In vivo degradation of a new concept of magnesium-based rivet-screws in the minipig mandibular bone.
Self-tapping of magnesium screws in hard bone may be a challenge due to the limited torsional strength of magnesium alloys in comparison with titanium. To avoid screw failure upon implantation, the new concept of a rivet-screw was applied to a WE43 magnesium alloy. Hollow cylinders with threads on the outside were expanded inside drill holes of minipig mandibles. During the expansion with a hexagonal mandrel, the threads engaged the surrounding bone and the inside of the screw transformed into a hexagonal screw drive to allow further screwing in or out of the implant. The in vivo degradation of the magnesium implants and the performance of the used coating were studied in a human standard-sized animal model. Four magnesium alloy rivet-screws were implanted in each mandible of 12 minipigs. Six animals received the plasmaelectrolytically coated magnesium alloy implants; another six received the uncoated magnesium alloy rivet-screws. Two further animals received one titanium rivet-screw each as control. In vivo radiologic examination was performed at one, four, and eight weeks. Euthanasia was performed for one group of seven animals (three animals with coated, three with uncoated magnesium alloy implants and one with titanium implant) at 12weeks and for the remaining seven animals at 24weeks. After euthanasia, micro-computed tomography and histological examination with histomorphometry were performed. Significantly less void formation as well as higher bone volume density (BV/TV) and bone-implant contact area (BIC) were measured around the coated implants compared to the uncoated ones. The surface coating was effective in delaying degradation despite plastic deformation. The results showed potential for further development of magnesium hollow coated screws for bone fixation.
Department of Cranio-Maxillofacial Surgery, Inselspital, Bern University Hospital and University of Bern, CH-3010 Bern, Switzerland; National Dental Centre Singapore, 168938, Singapore.
Benoit
B
Schaller
Department of Cranio-Maxillofacial Surgery, Inselspital, Bern University Hospital and University of Bern, CH-3010 Bern, Switzerland.
Nikola
N
Saulacic
Synthes Biomaterials, Eimattstr. 3, CH-4436 Oberdorf, Switzerland. Electronic address: SBECK2@its.jnj.com.
Stefan
S
Beck
RMS Foundation, Bischmattstr. 12, CH-2544 Bettlach, Switzerland.
Thomas
T
Imwinkelried
National Dental Centre Singapore, 168938, Singapore.
Bee Tin
BT
Goh
Department of Cranio-Maxillofacial Surgery, Inselspital, Bern University Hospital and University of Bern, CH-3010 Bern, Switzerland.
Ken
K
Nakahara
Department of Clinical Research, University of Bern, CH-3010 Bern, Switzerland.
Willy
W
Hofstetter
Department of Cranio-Maxillofacial Surgery, Inselspital, Bern University Hospital and University of Bern, CH-3010 Bern, Switzerland.
Tateyuki
T
Iizuka
D000497:Alloys / Q000737:chemistry; D000818:Animals; D001861:Bone Regeneration; D001863:Bone Screws; D008274:Magnesium / Q000737:chemistry*; D008334:Mandible / Q000000981:diagnostic imaging / Q000473:pathology; D023421:Models, Animal; D013552:Swine; D013556:Swine, Miniature; D014025:Titanium / Q000737:chemistry; D055114:X-Ray Microtomography
D000497:Alloys; D014025:Titanium; D008274:Magnesium
Absorbable implant; Biodegradable magnesium alloy plasmaelectrolytic coating; Bone rivet; Expandable screw; Miniature pigs; Osteosynthesis