Inside Dental Technology
Rhein83™ Equator Cast Bar Rehabilitation
Solving fixed denture complications with exceptional implant components
In 2005, a 67-year-old male patient had complete dentures fabricated by his dentist and a local dental laboratory. Four implants were placed in the anterior portion of the mandible and restored by integrating a custom cast metal framework with three laser-welded abutments. Unfortunately, the lower denture was neither comfortable nor stable. The male locator attachments on the bar did not engage the females in the denture correctly. In 2011, the entire lower denture was rehabilitated at the same facility. The teeth were replaced and the attachments were processed into a new denture. However, the restoration still lacked adequate retention and the attachments needed frequent replacement. The timeline between attachment replacements became shorter with each incident, and ultimately the dentist contacted the author’s laboratory to express his frustration with the declining condition of the case.
Multiple trouble-shooting scenarios were attempted, but eventually it was determined that the case needed to be entirely redone. The dentist withdrew the bar using an open tray impression technique. A gingival mask master model was poured and the custom cast bar was examined. The authors discovered that the cause of the poor fit and excessive attachment wear was related to welded attachments that loosened over time (Figure 1). Two of the three attachments had broken welds and were no longer rigidly attached to the bar. Replacing the bar with a more contemporary milled bar was not an option. The existing and loose attachments were removed from the bar. Large internal holes were evident where the stem of the attachment originally attached to the cast bar (Figure 2). The bars’ cavities were filled with a corroded material (most likely a composite or cement) (Figure 3). The material was cleaned out and large holes, approximately twice the diameter of a standard 2 mm threaded attachment, were left.
There were concerns about potentially warping the bar due to excessive welding. As such, the dental team researched larger diameter abutment replacement. This exploration indicated that the Rhein83™ Threaded Sleeve for Bonding Kit would be the best choice (Figure 4). This kit features an Equator™ attachment with a 1.6 mm thread diameter. The Equator attachment has the lowest profile of any attachment on the market, measuring 2.1 mm of vertical height and 4.4 mm in diameter. The attachment fits into a helicoil, a threaded insert that can be cemented into an oversized hole, and uses the helicoil’s internal threads to fasten a retentive element. The prefabricated titanium sleeve eliminates the need to drill and tap, provides a precision fit between the attachment and sleeve threads, and provides long-term conversion capabilities for removal and replacement should the attachment wear excessively. The existing casting’s attachment holes were cleaned and retentive grooves were made inside each hole to prevent rotation and the potential dislodging of the helicoil and attachment. Following the directions on the kit, the Equator was positioned into the helicoil and then attached to the Rhein83 paralleling mandrel. Using a surveyor and a paralleling mandrel ensured that all attachments would be at the proper path of insertion and parallel (Figure 5). Next, the helicoil was cemented into the holes using 3M ESPE metal-to-metal bonding cement (Figure 6). Once the cement was set, the excess was removed and the Equator attachments were screwed into the helicoils (Figure 7 and Figure 8). The Equator caps were placed on the attachments (Figure 9) and the entire bar was blocked out based on the optimum path of insertion. The master model was duplicated in silicone and a refractory model was poured. The refractory model was waxed and a custom cobalt chromium partial denture over-sleeve framework was cast. The three Equator housings were luted to the cast framework using acrylic, incorporating them into the skeleton strengthener for the new implant-retained lower denture (Figure 10 and Figure 11).
After the bar was removed from the patients’ mouth, he was no longer able to wear his existing lower denture, so it became a priority to complete the denture rehabilitation as quickly as possible. Two processes were completed simultaneously—the conversion of the custom implant bar attachment with a cast partial over-sleeve and in collaboration with dentist to establish centric occlusion and cosmetic considerations for the new dentures. The dentist was supplied with bite rims and a Gothic arch intraoral tracing device to verify vertical and centric relation. At this point, the centric relationship and cast framework procedures were merged and the esthetic try-in on top of the cast internal framework was returned to the doctor for patient evaluation and try-in. The try-in was returned from the doctor with instructions to process.
Prior to processing, the lower master model and bar assembly were duplicated in silicone (Figure 12). The duplicate model used implant Equator replica analogs supplied by Rhein83 to ensure that the newly cast framework fit the model properly during the processing procedures. The dentures were invested using a closed flask system and cured overnight. They were deflasked and finished following conventional denture techniques. The final step was to glass bead the interior of the framework and replace the attachment inserts. The lower denture was fitted, evaluated for fit and accuracy, and returned on the master model (Figure 13).
Upon completion, the case was returned to the office for patient delivery. The dentist commented that, “it took longer to screw down the bar than to deliver the dentures.” The success of the case was predictable based on three standards: good communication between the technician and the dentist, understanding the cosmetic and functional needs of the patient, and the integration of innovative products from the attachment leader, Rhein83.
Disclaimer: The preceding material was provided by the manufacturer. The statements and opinions contained therein are solely those of the manufacturer and not of the editors, publisher, or the Editorial Board of Inside Dental Technology.
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About the author
Jerry Kaizer, BS, CDT is the owner of Murray Kaizer Inc. in Farmington, CT. Todd Mercier is a Manager of Murray Kaizer Inc. In Farmington, CT.