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

El-Askary, Farid Sabry; Botros, Sara Adel; Nassif, Mohamed Salah Abdelaziz; Özcan, Mutlu (2017). Flexural strength of nano-hybrid resin composite as a function of light attenuation distance and specimen dimension. Journal of Adhesion Science and Technology, 31(5):520-529.

## Abstract

This study evaluated ascending order of light attenuation distance (0,2,4,8 mm) and specimen dimensions (2x2x10, 2x2x12, 2x2x15 mm3) differing from requirements of ISO 4049 (2x2x25 mm3) 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 analyzed using one-way, two-way ANOVA and Tukeys HSD post-hoc tests (α=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.

## Abstract

This study evaluated ascending order of light attenuation distance (0,2,4,8 mm) and specimen dimensions (2x2x10, 2x2x12, 2x2x15 mm3) differing from requirements of ISO 4049 (2x2x25 mm3) 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 analyzed using one-way, two-way ANOVA and Tukeys HSD post-hoc tests (α=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.

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