Evaluation of dentin desensitization protocols on the dentinal surface and their effects on the dentin bond interface

Objectives: To evaluate the effect of desensitizing agent containing calcium phosphate nanoparticles on the bond strength of etch-and-rinse adhesive system (Scotchbond Multi-Purpose), presence of precipitate, dentinal tubule obliteration and hybrid layer formation in dentin in comparison with potassium nitrate plus sodium fluoride or strontium chloride compounds. Methods: 150 bovine incisors were treated with (n = 10): G1, Desensibilize Nano P (Ca₃(PO₄)₂+5%KNO₃+0.9%NaF); G2, Desensibilize (10%SrCl₂+5%KNO₃); G3, Desensibilize KF2% (5%KNO₃+0.2%NaF); G4, Ultra EZ (3%KNO₃+0.25%NaF) and G5, no treated (control). Scanning electron microscopy was used to assess the incidence of precipitates (500×) and obliterated dentinal tubule counts (1.000×). The adhesive system was used after all desensitization treatments. The bond strength (n = 40) and the fracture pattern were evaluated. Confocal laser microscopy was used to quantify the hybrid layer formation in dentin. Results: G1 and G2 presented higher adhesive system bond strength (MPa) than G4 and G5, however no significant differences were observed in comparison with G3. Cohesive fracture was frequently found: G1 (58.5%), G2 (51.3%) and G3 (43.8%). G1 showed the highest incidence of precipitates and the highest number of blocked dentinal tubules. G1 and G2 presented similar hybrid layer formation and the highest hybrid layer formation values. Conclusions: Desensibilize Nano P (G1) favored the bond strength of the adhesive system to dentin, increased the precipitation of residues, obliteration of dentinal tubules, and hybrid layer formation in comparison with other agents. Clinical relevance: Desensitizers promote dentin obliteration, however, may affect dentin bonding.