Determination of residual monomer in autopolymerized denture base polymers.

Objectives: To quantify the amount of residual monomer leached from different acrylic polymer materials by using high pressure liquid chromatography (HPLC).
Methods: Two autopolymerized denture base polymers (Olympia Dental Supplier) were selected for testing. The specimens were prepared according to standardized mould (25mm diameter, 5 mm thickness). Two groups of specimen were prepared with two different acrylic materials and same manipulation method. Each group included 6 samples. All specimens were stored in a sealed glass flask and immersed in distilled water at 37˚C at time intervals of 1, 2, 6 and 12 hours, 1 day and 1 week. To determine the release of the monomer over time, 20µL of extract solution were injected at regular intervals into HPLC (Waters System) which was used to identify the residual monomer content. The analysis used an Agilent UV detector at 230 nm, an Ace 5 C18 column with a length of 25cm, manual injector system, binary pump, and particle size of 1µm as stationary phase. For mobile phase, a (50:50 volume ratio) mixture of Acetonitrile (HPLC grade) and distilled water was used, and the flow rate was 1 mL/min. Each specimen was injected three times (20µl) into the chromatographer and mean concentration was recorded in ppm as final monomer concentration of that specimen. The calibration curve was constructed with monomer concentration of 50 to 1600ppm in acetonitrile.
Results: The residual monomer content of chemical cure acrylic was higher than as recommended by ISO-1567 standard for denture base material. The higher residual monomer content in self-cure which acts as plasticizer, subsequently lead to reduce the properties of self-cure material. Statistically significant differences were found within the groups in the amount of residual monomer in the specimen at different time intervals. HPLC showed statistically significant differences among groups (P < .05) in the amount of eluted monomer.
Conclusions: Methods and conditions of acrylate polymerization can be responsible for the release of residual monomers. Due to the increased concerned of monomer leaching the evaluation of current and new products should be performed.