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In biomedical engineering field, Temporomandibular joint (TMJ) is considered as a bi-component joint composed by fossa and condyle. It is considered the most active human joint and it performs daily activities such as speaking and chewing. Due to cyclic loading, TMJ disorders impair TMJ function so that it is necessary to replace the natural joint with an alloplastic prosthesis TMJ orthopedic prosthesis are made of metal alloys and ultra high molecular weight polymers. According to the literature, TMJ replacement surgery is commonly performed worldwide achieving good outcomes. However clinical outcomes point out that TMJ prosthesis present reduced joint kinematics with a limited translational mobility compared to natural joint. In case of unilateral TMJ replacement, this result generates a unilateral hipomobility and a contralateral overload. According to previous studies, this is caused by lateral pterygoid muscle detachment during condylectomy of replacement surgery. To investigate this phenomenon, this study use computational simulation with Ansys software. Finite element analysis is performed with the aim of evaluating effect of unilateral and bilateral pterygoid muscle detachment on mechanical behaviour of a natural human mandible subjected to molar and incisal bite.