The effect of different surface preparation techniques on the survival probabilities of orthodontic brackets bonded to nanofill composite resin

Objective: To analyze the survival probabilities of different surface preparation techniques for bonding brackets to nanofill composite resin. Design: In vitro, laboratory study. Setting: Mahidol University, Bangkok, Thailand. Materials and methods: Thirty-five nanofill composite resin specimens/group were subjected to four surface preparation techniques as follows: (1) sandblast using aluminium oxide powder of 90 μm; (2) abrasion using diamond bur; (3) hydrofluoric acid etching for 2 min; and (4) 37% orthophosphoric acid etching for 30 s. Plastic conditioner was applied then brackets were bonded. Shear bond strength tests were carried out on a universal testing machine. Main outcome measures: Shear bond strength (MPa) and debonding force (N) were analyzed using Weibull analysis Results: The maximum stress and debonding force levels with a 95% probability of survival ranking from highest to lowest were: (1) sandblast group (4.2 MPa, 45.5 N); (2) diamond bur group (2.2 MPa, 25.3 N); (3) orthophosphoric group (1.9 MPa, 19.8 N); and (4) hydrofluoric group (0.8 MPa, 10.9 N). There was a significant difference in the adhesive remnant index scores between the surface preparation techniques (chi squared P< 0.001). Conclusion: Bonding orthodontic brackets to nanofill composite resin materials may result in lower bond strengths and special surface preparation techniques might be required to avoid increased numbers of bond failures. Surface treatment with sandblasting followed by plastic conditioner could increase the survival probability. The use of a diamond bur, orthophosphoric etching or hydrofluoric etching cannot be recommended.