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

DOI: 10.1016/ DOI Help

Authors: Slobodan Sirovica (Aston University; King’s College London) , Yilan Guo (University of Alberta) , Raymond Guan (University of Alberta) , Maximilian W. A. Skoda (ISIS Pulsed Neutron and Muon Source) , William M. Palin (University of Birmingham) , Alexander P. Morrell (Aston University; King’s College London) , Dan L. Romanyk (University of Alberta) , Richard A. Martin (Aston University) , Owen Addison (King’s College London; University of Alberta)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Dental Materials

State: Published (Approved)
Published: January 2020
Diamond Proposal Number(s): 15319

Abstract: Objective: 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. Methods: 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. Results: 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.

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

Subject Areas: Materials

Instruments: I16-Materials and Magnetism