Combined UV and IR Laser Ablation of Dentine

OBJECTIVE: The aim of this study was to increase the rate of removal of dentine tissue by a 213-nm laser through the introduction of an Er:YAG assisting laser. BACKGROUND DATA: The rate of dentine removal is increased by using a CO2 laser to assist a XeCl excimer laser. METHODS: Extracted human teeth were sliced parallel to the crown and exposed to 213-nm laser and Er:YAG laser beams that were spatially and temporally aligned. The 213-nm laser radiation was generated using a Q-switched Nd:YAG (5 nsec, 10 Hz) and three nonlinear crystals. The Er:YAG laser was free running with a pulse duration of 100 microsec and a pulse repetition rate of 10 Hz. A fluence range of 5-18.6 J/cm2 (213 nm) and 0.6-1.3 J/cm2 (Er:YAG) was used. Axial ablation rates were measured for different pulse energies and pulse overlaps. RESULTS: The ablation rate of dentine increased in most cases by a factor of two. The highest ablation rate achieved was 18.3 microm/pulse +/- 2.51, which is more than twice the highest ablation rate previously published using a 213-nm laser. Changes in the pulse superpositions that were investigated did not present a significant change in the ablation rate. CONCLUSIONS: The Er:YAG laser can be used to increase the removal rate of dentine by a short-pulse ultraviolet (UV) laser.