Systemic treatment in severe cases of recurrent aphthous stomatitis

thalidomide - 100mg/day; 6 months, tablets orally pentoxifylline - 400mg, three times/day; 6 months, tablets orally colchicine - 0.5mg/day for 7 days; 1.0mg/day for 7 days; 1.5mg/day as maintenance dose; 6 months, tablets orally dapsone - 25mg/day for 3 days; 50mg/day for 3 days; 75mg/day for 3 days; 100mg/day as maintenance dose; 6 months, tablets orally. Subjects will receive any of the drugs listed above, switching from one drug to another according to their response to treatment and severity of adverse effects. Subjects will be followed fortnightly for a 6-month period during medication use, and monthly for another 6 months of follow-up period. As an open trial designs it will be considered the thalidomide group as a comparator (active control) due to the good results registered in previous trials, nevertheless the study will show some characteristics of a crossover study since if a patient do not get any improvement or exhibit severe adverse effects to the first given drug, that subject will be allocated to another testing drug.