Thesis (M.Sc.)--Chulalongkorn University, 2012

The purpose of this study was to identify the remaining of demineralized dentin in phosphoric etched dentin which was restored with three contemporary 3-step bonding adhesives using mini-dumbbell shaped tensile test and chemical challenge on dentin-resin interface. Thirty-six non-carious human molars were randomly divided into 3 groups of 12 specimens each. Each tooth was cross-sectioned to expose dentin using sectioning machine. The sectioned dentin which was wet-ground to create smear layer using a diamond wheel-shaped bur with a high-speed handpiece was etched with 32-37.5% phosphoric acid for 15 seconds and rinsed off. Moist demineralized dentin was bonded either with All-Bond3®, OptiBond FL® or Scotchbond Multi-Purpose® following the manufacturers’ recommendations. A light-cured resin composite (Metafil CX®) was restored using an incremental technique. All bonded samples were trimmed into mini-dumbbell shaped specimens for tensile bond strength test. The fractured surfaces were examined under scanning electron microscope (SEM) to determine the failure mode. The characterization of the dentin-resin interfacial layer of 4bonded specimens for each adhesive before and after immersion in 6 mol/L HCl for 30 seconds and 1% NaOCl for 60 minutes was evaluated using SEM. One-way ANOVA demonstrated no statistically significant difference (p>0.05) in tensile bond strength values (approximately11-12 MPa) among groups. The thickness of dentin-resin interface was degraded after chemical modification in all adhesive groups. The results of this study suggest that phosphoric acid etched dentin bonded with these three adhesives cannot form the complete dentin-resin interface, regardless of differences in chemical compositions in primer and bonding resin and/or techniques to keep moist. Microleakage taken place at the remaining permeable demineralized dentin of the restored tooth may consequently lead to the post-operative hypersensitivity and toothache. This defective area was clearly identified by both mini-dumbbell shaped tensile test and chemical challenge which are the effective methods to predict the durability of restored tooth in 24 hours.