Effect of the angle of the screw on the stability of the mandibular sagittal split ramus osteotomy: A study in sheep mandibles

We compared the biomechanical stability of 60° and 90° angles for insertion of screws for fixation of sagittal split ramus osteotomies (SSROs) in 10 sheep mandibles in vitro. After 5 mm advancements, the osteotomies were fixed with screws 2 mm in diameter inserted with a torque control screwdriver at either 60° or 90° to the long axis of bone, in a matched pair experimental design. All specimens were then loaded in a physiological manner and the load-displacement of the osteotomies was recorded. Data for resistance to movement were compared by a paired t-test. The mean (SD) resistance to movement for the 60° and 90° screw insertions was 63.4 (27.7) N/mm and 59 (22.3) N/mm respectively. There was no significant difference between the groups. This correlates with clinical findings.