its concentration, and that the addition of this oligomer to resin matrix is somewhat limited due to viscosity concerns [18,19]. Higher concentrations of thiourethane increase the resin viscosity, complicating the addition of fillers and compromising the handling char acteristics of composite.…”