The microstructure of four cements, setting by different mechanisms (acid-base, dual cure, triple cure), was studied. The porosity of unpolymerized materials was detected by stereomicroscopy. After polymerization and storage in water or lactic acid solution, the porosity, filler distribution and gel layer, which was formed at the filler/matrixinterface of polymerized materials, were examined by confocal laser microscopy. For this purpose, the specimens were treated with fluorescent dye solution before the test. The results showed that hydrolytic degradation (pH 7) mainly involved the resin matrix, and the acid erosion (pH 3.5) involved the gel layer too. As regards the filler, materials with different setting mechanism released the glass particles in di!erent times. The loss of the filler particles occurred quicker in acid}base setting cements, and slower in triple-cured material.