Scanning electron microscope (SEM) evaluation of clinical failures of single crystal ceramic brackets

The objective of this work was to perform failure analysis on Starfire brackets that failed in clinical use. The failed brackets were examined with a scanning electron microscope (SEM) to obtain micrographs at magnifications of 20, 50, 100, and other magnifications, whenever necessary. With the aid of the micrographs, the fracture origin and the probable defect that initiated the fracture were identified. The percentages of failure origins for each area of the bracket were arch wire slot 36.0%, tie wing slot 22.0%, undetermined 11.0%, saddle 9.0%, impact 9.0%, during removal 7.5%, and parting area 5.5%. By observing the micrographs pertaining to each field failure, the primary causes of failure were internal defects 47.5%, machining interference 42.5%, and undetermined 10.0%.