A rapid method for accurate cast duplication

Dental Technology DANIEL

H. GEHL and

A rapid

method

S. HOWARD

PAYNE,

for accurate

Associate

Editors

cast duplication

Robert M. Morrow, Colonel, USAF (DC),* and USAF (DC)** Honolulu, Hawaii and Lackland AFB, Texas

Kenneth

D. Rudd,

Colonel,

0

the need to duplicate dental casts arises in order to make more ccasionally, diagnostic casts when the patient is unavailable or to construct a backup prosthesis in the event of breakage. Normally, it is easy to make a duplicate cast in the dental laboratory by using preconditioned reversible hydrocolloid and duplicating flasks. However, in a dental office with minimal laboratory equipment, this procedure can be formidable. The following technique is effective for duplicating casts accurately in a minimal amount of time and requires only equipment and material readily available in most dental offices. TECHNIQUE 1. Carefully examine the cast to be duplicated, remove nodules of stones, and fill the defects with wax (Fig. 1). 2. Soak the cast for five minutes in clear slurry water. This is made by soaking artificial stone casts or particIes in tap water for 48 hours. The resultant solution is slurry water. 3. Place the cast on a smooth surface such as a glass slab. 4. Select an oversized rim-lock impression tray (Fig. 2). 5. Proportion normal-setting alginate (irreversible hydrocolloid) , and mix it with one quarter more water than is used for making impressions. A mix approximately that is double the amount used for a single impression provides an adequate volume of material. 6. Mix the alginate and water. A smoother mix is obtained when the alginate is mechanically spatulated under reduced atmospheric pressure; however, this is optional. 7. Load the tray with the impression material. 8. Remove excess slurry water from the cast surface with an air syringe, and *Chief,

Prosthodontics,

**Director,

Dental

Dental

Services,

Service, Hickam Wilford

Hall

AFB, Hawaii.

USAF

Medical

Center,

Lackland

AFB, Texas. 665

666

Morrow

j. Prosthct. Dmt. December, 1971

and Rudd

Fig. 1. The cast to be drrplicated ih carefully examined Fig. 2. An oversize tray is used.

Fig. 3. Placing

the impression

material

on the cast with

a brush reduces the chances of voids

forming in the impression. Fig. 4. The seated tray should not contact

the cast.

coat the cast with a thin layer of the impression material using a brush or finger. This step will minimize voids in the impression (Fig. 3) . 9. Invert the loaded tray on the cast, and allow the excess to flow down the sides of the cast. Do not allow the tray to contact the cast (Fig. 4). 10. Place additional amounts of the alginate rnix around the sides of the cast to form a uniform thickness.

Volume 26 Number 6

Rapid method of accurate cast duplication

Fig. 5. A mix of plaster of Paris reinforces

Fig. 6. The air syringe facilitates 11. 12. to form The

667

the impression.

removal of the cast.

Allow the impression material to set. Make a thin mix of plaster of Paris, and cover the tray and alginate w ,ith it a coating of about s/s inch in thickness (Fig. 5). setting time of the plaster of Paris may be accelerated by using a slurry r-type

668

Morrow

and Rudd

.J. Prosthet.

I)ecember,

11ent. 1971

Fig. 7. The master cast and its duplicate.

mixture of milky liquid obtained by grinding casts on the cast trimmer in place (Ii water for the mix. 13. After the plaster has set, remove the glass slab. 14. Remove the cast from the alginate using an air syringe to facilitate srpararion (Fig. 6). 15. Examine the impression critically, and if acceptable, pour a stone mis irtto it. Re sure to select a stone which is compatible with the alginate you are usin,g to insure a better surface on the duplicate cast.l 16. Separate the cast from the impression material after the stone mis has set for 45 to 60 minutes (Fig. 7) .2 SUMMARY Duplicate casts are frequently needed for diagnostic procedures, treatment planning, and documentation. A method was described which permits the dentist i.o duplicate casts using materials normally available in most dental offices. The Wsultant cast demonstrates acceptable ;~ccuracy and surface drtail. It is axiomatic. tc: state that the accuracy of casts is a prerequisite to clinical success. References 1. Morrow, R. M., Brown, C. E., Jr., Stansbury, B. E., delorimer, Rudd,

D.:

J. A., Powrll, J. M., and

Compatibility of Alginate Impression Materials and Dental PROSTHET. DENT. 25: 556-566, 197 I. 2. Rudd, K. D., Morrow, R. M., and Bangc, .L\. .A.: Accurate Casts, J. PROSTHET. 545-554, 1969. COLONEL

K.

MORROW:

PSC #3, Box 5841 APO SAN FRANCISCO, COLONEL

CALIF.

96553

RUDD:

PSC #8, Box 369294 LACKLAND AFB, TEXAS

78236

Stonrs. DEYI’.

J. 21: