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Department of Restorative Dentistry and Endodontology

Department of Restorative Dentistry and Endodontology

Our research interests center on diagnosis, treatment, and prevention of diseases in the area of Conservative Dentistry, as well as scientific observation and analysis of their clinical pathosis. The technologies we employ are based on many different fields of dental science including microbiology, molecular biology, and dental materials science. We are continuing to pursue the investigations which are relevant to the topics of world wide interest, and maintaining the coherent programme of research which include collaborations with other institutes in Japan and in the foreign countries.


E-mail (below@, dent.osaka-u.ac.jp)
Mikako Hayashi
Associate Professor
Shousaku Itoh
Assistant Professor
Yuusuke Takahashi
Associate Professor
Assistant Professor
Tomomi Yamada
Assistant Professor
Yoko Asahi
Assistant Professor
Hazuki Maezono

Research Topics

Investigations and analyses of root fracture mechanisms and the mechanical properties of human dentin
WITH the aim of achieving long-term promising prognoses of endodontically treated teeth, the project is to investigate the fracture-resistance of endodontically treated teeth restored with post-core using adhesive materials. We conducted static and fatigue fracture tests and found that followed that the combination of a fiber post and an adhesive core was the most effective in protecting the remaining structures of pulpless teeth. In addition, to understand better the mechanisms of tooth fractures and prevent them, we are analysing the mechanical properties of dentin under dry and heated conditions. We are doing this by multiples analyses, including static and fatigue fracture tests, fractographic observations, radiography, FTIR, and nano-indentation, focused on microstructures, such as orientations of dentinal tubules.

Hayashi, et al., Dent Mater 22: 477-485, 2006
Hayashi, et al., Dent Mater 24:1178-1186, 2008
Hayashi, et al., J Dent Res 87: 762-766, 2008
Hayashi, et al., J Dent Res 89: 154-158, 2010
Department of Restorative Dentistry and Endodontology

Optimal adhesive treatment methods of pulpless teeth
EXPERIENCE has shown the importance of obtaining a firm and stable adhesion between root canal dentin and post-core materials to achieve long-term promising prognoses of pulpless teeth. We are investigating the optimal conditions for the firm adhesion of root canal dentin by micro tensile tests and fractographic observations focussed on key factors such as root canal irrigation, dentin bonding systems and the vertical locations in the root canal.

Hayashi et al., J Endodont 34: 583-586, 2008
Wu, Hayashi et al., Dentl Mater 25: 1484-1492, 2009
Department of Restorative Dentistry and Endodontology

Formation mechanisms and effective control methods of dental biofilm
Our works include the analysis of bacterial components and host factors, which involved in formation of dental biofilm (Fig. 1), using molecular biology, microbiology, biochemistry, histology, morphology techniques. Our long-term goal is to establish the optimum biofilm control methods on a scientific basis.
Recent our discoveries have clarified that azithromycin and some of autoinducer analogues, which are quorum-sensing (QS) related materials show an anti-biofilm activity (Fig. 2 and 3).

Noiri et al., J Periodont Res 45: 598-607, 1997
Noiri et al., J Denl Res 80: 1930-1934, 2001
Maezono et al., Antimicrob Agents Chemother 55: 5887-5892, 2011
Asahi et al., J Periodont Res 45: 255-261, 2010
Asahi et al., J Appl Environ 112: 404-411, 2012
Department of Restorative Dentistry and Endodontology

Pathology and treatment methods of refractory periapical periodontitis
Periapical periodontitis refractory to general root canal treatment is a big problem, our research include in vivo and in vitro study to evaluate the relevance of biofilm formation in root canal and periapical (extraradicular) area (Fig. 4). So called periodontopathic bacteria: Porphyromonas gingivalis, Fusobacterium nucleatum, and Tannerella forsythia and others, was detected frequently (Table1). Now, the relationship between clinical symptom and the bacterial species is searched statistically, and then the biofilm formation ability in P.gingivalis is in the genetic analysis in vitro.
Under the infected root canal treatment, Er: YAG laser irradiation against residual bacteria in the canal near the apex was useful (Fig. 5).

Noiri et al., J Endod 28: 679-683, 2002
Noguchi et al., Appl Environ Microbiol 71: 8738-8743, 2005
Department of Restorative Dentistry and Endodontology

Development of the purification method for mesenchymal stem cells
Cells composing of dentin-pulp complex are originated from mesenchymal stem cells. Thus, it is very important to purify this stem cell population. But, so far, nobody succeeded to purify pure mesenchymal stem cells. Recently, we find the easy purification method for the novel population including a large amount of mesenchymal stem cells. This novel population displayed a high activity of mineral production in both in vitro culture experiment and in vivo implantation experiment. Thus, we named this population as “HipOP (highly purified osteoprogenitors)” [1]. Furthermore, regression analysis of in vivo transplantation data showed a strong linear relationship between the mineralized tissue volume and the transplanted HipOP cell number [2]. Our project goal is to develop the further purification method for mesenchymal stem cells and apply these stem cells for the regenerative medicine.

Itoh, et al., J Cell Biochem 108: 368-377, 2009
Itoh, et al., Int J Mol Sci 13: 10229-10235, 2012
Department of Restorative Dentistry and Endodontology

Analysis of the mechanism of tertiary dentinogenesis for development of new pulp capping material
To clarify the mechanism of tertiary dentin formation caused by caries or trauma, we have tried to investigate the gene expression analysis and immuno-histochemical analysis after stimuli to the pulp. In addition, effect of the dentin matrix proteins on the healing process of dentin-pulp complex has been also studied. We focus on the development of new pulp capping material as a final destination. Department of Restorative Dentistry and Endodontology

Development of objective diagnostic method for dental carious lesions
For dental caries diagnosis and removal based on “Minimal intervention”, we designed objective diagnostic method of caries progression and carious lesion activity with color evaluation using CIE 1976 L*a*b* color system and c olor correction. After staining with a caries detector dye, the L* values of carious dentin were related to the degree of caries progression in lesions, and the a* values of carious dentin were related to the carious lesion activity before removal of carious dentinal tissues. In future, by examining the relationship between the color values of carious dentin and the prognosis of restoration, we aim at the establishments of objective diagnostic method for prognosis of restorations and objective standard for removal of carious lesions.

Iwami et al., Oper Dent 30: 83-89, 2005
Iwami et al., Dent Mater J 25: 584-590, 2006
Iwami et al., J Dent 35: 749-754, 2007
Iwami et al., J Dent 36: 143-151, 2008
Iwami et al., Laser Med Sci 26: 439-444, 2011
Department of Restorative Dentistry and Endodontology

Development of device for comfortable sound environment at dental clinic
Drilling sound at dental clinics has influence on sound environment and makes many patients unpleasant. We are investigating the influence of dental noise on patients from various viewpoints. The spectra of dental drilling sound were analyzed and it was found that the sound of dental drill have high frequency components above 20 kHz. We reported cortical hemoglobin-concentration by multi-channel near-infrared spectroscopy changes at front-cortical area while the high frequency sound was detected.
From the results of psychological experiments, not only conventional frequency components but also high frequency component up to 20 kHz of the drilling noise affects subjective impression. The goal of this project is to produce the effective device on air-conducted and bone-conducted drilling sound, which will give patients comfortable under dental treatment.

Yamada, et al., InterNoise 08: 401-409, 2008
Yamada, et al., InterNoise 10: 914-921, 2010
Department of Restorative Dentistry and Endodontology