Failure analysis: enamel fracture after debonding orthodontic brackets

Objective: To determine the location and size of enamel fracture (EF) when debonding a bracket. Materials and Methods: Tests on actual EF situations were conducted in different debonding load modes (tension, shear, and torsion) via mechanical testing, finite element model (FEM) analysis, and scanning electronic microscopy (SEM). Through these simultaneous analyses of the relationships among debonding load modes, value/distribution of stress, and actual enamel fracture location/size, an investigation was undertaken to explore the complex failure mode during enamel fracture after debonding of an orthodontic bracket. Results: The EF usually was located in the area where the force was exerted during various loading modes. The tensile, shear, and torsion debonding modes produce EF sizes and incidences with no significant differences. Findings on FEM matched the mechanical testing and SEM results. Conclusions: The EF locations coincided with the areas where the tensile, shear, or torsion force was exerted. Therefore, the dentist should give extra care and attention to these specific areas of enamel after debonding. The sizes and incidences of EF produced by these three debonding modes showed no significant difference. Thus, clinically, when the sizes and incidences of produced EF are considered, it should not matter which of these three exerting forces is used to debond a bracket.