Flexural strength of nano-hybrid resin composite as a function of light attenuation distance and specimen dimension

This study evaluated ascending order of light attenuation distance (0, 2, 4, 8 mm) and specimen dimensions (2 x 2 x 10, 2 x 2 x 12, 2 x 2 x 15 mm(3)) differing from requirements of ISO 4049 (2 x 2 x 25 mm(3)) on the flexural strength of nano-hybrid resin composite. Specimens (N = 160) were prepared accordingly and randomly assigned into groups for the factors studied. Specimens were photo-polymerized from increased distances through 1, 2, 3 and 5 overlapping cycles depending on the specimen length after which they were subjected to three-point bending test (0.5 mm/min). Data were statistically analysed using one-way, two-way ANOVA and Tukey's HSD post hoc tests (a = 0.05). Two-parameter Weibull modulus, scale (m) and shape ((0)) were calculated. Both light attenuation distance (p < 0.001) and specimen dimensions (p < 0.001) significantly affected the results. Regardless of the specimen dimensions, 0.2 mm polymerization distance resulted in significantly higher mean flexural strength compared to 4 and 8 mm. Polymerization distance did not significantly affect the mean flexural strength of specimens prepared according to ISO norms (p > 0.05). Weibull distribution presented the highest shape (m) for 10-8 mm (24.65), 12-4 mm (14.54), 15-2 mm (12.32), 25-2 mm (17.56), length-light distance combinations. Specimen dimensions prepared in accordance with ISO 4049 do not allow for comparison of the effect of light attenuation distance on the flexural strength of resin composite tested.