EFEITO DA DENSIDADE DE ENERGIA DE FOTOATIVADORES DE ALTA POTÊNCIA NAS PROPRIEDADES FÍSICO-MECÂNICAS DE UMA RESINA ORTODÔNTICA

Abstract

The objective of this study was to verify the effect of energy density and the time of exposure of third generation LED light curing agents on a commercially available orthodontic resin in the values of microhardness, shear, resin remaining index and degree of conversion. Three experiments were carried out: Experiment 1, the objective was to evaluate the degree of conversion (DC) and microhardness vickers (MHV) of the orthodontic resin using two third generation LEDs, as well as different photoactivation protocols. 80 ceramic brackets and 80 metallic brackets were required and divided into 16 experimental groups (n=10), with the following groups for each LED: control group, one half, one quarter of the control group time, turbo or plasma function for the Bluephase and Valo LEDs, respectively. Immediately after the polymerization, the DC and MHV assays of the specimens were performed. The experiment 2, aimed to verify the influence of different energy densities emitted by two high power LED photoactivators on the physical and mechanical properties of an orthodontic resin in metallic brackets. For this experiment, 80 carious cavity-free, superior human premolar teeth were used, and the buccal surfaces of the teeth were used for the bonding of the 80 metal brackets. The teeth were randomly divided into 8 experimental groups (n=10), with the following groups being a control group, half the time of exposure of the control group, one quarter of the time in the control group, plasma or turbo function for each LED studied, being Valo and Bluephase. After polymerization, the teeth and specimens were stored 24h at 37°C to perform the shear tests (SBS), resin remaining index (ARI) and MHV. The objective of experiment 3 was to verify the influence of different energy densities deposited by two different LED light-curing on the physical and mechanical properties of an orthodontic resin in ceramic brackets. For this experiment, it was necessary to have 80 carious free upper premolar human teeth, using the lingual or palatine surfaces of the teeth for bonding the 80 ceramic brackets. The teeth were randomly divided into 8 experimental groups (n=10), equal groups were formed for each Valo and Bluephase LEDs: one control group, one half-time control group exposure time, one-fourth time control group, function LED Bluephase turbo or LED Valo Plasma. After polymerization, the teeth and specimens were stored 24 hours at 37°C to perform the SBS, ARI and MHV tests. The results of each experiment were analyzed by specific statistical tests to determine whether or not there was a statistically significant difference. For experiment 1, 2 and two-way ANOVA and Tukey's test (α=0.05) were performed. Experiment 1 showed that the groups of ceramic brackets have low variation, but small changes in the increase of the values of the applied energy in total Joules increase the values of DC and MHV in the metallic brackets because it prevents the passage of light the DC and HVK decrease significantly, remaining within the parameters considered normal. Experiment 2 showed that both LEDs were effective both in the standard function and in the turbo or plasma, and the turbo or plasma functions gave similar results to the control, even effecting with the reduction of the time for the polymerization of the metal brackets. In the experiment 3 there was no statistically significant difference in the analyzed groups. The studied LEDs provided sufficient values of Joules in some experimental groups being sufficient to reach good values in DC, SBS and HVK. The use of LEDs with adequate power, being at least 1000 mW/cm2, or the use of a high power of between 2400 and 3200 mW/cm2 and a short period of exposure of between 3 to 6 seconds, are sufficient for the bonding of orthodontic accessories.