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 5mm advancements, the osteotomies were fixed with screws 2mm 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.