Energy Increase Under Dentinal Thickness During Photocuring

Objectives: To determine the increase in energy generated through different dentine thicknesses depending on the energy provided by different curing units on several exposition times and distances
Methods: Dentine discs 1, 2 and 4 mm thick, were obtained from healthy third molars stored in distilled water at 37°C. The cameral side of these specimens was placed in contact with a k type thermocuple connected to a multimeter. On the other side the radiation emitted by the curing units was applied. Units and conditions applied were: LED SPEC 3, (higher than 2000 mW/cm2 for 3 s); LED SPEC 3, (1200 mW/cm2 for 15 s); Halogen Lamp (QTH), (600 mW/cm2 for 40 s); Miniled Advantage Satelec, (800 mW/cm2 for 10 s). Guide light tip was set 0, 2 and 4 mm from the surface opposed to the thermocouple and the difference in temperature was registered. Four determinations were performed for every variable (thickness, unit and distance). The energy (J/cm²) applied to the thermocuple based on output determined for each unit and exposition lapse was determined. These values were ranked into five increasing categories of energy/surface. Scores for energy level (J/cm2): less than 0,2: 1; 0,21 to 0,5 : 2, 0,51 to 1,0 : 3; 1,01 to 3,0 : 4; more than 3,01 : 5. Spearman coefficient was applied in order to determine correlation between energy received and temperature increase. Friedman test was used to compare distance from the source and Kruskall-Wallis and Dunn test to compare units for each thickness and distance. P value was set at 0.05.
Results: Mean and standard deviation for variation in temperature (°C) ranged between 20,2 (3,2) and 1,3 (0,5). A significant correlation was found between temperature increase and energy (r=0,69). A significant difference was found for distances between 0 mm and the rest, and differences between units were significantly related to total energy and not significantly related to device output.
Conclusions: When pulpal alterations due to increase in temperature from photocuring processes are considered, not only unit output should be considered but application lapse and distance from dentinal surface must be also taken into account.