Bond Strengths of Nanocomposite Using Different Conditioners and Bonding Agents

Phosphoric-acid etching (H₃PO₄) releases matrix metalloproteinases (MMPs) whose activation is inhibited by chlorhexidine (CHX).  MMPs degrade collagen within the hybrid layer.  Conditioning with neutral ethylene-diamine-tetra-acetic acid (EDTA) may lessen release of MMPs.  Objectives: To determine best bonding protocol for Filtek-Supreme-Ultra (FSU) that will reduce effects of MMPs by testing two bonding agents with two different conditioners.  Methods: Sixty caries-free molars mounted in resin were randomly divided in to four groups (n=15).  Occlusal surfaces were reduced to expose flat enamel (E) surfaces.  Two groups were etched (H₃PO_4, 15s), rinsed (15s), lightly dried, lightly scrubbed with 2% CHX (60s) and lightly air dried.  Remaining two groups were conditioned with 17% neutral EDTA (60s), rinsed (15s) and blotted dried.  Dentin bonding agents Optibond Solo Plus (OBSP) or Adper Single Bond Plus (ASBP) were applied according to manufacturers’ instructions and photo-cured (30s).  Columns of FSU (2mm height by 2.38mm diameter) were photo-cured (40s).  Specimens were stored (24h) in de-ionized water (37°C) and shear tested in an Instron (crosshead speed 0.05mm/min).  After testing enamel, specimens were reduced to expose flat dentin (D) surfaces and bonding/testing protocols repeated for dentin-shear-bond-strengths.  Results: mean shear-bond-strengths recorded in MPa were:  E/H₃PO₄/OBSP 16.2, E/H₃PO₄/ASBP 14.0, E/EDTA/OBSP 21.0, E/EDTA/ASBP 13.7, D/H₃PO₄/OBSP 23.5, D/H₃PO₄/ASBP 12.0, D/EDTA/OBSP 17.2, D/EDTA/ASBP 9.3.  Data was skewed and analyses performed on log-transformed values. 3-way ANOVA indicated significant differences but inconsistent interactions.  Within dentin groups OBSP was significantly better than ASBP (p<0.0001) and H₃PO₄ superior to EDTA (p<0.0001).  Within enamel groups OBSP was significantly stronger than ASBP when using EDTA (p<0.0001), but not different using H₃PO₄ (p>0.08).  Conclusions: When using FSU it is best to use traditional H₃PO₄ etching, CHX and OBSP.