Objectives:
Aligned flake glass composites based on thin plates of glass have potential for use as dental composites. The purpose of this pilot study was to analyse the alignment of the flakes and the water uptake.
Methods:
A light cured resin composition was chosen based on Urethane Dimethacrylate (UDMA). 5, 1.0 and 0.1 micron thick flake glasses were mixed with the resin at various ratios, and then packed into disc shaped moulds and light cured. After setting, the composites were polished perpendicular to the disc surface and examined by Scanning Electron Microscopy (SEM) to characterise the alignment of the glass flakes. The diffusion coefficient for water diffusion was obtained from measuring weight changes following water immersion.
Results:
SEM micrographs showed that of the three flake glasses used, 1.0 and 0.1 micron flakes aligned almost parallel to the composite surface. The 5 micron thick flakes on the other hand were randomly distributed throughout the resin matrix. The alignment of the flakes was found to be related to their aspect ratios (ratio of flake length to flake thickness). Thin flakes with higher aspect ratios had a higher tendency to align than thick flakes with lower aspect ratio. It was expected that diffusion of water would be impeded by the aligned glass flake particles. However, there was an increase in the uptake of water. Water was thought to migrate by capillary action along the flake-resin interface, rather than diffuse through the thickness of the disc.
Conclusions:
Flake thickness and aspect ratio are critically important for obtaining a self-aligning flake composite. The high degree of alignment of flakes to the surface should give rise to excellent wear properties and anisotropic shrinkage.
Acknowledgements: This study was funded by the EPSRC/IMPACT QM Grant and was run in collaboration with PSP Dental, UK.