The effeCT Of COmbINeD bleaChINg aND mICRO- abRasION TheRapIes ON The INTeRfaCIal mICRO- mORphOlOgy aND sheaR bOND sTReNgTh Of TwO DeNTal aDhesIves TO hUmaN eNamel

In complex cases of enamel fluorosis or enamel dys-mineralization, combined bleaching and micro-abrasion therapies may be advocated. The aim of the present study was to investigate the effect of combined in-office bleaching and micro-abrasion on the bond strength of two dental adhesives bonded to surface enamel. The interfacial micro-morphology of the involved surfaces was also studied by using SEM. Materials and methods: A total of 26 extracted human premolars were used to prepare 52 samples exposing enamel surfaces. Samples were randomly assigned to two groups to test the bonding with two dental adhesives. Each group was further subdivided into 2 subgroups of 10 each according to the treatment sequence. Three samples from each subgroup were processed for SEM to study the interfacial micro-morphology. Samples were subjected to shear bond strength testing. Results: statistical analysis revealed that Rely-a light bond exhibited significantly higher shear bond strength when enamel was bleached then micro-abraded. However, when using Exite bond, the sequence of the treatment reported an insignificant difference. Conclusions: (1) The sequence of the treatment has an effect on the shear bond strength depending on the type of the adhesive used. (2) When combined bleaching and micro-abrasion therapy is considered before bonding with fluoride releasing bond, it could be advantageous to begin with bleaching procedures, while bonding with adhesives containing organic solvents is not affected by the sequence of the treatment. (3) Fluoride releasing adhesive systems together with subsequent micro-abrasion could reduce or eliminate the adverse effects of bleaching systems so they are recommended for immediate bonding of orthodontic brackets or esthetic composite veneers. (4) The micromorphological features at the tooth-restoration interface varied with the different surface treatments used.