Effect of LED curing unit type on the compressive strength of conventional and single-increase composite resins: an in vitro study

Abstract

Objective: To determine the effect of the type of LED curing unit on the compressive strength of conventional and single-increment (bulk fill) composite resins. Materials and methods: Two conventional resins (3M Filtek® Z350 XT and Palfique® LX5), two bulk-fill resins (Tetric N-Ceram® Bulk Fill and 3M Filtek® One Bulk Fill) and two LED curing units (3M Elipar® DeepCure-L, single-wavelength emission, and Bluephase® N G4, multi-wavelength emission). Eight experimental groups were formed, each with ten specimens (n = 80). The single-increment resin samples were prepared in 4×5 mm cylindrical moulds by applying a single 4 mm increment of material. Celluloid tape and a microscope slide were used for light curing for 20 seconds. Conventional resin samples were prepared in two increments of 2 mm each. The first increment was made in a 2×5 mm cylindrical mould, following the process described above; the sample was then transferred to a 4×5 mm mould, where the second increment was applied, repeating the same procedure.

The samples were coded and stored in distilled water inside an oven (24 h, 37 °C); they were then subjected to compression tests (0.5 mm/min) in a universal testing machine. The data were analysed using the Kruskal-Wallis statistical test. Results: No statistically significant differences in compressive strength were found between the light-cured resins using the 3M Elipar® DeepCure-L unit (p < 0.105) or the Bluephase® N G4 unit (p < 0.109). Conclusion: The type of LED curing unit did not significantly affect the compressive strength of the composite resins evaluated under the experimental conditions of this study.