Written by Bill Abbo, DDS, MS Monday, 01 February 2010 00:00
The biomechanical classification of a removable partial denture (RPD) based on the nature of the supporting tissue can be divided into 3 parts: tooth borne, tooth-mucosa borne, or entirely mucosa borne. The tooth-supported RPD usually has the edentulous space bounded by abutment teeth. The tooth-mucosa borne partial denture, in the majority of cases, are distal extensions bilateral or unilateral (Kennedy Class I and II). Finally, the last category (entirely mucosa borne) is usually not considered for definitive treatment, functioning in the cases when interim or transitional prostheses are required.
VERTICAL SEATING FORCES
The origin of the vertical seating forces on an RPD can be caused by mastication, swallowing, and parafunctional movements; resulting in tissue-ward movement of the extension base, as well as rotation around the fulcrum line. Different ways to counteract these movements include: use of the denture base, nonstress releasing clasps assemblies, and rests. In the case of a maxillary RPD, the major connector also counteracts these movements. On the other hand, for the tooth-borne removable partial denture, the vertical forces are counteracted by the teeth adjacent to the edentulous space, transmitting them to the teeth and from there to the underlying bone.
From the descriptions above, it is logical to assume that a tooth-borne partial denture would be more comfortable and less traumatic to the edentulous tissue and abutment teeth. In addition, it would provide the patient with enhanced retention. Since there would be no edentulous distal extension, minimal vertical seating movement would be counteracted by the soft tissues.
IMPLANTS AS AN ALTERNATIVE
Several years ago when a distal extension case presented to our practices, no alternative in the design of the removable partial denture was available. Common complaints associated with the Kennedy Class I and Class II removable partial denture are lack of stability, minimal retention, and unaesthetic retentive clasping. With the introduction of dental implants, the possibility of their placement in strategic locations within the edentulous space can transform a distal extension tooth-tissue borne partial denture into a tooth-implant borne partial denture, mimicking the tooth-borne partial denture.
OPTIONS HAVE INCREASED OVER TIME
The options for restoring edentulous areas have changed dramatically in the last 20 years, especially with the introduction of endosseous dental implants. Since the pioneering work by Bränemark,1 the use of osseointegrated implants to aid in restoring missing teeth has become the treatment of choice for all patients. Endosseous implants may vary in shape, length, width, surface coating; yet major brands all report a success rate of 95% in a period of 5 to 10 years.2-5
The conventional endosseous implant placement protocol, according to Bränemark, et al6 involves a healing period of 3 to 6 months with a submerged placement. For implants placed immediately into extraction sites, the protocol involves a healing period of just 8 to 12 months. The most important requirement for implant-supported restorations is osseointegration of the dental implant. This process can be affected by the bone quality, surgical technique, patient habits, and other factors. Nonaxial loading during function can contribute to loss of osseointegration; this loading can be the product of different causes, primarily by the incorrect implant localization and angulations.7 Fabrication of surgical guides for the correct placement of an endosseous implant is imperative to avoid aesthetic, functional, and phonetic complications.8,9
This article describes a simple technique to transform a bilateral distal extension (Kennedy Class I) tooth-mucosa borne RPD into a tooth-implant borne (Kennedy Class III) RPD.
Diagnosis and Treatment Planning
A 61-year-old white male reported to the dental office with a chief complaint of discomfort due to the lack of chewing efficiency and a desire to improve his appearance.
|Figure 1. Preoperative frontal view: mandibular teeth and edentulous maxillary ridge.||Figure 2. Preoperative occlusal view: mandibular teeth and edentulous ridges.|
|Figure 3. Diagnostic wax-up of the mandibular teeth showing locations of the 2 endosseous implants.|
The patient presented with a poor fitting maxillary complete denture, as well as a mandibular RPD. The RPD was uncomfortable due to movement every time he swallowed or chewed. The right second molar presented with an apical abscess. With a mobility type 2, the tooth had a poor prognosis and an extraction was recommended) (Figures 1 and 2).
