Objectives: To devise a method of high resolution real-time imaging of the ablation of mineralized tissues by Er:YAG laser.
Methods: Flat areas of dentine and enamel were exposed on the crowns of recently extracted teeth. They were sectioned longitudinally and polished, then bonded to a microscope slide by a self-etching dental bonding agent. This assembly was then placed on the stage of a tandem scanning confocal microscope (TSM, Noran Instruments, USA) and the handpiece of an Er:YAG laser (Opus20, OpusDent, USA) was mounted on a micromanipulator bolted to the TSM. Prior to laser ablation, a long working distance dry 20/0.35 NA lens was used to centre the 400 µm laser probe tip and tooth surface, after which the lens was replaced with a TSC 24/0.60 NA glycerine immersion lens for high resolution imaging focused through the 1mm thick slide, and glycerine was applied to the slide. This internally focusable immersion objective allows a 1.4mm working range, so protecting the lens face from potential damage from the laser. The teeth were ablated at e.g. 450 mJ power, 10 pps, in discrete sets of 5 pulses. Images were captured at 25 frames per second by an EM-CCD camera (Andor Technology, UK).
Results: Video-rate imaging of the ablation process efficiently recorded high clarity pulse by pulse structural changes in the dentine substrate.
Conclusion: Real-time confocal imaging obtains important data concerning the hard tissue ablation processes of an Er:YAG laser. This method can be applied to observe the ablation process and structural damage rendered to several clinically relevant applications of Er:YAG lasers - healthy and carious enamel and dentine, cuspal pits and salivary stones.