An indirect technique for fabricating a crown under an existing clasp

DENTAL SECTION

DANIEL

TECHNOLOGY

EDITOR

H. GEHL

An indirect technique an existing clasp

for fabricating

a crown under

Edward R. Raskin, D.D.S.* Booth Memorial Medical Center, Flushing, N.Y.

A

t times it is necessary to make, or remake, a crown under the clasp of an existing removable partial denture. The problem is usually compounded by the patient’s refusal to relinquish the denture for the time needed to fabricate the restoration. An indirect method that allows the patient to continue wearing the removable partial denture will be described. A review of the literature discloses a number of different methods of addressing this problem.lW3Some techniques are only partly indirect and require extensive chair time. This procedure allows the construction of any type of coverage the dentist feels is proper. TECHNIQUE 1. Anesthetize the involved tooth or teeth. 2. Make a wax or alginate (irreversible hydrocolloid) impression of the teeth to be prepared, which will be used in the fabrication of acrylic resin temporary crowns. 3. Make a counterimpression or a functional interocclusal registration with the removable partial denture in position in the mouth. 4. Adapt a mass of autopolymerizing acrylic resin to the removable partial denture framework and to the lingual surfaces of a few teeth adjacent to the teeth that will be prepared. The hardened acrylic resin stabilizes the removable partial denture after tooth preparation. Remove and reseat the partial denture. The acrylic resin should not lock the restoration in place. 5. Prepare the teeth, retract the tissue, and ready a sectional tray for the impression. 6. Temporarily thicken the involved clasp arms and rest outside the mouth with sticky wax. Dry the removable partial denture and build up the clasp with sticky wax to a thickness of 2 to 3 mm on all surfaces that do not contact the abutment tooth (Fig. 1). This is necessary since the impression will include the removable partial denture, its clasp, and the prepared teeth.

*Attending-in-charge,

580

Department

of Removable

Prosthesis.

Fig. 1. Sticky wax is added to external surfaces of occlusal rest and buccal and lingual arm.

Fig. 2. Area of clasp and adjacent tooih on partial denture is boxed with clay, and low-fusing metal is poured. 7. Reseat -the removable partial denture with its thickened clasp and rest in the mouth. It will be guided into position by the remaining clasps and the autopolymerized acrylic resin addition (see step No. 4). 8. Make a rubber base or, preferably, a polyether impression. Remove the impression from the mouth with the removable partial denture in the impression. 9. Carefully remove the partial denture from the OCTOBER

1983

VOLUME

50

NUMBER

4

FABRICATING

A CROWN

UNDER

AN EXISTING

CLASP

Fig. 3. Low-fusing

metal die is removed from cast. Lateral and cuspid teeth are prepared for a splint.

impression and make sure that no damage is done to the impression itself as the clasp arms are freed. Remove all fragments of sticky wax that are left within the impression material. The impression should include the prepared tooth or teeth as well as the “tunnels” created by the clasp arms. 10. Using the original wax impression, make a temporary crow:n (see step No. 2). Reseat the temporary crown on the tooth and return the removable partial denture to the mouth while the acrylic resin is still somewhat soft. A temporary crown that fits both the tooth and the partial denture clasp is now completed. LABORATORY THE CAST

PHASE: POURING

prior to cementation.

1. Use clay to box the removable partial denture tooth adjacent to the prepared tooth. 2. Making sure that the metal flows into the tunnels, pour low-fusing metal into the boxed area (Fig. 2). In this way, the low-fusing metal creates a die that duplicates the clasp arms and rest as well as the adjacent partial denture tooth. Set a dowel pin into the hardening metal. 3. Remove the boxing clay. Taper the low-fusing metal as necessary without removing it from the impression. Then pour the master cast in a routine manner (Fig. 3). 4. Using the removable metal clasp for establishment of the external contour, fabricate the crown on the die. Use of the die relief spacer prior to wax-up will ensure complete seating of the finished restoration (Fig. 4). 5. Return the restoration to the mouth at the patient’s next visit and make minor adjustments. Use temporary cementation until the restoration has been worn comfortably (Fig. 5). THE

JOURNAL

OF PROSTHETIC

Fig. 5. Completed lateral and cuspid splint in mouth

DENTISTRY

SUMMARY A method of restoring abutment teeth with full coverage under existing clasps has been demonstrated. This technique allows the patient to retain the prosthesis throughout the treatment period.

REFERENCES 1.

2.

3.

Keprznt

Lubovich. R. P., and Peterson, T.: The fabrication of a ceramic-metal crown to fit an existing removable partial denture clasp. J PROSTHET DENT 37:610, 1977. Loft, G. H., Reynolds, J. M., and Lundquist, D. 0.: An indirect-direct method of crown fabrication for existing removable partial denture clasps. J PROSTHET DENT 38:589, 1977. Garfield, R. E.: Replacing an abutment crown for an existing removable partial denture. J PROSTHET DENT 45~103, 1981. requestc

lo:

DR. EDWARD R. RAS~IN 57 THE HEMLOCKS ROSLYN ESTATES, NY 11576

581