Atrophic mandible fractures are frequently a challenge to stabilize. This study evaluated, through mechanical testing in vitro , the number of locking screws that is sufficient to withstand loading when applied with a locking reconstruction plate in the fixation of atrophic mandible fractures. Polyurethane mandibles with a simulated linear fracture at the midline were used as substratum. Results show that resistance of the fixation is poor when one and two screws are used on each side of the fracture. Three screws on each side of the fracture significantly increases the resistance to displacement. However, no additional strength is added to the construct when more than three screws per side are used.
Due to the lack of bone quantity and often quality, as well as inherent systemic issues secondary to the age and general health of the patient, atrophic mandible fractures can be difficult to treat. The treatment of such fractures differs from that of non-atrophic and/or dentate mandibles. The differences are related to the healing capacity of the patients who sustain the fractures, because they are often elderly people in whom bone regeneration is delayed, there is a reduced bone contact area due to atrophy, and there is a decreased blood supply and increased bone density and sclerosis. Conditions such as osteoporosis or osteomalacia may also be present. Besides the previous factors, this population usually presents concomitant medical issues that are an additional complication to their treatment.
The basic principles of the treatment are the same as for any mandibular fracture, i.e. reduction and immobilization of the fractured segments in order to restore form and function and ensure uneventful healing. These objectives may not be readily attainable in the atrophic mandible cases. Atrophic mandible fractures should be treated by load-bearing osteosynthesis, in which reconstruction plates are responsible for supporting the entire functional load until healing occurs.
More recently the use of locking plates and screws has emerged. This type of system was developed to provide advantages over conventional plates. The system is characterized by the presence of threads on the screws and plates that allow the screw to be locked to the plate, enhancing both primary and secondary stability. Adaptation of the plate is somewhat less critical and porosis of the bone surface under the plate is prevented.
Considering the growing number of elderly individuals in the general population, further studies on the treatment of atrophic mandible fractures should be carried out in order to provide a better understanding and improve the treatment of this growing demand population. Since only a few biomechanical investigations have been reported regarding the fixation of atrophic mandible fractures, the proposal of this study was to evaluate how many screws are necessary to stabilize an atrophic mandible fracture when locking reconstruction plates are used.