In prosthodontics, the fabrication of an acceptablerestoration relies on the use of a cast that exactly resem-bles the prepared tooth. Inaccurate restorations canresult when an unacceptable stone cast is used.1 A com-mon cause for inappropriate casts are fractures that canoccur during separation of the cast from an elastomer-ic impression, especially made in polyether, as a resultof the stiffness of the material.2,3 Fractures can be relat-ed to: (1) undercuts, (2) poor removal procedure, (3)failure to follow manufacturer’s instructions (for exam-ple, stone not properly set), or (4) rigidity of theimpression material.

This article describes a simple and inexpensive pro-cedure to prevent fracture of stone teeth when mastercasts are removed from elastomeric impressions. Theprocedure is easily accomplished with soapy slurrywater. Slurry water is defined as a saturated calcium sul-fate solution made by placing stone debris in a contain-er of water.4 The soapy water lubricates the impressionmaterial and the stone cast facilitating the removal ofthe cast.

PROCEDURE

1. Examine impression and determine its accuracy. 2. Follow adequate disinfection procedures.3. Box the elastomeric impression5 (Fig. 1).4. Mix a proper amount of dental stone according to

the manufacturer’s instructions.5. Pour the dental stone into the impression.6. Allow the stone to set.7. After the cast has set, remove boxing materials.8. Gently pry the impression with a laboratory knife

creating a 1.5 to 2.0 mm separation between thecast and the impression material (Fig. 2).

9. Immerse the poured impression in a clean rubberbowl filled with a mixture of slurry water and liq-uid dishwashing soap (Fig. 3).

10. Allow the impression to soak in this soapy waterfor at least 10 minutes.

11. The cast is then easily removed, soaked in pureslurry water for a few minutes, and trimmed. Allow

Procedure to prevent cast breakage during separation from elastomericimpressions

Daniel Galindo, DDS,a and Michael E. Haganb

University of Rochester, Eastman Dental Center, Rochester, N.Y.

This article describes a quick and simple procedure for removing dental stone casts from elastomericimpressions. Frequently, dental stone casts break at the time of separation because of the rigidity ofthe impression material. The materials used in this technique are inexpensive and easy to use. Whenthis method is properly used, it simplifies the removal of the cast from the impression, decreasing thechance of fracture of the cast. (J Prosthet Dent 1999;81:37-8.)

aResident, Department of Prosthodontics. bLaboratory Technician, Department of Prosthodontics.

JANUARY 1999 THE JOURNAL OF PROSTHETIC DENTISTRY 37

Fig. 1. Elastomeric impression is boxed with Mortite materi-al and boxing wax.

Fig. 2. Boxing material is removed. Laboratory knife is usedto gently separate cast from impression material.

the cast to dry and prepare for prosthodontic pro-cedures (Fig. 4).

SUMMARY

This procedure permits quick and easy separation ofcasts from elastomeric impressions. Slurry water anddishwashing soap are inexpensive and common materi-als found in a dental laboratory. The soapy water flowsinto the space between the cast and the impression,lubricating the 2 surfaces. After soaking for at least 10minutes, the cast is removed from the impression withthe use of minimal force. Proper use of this procedurewill help improve the quality of poured casts, prevent-ing the occurrence of tooth fractures and saving timeand materials.

REFERENCES

1. Rudd KD, Morrow RM, Bange AA. Accurate casts. J Prosthet Dent1969;21:545-54.

2. Moon MG, Holmes RG. Modifications of the impression to prevent castbreakage. J Prosthet Dent 1997;77:323-5.

3. Anusavice KJ. Phillips’ science of dental materials. 10th ed. Philadelphia:WB Saunders; 1996. p. 139-76.

4. Rudd KD, Morrow RM, Brown CE, Powell JM, Rahe AJ. Comparison ofeffects of tap water and slurry water on gypsum casts. J Prosthet Dent1970;24:563-9.

5. Galindo D, Graser GN. A simple procedure for boxing elastomericimpressions. J Prosthet Dent 1997;78:531-2.

Reprint requests to:DR DANIEL GALINDO

DEPARTMENT OF PROSTHODONTICS

UNIVERSITY OF ROCHESTER

EASTMAN DENTAL CENTER

625 ELMWOOD AVE

ROCHESTER, NY 14620-2989

Copyright © 1999 by The Editorial Council of The Journal of ProstheticDentistry.

0022-3913/99/$8.00 + 0. 10/1/94011

THE JOURNAL OF PROSTHETIC DENTISTRY GALINDO AND HAGAN

38 VOLUME 81 NUMBER 1

Fig. 3. Poured impression is immersed in clean rubber bowlfilled with solution of slurry water and dishwashing soap.Impression must be submerged in this solution for at least 10minutes. Fig. 4. Cast is easily removed without breakage of teeth.