The proper design of the screw and plate placement relative to each other in order to prevent the driving the screw out of the bone, maintain the integrity of the screw-plate and create a more robust system in order to improve the plate function are important in the treatment of fractures or abnormalities surgery of mandibular bone using screw and plate. As regards, no study so far has been done about the change in the angle of monocortical screw placement relative to the miniplates in these surgeries; the aim of this study is the investigation of the effect of the angle of monocortical screw placement in the miniplate stability in created fractures of sheep mandibular bone. 30 hemi-mandibles were cut from the mandibular angle and two pieces of bone were again fixed to the same position with a mini plate and in each sample with one of three angle of monocortical screw (45, 60, and 90°) relative to mini plates. Afterwards, mandibles were fixed in the universal testing machine that is used for tensile and shear tests. There were a significant difference between the mean tolerated tensile forces at the angle of 45 and 60 degree and at the angle of 45 and 90 degree. On the other hand, there was not a significant difference between the mean tolerated tensile forces at the angle of 60 and 90 degree. It seems that in cases where the surgeon faces with limited access during surgery or screw placement path interference with important anatomical elements, he can use a 60 degree screw angle
Key words: monocortical screw, stability miniplates, Mandible, tensile force
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