Measuring Intra-Canal Fluid Temperature Elevation and Ultrastructural Changes of Root Canal Surface During Irradiating With 940 Nm Diode Laser in Endodontic Treatment

Objective: The purpose of this study was to observe the temperature elevation and evaluate the duration of its decreasing from root canal irrigant, as well as to observe smear layer removal ability of root canal surface when using of 940 nm diode laser as assistant in root canal sterilization. Background: laser irradiation may cause a thermal injury to the root structure and the surrounding periodontal tissues. Diode laser is weakly absorbed by water and tooth hard structure so it does not remove smear layer. Combination of chemical irrigants with diode laser irradiation in endodontics has superior results in removing the smear layer. Materials and methods : For this study, a total of 32 sound single rooted extracted human teeth were used. Twenty of them were randomly divided into two groups (n=10): Group A irradiated with 1.5 W CW of 940 nm diode laser for total irradiation time of 20 s, Group B irradiated with 2.5 W in Pulsed mode with frequency of 20 Hz for the same duration. K-type thermocouple was used to record temperature of fluid inside the canal during the rest period of lasing cycle at cervical portion of the root. Twelve teeth were divided into 6 groups (a, b, c, d, e, and f), two per group, where used for scanning electron microscope (SEM) characterization of root canal surface. These teeth were treated with different chemical irrigants and different laser powers. Then, longitudinally sectioned and prepared for imaging. Results: temperature elevation in both groups was acceptable with no significant difference between them (P > 0.01), the SEM showed increased smear layer removal ability during combination of chemical irrigants with diode laser. Conclusion: both laser powers were safe to be used as assistant in root canal sterilization as the temperature of fluid decrease quickly within 2 s, and the SEM images showed that the best results were achieved during combination of chemical irrigants with laser.