implants - international magazine of oral implantology

_Micro-gap and the platform-switch- ing concept Many implant systems have an abutments used with conventional implant types that are flush with theimplantshoulderinthecontactzone.Thisresults intheformationofmicrocracksbetweentheimplant and the abutment. Numerous studies have shown thatbacterialcontaminationofthegapbetweenthe implantandtheabutmentadverselyaffectsthesta- bilityoftheperi-implanttissue.Ifabove-averageax- ial forces are exerted on the implant, a pumping ef- fect may ensue (depending on the positive inter- nal/externalconnectionattheinterface),whichmay then result in a flow of bacteria from the gap, caus- ingtheformationofinflammatoryconnectivetissue in the region of the implant neck.39–41 Berglundh and Lindhe evaluated the micro-gap oftheBrånemarktwo-stageimplantandfoundthat inflamed connective tissue existed 0.5 mm above and below the abutment–implant connection, whichresultedin0.5mmbonelosswithintwoweeks after the abutment had been connected to the im- plant.42 Ericsson et al. coined the term distance- sleeve-associated infiltrated connective tissue to describe this phenomenon. They interpreted this to be a biological protective mechanism against the bacteria residing in the microcrack, explaining the plaque-independent bone loss of approximately 1mm during the first year. This bone loss may result in a reduction of the marginal bone level in both the vertical and the horizontal dimensions.43 If the microcrack is located close to the bone, the creation of the biological width will occur at the ex- pense of the bone. The platform-switching effect was first observed in the mid-1980s. At the time, larger-diameter implants were often restored with narrower abutments (Ankylos, DENTSPLY Friadent; AstraZeneca; Bicon), as congruent abutments were oftenstillunavailable.Asitlaterturnedout,thiswas aremarkablecoincidence.44 Theplatform-switching conceptrequiresthatthismicro-gapbeplacedaway fromtheimplantshoulderandclosertowardtheaxis in order to increase the distance of this micro-gap from the bone as a protective measure. _Biological width The clinical term biological width denotes the di- mensions of periodontal and peri-implant soft-tis- sue structures such as the gingival sulcus, the junc- tional epithelium, and the supra-crestal connective tissues.45 According to measurements conducted by Gargiulo et al., the average biological width (from thebaseofthesulcustothealveolarbonemargin)is 2.04mm,ofwhich0.97mmisepithelialattachment and 1.07 mm is connective tissue attachment.46 These dimensions, however, are in no way static but subject to interindividual variation (from tooth to tooth and from patient to patient) and will also vary according to gingival type and implant concepts. Numerousstudieshaveshownthatboneresorp- tionaroundtheimplantneckdoesnotstartuntilthe implant is uncovered and exposed to the oral cavity. This invariably leads to bacterial contamination of the gap between the implant and the superstruc- ture.47–50 Boneremodellingwillprogressuntilthebi- ological width has been created and stabilised. This widthprogressesnotonlyapicallyalongthevertical axis (Fig. 1), but also 1 to 1.5 mm horizontally, ac- cording to studies conducted by Tarnow etal. This is the reason for maintaining a minimum distance of 3mmbetweentwoimplantsandplatformswitching in the aesthetic reconstruction zone in order to obtain intact papillae and stable inter-implant bone.51–53 _Summary Maintenance of crestal bone around dental im- plants is one of the critical factors that affect its longevity and aesthetic soft-tissue architecture. Preservationofsuchboneisamultifactorialprocess; as summarised in this article some other factors re- lated to crestal bone loss have been investigated. These includes bone volume, bone quality, soft-tis- suebiotype,conditionoftheadjacentteeth,implant design, implant dimensions, abutment design, aug- mentationprocedures,implantinsertiondepth,time of loading, time of restoration, frequency of pros- theticsecondary-componentreplacement,suturing techniques and patient compliance. Proper tissue maintenance and care, regular hy- gienic evaluations and patient education on proper methods for home care are vital. Continued evalua- tion via probing, radiographic assessment and oral examination will allow the clinician to ensure long- term maintenance and overall treatment success._ Editorial note: A list of references is available from the publisher. I clinical technique _ crestal bone management 24 I implants2_2011 Dr Mohammed A.Alshehri Consultant Restorative and Implant Dentistry at the Riyadh Military Hospital,Department of Dentistry P.O.Box 225763 Riyadh 11324,SaudiArabia dr_mzs@hotmail.com _contact implants