implants - international magazine of oral implantology

I research Fig. 1_Finite element model of an experimental mini implant in an idealised bone segment of an anterior mandibular jaw (left). Calculated strains in the implant. The maximum strain level is found in the area where the corticalis is penetrated (red spots in the middle). The picture on the right shows an overhead shot of the corticalis. In the grey area, the bone is overloaded.5 _Introduction Minidentalimplantswithadiameteroflessthan 3 mm have been used increasingly often in dental implantology.Severalyearsago,theyweretypically placed in combination with conventional implants and served as provisional solutions for the stabili- sationofdenturesduringthehealingphase.5 Today, they are also approved for long-term use. On the one hand, mini dental implants are placed to fix complete or partial dentures and contribute to in- creased stability. One the other hand, they are used as abutments for fixed bridges in specific situa- tions, e.g. in small gaps.12 _Risks of mini implants Although one-piece implants have been used for retention of definitive restorations for several years—thefirstapprovalwasgrantedin1997bythe US Food and Drug Administration (FDA) for today's 3M™ ESPE™ MDI Mini Dental Implants—there are still reservations in many practices regarding their suitability for permanent use. This is due to study results which reveal that implants with a reduced diametermighthaveahigherfailureratethancon- ventionalimplants.9,13 Inaninvestigationanalysing the biomechanics (FEM analysis) of mini implants, it was shown that, in comparison with conven- tional implants, those with a small diameter cause a significantly increased stress on the bone.7 Figure 1 shows the FE model of an experimental implant. In this investigation, the implants were surrounded by a thin bone segment representing bone loss in analogy with the clinical situation. The corticaliswasmodelledwitharelativelyhighthick- ness and the turn of the thread stood in contact with the corticalis. The presumed load was a force transmission of 150 N with an angle of 30° to the implant axis. The load on the implant and the bone under these conditions is represented in Figure 1. While the strains in the implant are 600 MPa and thus below the flow limit of the material, a load on the oral corticalis of up to 200 MPa was measured. Thisistwicethepermissiblelimitstressforthebone Mini implants: a useful complement to conventional implants? Authors_Dr Friedhelm Heinemann, PD Dr Torsten Mundt & Prof. Dr Christoph Bourauel, Germany 14 I implants1_2013 Fig. 1