Bond strengths and debonding characteristics of two types of polycrystalline ceramic brackets

To compare the shear bond strengths and modes of failure of three orthodontic brackets: a polycrystalline ceramic bracket, a collapsible polycrystalline ceramic bracket and a metal bracket.

Ninety extracted human premolar teeth were selected and examined at x3 magnification for any enamel defects. Three types of brackets and one orthodontic adhesive were used. One half of the sample was tested in a universal testing machine to determine the shear bond strength. The other half was debonded with the appropriate pliers and the tooth surface examined at x5 magnification. The site of failure was scored with the modified Adhesive Remnant Index (ARI). Teeth with an ARI grade of zero were examined in a SEM to determine any enamel fracture.

No statistically significant differences in bond strength among the samples were found (p > 0.159). The modes of failure after debonding with pliers were predominantly at the bracket-adhesive interface. The mean shear bond strength of the Clarity bracket was 10.78 +/- 2.74 MPa, the InVu bracket was 12.43 +/- 2.40 MPa and the metal bracket was 11.89 +/- 1.83 MPa. There were significant differences in the mean rank of the ARI grade between the three groups (p = 0.006). The Clarity and InVu (p = 0.011) and the Clarity and metal brackets (p = 0.005) were significantly different, but there was no difference between the InVu and metal brackets (p = 0.187).

All three samples had similar bond strengths. The risk of ceramic fracture on debonding was greatest for the InVu ceramic bracket.