[The implant denture in the laboratory]

The authors analyzed the numerous devices and prosthetic kits currently available for implant prosthodontics. Existing systems can be classified into two fundamentally different categories: the gold ring cylinder (or its equivalent in resin for casting) and the prosthetic abutment core or post concept. The former is based on connection of two nearly flat, horizontal surfaces by means of a screw, which avoids problems of parallelism; the latter can be likened to insertion of one part into another, like a crown that slides along the vertical axis of an abutment, with connection being obtained by cementation and/or screwing. Prosthetic abutment core or post: Whether monoblock or multiblock, the implant core or post is very similar to a conventional metallic abutment. Construction of the implant prosthesis is generally no problem when parallelism has been respected during surgery; if problems are encountered with parallelism, options include: 1. Adjustment of the abutment core by grinding, 2. Use of a telescope to achieve parallelism, 3. Use of a bendable prosthetic abutment core, 4. Use of a prosthetic abutment core preangulated 10 degrees-20 degrees, 5. A combination of the above solutions. The implant prostheses may be screwed, cemented or clipped in position. Gold ring cylinder concept The gold ring cylinder (or its equivalent in resin for casting) theoretically eliminates problems of parallelism, but at the same time restricts the implant prosthesis to screw techniques. A special protocol is required for the impression and construction of the prosthesis. Impression with plaster is often the best method for total edentulism whereas "open" impression trays are advisable for partial prostheses. In the laboratory, use of a machined gold ring cylinder provides optimum precision, but intra-oral verification remains necessary. Implant prosthodontics unquestionably represent a new type of "know how": both the dentist and the dental lab technician must acquire the necessary training and adapt their work routines.