IM0110

18 I I case report _ CAD/CAM Fig. 6_Compartis ISUS bar attach- ment made of pure titanium; the at- tachment could be inserted without manual after-processing. Fig. 7_Completed implant-retained prosthesis for the lower jaw. Fig. 8_Good fit with a CAD/CAM pro- duced attachment construction made of pure titanium. implants1_2010 _Optimising the manufacturing technology Despite of the high and well documented survival ratesofattachmentconstructions,thequestionarises whetherthestrategiescanbefurtheroptimisedinor- dertoavoiddefectsattributabletothetechnique.The traditional way of manufacturing attachment con- structions is by casting. However, the larger the cast object, the more problems use to arise in terms of porosity and warpage which, on the one hand, in- creasetheriskofmechanicalfailureand,ontheother hand, impair the proper fit (Jemt et al.1999; Fig. 2). Relatively early, the well-known casting problems have led to the establishment of alternative tech- niques. The application of pre-fabricated implant components,whichthenwerematedbymeansofsol- dering or laser welding, was one way to improve the fit; however, in particular with large constructions, this procedure has the disadvantage of very time- consuming manual post-processing. Furthermore, there is the risk that the mechanical ability to cope with pressure may be reduced in the area of the join- ing point. In addition to that, from the economical point of view, it would make sense to use largely biocompati- ble material of sufficient mechanical strength for the manufacture, such as pure titanium or a Co-Cr alloy. However,theprocessingofsuchalternativematerials does not provide a sufficiently exact fit with the cur- rentcastingtechniques.In-vitroexaminationsofcast implantsuprastructuresmadeofnon-metallicmate- rials showed gaps of 200 to 300 µm between the suprastructure and the implant arrangement (DeTor- res et al. 2007). Compared to that, cast structures made of noble metals featured median gaps of 40 to 50 µm (Takahashi and Gunne 2003). The use of alter- native materials therefore requires an alternative processing technology, and be it just to achieve the necessary precision. In the ideal case, the supracon- struction is cut from a prefabricated solid material in order to safely exclude inhomogeneities. With this thought in mind, the manufacture of supraconstruc- tions with cutting technological means utilising the CNCprocessstartedalreadymorethantenyearsago. In-vitro examinations with this CAM technology showed that the precision achievable in such con- structions, with median gap widths between 20 and 30 µm is better than the accuracy of fit achieved with cast frames made of noble metals (Takahashi and Gunne 2003). Modern scanning and software tech- nology allows expanding this manufacturing princi- plealsototheareaofthevirtualconstruction.Hence, thealreadywell-knownprocessofCNCcuttingissup- plemented with the option of a purely virtual con- struction.Meanwhilethereareseveralmanufacturers offering this technology (e.g. Compartis ISUS of DeguDent). _Case presentation The manufacturing process is documented below on the example of an attachment utilising the Com- partisISUSsystem.Afterexposureoftheimplants,the next appointment is devoted, as usual, to making a castingwithimpressionmaterialwhichhasahighfi- nal hardness and hence guarantees a secure fixing of the casting posts (e.g. Impregum, 3M ESPE, or Mono- pren transfer, Kettenbach Dental; Fig. 3). In the ideal case, the casting appointment will al- ready include the determination of the jaw relations and a casting for the model for the opposite jaw. Af- ter that, the work model is manufactured with the help of a removable gingiva mask in the area of the implants.Whenthefirstcheckbiteistaken,afirstpro- visional model can be mounted straight away. Based on this working material a tooth arrangement is pre- paredfromplastic.Itisusefuliftheinformationabout thecolourandtheshapesoftheteethisalreadyavail- able during this work step (Fig. 4). The tooth arrangement can be tried on at the next appointment, and corrected if needed. So, the exact jawrelationscanbedetermined,andsufficientinfor- mation will be collected for the definitive tooth arrangement. At this appointment, also the precision ofthecastingshouldbecheckedwithatransferjig.For this key, the posts on the work model can be blocked with plastic and a metal reinforcement. The key must thenfitontotheimplantsinthemouthwithoutcaus- ing tension or shifting around. For the exact determi- Fig. 7 Fig. 8Fig. 6