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implants international magazine of oral implantology

I case report 26 I implants3_2014 _Historical development of double crown systems From literature it is known that Starr was probably the first who reported, in 1886, about a removable bridge made of double crowns. In English literature Peeso (1924) reported about possible applications of thedoublecrownsystems.InGermanyitwasHäuplin 1929andBöttgerin1961.Thebreakthroughofdouble crown systems took place in Germany in 1969 with Körber(1988)whoadvocatedtheuseofconicalcrowns withadefinedangleofconvergence.Overthedecades the conical crown has become known as "German crown"whichreferstothefrequentuseintheGerman- speaking area until today. According to Körber (1988) double crown systems should include, among other things, exactly fitting pillar integration, secondary splinting with an axial directed periodontal load and firmsupportduringfunctionwhichiseasilyremovable for hygienic reasons. Furthermore, the production shouldbeasefficientaspossibleandahigheconomic effect should arise by a very long survival rate, which canbeexpected. Körber(1988)distinguishestelescopesaccordingto theirform: Cylindricaltelescope:Ithardlytoleratestechnicalinac- curaciesandistherefore,accordingtoKörber,classified asproblematicinmanufacturing. Cone-shapedtelescope:Withregardtothefitthereisa high tolerance, it allows production with a low error rate. Resilience telescope: Primary and secondary parts shouldhavesomebacklashintheocclusalregioninor- dertohavesomespaceontopofeachotherunderload. The telescope should only undertake the functions of friction and indirect connection of the retaining teeth (bracing). _Definition of the cone angle for double crown systems Thethreesystems—thetelescopecrown,theconical crown and the resilience telescope—are double crown systems,whichdifferbythetypeoffitandadhesion.The determining factor for the strength of adhesion is ac- cordingtoHeners(1990),theconvergenceangle. In the early days of implant dentistry one was still sceptically about the use of double crown systems on implants.Atthistime,asoneofthefirstcolleaguesthe dentistDrNikolaLauxfromHamburg,Germany,intro- duced the use of telescopic crowns on implants (IMC cylinderimplants)in1984(Figs.2a&b).In1996,twoof the authors (Vollmer, R. and Vollmer, M.) provided a mandibularremovableprosthesiswithsiximplantsand telescope crowns with secondary parts made of Teflon already(Figs.3a&b). _The material PEEK—A historical review Foralongtime,plasticswerefrequentlyusedinthe dental field. Light weight, an easy processing ability comparedtometalsandceramics,aresomeoftheben- efits. The most known plastics are Polyoxymethylene (POM)andPolymethylmethacrylate(PMMA). PEEK (Polyetheretherketone) is a newer polymer which is also used for medical products since the mid- 90s (Fig. 5). The material was developed in 1978 and mainlyusedformechanicalengineeringandintheau- tomobileindustryinitially.Meanwhile,PEEKisusedfor the production of biomaterials in medicine, e.g. for ar- tificial vertebral bodies, anchoring screws, artificial Telescopic crown:α = 0 ° (clearance only) Conical crown:0 ° < α < 8 ° Resilience telescope:α may only be so large that just an adherence occurs Largest recommended convergence angle:α < 10 ° (with double crown systems according to Muhs,2006) Convergence angle α value at various double crowns: 1.Straightforward extensibility after losing a primary crown. 2.Possibility of extra-oral repairing. 3.Better and easier periodontal hygiene compared to fixed prostheses. 4.Parallelisation of abutment teeth in the case of divergences. Advantages of the double crown technique 1.Complicated,precise and technical manufacturing, high demands on the technician. 2.High costs for the work of the technician and for the material (e.g.use of precious metal,electroplating). 3.In order to achieve aesthetic results,an intensive substance reduction of the abutment teeth must take place.If this is not possible,the result in the anterior areas of the jaws is aesthetically often unsatisfactory. 4.The use of ceramic veneers fusing to the secondary parts in the front area is risky (chipping). 5.Loss of adhesion and pull-off force after a certain time. 6.Missing or difficult possibilities of activation (post elec- troplating,fabrication of additional attachments). 7.When using an inexpensive base metal (non-precious metal) / Eco-gold combination,corrosion can occur leading to excessive friction. Disadvantages of the double crown technique

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