international magazine of oral implantology

research _ implant geometries I I 09implants1_2011 Fig. 5_Total of equivalent stress obtained for the MDIs and the corre- sponding standard implants. (a) Maximum values obtained at the cervical region of the alveolar bone, (b) occlusal view of the stress distri- bution. The arrow indicates the direc- tion of the applied load. Table 1_Description of the numerical models used in the study and their loading conditions. implants served for comparison: 5.5x9mm, 5.5x11mm, and 5.5x13mm. According to their clinical applications, full osseointegrated condition was considered for the numerical analysis of the above-mentioned models. Young’s modulus of the different components was chosen to match the bonequalityintheanatomicalregions(mandibulary and maxillary posterior bone) where the short im- plants are typically inserted: 110 GPa for the im- plants, 20 GPa for cortical bone, and 300 MPa for cancellous bone. Typically, short implants are in- serted in the posterior jaw region, thus the cortical layer in the idealised bone model had a thickness of 0.5mm. _Implant geometries of group 2 (mini implants) Two mini implants were studied with a diameter of 2.5mm and a length of 15mm and 17mm, re- spectively. Six commercially available standard im- plants were used as a reference: 3.3x15mm, 3.7x15mm, 4.2x15mm, 3.3x17mm, 3.7x17mm, and 4.2x17mm. According to their clinical applica- tions, immediate loading condition was considered for the numerical analysis of the mini implant mod- els. This has been done by considering a contact sit- uationattheboneimplantinterface.ACoulombfric- tionmodelwithacoefficientoffrictionof0.5wasse- lected for the contact analysis.15 Young’s modulus of the different structures was chosentobe110GPafortheimplants,20GPaforcor- tical bone, and 1,000 MPa for the cancellous bone. Typically,miniimplantsareinsertedintotheanterior mandibularjawregion,thusthecorticallayershada thickness of 1.2mm. Figure 2 displays the idealised bone segments with the inserted implants. The mini implants were inserted into the bone segments (left) such that the screw threads did touch the cortical bone. Short im- plants were combined with an idealised bone seg- ment that ensured sufficient distance to the basal cortical layer to simulate adequate distance to the nervecanal.Forthewhole13models,implantswere subjected to a load at an angle of 308 from the im- plantaxis.Loadingdirectionwasadjustedanalogous to the ISO standard 1480118. The magnitude of the applied force was 300 N for comparing group 1 and 150 N for comparing group 220. The end faces were constrained in all three degrees of freedom (Fig. 2). Model Loading condition No.of elements No.of nodes Comparing group 1 Shorty 5.5 x 5mm Delayed loading 116,167 22,315 Shorty 5.5 x 7mm Delayed loading 127,367 24,176 tioLogic 5.5 x 9mm Delayed loading 146,890 27,990 tioLogic 5.5 x 11mm Delayed loading 152,218 28,764 tioLogic 5.5 x 13mm Delayed loading 162,185 30,377 Comparing group 2 Mini 2.5 x 15mm Immediate loading 151,851 34,870 Mini 2.5 x 17mm Immediate loading 179,773 41,481 tioLogic 3.3 x 15mm Immediate loading 127,569 27,685 tioLogic 3.3 x 17mm Immediate loading 141,938 30,925 tioLogic 3.7 x 15mm Immediate loading 136,560 29,650 tioLogic 3.7 x 17mm Immediate loading 148,259 32,245 tioLogic 4.2 x 15mm Immediate loading 145,351 31,427 tioLogic 4.2 x 17mm Immediate loading 167,624 20,393 Table I Fig. 5a Fig. 5b