Fractographic analysis of in vivo-failed orthodontic brackets

OBJECTIVES: The purpose of this study was to characterized the type of fracture of in vivo-failed orthodontic stainless steel brackets and reveal the mechanism implicated in failure. MATERIALS AND METHODS: Collected samples of failed brackets, following at least 12 months of service intraorally, which showed fractured at the base-wing interface were subjected to microscopic investigation with optical and SEM and X-ray electron probe microanalysis. RESULTS: The investigated interfaces showed a mixed type of failure cohesive/adhesive at the solder-base interface. SEM/EDS analysis revealed the dissolution of soldering alloy and precipitation of inorganic complexes composes of Ca, P, K, and Na. Elemental composition of the soldering phase indicated that the soldering alloy comprised mainly of Au. Ageing of brackets in the oral cavity resulted in the precipitation of ions and complexes which locally resulted in masking off the surface characteristics of the material. CONCLUSIONS: The failure of two-piece, soldered orthodontic brackets it seems to be attributed to soldering phase failure during clinical service.