Influence of energy dose on composite resin properties

Abstract

Introduction: Composite resin is one of the most used materials in dentistry and its properties depend directly on the dose of energy supplied during light-activation, in order to obtain good clinical performance, having knowledge about the properties of the resin and the photoactivation process is essential for the success of restorations. Objective: To evaluate the effect of different doses of energy, when varying the photoactivation times (10, 20, 40, 60 and 120 seconds), on some composite resin properties: degree of conversion, microhardness, diametral tensile strength and modulus of elasticity. n order to obtain good clinical performance, having knowledge about the properties of the resin and the photoactivation process is essential for the success of restorations. Materiais e Métodos: 50 samples were made for each group (n=10), with the aid of a silicone matrix, using conventional nanohybrid composite resin (Aura, SDI, color DC2), with a pattern and cylindrical shape according to the specification of each methodology. For photoactivation of the resinous composite, a photopolymerizing device with LED unit (Radii-Xpert, SDI) of approximately 869 mW/cm2 of light intensity was used. The power of the device was previously measured (415mW) in specific equipment and the irradiance measured by dividing this power by the area of the photoactivator tip (7.8mm). Thus, according to time, the energy dose was calculated for 10s, 20s, 40s, 60s and 120s of photoactivation. These values were considered for all tests performed in this study. The degree of conversion of the non-polymerized and polymerized states was evaluated immediately after making the samples in the shape of cylinders with a diameter of 4mm and a thickness of 2mm, using the Fourier Transform Infrared Spectrophotometer – FTIR. For the microhardness (Knoop test) and the calculation for the modulus of elasticity, the specimens measuring 2mm thick and 5mm in diameter were submitted to the microdurometer. For the tensile compression test, in order to evaluate the diametral tensile strength, two increments of resin, 1.5mm thick each, were inserted into a matrix made of silicone by adding 6mm in diameter by 3mm in thickness and, 24 hours after they were made, the samples were then taken to the Universal testing machine (EMIC, DL 2000), with a loading speed of 0.5 mm/min, until the sample fractured. All data obtained were analyzed according to their distribution and significance level of α = 0.05. Results: It was possible to observe that the photoactivation time lower than that recommended by the manufacturer, 10s, negatively interfered in most of the properties under study, except for the degree of conversion and diametral tensile strength, which were similar to the other evaluated groups. The higher times (40s, 60s and 120s) did not induce improvements in the properties when compared to the 20s time (recommended by the manufacturer). Despite the thickness of the samples and 2mm, the base showed lower microhardness, modulus of elasticity and degree of conversion, regardless of the photoactivation time. Conclusion: It is therefore concluded that it is extremely important to at least follow the manufacturer's recommendation time, since, when insufficiently photoactivated, the properties of the resin can be compromised.