Stabilizing and Securing an RPD With a Single Implant

INTRODUCTION
Dental implants provide a stable foundation for fixed and removable prostheses. The benefits of dental implants to stabilize complete overdentures is well documented.^1-3 Less often reported are cases involving the use of dental implants to stabilize removable partial dentures (RPD).
The stability of RPDs is dependent on the oral anatomy and available teeth to clasp to. Poor RPD stability occurs with highly resorbed ridges and an inadequate number of suitable abutment teeth. RPDs with distal extensions, Kennedy Class I and II, generally have less stability than those engaging distal abutment teeth. The loss of even one distal abutment tooth can lead to RPD instability.^4,5
Clasping anterior teeth creates several problems. First, unacceptable aesthetic results can occur when anterior teeth are clasped and are visible when the patient smiles. Second, anterior teeth provide inadequate stability for RPDs that do not have distal abutment teeth. Third, anterior teeth can be lost due to excessive loading.^4-6
Dental implants provide support wear suitable abutment teeth are not present.⁷ A properly positioned implant can permit the fabrication of a stable RPD that was not possible before. In addition, the use of an overdenture abutment eliminates the need for an unaesthetic clasping system. The clinical case described below is one in which the placement of a single implant permits delivery of a stable and aesthetic unilateral distal extension removable partial overdenture.

CASE REPORT
Diagnosis and Treatment Planning
A 47-year-old female smoker presented with the chief concern of a poorly fitting maxillary RPD with an unaesthetic anterior clasp. The patient was found to have a Kennedy Class II partially edentulous arch. Teeth Nos. 1 to 7, 12, and 14 to 16 were missing (Figure 1). Her original RPD had an I-bar metal clasp that engaged the buccal of tooth No. 8. The patient did not regularly wear this RPD because it had poor stability and was unaesthetic.

Figure 1. Preoperative smile, without removable partial denture (RPD) in place.	Figure 2. Preoperative clinical view showing severe maxillary right ridge resorption.
Figure 3. Clinical view of Zest LOCATOR Abutment (Zest Anchors) in positioned in maxillary right quadrant.	Figure 4. Closer view of Zest LOCATOR Abutment in site No. 6.
Figure 5. View of underside of RPD showing over-denture attachment.	Figure 6. Postoperative clinical view with RPD in place.

Figure 7. Postoperative smile with new RPD in place.

Clinical evaluation revealed severe resorption of the maxillary right residual alveolar ridge (Figure 2). Minimal bone existed between the crest of the alveolar ridge and the floor of the maxillary sinus in site Nos. 1 to 4. Treatment plans that included sinus grafting, multiple implant placement, and fixed restorations were discussed. Due to financial limitations, the patient did not accept a fixed rehabilitation option. However, the patient did accept treatment that included fabrication of a maxillary removable partial denture. A single implant retained overdenture abutment would be used to secure the right distal extension. A traditional clasping system would be employed on the left side.

Treatment Protocol
A regular diameter, 4.0 x 10 mm, dental implant (PrimaConnex [Keystone Dental]) was placed in site No. 6. Following osseointegration of the dental implant, an over-denture abutment was secured to the implant. (LOCATOR implant attachment systems [Zest Anchors]) (Figures 3 and 4). The maxillary removable partial over-denture was fabricated that would engage the abutment in site No. 6 (Figure 5). Excellent retention provided by the over-denture abutment precluded the need for further clasping on the right side. Tooth No. 13 was engaged using a T-bar clasp and a mesialocclusal rest.
Pink acrylic replicated the natural soft-tissue architecture and permitted placement of appropriate sized teeth (Figure 6). The final result provided a stable and functional RPD with a highly aesthetic appearance for the patient (Figure 7).

