New Technology helps create Prosthetics with Predictable Results
Digitally designing and milling hybrid bars for use in telescopic denture solutions
By Luke S. Kahng, CDT
In the past, multiple implant prosthetics have been fabricated using two separate pieces for the implant bars and framework restorations. This approach, known as a telescopic denture, remains a viable option. In the author's opinion, it is the best prosthetic method to offer patients in terms of longevity and serviceability. However, this treatment option is more costly than a single prosthetic restoration, and that factor often becomes a deterrent to patients accepting this type of treatment approach.
In this case study, the author will explore how to utilize the latest technology to create this type of restoration using an in-house CAD/CAM system.
The patient, a woman in her 50s, presented as nearly edentulous in the maxillary with multiple implants planned. At this point in her staged treatment, she had two maxillary and two mandibular implants. This article will focus on restoring the upper and lower anterior areas, teeth Nos. 7 through 10 and teeth Nos. 22 through 27.
In Figure 1, the author was given an occlusal view of the missing maxillary anterior teeth Nos. 7 through 10 and the Straumann implants prior to the restoration being completed and placed in the patient's mouth. Figure 2 shows the two implants that were intended to retain the prosthetic for the mandibular anterior teeth Nos. 22 through 27. The author poured up the models from the impressions and added the soft tissue in order to examine the position of the teeth (Figure 3). On the model, the rough wax-up of the prosthetic could be seen with the patient's Class 1 bite and contour before the CAD system work was completed (Figure 4).
A Freedom HD scanner (DOF USA Inc., dof-usa.com) was used to scan and design the case within the laboratory's CAD/CAM Department (Figure 5). The latest acquisition within this department was a wet/dry Datron D5 5-axis milling machine (Datron Dynamics, datrondynamics.com) (Figure 6), controlled with hyperDENT CAM software and Abutment Creator (FOLLOW-ME! Technology North America, follow-me-tech.com). With the scanning software's precise design capabilities and hyperDENT's high-performance calculations, the author was able to mill two mini-hybrid bars (Figure 7), upper and lower. Both were fabricated with titanium and demonstrated an excellent, snug fit of the metal framework to the titanium bar. On the model, the milled titanium bar was screwed down for a fit check (Figure 8) and the wax-casted framework, which was fabricated with white precious metal, was seated (Figure 9).
The wax denture teeth were used to create a putty matrix for the denture tooth set-up (Figure 10). The metal framework was fabricated to leave enough room for the thickness of the porcelain buildup to be applied. The mini-bar for teeth Nos. 7 through 10 incorporated two holes, which are visible in Figure 11, for easy tightening or loosening of the framework in the mouth. The two-piece bar and framework for teeth Nos. 7 through 10 was tried in the mouth (Figure 12) for a fit and quality check.
Figure 13 shows a facial view of the two-piece titanium bar and metal framework tried in the patient's mouth. An A2 base of GC Initial MC Porcelain (GC America Inc., gcamerica.com)) was used for the buildup of the 10-unit case (Figure 14) as seen in this protrusive view. Note the change in incisal area translucency and halo effect of the porcelain application. The lower hybrid bar with the porcelain overlaid 6 units for teeth Nos. 22 through 27 was placed on top of the mandibular bar (Figure 15), after which the maxillary hybrid bar was seated and the 4-unit bridge placed on top (Figure 16).
An inside view of the lingual contour of the lower teeth Nos. 22-27 seated on the model demonstrates the harmony of the multi-layered porcelain coloring used for the restorations (Figure 17). The author photographed the restorations on the models from behind in order to ensure an inside look at the contact support (Figure 18). The left-side view (Figure 19) allows the reader to discern color differentiation as well as occlusal contact support for the finished restorations, as does the centric view (Figure 20).
The author would like to thank Anthony Giannini, DDS, for permission to use the in-office images taken of the finished restorations in the patient's mouth. Figure 21 shows the lower bar immediately after seating. Next, in a retracted view, the dentist shares a centric bite image (Figure 22). Figure 23 is of the occlusal view for the maxillary teeth Nos. 7 through 10.
This technique for creating a hybrid restoration has been practiced for many decades but is not used as frequently today. In the author's opinion, it is unquestionably the best method for this type of case work, even though it is labor intensive and the material is expensive. The work also must be done by a highly skilled dental technician in order to produce excellent benefits such as everything being removable and the bar being able to be torqued upward or downward easily.
The bar will stay in place in the mouth, but the framework is completely removable and can be easily repaired if necessary, making it a more serviceable option. One cautionary note is that the final incisal length must be measured precisely in order for the porcelain application to be predictable in design. The fit, however, if the restoration is properly fabricated, is perfect. It will be tight, not loose, and can be easily and accurately created. The patient was completely happy with the results, which in the end is the main goal.
About the author
Luke S. Kahng, CDT
LSK121 Oral Prosthetics
This article was double-blind peer reviewed by members of IDT's Editorial Advisory Board