Influence of fluoride varnish on shear bond strength of a universal adhesive on intact and demineralized enamel.

Abstract

The aim was to evaluate the effect of fluoride varnish on the shear bond strength (SBS) on polished and non-polished intact and demineralized enamel. Bovine incisors (half demineralized) were used. Bifluorid 12™ was applied. Bonding was made with Futurabond®M + and GrandioSO, 24h and 7days after varnishing. In some groups, varnish was removed by polishing before bonding. SBS was measured. Fracture type was determined by stereomicroscopy and scanning electron microscope (SEM) observations of the enamel surface were made. Between-group differences were determined by one-way ANOVA and the Tukey test. Associations between study factors and fracture modes were analysed using contingency tables and Pearson's chi-squared test. For intact enamel, SBS on varnished enamel at 24h was significantly less than in the other groups. SBS recovered 7days after varnishing. Varnish elimination after 24h significantly increased the SBS. However, removal at 7days did not modify SBS. SBS on demineralized enamel groups was significantly less than in intact enamel, except for demineralized enamel varnished and removed at 7days. Demineralized enamel was associated with cohesive enamel fractures and intact enamel with cohesive fractures of the composite and adhesive fractures. SEM of varnish surfaces showed a homogenous layer scattered with amorphous precipitate. In conclusion, on intact enamel fluoride varnish had a negative effect on SBS at 24h, which disappeared after 7days. On demineralized enamel, varnish did not reduce SBS at either time. Polishing the varnished enamel surface showed a similar SBS to intact enamel after 7days.