OBJECTIVES: Ultra-high-speed (UHS) videography was used to visualize the fracture phenomena at the resin-dentin interface during micro-tensile bond strength (μTBS) test. We also investigated whether UHS videography is applicable for failure-mode analysis. METHODS: Ten human mid-coronal dentin surfaces were bonded using Clearfil SE Bond either in self-etching (SE) or etch-and-rinse (ER) mode. After 24-h water storage, the samples were cut into beams for μTBS test and tested at a cross-head speed of 1 mm/min. The fracture phenomena at the bonded interface were captured using a complementary metal-oxide-semiconductor digital UHS camera at 299,166 frames per second. The failure modes were classified using UHS videography, followed by scanning electron microscopy (SEM) analysis. The failure-mode distributions determined by UHS videography and SEM analysis were statistically analyzed using Fisher's exact test with Bonferroni correction. RESULTS: The crack-propagation speed exceeded 1,500 km/h. No significant difference was found between the SEM and UHS videography failure-mode distributions in the SE mode. A significant difference appeared between them in the ER mode. Significant differences in the incidence of cohesive failures within the adhesive and at the adhesive-composite interface between the SE and ER modes were identified by both SEM and UHS videography. SIGNIFICANCE: UHS videography enabled visualization of the fracture dynamics at the resin- dentin interfaces under tensile load. However, the resolution at such high frame rate was insufficient to classify the failure mode as precisely as that of SEM. Nevertheless, UHS videography can provide more detailed information about the fracture origin and propagation.

Department Bioengineering Department of Precision Engineering The University of Tokyo 7 3 1 Hongo Bunkyo ku Tokyo 113 8656 Japan

Department of Cariology and Operative Dentistry Graduate School of Medical and Dental Sciences Tokyo Medical and Dental University 1 5 45 Yushima Bunkyo ku Tokyo 113 8510 Japan

Department of Cariology and Operative Dentistry Graduate School of Medical and Dental Sciences Tokyo Medical and Dental University 1 5 45 Yushima Bunkyo ku Tokyo 113 8510 Japan; Institute of Dental Medicine 1st Faculty of Medicine of the Charles University and General University Hospital Prague Karlovo namesti 32 Prague 121 11 Czech Republic

Department of Operative Dentistry Kagoshima University Graduate School of Medicine Dentistry and Pharmaceutical Sciences 2 5 1 Shikata cho Kita ku Okayama 700 8525 Japan

Department of Operative Dentistry School of Dentistry Lutheran University of Brazil Avenue Martinho Lutero 301 CEP96501 595 Cachoeira do Sul Rs Brazil

Department of Oral Biology College of Dental Medicine Georgia Regents University 1120 15th Street CL 2112 Augusta Georgia 30912 1129 USA

Department of Oral Prosthetic Engineering Graduate School of Medical and Dental Sciences Tokyo Medical and Dental University 1 5 45 Yushima Bunkyo ku Tokyo 113 8510 Japan

Department of Restorative Dentistry School of Dentistry University of Washington 1959 NE Pacific Street Seattle Washington 98195 7456 USA

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