Abstract
ABSTRACTThe presence of porosities at the dentin/adhesive interface has been observed with the use of new generation dentin bonding systems. These porosities tend to contradict the concept that etching and hybridization processes occur equally and simultaneously. Therefore, the aim of this study was to evaluate the micromechanical behavior of the hybrid layer (HL) with voids based on a self-etching adhesive system using 3-D finite element (FE) analysis. Material and Methods: Three Fe models (Mr) were built: Mr, dentin specimen (41x41x82 μm) with a regular and perfect (i.e. pore-free) HL based on a self-etching adhesive system, restored with composite resin; Mp, similar to M, but containing 25% (v/v) voids in the HL; Mpp, similar to Mr, but containing 50% (v/v) voids in the HL. A tensile load (0.03N) was applied on top of the composite resin. The stress field was obtained by using Ansys Workbench 10.0. The nodes of the base of the specimen were constrained in the x, y and z axes. The maximum principal stress (σmax) was obtained for all structures at the dentin/adhesive interface. Results: The Mpp showed the highest peak of σmax in the HL (32.2 MPa), followed by Mp (30 MPa) and Mr (28.4 MPa). The stress concentration in the peritubular dentin was high in all models (120 MPa). All other structures positioned far from voids showed similar increase of stress. Conclusion: Voids incorporated into the HL raised the σmax in this region by 13.5%. This behavior might be responsible for lower bond strengths of self-etching and single-bottle adhesives, as reported in the literature.
Highlights
The structural behavior of the adhesive layer plays an important role in maintaining the integrity of the dentin-resin bond over time[1]
The peak of Vmax was observed in the peritubular dentin (Figure 3) for all models (Figure 4).This behavior was similar in all other structures of the dentin/adhesive interface that showed an increase of Vmax in Mp when compared with Mr and in Mpp when compared with Mp (Figure 4 and 5)
The Vmax in the peritubular dentin was observed in its upper border, exactly where the resin tags start (Figure 3)
Summary
The structural behavior of the adhesive layer plays an important role in maintaining the integrity of the dentin-resin bond over time[1]. Self-etching adhesive systems have been introduced to allow dry bonding based on shallower demineralization with the formation of thinner hybridization of dentin. A more homogenous dentin/adhesive interface is expected to be recreated[5]. Self-etching adhesives reduce the steps necessary for bonding in comparison with etch-and-rinse adhesives. Because many self-etching adhesives leave the bottom of smear plugs intact, they tend to create resin-dentin bonds that exhibit less dentin sensitivity[5,6]. Self-etching adhesives are used in order to form a stable and strong biopolymer[18], lower bond strength has been reported[4] mainly
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