This study evaluates the effectiveness of topical NAVS naphthalan in the treatment of oral lichen planus (OLP) and recurrent aphthous stomatitis (RAS). Half of participants with OLP and RAS will receive topical NAVS naphthalan in adhesive paste, while the other half will receive 0.05%-betamethasone dipropionate in adhesive paste. Our hypothesis is that NAVS could be efficient in the treatment of OLP and RAS, with effects comparable to that of topical steroids.