#ALGINATE IMPRESSION RECORDS NDT PC#

#ALGINATE IMPRESSION RECORDS NDT PC#

Twenty seconds before the end of the respective working time of each material, a clean test die sprayed with poly-tetrafluoro-ethylene separating agent (Dri-Film Lubricant, Synco Chemical Corp, Bohemia, NY) was centered and pressed into the alginate-filled PC ring mold. The ring mold was then slightly overfilled, and the alginate vibrated within the ring mold for 10 seconds (Lab Vibrator Model HV-1, Healthco Inc, Boston, Mass) to reduce air incorporation into the impressions. 15 The PC ring mold was then placed on a 60 × 60-mm glass plate sprayed with a separating agent to prevent the alginate from sticking to the glass. When a ring mold was reused, any remaining adhesive was removed with alcohol before a fresh coat of adhesive was applied, to ensure optimal adhesion. 14 The mixed alginate was then placed into a polyvinyl carbonate (PC) ring mold (6 × 26 mm ) coated with tray adhesive (Hold, Water Pik Inc, Fort Collins, Colo) and allowed to dry for at least 4 minutes, as indicated by the manufacturer.

Distilled rather than tap water was used because potential ion concentrations that might be present in tap water could possibly interfere with alginate chemical reactions. The alginate powder was mixed with water utilizing an electric alginate mixer (Alginator, Cadco Dental Products, Oxnard, Calif). The necessary amount of water was measured with the cylinder provided by each manufacturer. Before scooping, the powder was fluffed (container tipped back and forth twice) to reduce powder compaction. Two scoops of alginate were used for each impression, using the scoop provided by each manufacturer. Although recent investigations included extended-storage alginate materials, 10– 12 these investigations evaluated impression dimensional change indirectly via measurements on gypsum casts, which incorporate the confounding variable of gypsum expansion. 5, 11 These companies will accept extended-storage alginate impressions, which then are poured and the resultant casts scanned or digitized. These materials can be used for any alginate application but in particular are recommended by the digital model companies. 3, 8– 10 Recently, extended-storage alginate impression materials have been marketed with claims that the materials exhibit dimensional stability for up to 100 hours. In previous studies evaluating the effect of storage time, 8– 11 the recommended maximum storage time before pouring of a conventional alginate impression with gypsum is typically as soon as possible but no longer than 30 minutes. 1, 4– 7 Consequently, alginate impressions are not dimensionally stable, leading to decreased dimensional accuracy over time. In addition to water evaporation, impression shrinkage is related to syneresis and associated water exudation onto the impression surface caused by continuing contraction of the colloidal skeletal network even in 100% humidity.

Alginate impression records ndt