The study used samples of material and an upper complete denture, made by Eclipse Resin System (DENTSPLY International Inc. - DeguDent GmbH, Hanau Germany). By 3D scanning (Roland 3D laser scanner, model LPX-1200) was obtained the geometric model of the complete denture. This was imported into o finite element software - ABAQUS/CAE V6.6 and was determined the state of stress and the stress intensity factors for three located defects. For Eclipse Base Plate there were obtained following mechanical properties: the tensile strength - σU=59.49 MPa, Young's modulus - E=2908.45 MPa and fracture toughness KC=24.93 MPa √mm. Defects located on palatal mid-line of upper complete denture, especially those at the junction between different support areas, generate tensile stress and deformation which can determine possible mid-line fractures Schlagwörter: complete dentures, fracture mechanics