Slobodan Sirovica1, Yilan Guo2, Raymond Guan2, Maximilian W A Skoda3, William M Palin4, Alexander P Morrell5, Dan L Romanyk6, Richard A Martin7, Owen Addison8. 1. Aston Institute of Materials Research, School of Engineering & Applied Science, Aston University, Birmingham, B4 7ET, UK; Faculty of Dental, Oral and Craniofacial Science, King's College London, Guy's Hospital, London, SE1 9RT, UK. Electronic address: slobodan.sirovica@kcl.ac.uk. 2. Faculty of Medicine and Dentistry, University of Alberta, Edmonton, T6G 1C9, Canada. 3. ISIS Pulsed Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, OX11 0QX, UK. 4. College of Medical and Dental Sciences, Institute of Clinical Sciences, School of Dentistry, University of Birmingham, Mill Pool Way, Edgbaston, Birmingham, B5 7EG, UK. 5. Aston Institute of Materials Research, School of Engineering & Applied Science, Aston University, Birmingham, B4 7ET, UK; Faculty of Dental, Oral and Craniofacial Science, King's College London, Guy's Hospital, London, SE1 9RT, UK. 6. Faculty of Medicine and Dentistry, University of Alberta, Edmonton, T6G 1C9, Canada; Department of Mechanical Engineering, University of Alberta, Edmonton, T6G 1H9, Canada. 7. Aston Institute of Materials Research, School of Engineering & Applied Science, Aston University, Birmingham, B4 7ET, UK. 8. Faculty of Dental, Oral and Craniofacial Science, King's College London, Guy's Hospital, London, SE1 9RT, UK; Faculty of Medicine and Dentistry, University of Alberta, Edmonton, T6G 1C9, Canada.
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. SIGNIFICANCE: 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.
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. SIGNIFICANCE: 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.
Authors: Richard A Martin; Owen Addison; Slobodan Sirovica; Johanne H Solheim; Maximilian W A Skoda; Carol J Hirschmugl; Eric C Mattson; Ebrahim Aboualizadeh; Yilan Guo; Xiaohui Chen; Achim Kohler; Dan L Romanyk; Scott M Rosendahl; Suzanne Morsch Journal: Nat Commun Date: 2020-04-15 Impact factor: 14.919
Authors: Luis Felipe Marques de Resende; Anderson Catelan; Kusai Baroudi; Alan Rodrigo Muniz Palialol; Alexandre Marques de Resende; Ana Carolina Andreucci; Rayssa Ferreira Zanatta; Priscila Christiane Suzy Liporoni Journal: Eur J Dent Date: 2021-08-24