Please activate JavaScript!
Please install Adobe Flash Player, click here for download

international magazine of oral implantology

I research _ implant geometries 10 I implants1_2011 _Results Displacements were determined from post- processor plots at the point of force application at the abutment (compare Fig. 2), maximum bone stresses were taken from the second bone element layer surrounding the implant (i.e., at a 0.2mm dis- tance from the implant surface), to omit con- tact artefacts. Correspondingly, maximum stresses intheimplantsweredeterminedinthesecondinner implant element layer to omit artefacts due to the force application, and cancellous bone strains fol- lowed the same strategy as applied in cortical bone stress determination. The highest displacement at the abutment was observed with the shortest implant (290mm, im- plant: 5.5x5mm). By increasing the length of the short implants, the displacement noticeably de- creased (Fig. 3a). Regarding the MDIs, the displace- ment was higher with the small diameter (223mm) than with the wide diameter implants (65–120mm, Fig. 3b). Determined cortical bone stresses of the shortimplantFEmodelsaredisplayedinFigure4.The stress was higher with short implants than with the standardimplants.Moreover,stressdistributionwas wider and covered more area of the cortical bone with the standard implants than with the short im- plants (Figs. 4a and b). Figure 5a and b display the cortical bone stresses determined with the mini im- plantFEmodels.ThestresswashigherwiththeMDIs (206 MPa, Ø2.5mm) than with the wider diameter implants (57–109 MPa, Ø3.3–4.2mm). The magni- tudeofthestressdecreasedbyincreasingthediam- eter of the implant. Additionally, the distribution of thestresswaswiderwiththeMDIsthanthestandard widediameterimplants(Figs.5aandb).Concerning the stress in the short implants, a decrease of the maximum stress was observed by increasing the length of the implants (700 MPa for 5.5x5mm and 213MPafor5.5x13mm,Fig.6a).However,themax- imumstressvaluesobtainedfortheMDIsandstan- dardimplantsshowedanon-uniformbehaviour(Fig. 6b) due to interplay of multiple factors, such as im- plant diameter, implant length, and screw configu- ration. Nevertheless, the stress distribution covers a wider region in the case of the MDIs than for the standard implants (Fig. 6c). Higheststrainvalues(22,000and16,000µstrain) weredeterminedwiththeshortimplants(5.5x5mm and 5.5x7mm) and decreased by increasing the lengthoftheimplants(8,000µstrain,5.5x13mm).A more homogeneous strain distribution was ob- servedbyincreasingthelengthoftheimplants(Figs. 7a and b). The strain was higher with the MDIs than with the wide diameter implants (3.3–4.2mm) and the strain distribution was more homogeneous by increasing the diameter of the implants (Figs. 8a–b). _Discussion Inadditiontoconventionaldentalimplants,there aresocalledshortandminiimplantsforcertainclin- ical applications. Even for these implants, there are numerous different commercial geometries avail- ableonthemarket.Basedonthis,thepurposeofthis study was to numerically analyse selected dimen- sions of short and mini implants and compare them totheconventionalstandardimplants,todetermine whether limit dimensions for the length and the di- ameter of a dental implant can be postulated. The analysis was based on the FE method and included stressandstraindistributionsinthebonearoundthe implants, implant stresses, and implant micromo- tions. One of the limitations of the present study was thattheanatomicalsituationcouldofcoursenotbe reproducedperfectly.Anidealisedbonegeometryas an implant bed was used and differentiation be- tween the anterior and posterior jaw segments was accomplished by consideration of only the cortical layer thickness and the cancellous bone quality, i.e., the respective Young’s modulus. Together with fur- ther typical limitations of an FE study, a predictabil- ityof20%canbeassumedforthepresentedresults. Short implants offer several surgical advantages Fig. 6_Von Mises stress values ob- tained for (a) the short implants and the corresponding standard im- plants, (b) the MDIs and the corre- sponding standard implants, (c) stress distribution of the MDIs and standard implants. Fig. 6b Fig. 6a Fig. 6c