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.
Zirconia-Based Prostheses
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.
Removable Prostheses
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.
Electro-Milled Prostheses
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.
Marius Bridge
Another type of fixed removable prosthesis is the Marius Bridge, which was first described by Yvon Fortin.20 This prosthesis was originally utilized for divergent implants or angled implants in the forerunner to “all-on-6” or “all-on-4” designs. What sets this prosthesis apart is the design of the substructure bar. With this prosthesis, the substructure bar is fabricated to be continuous in the emergence of the residual ridge when viewed from the lateral aspect. The design utilizes two posterior attachments and engages the anterior undercut in the bar as a retentive element.
This prosthesis provides less palatal coverage in the maxilla. When one compares this prosthesis to the EMI described above, the former does not take into account the anterior residual ridge morphology and the path of insertion is dictated solely by the substructure bar. This will often result in greater palatal coverage, and for some patients it may be significant. Both of these prostheses, in addition to providing a solution for facial soft tissue deficits, also solve divergent implant positions that do not allow for a restoration to be screw-retained. By taking the implant position out of the esthetic equation, the prosthesis is an excellent alternative. For the most part, these restorations are in a denture format and utilize the soft tissue as a supporting base, while the implants serve as the retentive component through a variety of attachment mechanisms. Even with two implants and a denture, the oral health quality of life for patients is dramatically improved with newly found confidence due to the stability gained. This results in the patient making better food choices, which can improve one’s overall systemic health.
Final Thought
The most rapid changes that are happening in prosthodontics are due to the digital revolution and virtual design. In the recent past, clinicians did everything manually, and today we create high-quality restorations digitally. When the proper prosthesis is chosen for each case and is fabricated with precision, it will fit extremely well and provide years of function and esthetics. Thus we provide an expedited return to normal function and esthetics for edentulous patients.
Disclosure
Frank J. Tuminelli, DMD, FACP, has no conflicts of interest to disclose relative to this article. Radi Al Masri, BDS , MS, PhD, FACP, has no conflicts of interest to disclose relative to this article.
About the authors
Frank J. Tuminelli, DMD, FACP
Immediate Past President, American College of Prosthodontists
Graduate Program Director
New York Hospital Queens
Queens, New York
Radi Al Masri, BDS, MS, PhD, FACP
Associate Editor,
Journal of Prosthodontics
Associate Professor
School of Dentistry
University of Maryland, Baltimore
Baltimore, Maryland
References
1. Drago C, Howell K. Concepts for designing and fabricating metal implant frameworks for hybrid implant prostheses. J Prosthodont. 2012;21(5):413-424.
2. Jemt T. Failures and complications in 391 consecutively inserted fixed prostheses supported by Branemark implants in edentulous jaws: a study of treatment from the time of prosthesis placement to the first annual checkup. Int J Oral Maxillofac Implants. 1991;6(3):270-276.
3. Naert I, Quirynen M, van Steenberghe D, Darius P. A study of 589 consecutive implants supporting complete fixed prostheses. Part II: Prosthetic aspects. J Prosthet Dent. 1992;68(6):949-956.
4. Hemmings KW, Schmitt A, Zarb GA. Complications and maintenance requirements for fixed prostheses and overdentures in the edentulous mandible: A 5-year report. Int J Oral Maxillofac Implants. 1994;9(2):191-196.
5. Goodacre CJ, Bernal G, Rungcharassaeng K, Kan JY. Clinical complications with implants and implant prostheses. J Prosthet Dent. 2003;90(2):121-132.
6. Drago CJ, Peterson T. Treatment of an edentulous patient with CAD/CAM technology: a clinical report. J Prosthodont. 2007;16(3):200-208.
7. Kapos T, Evans C. CAD/CAM technology for implant abutments, crowns, and superstructures. Int J Oral Maxillofac Implants. 2014;29 suppl:117-136.
8. Kapos T, Ashy LM, Gallucci GO, et al. Computer-aided design and computer-assisted manufacturing in prosthetic implant dentistry. Int J Oral Maxillofac Implants. 2009;24 suppl:110-117.
9. Goodacre CJ, Bernal G, Rungcharassaeng K, et al. Clinical complications in fixed prosthodontics. J Prosthet Dent. 2003;90(1):31-41.
10. Baig MR, Rajan G, Rajan M. Edentulous arch treatment with a cad/cam screw-retained framework and cemented crowns: A clinical case report. J Oral Implantol. 2009;35(6):295-299.
11. Takaba M, Tanaka S, Ishiura Y, Baba K. Implant-supported fixed dental prostheses with cad/cam-fabricated porcelain crown and zirconia-based framework. J Prosthodont. 2013;22(5):402-407.
12. Li RW, Chow TW, Matinlinna JP. Ceramic dental biomaterials and CAD/CAM technology: State of the art. J Prosthodont Res. 2014;58(4):208-216.
13. Taylor TD, Klotz MW, Lawton RA. Titanium tattooing associated with zirconia implant abutments: A clinical report of two cases. Int J Oral Maxillofac Implants. 2014;29(4):958-960.
14. Bavbek AB, Ozcan M, Eskitascioglu G. Radioactive potential of zirconium-dioxide used for dental applications. J Appl Biomater Funct Mater. 2014;12(1):35-40.
15. Sillard R. The electro-milled fixed-removable implant prosthesis. Implant Soc. 1992;3:13-15.
16. Kim Y, Oh TJ, Misch CE, Wang HL. Occlusal considerations in implant therapy: Clinical guidelines with biomechanical rationale. Clin Oral Implants Res. 2005;16(1):26-35.
17. Rilo B, da Silva JL, Mora MJ, Santana U. Guidelines for occlusion strategy in implant-borne prostheses. A review. Int Dent J. 2008;58(3):139-145.
18. Berger JC, Driscoll CF. Rehabilitation of a spark erosion prosthesis: A clinical report. J Prosthodont. 2006;15(2):113-116.
19. Toljanic JA, Antoniou D, Clark RS, Graham L. A longitudinal clinical assessment of spark erosion technology in implant-retained overdenture prostheses: A preliminary report. J Prosthet Dent. 1997;78(5):490-495.
20. Fortin Y, Sullivan RM, Rangert BR. The Marius implant bridge: Surgical and prosthetic rehabilitation for the completely edentulous upper jaw with moderate to severe resorption: a 5-year retrospective clinical study. Clin Implant Dent Relat Res. 2002;4(2):69-77.