A complete dental examination was performed along with a review of the patient’s medical history. There were no medical findings that would contraindicate dental care, including elective surgery.
Several treatment options were proposed: (1) Extraction of all mandibular teeth followed by upper and lower complete dentures; (2) complete upper denture with full coverage restorations on all mandibular teeth, 3 endosseous implants on the posterior edentulous area with single unit restorations; (3) complete upper denture with full coverage restorations on all mandibular teeth; 2 endosseous implants localized on strategic localization, and a removable partial denture; and (4) complete upper denture with full coverage restorations on all mandibular teeth, and an RPD.
The patient selected option 3 due to financial restrictions. At some time in the future, the patient would be able to go ahead with the placement of a third endosseous implant, the removal of the RPD, and the placement of fixed full-coverage restorations placed on the implants.
A complete wax-up for all mandibular teeth was then fabricated by the dental laboratory technician. In doing so, the locations for the endosseous implants were determined (Figure 3).
After the extraction of the right second molar, 2 endosseous implants 4.3 mm internal connection (Nobel Biocare AB) were placed at the location of the first molars by using a prefabricated surgical guide.
All mandibular teeth were prepared 360° for full-coverage metal ceramic restorations, using a buccal shoulder and lingual chamfer preparation design (Figure 4). The design for the mandibular RPD was completed in the form of a tooth-implant borne prosthesis. Rest seats, guide planes, and contours were designed to receive the RPD.
|Figure 4. Mandibular preparations with the impression copings placed.||Figure 5. Metal-ceramic full-coverage restorations, after cementation.|
A custom tray was fabricated (Triad [DENTSPLY International]) for the impression of the mandibular teeth. Retraction cord “00” (Ultrapak [Ultradent Products]) impregnated with hemostatic solution (Hemodent [Premier Dental Products]) was placed for gingival retraction on all mandibular teeth. (Note: Nonepinephrine only hemostatic solutions should be used with the specially braided Ultrapak cord [per manufacturer recommendations] due to the volume of solution potentially carried by this cord design.) An impression was taken using a light body/heavy body vinyl polysiloxane (VPS) impression material (Kerr) to record all mandibular teeth. After fabrication of the restorations in the dental laboratory, each crown was tried-in and evaluated for marginal integrity, occlusion, and aesthetics. (Visual, tactile, and radiographic assessments of the marginal integrity were performed.) The teeth were cleaned with plain flour pumice (Whip Mix) and treated with chlorhexidine (Zila Pharmaceuticals), and the internal surface of the crowns cleaned with alcohol. A thin coat of resin-modified glass ionomer cement (FujiCem [GC America]) was placed into the internal surface of the metal ceramic crowns and delivered with finger pressure (Figure 5).
Custom trays were used for the impression of the maxillary and mandibular arches, the edentulous areas of the trays were border molded. For the mandibular arch, a closed-tray impression technique (implant level impression) was performed to record the location of the implants as well as the preparations on the crowns for the mandibular teeth. The maxillary impression was also performed utilizing a VPS impression material (medium body) (Kerr).
The mandibular impression was poured using type IV gypsum (Microstone Stone [Whip Mix]). The maxillary impression was also poured in an appropriate stone.
|Figure 6. Metal framework try-in of mandibular removable partial denture (RPD). (Note projection of the healing abutment.)||Figure 7. Final view of maxillary complete denture, and mandibular RPD; converted from a Kennedy Class I to a Kennedy Class III, due to the location of the endosseous implant.|
|Figure 8. Postoperative occlusal view of the new mandibular RPD.|
A record base and occlusal rims were fabricated for the maxillary arch. After verification of the fit of the mandibular RPD (Figure 6), occlusal rims were fabricated and the vertical dimension determined. An interocclusal registration (with the occlusal rims in place) was taken using a VPS bite registration material (Exabite [GC America]) by guiding the patient into the centric occlusion position. The mandibular RPD and maxillary complete denture were then completed at the dental laboratory (Figures 7 and 8).
