Degree of polymerisation of dental adhesives on bleached dentin

Methods: Dentin disks (1mm thick) were bleached with Opalescence Xtra Boost (Ultradent) for 30 min and bonded with the tested adhesives immediately after bleaching (T0), and after 24 h (T1) or 14 days (T2) of storage in 100% humidity environment at 37%. Adhesives were applied on unbleached dentin disks as controls (Ctrl). Extent of polymerisation (Ep) of the bonded interfaces was obtained with differential scanning calorimetry (DSC) at 20s, 40s and 60s. Data were statistically analysed with two-way ANOVA.

Results: Data showed that the extent of polymerisation obtained from DSC exotherms was significantly lower in specimens immediately after bleaching compared to controls, while increased extent of polymerisation after storage was confirmed for all adhesives. No difference was found between control specimens and bleached dentin stored up to 14 days. Ep of both controls and bleached specimens increased when curing time was prolonged (40 s and 60 s) regardless the tested adhesive (pƒ¬0.05). Ep differences between the adhesives followed a similar trend (with minor exceptions) for all specimens (Ctrl, T0, T1 e T2) and were in the order: Scotchbond MP > Clearfil Protect Bond > One-Step > Xeno III (pƒ¬0.05).

Conclusions: This study supports the hypothesis that polymerization of monomers of dental adhesives is reduced after bleaching of the dentin surface due to residual oxygen and that delaying adhesive restoration of bleached teeth may improve the clinical performance of bonding procedures.