Parameters influencing increase in pulp chamber temperature with light-curing devices: Curing lights and pulpal flow rates

This laboratory study examined the effects of curing lights with different light intensities and changing flow rate on the increase in pulpal temperature during the light curing process and the rate of the subsequent decrease in temperature after the termination of light curing. The tip of a temperature sensor was positioned on the pulpal dentinal wall of the buccal side of the maxillary premolar. Metal tubes were inserted in the palatal and buccal root of the tooth, one for water inflow and the other for water outflow. The tubes were connected to a pump to control the flow rate. The water flow rate was set to 4.2 μl/minute, 28 μl/minute or 70 μl/minute. At each flow rate, the unprepared tooth was light cured from the buccal side 1 nun from the buccal surface, using four different curing lights. The temperature data were recorded and stored on a computer every second for three minutes. The curing lights that were used were: Astralis 10 (QTH_high, Ivoclar Vivadent), Bluephase 16i (LED_conv, Ivoclar Vivadent) and two experimental LED-curing lights (LED_exp2000, LED_exp3000, Ivoclar Vivadent). The power densities were 1200 mW/cm², 1600 mW/cm², 2000 mW/cm² and 3000 mW/cm², respectively. The curing lights, LED_conV, LED_exp2000 and LED_exp3000 were activated for 60 seconds, and the QTH_high was activated for 30 seconds. The maximum intrapulpal temperature (T_MAX) and of temperature change at 30 seconds after turning off the light (S_30LO) were analyzed by two-way ANOVA with a post-hoc Tukey test (p<0.05). The influencing factors were the flow rates and curing lights. Results: The T _MAX ranged from 41.0°C to 53.5°C. There was a difference between the curing lights (p<0.05), with LED_exp3000> LED _exp2000> LED_conv> QTH_high. There was no difference in T_max between the different flow rates (p>0.05). Both the curing lights and flow rates affected the S_30LO) (p<0.05). The S_30LO was LED_exp3000> LED_exp2000> LED_conv, QTH_high (p<0.05). The S_30LO, at 70 μl/minutes was higher than at 4.2 μl/minutes and 28 μl/minutes (p<0.05). Clinical Implication: Because the increase in temperature is directly related to the light intensity and exposure time, curing devices with high power density (>1200 mW/cm²) should only be activated for a short period of time (<15 seconds) even in teeth without cavity preparation' The flow rate had only a negligible effect on the temperature increase.