Modelling ATR-FTIR Spectra of Dental Bonding Systems to Investigate Composition and Polymerisation Kinetics

Abstract

Component ratios and kinetics are key to understanding and optimising novel formulations. This warrants investigation of valid methods. Attenuated Total Reflectance Fourier Transform Infra-Red (ATR)-FTIR spectra of separate primers/adhesives were modelled using summed spectra of solvents (water, ethanol), methacrylate monomers (HEMA (hydroxyethyl methacrylate), Bis-GMA (bisphenol A glycidyl methacrylate), and 10-MDP (10-methacryloyloxydecyl dihydrogen phosphate)), and fillers, multiplied by varying fractions. Filler loads were obtained following their separation from the adhesives, by analysing three repetitions (n = 3). Spectral changes during light exposure at 37 °C (20 s, LED 1100–1330 mW/cm2) were used to determine polymerisation kinetics (n = 3). Independent samples T-test was used for statistical analysis (significance level of 5%). FTIR modelling suggested a primer solvent percentage of OBFL (Optibond FL) (30%) was half that of CFSE (Clearfil SE 2) (60%). OBFL included ethanol and water, while CFSE included only water. Monomer peaks were largely those of HEMA with lower levels of phosphate monomers. OBFL/CFSE adhesive model spectra suggested that both contained equal volumes of Bis-GMA/HEMA, with CFSE having 10-MDP. Filler levels and spectra from OBFL (48 wt.%) and CFSE (5 wt.%) were different. Both systems reached a 50% conversion rate within seconds of light exposure. The final conversion for OBFL (74 ± 1%) was lower compared to CFSE (79 ± 2%) (p < 0.05). ATR-FTIR is a useful method to investigate relative levels of main components in bonding systems and their polymerisation kinetics. Such information is valuable to understanding such behaviour.

Methacrylate peak determination and selection recommendations using ATR-FTIR to investigate polymerisation of dental methacrylate mixtures

“…The difference spectra shown in this study confirm that the changes seen during the time of spectral acquisition are mainly due to the polymerisation reaction of methacrylates, corroborating findings from previous studies [ 11 , 13 ]. This is a simple and useful method to understand peak shifts during setting kinetics, although it can be used for a variety of different studies such as changes upon reaction of different materials, biological samples before and after treatment, material mixtures or aging processes [ 49 , 50 ].…”

“…In methacrylates, polymerisation occurs with an opening of a carbon-carbon double bond, leaving a free valence available for reaction with other monomers, which may then co-polymerise. Absorbance changes include shifts in the 1700 cm -1 carbonyl region, loss of the 1635–1640 cm -1 [ v (C = C)] peak, and loss of the 1300–1320 cm -1 [ v (C-O)] doublet, with consequent shift to lower wavenumbers [ 13 ].…”

“…It may also be time consuming, due to Raman scattering being a weak effect, with signal strength issues, leading to a steeper learning curve [ 21 ]. ATR-FTIR sample preparation and method is a simple, rapid and easy access tool that allows spectra to be acquired before, during and after light curing, allowing the operator to cure in situ without interfering with the measurement [ 13 ]. ATR-FTIR has also been proven convenient to study setting kinetics in glass ionomer cements, calcium silicates and bone cements [ 11 , 12 , 22 , 23 ].…”

A Review on Current Trends of Polymers in Orthodontics: BPA-Free and Smart Materials

“…Polymers 2021, 13, x FOR PEER REVIEW 3 of 12 improve a match with commercial fillers due to the composite having better esthetic properties and due to a potentially higher depth of cure [48,49]. Furthermore, the lower water sorption and water solubility of U-(bis-GMA)-Mod is due to its greater hydrophobicity, making it ideal for use as an adhesive system that requires more hydrophobic monomers [50,51].…”

“…However, U-(GDMA)-Mod had a greater resistance than U-(bis-GMA)-Mod to leaching in organic solvents, and both monomers were free of BPA. The authors concluded that U-(bis-GMA)-Mod was better than U-(GDMA)-Mod in terms of its higher refractive index, which would improve a match with commercial fillers due to the composite having better esthetic properties and due to a potentially higher depth of cure [ 48 , 49 ].…”