Objectives: The purpose of this study is to analyse and compare stess distrubiton on bone screws and plate systems in locking and non-locking screw–plates design with two different size of lateral mandibular defects.

Methods: Solid mathematical model of the mandible was created by three dimensional finite elements analysis and two different lenght lateral resection was performed on model. Models were reconstructed with two different reconstruction plate system including three 2.4 mm titanium screws. Then resected bone lenght (2.5–5 cm) varied. Realistic mastication force was applied by simulating natural muscles vectors. The effects of plate–screw types to the stress formation on bone and hard-ware system were evaluated and compared.

Results: The stress values of the cortical bone, plate and screw system of the conventional plate model was higher than the locking system model. The highest stress values were measured in the proximal segment especially in conjuction with convansional screw system. Furthermore, in use with locking system, the distribution of the stress on bone surface more homogeniously in both defect size. On the other hand in locking system, plates can subjected to much excessive force related with increasing defect size. Besides this, in large defect size a fatigue fracture of the plate itself can be occured by using locking system. On the bone surface, the amount of stress was less than conventional system and stress spreads wider area.

Conclusion: It is evident that in the reconstruction model, the use of locking system offer an additional advantage over the conventional system particularly in small (25 mm) defects.

Key words: locking plate; segmental resection; reconstruction; FEA; mechanical stress