A rubber-base impression technique for fixed partial dentures

A RUBBER-BASE IMPRESSION TECHNIQUE FOR FIXED PARTIAL,

DENTURES

JOHN L. YODER, B.S., D.D.S.,” AND KEITH

E. THAYER,

State University

Iowa City, Iowa

of Iowa,

College

of

Dentistry,

B.A., D.D.S., MS.**

who usesrubber-base impression materials must give active thought T to the technique of making a good impression. Every part of the impression proHE DENTIST

cedure must be sufficiently clear in his mind to make the actions meaningful. This article describes a basic procedure for the use of rubber-base impression material for fixed partial denture impressions. CONSTRUCTING

THE

INDIVIDUALIZED

TRAY

An impression of the complete dental arch is made in a custom-made tray for easy articulation of casts and for good results in the finished restoration. The extent of the tray is outlined with a pencil on the diagnostic cast (Fig. 1) and includes all of the crowns of the teeth and the soft tissue for 3 to 4 mm. gingivally to the teeth.l Extreme undercuts in the casts should be avoided in the outline for the tray. A spacer is placed on the diagnostic cast so the impression material will be maintained at the desired thickness of 2 mm. inside the tray2s3when it is in position in the mouth. The spacer is built up by dipping the cast into melted wax or by adapting a layer of baseplate wax or wet asbestos over the cast. The spacer is trimmed to the penciled outline on the cast. Three widely separated stops located outside the area of the restoration are necessary to form a tripod for the support, stability, and positioning of the tray” (Fig. 2). The stops are formed by cutting holes in the spacer at the places selected for stops and by allowing the tray material to be forced into the holes against the cast. When the tray is transferred to the mouth, the stops will rest on the teeth or soft tissue at the desired places. The tray is made from self-curing acrylic resin tray material. It must be sufficiently thick to prevent distortion and should extend over the spacer and contact the soft tissue so that the impression material will be adequately confined. When the tray material has cured, the tray is trimmed, the wax spacer is removed, and the edgesare smoothed (Fig. 3). TISSUE

RETRACTION

The gingival tissue must be retracted after the abutments have been prepared. The items for adequate, controlled retraction include an epinephrine-impregnated *Instructor, Health Service **Associate

Department of Crown Training Grant DT35. Professor and Chairman,

and

Bridge;

Department 339

Recipient of Crown

of Fellowship and Bridge.

Funds,

U. S. Public

340

YODER

Fig.

AND

1.

Fig.

Fig.

Fig.

I.-A

penciled

outline

J. Pros. Den. March-April, 1962

THAYER

2.

3.

of the extent

of the acrylic

resin

tray

is drawn

on the diagnostic

oast. Fig. 2 .-The finished tray. Fig. 3.-The

wax

spacer

completed

is removed acrylic

resin

in tray

selected

places

to provide

is ready

to try

in the mouth.

spaces

for

stops

in

the

RUBBER-BASE

IMPRESSION

341

TECHKIQI’E

cord, instruments for packing the cord into the gingival crevice, and sufficient equipment to keep the tissue dry (Fig. 4). The tissue to be retracted is kept dry by cotton rolls, gauze sponges, and a saliva ejector. When the retracting cord becomes wet, it will tend to swell and be more difficult to place in the crevice, and the epinephrine will be diluted. Also, if the cord becomes moist, it will tend to slip out of the crevice. The moisture of the tissue is enough to activate the epinephrine in the cord. The cord is available in two ply or four ply continuous lengths and may be cut into shorter lengths as needed. The strands may be separated as desired. A. single strand is convenient for packing into a small, tight gingival crevice. For larger, less resilient crevices, two, three, or four strands may be placed in one sin-. gle application.

Fig. 4.-The cords used for gingival tissue retraction. The and placing the cord into the gingival crevice are ready for use.

materials

for

drying

the

tissues

A thin blade, blunt end instrument, such as one of the plastic ones, is used to pack the cord into the crevice. Care must be exercised to prevent laceration of the gingival tissue. The end of the cord is tucked into the depth of the gingival crevice, and the rest of the cord is packed around the entire circumference of the tooth. To retract firm tissue, the cord is twisted, held tightly against the neck of the tooth, and packed into the crevice. The cord is left in place for 3 to 5 minutes to produce adequate retraction of the tissue and to control hemorrhage (Fig. 5). The cord is removed, and the tissue is flushed with warm water and dried gently with a few short blasts of warm air. The preparations are examined, and the finish lines are appraised and altered if necessary. If hemorrhage is severe or if retraction is insufficient, the retraction procedures are repeated. A single strand of the retraction cord is allowed to remain in the bottom of the crevice while the impression is made if the crevice i:j deep.5

342

YODER

Fig.

5 .-The

retraction

cord

is placed

AND

THAYER

in the

gingival

J. Pros. Den. March-April, 1962

crevice

Fig.

Fig.

Fig. 6.-The Fig. 7.-The the syringe.

around

the

prepared

molar.

6.

7.

impression materials are measured syringe material is aspirated from

onto the the mixing

pads in preparation pad directly into

for mixing. the barrel of

yLl~r

MAKING

‘2”

RUBBER-BASE THE

IMPRESSION

343

TECHNIQUE

IMPRESSION

The previously formed acrylic resin impression tray is observed in the mouth, and any undesirable extension or impingement upon the soft tissue is relieved. The tray is dried thoroughly, and a thin coating of tray adhesive is applied to the inside of the tray. The entire surface of the tray to be covered by impression material, including the borders, is coated with the adhesive. The adhesive is allowed to dry for at least 10 minutes, because drying is essential for adherence of the rubber-base impression material to the tray. The drying may be hastened by a few blasts of air. The double mix technique is used. A light-bodied rubber-base impression material is used for syringe application to the tooth preparations, and a heavy-bodied material is used for filling the tray. Both of these materials are measured and mixed according to the manufacturer’s directions’ (Fig. 6). Any deviation from these directions will alter the setting characteristics of the material and may result in a faulty impression.

