Biomechanical testing of resorbable screws used for mandibular sagittal split osteotomies

Purpose: The object of the study was to determine the suitability of specif ic 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 po lylactic acid-polyglycolic acid copolymer were placed in an inverted L-patt ern in overlapping urethane blocks representative of sagittal split mandibu lar surgery. In an in vitro model at room temperature, the test specimens w ere 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 failu re. Results: In static testing, three 2.5-mm resorbable screws sustained an ave rage 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). Sev eral of these test specimens did not ultimately fail and were further evalu ated by static testing with an average load of 77.4 Kp until fixation failu re 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 c opolymer may be effective in fixation of the postoperative unrestrained sag ittal split mandibular osteotomy.