School of Dental Medicine, University of Zagreb, Croatian Dental Society - Croatian Medical Association
Abstract
Type IV gypsum (stone gypsum) is an essential material in prosthetic treatment. Improper handling can change hardness, expansion and compressive strength and it is the most common reason for inaccurate casts. In that case even the most perfect impressions will result in inadequate prosthetic treatment. Using optical instruments-digital camera (2.5 million pixels) and digital microscope we attempted to identify the visual appearance of inadequate casts and relate them to specific causes. All casts were poured in highly controlled conditions and only one factor, whose influence we tried to determine, was changed during the procedure. Most common mistakes are: outdated gypsum, incorrect powder to water ratio, mixing without a vacuummixer, pourring without a vibrator and etching by alginate acid. All the mistakes were visualised, easily recognized and categorized by using digital optical equipment