The healing abutments on the 2 implants were removed and the ball attachments placed and torqued. The inside area of the RPD, where the implants were located, was relieved. This was done to ensure that there was no contact between the ball attachments and the RPD. The attachments were then retrofitted to the RPD, using an acrylic resin (GC America).
The patient was satisfied with both the function and aesthetics of his new RPD. Regular follow-up visits revealed that periodontal and peri-implant conditions were stable, there was no evidence of intrusion or mobility problems of any of the abutment teeth, as well as no visible changes in the bone levels of the natural teeth or implants. The duration of the observation time was of 49 months; a longer observation period is necessary to determine the long-term prognosis of the tooth-implant borne partial denture.
To date, the number of RPDs placed with implants and natural teeth has been very limited. Mitrani, et al10 reported that the bone loss on posterior implants used for the distal extension on an RPD is less than 1.0 mm after its functional loading, and less than that when the implants are used only as a vertical stop and using resilient attachments.
Brudvik11 reported that when the implants are connected with other attachments, including conventional clasping on the other teeth (or precision crowns), lateral stability and retention could be enhanced. Extracoronal attachments such as an O-ring should be utilized when a single implant abutment is used on an RPD. On the contrary, stress relief such as a resilient wire should be used when intracoronal attachments are used.11
Due to the difference in structure of implants and natural teeth, their mobility also differs. If a combination of implants and natural teeth is necessary, possible overloading of the implant(s) and the potential for intrusion of the natural teeth should be monitored carefully. The natural teeth, which were used as abutments in this case showed no mobility and had adequate crown-to-root rations.
The author presented this case report article because discussion regarding the application of implants with RPDs is limited in the literature. It is the author’s opinion that patients can benefit greatly with this treatment approach when performed with proper diagnosis, treatment planning, and technique.
- Bränemark PI. Introduction to osseointegration. In: Bränemark PI, Zarb GA, Albrektsson T, eds. Tissue-Integrated Prostheses: Osseointegration in Clinical Dentistry. Hanover Park, Ill: Quintessence Publishing, 1985:11-17.
- Wennström JL, Ekestubbe A, Gröndahl K, et al. Implant-supported single-tooth restorations: a 5-year prospective study. J Clin Periodontol. 2005;32:567-574.
- Gotfredsen K. A 5-year prospective study of single-tooth replacements supported by the Astra Tech implant: a pilot study. Clin Implant Dent Relat Res. 2004;6:1-8.
- O’Brien GR, Gonshor A, Balfour A. A 6-year prospective study of 620 stress-diversion surface (SDS) dental implants. J Oral Implantol. 2004;30:350-357.
- Romeo E, Lops D, Margutti E, et al. Long-term survival and success of oral implants in the treatment of full and partial arches: a 7-year prospective study with the ITI dental implant system. Int J Oral Maxillofac Implants. 2004;19:247-259.
- Bränemark PI, Hansson BO, Adell R, et al. Osseointegrated implants in the treatment of the edentulous jaw. Experience from a 10-year period. Scand J Plast Reconstr Surg Suppl. 1977;16:1-132.
- Taylor TD, Agar JR, Vogiatzi T. Implant prosthodontics: current perspective and future directions. Int J Oral Maxillofac Implants. 2000;15:66-75.
- Solow RA. Simplified radiographic-surgical template for placement of multiple, parallel implants. J Prosthet Dent. 2001;85:26-29.
- Tsuchida F, Hosoi T, Imanaka M, et al. A technique for making a diagnostic and surgical template. J Prosthet Dent. 2004;91:395-397.
- 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.
- Brudvik JS. Advanced Removable Partial Dentures. Hanover Park, Ill: Quintessence Publishing; 1999:153-159.
Disclosure: Dr. Abbo reports no conflicts of interest.
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