Abstract
The objective of this study was to evaluate the coumarin-based iodonium hexafluoroantimonate (P3C-Sb) in the polymerization kinetics of an experimental model adhesive resin both in presence of solvent and acid monomer content. A monomer mixture based on Bis-GMA, TEGDMA and HEMA was used as a model adhesive resin. Initially a screening was performed to evaluate P3C-Sb concentrations (0.25, 0.50, 1, 2, 4 mol%). Four photoinitiator systems using P3C-Sb at 2 mol% were evaluated: CQ + EDAB (control), P3C-Sb + CQ, P3C-Sb + EDAB and P3C-Sb + EDAB + CQ. Additionally, the performance of the photoinitiator systems in the presence of ethanol and acidic monomer at four different concentrations (0, 10, 20, 40 wt%) were evaluated. Real-time Fourier transform infrared spectroscopy was used to evaluate degree of conversion (DC) and rate of polymerization (RP). The ternary initiation system P3C-Sb + CQ + EDAB showed similar DC and RP to CQ + EDAB into the model adhesive resin without ethanol, however, in the presence of solvent, P3C-Sb + CQ + EDAB showed the highest polymerization kinetics. An inhibitory polymerization effect was observed when a solvent was introduced to adhesive resin using CQ + EDAB. Polymerization reaction was affected by the presence of acidic monomer irrespective of initiation system used. Adhesive resins with CQ + EDAB and P3C-Sb + CQ + EDAB as initiation systems showed similar DC to CQ + EDAB in presence of acidic monomer. The use of P3C-Sb as a third component of the initiation system seems to be an interesting alternative to improve the polymerization kinetics of simplified dental adhesives which showed to be less sensitive to the residual presence of solvent before photoactivation and it was similar polymerization behavior to CQ + EDAB in presence of acidic monomer.
Highlights
Developing of simplified dental adhesive systems has been one of the mayor progress of the dental adhesive technology over the last years
CQ, as being relatively hydrophobic, has difficulties in initializing the polymerization in the presence of solvents such as ethanol or water, and showed a reduced degree of conversion, rate of polymerization and tensile strength of adhesive resins [3, 7, 14]; in addition, tertiary amine is chemically unstable in acidic material, because a reaction acid–base may occur between the acidic components and basic amines leads to the formation of undesirable quaternary ammonium salts, which reduces the longevity of adhesion to dentin over time [2, 8, 15]
P3C-Sb concentrations at 4 and 2 mol% showed the higher degree of conversion and polymerization rate, P3C-Sb adhesives with 4 mol% concentration saturates the solution forming a precipitate
Summary
Developing of simplified dental adhesive systems has been one of the mayor progress of the dental adhesive technology over the last years. One-bottle adhesive systems using the Boeira et al Appl Adhes Sci (2017) 5:2 total-etch technique or self-etching approach consists in complex formulations of different types of monomers (monofunctional, cross-linkers and acidic functional), solvents and initiation system that has caused some problems such as inhibition of polymerization [1,2,3], reduced shelf-life [2], phase separation and potentially creating a more porous dentin/adhesive interface [4, 5]. These systems has been widely studied in order to improve their adhesive performance [6]. CQ, as being relatively hydrophobic, has difficulties in initializing the polymerization in the presence of solvents such as ethanol or water, and showed a reduced degree of conversion, rate of polymerization and tensile strength of adhesive resins [3, 7, 14]; in addition, tertiary amine is chemically unstable in acidic material, because a reaction acid–base may occur between the acidic components and basic amines leads to the formation of undesirable quaternary ammonium salts, which reduces the longevity of adhesion to dentin over time [2, 8, 15]
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