Effect of Optical Wedge Rotary on Ablation Efficiency of Femtosecond Laser on Dental Hard Tissue and Restorative Materials

Objective: Femtosecond laser (fs-laser) is a novel tooth preparation tool but its ablation efficiency is insufficient. The purpose is to establish a new fs-laser tooth ablation method based on a dual-wedges path ablation system, and explore the efficiency of tooth hard tissue and dental restorative materials ablation. Materials and methods: Extracted third molars, pure titanium, cobalt-chromium alloy, gold alloy, and 3Y-zirconia were prepared into samples. These samples were rotary ablated by an fs-laser with dual-wedges. The wavelength was 1030 nm and the pulse duration was 250 fsec. Laser parameters were set as a repetition frequency of 25 kHz, the power percentages as 50% for dental tissues, and 60% for restorative materials. The optical wedge angle was set as 0°, 20°, 40°, 60°, and 80° for restorative materials, 0°, 20°, 30°, 40°, and 60° for enamel, and 0°, 10°, 20°, 30°, and 40°for dentin. Three times of ablation was processed at each parameter to obtain total 90 ablation microcavities of 6 kinds of materials. The diameter, depth, and volume of microcavities were measured by confocal laser microscopy and plotted against optical-wedge-angle in curves of different materials. One-way analysis of variance (ANOVA) was used to test whether the ablation efficiency between different angles was statistically significant. Results: The ablation efficiency of each material at different optical-wedge-angle was statistically significant (p < 0.05) and tends to be correlated. For dental hard tissue, the enamel ablation efficiency was 208.1 times and dentin ablation efficiency were 65.2 times than before when the wedge angle was 40°. For pure titanium, zirconia, cobalt-chromium, and gold alloys, the ablation efficiencies were 3.1, 10.7, 81.5, and 128.8 times than before when the rotation angle was 80°. Conclusions: The ablation efficiency of dental hard tissues and restorative materials was significantly increased with the increase of laser oblique incidence angle. Clinical Trial Registration number: PKUSSIRB-201949124