CAD0210

16 I I case report _ 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 to the technique. The traditional way of manufacturing attachmentconstructionsisbycasting.However,the larger the cast object, the more difficulties arise in termsofporosityandwarpage,whichincreasetherisk ofmechanicalfailureandimpairtheproperfit(Fig.2).10 Relatively early on, the well-known casting prob- lems led to the establishment of alternative tech- niques. The application of pre-fabricated implant components, which were then joined by means of soldering or laser welding, was one way to improve the fit. However, with large constructions in par- ticular, this procedure has the disadvantage of very time-consuming manual post-processing. Further- more, there is the risk that the mechanical ability to copewithpressuremaybereducedintheareaofthe joining point. From an economical point of view, it would make sense to use largely bio-compatible material of suf- ficientmechanicalstrengthformanufacture,suchas puretitaniumoraCo-Cralloy.However,theprocess- ing of such alternative materials does not provide a sufficiently exact fit with the current casting tech- niques. In vitro examinations of cast implant super- structures made of non-metallic materials showed gaps of 200 to 300 µm between the superstructure andtheimplantarrangement.11 Comparedtothis,cast structures made of noble metals featured median gap widths of 40 to 50 µm.12 The use of alternative materials therefore requires an alternative process- ing technology in order to achieve the necessary precision. In the ideal case, the superstructure is cut from a prefabricated solid material in order to safely exclude inhomogeneities. Withthisinmind,themanufactureofsuperstruc- tures with cutting technological means utilising the computerisednumericalcontrol(CNC)processbegan more than ten years ago. Invitro examinations using this CAM technology demonstrated that the preci- sion achievable in such constructions, with median gap widths between 20 and 30 µm, is better than the accuracyoffitachievedwithcastframesmadeofno- blemetals.12 Modernscanningandsoftwaretechnol- ogyallowsexpansionofthismanufacturingprinciple to virtual construction. Hence, the already well- known process of CNC cutting is supplemented with the option of a purely virtual construction. Several manufacturers offer this technology, for example Compartis ISUS (DeguDent). _Case presentation The manufacturing process of an attachment utilising the Compartis ISUS system is documented below. After exposure of the implants, the next appointment was devoted, as usual, to making a castingwithimpressionmaterialthathasahighfinal hardness and hence guarantees a secure fixing of the casting posts (for example, Impregum, 3M ESPE; Monopren transfer, Kettenbach Dental; 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 removable gingiva mask in the area of the im- plants. When the first check-bite is taken, a first pro- visional model can be mounted immediately. Based onthisworkingmaterial,atootharrangementispre- pared from plastic. It is useful if the information aboutthecolourandtheshapesoftheteethisalready available during this work 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. At this appointment, the precision of the casting should also be checked with a transfer jig. For this jig, the posts on the work model can be blocked with plastic and a metal reinforcement. Fig. 6_Compartis ISUS bar attachment made of pure titanium; the attachment could be inserted without manual post-processing. Fig. 7_Completed implant-retained prosthesis for the lower jaw. CAD/CAM 2_2010 Fig. 6 Fig. 7