What question did this study set out to answer?

This research aims to investigate how different concentrations and treatment times of sodium hypochlorite affect enamel surface and bond strength for orthodontic attachments.

April 4, 2026BMC Oral Health0 citationsOpen Access

Influence of sodium hypochlorite concentration and treatment time on enamel surface morphology and shear bond strength for orthodontic attachments: an in-vitro study

DZDanqing Zheng CLC. L. LiXi'an Jiaotong University TWTong WangTianjin University of Science and Technology

Key Points

This research aims to investigate how different concentrations and treatment times of sodium hypochlorite affect enamel surface and bond strength for orthodontic attachments.
Conducted in-vitro on 60 extracted premolars divided into ten groups.
Applied sodium hypochlorite at varying concentrations and times before phosphoric acid etching.
Examined surface morphology using scanning electron microscopy (SEM) and analyzed data with ImageJ software.
Measured shear bond strength (SBS) using a universal testing machine (UTM) and performed statistical analyses with ANOVA.
Sodium hypochlorite treatment significantly enhanced enamel morphology and increased SBS in a concentration- and time-dependent manner.
Highest SBS recorded was 276.01 N with 10% NaOCl for 60 seconds, surpassing shorter application times.
Statistical analysis confirmed significant interactions between concentration, exposure time, and bonding outcomes.

Abstract

Clear aligner therapy is widely used because of its aesthetics and comfort; however, repeated debonding of resin attachments remains a clinical concern. This study evaluated the effects of sodium hypochlorite (NaOCl) pretreatment applied prior to phosphoric acid etching on enamel surface morphology and shear bond strength (SBS). Sixty extracted premolars were randomly assigned to ten groups (n = 6 per group) in a staged experimental design. The enamel surfaces were pretreated with NaOCl at concentrations of 0%, 3%, 5.25%, or 10% for 30 s or with 5.25% and 10% for 20, 40, or 60 s before acid etching. Surface morphology was examined using scanning electron microscopy (SEM), and surface characteristics were semi-quantitatively analyzed using the ImageJ software. Standardized resin attachments were bonded, and the SBS was measured using a universal testing machine (UTM). Data were analyzed using one-way and two-way analysis of variance (ANOVA) with Tukey’s post-hoc test (α = 0.05). NaOCl pretreatment altered enamel surface morphology and increased SBS in a concentration- and time-dependent manner. SBS values were significantly higher in the 5.25% (226.60 ± 22.17 N; 113.30 ± 11.09 MPa) and 10% (239.21 ± 51.52 N; 119.61 ± 25.76 MPa) groups than in the control (P < 0.05). The highest SBS was observed with 10% NaOCl for 60 s (276.01 ± 63.67 N; 138.01 ± 31.84 MPa), which was significantly greater than shorter application times at the same concentration (P < 0.001). Two-way ANOVA demonstrated significant effects of both concentration and exposure time, as well as their interaction (P < 0.001). NaOCl pretreatment applied prior to phosphoric acid etching significantly enhanced the SBS of resin attachments under controlled in vitro conditions. These findings suggest that NaOCl may influence enamel surface characteristics and bonding performance; however, further studies are warranted to clarify the underlying mechanisms and evaluate its clinical applicability.

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