Richardson, Elizabeth Mary (2010)
M.Phil. thesis, University of Birmingham.
AIM: 1. To determine in vitro bond strength of metal and ceramic orthodontic brackets when using etch and separate primer, or self-etching primer (SEP) 2. To assess remaining adhesive following removal of orthodontic bracket METHOD: 180 previously extracted teeth were randomly allocated to one of six test groups. Each was subjected to either separate etch and primer or SEP and then bonded with an orthodontic bracket. These were metal (3M Unitek Victory), metal reinforced ceramic (3M Unitek Clarity) and poly-crystalline ceramic (3M Unitek Transcend). Samples were stored at 37 degrees C for 24 hours. Each bracket was debonded using shear force applied by the Instron Universal testing machine. Samples were examined under x10 light microscopy and allocated an Adhesive Remnant Index (ARI) score. RESULTS: Variation in shear bond strength (SBS) was seen across all groups. Lowest SBS was recorded with Victory series brackets bonded with SEP (7.08 MPa) and the highest was with Clarity series brackets bonded with separate etch and primer (15.96 MPa). Pooled data showed significantly higher SBS with separate etch and primer than SEP (T=2.83, p<0.01). Significant correlation for ARI score was found with Clarity series brackets and SEP. Multiple Chi squared analysis showed no significant correlation between test group and ARI score. CONCLUSION: Separate etch and primer provides a significantly greater bond strength then SEP. Greater amounts of adhesive remain on the tooth surface when SBS exceeds 12.4 MPa. CLINICAL RECOMMENDATION: Adequate bond strengths are obtained when Clarity series brackets are bonded with SEP.
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