implants UK - the journal of oral implantology

18 I implants1_2011 Iresearch_ Toothless jaws _Optimising the manufacturing technology Despite the high and well-documented survival rates of attachment constructions, the question arises as to whether the strategies can be further optimised in order to avoid defects attributable tothetechnique.Thetraditionalwayofmanufacturing attachment constructions is by casting. However, the larger the cast object, the more difficulties arise in terms of porosity and war age, which increase the risk ofmechanicalfailureandimpairtheproperfit(Fig.2).10 Relatively early on, the well-known casting prob- lemsledtotheestablishmentofalternativetechniques. Theapplicationofpre-fabricatedimplantcomponents, which were then joined by means of soldering or laser welding, was one way to improve the fit. However, with large constructions in particular, this procedure hasthedisadvantageofverytime-consumingmanual post-processing. Furthermore, there is the risk that the mechanical ability to cope with pressure may be reducedintheareaofthejoiningpoint. From an economical point of view, it would make sense to use largely bio-compatible material of suf- ficient mechanical strength for manufacture, such as puretitaniumoraCo-Cralloy.However,theprocessing of such alternative materials does not provide a suf- ficiently exact fit with the current casting techniques. In vitro examinations of cast implant superstructures madeofnon-metallicmaterialsshowedgapsof200to 300 μm between the superstructure and the implant arrangement.11 Comparedtothis,caststructuresmade of noble metals featured median gap widths of 40 to 50 μm.12 The use of alternative materials therefore requires an alternative processing technology in order toachievethenecessaryprecision.Intheidealcase,the superstructure is cut from a prefabricated solid mate- rialinordertosafelyexcludeinhomogeneities. With this in mind, the manufacture of superstruc- tures with cutting technological means utilising the computerised numerical control (CNC) process began more than ten years ago. In vitro examinations using this CAM technology demonstrated that the precision achievable in such constructions, with median gap widths between 20 and 30 μm, is better than the ac- curacy of fit achieved with cast frames made of noble metals.12 Modern scanning and software technology allows expansion of this manufacturing principle to virtual construction. Hence, the already well known process of CNC cutting is supplemented with the option of a purely virtual construction. Several manu- facturersofferthistechnology,forexampleCompartis ISUS(DeguDent). _Case presentation Themanufacturingprocessofanattachmentutilis- ing the Compartis ISUS system is documented below. After exposure of the implants, the next appointment was devoted, as usual, to making a casting with im- pression material that has a high final hardness and hence guarantees a secure fixing of the casting posts (forexample,Impregum,3MESPE;Monoprentransfer, KettenbachDental;Fig.3). In the ideal case, the casting appointment would entail the determination of the jaw relations and a casting for the model of the opposing jaw. After that, the work model is manufactured with the help of a re- movablegingivamaskintheareaoftheimplants.When the first check-bite is taken, a first provisional model can be mounted immediately. Based on this working material,atootharrangementispreparedfromplastic. It is useful if the information about the colour and the shapesoftheteethisalreadyavailableduringthiswork step(Fig.4). The tooth arrangement can be tried on at the next appointment and corrected if needed. The exact jaw relations can thus be determined and sufficient in - formation will be collected for the definitive tooth arrangement.Atthisappointment,theprecisionofthe casting should also be checked with a transfer jig. For thisjig,thepostsontheworkmodelcanbeblockedwith plasticandametalreinforcement. Thejigmustthenfitontotheimplantsinthemouth without causing tension or shifting around. For the exact determination of the accuracy of the casting fit, it is advisable to perform the Sheffield Test. A screw is mounted and fastened on the post on one side of the Fig. 6_Compartis ISUS bar attachment made of pure titanuim, the attachment could be inserted without manual post-processing. Fig. 7_Completed implant-retained prothesis for the lower jaw. Fig. 6 Fig. 7