Abstract
A dentin-cement-prosthesis complex restored with either all-porcelain, cured resin-composite, or cast base metal alloy and cemented with either of the different resin cements was trimmed into a mini-dumbbell shape for tensile testing. The fractured surfaces and characterization of the dentin-cement interface of bonded specimens were investigated using a Scanning Electron Microscope. A significantly higher tensile strength of all-porcelain (12.5 ± 2.2 MPa) than that of cast metal (9.2 ± 3.5 MPa) restorations was revealed with cohesive failure in the cement and failure at the prosthesis-cement interface in Super-Bond C&B group. No significant difference in tensile strength was found among the types of restorations using the other three cements with adhesive failure on the dentin side and cohesive failure in the cured resin. SEM micrographs demonstrated the consistent hybridized dentin in Super-Bond C&B specimens that could resist degradation when immersed in hydrochloric acid followed by NaOCl solutions whereas a detached and degraded interfacial layer was found for the other cements. The results suggest that when complete hybridization of resin into dentin occurs tensile strength at the dentin-cement is higher than at the cement-prosthesis interfaces. The impermeable hybridized dentin can protect the underlying dentin and pulp from acid demineralization, even if detachment of the prosthesis has occurred.
Highlights
Dentin is more susceptible to degradation by acid and wear when exposed to the acidic oral cavity compared with enamel due to the smaller crystal size of hydroxyapatite, the presence of tubules, and its greater organic content
The failure mode of PanaviaF specimens mostly occurred with mixed failure of adhesive on the dentin side interface and cohesive failure in the hybridized smear layer and resin (Figure 3(b)), while adhesive failure on the demineralized dentin interface was mostly found in Single-Bond + RelyX
The hybridized dentin before and after chemical immersion was consistent and continually attached (Figure 4). These results suggested that dentin conditioned with 10% citric acid and 3% ferric chloride (10-3) solution, rinsed, and gently air-dried could provide permeability for complete infiltration of 4-methacryloyloxyethyl trimellitate anhydride in methyl methacrylate initiated by tri-n-butyl borane (4-META/MMA-TBB) in the presence of poly(methyl methacrylate) (PMMA) resin to form an impermeable hybridized dentin layer which could resist the acid and NaOCl challenge
Summary
Dentin is more susceptible to degradation by acid and wear when exposed to the acidic oral cavity compared with enamel due to the smaller crystal size of hydroxyapatite, the presence of tubules, and its greater organic content. The retention provided by acid-base cements has been evaluated in terms of crown retention by using the pulling force required to remove the crown [11,12,13]. With this technique it is difficult to control the size of the interfacial area and the stress distribution, mainly shearing stress, through the tooth-cement-prosthesis junctions. Tensile strength measurement using dumbbell specimens is a widely accepted methodology
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