Mechanical And Finite Element Analysis Of Two Kinds Anchoring Nails On The Mandibular Condyle

PURPOSE: Comparing and analyzing the pull out force and form of the traditional anchoring nail and improved anchoring nail,which were planted in the inferior border of mandibular condyle during the open surgery of TMJ Anchorage.And analyzing the stability of two kinds medical anchoring nails implanted into the mandibular condyle through finite element analysis.METHODS: 10 new resected condyles were obtained from patients.Traditional and improved anchoring nails with 3-0 anchoring lines,improved anchoring nail with 2-0 anchor line were implanted respectively in the cortical bone of the inferior border of mandibular condyle.Each group was tested by tensile tester to observe the cortical bone damage,anchor nail breakage or loosening and line fracture,etc.And throughing establishing the model of finite element,comparing the stability of two kinds medical anchoring nails implanted into the mandibular condyle.RESULTS: The cases of bone cortex damage,anchoring nail fracture and loosening were not occurred,except the line fracture.Maximum tensile force of traditional anchoring nails with 3-0 anchoring line is(25.89±2.64)N,improved anchoring nail with 3-0 anchoring line is(25.89±2.64)N,improved anchoring nail with 2-0 anchoring line is(>50)N.There was significant differentiation between traditional and improved anchoring nail with 3-0 anchoring line(p<0.05);there was also significant differentiation between traditional anchoring nail with 3-0 anchoring line and improved anchoring nail with 2-0 anchoring line.In the finite element model,the minimum longitudinal pulling force of the traditional anchoring nail is 481.5N(the axial pulling force of the anchoring nail is limited and the longitudinal pulling force is usually relatively large),the minimum lateral pulling force is 261.6N,the minimum spin-out force is 48.2N(assuming the minimum friction coefficient);the minimum longitudinal pullout force of the improved anchor nail is 795.9N,the minimum lateral pulling force is 516 N,the minimum spin-out force is 200 N.CONCLUSION: Traditional and improved anchoring nails can be successfully implanted in the mandibular condyle without nail fracture,loosing and cortical bone damage;improved anchoring nail is more fitful with the condylar anatomical shape,safer and more comfortable.The 2-0 anchoring line can bear more tension and has more advantages than traditional anchoring nail.The finite element analysis showed that the improved anchoring nail is more stable than the traditional anchoring nail.