GM priming effect on not-decalcified and smear layer-free dentin

Objectives: EDTA conditioning is mandatory to remove the smear layer on dentin surface because it minimizes the contraction gap width. However, it has been still discussed that which dentin surface, inorganic-rich or organic-rich, is suitable for bonding. The top surface, approximately 0.3 ìm in thickness, of EDTA-conditioned dentin is slightly decalcified. The aim of this study was to investigate the efficacy of a commercial dentin bonding agent to not-decalcified, smear-layer free dentin.

Methods: Eighty extracted human teeth were used. The specimens were divided into four groups, not conditioned, chemically conditioned with EDTA or 40% phosphoric acid gel and physically conditioned with high pressure (4 MPa) water spray. The flat dentin surface was prepared and a resin composite (Palfique Estelite, Tokuyama, Japan) was bonded to dentin surface mediated with a dentin bonding agent (Clearfil Photo Bond, Kuraray, Japan). For the half of specimens, the dentin surface was primed with 35% glyceryl mono-methacrylate (GM) solution after conditioning. The shear bond strength was measured ten minutes after polymerization of the composite. The results obtained were statistically analyzed by Fisher's PLSD p<0.05)

Results: The bond strength of the no-conditioned group (4.50±1.37, 3.70±0.65 MPa, w/wo GM priming) was significantly increased by phosphoric acid-conditioning (7.03±1.92, 4.89±1.51), EDTA-conditioning (8.17±1.72, 7.28±1.71) and the water spray conditioning (8.23±1.92, 6.55±1.43). The difference among the three conditioning group with GM priming was insignificant.

Conclusion: When the smear layer was removed, the shear bond strength was significantly increased regardless of removing methods employed in this study. The GM priming did not increase the bond strength of the EDTA conditioning group. It was reported that the contraction gap formation was prevented completely by EDTA conditioning and GM priming. The efficacy of dentin adhesive should be evaluated consistently by three dimensional cavities rather than bond strength measurement to flat dentin surface.