An experimental and theoretical study of the effect of sample thickness on the Shore hardness of elastomers

Objective ore hardness test is a quick and convenient way to measure hardness of elastomers. The test specifies that the specimen should be at least 6 mm thick; however, published work in the literature indicates that workers often use much thinner samples. The aim of this study was to investigate the effect of thickness on the measured hardness of a range of dental elastomers and develop a theoretical relationship to predict the effect. s al silicone elastomers were selected to give a range of hardness values. Shore A scale hardness measurements were made on standard thickness samples, and those of lower thicknesses. A theoretical analysis was derived, whereby the effect of thickness of the sample on its measured hardness can be predicted and was tested using the results obtained. s sults show reasonable agreement between theoretical and experimental values. The measured Shore hardness increased inversely with thickness, the effect being most pronounced with thin samples. Results ranged from 66.3 ± 1.6–80.9 ± 0.4 for 1 mm thick to 35.0 ± 1.7–69.1 ± 0.6 for the 6 mm thickness. Ratio of the measured hardness of 1 mm/6 mm ranged from 1.97 for the softest material to 1.17 for the hardest. icance ements obtained with a Shore A hardness tester on samples of less than the specified 6 mm thickness will give erroneously high values, the error being greater as thickness decreases. The theoretical treatment proposed gives a basis on which data obtained from studies that used thinner specimens can be better analysed.