Long-term nanomechanical properties and gelatinolytic activity of titanium tetrafluoride-treated adhesive dentin interface.

Objective: This study investigated the effects of dentin pretreatment with 2.5% titanium tetrafluoride (TiF) on nanomechanical properties, and the in situ gelatinolytic activity of the dentin-resin interface, for up to 6 months.

Methods: Twenty-four human teeth were prepared by exposing occlusal flat dentin surfaces, and were randomly assigned to experimental groups, according to application or non-application of a TiF pretreatment, and to the adhesive systems (Clearfil SE Bond or Scotchbond Universal). Resin composite (Filtek Supreme Ultra) was built up incrementally on the teeth in all the groups. Then, the specimens were sectioned and randomly selected for evaluation at 24h, 3 months and 6 months of storage time. The reduced modulus of elasticity (E) and the nanohardness of the underlying dentin, as well as the hybrid layer and the adhesive layer were measured using a nanoindenter. Gelatinolytic activity at the dentin-resin interfaces was assessed by in situ zymography using quenched fluorescein-conjugated gelatin at 24h and 6 months. Statistical analyses were performed with ANOVA and Tukey's tests.

Results: There were no differences in E and nanohardness values between adhesives systems and pretreatment (p=0.1250). In situ zymography showed significantly higher gelatinolytic activity after 6 months for all the experimental groups (p=0.0004), but no differences between the adhesive systems (p=0.7708) and the surface pretreatment (p=0.4877).

Significance: Dentin pretreatment with 2.5% TiF followed by self-etching adhesive systems did not influence nanomechanical properties or gelatinolytic activity of the adhesive-dentin interface layers, over time.