In vitro study evaluating the shear bond strength of metal brackets to lithium disilicate ceramic support using a universal adhesive

Introduction: The number of adult patients who seek an orthodontic treatment is increasing. These patients often have lithium disilicate ceramic restorations. The orthodontist has to find a procedure to bond effectively brackets to these restorations. In 2011, a new family of adhesives was introduced, universal adhesives, which are capable of bonding to ceramic and are said “multi-mode” because they can be used in etching-rinse or self-etching protocol on tooth surface. The objective of this in vitro study was to evaluate the shear bond strength (SBS) of metal brackets to lithium disilicate ceramic support using a universal adhesive.

Materials and methods: Forty machinable lithium disilicate blocks (IPS e.max CAD, Ivoclar) were prepared according manufacturer’s instructions. Each specimen was randomly assigned to one of four groups (n=9 or 10) defined by the pretreatment protocol. Protocol 1: Hydrofluoric Acid 9 % (HF) + Silane + Orthodontic adhesive (Transbond™ XT Light Cure Adhesive Primer, 3M ESPE), protocol 2: HF + Universal adhesive (UA) (Scotchbond Universal®, 3M ESPE), protocol 3: UA only, protocol 4 : Monobond Etch & Prime® (Ivoclar) + UA. Then, a bracket of upper cuspid (3M ESPE) was bonded to each specimen with a composite resin (Transbond™ XT, 3M ESPE). SBS was measured between ceramic and bracket with a universal testing machine. A one-way ANOVA (ANalysis Of Variance) followed by Tukey’s post-hoc test was performed to investigate SBS differences between groups.

Results: Protocol 2 (43 MPa) and protocol 4 (36 MPa) showed the highest SBS values and were statistically different from protocol 1 (25 MPa) and protocol 3 (21 MPa).

Conclusion: Despite the lower bond values obtained in the study, but higher than the minimum expected, the application of UA alone appears to be a safe procedure that seems to provide sufficiently strong and resistant bonding between the ceramic and the bracket. However, clinical studies are needed before a recommendation can be made.