Bond Strengths of Orthodontic Self-etching Primers on Ground Enamel

Objectives: The purpose of this study was to measure and compare the in vitro tensile strength of ground human enamel using three orthodontic self-etching primers with Transbond (37% phosphoric etch) as a control. Methods: Non-carious, extracted human third molars stored less than three months in 0.25% sodium azide solution were sectioned into buccal and lingual halves and mounted in acrylic. Surface enamel was exposed using 120-grit SiC paper followed by 600-grit SiC paper. Specimens were pumiced and air dried for 5 seconds and then randomly assigned to one of the four test groups. Manufacturers' instructions were followed in the application of the adhesives. Ideal 1 (I1, GAC), First Step (FS, Reliance), Transbond Plus (TP, 3M Unitek), and Transbond with 37% phosphoric acid (TPA, 3M Unitek) were used to bond orthodontic cement cones using an inverted cone mold (3-mm base, 4-mm height). Specimens were stored for 24 hours in 37C at 100% RH. Specimens were debonded using an Instron machine at a crosshead speed of 0.5 mm/min. Data were analyzed by one-way ANOVA. After debonding, the Adhesive Remnant Index (ARI) at the bond site was recorded. Results: Means and standard deviations of tensile bond strength (MPa, n=8) were: I1 - 12 (6); FS – 25 (12); TP – 25 (10); TPA – 26 (7). ANOVA showed no significant differences among the tensile bond strengths of the self-etching primers FS, TP, and the control, TPA. ARI (%) results were: I1 - A69/C31; FS - A39/C40/T21; TP - A90/C10; TPA - A86/C14. Conclusion: All three self-etching primers had bond strengths greater than 11 MPa to ground enamel. Products were supplied by the manufacturers.