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

Abstract

Investigation of polymerisation kinetics using ATR-FTIR systems is common in many dental studies. However, peak selection methods to calculate monomer-polymer conversion can vary, consequently affecting final results. Thus, the aim of this study is to experimentally confirm which method is less prone to systematic errors. Three commercial restorative materials were tested–Vertise Flow (VF), Constic and Activa Bioactive Restorative Kids. Firstly, Attenuated Total Reflectance Fourier Transform Infra-Red (ATR-FTIR) (Spectrum One, Perkin-Elmer, UK) spectra of monomers were acquired—10-methacryloyloxy decyl dihydrogen phosphate (10-MDP), bisphenol-A glycidyl dimethacrylate (Bis-GMA), 2-hydroxyethyl methacrylate (HEMA), triethyelene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA) to investigate proportionality of methacrylate peak heights versus concentration. Spectral changes upon light exposure of 2 mm discs of the restorative materials (irradiated for 20 s, LED curing unit 1100–1330 mW/cm2) were assessed to study polymerisation kinetics (n = 3), with continuous acquisition of spectra, before, during and after light exposure. Peak differences and degrees of conversion (DC %) were calculated using 1320/1336, 1320/1350 and 1636/1648 cm-1 as reaction/reference peaks. Inferential statistics included a MANOVA and within-subjects repeated measures ANOVA design (5% significance level). Proportionality of methacrylate peak height to concentration was confirmed, with the 1320/1352 cm-1 peak combination showing the lowest coefficient of variation (8%). Difference spectra of the polymerisation reaction showed noise interference around the 1500–1800 cm-1 region. Across the different materials, DC % results are highly dependent upon peak selection (p<0.001), with higher variability associated to the 1636 cm-1. Significant differences in the materials were only detected when the 1320 cm-1 peak was used (p<0.05). Within the same materials, methods were significantly different for Constic and Activa (p<0.05). It is possible to conclude that the 1320 cm-1 peak is more adequate to assess polymerisation of methacrylates and is therefore recommended.

Monomer Conversion, Dimensional Stability, Biaxial Flexural Strength, Ion Release, and Cytotoxicity of Resin-Modified Glass Ionomer Cements Containing Methacrylate-Functionalized Polyacids and Spherical Pre-Reacted Glass Fillers

“…FTIR spectra for the region from 800 to 2000 cm −1 before and after curing were recorded. The degree of monomer conversion ( , %) was calculated using the following equation [ 27 ]: where and are the absorbance of the C–O peak (1320 cm −1 ) [ 28 ] above the background level at 1335 cm −1 before curing and after curing at time t, respectively.…”

“…where ∆A 0 and ∆A t are the absorbance of the C-O peak (1320 cm −1 ) [28] above the background level at 1335 cm −1 before curing and after curing at time t, respectively.…”

Rheological Properties, Surface Microhardness, and Dentin Shear Bond Strength of Resin-Modified Glass Ionomer Cements Containing Methacrylate-Functionalized Polyacids and Spherical Pre-Reacted Glass Fillers

“…However, the absorbance of the C–O peak of CM and CMH was weaker than that of VB. FTIR peaks at ~1700–1720 cm −1 (C=O stretch, methacrylate group, and polyacids), 1635 cm −1 (C=C stretch of methacrylate group and O-H stretch of water), and 1452 cm −1 (C–H scissor, polyacids, and methacrylate group) were also detected [ 28 , 29 ].…”

Determination of Dental Adhesive Composition throughout Solvent Drying and Polymerization Using ATR–FTIR Spectroscopy

“…where A 0 and A t are the C-O stretch absorbance at 1320 cm −1 above background level at 1345 cm −1 initially and at time t after start of polymerization [23]. The maximum degree of polymerization was calculated by finding the y axis intercept of the linear extrapolation of the late time D C data versus reciprocal of time.…”

“…As it is non-destructive, requires very small amounts of material, and can detect minimal changes in important functional groups, it is ideal to study the reaction kinetics of dental polymers. Sample sizes required for reaction kinetic studies are very small, due to the high reproducibility and small error variation in the technique [23]. The aim of this study was, therefore, to develop a simple, rapid FTIR technique that is able to simultaneously assess the drying rates, changes to composition, and subsequent polymerization kinetics using a minimal amount of sample.…”