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international magazine of oral implantology

research _ implant geometries I in their retrospective analysis over 5 years of 2,514 MDIswhichequallysupportedfixedandremovable prostheses found the overall implant survival rate of 94.2%. Initial stability is important for the suc- cessful osseointegration and high implant success rate. It is stipulated with bone quality, implant de- sign,andsurgicaltechniquethatisused.5 Someau- thors3, 4 recommend bone drilling to the depth of only one-third of the length of the MDI. The obvi- ous reason is the dense bone structure of the mandible of the treated patient, but such dense bone structure contributed to the good initial sta- bility of the implanted MDIs. The study of Balkin etal.2 ,inwhichtheyusedahistologicalanalysis,re- vealed that the quality of the osseointegration of MDIs could be compared with the quality of larger diameter implant osseointegration. Ertugrul and Pipko5 in their in vitro study revealed that implants of larger diameter are more stable under lateral forces than MDIs. Implant displacements obtained in the present study are in agreement with these observations. MDIs showed a displacement of 223mm, whereas thewiderdiameterimplantsofthesamelengthhad a displacement range of 55–120mm. A similar ob- servation was for the strain, MDIs had strains of 19,000–24,000 µstrain, whereas wider diameter implants had strains of 3,000–11,000 µstrain. Moreover,thestresswithintheimplantswashigher and widely distributed at the cervical one-third of theMDIsthanforwideimplants.Intotal,thiscould be one of the reasons to explain the failure case withsmalldiameterimplants26 suchasatypicalim- plantlocation,extremedivergenceofimplantaxes, infection,implantrejection,andpoorprosthesisfit. Usually, dental implants are made of titanium Grade 4 or 5. The ultimate strength for these alloys is given to be around 550 MPa (Grade 4) and 900 MPa (Grade 5), fatigue limits of 425 MPa (Grade 4) and 510 MPa are listed. Consequently, the fatigue limitisexceededincertaincases,indicatingtherisk of permanent loading fracture in the case of im- plants with a reduced diameter. _Conclusions Shortandminiimplantshavesignificantclinical advantages. However, from a biomechanical point ofviewitseemsthattheboneloadingaroundshort and mini implants is increased compared to stan- dard implants. Additionally, the presented results showthatthereisanincreasedriskofoverloadand fracture for mini implants, especially when tita- niumGrade4isused.Consequently,consideringan increased number of implants is recommended whenshortorminiimplantsshallbeinserted.Ade- tailedbiomechanicalanalysisofvariousclinicalsit- uations will be performed to determine the neces- sarynumberofimplantsintheseclinicalsituations. _Acknowledgements The authors wish to thank Dentaurum Implants Company for the kind cooperation in providing im- plant geometries for the FE models._ First published in: Biomed Tech 2010; 55:341–350, 2010 by Walter de Gruyter • Berlin • New York. DOI 10.1515/BMT.2010.049 Editorialnote:Alistofreferencesisavailablefromthepub- lisher. Fig. 8_Equivalent of total strain obtained for the MDIs and the corresponding standard implants. (a) Maximum values obtained, (b) strain distribution. I 13implants1_2011 Prof Dr rer nat Christoph Bourauel Endowed Chair of OralTechnology, Rheinische Friedrich-Wilhelms University, Welschnonnenstr.17, 53111 Bonn,Germany Phone:+49 228 287-22332/22388 bourauel@uni-bonn.de 1 Endowed Chair of OralTechnology,Rheinische Friedrich-Wilhelms University,Bonn,Germany 2 Department of Prosthodontics,Gerodontology and Biomaterials,University of Greifswald,Greifswald, Germany _contact implants Fig. 8b Fig. 8a