An improved method to maintain prqer tuekh relation while processing distal-extension denture bases

Don G. Carver, D.D.S., Raymond Rim,* and Thomas J. Balshi, D.D.S. Fort Washington, Pa

C hanges in interocclusal distance and occlusal inter- cuspation of properly articulated denture teeth may occur during the acrylic resin packing and curing

*L)rnr;ll Terhnici;ln

process, particularly in distal-extension prostheses. Movement of denture teeth can tx avoided when both the framework and the teeth are held in the lower half of the flask and the acrylic resin is packed from the lingual side.

Fig. 1. Half-flasked distal-extensron removable partial denture after boil out. All of master cast and partial denture is covered with stone in lower half of flask except waxed areas on lingual surface of denture base.

Fig. 2. Lingual view of retention device and teeth ready to receive acrylic resin.

Fig. 3. Lateral placement and compaction of acrylic resin dough. Firm hand pressure is required.

Fig. 4. Trial pack prior to removal of excess acrylic resin.

140 JANUARY 1986 VOLUME 55 NIJMRFR I

MAINTAINING TOOTH RELATION DURING BASE PROCESSING

LABORATORY PROCEDURE

The teeth are set and the denture base waxed to the master cast in the usual manner. The cast is invested in a half-flasking procedure that is different than the normal protocol (Fig. 1). All of the master cast, partial denture framework, teeth, and all of the wax except the lingual flanges are covered with stone in the lower half of the flask.

After removal of the wax during the boil out, the retentive clasping arm and the distal-extension retentive framework are exposed beneath the teeth, which have been embedded in the dental stone used in half flasking (Fig. 2). Proper placement of the dental stone over the entire occlusal and the buccal and labial interproximal surfaces provides retention adequate to keep the denture teeth in proper position during the boil out and packing procedures. Because the top cap of improved dental stone

overrides the occlusal surfaces, a change in the vertical dimension of occlusion during the packing process is reduced to an absolute minimum.

The acrylic resin dough is packed from the lingual aspect (Fig. 3). After placement and lateral compaction, the resin dough is trial packed (Fig. 4). Excess acrylic resin is removed in the usual manner. A small amount of additional acrylic resin is added, and the denture flask is closed to a metal contact of the upper and lower members of the flask. The acrylic resin is cured according to the manufacturer’s directions, and the denture is deflasked and finished.

Re,4mnt reyue\1.\ to: DR. DON G. GARVER 1244 FORT WASHINGTON AVE.,

STE. M-l FORT WASHINGTON, PA 19034

Use of the personal computer to design processing conditions for improving dental die accuracv J

Henry Lee, Ph.D.* South El Monte. Calif.

A dental die is intended to be a replica of a tooth as exact as possible so that restorations made on it are as accurately fitting as possible.‘, ’

Dental dies are made from impressions of the natural tooth. Elastometric impression materials are polysilox- ane, polysulfide, or polyether formulas containing mono- mers, catalysts, and fillers. They are designed to possess a number of characteristics of properties, including fast set, low toxicity, and low shrinkage on setting (polymer- ization).3

Dental dies are made of dental stone or epoxy resins. Dental stone is selected for its low toxicity and hardness and because it expands slightly on setting. Epoxy resin die formulas are used because of their high hardness and low setting or polymerization shrinkage.3-6

This article outlines a process for improving the accuracy of most impression-die systems and shows how the process steps may be calculated manually or with the aid of a personal computer. Although the examples and discussion necessarily evolve around epoxy resin die materials,7s8 the concepts apply to other types of die materials as well.

*Prcsitlrnc. Ix? I’harmaceuricals.

THE JOURNAL OF PROSTHETIC DENTISTRY

REVIEW OF STANDARD PROCESS

The typical die is made in the following manner. 1. The impression material is mixed at room temper-

ature and placed in an impression tray. 2. The tray is placed in the patient’s mouth. The

patient’s teeth are at a temperature of about 32” C. 3. The impression is allowed to set and is then

removed from the patient’s mouth where it cools to room temperature.

4. Dental stone or epoxy resin material is mixed at room temperature and then poured into the impres- sion.

5. When the die material has hardened, forming the die, it is removed from the impression.

GRAPHIC PRESENTATION OF THE STANDARD PROCESS

The steps in making a die may be visualized on a graph showing the percent of dimension change in the vertical direction (Fig. 1). Above the horizontal temper- ature line is positive expansion and below the line is negative expansion (shrinkage).

The process of making a die as described may be viewed as a series of steps (Fig. 1) in changes of the dimension and temperature of the die.

141