The purpose of the present study was to test the applicability of cone beam computed tomography (CBCT) to evaluate the integrity of the cortical sinus close to periapical lesions. Two observers analyzed samples of 64 alveoli of first molar roots in macerated swine maxillas prepared with perchloric acid to simulate periapical lesions. The specimens were evaluated using CBCT (55-mm high and 100-mm diameter cylinder at 0.2-mm voxel resolution) for the presence of oroantral communication (OAC) caused by the simulated lesions. Sensitivity, specificity, and accuracy were calculated. Fair values were obtained for accuracy (66%-78%) and good values for specificity (70%-98%), whereas the values for sensibility showed relevant variation (41%-78%). For this reason, the interobserver agreement score was weak. CBCT proved capable of evaluating the integrity of the cortical sinus (absence of oroantral communication) when it lies close to an apical periodontitis lesion. However, the low interobserver agreement reflects the difficulty in performing diagnoses when OAC is adjacent to a periapical lesion, using the acquisition protocol adopted in this research. This could be attributed to the high level of image noise.