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An in situ study on the comparison of fluoride uptake and bond strength of composite resin on fluoridated enamel.

The aim of this in situ study was to compare the fluoride uptake and composite resin bond strength on enamel fluoridated with Duraphat (2.26 wt% fluoride). Six enamel specimens were prepared from the labial surfaces of 39 bovine incisors. The enamel samples were embedded into epoxy resin, and ground flat (800 grit). One specimen served as negative control (no fluoride treatment). The other samples were fluoridated with Duraphat for 24 hours under moist conditions, and one of them served as positive control. The remaining four samples were inserted in both buccal aspects (with a total of 12 samples originating from 3 teeth) of 13 intraoral mandibular appliances. The appliances were worn by 13 persons for a period of 6 days, 24 hours per day. The samples were also brushed twice a day, in situ, with a fluoride-free toothpaste. During meals, the appliances were stored in saline. After in situ periods of 36, 72, 108, and 144 hours, three samples each were remounted. One specimen was used for analysis of both alkali-soluble and acquired fluoride. The other two specimens served for shear bond strength testing of a light-cured composite resin. While the KOH-soluble fluoride increased significantly (p < 0.001, ANOVA) after application of the fluoride lacquer and decreased slowly with time, both the acquired fluoride and bond strengths of the composite resin did not differ significantly from the non- and fluoridated controls. The application of highly concentrated fluoride lacquers results in an increase of alkali-soluble fluoride, but does not adversely affect enamel bond strength of composite resin.