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. KEYWORDS 940 nm diode laser, endodontics, smear layer

The results of this in vitro study showed that the dual wavelength laser system obtained a significantly higher bactericidal effect on E. faecalis than Er,Cr:YSGG laser, reaching a depth of 1000 μm of dentin.

The aim of this study was to assess the effectiveness of dual wavelength (2780 nm Er,Cr:YSGG, 940 nm diode) laser in elimination of smear layer comparing it with Er,Cr:YSGG laser in terms of radicular dentin permeability and ultrastructural changes of root canal walls. Fifty-one sound single-rooted extracted teeth were instrumented up to size F4 and divided into three groups: group Co, non-irradiated samples; group A, irradiated with Er,Cr:YSGG laser; group B, irradiated with the dual wavelength laser. Afterward, the roots were made externally impermeable, filled with 2% methylene blue dye, divided horizontally into three segments reflecting the cervical, middle, and apical thirds then examined under microscope. Using analytical software, the root section area and dye penetration area were measured, and then, the percentage of net dye penetration area was calculated. Additionally, scanning electron microscope investigations were accomplished. Analysis of variance (ANOVA) showed significant differences between all groups over the three root thirds. Dye permeation in dual wavelength laser group was significantly higher over the whole root length: cervical, middle, and apical compared to Er,Cr:YSGG laser group and non-irradiated samples (p < 0.001). Scanning electron micrographs of dual wavelength irradiated samples showed a distinctive removal of smear layer with preservation of the annular structure of dentinal tubules. Er,Cr:YSGG laser root canal irradiation produced uneven removal of smear layer, in efficient cleanliness especially in the apical third. There was no sign of melting and carbonization. Within the studied parameters, root canal irradiation with dual wavelength laser increased dentin permeability.