Bond strength of amorphous calcium phosphate-containing orthodontic composite used as a lingual retainer adhesive

To evaluate the shear bond strength and fracture mode difference between amorphous calcium phosphate (ACP)-containing adhesive and conventional resin-based composite material used as an orthodontic lingual retainer adhesive.

Forty crowns of extracted lower human incisors were mounted in acrylic resin, leaving the buccal surface of the crowns parallel to the base of the molds. The teeth were randomly divided into two groups: experimental and control, containing 20 teeth each. Conventional lingual retainer composite (Transbond-LR, 3M-Unitek) and ACP-containing orthodontic adhesive (Aegis-Ortho) were applied to the teeth surface by packing the material into the cylindrical plastic matrices with a 2.34-mm internal diameter and a 3-mm height (Ultradent) to simulate the lingual retainer bonding. For shear bond testing, the specimens were mounted in a universal testing machine, and an apparatus (Ultradent) attached to a compression load cell was applied to each specimen until failure occurred. The shear bond data were analyzed using Student's t-test. Fracture modes were analyzed by chi(2) test.

The statistical test showed that the bond strengths of group 1 (control Transbond-LR, mean: 24.77 +/- 9.25 MPa) and group 2 (ACP-containing adhesive, mean: 8.49 +/- 2.53 MPa) were significantly different from each other. In general, a greater percentage of the fractures were adhesive at the tooth-composite interface (60% in group 1 and 55% in group 2), and no statistically significant difference was found between groups.

The ACP-containing Aegis-Ortho adhesive resulted in a significant decrease in bond strength to the etched enamel surface.