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.
Highlights
Fourier Transform Infra-Red Spectroscopy (FTIR) is able to quantify infra-red light absorbance and transmittance, resulting from changes in the dipole moment of bonds in molecules, which display vibrational patterns [1]. It is a technique widely used for material characterization, namely organic materials such as polymers, with high applicability in many different fields [2, 3]. It is understood as a reference technique for the study of polymerisation kinetics of dental materials, especially useful when coupled with Attenuated Total Reflectance (ATR) accessories, as recognized by the Academy of Dental Materials [4]
Free-radical addition polymerisation reactions in these materials are activated by blue light, and they can be monitored using real-time ATR-FTIR systems [6]
In order to confirm methacrylate peak heights are proportional to the concentration of methacrylate groups in each monomer, an equation relating to the moles of monomer per unit volume was used
Summary
Fourier Transform Infra-Red Spectroscopy (FTIR) is able to quantify infra-red light absorbance and transmittance, resulting from changes in the dipole moment of bonds in molecules, which display vibrational patterns [1]. It is a technique widely used for material characterization, namely organic materials such as polymers, with high applicability in many different fields [2, 3]. In dentistry it is understood as a reference technique for the study of polymerisation kinetics of dental materials, especially useful when coupled with Attenuated Total Reflectance (ATR) accessories, as recognized by the Academy of Dental Materials [4]. Methacrylate polymerisation monitoring is researched with resin composites and with other dental materials containing resin monomers, such as dental adhesive systems, resin-modified glass ionomers and compomers [11,12,13,14]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
