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

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, twoway ANOVA and Tukey's HSD post-hoc tests (=0.05). Two-parameter Weibull modulus, scale (m) and shape (0) were calculated. Both light attenuation distance (p0.001) and specimen dimensions (p0.001) 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.

Effect of light-curing distance and curing time on composite microflexural strength

“…Our results were similar to other work that showed curing at 2-or 8-mm using the MCT did not affect the µ-FS 23) . In addition, our results agreed to some extent with another study which reported a significant difference in µ-FS between 2-and 8-mm but not 0-mm of a 2-mm thick nanohybrid composite when cured with a SLED unit 27) .…”

“…Exploring the effect of curing with the MCT, compared to the CRE, regarding µ-FS when cured at different distances, and with different units, would aid in the understanding of composite clinical performance. Different sample dimensions have been reported when using the µ-FS test 21,27,28) . The specimen dimensions selected in our study were smaller than the active diameter of the light guide tip for the LCUs explored, to allow for one-shot curing 21,27,29) .…”

“…Different sample dimensions have been reported when using the µ-FS test 21,27,28) . The specimen dimensions selected in our study were smaller than the active diameter of the light guide tip for the LCUs explored, to allow for one-shot curing 21,27,29) . The 2-mm and 8-mm curing distances selected in our study were to represent the best and worst clinical case scenarios, respectively, compared to the 0-mm typically performed in laboratory studies 5) .…”

Cellular differentiation, bioactive and mechanical properties of experimental light-curing pulp protection materials

“…curing resin-based specimens prepared in accordance with ISO 4049 (25 mm x 2 mm x 2 mm) may receive a non-uniform distribution of energy during the photo-polymerization procedure, which may in turn, affect their flexural strength. Therefore, smaller specimen (10 mm × 2 mm × 2 mm) were used in this study to reduce the variable effect of distance on resin polymerization as described in a previous study[22]. The experimental resin-based materials were inserted into rectangular silicone molds.…”

Influence of irradiation distance on the mechanical performances of resin composites polymerized with high-irradiance light curing units

“…ISO 4049 stipulates that a specimen should be fabricated with dimensions of 2 mm × 2 mm × 25 mm for the FS test. However, three overlapping irradiation sequences are required to fabricate a specimen with a length of 25 mm due to the smaller diameter of the LCU (10 mm), resulting in nonuniform polymerization [ 39 ]. Therefore, we prepared specimens with dimensions of 2 mm × 2 mm × 8 mm for the FS test in this study, enabling single light curing.…”