polymers Article Release and Recharge of Fluoride Ions from Acrylic Resin Modified with Bioactive Glass Zbigniew Raszewski 1 , Danuta Nowakowska 2 , Wlodzimierz Wieckiewicz 2 and Agnieszka Nowakowska-Toporowska 2, *   Citation: Raszewski, Z.; Nowakowska, D.; Wieckiewicz, W.; Nowakowska-Toporowska, A. Release and Recharge of Fluoride Ions from Acrylic Resin Modified with Bioactive Glass. Polymers 2021, 13, 1054. https://doi.org/10.3390/ polym13071054 Academic Editor: Evangelia Vouvoudi Received: 20 February 2021 Accepted: 19 March 2021 Published: 27 March 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Spofa Dental Kerr Company, 506-01 Jiˇ cin, Czech Republic; Zbigniew.Raszewski@kavokerr.com 2 Department of Prosthodontics, Wroclaw Medical University, 50-425 Wroclaw, Poland; danuta.nowakowska@umed.wroc.pl (D.N.); protetyka.stom@umed.wroc.pl (W.W.) * Correspondence: agnieszka.nowakowska-toporowska@umed.wroc.pl Abstract: Background: Oral hygiene is essential for maintaining residual dentition of partial denture wearers. The dental material should positively affect the oral environment. Fluoride-releasing dental materials help to inhibit microbial colonization and formation of plaque as well as to initiate the remineralization process in the early cavity area. Aim: To evaluate fluoride ion release and recharge capacity, sorption, and solubility of polymethyl methacrylate (PMMA) dental resin modified with bioactive glass addition. Materials and methods: Two bioactive glass materials (5 wt% Kavitan, 10 wt% Kavitan, and 10 wt% Fritex) and pure 10 wt% NaF were added to dental acrylic resin. After polymerization of the modified resins, the release levels of fluoride anions were measured based on color complex formation by using a spectrophotometer after 7, 14, 28, and 35 days of storage in distilled water at 37 ◦ C. Subsequently, specimens were brushed with a fluoride-containing tooth paste on each side for 30 s, and the fluoride recharge and release potential was investigated after 1, 7, and 14 days. Sorption and solubility after 7 days of storage in distilled water was also investigated. Results: The acrylic resins with addition of 10% bioactive glass materials released fluoride ions for over 4 weeks (from 0.14 to 2.27 μg/cm 2 ). The amount of fluoride ions released from the PMMA resin with addition of 10 wt% Fritex glass was higher than that from the resin with addition of 10 wt% Kavitan. The acrylic resin containing 10 wt% NaF released a high amount of ions over a period of 1 week (1.58 μg/cm 2 ), but the amount of released ions decreased rapidly after 14 days of storage. For specimens containing 5 wt% Kavitan glass, the ion-releasing capacity also lasted only for 14 days. Fluoride ion rechargeable properties were observed for the PMMA resin modified with addition of 10 wt% Fritex glass. The ion release levels after recharge ranged from 0.32 to 0.48 μg/cm 2 . Sorption values ranged from 10.23 μm/mm 3 for unmodified PMMA resin to 12.11 μm/mm 3 for specimens modified with 10 wt% Kavitan glass. No significant differences were found regarding solubility levels after 7 days. Conclusions: The addition of 10 wt% Fritex and 10 wt% Kavitan bioactive glass materials to heat-cured acrylic resin may improve its material properties, with bioactive fluoride ion release ability lasting for over 4 weeks. The resin modified with 10 wt% Fritex glass could absorb fluoride ions from the toothpaste solution and then effectively release them. Addition of fluoride releasing fillers have a small effect on sorption and solubility increase of the modified PMMA resin. Clinical significance: The addition of bioactive glass may be promising in the development of the novel bioactive heat-cured denture base resin. Keywords: PMMA; bioactive acrylic resin; glass filler; fluoride release; fluoride recharge 1. Introduction Colonization of the oral cavity by bacteria and formation of dental and denture plaque result in the initiation of caries lesions [1]. Caries is particularly problematic for patients wearing partial removable dentures. The denture base covers the oral mucosa and a large part of the teeth surface, thereby making it difficult to maintain proper oral hygiene of these Polymers 2021, 13, 1054. https://doi.org/10.3390/polym13071054 https://www.mdpi.com/journal/polymers