Objectives: The class A alginates exhibit good properties of dimensional accuracy and reproduction of details, comparable to other impression materials used to produce accurate impressions for fixed prosthesis. Besides, they are cheaper an easier to use. The purpose of this investigation was too assess the accuracy of Class A alginates for fixed prosthodontic applications. Methods: A master die was made of Myerson resin representing a preparation for a porcelain-fused-to-metal-restoration on a maxillary central incisor. A metal coping was made on it, with a 71% gold alloy. The master die was duplicated eight times with two different Class A alginates (Neocolloid and Aroma fine) and the sixteen impressions were immediately poured with a Type IV dental stone (GC Fujirock Pastel Yellow). In order to evaluate marginal fit of the coping, a device was developed to facilitate reproducible photographing of the margins, through a microscope at 50 X, with a digital camera. The marginal fit analysed using software connected to the microscope. before on the master die, then on the sixteen dies stone. The marginal precision measured photographically every 20 degrees around the specimens. The photographs were examined independently by two observers to assess the marginal gaps between the metal coping and the master die and the two groups of stone dies. Results: The average gap found between the master die and the metal coping was 60.6 micron. The average gaps found between each die stone and the metal copingwere 78.8 micron, using Neocolloid Alginate and 165.8 micron using Aroma fine. Conclusions: The results of this in vitro investigation show that the combination of Neocolloid alginate and GC Fujirock PastelYellow is more accurate than that the same stone and Aroma fine. This combination may be effective for fixed prosthetic applications.

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