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.
