The present study determines the stress field in the region of the labial flange of the complete upper denture (CUD). Using commercial edentulous molds and standardized procedures eight identical CUDs were fabricated with an initial fraenal notch of 5 mm. Three addition notch conditions were produced by deepening the notch two times giving a total depth of the notch of 7 and 9 mm respectively. Finally an incisal diastema of 7 mm was created in every CUD. Three elements rosette strain gauge was cemented onto the midline of each denture specimen near the fraenal notch, for calculating the two principal stresses and the maximum shear stress. It is less possible that a failure crack in a CUD will be initiated from the region of the fraenal notch, due to the compressive nature of the principal stresses (they are varied significantly among the four notch conditions with P=0.035 for σ(1) and P=0.007 for σ(2)) and the low value of the maximum shear stress. The creation of an incisal diastema significantly decreased the values of the principal stresses σ(1) (P=0.012) and σ(2) (P=0.025). Further investigation is needed to detect the region of the CUD where a failure crack may be initiated.