Fig.

8.

Fig.

Fig. S.-The tip of the syringe nozzle is placed into the full material is allowed to build up, forcing it ahead of the tip. Fig. 9.-The inner surface of the impression must be accurate

9.

depth after

of the removal

crevice, from

and

the

the mouth.

344

YODER

Fig.

IO.-An

indexed

matrix

AND

J. Pros. Den. March-April, 1962

THAYER

base is used to permit

reassembling

of the dies.

The impression material is mixed to a homogeneous consistency by either spatulation or stirring. The blade of the spatula is covered with the brown paste (the accelerator). By drawing the brown into the white paste (the base), it will be easier to mix the material and clean the spatula later. The mixing time is approximately 45. seconds for most rubber-base impression materials. The syringe material is mixed and aspirated directly from the pad (Fig. 7) or from a dappen dish into the barrel of the syringe. The tray material is mixed in a similar manner as the syringe material, and the tray is loaded by picking up the entire mass of the mix on the spatula. All teeth and the surrounding tissues must be thoroughly dry. The filled syringe is carried to the mouth, and the tip of the syringe nozzle is placed into the deepest part of the most distal crevice (Fig. 8). The impression material is injected into the crevice and around the circumference of the tooth by continuous pressure on the syringe until the abutment is completely covered. The tip of the nozzle of the syringe is kept-in contact with the tooth and buried in the rubberbase impression material at all times. The material is pushed ahead of the nozzle

Fig.

11 .-The

dies are separated

into units

of convenient

size.

Volume Number

12 2

RUBBER-BASE

IMPRESSION

TECHNIQUE

345

rather than to allow the tip of the syringe to drag it along. With continuous pressure, the syringe is moved to the next abutment tooth, and the process is repeated until all preparations are covered. Most air pockets are eliminated by careful use of the syringe. A small amount of the syringe material is ejected onto the teeth and under the lip in the opposite dental arch to serve as a guide to the progress of the setting of the material. The loaded tray is carried into place, seated with a firm, direct pressure, and then merely stabilized to prevent its movement while the impression material sets. Excess pressure on the tray while the material cures will cause distortion of the impressions. The curing is complete as soon as the test material does not retain an indentation from an instrument.l However, the impression is left in the mouth for an additional 2 or 3 minutes. A period of 10 minutes from the start of the mix is sufficient time for most rubber-base materials to set. 3,6 The setting time of the rubberbase materials is affected by humidity and temperature.1~2~6 An increase in either factor will shorten the time required for setting. After the impression material has set completely, the tray is removed in such a way as to minimize distortion and prevent tearing. The impression is rinsed and dried gently so that the inner surface may be examined for correctness (Fig. 9). A faulty impression may be due to air bubbles, incomplete set of the material, insufficient impression material, torn edges, creases, incomplete mixing, nonadhesion of the material to the tray, or too little or too much bulk of the material in some locations. The finish lines of the preparations should be clearly discernible in their entirety. CONSTRUCTING

THE

DIES

The die material is mixed following the manufacturer’s recommendations and is vibrated into the impression. The dies and cast should be formed in the impression within 1 hour for accurate results.? We use an indexed matrix base (Fig. 10) which permits separation and reassembly of the cast and dies with all parts held rigidly in place. After the die material has set, the unit is separated into individual dies (Fig. 11) . The dies are trimmed carefully to expose the finish lines of the abutment preparations and may be manipulated easily for unobstructed vision to all surfaces. COMPLETING

THE

FIXED

PARTIAL

DENTURE

The fixed partial denture is completed on the dies, and the occlusion is observed on the articulator. After completion, the accuracy of the fit is checked closely on the dies. The final adjustments of the occlusion are made in the mouth. SUMMARY

Mercaptan rubber is an impression material that can be used for making single or multiple restorations. A knowledge of the properties of the material and the use of a sound procedure aid in obtaining satisfactory and consistent results.

346

YODER

AND

THAYER

J. Pros. March-April,

Den. 1962

REFERENCES

1. Skinner, 2. 3. 4. 5. 6.

E. W.: The Properties and Manipulation of Mercaptan Base and Silicone Base Impression Materials, D. Clin. N. America, pp. 685-697, November, 1958. Phillips, R. W.: Physical Properties and Manipulation of Rubber Impression Materials, J.A.D.A. 59 ~454-458, 1959. Sturdevant, C. M.: Mercaptan Rubber Impression Technique for Single and Multiple Restorations,. D. Clin. N. America, pp. 699-711, November, 1958. Johnston, J. F., Phillips, R. W., and Dykema, R. W.: Modern Practice in Crown and Bridge Prosthodontics, Philadelphia, 1960, W. B. Saunders Company, pp. 200-207. Hailey, R., Jr.: The Use of Rubber Base Impression Materials for Dependable Results, D. Digest 63:394-400, 1957. Miller, W. A. C., Jr., Hansen, W. C., Dickson, G., and Sweeney,. W. T.: Physical PropertlmesOof Synthetic-Rubber-Base Dental Impression Materials, J.A.D.A. 60:211-223,

7. Fournier, D: F. : The New Rubber Base Impression Materials : The Importance Pour-up of the Impressions, Arizona D. J. 5:76-79, 1959. STATE UNIVERSITY OF IOWA COLLEGE OF DENTISTRY IOWA CITY, IOWA

of an Early