In vitro analysis of monomer leaching in modern dental materials: CAD milled, printed, traditional heat-processed, and auto-polymerizing denture base resins.

Purpose: Denture fabrication has shifted from traditional heat-processed and auto-polymerizing materials to computer-aided design and computer-aided manufacturing (CAD-CAM) milled and printed materials. The monomer in traditional materials can induce an allergic reaction in some patients. With the rise in the edentulous population and increasing demand for the fabrication of dentures, these newer materials should be studied for monomer leaching. The purpose of this study was to evaluate the ratio of residual monomer in materials being used for denture bases: CAD-milled polymethylmethacrylate (PMMA), printed denture base resin, heat-processed PMMA, and auto-polymerizing PMMA comparatively.

Materials and methods: Milled, printed, heat-activated, and auto-polymerizing denture base specimens (n = 3 for each group, each test run three times) were fabricated according to manufacturer recommendations. Specimens were first immersed in deuterated chloroform (CDCl₃), a deuterated organic solvent, to evaluate monomer leaching and to observe physical properties of the materials. NMR spectroscopy was used to evaluate the dissolution of materials and residual monomer to crosslinked polymer ratios at 1, 4, and 9 days. A second group of specimens was then immersed in deuterium oxide (D₂O) to evaluate if the residual monomers would leach out of the system. The solution was then analyzed using nuclear magnetic resonance (NMR) spectroscopy for 1 month. The deuterated forms of chloroform (CDCl₃) and water (D₂O) were used to enable sample characterization by NMR.

Results: While the heat-processed, auto-polymerizing, and milled specimens possessed residual monomers, no significant monomer leaching was noted in the printed specimen, while immersed in CDCl₃. Similarly, the printed specimen was most resistant to dissolution, as compared to the rest; dissolution of the specimen is indicative of little to no cross-linking. No detectable dissolution of monomer was seen when all specimens were immersed in D₂O for up to 1 month.

Conclusions: Residual monomers were not found in the printed denture material in this study in either CDCl₃ or D₂O, whereas CAD-milled and traditionally processed denture bases still have residual monomers within their respective systems when immersed in organic solvent. None of the specimens tested leached monomers into D₂O.