Primary dentin etching time, bond strength and ultra-structure characterization of dentin surfaces

To evaluate the effect of shortening the etching time on roughness, microhardness and bond strength of three adhesive systems to primary tooth dentin.

Flat dentin surfaces from primary molars were randomly assigned to six experimental groups. Three different adhesive systems were used: an etch-and-rinse adhesive (Single Bond), a two-step self-etching (Clearfil SE Bond), and a one-step self-etching (One-Up Bond F) adhesive. In half of the specimens, the recommended etching time was used, in the other half the etching time was 50% reduced. After applying the adhesive, resin composite build-ups were constructed and stored in a humid environment for 24h at 37 degrees C. Specimens were sectioned into 1mm(2) beams and tested for microtensile bond strength (MTBS). Debonded surfaces were analyzed by scanning electron microscopy (SEM). Additional surfaces were conditioned for microhardness measurements (KHN) and for atomic force microscopy (AFM) analysis. Intertubular and total surface roughness (Ra) were recorded. Results were analyzed with ANOVA and Student-Newman-Keuls tests (P<0.05).

Single Bond and Clearfil SE Bond showed higher MTBS than One-Up Bond F. Bond strength and intertubular roughness increased when Single Bond and One-Up Bond F were used with a reduced etching time. For Clearfil SE Bond no differences in MTBS were detected when reducing the etching time. The application of phosphoric acid, Clearfil SE Bond primer and One-Up Bond F decreases dentin microhardness.

Shortening One-Up Bond F application time and reducing the etching time of phosphoric acid to one-half of the manufacturer's recommended etching time when using Single Bond are recommended when bonding to primary dentin.