An investigation of the rheological properties of 10 vinyl-polysiloxane impression materials

Shark fin test and impression quality: A correlation analysis

OBJECTIVES

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Polymers in dentistry

There is a wide choice of materials available for restorative dentistry covering a range of requirements. Fundamental knowledge about the properties of the polymers in use in dentistry is an advantage as it provides information relevant to clinical practice. Dentistry, perhaps, has the unique distinction of using the widest variety of materials, ranging from polymers, metal and metal alloys, ceramics, inorganic salts and composite materials. In the present paper, polymers and polymer composites used directly or indirectly for restorations, prostheses or for production of appliances in dentistry is discussed.

The effect of a shear load on the viscosities of 10 vinyl polysiloxane impression materials

The viscosities of 10 vinyl polysiloxane impression materials with and without the effect of a shear load were studied. Samples of each impression material were divided into two groups. An initial shear load of 5.12 rpm was applied to group A samples for 10 seconds. No shear load was applied to group B samples during the same interval of time. The viscosities of two groups of samples were compared at 60 seconds. Results indicated that there were statistically significant differences among the group A or B samples of the impression materials. There were no statistically significant differences between the group A and B samples of five impression materials. The group A samples displayed significantly lower viscosities than group B samples for two impression materials. The group A samples also displayed significantly higher viscosities than group B samples for three impression materials. It was concluded that the effect of a shear load had no consistent effect on the viscosities of a group of vinyl polysiloxane impression materials.