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 degrees and 90 degrees 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 degrees or 90 degrees 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 degrees and 90 degrees 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.