Author(s)

Yukihiro Naganuma^1*, Kouki Hatori², Masahiro Iikubo³, Masatoshi Takahashi⁴, Yoshihiro Hagiwara⁵, Kazuto Kobayashi⁶, Atsushi Takahashi¹, Kumi Hoshi¹, Yoshifumi Saijo⁷, Keiichi Sasaki⁸

¹Clinics of Dentistry for Disabled, Tohoku University Hospital, Sendai, Japan.
²Department of Prosthetic Dentistry, Ohu University School of Dentistry, Koriyama, Japan.
³Division of Dental Informatics and Radiology, Tohoku University Graduate School of Dentistry, Sendai, Japan.
⁴Division of Dental Biomaterials, Tohoku University Graduate School of Dentistry, Sendai, Japan.
⁵Department of Orthopaedic Surgery, Tohoku University School of Medicine, Sendai, Japan.
⁶Honda Electronics Co. Ltd., Toyohashi, Japan.
⁷Biomedical Imaging Laboratory, Graduate School of Biomedical Engineering, Tohoku University, Sendai, Japan.
⁸Division of Advanced Prosthetic Dentistry, Tohoku University Graduate School of Dentistry, Sendai, Japan.

Introduction: A scanning acoustic microscope (SAM) is an apparatus for imaging acoustic properties. This apparatus can non-invasively and rapidly evaluate the hardness of materials in the elastic region. This device shows great potential for the diagnosis of dental caries in the clinical setting. However, since the tissue elastic modulus measured using a SAM is a property of the elastic region and the Knoop hardness is a property of the plastic region, the hardness properties differ completely. Therefore, we investigated whether the acoustic impedance measured using a SAM is related to the Knoop hardness, which is used as the standard for removal of carious dentin. Method: Polished sections were prepared from 20 extracted carious wisdom teeth. The acoustic impedance and Knoop hardness were measured for each section. In addition to comparing carious and healthy dentin in SAM images, we evaluated the difference between the carious and healthy dentin in terms of the acoustic impedance and Knoop hardness. We also evaluated the correlation between the Knoop hardness and acoustic impedance. Results: The SAM images were visualized as two-dimensional color images based on the acoustic impedance values. The mean acoustic impedance of carious dentin was significantly lower than that of healthy dentin, showing a similar trend as Knoop hardness. A strong correlation was observed between the two. Discussion: The acoustic impedance values obtained through acoustic microscopy differed significantly between carious and sound dentin. Both types of 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.

Scanning Acoustic Microscope, Acoustic Impedance, Caries, Knoop Hardness

Naganuma, Y. , Hatori, K. , Iikubo, M. , Takahashi, M. , Hagiwara, Y. , Kobayashi, K. , Takahashi, A. , Hoshi, K. , Saijo, Y. and Sasaki, K. (2023) Application of Scanning Acoustic Microscopy for Detection of Dental Caries Lesion. Open Journal of Stomatology, 13, 12-24. doi: 10.4236/ojst.2023.131002.