IADR Abstract Archives
Spatial Heterogeneity of Post-Cure Conversion in Photo-Polymerised Dental Composites
Objectives: To investigate whether the heterogeneity of photo-polymerisation at inter-particulate length scales changes after the completion of photo-curing in experimental di-methacylate resin-based composites.
Methods: A photo-polymerizable experimental composite was formulated by combining BisGMA and TEGDMA monomers (60:40 wt% ratio) with a 1 wt/% Lucirin-TPO photo-initiator and monodispersed 7.75µm nominal diameter SiO2 microspheres. Films of composite were prepared on CaF2 optical substrates and photo-cured for 20s at an irradiance of 2000 mW/cm2. Fourier Transform Infrared (FTIR) spectro-microscopy was performed at the Canadian Light Source using an Agilent Cary 670 spectrometer with a Cary 620 Microscope and 128x128 pixel Focal Plane Array detector. 2D imaging was repeated on the same region of the photo-cured composite 16 mins following light irradiation and then at nine further time-points over a period of 14 hrs. Second derivative spectra were used to calculate spatially-resolved degree of conversion, and a custom code was used to calculate radially-averaged conversion of reactive end-groups as a function of distance from each particle centre with time. Pearson correlation statistics were performed on resulting data.
Results: Radially increasing conversion of reactive end-groups from the centre of each filler particle outwards into the resin matrix was observed (5-10% difference), consistent with previous reports. A significant increase in reactive end-group conversion occurred up to 4-6 hrs post-cure followed by a plateau. Differences in the degree of post-cure conversion were observed, with the largest change seen in closer proximity to the filler particles.
Conclusions: Filler particles in photo-polymerised composites restrict local monomer mobility and limit the local polymerisation of the adjacent matrix. Post-cure conversion occurs due to radical diffusion within the polymer system and it appears that regions of lower conversion have more potential for post-cure reaction, but in the system studied do not reach the same levels as the inter-particulate polymer matrix.
Methods: A photo-polymerizable experimental composite was formulated by combining BisGMA and TEGDMA monomers (60:40 wt% ratio) with a 1 wt/% Lucirin-TPO photo-initiator and monodispersed 7.75µm nominal diameter SiO2 microspheres. Films of composite were prepared on CaF2 optical substrates and photo-cured for 20s at an irradiance of 2000 mW/cm2. Fourier Transform Infrared (FTIR) spectro-microscopy was performed at the Canadian Light Source using an Agilent Cary 670 spectrometer with a Cary 620 Microscope and 128x128 pixel Focal Plane Array detector. 2D imaging was repeated on the same region of the photo-cured composite 16 mins following light irradiation and then at nine further time-points over a period of 14 hrs. Second derivative spectra were used to calculate spatially-resolved degree of conversion, and a custom code was used to calculate radially-averaged conversion of reactive end-groups as a function of distance from each particle centre with time. Pearson correlation statistics were performed on resulting data.
Results: Radially increasing conversion of reactive end-groups from the centre of each filler particle outwards into the resin matrix was observed (5-10% difference), consistent with previous reports. A significant increase in reactive end-group conversion occurred up to 4-6 hrs post-cure followed by a plateau. Differences in the degree of post-cure conversion were observed, with the largest change seen in closer proximity to the filler particles.
Conclusions: Filler particles in photo-polymerised composites restrict local monomer mobility and limit the local polymerisation of the adjacent matrix. Post-cure conversion occurs due to radical diffusion within the polymer system and it appears that regions of lower conversion have more potential for post-cure reaction, but in the system studied do not reach the same levels as the inter-particulate polymer matrix.