Effect of different surface conditioning methods and low pH solutions on the shear bond strength of orthodontic brackets to newly introduced CAD/CAM materials

Abstract

Aim: To evaluate the shear bond strength (SBS) of ceramic and metallic orthodontic brackets bonded to lithium disilicate ceramics or hybrid ceramics and subjected to different surface conditioning treatments.

Materials and methods: In total, 300 specimens were fabricated from GC LiSi (lithium disilicate) and GC Cerasmart (hybrid) ceramic blocks. The specimens were divided into four groups according to the following surface treatments: hydrofluoric acid (HF); sandblasting with 50 μm aluminum oxide; Monobond Etch and Prime; and erbium-doped yttrium aluminum garnet (Er-YAG) laser. Metal (Victory Series) and ceramic (Clarity) brackets were bonded using an orthodontic adhesive resin (Transbond XT; 3M Unitek, CA, USA). The specimens were then stored in three different mediums (artificial saliva, mouth rinse, and gastric juice) and thermocycled. An SBS test was performed after 1 week. The surface morphology was examined after the conditioning treatments using a scanning electron microscope. Data were analyzed using analysis of variance, t-test, and Duncan test.

Results: The SBS data revealed that the type of computer-aided design/computer-aided manufacturing (CAD/CAM) block and surface conditioning method significantly affected the SBS. The highest SBS was recorded (10.112 MPa) for the HF-treated hybrid ceramic blocks stored in the saliva medium, while the lowest SBS (1.862 MPa) was reported for the Er-YAG laser-treated lithium disilicate ceramic blocks stored in the gastric juice medium. GC Cerasmart exhibited better bond strength than that of GC LiSi; however, no significant difference was observed between the ceramic and metal brackets.

Conclusion: The CAD/CAM material, surface conditioning method, and medium affect the SBS.

Keywords: Hybrid ceramic; Lithium disilicate ceramic; Orthodontic bracket; Shear bond strength; Surface treatment; gastric juice.

Fig. 1

Metal and ceramic brackets cemented on the test specimen.

Fig. 2

The knife edge chisel tip was positioned to edge of base of bracket.

Fig. 3

Scanning electron microscope images of the GC LiSi blocks (2000× magnification) under different surface conditioning treatments A) Control; B) Hydrofluoric acid etching; C) Monobond Etch & Prime; D) Sandblasting; E) Laser.

Fig. 4

Scanning electron microscope images of the GC Cerasmart blocks (2000× magnification) under different surface conditioning treatments.

Fig. 5

Scanning electron microscope image of the retention mechanism of the orthodontic brackets with a metallic mesh at the metal bracket base (50× magnification).