The effect of a post-polymerization treatment on the leaching of methacrylic acid (MA) and benzoic acid (BA) from the reline resins [Kooliner (K), New Truliner (N), Ufi Gel hard (U), and Tokuso Rebase Fast (T)] was evaluated. Specimens of each material were divided into two groups: Group C (control) - left untreated; Group WB (water-bath) - immersion in water at 55 +/- 1 degrees C for 10 min. Specimens were placed in artificial saliva at 37 +/- 1 degrees C and, after 1-, 3-, 5-, 24-h and 3-, 7-, 14-, and 30-day intervals, aliquots were removed and analyzed using high performance liquid chromatography. Data were analyzed by using Wilcoxon, Mann-Whitney or Kruskal-Wallis tests (alpha = 0.05). At 1 h, the concentration of MA released from U control specimens was higher than those of the other ones, and decreased after 3 h. WB specimens released lower amounts of MA than control specimens only for material U, at the 1- and 3-h periods. For all control specimens, concentrations of leached BA progressively decreased within 5 h and from 24 h to the end. WB specimens released significantly lower amounts of BA than did the control groups. The highest concentration of MA was leached from control specimens of Ufi Gel hard. Water-bath post-polymerization treatment caused a significant reduction in elution of BA. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123:732-739, 2012