David B. Rosen, D.M.D.- Practice Limited to Periodontics & Dental Implants
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David B. Rosen, D.M.D.- Practice Limited to Periodontics & Dental Implants
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Removable Partial Dentures for Periodontally Compromised Teeth - Design Considerations In ever-increasing numbers patients are expressing a desire to retain their natural teeth, even in the face of significant periodontal disease. As patients live longer we are faced with the prospect of retaining teeth with a periodontally compromised prognosis. When regenerative periodontal procedures are successful the long-term prognosis may improve dramatically. Yet when initial disease is severe or periodontal regenerative procedures do not result in total repair the restorative dentist can be faced with the probable loss of one or more teeth in a five-year time span. This reality, as well as the costs of a new prosthesis, suggests that removable appliances be designed to take into account replacing questionable teeth in the future. McGiveny and Castleberry discuss the design of removable partial dentures that can tolerate the loss of teeth at a future date. Such designs rely on three elements: maintaining adequate vertical support to prevent impingement of the partial denture on the soft tissues, the ability to add direct retainers when key abutment teeth are lost and the convenient addition of prosthetic teeth and resin base materials when natural teeth are lost subsequent to insertion of the original appliance. Maintaining Vertical Support It was Dr. Krohl, a San Francisco prosthodontist, who suggested the use of multiple rest seats for sustaining vertical support while improving stress distribution in removable partial denture designs. Many research articles have been published establishing the rest seat as the primary mechanism for stress distribution in removable partial dentures. In periodontally involved dentitions where some teeth have a questionable prognosis an effort should be made to place rest seats in a majority of the teeth involved with the framework. These rests should be placed as close to the long axis of the tooth as possible. In teeth with periodontal involvement this will greatly aid in stress distribution and minimize the potential damage from lateral forces. Rest seats should have adequate bulk without interfering with the occlusion. To achieve adequate bulk in the rest seat and framework connector may mandate the preparation and restoration of the cingulum of anterior teeth or the proximal surfaces of posterior teeth. Enameloplasty may be needed in posterior interproximal embrasures to avoid the occlusion while giving the rest seat adequate bulk inside locations that dissipate loads axially. Occluded models are helpful in determining the location of such rest seats. Adding Direct Retainers In periodontally involved teeth it is desirable to reduce the torque producing traits of clasps to improve tooth longevity. Hansen et al suggest the use of .0032 nickel-chromium wire for this purpose. It can be bent for use as a circumferential or I-bar type clasp and attached to a replacement denture base should an abutment tooth be lost. If the new abutment tooth has contour deficiencies that reduce the ability to gain retention on the replacement abutment, the tooth can be recontoured with burs or resin to provide optimal retention. Addition of Prosthetic Teeth and Denture Bases It is frustrating to lose an abutment tooth on an existing partial denture and have no way to tie in a replacement in the existing partial denture framework. In periodontally involved teeth designating areas for the location of beads or meshwork within the framework can facilitate the addition of teeth subsequently lost to periodontal disease. These meshwork or bead areas can be located near the questionable teeth to insure adequate retention for an additional tooth or teeth. The meshwork or beaded areas are filled with resin in the original appliance. When requesting this process the laboratory should be advised to minimize the relief beneath the open meshwork to avoid thickening the rest of the major connector. In the lower arch, you may wish to adjust the finish line of the major connector just distal to the anterior abutment tooth to facilitate a transition from tooth to tissue born prosthesis. In those cases where patients opt to retain multiple questionable teeth, the clinician may consider large resin bases with segmental partial denture frameworks. Individual castings are vastly superior to acrylic bases with embedded wire clasps, providing the patient with increased appliance stability but maintaining the flexibility of the resin-bases transitional prosthesis.
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