IN-VITRO STUDY OF THE NUMBER OF SURFACE-DEFECTS IN MONOPHASE AND 2-PHASE ADDITION SILICONE IMPRESSIONS

Statement of problem. Monophase addition-cured silicone impression mat erials in stock traps are considered to be alternatives to two-phase s ystems used with custom traps. Purpose. This study compared the number of surface defects in addition-cured silicone impressions recorded wi th monophase materials in stock trays and two-phase impressions in cus tom trays. Methods. The number of voids visible on the surface of impr essions recorded in vitro were counted. Two monophase impression mater ials (President Monobody system 75, Bayer Cutter) in stock trays were compared with impressions recorded with two-phase addition silicone ma terials (President Plus light-body/regular-body and Zhermack Elite lig ht-body/medium-body) in custom trays. A total of 200 automixed impress ions, 50 with each material, were recorded of 50 dentoform molar teeth prepared for full veneer crowns. Impressions were examined for surfac e voids anywhere on the prepared part of the tooth by a trained examin er. Results. Mean number of voids observed for the monophase impressio ns were 3.0 +/- 2.2 for President Monobody system and 3.4 +/- 2.0 for Payer Cutter system. Mean number of voids for the two-phase materials were 0.8 +/- 1.0 for President Plus, and 1.0 +/- 1.1 for Zhermack Elit e. No significant differences were observed for number of voids betwee n the monophase materials or between the two-phase systems (ANOVA and Neuman-Keuls, p > 0.05). However, both two-phase materials in custom t rays had significantly fewer surface voids than the two-monophase mate rials (ANOVA and Neuman-Keuls, p < 0.001) used in stock trays. Conclus ion. Monophase addition-cured impression materials in stock trays carr ies an increased risk of void formation on the surface of the impressi on when compared with two-phase addition silicone materials in custom trays.