The influence of bis-EMA vs bis GMA on the degree of conversion and water susceptibility of experimental composite materials

Abstract

Objective. The aim of this work was to assess the influence of the bis-EMA content on the degree of conversion (DC) and its effect on the water sorption and solubility. Materials and methods. In a polytetrafluorethylene (PTFE) mould, 30 samples (Ø = 5 mm, height = 2 mm) of four experimental dental composite resins were cured for 10 s, 20 s and 40 s. The DC was analysed by Fourier Transform (FT)-Raman spectroscopy. To analyse sorption and solubility, six samples (Ø = 15 mm and thickness = 1 mm) of each composite (n = 72) were stored in water at 37°C for different storage periods: 24 h, 7 days and 30 days. Results. When cured for 20 or 40 s the DC increased with the increasing content of bis-EMA. However, the presence of 15 wt% of bis-GMA did not affect the DC, except when cured with 10 s irradiation time. This study also found a correlation between the content of bis-EMA and the reduced values for sorption and solubility, for all storage times used, when the materials were cured with 20 s. Conclusions. The DC of mixtures with higher content of bis-EMA is affected by the presence of bis-GMA at lower energy density delivered from the curing device, suggesting that the restrictions caused by the presence of hydrogen bonds is dependent of the irradiation time used.

Key Words::

• dental composites
• bis-EMA
• hydrogen bonds
• energy density
• FT-Raman spectroscopy

Acknowledgements

The authors would like to acknowledge VOCO GmbH, Cuxhaven, Germany, for manufacturing the experimental composites and Fibre and Polymer Technology, School of Chemical Science and Engineering, Royal Institute of Technology (KTH), Stockholm, Sweden for providing the Raman spectroscope. Many thanks also to Professor Einar Jensen, Department of Pharmacy/Faculty of Health Sciences, The Arctic University of Norway, Tromsø, Norway for help providing the facilities for the sorption and solubility analysis and Dr John Tibballs, Nordic Institute of Dental Materials (NIOM), Oslo, Norway for help and advice concerning the statistical analysis performed.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.