Background and Aim: Oral lichen planus of chronic mucosal inflammatory disease with etiology is unknown. There is evidence that thyroid disease, especially hypothyroidism, is associated with oral lichen planus based on immunologic pathogenesis. The aim of this study was to evaluate the prevalence of oral lichen planus and related factors in thyroid patients referred to Endocrinology and Metabolism Research Institute of Iran University in 2017_2018

Materials and Methods: In this cross-sectional study, 1200 individuals with a definitive diagnosis of thyroid disease at Endocrinology and Metabolism Center of Iran University were surveyed and the existing information form was completed for them.   Patients were examined in the light of a flashlight and with the help   of this dentist. In case of observation, oral licorice was recorded in   the form of information. The data were analyzed by SPSS19 and KAIO.

Results: A study was conducted on 1,200 thyroid patients, of which 995 (83%) had hypothyroidism and 205 (17%) had hyperthyroidism, of which 1016 female patients (84.7%) had hyperthyroidism. And 184 male patients (15.3%).

Of these, 63 (5.3%) patients had oral lichen planus, with a frequency of reticular type of 47.6%, a type of papule 22.2%, a type of plaque type 17.5% and an atrophic, erosive and atrophic type % They were. . Given the prevalence of oral lichen planus, its true level in society is estimated at 95% of at least 4% to 6.6%. In patients with thyroid problems, the frequency of oral lichen planus with female sex (P <0.05), age 57 (P <0.001), cigarette smoking (P <0.02), skin lichen planus (01 (P <0.05), levothyroxine consumption (P <0.05) and no drug use for other systemic diseases (P <0.02).

 Conclusion: The incidence of lichen planus in patients with thyroid disease in this study was slightly higher than the usual oral lichen planus in the usual population.