Increased Temperature and Morphological Change of Bovine Dentin Irradiated by a Free Electron Laser : Comparison with an Er:YAG laser

NEMOTO Shogo, IWAI Hitoshi, SUZUKI Hideaki, KAMIYA Naotaka, IWAI Hitoshi, IKI Koji, IKEMI Takuji

doi:10.11471/shikahozon.53.419

The variable-wavelength free electron laser (FEL) can provide valuable information when trying to improve the Er:YAG laser or to develop a novel laser for dental use. In this study, we evaluated the thermal and morphological changes of bovine dentin when irradiated with an FEL (Laboratory for Electron Beam Research and Application, Institute of Quantum Science, Nihon University), and compared the results with those for the conventional Er:YAG laser. Regarding the experimental conditions, the wavelength, energy density, pps (pulses per second) and irradiation time were set to be identical between the FEL and Er:YAG laser groups. FEL was irradiated without water cooling, whereas Er:YAG was irradiated with or without water cooling. A dentin specimen (7×7×1.5mm) was prepared from a bovine tooth and then irradiated by the FEL or Er:YAG laser on the surface of the labial or pulpal side, during which the temperature change of both sides was monitored using a radiation thermometer. In addition, the morphological change of the dentin surface after laser irradiation was observed by a scanning electron microscope. The following results were obtained: 1. In both the 3pps and 5pps conditions, the temperature increase was lowest for FEL on both the labial and pulpal sides, followed by Er:YAG with water cooling. The temperature increase was highest for the Er:YAG laser without water cooling and was always higher at 5pps than at 3pps for both the labial and pulpal sides. 2. Regarding morphological changes after irradiation observed by SEM, the Er:YAG laser produced a scar with a diameter of around 200μm with a sharp margin. The scar created by a C400F chip was around 500μm, which was greater than that created by FEL. 3. SEM observations of the longitudinal section of the irradiated sample showed a similar configuration for all groups. In the dentin irradiated by FEL, dentinal tubules were clearly observed. The dentin irradiated by Er:YAG with water cooling showed both exposed dentinal tubules and lava-like substances with laser exposure of dentinal tubules.

Increased Temperature and Morphological Change of Bovine Dentin Irradiated by a Free Electron Laser : Comparison with an Er:YAG laser

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