Purpose: To investigate (1) the tensile bond strengths of four commercial dentin bonding systems to bovine crown and root dentin and (2) the structure of the hybrid layers for each system bonded to the two dentin substrates.
Materials and methods: Superficial surfaces were exposed in bovine crown and root dentin. The teeth were embedded in plaster and a 3 mm diameter bonding area was demarcated. The four bonding systems used were All-Bond 2, Super-Bond D-Liner Plus, Clearfil Liner Bond II, and ProBond. Bonding procedures followed the manufacturers' instructions with the exception of Super-Bond D-Liner Plus where the primer was left in situ for 60 seconds. Tensile bond strengths were tested after 24-hour storage in 37 degrees C deionized water. Specimens were also prepared for SEM observation of the hybrid layer, after treatment with 10% phosphoric acid, and 10% phosphoric acid and 5% sodium hypochlorite.
Results: Statistically lower bond strengths to crown dentin when compared with root dentin were observed for All-Bond 2, whereas Liner Bond II showed the opposite (P < 0.01). Both ProBond and Super-Bond D-Liner Plus showed no statistical differences between crown and root dentin (P > 0.05). Hybrid layers could be observed for All-Bond 2, Liner Bond II and Super-Bond D-Liner Plus, with no apparent differences between the hybrid layers of crown and root dentin. In the case of ProBond, where the smear layer was not removed during the priming stage, it appeared that the primer had infiltrated and caused hybridization of the smear layer. The differences in bond strength were thought to be related to the different bonding mechanisms of each material, as well as possible variations in the crown and root dentin substrates.