[en] The aim of this study is to evaluate the microstructure and the mechanical resistance of ceramic substrates of alumina and infiltrated with poly (methyl methacrylate) for possible applications in fixed dental prostheses. Initially the alumina samples were characterized as to particle size and mineralogical composition. Specimens were prepared and subjected to infiltration at low and high pressure for periods of 6 and 12 hs. The infiltrated specimens were analyzed with respect to porosity, bulk density and fracture surface morphology by scanning electron microscopy (SEM). The specimens were also subjected to mechanical tests of bending resistance. The infiltration of the polymer in the porous substrate with Alglass alumina sample for a period of 12 hs obtained the best results, with reduction of porosity close to 45.24%, density of 2.66 ± 0.03 g/cm³ and increased mechanical resistance close to 68% in relation to the Alcoa alumina sample infiltrated under the same conditions and to the Alglass alumina samples infiltrated by a period of 6h when compared with the alumina without polymer. It can be concluded that the infiltration of PMMA improves the properties of ceramic substrates, forming a promising material for use in dental infrastructure; however the alumina substrates used in this study with and without infiltration of PMMA presented flexural resistance below to the recommended values in ISO 6872 standard. (author)