Prosthesis Options for Edentulous Patients
A review of available removable and fixed solutions
Frank J. Tuminelli, DMD, FACP | Radi Al Masri, BDS, MS, PhD, FACP
The choices available for restoration of the completely edentulous arch are varied. The options can be separated broadly into two categories: removable and fixed. Fixed/nonmovable prostheses can be subcategorized based on material choices and whether they are supported by natural teeth or endosseous dental implants.
Each choice of prosthesis has advantages and disadvantages, and final selection should be made based on the oral health issues with which the patient presents, the recommended treatment plan, and the materials selected for treatment. Although essentially all prosthetic options will provide adequate function in the edentulous arch, the esthetics of each is different, as is the complexity of fabrication. In addition to the conventional modes of treatment, the advent of CAD/CAM has expanded the menu of potential designs and materials, decreased delivery time, extended prosthesis longevity, and improved patient acceptance.
This article will provide a brief overview of some of the most commonly used prostheses in clinical practice today, focusing on the characteristics, advantages, and disadvantages of each.
The “Hybrid” Prosthesis
The “hybrid” prosthesis is widely utilized today. It consists of denture teeth embedded in an alveolar substitute that can be either acrylic or composite with an internal metal substructure.1 This prosthesis is cost-effective and the fabrication of the prosthesis is straightforward, providing an option for all patients. The hybrid prosthesis was one of the very first utilized when implant-retained full-arch restorations were introduced in the United States. It has years of track history, providing excellent function and esthetics2,3 with a success rate of 90%.4
The complications with this prosthesis include teeth “popping” off, acrylic chipping and staining, and in rare instances, fracture of the metal substructure.5 With the exception of fractures, most repairs are managed in the office, and the prosthesis can deliver years of satisfactory service. With the advent of CAD/CAM, the substructure bars can be milled and made from metals such as chrome cobalt and titanium.6 This leads to a very accurate fit without the complications inherent in casting procedures.7 It also reduces cost since these metals are not precious alloys.8
The Metal-Ceramic Prosthesis
Another widely utilized fixed prosthesis is a metal-ceramic restoration consistent with those used for dentate patients.9 This is a familiar design to all restorative dentists. Its main advantage is that it is custom fabricated for each patient. This means the esthetics can be individualized; the ability to replace alveolar tissue with pink porcelains, for example, aids in providing an esthetic final result. When restoring multiple dental implants, there are variations on the design allowing for a substructure bar to be fabricated, and then individual crowns are cemented or screwed to the bar.10 This helps in hiding problematic implant access screw holes. It also gives one the ability to manage complications such as porcelain fracture without involving the entire prosthesis.10
The disadvantages for this prosthesis are the increased cost and increased risks of porcelain fracture and catastrophic bar failure.11 Depending on the design, this prosthesis also requires removal from the mouth and a return to the laboratory for repairs.
A metal-ceramic prosthesis also can vary in complexity depending on implant angulations. It also provides a solution through the use of attachments to have a splinted prosthesis that is not fabricated as one piece.
The new generation of prostheses is the monolithic zirconia-based restoration. These are CAD/CAM fabricated and milled from solid blocks of zirconia. These can either be colored or cut back and layered to create excellent esthetics. The monolithic construction makes them nearly indestructible. They are highly biocompatible and the accuracy of fit is excellent.12
The disadvantages are cost, potential wear of metal interfaces where they meet the zirconia,13 and the emission of radiation, though the levels are relatively low.14 Some patients may find reports of zirconia’s radioactivity online, so it is wise to address this concern up front and clear up misinformation or misconceptions. Evidence shows that radiation levels inherent in the degradation of zirconia are below the threshold one sees in our natural environment, and are therefore not significant.14 In addition, this prosthesis requires meticulous impression procedures and an accurate verification of the master cast. There is no ability to correct the prosthesis since it is milled and then sintered. Therefore, a misfitting prosthesis will result in a costly remake.
With the evolving nature of dentistry into the digital world, this restoration will likely become more widely utilized due to its unique advantages. As manufacturing costs decrease, it will become accessible across a larger economic scale. It is anticipated with the move to “metal-free” prostheses, monolithic zirconia will become a go-to solution.
If a fixed solution is not possible for a number of reasons (eg, a lack of osseous and soft tissue facial support, an incompatible number of implants, and/or economic considerations), a removable solution will supply excellent function and esthetics. There are retentive mechanisms that can be employed such as splinting the implants with a bar or using individual implants as anchors.
Due to the varied mechanisms of attachments and choices for the dental provider, a complete review of this prosthesis segment is beyond the scope of this article. One example worth mentioning, however, is the widely used LOCATOR® attachment (Zest Anchors, www.zestanchors.com). It is compatible with most major implant designs and provides a variety of retentive elements. These can be used in combinations to provide different levels of retention. They are also durable and very easy to replace by the dentist at a reasonable cost.
In addition to conventional removable prostheses that move during function, there are removable prostheses that are not moveable under function and act in a fashion similar to fixed prosthesis, but can be removed by the patient to clean the underlying tissues. These “fixed removables” fall into two broad categories of design.
The electro-milled prosthesis (EMI) was first described by Sillard.15 This consists of a substructure bar that is screw-retained and remains in the mouth at all times. Over the substructure bar, the final prosthesis can be attached by a wide variety of mechanisms. Too numerous to outline here, these attachments are rigid, non-resilient, and very retentive. The superstructure has a metal internal surface that fits precisely against the substructure bar. There is no movement because the prosthesis functions as a large precision attachment. These restorations are treated as a fixed dental prostheses in terms of occlusal development with a canine guided or anterior disclusive component.16,17
The disadvantage of this design is two-fold. Materials can break and wear, as can the attachment mechanisms.18 This can lead to the need to remove the prosthesis from the mouth and seek laboratory intervention. In general, EMIs will provide years of service and comfort. They are primarily indicated in patients who desire a fixed solution but who have significant orofacial deficits that do not allow use of a one-piece prosthesis because oral hygiene cannot be accomplished.19 The EMI’s design allows the patient to remove the suprastructure, brush the substructure bar, and perform routine hygiene around the implants.