Shark fin test and impression quality: a correlation analysis

To evaluate the correlation between the shark fin test and the dimensional accuracy of impressions, surface detail reproduction of impressions and rheological properties of impression materials within the manufacturer's recommended working time.

Four chemically different types of impression material (Flexitime: VPS; Fusion: Polyether/VPS blend; Impregum: classical Polyether; P2: new Polyether) were subjected to the shark fin test as well as three other test regimes. Dimensional accuracy was determined as being the discrepancy in diameter between a steel master cone and stone dies poured from impressions taken from the steel master cone at defined 30s intervals after mixing within the manufacturer's recommended working time. Surface detail reproduction was calculated as being the difference in average arithmetic roughness (Ra) between a ground dentin surface and the corresponding area of the impressions, taken at the same 30s intervals. Phase angle and storage modulus were measured using a rotational rheometer. Spearman's Rho was used for correlation analysis.

With respect to the majority of impression materials used, significant correlations mainly exist between shark fin test data, phase angle and storage modulus. No correlation was found between the results of the shark fin test versus dimensional accuracy, respectively, surface detail reproduction.

Results obtained from the shark fin test within the manufacturer's recommended working time do not allow predictions regarding the dimensional accuracy or surface detail reproduction of impressions as clinically relevant material characteristics.