In vitro Evaluation of Effect of Dental Bleaching on the Shear Bond Strength of Sapphire Orthodontics Brackets Bonded with Resin Modified Glass

This study aimed to assess the effect of various types of bleaching agents on the shear bond strength of sapphire brackets bonded to human maxillary premolar teeth using resin modified glass ionomer cement (RMGIC) and to determine the site of bond failure.

Thirty freshly extracted maxillary human premolars were selected and assigned into three equal groups, ten teeth in each. The first group was the control (unbleached) group; the second group comprised teeth bleached with hydrogen peroxide group (HP) 37.5% (in-office bleaching) while the third group included teeth bleached with carbamide peroxide group (CP) 16% (at-home bleaching). The teeth in the experimental groups were bleached and stored in water one day then bonded with sapphire brackets using RMGIC with the control group and left another day. De-bonding was performed using Instron universal testing machine. To determine the site of bond failure, both the enamel surface and bracket base of each tooth were examined under magnifying lens (20X) of a stereomicroscope.

Results showed statistically highly significant difference in the shear bond strengths between control group and both of bleaching groups being low in the control group. Score III was the predominant site of bond failure in all groups.

RMGIC provides adequate bond strength when bonding the sapphire brackets to bleached enamel; this bonding was strong enough to resist both the mechanical and masticatory forces. Most of the adhesive remained on the brackets, so it reduced the time required for removal of the bonding material's remnants during enamel finishing and polishing.