LAUSR

ObjectivesTo evaluate the critical bond strength (σ) of ceramic and metal brackets to a lithium disilicate-based glass–ceramic.Materials and methodsTwo hundred and forty ceramic specimens (IPS e-max CAD) were randomly distributed in 12 experimental groups (n = 20). Two ceramic brackets (monocrystalline, BCm; and polycrystalline, BCp) and a metal bracket (BM) were bonded to glass–ceramic specimens after one of the following surface treatments: HF—hydrofluoric acid applied for 60 s; S—silane applied for 3 min; HFS—HF followed by S; and MDP—application of an adhesive containing a phosphate monomer (MDP). All brackets were bonded to the treated glass–ceramic using a resin cement, stored in 37 °C water for 48 h before shear bond strength testing. Optical (OM) and scanning electron (SEM) microscopies were used for fractographic analysis. Data was statistically analyzed using Kruskal–Wallis and Student–Newman–Keuls (α = 0.05).ResultsBCm bonded to glass–ceramic treated with either HFS or HF showed the highest median σ values, respectively, 10.5 MPa and 8.5 MPa. In contrast, the BCp bonded to glass–ceramic treated with MDP showed the lowest median σ value (0.8 MPa), which was not statistically different from other MDP-treated groups.ConclusionsThe failure mode was governed by the glass–ceramic surface treatment, not by the bracket type. Quantitative (σ values) and qualitative (fracture mode) data suggested a minimum of 5 MPa for brackets bonded to glass–ceramic, which is the lower critical limit bond strength for a comprehensive orthodontic treatment.Clinical relevanceBonding brackets to glass–ceramic requires micromechanical retention.