Abstract: Objective: To investigate the influence of sodium hypochlorite and alcohol disinfection in the enamel during acid etching, and to provide reference for the orthodontic treatment.Methods: Sixty extracted permanent teeth were selected and randomly divided into two groups (group A and group B), with 30 teeth in each group.The teeth in group A were pretreated with 5.25% sodium hypochlorite and the teeth in group B were pretreated with 75% alcohol. After pretreatment, group A and group B were randomly divided into three groups (groups A₀, A₁, A₂, B₀, B₁,and B₂), with 10 teeth in each group and the teeth were etched with 37% phosphoric acid for 0,15 and 30 s. Forty extracted deciduous teeth were selected and randomly divided into 2 groups (group C and D), with 20 teeth in each group. In group C, the teeth were pretreated with 5.25% sodium hypochlorite; in group D, the teeth were pretreated with 75% alcohol.After pretreatment, group C and group D were randomly divided into two groups (groups C₀,C₁,D₀,and D₁) with 10 teeth in each group, and the teeth were etched with 37% phosphoric acid for 0 and 30 s.The morphology of enamel was observed by scanning electron microscope(SEM) after the extracted teeth were cleaned with ultrasound; the pore diameters of enamel surface were detected and the shear strength of samples in each group was detected.Results: The differences in pore diameters between various groups were statistically significant (P<0.01).In the permanent teeth test group, the pore diameter in group A₂ was the maximum (P<0.01), the surface protein residues were less, and the enamel was fully exposed, and the shear strength was the highest(P<0.01).The pore diameter in group B₁ was the minimum (P<0.01), the surface protein residues were more, and the shear strength was the lowest(P<0.01).In the deciduous teeth test group, the pore diameter in group C1 was the maximum (P<0.01), the surface protein residues were less, and the shear strength was the highest(P<0.01).The pore diameter in group D₁ was the minimum, and the surface protein residues were more, and the shear strength was the lowest(P<0.01).Conclusion: Compared with the traditional alcohol disinfection method, pretreatment of 5.25% sodium hypochlorite in tooth enamel for 30 s can significantly increase the surface roughness and cleanliness of enamel, and enhance the shear strength of orthodontic bracket.

Key words: sodium hypochlorite, acid etching, enamel, scanning electron microscope