Comparison of in-vitro bond strengths between resin-modified glass ionomer, polyacid-modified composite resin, and giomer adhesive systems

Introduction: The purpose of this in-vitro study was to compare the shear bond strength of orthodontic brackets bonded to tooth enamel with 4 adhesives: a commercially available giomer material, a polyacid-modified composite resin (PMCR), a resin-modified glass ionomer (RMGI), and a standard resin-based composite (RBC) adhesive. Materials: Eighty extracted human molars were collected and divided into 4 groups (n = 20). Two stainless steel premolar brackets were bonded to each tooth with 1 of the 4 adhesives, according to each manufacturers' instructions. One bracket was tested for shear bond strength at 1 hour and the other at 7 days. A shear force was applied to the bracket/tooth interface with a chisel-shaped rod attached to a universal testing machine at a crosshead speed of 0.5-mm per minute until bracket failure. The force in newtons was recorded. Debonded enamel surfaces were examined under a stereomicroscope to assess the amount of residual adhesive. Results: A 2-factor analysis of variance detected significant differences among adhesive types and time of load test. The Tukey HSD test determined that the RBC and the RMGI adhesives had significantly higher shear bond strength than the giomer and the PMCR materials at both 1 hour and 7 days. The chi-square test detected a significant difference in adhesive remnant index scores. The bracket/resin interface was the most common site of failure for all groups except the RMGI group. Conclusions: RMGI orthodontic cement provides acceptable bond strength in vitro. Further clinical research is needed to validate this laboratory finding.