Dental composites used to fill cavities will decay over time. The article “In vitro Aging Behavior of Dental Composites Considering the Influence of Filler Content, Storage Media and Incubation Time” (PLoS ONE, April 9, 2018) reported on a study to measure the hardness (MPa) of a particular type of resin after 14 days stored in artificial saliva, lactic acid, citric acid, or 40% ethanol.

Use a Kruskal–Wallis test with significance level .05 to determine whether true average hardness differs by liquid medium.

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Saliva 542.18 508.31 473.44 514.33 488.41 Lactic 478.99 501.15 488.97 463.68 471.14 Citric 427.97 388.59 378.01 341.61 395.12 Ethanol 482.96 451.48 436.69 424.42 465.64 Saliva 477.46 501.71 513.65 471.46 421.90 Lactic 568.14 494.15 494.99 483.89 520.33 Citric 433.59 353.03 344.90 387.09 501.81 Ethanol 387.59 322.55 277.84 367.36 385.75