Abstract
The aim of this study was to evaluate the influence of a low-viscosity bonding resin applied over a self-etching adhesive system on the microtensile bond strength (μTBS) of indirect restorations. Comparisons were made using One Up Bond F (OB) self-etching adhesive system, Single Bond (SB) one-bottle adhesive system and Scotchbond Multi Purpose Plus (SMP) bonding component. Thirty bovine incisors were extracted and decoronated at the cementoenamel junction. The labial surfaces were ground so that superficial dentin and deep dentin were exposed. The specimens were randomized to three groups (n=10): G1- OB; G2- OB + SMP; G3- SB. In G2, a layer of the SMP bonding was applied over the OB adhesive system. Indirect composite restorations were bonded using dual-cure cement under 500 g load for 5 min. The specimens were serially sectioned with a bonding area of ± 1.0 mm2 in 3 regions: enamel (E), superficial dentin (SD) and deep dentin (DD). The sticks were fixed with cyanoacrylate adhesive and submitted to μTBS test at a crosshead speed of 0.5 mm/min in a mechanical testing machine (EMIC DL 2000). The fractured specimens were examined under scanning electron microscopy to determine the failure mode. Data were analyzed by one-way ANOVA followed by Tukey's test (p<0.05). μTBS means (in MPa) were: G1/E: 15.5 ± 3.5b; G1/SD: 22.7 ± 7.6a; G1/DD: 19.4 ± 9.4a; G2/E: 15.9 ± 5.8b; G2/SD: 19.9 ± 6.9a; G2/DD: 15.3 ± 4.9a; G3/E: 23.2 ± 7.3a; G3/SD: 20.4 ± 8.2a; G3/DD: 19.1 ± 8.7a. The results showed that the use of a low viscosity bonding resin did not affect the μTBS means when associated with a self-etching adhesive system. The self-etching adhesive system was significantly more efficient in dentin than in enamel, while the one-bottle system was significantly more efficient in enamel when compared to the self-etching adhesive system.
Highlights
A stable adhesion between resin composite and tooth is essential for the clinical success of restorations and depends on an ideal interaction between the dental substrate and the adhesive system, resin cement and indirect restoration
SEM observation showed that failures from this group involved typically cohesive fracture of the composite (Figure 1)
For specimens treated with one-bottle adhesive (G3), failures were partially adhesive between dentin and the adhesive layer, and partially cohesive of the adhesive layer (Figure 3)
Summary
A stable adhesion between resin composite and tooth is essential for the clinical success of restorations and depends on an ideal interaction between the dental substrate and the adhesive system, resin cement and indirect restoration. Self-etching adhesive systems have been recently introduced to the roll of restorative materials. As these bonding systems are applied directly to the smear-covered dentin, the acid etching step is eliminated[16]. The mild acidity of these materials is responsible for their inability to remove the smear plugs upon conditioning[5]. The acid conditioning primer dissolves and incorporates the smear layer, as it etches dentin and envelops the collagen fibrils and hydroxyapatite crystals[12]. It is assumed that no gap or voids exist because demineralization of the inorganic components and resin infiltration into the collagen fibrils occurs simultaneously to the same depth of demineralized dentin[7]
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