Effect of an elastomeric urethane monomer on BisGMA-free resin composites containing different co-initiators

Effect of elastomeric urethane monomer on physicochemical properties and shrinkage stress of resin composites

This study aimed to evaluate the effect of an elastomeric urethane monomer (Exothane-24) in different concentrations on physicochemical properties, gap formation, and polymerization shrinkage stress of experimental resin composites. All experimental composites were prepared with 50 wt.% of Bis-GMA and 50 wt.% of TEGDMA, to which 0 wt.% (control), 10 wt.%, 20 wt.%, 30 wt.%, and 40 wt.% of Exothane-24 were added. Filler particles (65 wt.%) were then added to these resin matrixes. Ultimate tensile strength (UTS: n = 10), flexural strength (FS: n = 10), flexural modulus (FM: n = 10), hardness (H: n = 10), hardness reduction (HR: n = 10), degree of conversion (DC: n = 5), gap width (GW: n = 10), and polymerization shrinkage stress in Class I (SS-I: n = 10) and Class II (SS-II: n = 10) simulated configuration. All test data were analyzed using one-way ANOVA and Tukey's test (α = 0.05;  = 0.2). Exothane-24 in all concentrations decreased the H, HR, DC, GW, SS-I, and SS-II (p < 0.05) without affecting the UTS, and FS (p > 0.05). Reduction in FM was observed only in the Exothane 40% and 30% groups compared to the control (p < 0.05). Exothane-24 at concentrations 20% and 30% seems suitable since it reduced GW and polymerization SS without affecting the properties of the composite resins tested, except for H.

Combined use of novel chitosan-grafted N-hydroxyethyl acrylamide polyurethane and human dermal fibroblasts as a construct for in vitro-engineered skin

A rich plethora of information about grafted chitosan (CS) for medical use has been reported. The capability of CS-grafted poly(N-hydroxyethyl acrylamide) (CS-g-PHEAA) to support human dermal fibroblasts (HDFs) in vitro has been proven. However, CS-grafted copolymers lack good stiffness and the characteristic microstructure of a cellular matrix. In addition, whether CS-g-PHEAA can be used to prepare a scaffold with a suitable morphology and mechanical properties for skin tissue engineering (STE) is unclear. This study aimed to show for the first time that step-growth polymerizations can be used to obtain polyurethane (PU) platforms of CS-g-PHEAA, which can also have enhanced microhardness and be suitable for in vitro cell culture. The PU prepolymers were prepared from grafted CS, polyethylene glycol, and 1,6-hexamethylene diisocyanate. The results proved that a poly(saccharide-urethane) [(CS-g-PHEAA)-PU] could be successfully synthesized with a more suitable microarchitecture, thermal properties, and topology than CS-PU for the dynamic culturing of fibroblasts. Cytotoxicity, proliferation, histological and immunophenotype assessments revealed significantly higher biocompatibility and cell proliferation of the derivative concerning the controls. Cells cultured on (CS-g-PHEAA)-PU displayed a quiescent state compared to those cultured on CS-PU, which showed an activated phenotype. These findings may be critical factors in future studies establishing wound dressing models.

Effect of preheating on mechanical properties of a resin-based composite containing elastomeric urethane monomer

This study investigated the effect of preheating an elastomeric urethane monomer (Exothane-24) experimental resin composite on its physicochemical properties. Two resin matrices were formulated: (a) 50 wt% Bisphenol-glycidyl methacrylate (Bis-GMA) and 50 wt% triethylene glycol dimethacrylate (TEGDMA); and (b) 20 wt% Exothane-24, 40 wt% Bis-GMA and 40 wt% TEGDMA. A photoinitiator system (0.25 wt% camphorquinone and 0.50 wt% ethyl-4-dimethylamino benzoate) and 65 wt% of the inorganic filler (20 wt% 0.05 μm silica and 80 wt% 0.7 μm BaBSiO₂ glass) were added to both matrices. These formulations were then assigned to four groups: Exothane-24 (E); Exothane-24 plus preheating (EH); no Exothane-24 (NE); and no Exothane-24 plus preheating (NEH). NEH and EH were preheated at 69 °C. The dependent variables were as follows: film thickness (FT); polymerization shrinkage stress (PSS); gap width (GW); maximum rate of polymerization (Rp_max); and degree of conversion (DC). Data were statistically analyzed by two-way ANOVA and Tukey's test (α = 0.05). Preheating reduced FT for both composites. PSS and GW were significantly lower for EH, when compared with E. The DC for EH and NEH and the Rp_max for EH increased significantly. Preheating improved most of the physicochemical properties (FT, PSS, GW, and DC) of the experimental resin composite containing Exothane-24.

The use of an elastomeric methacrylate monomer (Exothane 24) to reduce the polymerization shrinkage stress and improve the two-body wear resistance of bulk fill composites

OBJECTIVES

Characterize the chemical structure of an elastomeric monomer (Exothane 24) and evaluate the degree of conversion (DC), polymerization shrinkage stress (PSS), rate of polymerization (Rp), flexural strength (F_Strenght), flexural modulus (F_Modulus), Vickers hardness (V_Hardness) and two-body wear resistance of dental bulk fill composites (BFCs) containing Exothane 24.

METHODS

The Exothane 24 was characterized using mass spectroscopy, elemental analysis, ¹³C- and ¹H NMR. BFCs were formulated containing Exothane 24 (E10, E25, and E50). Similar BFCs containing regular UDMA (U10, U25, and U50), commercial conventional, and BFCs were used as control groups. ATR-FTIR spectroscopy was used to measure DC and the Rp of the composites. The PSS was measured using the universal testing machine method. Specimen bars were used to assess the F_Strenght, F_Modulus, and V_Hardness. RBCs were submitted to a two-body wear test using a chewing simulator machine; the rate and volumetric wear loss were evaluated using an optical scanner. Data were analyzed statistically with α = 0.05 and β = 0.2.

RESULTS

Exothane 24 is a urethane isophorone tetramethyl methacrylate monomer with polymerization stress-relieving properties. No differences were found in the DC up to 4 mm in depth for E25. All BFCs had similar F_Strenght, except for E50. E25 had the lowest volumetric wear loss and wear rate. E25 had approximately 30% lower PSS and slower Rp than commercial BFCs with similar wear resistance to conventional commercial composites.

SIGNIFICANCE

The Exothane 24 reduced the PSS and increased the wear resistance of BFCs; however, the formulation is important to optimize the properties of the BFCs.