Effect of pulse-width-modulated LED light on the temperature change of composite in tooth cavities

The purpose of this study was to investigate the effects of the radiant emittance and cure time of pulse width modulation (PWM)-controlled LED light on the temperature change of composite and dentin.

Class I cavities (M-D 6mm, B-L 4mm, Depth 2.5mm) were prepared on 30 extracted human molars and vertically sectioned to expose the mesial side of the cavity and tooth. Cavities were filled with Bulk Fill Posterior Restorative (BFP, 3M ESPE) and cured with an LED light. The duty ratio (% of time the light is on) and cure time of the LED light were controlled using an Arduino UNO microcontroller (PWM) as follows (6 groups, n=5): 10%/100 s, 30%/33.3s, 50%/20s, 100%/10s, Increase mode (0→100%)/20s, and Decrease mode (100→0%)/20s. All measurements were performed at 100Hz PWM with the constant total radiant exposure. Thermograms of the specimens were recorded using an infrared thermal camera (VarioCamhr head 700, InfraTec GmbH) for a pre-cure time of 20s, cure time, and a post-cure time of 100s at room temperature of 30±0.5°C. Temperature change data on the composite and dentin surfaces were collected at incremental distances of 0.625mm and 1mm from the top of the cavity to the pulp. Data were statistically analyzed using two-way ANOVA and Tukey's post-hoc test at α=0.05.

A rapid temperature increase occurred within the cavity during light curing. The maximum temperature rises (ΔT_max) were observed at 0.625mm apical from the top and middle of the cavity. The ΔT_max ranged from 7.62 to 16.74°C at 0.625mm apical from the top, 4.83 to 11.39°C at the floor of the cavity, and 3.16 to 8.09°C in the dentin 1mm beneath the cavity base. The ΔT_max of composite and dentin increased and the time to reach ΔT=5°C decreased with increasing duty ratio at constant radiant exposure. In the Increase mode, ΔT_max was lower than that of 50%/20s mode. The ΔT_max in the Decrease mode was similar to that of 100%/10s mode.

The PWM-LED curing light system controlled by a microcontroller provided a useful tool of varying the radiant emittance and cure time with constant radiant exposure to evaluate temperature change of composite and dentin. These result will be helpful to determine proper curing modes with varying radiant emittance of the LED curing light for decreasing temperature change of composite and dentin. At constant radiant exposure and cure times, the Increase mode showed lower and slower temperature rises than the 50%/20s and Decrease mode. Within the limitations of this in vitro study, when radiant exposure is constant, a curing light with lower radiant emittance can induce relatively low thermal transfer, thereby decreasing the risk of pulpal damage.