Bond strength of ceramic brackets bonded to enamel with amorphous calcium phosphate-containing orthodontic composite

The aim of this in vitro study was to compare the shear bond strength (SBS) and failure modes of a conventional resin-based composite with a recently developed amorphous calcium phosphate (ACP)-containing orthodontic composite system. Forty freshly extracted human maxillary premolar teeth were randomly divided into two equal groups. Conventional composite (group 1; Transbond-XT; 3M Unitek) and ACP-containing orthodontic composite (group 2; Aegis-Ortho; Harry J. Bosworth Co.) were used for bonding ceramic orthodontic brackets. The SBS of these brackets were measured and recorded in megapascals (MPa). Adhesive remnant index (ARI) scores were determined after bracket failure. Data were analysed with a Student's t-test for two independent variables and Pearson's chi-square tests. Statistical analysis showed that the bond strength of group 1 (mean: 36.7 +/- 6.8 MPa) was significantly higher than group 2 (mean: 24.2 +/- 5.4 MPa; P < 0.01). Although a greater percentage of the fractures were cohesive at the composite interface (Score 1 + Score 2 = 70 per cent in group 1 and 90 per cent in group 2), statistically significant differences were observed between the groups (P < 0.05). The ACP system is suitable for bonding ceramic orthodontic brackets due to the lower SBS values compared with conventional composite. The ACP-containing composite is recommended for use in clinical orthodontic practice in order to achieve lower decalcification scores under ceramic orthodontic brackets.