The effect of crystal growth on shear bond strength of metallic brackets and atomic force microscope topographic evaluation of treated enamel

the residual adhesive after debonding using two concentrationsof sulfated polyacrylic acid and the conventional acid etchant, andthe topography of treated enamel using Atomic Force Microscopicexamination (AFM).Methodology: A total of 75 premolars were divided into threegroups; 20 teeth each for shear bond strength test, and 5 teeth eachfor AFM. Three solutions were used; Solution I, 37% phosphoricacid, and two concentrations of sulphated polyacrylic acid(Solutions II, and III). Brackets were bonded, and the shear bondstrength was measured using a universal testing instrument at acrosshead speed of 1mm/min. The residual adhesive was exploredusing a stereomicroscope at 20 times magnification, and quantifiedusing the ARI. The topographic pattern of treated enamel wasevaluated, using AFM, and an untreated enamel as a negativecontrol.Results: Solutions II and III, demonstrated lower shear bondstrength (10.6MPa, 6.1MPa), compared with that of acid etchant(17.5 MPa). A significant difference in the distribution of ARIscores was found between group I and II, III (P ;0.001), with more cement remaining on the teeth of group I. The AFM imagesshowed a noticeable difference in the surface topography, withcrystal deposits on the enamel surfaces treated with solution II.Conclusions: The concentration of 30% sulfated polyacrylicacid can be considered as an alternative to phosphoric acid. Theshear bond strength value obtained was above the minimum of theclinically accepted for orthodontic use.