Dentin Ablation by Er:YAG Laser : Study on the Ablated Depth and Dentin Surface Condition

Abstract

Since the wavelength of Er:YAG laser closely matches the absorption wavelength of water, it has been reported that dentin for irradiation which contains water could be ablated by the laser. However, it is difficult to estimate the depth of dentin to be ablated by Er:YAG laser because it is considered to depend not only on the irradiation's energy output, pulse count, duration, method and shape of the tip, but also the properties of the dentin for irradiation. As for dentin for irradiation, it seems possible that affected dentin which may contain much water in the oral environment can be selectively and successfully removed by using Er:YAG laser. In this study, therefore, the ablating capacity of Er:YAG laser of different irradiation energies was examined in relation to the change in surface layer properties of test dentin for irradiation, that is, sound bovine dentin and artificially decalcified dentin. The ablated depth was determined after the test dentin surface was contact-irradiated by using the tip of a C400F at the same total energy and duration of irradiation. The influence of laser irradiation was examined by X-ray diffraction analysis(XRD), and the changed surface layer properties of the test dentin were observed by scanning electron microscope(SEM). The depth of dentin ablated by Er:YAG laser was found not to depend on the total amount of energy but was influenced by the energy output per pulse under the present experimental conditions. A good linear correlation was observed between the ablated depth and the energy output in sound dentin, suggesting that it may be possible to predict the depth to be ablated. In the case of decalcified dentin which seems to contain much water, the ablated depth tended to be greater compared with sound dentin. The depth of 240-290μm was observed at 56-112mJ/pulse・10sec, the level of which may serve as a predictor of the depth to be ablated. XRD findings of both dentin conditions indicated that a clearer structure of hydroxyapatite crystal could be obtained by Er:YAG laser irradiation. From SEM findings, various ablated forms were observed to be caused by the laser irradiation depending on the different conditions of the dentin surface layer, even though the energy output was the same.