Purpose: To study the effect of the varnish type, application time and surface polishing on the shear bond strength (SBS) of a universal adhesive in healthy and demineralized bovine enamel.
Materials and methods: 432 bovine primary central incisors were assigned to 18 groups according to enamel mineralization [healthy and demineralized], topical varnish [Clinpro White Varnish (CWV; 3M Oral Care) and Profluorid (PFV, Voco)], remineralization time [24 h or 21 days] and polishing or not of the enamel surface. Adhesion was tested using Futurabond M (Voco)+ and GrandioSO (Voco). Sheer bond strength (SBS) was measured and the fracture mode studied. The statistical analysis was performed using two-way ANOVA, Tukey's test, and Pearson's chi-squared test.
Results: In healthy bovine enamel, CWV reduced SBS at 24 h and 21 days; polishing significantly improved SBS. PFV increased SBS in healthy enamel at 21 days and demineralized enamel at 24 h and 21 days; polishing had no effect on SBS. The application time and polishing of the enamel surface affected the behavior of varnishes with respect to SBS. There was a correlation between the type of fracture and the degree of mineralization as well as the timepoint of varnish application.
Conclusions: Remineralization of demineralized enamel with fluoride varnishes permits the recovery of the bond strength obtained in healthy enamel. Of the two varnishes studied, PFV had the highest SBS and more uniform behavior, regardless of the application timepoint, degree of mineralization, and surface treatment of the enamel..
Keywords: demineralization; enamel; fluoride varnish; remineralization; shear bond strength; tricalcium phosphate.