Photo-polymerisation variables influence the structure and subsequent thermal response of dental resin matrices

Slobodan Sirovica*, Yilan Guo, Raymond Guan, Maximilian W.a. Skoda, William M. Palin, Alexander P. Morrell, Dan L. Romanyk, Richard A. Martin, Owen Addison

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review


    The structure of the polymer phase of dental resin-based-composites is highly sensitive to photo-polymerisation variables. The objective of this study was to understand how different polymer structures, generated with different photo-polymerisation protocols, respond to thermal perturbation.

    Experimental resins were prepared from a series of Bis-GMA/TEGDMA blends (40/60, 50/50 and 60/40 wt.%), with either Camphorquinone/DMAEMA or Lucirin TPO as the photo-initiator system. Resins were photo-polymerised, in a disc geometry, at either relatively ‘high’ (3000 mW cm−2 for 6 s) or ‘low’ (300 mW cm−2 for 60 s) irradiances ensuring matched radiant exposures (18 J cm−2). Specimens were heated, from 20−160 °C at a rate of 5 °C min−1, whilst simultaneous synchrotron X-ray scattering measurements were taken at 5 °C increments to determine changes in polymer chain segment extension and medium-range order as a function of temperature. For each unique resin composition (n = 3), differential scanning calorimetry was used to measure glass transition temperatures using the same heating protocol. A paired t-test was used to determine significant differences in the glass transition temperature between irradiance protocols and photo-initiator chemistry at ɑ = 0.05.

    Resins pre-polymerised through the use of TPO and or high irradiances demonstrated a reduced rate of chain extension indicative of lower thermal expansion and a larger decrease in relative order when heated below the glass transition temperature. Above the transition temperature, differences in the rate of chain extension were negligible, but slower converted systems showed greater relative order. There was no significant difference in the glass transition temperature between different photo-initiator systems or irradiance protocols.

    The evolution of chain extension and medium-range order during heating is dependent on the initial polymer structure which is influenced by photo-polymerisation variables. Less ordered systems, generated at faster rates of reactive group conversion displayed reduced chain extension below the glass transition temperature and maintained lower order throughout heating.
    Original languageEnglish
    Pages (from-to)343-352
    Number of pages10
    JournalDental Materials
    Issue number3
    Early online date7 Jan 2020
    Publication statusPublished - Mar 2020

    Bibliographical note

    © 2020, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International

    Funding: Science and Technology Facilities Council(award no. ST/L502510/1) and the Royal College of Surgeons of England Small Grants Scheme(Faculty of Dentistry).


    • Differential scanning calorimetry
    • Fourier Transform Infrared Spectroscopy
    • Photo-polymerisation
    • Polymer structure
    • Resin matrices
    • Synchrotron X-ray scattering
    • Thermal perturbation


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