Various parameters related to the mobility of the upper lip in a sample of 200 patients, have been considered in order to establish the correlation these have with the extent of lip mobility and the relative visibility of their teeth. From this study it was clear that a large number of patients, with a low index of tooth visibility, could benefit, from the viewpoint of their periodontal health, from the application of prosthetic margins above the gums. This would not damage the aesthetic aspect because the margins in question would only be visible with the lips contracted or, in certain patients, never.