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international magazine of oral implantology

I research _ implant geometries 08 I implants1_2011 publications address the issue of implant length as a predictor of implant survival6,7,10,13,23–25,30,31,33–35 . These studies have produced conflicting results. Some studies report higher failure rates with short implants7,13,23,30,33,35 , others report high survival rates.6,10,24,25,31,34 Studies that report favourable sur- vival rates tend to be found in recent publications, indicating that the clinical performance of short implants might have improved over the past few years. In addition to standard and short implants, there are the implants of smaller diameters, which are called mini dental implants (MDIs). Those are gener- ally 2.75 mm to 3.30mm in diameter, and they are frequentlyusedincasesoflimitedbonevolume.Sev- eralMDIsexistwithevensmallerdiameters,ranging from 1.8mm to 2.4mm.28, 29 In the beginning, the mainapplicationofMDIswastoserveastheremedy and provisional instrument for insertion of provi- sional restorations during the osseointegration phase of conventional standard (larger diameter) endosseus implants.1, 2, 12 The assumption was that MDIs are unable to provide functional load of im- plantsupportedprostheses.2, 11 Inthecourseoftime, itwasobservedthatthoseimplantsosseointegrated very well clinically.12 It became clear that, in combi- nation with a minimally invasive implant insertion protocolfortheMDIs,theycouldprovideasatisfac- tory prosthodontic rehabilitation effect.12, 29 TheadvantageinuseofMDIsistheminimallyin- vasive,singlestageplacementprocedure2, 11 incom- parison to the procedure for conventional implants (diameter 3.5 and wider). The philosophy of MDI in- sertionisaminimallyinvasivetechniqueofinserting theimplantintothebonethroughasmallopeningof thesofttissue,butnotapreparedbonesite.2,11 There- fore, the bone damage and bone wound during im- plantationisminimised.Bleedingandpostoperative discomfort are reduced12 and healing time is short- ened.Itisrecommendedtoloadsuchimplantsimme immediately.2 The purpose of the present study was to numerically analyse the biomechanical differ- ences of short and narrow (mini) dental implants to the standard ones according to their clinical appli- cations. This study tested some of the available geometriesforthenarrowaswellasshortimplants. The magnitude of micromotion of implants was in- vestigated, in addition to the magnitude and distri- bution of stresses and strains in the alveolar bone around the implants. _Materials and methods A total of 13 three-dimensional finite element (FE) models were developed: two models for short implants, three for the corresponding standard im- plants, two for mini implants, and finally six models for the corresponding standard implants (Table I). The geometries of the implants were constructed from the CAD/CAM data that were generated and provided by a Dental Implant company and subse- quently fed into the FE program MSC. Marc/Mentat 2008. According to several previous studies15 , the tetrahedral element type (4-nodes) was selected for model generation and the bone in its two compo- nents(corticalandcancellousbone)wasmeshedus- ing a coarsening factor of 1.5mm to gradually en- large the tetrahedral element size from the implant contact region (0.2mm) to the external surface (0.5mm). As in the previous studies, the non-linear incremental Full Newton-Raphson solver was used15runningonasmallDellservercluster(Power Edge 1950, 20 cores, 40 GB RAM). _Implant geometries of group 1 (short implants) Two short implants were investigated with a di- ameter of 5.5mm and a length of 5mm and 7mm, respectively. Three commercially available standard Fig. 3_Implant displacements ob- tained for (a) the short implants and the corresponding standard implants after loading of 300 N in 308 from the implant axis, (b) the MDIs and the corresponding standard implants after loading of 150 N in 308 from the implant axis. Fig. 4_Total of equivalent stress ob- tained for the short implants and the corresponding 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 direction of the applied load. Fig. 3b Fig. 3a Fig. 4b Fig. 4a