Please activate JavaScript!
Please install Adobe Flash Player, click here for download
ePaper created 2018-03-23, 14:16:40 | version 1.38.0
18 Dental Tribune Middle East & Africa Edition | May-June 2015implant tribune > Page 20 The passive abutment ByDr.PetrosYuvanoglu,Greece andDr.EroPandelias,Greece O ne of the main problems faced by both prostho- dontists and dental tech- nicians, with regards to implant supported dental prostheses is the problem of producing a re- peatable passive fit which would eliminate the need for complex and intense laboratory proce- dures, usually undertaken to improve the fit of castings e.g. sectioning and soldering. The Passive Abutment (Fig. 1) is unique to Southern Im- plants and has been in clinical use since 1998. It allows one to achieve a predictable passive fit of cast structures in a practical way. The unsatisfactory fit of prostho- dontic work on implants is due not only to the distortion caused by the physical process of invest- ing, casting and sandblasting, but also from the distorting forc- es which develop when the cast- ing is exposed to repeated high temperature cycles while bak- ing porcelain. All these parame- ters cause the collection and en- trapment of energy resulting in tensions, which are then trans- ferred to the prosthetic screws. Consequently we have fractures of screws, destruction of the prosthesis (porcelain fracturing) and perimplantitis. Finally there is breakdown of relationship be- tween the patient and the dental practitioner and tension among members of the implantology team as well (technician/den- tist/prosthodontist/surgeon). After years of research by South- ern Implants, the first prosthetic abutment with a passive fit was presented to the dental implant market in 1994. The philosophy of the passive abutment is innovative in the field of dental implantology and has reduced the stress experi- enced by the technician and the dentist, especially when it comes to the fit of the prosthesis. By reviewing data from x-rays of patients who have dental im- plants with fixed prostheses, one can see marked differences be- tween those with passive abut- ments and those without. Passive fit is achieved by luting a premachined titanium interface component onto the finished prosthesis, using the laboratory master model as the blueprint for fit. The luting takes place in the dental lab by the dental tech- nician. No additional clinical steps are required. The discrepancy between the passiveringandimplantreaches as low as 2 microns, independ- ent of the length of the span of the bridge. The titanium interfa- cial component is kept separate from the manufacturing of the casting and is therefore not sub- jected to degradation by heat- cycles or devesting and finish- ing procedures as a cast-to gold cylinder would. The integrity of the machined part is therefore maintained in the original con- dition. The passive abutment kit in- cludes a titanium ring, which will not be subject to external physical forces and is cemented to the porcelain superstructure after the aforementioned is cast and polished. Description The Passive Abutment consists of four components (Fig. 2) 1. Plastic cylinder - this com- ponent is incorporated into the wax-up of the structure and thus becomes part of the casting. 2. Titanium interfacial compo- nent (6 mm) - this pre-machined component forms the final inter- face between the casting and the implant. 3. Luting screw - this small screw is used to clamp the in- terfacial component onto the laboratory analogue during the process of luting the casting onto the interfacial component. 4. Prosthetic screw - this screw retains the completed prosthesis to the implant at final placement and provides a compressive force across the cement line. Overview of use The plastic cylinder is incorpo- rated into the wax-up and be- comes part of the cast structure. The casting may then undergo further laboratory processing e.g. ceramic firing, finishing and polishing before being as- sembled with the interfacial component. The titanium inter- facial component is kept sepa- rate from the manufacturing of the casting and is therefore not subject to degradation by heat- cycles or de-vesting and finish- ing procedures as a ‘cast to gold’ cylinder would. The integrity of the machined part is therefore maintained in its original condition. The finished cast structure is as- sembled with the interfacial ring by luting before placement in the patient’s mouth by the dental technician. Both titanium ring as well as the prosthesis, need to be sandblasted and cleaned by air pressure and not with a ultra- sonic bath. Fig. 1. The Passive Abutment Fig. 3. Comparing Fitting Surfaces Fig. 2. The Passive Abutment Assembly Fig. 4. Different Radiographic Appearance Of The Same Miss Fit Depending On X-Ray Beam Angulation/Orientation Fig. 5. Cast Plastic vs. Passive Abutment For assembly, the titanium in- terfacial component is clamped to the analogue on the master model by means of the luting screw. The luting screw ensures that the interfacial component is held in full contact with the im- plant analogue. The finished prosthesis is then luted to the clamped interfacial ring using a dual-cured resin ce- ment. In this way the resin cement serves as a space filler between the casting and the interfacial ring, thus compensating for any minor casting and finishing dis- crepancies, so eliminating mis- fit of the casting to the implant. At placement in the mouth, the prosthetic screw retains the completed prosthesis (both cast- ing and interfacial ring together) to the implant and maintains a compressive force over the ce- ment line. This is achieved be- cause the prosthetic screw en- gages onto the casting and not onto the interfacial ring. The cement is therefore not respon- sible for retention of the prosthe- sis, but is merely a space filler.