Stability of bonds made to superficial vs. deep dentin, before and after thermocycling

Bonding stability of resinous adhesives to dentin is still problematic and may involve regional variations in dentin composition. This study is to evaluate the effect of dentin depth on the stability of resin-dentin bonds under thermocycling challenge.Dentin slabs with two flat surfaces parallel to the tooth axis were obtained from extracted human third molars. The slabs were randomized into eight groups according to the location of dentin [deep dentin (DD) or superficial dentin (SD)], the adhesive treatment (Single Bond 2 or Clearfil S(3) Bond), and the storage treatment (thermocycling for 5000 times vs. no). After the adhesive treatment and composite buildup on the dentin slabs, the micro-shear bond strength (μSBS) of each group was detected. The concentrations of cross-linked carboxyterminal telopeptide of type I collagen (ICTP) were also evaluated using an immunoassay to detect the degree of collagen degradation in each group.Dentin depth, adhesive treatment and storage treatment all showed significant effects on both the μSBSs and the ICTP values (P<0.05). Regardless of the adhesive type, thermocycling decreased the μSBSs and increased the ICTP values (P<0.05). The DD groups showed significantly lower μSBSs and higher ICTP values than SD groups after thermocycling aging (P<0.05). The treatment with Single Bond 2 significantly increased the ICTP values (P<0.05), whereas Clearfil S(3) Bond showed no effect on the ICTP values (P>0.05).Deep dentin showed significantly more bond degradation after thermocycling than did superficial dentin.