Is high-power laser irradiation a time efficient method to debond zirconia restorations?

We aimed to assess the time efficiency of an Er,Cr:YSGG laser at 7.5 W for removing adhesively bonded zirconia structures, evaluating (1) temperature safety (<44 °C), (2) cytotoxicity, (3) phase transformation, and (4) debonding.

Zirconia-resin cement-resin composite specimens were subjected to laser irradiation and monitored using an infrared camera. Cytotoxicity was evaluated by laser irradiating murine cells, with cell viability and proliferation assessed at 24 h and 7 days post-irradiation. Changes in zirconia surface roughness and morphology were analyzed and the localized tetragonal to monoclinic phase transformation (t → m) in the laser-irradiated zirconia was investigated using SEM/EBSD. The shear bond strength of laser irradiated 2 and 3 mm thick resin-bonded zirconia slices was tested. Additionally, a pull-off test was conducted on resin-bonded zirconia crowns to evaluate the laser's efficiency in removing clinically relevant specimens.

Mean temperatures across the specimens' layers were between 27.2 and 28.8 °C. Cell proliferation significantly increased following laser irradiation at both time points; however, a marked decrease in cell viability was observed after 7 days. While irradiation did not alter surface roughness, microcracks formed on the zirconia surface and triggered t → m phase transformation in these regions. Shear bond strength was significantly reduced in both the 2 and 3 mm irradiated zirconia groups, with most samples showing spontaneous debonding during irradiation. No significant difference in pull-off force was found between the non-irradiated and irradiated zirconia crowns.

Laser irradiation at 7.5 W for 120 s is not a time efficient method to remove zirconia crowns.