Biomechanical testing of resorbable screws used for mandibular sagittal split osteotomies

Purpose: The object of the study was to determine the suitability of specific resorbable screws for fixation of mandibular sagittal split osteotomies by in vitro biomechanical strength testing. Materials and Methods: Resorbable screws (2.5 mm diameter) composed of a polylactic acid-polyglycolic acid copolymer were placed in an inverted L-pattern in overlapping urethane blocks representative of sagittal split mandibular surgery. In an in vitro model at room temperature, the test specimens were statically loaded until tensile failure occurred. On a different set of test specimens, dynamic testing was done in an in vitro water bath at body temperature through cyclic loads representative of mastication until failure. Results: In static testing, three 2.5-mm resorbable screws sustained an average peak load of 131 Kiloponds (Kp) (standard deviation, 5.2 KP) with 5.5% strain at yield. In dynamic testing, the resorbable screws tolerated a 45.3-Kp load for an average of 340,675 cycles (22,783 standard deviation). Several of these test specimens did not ultimately fail and were further evaluated by static testing with an average load of 77.4 Kp until fixation failure occurred. Conclusions: These laboratory results indicate a relatively high resistance to biomechanical loads representative of mastication and suggest that 2.5-mm resorbable screws of this particular polylactic acid-polyglycolic acid copolymer may be effective in fixation of the postoperative unrestrained sagittal split mandibular osteotomy.