Publications (2)4.42 Total impact
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ABSTRACT: Excessive etching of the dentin may decrease bond strength because the adhesive may fail to completely infiltrate to the base of the over-etched demineralized collagen network. The purpose of the present study was to evaluate the influence of increasing etching times on the microtensile bond strength of Single Bond and the leakage of silver ions within the hybrid layer. After etching occlusal dentin for 15, 30, or 60 seconds with 35% phosphoric acid gel, Single Bond was applied and cured for 10 seconds. Z100 was added and cured for 60 seconds. After 24 hours of water immersion, the teeth were sectioned into slices 0.7 mm thick, and hour-glass-shaped specimens were prepared. Alternate slices were either dried for 30 minutes in air, kept wet, or they were coated with fingernail varnish except for 0.5 mm around the bonded area. Only the varnished samples were then stained with 50% AgNO3. Microtensile bond strength was tested using a Vitrodyne V-1000 universal tester. The samples of the stained group were embedded in self-curing PMMA and polished. All samples were observed with an SEM. Nanoleakage of silver ions was measured by exposure to laser ablation with an inductively connected plasma mass spectrometer and by electron dispersive elemental analysis. Increasing etching times seemed to have a negligible effect on bond strength of Single Bond, producing an average value of ca 38 MPa. However, the silver uptake increased upon prolonged etching times. Short-term results suggest that overetching has no detrimental effect on bond strength values of Single Bond. However, increased silver uptake, depending on the etching time, raises concern about the long-term stability of the bond.
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ABSTRACT: Primers and adhesives containing hydroxyethyl methacrylate (HEMA) are placed on moist dentine even though several studies indicate that water may interfere with the polymerization reaction. The purpose of this study was to evaluate the influence of increasing amounts of water on the physical properties of a model dentine primer resin (HEMA) and model dentine bonding resin (a mixture of HEMA and Bis-GMA). Miniature (ca 10 x 0.5 mm (long x thick) hour-glass shaped and parallel-sided specimens were created by casting the monomer or comonomer mixtures into appropriately shaped moulds. The water content was either 0, 5, 9, 17 or 29 vol%. One hour after polymerization, half the specimens were subjected to physical testing under dry conditions. The other half were immersed in water for 24 h and then tested while wet. The ultimate tensile strength (UTS), modulus of elasticity (E), percent elongation at failure, and toughness were calculated. The properties of the dry-stored primer and bonding resins were not altered by water incorporation up to 9 vol%. Higher water content lowered the physical properties (P < 0.05). Immersion of primers polymers in water for 24 h significantly decreased their properties. Water immersion of the bonding resins was unaffected only for specimens containing 0 or 5 vol% water. The plasticizing effects of extrinsic water are far more important than the effects of intrinsic water in poly-HEMA resin. Hybrid layers composed primarily of poly-HEMA would be expected to be more elastic than those made with bifunctional, cross-linked polymer chains.
Georgia Health Sciences University
Augusta, Georgia, United States
- Department of Oral Biology
University of California, Los Angeles
Los Angeles, California, United States
- School of Dentistry