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Structural evidences of the microfilled composites.

The new composite concept of microfilled composites has certain advantages, such as polishability, permanent smoothness, and high abrasion resistance. In the mouth, however, these new materials are not perfect and they often fail in stress-bearing restorations. In the present study, the weak links and imperfections of these materials are determined by means of direct and indirect SEM techniques. The chemical adhesion between polymer blocks and polymer matrix is questionable; fractures occur most often at the filler-matrix interface. In vivo, there is still a certain preferential wear of the resin matrix. In Estic Microfill, rear weak zones with starlike condensations are observed, which could be related to a certain incompatibility of its composing resins and/or to incomplete and inhomogeneous polymerization. In a fractured Isopast restoration, the polymer blocks are clearly revealed, scattered in a three-dimensional polymerized matrix network.