Release of dibenzoyl peroxide from polymethyl methacrylate denture base resins: An in vitro evaluation

Objectives. Dibenzoyl peroxide (BPO), an initiator in polymethyl methacrylate denture base resins, has been associated with allergic reactions in human patients. This study evaluated the content of BPO in acrylic denture base materials (ADBM) prior and subsequent to recommended and additional post-polymerization, and subsequent to storage in varying solutions. The goal was to determine differences in BPO content in ADBMs, to determine whether differences are seen in BPO release over time and to test different procedures for additional BPO reduction. Methods. Three heat-polymerizing, two auto-polymerizing and a microwave polymerizing "hypoallergic" ADBM were investigated. Five samples (empty set 414.57 mg) were polymerized according to manufacturers' instructions from each of the six acrylic resins for each of the variables to be investigated. For each material the BPO content was measured as delivered by the manufacturer and subsequent to recommended and post-polymerization protocols. The BPO content was also evaluated after storage in distilled water (22 degrees C, 192 h), in artificial saliva (35 degrees C, 192 h), in ethanol, potassium permanganate and ammonium ferric(II) sulfate solutions (22 degrees C, 48 h). Results. High performance liquid chromatography (HPLC) and indirect iodometry were used to detect BPO concentrations. Significant differences were noted in BPO concentrations between the polymers as delivered from the manufacturer (0.13-1.20%), subsequent to polymerization (0.05-0.32%) and to the various treatment and storage procedures (H and U-tests, p < 0.05). The microwave polymerizing ADBM contained the lowest initial level of BPO. No reduction of BPO content was noted after 8 days of storage in artificial saliva or water. The most notable reduction (63-95%) occurred subsequent to post-polymerization cycles. Significance. BPO was detected in all investigated ADBMs. it is unlikely, under oral conditions, that BPO is released from the investigated ADBMs. The BPO concentration can be reduced effectively by additional post-polymerization. (C) 2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.