There are a lot of diseases which show the abnormal elastic property. Although many medical doctors and dentists have noticed the change of tissue elasticity due to the disease, the diagnostic device to examine the tissue elastic property objectively has not well developed.At Tohoku University, acoustic microscopy (AM) for medicine and biology has been developed and applied for more than 20 years. Application of AM has three major features and objectives. First, specifi c staining is not required for characterization or observation. Second, it provides the elastic property and information of

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13 Open Journal of Stomatology dentins were visualized using two-dimensional color images. A strong correlation was observed between the acoustic impedance value, which indicates the hardness of the elastic region, and the Knoop hardness, which indicates the hardness of the plastic region. The results of the present study indicate that acoustic impedance accurately reflects the hardness of dentin.

Biomedical photoacoustic (PA) imaging system has the unique capability of combining high optical contrast with high ultrasound (US) resolution in a single modality. PA imaging system with 532 nm laser and 50 MHz US transducer has been developed. When the laser with the wavelength of 532 nm is used, PA signals are reflected from blood vessels. Patients with unilateral occlusion due to the extraction of unilateral molars are often seen in dental practice. Although the period of the unilateral occlusion induces the changes of masseter muscle (MM), it is not known that how blood vessels and tissue elasticity of MM are affected by the unilateral occlusion. In this study, we aimed to evaluate the sequential changes of MM due to the unilateral occlusion in rats with PA imaging system. PA signals from the MM of the non-occlusal side were significantly lower than that of the occlusal side, and US signals from the MM of the occlusal side were significantly higher than that of the non-occlusal side depending on the period of the unilateral occlusion. Unilateral occlusion affected both the blood vessels and the tissue elasticity. The PA imaging system could evaluate blood circulation and tissue elasticity simultaneously.

The aim of this study was to assess the utility of an actuator-driven pulsed water jet (ADPJ) as a hardness-dependent carious dentin removal device by using different outputs. Thirty-six plane surface dental caries samples were treated with the ADPJ at 150, 200, and 250 voltage (12 teeth each). The Knoop hardness number (KHN) and Ca/P mass ratio were measured at 70 μm from the deepest point of the removing groove. Furthermore, three other teeth samples were manually treated with the ADPJ at the three above mentioned voltages (one tooth each) for 1 min. The KHN and Ca/P mass ratio were measured at 70 μm from the surface of the residual dentin part. In both the KHN and Ca/P mass ratio, higher residual dentin depended on the applied voltage of ADPJ. The ADPJ enabled the removal of softened carious dentin in an applied voltage-dependent manner.