The lower jaw is frequently exposed to fracture, by accidents, violence, accidental falls, sports injuries, pathological fracture, etc. We have investigated the behaviour of mandibular bone in a particular clinical case of fracture, in which we experimentally applied two osteosynthesis plates and analyzed the effects of occlusal loading on the fracture line by finite element method. We observed that in this case, maximum deformations occur in the mandibular condyles and the maximum and minimum normal stresses occur in the osteosynthesis plates. Even if bite and mastication determine important efforts on osteosynthesis plates, titanium alloy supports well these loads, and, as an important aspect, the bone parts during healing are not the object of excessive mechanical loads.