dental materials 25 ( 2 0 0 9 ) 662–671 available at www.sciencedirect.com journal homepage: www.intl.elsevierhealth.com/journals/dema Effect of water-bath post-polymerization on the mechanical properties, degree of conversion, and leaching of residual compounds of hard chairside reline resins Vanessa M. Urban a , Ana L. Machado b,* , Carlos E. Vergani b , Eunice T. Giampaolo b , Ana C. Pavarina b , Fernando G. de Almeida c , Quezia B. Cass c a Department of Dentistry, Ponta Grossa State University, Ponta Grossa, Paraná, Brazil b Department of Dental Materials and Prosthodontics, São Paulo State University, Araraquara, São Paulo, Brazil c Department of Chemistry, São Carlos Federal University, São Carlos, São Paulo, Brazil article info Article history: Received 25 January 2007 Received in revised form 23 September 2008 Accepted 22 October 2008 Keywords: Hard chairside reline resins Residual monomer Plasticizer HPLC Post-polymerization Hardness Flexural strength Degree of conversion abstract Objectives. This study evaluated the effect of water-bath post-polymerization at 55 ◦ C for 10 min (WB) on the content and leaching of residual compounds, degree of conversion, flex- ural strength, and hardness of hard chairside reline resins (Kooliner: K, New Truliner: N, Ufi Gel hard: U, and Tokuso Rebase Fast: T). Methods. Leaching experiments were made by storing specimens (n = 48) in artificial saliva at 37 ± 1 ◦ C and analyzing residual monomers and plasticizer by HPLC. Analysis of residual monomer and plasticizer content (n =48) was also made by HPLC. Degree of conversion (n =40) was analyzed by using FT-Raman spectroscopy. A 3-point loading test was used to evaluate the flexural strength of the specimens (n = 80). One fragment of each flexural test specimen was then submitted to Vickers microhardness test. Results. WB produced a significant decrease (p < 0.050) in the amount of residual compounds eluted from the materials within the first hour of immersion. With the exception of material U, WB decreased the duration of release of the residual compounds evaluated. All materials evaluated exhibited significantly (p < 0.050) lower values of residual monomer and plasti- cizer (material N) after WB compared with the control groups. WB increased the degree of conversion of K and T resins and the hardness of N, K, and T resins (p < 0.050). Only material K showed an increase in flexural strength after WB (p < 0.050). Significance. Immersion of relined dentures in water at 55 ◦ C for 10 min can be used to reduce the amounts and duration of release of residual compounds and improve mechanical prop- erties of some of the materials evaluated. © 2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. 1. Introduction Continuing bone resorption leads to a poor fit and a lack of support of the denture base. Therefore removable prosthe- ∗ Corresponding author at: Department of Dental Materials and Prosthodontics - Araraquara Dental School, R. Humaitá, no 1680, Araraquara, SP, CEP: 14801-903, Brazil. Tel.: +55 16 3301 6410; fax: +55 16 3301 6406. E-mail address: cucci@foar.unesp.br (A.L. Machado). ses may require periodic relining to reestablish tissue support for the denture base. Some autopolymerizing acrylic resins have been developed specifically as hard chairside reline resins for relining dentures directly in the mouth [1,2]. These 0109-5641/$ – see front matter © 2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2008.10.017