The critical bond strength of orthodontic brackets bonded to dental glass–ceramics

• Published in: Clinical oral investigations 2019-12, Vol.23 (12), p.4345-4353
• Main Authors: Di Guida, Luís Antônio, Benetti, Paula, Corazza, Pedro Henrique, Della Bona, Alvaro
• Format: Article
• Language: English
• Subjects: Bond strength; Ceramics - chemistry; Dental Bonding; Dental cement; Dental Etching - methods; Dental Stress Analysis; Dentistry; Humans; Lithium; Materials Testing - methods; Medicine; Microscopy, Electron, Scanning; Original Article; Orthodontic Brackets; Orthodontics; Resin Cements - chemistry; Shear Strength; Surface Properties
• ISSN: 1432-6981; 1436-3771
• DOI: 10.1007/s00784-019-02881-5

Objectives To evaluate the critical bond strength ( σ ) of ceramic and metal brackets to a lithium disilicate-based glass–ceramic. Materials and methods Two 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). Results BCm 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. Conclusions The 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 relevance Bonding brackets to glass–ceramic requires micromechanical retention.