Changes in retentive force in each test substance over time (Figs. 
There was no significant difference in the retentive force of the control and DW immediately after application and after 10, 20, and 30 min (p < 0.05). PK showed significantly lower retentive force after 30 min than immediately after application (p < 0.05). Moreover, no significant differences were found among the retentive forces immediately after application and at any time point, except at 30 min (p < 0.05). NP has significantly lower retentive force immediately after application than after 10, 20, and 30 min; however, there were no significant differences among the other time points (p < 0.05). BT has significantly higher retentive force immediately after application than after 10, 20, and 30 min; however, there were no significant differences among the other time points (p < 0.05).