Degree of conversion and residual monomer elution of 3D-printed, milled and self-cured resin-based composite materials for temporary dental crowns and bridges

Abstract

The aim of this work was to investigate the elution of residual monomers as a function of the manufacturing process, which are CAD/CAM manufacturing, self-curing and 3D printing. The experimental materials used consisted of the base monomers TEGDMA, Bis-GMA and Bis-EMA and 50 wt.% fillers. Additionally, a 3D printing resin without fillers was tested. The elution of the base monomers into the different media (water, ethanol and ethanol/water (75/25 vol. %)) at 37 °C over a period of up to 120 d as well as the degree of conversion (DC) by FTIR were investigated. No monomer elution could be detected in water. Most residual monomers in both other media were released from the self-curing material whereas the 3D printing composite released relatively little. The CAD/CAM blanks released hardly any quantitatively detectable amounts of monomers. Relative to the base composition, TEGDMA eluted less than Bis-GMA and Bis-EMA. DC did not correlate with residual monomer release; thus, leaching was determined not only by the amount of residual monomers present but by further factors as possibly network density and structure. The CAD/CAM blanks and the 3D printing composite showed similar high DC but lower residual monomer release from the CAD/CAM blank, likewise the self-curing composite and the 3D printing resin exhibited similar DC but different monomer elution. In terms of residual monomer elution and DC, the 3D printing composite seems promising as a new material class for the use as temporary dental crowns and bridges. Graphical Abstract

Considerations about Cytotoxicity of Resin-Based Composite Dental Materials: A Systematic Review

“…Methacrylate-based composite materials have been used as filling materials in dentistry since the 1960s [ 4 ]. Since then, there have been many developments in the field of dental material science, resulting in the production of a new class of materials with versatile applications.…”

“…Activated photo-initiators generate free radicals, which convert double C=C bonds of methacrylate monomers into single C-C bonds, triggering a chain reaction. It should be noted that polymerization is never fully complete, and the maximum conversion of monomers in the cured composite is measured as the Degree of Conversion of resin [ 3 , 4 , 10 , 11 , 15 , 24 ]. Reduction in the filler–matrix ratio, as well as using nano-filled composites rather than particle-filled materials, tend to increase the Degree of Conversion [ 22 ].…”

“…The time of irradiation, effective wavelength, and light intensity of the curing lamp, and its distance from the material’s surface all influence the curing depth [ 22 ]. Due to incomplete conversion, as well as aging, mechanical weardown, hydrolysis, and enzymatic degradation over time, the elution of uncured, leachable monomers—as well as initiators and other additives—into the liquids of the oral cavity occurs [ 3 , 4 , 7 , 11 , 12 , 24 , 25 , 26 ].…”

“…In the oral cavity, RBCs are exposed to saliva, food, bacteria, and by-products of their metabolism, changes in pH and temperature, as well as mechanical weardown [ 12 ]. In commercially available RBCs, there is some extent of degradation and solution leading to the elution of toxic components, making local exposure via both direct contact of dentin, pulp, and gingival cells as well as indirect exposure of gingiva via saliva possible and worth consideration [ 4 , 12 , 25 , 32 ]. Concerns have been raised regarding the allergies and hypersensitivities in patients as well as cytotoxic, mutagenic, and estrogenic effects on cells exposed to residual monomers [ 4 ].…”

“…In commercially available RBCs, there is some extent of degradation and solution leading to the elution of toxic components, making local exposure via both direct contact of dentin, pulp, and gingival cells as well as indirect exposure of gingiva via saliva possible and worth consideration [ 4 , 12 , 25 , 32 ]. Concerns have been raised regarding the allergies and hypersensitivities in patients as well as cytotoxic, mutagenic, and estrogenic effects on cells exposed to residual monomers [ 4 ]. Biocompatibility is important not only for the patients but also for the medical professionals [ 30 ].…”