The smear layer groups were compared by thirds’ mean rank using the Kruskal-Wallis test.

The smear layer groups were compared by thirds’ mean rank using the Kruskal-Wallis test.采用克鲁斯卡尔-沃利斯检验（Kruskal-Wallis test），按平均秩的三等分对玷污层（smear layer）各组进行比较。