Abstract
Purpose To determine the hardness and Young's moduli of both commercial and experimental vinyl poly siloxane (VPS). Methods The purpose of this study was to develop a medium-bodied experimental (Exp-I, II, III, IV, and V) VPS impression materials and to analyse their effects on hardness and Young's modulus and compare them with three commercial VPS materials (Aquasil, Elite, and Extrude) using Shore A hardness tester. Measurements were recorded after 1, 24, 72, and 168 hours of mixing. The results were analysed with one-way ANOVA and post hoc Tukey's test using the SPSS PASW statistical 22 software. Results Commercial and experimental vinyl polysiloxane exhibited higher Shore A hardness values with time (i.e., 1 hour after mixing, 24 hours after mixing, 72 hours after mixing, and 1 week after mixing). All Comml and Exp VPS demonstrated a significant increase (ANOVA, p < 0.05) in hardness at increasing time points. Generally, all commercial VPS exhibited significantly higher values for Shore A hardness compared to all Exp formulations. For commercial products, Elt M presented significantly highest values at all-time points followed by Aq M then Extr M. Exp-I was significantly harder than all other Exp VPS at all-time points. Young's modulus values were directly related to Shore A hardness; materials with higher Shore A hardness values had higher Young's moduli. Conclusion Continued polymerisation of elastomeric impression materials results in increased hardness over time. Hardness, Young's moduli, and rigidity of the set commercial and experimental VPS materials were within the required limits. Shore A hardness and Young's moduli were directly proportional to each other, and commercial and experimental materials had enough rigidity to contain the stone during pouring.
Highlights
The ability of a material to resist surface indentation or penetration is called its hardness [1]
At all-time points studied for commercial products, Elite HD monophase (Elt M) showed the highest values followed by Aquasil ultra monophase (Aq M) Extr M
The novel experimental vinyl polysiloxane impression materials had comparatively lower hardness and Young’s modulus yet these materials were within the normal range of stain-in-compression according to ISO4823 (2007) [15]
Summary
The ability of a material to resist surface indentation or penetration is called its hardness [1]. A variety of tests are available to measure hardness. These tests are defined by the geometry and dimensions of their indenters and the amount of load applied. The load per unit surface area of the indentation gives the hardness number [2, 3]. Knoop, Vicker, Rockwell, and Barcol are used to measure the hardness of rigid materials such as metals, alloys, and rigid. These methods cannot be used for elastic materials, such as elastomers, where the deformation is elastic rather than permanent [1]
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