Novel Glassflake Resin Composites

Purpose: Glassflakes (GFs) are high aspect ratio glass platelets that are widely used in anti-corrosion coatings for the oil industry due to the unique layering characteristic (overlap and align parallel to substrate surfaces as a corrosive barrier). GFs have also been used as planar reinforcements for varies composites and demonstrated better mechanical properties compared with fiber reinforced composites. The aims of the present study were to explore the feasibility of formulating glassflake dental resin composites with suitable depth of cure and glassflake alignment. Methods and Materials: Four glassflake resin composites were formulated by incorporating increasing amount of micronised borosilicate glassflakes GF001 (30-60 wt%) in a 50:50 wt% BisGMA/TEGDMA mixture with a photo-initiator system of CQ and DMAEMA. Cylindrical specimens (4 mm diameter x 4/2 mm thickness, n=8) of each groups were light cured with an Elipar S10 LED curing light and the light output at the bottom surface of the specimen was measured using a laboratory grade NIST-referenced USB-4000 spectrometer. The morphology of the GFs and the resultant GF resin composite were studied by Scanning Electron Microscopy (SEM). Post-irradiance hardness of both top and bottom surfaces (VT and VB) of GF resin composites after 24 h dry storage at 37°C was measured and the differences between groups were compared using one-way ANOVA (P<0.05) followed by Tukey’s post hoc test. Results: Glassflakes GF001 demonstrated a high aspect ratio with a thickness between 1.1 and 1.5 µm. Cross sessional SEM images of the GF resin composites showed alignment of GFs orientated along the applied force. GFs were more densely packed and better aligned with an increase in the amount of GFs. All GF resin composites presented lower VB than VT where VB/VT were all above 75%, however there was no significant difference between the hardness among groups. The light output (irradiance) at the bottom surface of GF resin composites decreased with an increase in the amount of GFs. The bottom irradiance of 4 mm resin composite specimens with lower GFs (30 and 40 wt%) and all 2 mm specimens provided higher irradiance than the minimum clinical acceptable irradiance. Conclusion: Glassflakes were successfully incorporated in dental resin composites and demonstrated alignment along the applied force. The amount of incorporated glassflakes showed influences on the depth of cure of glassflake resin composites and the alignment of the glassflakes