Malacarne-Zanon et al polymer structure. Moreover, the increased con- centration of water in AP, in conjunction with in- compatibilities between co-initiators and the very acidic and hydrophilic phase, could have rendered lower monomer polymerization, determining the formation of a loosely compact polymer that is prone to rapidly absorb water/silver.37-39 One could argue that the polymerization of AP and OU the self-etching adhesives evaluated in this study in- side a mold could have interfered with their opti- mal polymerization and, as a consequence, have led to a greater permeability of these materials. The idea that the acidity of these simplified adhe- sives is neutralized when they are applied to den- tin due to a reaction with hydroxiapatite crystals, favor the belief that the degree of conversion of such materials would be improved under such condition. However, previous studies on polymer- ization of self-etching adhesives have shown that they can achieve a similar degree of conversion when polymerized in a mold for an extended pe- riod (91% after 60 s of irradiation)40 or when they are applied on dentin (79% - 93%).41 Accordingly, the photoactivation time employed in this study (80 s) would have been enough to produce a compara- ble and clinically relevant degree of conversion to that produced when these materials are polymer- ized on dentin. The increased permeability found in the one-step, self-etching adhesives evaluated in this study is in accordance with the results of increased water diffusion through dentin inter- faces bonded to similar simplified adhesives, even though, in the former study, they had been exten- sively photo-activated prior to the testing of their permeability.40 Apart from the differences in the amount of silver deposited, which were found to be greatly related to the material’s hydrophilicity,36 this study identified differences in the pattern and in the spe- cific location of silver deposition over the superfi- cies analyzed. It is worth noting that all adhesives evaluated depicted silver permeation only or most- ly along the interface with the epoxy resin, i.e., in the superficies of the specimen, though everyone had been produced in confinement, inside a mold, covered with a glass slide in an attempt to exclude oxygen inhibition layer in the superficies.42-44 Thus, a different location of a silver deposition might be explained only by the non-homogeneity of polym- erization in the bulk of specimens35 due to phase October 2010 - Vol.4 separation of very different elements.45 Volatile solvents and hydrophilic monomers with a low molecular weight might have concentrated near the adhesive surface, causing lower monomer po- lymerization in this area.34,35 Consequently, differ- ences in the quality of polymerization through the specimen determined the spatial anisotropy of the cured polymer, and, finally, the spatial distribution of silver particles. Strong evidence of phase separation was spe- cifically observed in SE-PB specimens. Although we were careful to achieve a proper mixture of the primer and the bond components of the adhesive system, the micrographs depicted two very dis- tinct phases over the specimens - one deficiently and another greatly infiltrated by silver particles. Such a great difference leads us to speculate that primer and bond liquids do not mix properly. Chemical incompatibilities between these two liq- uids could be responsible for their non-miscibility. The self-etching primer applied in this study is basically a mixture of hydrophilic monomers, sol- vated in water. In contrast, the bond component of the system is composed of a great quantity of hy- drophobic monomers, which are not miscible with water.45 The reduced miscibility of the primer and the adhesive can therefore determine the mainte- nance of two different phases slightly attached by very hydrophilic and weak linkages. This study’s results showed that a great num- ber of silver ions were able to diffuse through sim- plified, more hydrophilic adhesives, even though they were polymerized over an inert, water-free substrate, i.e., a brass mold. Additionally, a great silver diffusion was observed through the primer of a multi-step adhesive system. Thus, despite being clinically more stable,10 the three-step etch-and- rinse adhesives and two-step self-etch systems may also produce degradable bonded interfaces limited by the stability of their bond agents over the instability of their primers.46 Therefore, future research should be done to clinically bond hydro- phobic materials to dental tissues. ocnLusIons Within the limits of the present study, it can be conclude that simplified, hydrophilic adhesives allow higher fluid diffusion than less hydrophilic ones that must be applied to dentin in multiple steps. High fluid diffusion can be related to the 437 European Journal of Dentistry