Effect of Speed of Loading on Compressive Strength and Flexural Strength of Dental Resin-Composites

Objective: To investigate the effect of speed of loading on compressive strength and flexural strength for a range of dental resin-composites of varied composition.
Materials and Methods: For compressive strength testing, fifteen cylindrical specimens
(4 mm diameter × 6 mm length) were prepared from each material using stainless steel split molds. Each specimen was irradiated from top and bottom in the mold and from radial direction after removing from the mold (40 s each) using a visible light curing unit (Optilux 501, Kerr, Orange Co., USA) with irradiance of 650 mW/cm2. For flexural strength testing, fifteen bar-shaped specimens (25 mm length x 2 mm width x 2 mm height) were prepared from each material using stainless steel split molds. Each specimen was irradiated in five overlapping sections (40 s each) on the upper and lower surfaces starting from the center of the specimen using the visible light curing unit described above. Specimens were stored in distilled water at 37°C in an incubator for 24 h. Loading of specimens until fracture, for both compressive strength and flexural strength, was carried out in a universal testing machine (model 3365, Instron, High Wycombe, UK) at three different cross-head speeds: 1 mm/min (n = 5), 3 mm/min (n = 5) and 5 mm/min (n = 5). Data were analyzed using a One-way ANOVA and Bonferroni post-hoc test.
Results: Considering all cross-head speeds applied, mean data for compressive strength ranged from 349 to 434 MPa, and for flexural strength ranged from 84 to 182 MPa. Linear regression analysis revealed a strong positive correlation between the applied cross-head speeds and both the compressive strength and flexural strength values.
Conclusions: Changing the cross-head speed resulted in variation in strength values of the investigated resin-composites. The values of compressive strength and flexural strength depend principally on the extent of filler loading and the type of resin system.