Combined UV and IR laser ablation of dentine

Objective: The aim of this study was to increase the rate of removal of den tine tissue by a 213-nm laser through the introduction of an Er:YAG assisti ng laser. Background Data: The rate of dentine removal is increased by usin g a CO2 laser to assist a XeCl excimer laser. Methods: Extracted human teet h 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 ra diation was generated using a Q-switched Nd:YAG (5 nsec, 10 Hz) and three n onlinear crystals. The Er:YAG laser was free running with a pulse duration of 100 mu sec and a pulse repetition rate of 10 Hz, A fluence range of 5-18 .6 J/cm(2) (213 nm) and 0.6-1.3 J/cm(2)(Er: YAG) was used. Axial ablation r ates 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 mum/pulse +/- 2.51, which is mo re 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.