Abstract
The of this study aim was to develop a rapid method to determine the chemical composition, solvent evaporation rates, and polymerization kinetics of dental adhesives. Single-component, acetone-containing adhesives One-Step (OS; Bisco, Anaheim, CA, USA), Optibond Universal (OU; Kerr, Brea, CA, USA), and G-Bond (GB; GC, Tokyo, Japan) were studied. Filler levels were determined gravimetrically. Monomers and solvents were quantified by comparing their pure Attenuated Total Reflectance-Fourier Transform Infra-Red (ATR–FTIR) spectra, summed in different ratios, with those of the adhesives. Spectral changes at 37 °C, throughout passive evaporation for 5 min, then polymerisation initiated by 20 s, and blue light emitting diode (LED) (600 mW/cm2) exposure (n = 3) were determined. Evaporation and polymerisation extent versus time and final changes were calculated using acetone (1360 cm−1) and methacrylate (1320 cm−1) peaks. OS, OU, and GB filler contents were 0, 9.6, and 5.3%. FTIR suggested OS and OU were Bis-GMA based, GB was urethane dimethacrylate (UDMA) based, and that each had a different diluent and acidic monomers and possible UDMA/acetone interactions. Furthermore, initial acetone percentages were all 40–50%. After 5 min drying, they were 0% for OS and OU but 10% for GB. Whilst OS had no water, that in OU declined from 18 to 10% and in GB from 25 to 20% upon drying. Evaporation extents were 50% of final levels at 23, 25, and 113 s for OS, OU, and GB, respectively. Polymerisation extents were all 50 and 80% of final levels before 10 and at 20 s of light exposure, respectively. Final monomer polymerisation levels were 68, 69, and 88% for OS, OU, and GB, respectively. An appreciation of initial and final adhesive chemistry is important for understanding the properties. The rates of evaporation and polymerisation provide indications of relative required drying and light cure times. UDMA/acetone interactions might explain the considerably greater drying time of GB.
Highlights
Whilst the monomer spectra are dominated by peaks, due to the methacrylate groups, there are other characteristic peaks that help identify specific monomers
This study showed that the Fourier-transform infra-red (FTIR) method employed could detect significant differences in evaporation rates, so the second null hypothesis was rejected
Whilst 50% of the acetone could evaporate from thin films of Bis-GMA-based OS and Optibond Universal (OU) adhesives in under 25 s, acetone evaporation was much slower from the urethane dimethacrylate (UDMA)-based GB formulation
Summary
The bonding of restorative materials to dentine involves the replacement of the mineral hydroxyapatite phase with a resin-rich layer that is capable of enveloping the collagen network [1,2]. This hybrid layer is the singular most important mechanism for securing a bond to dentine [2,3]. For it to be stable, this layer should guarantee a continuous and insoluble link between the restorative material and the underlying substrate. The formation of the hybrid layer and its stability depends upon the nature and chemistry of the adhesive system used
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