Variables influencing the bond strength of metal orthodontic bracket bases.

The purpose of this study was to examine the retention variables that exist between commercially available bracket bases. Premolar bracket bases from seven manufacturers were examined in the scanning electron microscope (SEM) as received. They were then bonded to human premolars with Dynabond and, after storage in water for 24 hours, tested to failure in shear. The bond-fracture surfaces were also examined in the SEM. Comparison of the SEM observations and shear strength data led to the following conclusions: (1) Weld spots reduce the retentive area. (2) Weld spurs could be responsible for lower bond strengths in some foil-mesh samples. (3) Weld spots on the edges of attachment bases should be avoided to prevent a poor marginal resin-mesh seal. (4) Bracket bases should be designed to prevent air entrapment under the base. (5) The best resin penetration and bond strength were obtained with a fine mesh bracket base of the woven mesh type.