Bond Strength And Failure Mode Of Two Adhesives for Orthodontics

"Objectives:", this study was conducted in order to compare the bond strength and failure mode between total etching and self etching systems used for brackets cementation. "Methods:", After calculating the sample size using a statistical formula, twenty human first premolars were randomly divided into two groups: 10 for the total etching system (Transbond™ XT, 3M Unitek, St. Paul, Minnesota, USA) and 10 for the self etching system (Transbond™ Plus Self Etching Primer + Transbond™ XT, 3M Unitek, St. Paul, Minnesota, USA). Standard brackets (Ortho Organizers, California, USA) were cemented and after 24 hours submitted to thermal cycling of 5000 times. Subsequently, shear bond strength tests were performed applying the force at the bracket/enamel interface using the universal testing machine Instron® (crosshead speed of 1.5 mm/min). Data were calculated in MPa by dividing the force by the area of the bracket base. Finally, enamel surfaces and bracket bases were observed using a stereomicroscope (Stemi 2000C, Carl Zeiss, Göttingen, Germany) in order to determinate the adhesive failure. "Results:", the results in terms of bond strength showed a statistical significant difference (p<0.05) between the two adhesive systems, presenting higher values the total-etching system (28,98 MPa vs. 18,67 MPa). The predominant failure modes presented for both systems were at the adhesive-enamel interface (80% and 70% respectively). No failures were observed between or within the dental substrates. "Conclusion:", it was concluded that the bond strength between the enamel and the adhesive and the failure mode are influenced by the dental substrate pre-treatment and the chemical composition of the adhesive. Therefore, the in-vitro bond strength obtained when a self- etching system is used in orthodontics, produce enough micro-mechanical retention with a lower risk of damage to the dental tissue.