Evaluation of shear bond strength with different enamel pretreatments: an in vitro study

Bonding procedures are time consuming and debonding of brackets is a common problem encountered in orthodontics.

The purpose of this in vitro study was to evaluate the shear bond strength (SBS) with different enamel pretreatment (acid etching, air abrasion, and bur abrasion) to enhance the bonding performance.

A total of 60 extracted premolars for orthodontic purposes were randomly assigned to three groups based on conditioning method: Group I - conventional etching with 37% phosphoric acid; Group II - air abrasion with 50 μm aluminum oxide; and Group III - bur abrasion with diamond fissure (#330, MANI, Dia-Burs, New Jersey, USA). After storing the specimens for 24 h in distilled water at 37°C, SBS was measured with Universal testing machine (Lloyd Universal testing machine-Model No. L.R 100K, UK). The shear force at a crosshead speed of 1 mm/min was transmitted to brackets. The adhesive remnant index (ARIs) scores were recorded after bracket failure.

Descriptive statistics, multiple comparisons of the SBS of different groups, were performed by analysis of variance. The Tukey's test was used to evaluate differences in ARI scores between groups. All statistical evaluations were calculated using the Statistical Package for Social Sciences Windows, release 10.0.0 (SPSS Inc., Chicago, Illinois, USA).

The analysis of SBS variance (P < 0.01) and Chi-square test of ARIs scores (P < 0.01) revealed significant differences among three groups tested. The SBS in Group I (mean: 8.822 ± 0.92 MPa) and Group III (mean: 6.015 ± 0.87 MPa) was significantly higher than Group II (mean: 3.824 ± 0.57 MPa). The ARI was used to evaluate the residual adhesive on the enamel after bracket removal. The Tukey's test was used to evaluate differences in the ARI scores among the groups.

The current findings indicate that enamel surface preparation using bur abrasion results in a significant higher than air abrasion; within the limitations of this study recommend bur abrasion as a viable alternative to acid etching.