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This study evaluated the effects of two in-office bleaching agents (Beyond and Opalescence Boost) with different pH on the structure and mechanical properties of human enamel in vitro and in situ. One hundred and eight enamel slabs were obtained from freshly extracted premolars. The specimens were randomly distributed into nine groups (n=12), and the human saliva (HS) in the volunteers' oral cavities was used to simulate the in situ condition: Beyond + HS, Opalescence Boost (O-Boost) + HS, Control + HS, Beyond + artificial saliva (AS), O-Boost + AS, Control + AS, Beyond + distilled water (DW), O-Boost + DW, and Control + DW. The bleaching treatments were performed on the first and eighth day, and the total bleaching time was 90 minutes. Baseline and final surface roughness (RMS), surface morphology, microhardness, and fracture toughness (FT) were measured before the treatment and on the fifteenth day, respectively. Compared with control groups, surface alterations on enamel were found in the Beyond + AS and Beyond + DW groups under atomic force microscopy evaluation. Two-way analysis of variance and Tukey test revealed that the RMS showed significant intergroup differences for both storage condition and bleaching agent, whereas microhardness and FT revealed no significant alteration. The results indicated that in-office bleaching agents with low pH values could induce enamel morphology alterations under in vitro conditions. The presence of natural HS could eliminate the demineralization effect caused by low pH.

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Background: Dentine hypersensitivity occurs easily on exposed dentine. This study aimed to evaluate the effectiveness of a novel bioactive glass-containing toothpaste on dentine permeability and remineralization. Methods: Thirty dentine discs were divided into three groups of 10 specimens each. The groups corresponded to the following brushing treatments: no brush, distilled water, and bioactive glass-containing toothpaste (Novamin). The toothpaste was applied twice a day for 7 days. Dentine permeability was measured after ethylene-diamine-tetraacetic acid (EDTA) etching, initial application, 3-day application, 7-day application and citric acid challenge, respectively. The dentine morphology was investigated using scanning electron microscopy (SEM). Attenuated total reflection Fourier transform infrared (ATR ⁄ FTIR) spectroscopy was performed to monitor the mineral variation on demineralized dentine. Qualitative information of elemental variation before and after treatments on completely demineralized dentine was detected by energy dispersive X-ray (EDX) analysis. Results: The bioactive glass-containing toothpaste significantly reduced dentine permeability after the 7-day treatment and showed, under SEM, excellent resistance to acid challenge compared to the other groups. ATR ⁄ FTIR and EDX revealed increased mineral content after treatment with Novamin. Conclusions: As the innovative bioactive glass-containing toothpaste occlude dentinal tubules and resist acid challenge, it may be useful for the treatment of dentine hypersensitivity and dentine remineralization.