Shear Bond Strength with Flash-Free Brackets and Different Bonding Protocols

Objectives: The Flash-Free Adhesive-coated appliance system was recently introduced to eliminate the need for excess material removal and marginal gaps after bracket placement that may result in white-spots and caries formation. The objectives were to compare different bonding protocols, shear bond strengths and Adhesive Remnant Index between pre-pasted Flash-Free brackets and conventional stainless-steel brackets.
Methods: 105 extracted premolars were pumiced, mounted and randomly divided into seven groups (N=15) with different surface conditioning (+/- 37% H₃PO₄), choice of primers (Transbond-MIP, Assure-Plus or self-etching Transbond-Plus); and protective-sealant (ProSeal) application (+/-). All Flash-Free brackets and metal brackets (control) were bonded under a constant pressure, and excessive adhesives were removed before light curing.
All bonded teeth were thermocycled 500 cycles (5^o and 55^oC) and shear bond strengths (SBS) were determined using an Instron testing machine (1mm/min). Modified Adhesive Remnant Index (ARI) 1-5 were scored (no adhesive - all adhesive on bracket) to determine the bond failure mode. Difference in SBS and ARI’s among the groups were statistically analyzed (ANOVA, Tukey’s HSD, p≤0.05)

Results: Significant differences in SBS were found among the groups studied (p<0.0001). Conventional bonding with metal bracket yielded the highest SBS (12.5 MPa) which was significantly higher than all Flash-Free ceramic bracket groups except when total-acid-etching and Assure-Plus primer was used (10.5 MPa). Use of self-etch-primer and protective sealant yielded significantly lower bond strengths (5.4 MPa). ARI of Flash-Free brackets scored significantly higher for self-etch and surface-sealed group (ARI=4.7). The total-etch and primed Flash-Free groups left significantly more resin on tooth surfaces after debonding (p<0.001) with ARI’s ranging 1.6-2.5 compared to that with metal brackets (ARI =3.2)
Conclusions: Flash-Free system yields clinically acceptable shear-bond-strengths compared to metal brackets, except when self-etch primer and protective-sealant are used. Frequent failure mode that occurs cohesively or at the resin-bracket interface in the Flash-Free bracket system may require more cleanup after debonding.