OBJECTIVES: To evaluate the effect of smear layer deproteinization using hypochlorous acid (HOCl) with/without metal chlorides (SrCl2 and ZnCl2) on the microtensile bond strength (µTBS) of two simplified adhesives to dentin. METHODS: Human dentin surfaces with a standardized smear layer were pretreated using a 105 ppm HOCl solution with/without SrCl2 (0.05 M, 0.1 M, 0.2 M, 0.4 M) or ZnCl2 (0.05 M, 0.1 M, 0.2 M) for 5 s, 15 s, or 30 s. After the deproteinizing solution was washed out with water for 5 s, 15 s, or 30 s, pretreated surfaces were bonded with one-step self-etch adhesive Bond Force II or universal adhesive Clearfil Universal Bond Quick, and µTBS was measured after 24 h. Additionally, the deproteinizing effects of HOCl solutions with/without the metal chlorides were compared by measuring changes in the amide:phosphate ratio using attenuated total reflection Fourier transform infrared spectroscopy. Statistical analysis was performed using multifactor ANOVA, Tukey's post hoc tests and t-tests (p < 0.05). RESULTS: Pretreatment with pure HOCl for 15 s and 30 s significantly decreased the amide:phosphate ratio (p < 0.05), indicating effective deproteinization, but the µTBS of both adhesives increased significantly only if HOCl was washed out for 30 s (p < 0.05). Increasing the concentrations of metal chlorides enabled shortening of the wash-out time down to 5 s while maintaining the improved µTBS (p < 0.05). The deproteinizing effect of HOCl was not significantly altered by the addition of metal chlorides (p > 0.05). SIGNIFICANCE: The effectiveness of smear layer deproteinization using HOCl can be improved by the addition of metal chlorides, as their increasing concentration allowed to shorten the wash-out time from 30 s down to 5 s.

Department of Advanced Biomaterials Graduate School of Medical and Dental Sciences Medical and Dental Science and Technology Tokyo Medical and Dental University 1 5 45 Yushima Bunkyo ku Tokyo 113 8549 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 8549 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 8549 Japan; Department of Operative Dentistry Faculty of Dentistry Chulalongkorn University 34 Henri Dunant Road Pathumwan Bangkok 10330 Thailand

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 8549 Japan; Department of Regenerative Dental Medicine Tokushima University Graduate School of Biomedical Sciences 3 18 15 Kuramotocho Tokushima 770 8504 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 8549 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 Regenerative Dental Medicine Tokushima University Graduate School of Biomedical Sciences 3 18 15 Kuramotocho Tokushima 770 8504 Japan

Department of Restorative Dentistry and Periodontology Faculty of Dentistry Chiang Mai University Suthep Muang Chiang Mai Chiang Mai 50200 Thailand; Center of Excellence in Materials Science and Technology Chiang Mai University Suthep Muang Chiang Mai Chiang Mai 50200 Thailand

Faculty of Dentistry Bangkokthonburi University 16 10 Leab Klong Taweewatana Rd Taweewatana Bangkok 10170 Thailand

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