KTR Dental

A Simplified Custom Impression Technique

Steven J. Sadowsky, DDS
University of Southern California School of Dentistry, Los Angeles, Calif

The use of a custome impression tray has long been recommended for improved accuracy of elastomeric impression materials. (1-3) Finger (4) noted that a thick layerof addition-polymerizing silicone causes distortion ofthe impression material because of the relatively high thermal coefficient. Eames et al (5) evaluated the effect of bulk on accuracy and demonstrated that the interface space of 2 mm produced the most accurate impressions when compared with larger spaces.

Autopolmerizing acrylic resin, thermoplasic resin, and light-polymerized acrylic resins have all been used to fabricate custom impression trays to limit the bulkof impression material. The 2-step, 2-mm relief space putty-wash impression technique was also shown to be an accurate alternative method for fabricating stone dies. (6) However, these techniques require additional materials and expense. Clear plastic matrices are routinely fabricated in preparation for fixed prosthodontic treatment. In fact, Preston (7) described the multiple benefits of using a polypropylene matrix, which included guides for esthetic control, waxing, preparation, and both the trial and definitive restoration. This article describes the use of such a matrix to dodify a stock tray, precluding the need for a custom tray or putty-wash system.

PROCEDURE

1. Make a vacuum-formed, 0.20-inch-thick, clear template (Buffalo Dental Mfg Co, Syosset, NY) on the diagnostic cast using the vacuum adapter (Vacuum Forming Machine #101; keystone Industries, Myerstown, Pa).
2. Cut the template at the interproximal junction of the tooth or teeth to be prepared, leaving 3 mm of matrix beyond the cervical finish line on the buccal andlingual surfaces, for correct seating.
3. After syringing the wash impression material (Star VPS; Danville Engineering, San Ramon, Calif) on the preparation(s), fill the internal portion of the adapted template with higher-viscosity impression material and seat over the preparation(s) (Fig. 1).
4. Fill the stock tray with higher-viscosity impression material and seat intraorally.
5. Allow the material to polmerize according to the manufacturer's recommendations (fig. 2).

REFERENCES

1. Phillips RW. Physical properties and manipulation of rubber base impreeion materials. J Indiana State Dent Assoc 1968;47:105-8
2. Williams PT, Jackson DG, Bergman W. An evaluation of time-dependent dimensional stability of eleven elastomeric impression materials. J Prosthet Dent 1984;52:120-5
3. Chee WW, Donavan TE. Polyvinyl siloxane impression materials: A review of properties and techniques. J Prosthet Dent 1992;68:728-32.
4. Finger WJ. Significance of filler content to properties of silicone impression materials. Dent Mater 1988;4:33-7
5. Eames WB, Sieweke JC, Wallace SW, Rogers LB. Elastomeric impression materials: effect of bulk on accuracy. J Prosthet Dent 1979;41:304-7
6. Nissan J, Laufer BZ, Brosh T, Assif D. Accuracy of three polyvinyl siloxane putty-wash impression techniques. J Prosthet Dent 200;83:161-5.
7. Preston JD. A systematic approach to the control of esthetic form. J Prosthet Dent 1976;35:393-402.

Copyright © 2005 by The Editorial Council of The Journal of Prostetic Dentistry. 2005;94:468-9

Reprinted with premission from Steven J. Sadowsky, DDS