The effect of resin composite thickness and light exposure time on the curing depth of three high viscosity bulk-fill resin composites

Abstract

Objectives: To evaluate the influence of resin composite thickness and light exposure time on the depth of cure of three high viscosity bulk-fill resin composites by using the Knoop microhardness (KHN) profile. 

Material and Methods: Three bulk-fill materials (Tetric^®  N-Ceram Bulk Fill – TNBF; SonicFill^TM– SF; Fitek^TM Posterior Restoration Bulk Fill – FBF) were prepared using a metal mold with four different thicknesses (2, 3, 4, and 5 mm) (n=15). Fifteen conventional nanocomposite (Filtek^TMZ350 XT; Z350) were prepared for 2 mm thickness. The 2, 3, 4 mm thickness groups were cured for 20 seconds and the 4, 5 mm thickness groups were cured for 40 seconds using a light emitting diode (LED) (1,200 mW/cm²). All specimens were stored in the dark storage (37ºC, 24 hours) before submitting to KHN test. Data were analyzed using one-way ANOVA, Tamhane’s T₂ post-hoc test, and independent samples t-test (α=0.05).

Results: With increasing specimen thickness, all bulk-fill materials showed significant decrease in KHN (p<0.05). At 4 mm, only FBF achieved the optimal Knoop microhardness ratio (80% KHR). With increasing light exposure time to 40 seconds, all bulk-fill materials increased in KHN and reached 80% KHR at 4 mm. However, at 5 mm, KHR of all materials was less than 80%.

Conclusions: With respect to KHR, all bulk-fill materials can safely be used for bulk filling up to 4 mm depth using 40 seconds of curing light.