MAINTENANCE OF EQUILIBRIUM IN REVERSIBLE HYDROCOLLOID IMPRESSIONS

III. A REPORT ON TESTS MADE WITH FIVE STOCK IMPRESSION MATERIALS

¹ Beverly Hills, Calif.

1. In this series of papers, tests following standard procedures have been made with 7 stock reversible hydrocolloid impression materials, and 4 materials supplied by manufacturers, representing 8 different brands.

2. Reversible hydrocolloid impression materials must produce accurate control dies when impressions are poured immediately to be considered acceptable.

3. Reasonable latitude of time between making the impression and pouring the model for accuracy is desirable, but the manufacturer should state specifically the time limit such accuracy may safely be maintained.

4. The materials by brands divide equally into a group which tends to contract at a critical point and a group which tends to expand at a critical point.

5. After the critical point is reached, the contracting group produces oversized dies. The expanding group produces undersized dies.

6. Since natural agar is the base for all reversible hydrocolloid impression materials, a study of fillers used which may cause expansion or contraction is indicated.