The effect of diode laser-activated bleaching on thermal changes and color outcomes of non-vital teeth using different laser parameters: an in vitro study

Purpose: To evaluate the effect of laser application in internal bleaching on thermal changes and color outcomes of non-vital anterior teeth using different laser parameters. Methods: Sixty extracted maxillary lateral incisors were endodontically treated and were artificially stained using black tea. Palatal access was prepared in all teeth. Teeth were subjected to one of six bleaching protocols (n = 10); internal bleaching with 35% H₂O₂ (JW Next, Heydent) + laser activation using diode laser 940 nm wavelength (EpicX, Biolase) with 2 W power output for 30 s, wait for 7 min, then a second application for 30 s, or the same protocol with a power output of 3W or 4W, or combined internal/external bleaching + laser activation with 2 W, 3 W or 4 W. The color baseline was measured after staining and again following different treatments using a digital spectrophotometer (Easyshade), then color change ΔL was calculated. A K-type thermocouple was used to measure the temperature changes during laser irradiation. The collected data were analyzed statistically by the Kruskal–Wallis test followed by Dunn’s test for pair-wise comparisons (P = 0.05). Results: Within the 2 W, 3 W, and 4 W laser outputs, internal application of H₂O₂ showed statistically significantly lower ΔL (p < 0.05) than internal/external application. Within internal or internal/external bleaching, there was no statistically significant difference between ΔL of the three laser outputs (P > 0.05). Using 2 W or 3 W laser outputs revealed no statistically significant difference in ΔT after internal only or internal and external application of H₂O₂ (p > 0.05). While significantly higher ΔT was recorded using 4 W laser output, which reached 11.8 °C with internal bleaching and 23.1 °C internal and external application (P < 0.05). Conclusions: Nine hundred forty nanometer diode laser activation with 2 W power output for combined internal/external bleaching was found to be the most efficient protocol for non-vital teeth whitening while maintaining the thermal effect within the safe limits.