Temperature variation at the external root surface during 980-nm diode laser irradiation in the root canal

Objective To assess the temperature variation in the cervical, middle and apical thirds of root external wall, caused by 980-nm diode laser irradiation with different parameters. Methods The roots of 90 canines, had their canals instrumented and were randomly distributed into 3 groups (n = 30) according to the laser potency (1.5 W, 3.0 W and 5.0 W). Each group was subdivided into 3 (n = 10) according to the frequency (CM, 100 Hz and 1000 Hz), and each subgroup divided into 2 (n = 5): dried canal or filled with distilled water. The maximum temperature values were collected by 3 thermocouples located at each third of the root external wall and recorded by digital thermometers. Results The groups irradiated in the continuous mode (CM) presented the highest values (11.82 ± 5.78), regardless of the canals were dry or not, which were statistically different (p < 0.01) from those obtained with 100 Hz (6.22 ± 3.64) and 1000 Hz (6.00 ± 3.36), which presented no statistical difference between them (p > 0.01). The groups irradiated with 5.0 W presented the greatest temperature variation (12.15 ± 5.14), followed by 3.0 W (7.88 ± 3.92) and 1.5 W (4.02 ± 2.16), differing between them (p < 0.01). The cervical third of the root presented the highest temperature rises (9.68 ± 5.80), followed by the middle (7.66 ± 4.87) and apical (6.70 ± 4.23), with statistical difference among them (p < 0.01). After 30 s from the end of irradiation, all the specimens presented temperature variation lower than 10 °C. Conclusions Application of 980-nm diode laser in the root, at 1.5 W in all operating modes, and 3.0 W, in the pulsed mode, for 20 s, can safely be used in endodontic treatment, irrespective of the presence of humidity.