Edge-strength of flowable resin-composites

Objectives: To evaluate in vitro the failure-forces of flowable composites at different distances from an interface edge of a bulk material. Methods: Seven materials were investigated. An edge-strength testing instrument (CK10) was used in this study. Fourteen disc specimens were prepared (12 mm × 2.5 mm) for each material using Teflon moulds, with a layering technique and light curing at 500 mW/cm². Measurements were made (n = 5 per distance) at 0.4 mm until 1.0 mm distance from the edge with 0.1 mm interval. All specimens prepared were stored in distilled water at 37 °C for 1 week. The failure-force was recorded for each test and the failure mode was examined under the integral microscope of the CK10. One-way ANOVA followed by Tukey post-hoc test at the significance level of 0.05 was used for statistical analysis. Results: The highest failure-force at 0.5 mm (edge-strength) was found with Grandio flow (130.2 N) while the lowest was with Filtek flow (103.6 N). Significant correlation was found between the failure-forces and the increasing distance from the edge in all flowable composites giving coefficients ranging from r² = 0.98 to 0.95. However, no correlation was found between the failure-forces and the percent filler (wt.%) of flowable composites at all distances. Two modes of failure were observed cracking and chipping. Conclusions: Edge-strength of flowable composites could be used to differentiate between materials and predict their clinical margin performance. Edge-fracture resistance of flowable composites is lower towards the margins than towards the centre of restoration.