CAD/CAM international magazine of digital dentistry

research _ SFI-Bar I I 19CAD/CAM 3_2012 _Discussion It is imperative that the block-out procedure around the bar assembly is correct. Otherwise acrylic will enter an undercut area and cure, thus locking the denture to the bar assembly. As a consequence, therewouldbenooptionbutto cutthedenturefromthebarto freeit.Thiswillnotonlyruinthe denture, but may also damage the bar—a very costly andtime-consumingmistake.TheEclipisdesignedfor use with the two-implant bar and should be picked up with a self-curing resin as explained. The T clip is for a laboratory-processed denture on four or more implants, as the plastic inserts correct any processing errors.Itmustnotbeusedinatwo-implantsituation. Several studies have shown that conventional bar- and clip-retained overdentures transfer signifi- cant stress to the supporting peri-implant tissues (mainlybone).9–11 ThekeytotheSFI-Barsystemisthat the bar is assembled in the patient’s mouth without the use of soldering, laser welding or conventional bonding techniques, thus reducing stress transmis- sion to and bone loss around the implants. Studies have demonstrated that any laboratory-based tech- niquethatrequiresamastercastmadefromadental impression will result in a bar that is not truly pas- sive.8, 9 As a result, several authors have suggested that the only way to achieve a passive fit would be to assemble the framework intra-orally and then bondthebridgeponticinplace.12,13 Thisisthemethod employed with this system. There is no casting, soldering, laser welding or bonding of components when fabricating the de- finitive bar. This, combined with the universal ball- joint nature of the components, ensures a true pas- sive fit when the bar is assembled. The finite element analysis clearly shows the stress-free nature of the bar when being assembled and when the prosthesis experiences loading (Figs. 2a–c). No laboratory time is required to fabricate the bar and there are no costly implant components or gold-alloycharges.Clinically,thereisnoneedforthe bar sections to be soldered in an attempt to achieve passive fit—a step that may need repeating—as with the conventional method. Therearenosolderedorlaser-weldedjoints,sothe bar assembly has no inherent weak points that may fracture or corrode. The bar is assembled by the cli- nician, who also attaches the E clip intra-orally. The reduced number of clinical appointments, laboratory timeandcomponentcostsresultinreducedtreatment costs for the patient. In the case presented, for exam- ple, the bar assembly was completed in only six min- utes.Thisisapproximatelythesametimeittakesfora polyetherimpressionmaterial(likeImpregum)toset! _Conclusion The SFI-Bar is relatively inexpensive compared with conventional gold castings and CAD/CAM op- tions.Theoverallcostoftheprosthesisandtreatment time are significantly reduced compared with con- ventionalandCAD/CAMtechniques.Precision-milled components provide an improved quality of fit. The physicalandmechanicalpropertiesofthecomponent materials can be controlled accurately, which is diffi- cult to achieve with conventional casting methods. TheSFI-Barcanbeconnectedtotwoormoreimplants to create a full-arch bar if needed, while the SFI-Bar system produces a bar assembly that seats passively as demonstrated by finite element analysis. The pas- sive-fit bar assembly can result in greatly reduced stress transmission to the supporting implants. Studies have demonstrated that this is also a viable treatment option for immediate-loading situations in the mandible, provided that the implants achieved insertion torques exceeding 50 Ncm approximately._ The finite element data and images were kindly provided by Dr Ludger Keilig, Endowed Chair of Oral Technologies, UniversityofBonn,Germany. Disclaimer: The SFI-Bar, implant adapters and E clips were provided by Cendres+Métaux. The author did not receive anyfinancialinducementstowritethisarticleorpayment towards laboratory charges, nor was any other kind of paymentgivenorreceived. Dr Tussavir Tambra BDS,DDS,MS Prosthodontics (Michigan) Wolverhampton United Kingdom dr.tambra@hotmail.co.uk CAD/CAM_contact Fig. 14bFig. 14a