The effect of different light-curing units on tensile strength and microhardness of a composite resin

Abstract

The aim of this study was to evaluate the influence of different light-curing units on the tensile bond strength and microhardness of a composite resin (Filtek Z250 – 3M/ESPE). Conventional halogen (Curing Light 2500 – 3M/ESPE; CL) and two blue light emitting diode curing units (Ultraled – Dabi/Atlante; UL; Ultrablue IS – DMC; UB3 and UB6) were selected for this study. Different light intensities (670, 130, 300, and 600 mW/cm2, respectively) and different curing times (20s, 40s and 60s) were evaluated. Knoop microhardness test was performed in the area corresponding to the fractured region of the specimen. A total of 12 groups (n=10) were established and the specimens were prepared using a stainless steel mold composed by two similar parts that contained a cone-shaped hole with two diameters (8.0 mm and 5.0 mm) and thickness of 1.0 mm. Next, the specimens were loaded in tensile strength until fracture in a universal testing machine at a crosshead speed of 0.5 mm/min and a 50 kg load cell. For the microhardness test, the same matrix was used to fabricate the specimens (12 groups; n=5). Microhardness was determined on the surfaces that were not exposed to the light source, using a Shimadzu HMV-2 Microhardness Tester at a static load of 50 g for 30 seconds. Data were analyzed statistically by two-way ANOVA and Tukey's test (p<0.05). Regarding the individual performance of the light-curing units, there was similarity in tensile strength with 20-s and 40-s exposure times and higher tensile strength when a 60-s light-activation time was used. Regarding microhardness, the halogen lamp had higher results when compared to the LED units. For all light-curing units, the variation of light-exposure time did not affect composite microhardness. However, lower irradiances needed longer light-activation times to produce similar effect as that obtained with high-irradiance light-curing sources.

Compressive Strength of Composite Resins at Different Exposure Time Using LED and Halogen Units

“…Similar results were obtained in a study conducted by Eduardo Batista Franco et al in which they concluded that better results were obtained with halogen light as compared to led light in term of strength of the material. 24 Similar pattern were followed for the other material used in the study that is Filtek P60. However, when comparing the results of FiltekZ250 and Filtek P60 the compressive strength of P60 at 20 seconds was markedly increased when cured by halogen light.…”

“…Though, the degree of conversion is greatly depends on the energy dose of the light curing unit. 24 For the successful outcome of the restorative material, it should have the mechanical properties similar to that of tooth structure. Several of the masticatory forces are of compressive nature and therefore compressive strength is considered to play important role in the masticatory process.…”

Impact of light intensity on the polymerization kinetics and network structure of model hydrophobic and hydrophilic methacrylate based dental adhesive resin

“…The effect of irradiation time, at low and high light intensities, as well as ramp‐curing on the DC and polymerization shrinkage of composite restorations has been investigated . The impact of different light curing units (LCU) on the polymerization of commercially available composite resins has been studied, but the efficiency of the LCU is dependent on the spectral absorbance of the photosensitizer in the resins . In general, higher light intensity has been proposed to increase the mechanical properties and depth of cure of the composite resin .…”

“…[13][14][15] The impact of different light curing units (LCU) on the polymerization of commercially available composite resins has been studied, but the efficiency of the LCU is dependent on the spectral absorbance of the photosensitizer in the resins. 14,[16][17][18] In general, higher light intensity has been proposed to increase the mechanical properties and depth of cure of the composite resin. 19 Higher light intensity is expected to reduce the curing time without compromising the material properties.…”

Does the light source affect the repairability of composite resins?

“…7 To overcome some of these shortcomings, the use of light-emitting solid-state diode (LED) technology was proposed in the mid-1990s. 8 Instead of the hot filaments used in halogen bulbs, LEDs use junctions of doped semiconductors to generate light. LEDs do not require filters as the spectral output because the blue LED falls within the absorption spectrum of the camphorquinone photoinitiator (400-500 nm).…”