Primary dentin microhardness after different conditioning treatments for resin bonding

Mechanical properties of the bonded interface and those of the surface dentin layer in which the bonded procedure is produced, affect attained bond strength. Objectives: The aim is to determine if primary dentin microhardness (MH) is affected by different chemical dentin pre-treatments performed for resin bonding. Methods: Dentin discs were obtained by transversally sectioning the crowns of human primary first molars. Knoop MH was measured after different treatments: (1) polished up to 4000 grit, (2) polished and etched (37% ortophosphoric acid) for 7s or 15 s, (3) polished, etched for 7s or 15 s and treated with 5% NaOCl for 2 min. Indentations (n=20) were performed on moist surfaces with a standard Knoop MH tester (20 g, 5 s). Data were expressed in Knoop Hardness Numbers (KHN) and analysed by one-way Anova and SNK multiple comparisons (P<0.05). Results: Dentin KHN decreased after acid etching, regardless of etching time. NaOCl treatment after acid etching lowered MH. Conclusions: Treating dentin with either H₃PO₄ and/or NaOCl caused marked reduction of its surface hardness. Acknowledgements: CICYT/FEDER MAT2004-06872-C03-02.