Surface Treatment and Ceramic Type Effects on Orthodontic Bracket Strength

Objectives: To compare effects of ceramic surface treatments on in-vitro bracket bond strength.
Methods: Ceramic surfaces tested: (1) feldspathic (F) porcelain (Vitablocs® Mark II, VITA), (2) lithium disilicate (LD) (IPS e.max®-CAD, Ivoclar), (3) zirconia (Z) (CAP-Z Complete, CAP Technologies). Ceramic surface treatments: (A) bur-roughened equivalent (45µm diamond); (A) followed by air particle abrasion (APA: 25µm Al₂O₃) or, (A) followed by glazing (GLAZE). APA or Bur-roughened surfaces of F and LD were further treated with hydrofluoric acid (HFA)+silane, or silane-alone. All ceramic surfaces had an MDP-primer applied (Assure Plus, Reliance Orthodontics). Glazed surfaces of F, LD, and Z used MDP-primer only, as did APA and Bur-roughened surfaces of all ceramics. Brackets (APC II Victory, 3M-Unitek) were bonded to all surfaces. Controls were acid-etched bovine enamel using conventional primer (Transbond XT) or no etching and only MDP-primer. Bonded specimens were thermocycled, water-stored in 37°C for 7d, and tested in shear on a universal testing machine (Model 5844, Instron). N=10/group Shear strengths were compared using a 1-way ANOVA, and Tukey’s post-hoc test (pre-set alpha of 0.05).
Results: Table presents results. Use of only MDP-primer on bovine enamel provided strength not different from conventional enamel acid etching (CEAE) (20s). MDP-primer only on glazed ceramics produced strengths lower than CEAE, and showed no cohesive ceramic failures. HFA-silane-MDP treatment of all F and LD APA or Bur-roughened ceramics demonstrated highest strengths, but also showed cohesive enamel failures. Strengths of silane-MDP applied on F and LD APA or Bur-roughened surfaces were not different from the CEAE control, but showed ceramic cohesive failures. Strengths of MDP-primer to APA or Bur-roughened Zirconia surfaces did not differ from the CEAE control, with no ceramic fractures.
Conclusions: Although high bond strengths of brackets to ceramics are attainable, clinicians should be aware of the potential for cohesive ceramic failure at bracket removal.