Bond strengths of single-bottle dentin adhesives to caries-affected dentin

There is concern that some acidic conditioners may not be strong enough to adequately etch sclerotic or caries-affected dentin. The hypothesis that was tested was that there were no significant differences in the bond strengths of single-bottle bonding systems to normal or caries-affected dentin, regardless of the strength of the phosphoric-acid conditioner. Extracted teeth with coronal caries extending into mid-dentin were prepared by grinding the occlusal surface flat. This left a central region of caries-affected dentin surrounded by normal dentin. The One-Step bonding system was used to bond dentin following etching with 10 or 32% phosphoric acid. The Single Bond system was used after etching dentin with 10 or 35% phosphoric acid. After 24 hours in water, serial vertical sections were made through the bonded teeth to create slabs 0.7 mm thick. Each tooth yielded four to five slabs, some of which included normal dentin, while others included caries-affected dentin. Each slab was trimmed into an hourglass configuration to limit the test area to normal or caries-affected dentin. The results obtained with One-Step following etching with 10% phosphoric acid showed lower (P < 0.05) tensile bond strengths to caries-affected dentin compared to normal dentin (36.9 +/- 8.0 MPa vs 47.7 +/- 6.5 MPa, respectively). This difference disappeared when using 32% phosphoric acid (49.7 +/- 6.1 MPa vs 45.0 +/- 7.2 MPa, respectively). Bonds made to caries-affected dentin with Single Bond were always lower than bonds to normal dentin regardless of the strength of the phosphoric acid. Scanning electron microscopy of polished cross sections sequentially challenged with acid and NaOCl revealed loss of the middle of the hybrid layers created by either bonding system in caries-affected dentin etched with 10% phosphoric acid. It is clear that 32-35% phosphoric acid is required to adequately etch caries-affected dentin in order to produce high bond strengths and well-infiltrated demineralized dentin.