DISCUSSION
Conventional RPDs can have poor stability, minimal retention, and unaesthetic clasps. Distal extension RPDs, Kennedy Class I and II, typically have less retention than RPDs with distal abutment teeth. In addition to aesthetic problems, clasping of anterior teeth can lead to excessive tooth loading and accelerated tooth loss. A conventional RPD can become useless if a strategically positioned tooth is lost.⁴
In the case presented, the patient had a Kennedy Class II partially edentulous arch. The maxillary right posterior residual ridge was highly resorbed and narrow. The maxillary right sinus floor was in close proximity to the residual ridge crest in the bicuspid to molar areas. Due to finances, fixed restoration was not an option. The patient did not wear her current conventional RPD due to its poor retention, lack of stability, and unaesthetic I-bar clasp on tooth No. 8.
The use of implants to retain complete over-dentures is well documented.1-3 Less documented is the use of implants to retained partial removable over-dentures. Patients with implant supported RPDs reported and improved function, improved aesthetics.6 The use of implants to support RPDs provides the patient benefits often not possible with conventional tooth supported RPDs. Compared to fixed treatment options, implant-retained RPDs are highly cost-effective.⁸
Over-denture abutments can tolerate varying degrees of divergence. The system employed can tolerate divergence of up to 40°.^9,10 This is of great benefit when creating a path of draw for the implant-retained RPD. Highly resorbed ridges can make ideal implant placement difficult.
In the case presented, the use of an implant supported over-denture abutment provided enough retention to eliminate the need for a clasp on that side of the RPD. This greatly enhanced the aesthetic quality of the RPD. Due to the high degree of RPD stability and aesthetic appearance, the patient felt confident in function and when smiling.

CONCLUSION
The use of a single implant overdenture abutment can permit fabrication of a stable, functional, and aesthetic RPD.

References

1. Feine JS, Carlsson GE, Awad MA, et al. The McGill consensus statement on overdentures. Mandibular two-implant overdentures as first choice standard of care for edentulous patients. Montreal, Quebec, May 24-25, 2002. Int J Oral Maxillofac Implants. 2002;17:601-602.
2. Vogel RC. Implant overdentures: a new standard of care for edentulous patients—current concepts and techniques. Compend Contin Educ Dent. 2008;29:270-278.
3. Cavallaro JS Jr, Tarnow DP. Unsplinted implants retaining maxillary overdentures with partial palatal coverage: report of 5 consecutive cases. Int J Oral Maxillofac Implants. 2007;22:808-814.
4. Brudvik JS. Advanced Removable Partial Dentures. Chicago, IL: Quintessence Publishing; 1999.
5. Mitrani R, Brudvik JS, Phillips KM. Posterior implants for distal extension removable prostheses: a retrospective study. Int J Periodontics Restorative Dent. 2003;23:353-359.
6. Budtz-Jørgensen E, Bochet G, Grundman M, et al. Aesthetic considerations for the treatment of partially edentulous patients with removable dentures. Pract Periodontics Aesthet Dent. 2000;12:765-774.
7. Vogel RC. Expanding the benefits of implant therapy: implant-retained removable partial dentures. Functional Esthetics and Restorative Dentistry. 2008;2:2-5.
8. Mijiritsky E, Ormianer Z, Klinger A, et al. Use of dental implants to improve unfavorable removable partial denture design. Compend Contin Educ Dent. 2005;26:744-750.
9. Schneider AL, Kurtzman GM. Restoration of divergent free-standing implants in the maxilla. J Oral Implantol. 2002;28:113-116.
10. Schneider AL. Simplifying divergence challenges of a combination root and implant overdenture attachment case. Dent Today. 2006;25:96,98.

Dr. Mahn is a periodontist in private practice in Manassas, Va. He graduated from State University of New York Stony Brook Dental School in 1990 and completed his periodontal residency at the Medical College of Virginia School of Dentistry in 1992. He also completed a residency on temporomandibular disorders/orofacial pain at New York University College of Dentistry in 1996. Dr. Mahn’s practice emphasizes perioplastic, regenerative, and dental implant therapies. He has several publications and has lectured on these topics. He can be reached at (703) 392-8844 or dmahn@cox.net.

Disclosure: Dr. Mahn reports no disclosures.