Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Aims: To evaluate both cosmetic and functional effects of temporalis muscle atrophy, by means of clinical examination, magnetic resonance imaging (MRI), and electromyographic (EMG) activity in patients who underwent craniotomy in order to treat refractory mesial temporal lobe epilepsy (MTLE). Methods: A total of 18 controls and 18 patients who underwent surgery for MTLE were investigated. The ternporalis muscle volume of the patients was assessed by a 3D reconstruction. The image analysis software (ITK-SNAP) was used for the 3D reconstruction. In addition, the amplitude of the EMG signal during a maximum voluntary clench was recorded from both temporalis muscles by surface electrodes. The presence of temporomandibular disorder (TMD) signs was assessed by clinical examination that was performed only after surgery. Data were analyzed statistically by means of the Mann-Whitney U test, paired t-test, Pearson chi(2) and linear regression. Results: The volume of the ternporalis muscle of the operated side was significantly reduced (P = .004). The EMG results confirmed the presence of muscle atrophy, the amplitude of the EMG signal being significantly decreased on the operated side (P < .05). Also the patients' maximum mouth opening after surgery was significantly reduced compared to that of the controls (P < .0001). Patients presented facial asymmetry, signs of TMD (pain, disc displacement, and joint sounds), and masticatory abnormalities. Conclusion: These preliminary results showed that, despite the good control of seizures, some patients may experience cosmetic and functional abnormalities of temporalis muscle secondary to atrophy and fibrosis. J OROFAC PAIN 2010;24:391-397244391397Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [05-59258-0, 07/01676-7, 07/59340-4]