SR-PLLA and SR-PGA miniscrews: biodegradation and tissue reactions in the calvarium and dura mater

The biocompatibility and degradation of self-reinforced poly-L-lactide (SR- PLLA) and polyglycolide (SR-PGA) miniscrews, vs titanium miniscrews? was st udied in frontal bone osteotomies in 20 lambs, where they were used for pla te fixation, At follow-up at 4, 6, 12, 26, 52 and 104 weeks, no clinical fo reign body reaction, infection or other complications had occurred. Histolo gically, PGA material was hydrolyzed and fragmented at 4-6 weeks and was re sorbed by 12 weeks, whereas the SR-PLLA miniscrews retained their integrity and holding power for 26 weeks and were mostly resorbed at 2 years. Accord ing to histological and histomorphometric analyses and plain film radiograp hy, the degradation of PGA miniscrews was accompanied by a typical non-spec ific foreign-body reaction and initial transient osteolysis with decreased osteoid formation around the screw channel, but compensatory intense osteoi d formation and bone remodelling followed after resorption of the polymer. The foreign body reactions to PLLA and titanium were considerably milder. A ll miniscrews were commendably strong and could be satisfactorily tightened against the plate. SR-PLLA miniscrews offer fixation stability for half a year, whereas rapidly degrading SR-PGA miniscrews may be used when short-te rm fixation is needed.