ACP Messenger, Fall 2015, IN THE LAB
BY STEPHEN F. BALSHI, MBE
Patient education for prosthetic maintenance comes from years of collaboration between prosthodontists and dental laboratory technicians.
Screw-retained complete-arch dental implant rehabilitations have existed for over 50 years. From the beginning, Professor Brånemark restored his patients with a fixed denture or hybrid prosthesis. This prosthesis consisted of manufacturer’s denture teeth processed to a cast metal framework with acrylic resin. In today’s marketplace, there are many different options for restoring a complete-arch of dental implants, including various ceramic materials. However, with the All-on-4® treatment concept becoming so popular over the last handful of years as an economic solution, the screw-retained acrylic-veneered hybrid continues to be one of the more popular solutions as a definitive prosthesis.
While the implant-supported acrylic-veneered hybrid has been a long-standing solution for the fully edentulous patient, it does require prosthodontic maintenance and can also experience prosthodontic complications. Denture tooth fracture or debonding from the acrylic resin base are probably the two most common complications experienced with these restorations. All patients who function with an implant-supported acrylic hybrid will experience occlusal wear to the denture teeth over time. It is a built-in buffer to a rigid system that works quite favorably from a biomechanics standpoint. However, as the teeth wear, patients experience alteration of the occlusal scheme, guidance in excursive movements, and the loss of vertical dimension of occlusion.
The dental laboratory process to replace the worn teeth and acrylic resin base is called a “Retread.” In a manuscript authored by Balshi et al and accepted for publication in the International Journal of Prosthodontics, a retread is defined as, “the removal of worn veneering material on an implant-supported framework followed by the replacement of new veneering material at a desired vertical dimension of occlusion on the same implant-supported framework.” The results of this manuscript indicate that it takes an average of seven (7) years for the patient to wear down acrylic denture teeth to the point at which they need replacement. This data is based on a sample of 205 arches. An example of a worn implant-supported hybrid prosthesis is illustrated in Figure 1. Following the retread procedure in the dental laboratory, the same framework is illustrated in Figure 2.
Digital dentistry has recently invaded the hybrid prosthesis market. The same retread procedure that we’ve been performing for years can now also be done as a fully milled acrylic resin veneer where there are no individual denture teeth. This is a “game-changer” for the hybrid prosthesis because it will dramatically reduce the number of prosthetic complications that are seen with this type of restoration. Once the desired vertical dimension of occlusion is established, it is optically scanned and a new digital tooth setup is made (Figures 3a-c). The technology can be applied to frameworks that are “wrap-around” style (Figure 4a-b) or cases that have polished metal on the intaglio and/or lingual surfaces (Figure 5a-b). Early unpublished results show a complication rate less than one percent (1%).
It is expected that the fully milled resin veneer will wear at the same rate or even a little slower than manufacturer’s denture teeth. In other words, the biomechanical “buffer” that exists with a traditional hybrid prosthesis still exists with the fully milled acrylic resin hybrid. A digital record of the case is stored when the next retread procedure is needed in the future.
Prosthodontists would be wise to discuss wear factors and retread procedures with patients at the initiation of implant prosthodontic treatment. It would be beneficial for this information to be included in the written informed consent for treatment. This prior patient education will inevitably avoid surprises and confrontations between the patient and the prosthodontist when retreads are required.
Life Expectancy Of The Fixed Complete Denture in PDF Format