Lichen planus is a mucocutaneous, chronic inflammatory and very common dermatological disease. The importance of this disease is related to its frequency in the general population, its multiplicity of aspects, and its possible connection with malignancy. In the skin the lesions consist of reddish or white papules that can present a central depression. The buccal lesions are often multiple, bilateral, striated and appear as whitish plaques in the reticular form and exposing the connective tissue, in the erosive or atrophic form and rarely the bullous. Basal epithelial cells are the main target in lichen planus. The mechanism of basal cell damage is related to a cellular immunization process involving Langerhans cells, T lymphocytes and macrophages. Lichen planus is a middle aged disease that affects men and women in almost the same proportion. Patients with Hepatitis C virus and HIV patients are also more likely to develop oral lichen planus due to adverse effects of their drug therapies, as well as the use of Interferon (IFN) alpha, Ribavirin, and Zidovudine (for patients HIV). Children are rarely affected. Frequently, the severity of the disease is parallel to the patient’s degree of stress, and immunosuppression.

Objective: To evaluate and compare the electromyographic (EMG) activity of masseter, temporalis, mentalis and orbicularis oris muscles during function in patients with different facial growth patterns.

Materials and methods: 75 subjects (38 males and 37 females) with no history of previous orthodontic treatment, jaw surgeries, facial trauma and temporomandibular joint disorder were taken and divided into three groups based on their mandibular plane angle and gonial angle as hypodivergent, normodivergent and hyperdivergent. Lateral cephalograms were traced manually to determine facial type. Electromyographic recordings were done and muscle activities were evaluated at clenching position.

Results: For temporalis hypodivergent group had the highest activity but the difference was not statistically significant (p=0.904). For orbicularis oris hypodivergent group had the highest activity and this difference was statistically significant (p=0.007). For mentalis hypodivergent group had the highest muscle activity and this difference was not statistically significant (p=0.052). Only orbicularis oris muscle showed statistically significant difference in all the three groups during maximum clenching.

Conclusion: Different facial growth patterns had a significant effect on the EMG activity of facial muscles during function. Orbicularis oris muscle activity showed significant difference among the three groups. Muscle activity was higher for the hypodivergent group as compared to the other groups. This indicates that the musculature in hypodivergent patients is strong and in hyperdivergent group is weak. This must be kept in mind while diagnosing and making the treatment plans for both the facial types.