RESUMEN
AIM: The present study assessed a fracture analysis and compared the shear bond strength (SBS) of two 2-step etch-and-rinse (E&R) adhesives when bonding ceramic orthodontic brackets to bovine enamel. MATERIALS AND METHODS: Thirty healthy bovine mandibular incisors were selected and were equally and randomly assigned to 2 experimental groups. Ceramic brackets (FLI Signature Clear®, RMO) were bonded onto bovine enamel using an adhesive system. In group 1 (n=15), the conventional E&R adhesive (OrthoSolo®+Enlight®, Ormco) was used, and in group 2 (n=15), the new E&R adhesive limited to ceramic bracket bonding (FLI ceramic adhesive®: FLI sealant resin®+FLI adhesive paste®, RMO) was used. In order to obtain appropriate enamel surfaces, the vestibular surfaces of mandibular bovine incisors were flat ground. After bonding, all the samples were stored in distilled water at room temperature for 21 days and subsequently tested for SBS, using the Instron® universal testing machine. The Adhesive Remnant Index (ARI) scores were evaluated. Failure modes were assessed using optical microscopy at magnification ×40. A statistic data analysis was performed using the Mann-Whitney U-test (P<0.05). RESULTS: The test showed a significant difference (P=0.00155) between the two groups for the SBS values. Group 1 had significantly higher SBS values (9.79 to 20.83MPa) than group 2 (8.45 to 13.94MPa). Analysis of the ARI scores revealed that most of the failures occurred at the enamel/adhesive interface. A statistically significant difference was found for the ARI scores between the two groups (P=0.00996). Only two fractured brackets, which remained bonded onto the bovine enamel, were reported. Both occurred in group 1. CONCLUSION: When bonded to ceramic brackets, FLI ceramic adhesive® (RMO) was demonstrated to be very predictable and safe for clinical application in enamel bonding, whereas the results obtained with the conventional adhesive system (OrthoSolo®+Enlight®, Ormco) were less reproducible and revealed slightly excessive shear bond strength values.