Robert Kreyer, CDT, and Jochen Könnecker, CDT offer advice on how to ensure a precision fit for implants
Because implants do not have a periodontal ligament and do not move like natural teeth in their sockets, the degree of precision has to be exceptional for any implant-borne restoration. An ill-fitting implant restoration subjects implants to detrimental forces and may lead to failure of the implant and restoration.
The popularity of milled-titanium substructures has required development of alternative techniques to ensure predictable success. Traditional impression making, combined with the inherent inaccuracy of master model fabrication techniques and finicky material properties, require new technique processes to ensure passively fitting, precision implant restorations.
CAD/CAM titanium milled bars can be problematic to laser welding after sectioning due to this material’s specific properties. A special laser, capable of flooding the working chamber with a precious gas such as Argon to displace any oxygen, would be a requirement in any attempt to weld titanium.
Due to limited access of high-end laser welders in most dental laboratories, techniques must be utilized to avoid costly remakes. To avoid remakes, it should be a mandatory technical procedure to fabricate a verification index. The sole purpose of the verification index is to ensure that the analogs in the master model are positioned in relation to each other exactly the same way as the implants are positioned to each other in the mouth. Today, every CAD/CAM or digitally designed bar manufacturer requires the master model to be verified before submitting a titanium substructure for milling.
To make a verification index, it is best to use non-indexed metal temporary cylinders or non-indexing impression copings if available for the pertinent implant brand at hand. Plastic temporary cylinders are less suitable for this purpose because of their radiotranslucency. The implant/abutment interface is often located below the crest of the tissue, and a passive seat of the verification index can be confirmed only with a panograph.
The cylinders are secured with a corresponding screw to the analogs in the working model and connected to each other with Visio-Form™ (3M™ ESPE™) and/or Triad® (Dentsply Trubyte®) light-cure material to form a bar. After the connector material is cured, remove the bar from the model, and adjust the index until it seats without impinging on the soft tissue. Remove the index and the soft-tissue moulage from the working model and reposition the index back on the model. Hand tighten only one screw in a terminal abutment and verify that all cylinders seat properly.
At the time of try-in, fasten the index with only one screw in a terminal cylinder and observe if any of the other temporary cylinders do not seat completely on the remaining implants. In case the abutment/implant interface is too far below the tissue and seating cannot be observed visually, take an x-ray to ascertain proper seating. Should the index not seat passively, section the index and fasten each cylinder with a screw to the corresponding implant and lute the index in the patient’s mouth back together with GC Pattern Resin™ (GC America) or light cure material. Send the index and all model work back to the laboratory to reposition the analogs if necessary in the existing working model.
Upon return of the seating index from the try-in appointment, inspect the index if it has been sectioned and re-luted by the dentist. In case the index was re-luted, the offending analog needs to be removed from the working model. Grind out the analog by carefully removing the stone around the analog to be repositioned. Care should be taken not to damage the abutment/analog interface of the analog. After removing the analog from the stone model, screw the now free analog onto the verification index, and screw the index back onto the remaining analogs of the working model. Ensure that the repositioned analog does not touch or bind on the stone around the hole in the working model. Use GC Pattern Resin™ or light-cure material to reattach the analog in the new position into the model. Now the model is ready to be scanned for any CAD/CAM bar restoration.
Robert E. Kreyer, CDT, is a member of the American Prosthodontic Society and is the author of numerous published articles on removable prosthetics. Robert is a registered continuing education (CE) provider for the Dental Board of California and the National Board of Certification in Dental Technology. Robert is the Director of Removable Prosthodontics for MicroDental in Dublin, CA, and he teaches CE courses in removable prosthetics for Ivoclar Vivadent at the Implant Esthetics Center of Excellence (IECE) in Sarasota, FL. He can be reached at www.PersonalizedDenture.com.
Jochen Könneker is a certified dental technician (Dental Technician Guild, lower Saxony, Hannover 1986) from Germany, first introduced to the field of implant technology more than 20 years ago as an in-house, all-around technician for a prosthodontist in Beverly Hills, CA. Today, he leads the implant department at MicroDental in Dublin, CA. Jochen was granted a fellowship in the ICOI, graduated from Dr. Carl Misch’s International Implant Institute’s prosthetic courses I, II, and III, and founded genieoss.com in 2010.
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