Urethane Macromonomers: Key Components for the Development of Light-Cured High-Impact Denture Bases

The development of high-impact denture base formulations that are suitable for digital light processing (DLP) 3D printing is demanding. Indeed, a combination of high flexural strength/modulus and high fracture toughness is required. In this contribution, eight urethane macromonomers (UMs1-8) were synthesized in a one-pot, two-step procedure. Several rigid diols were first reacted with two equivalents of trimethylhexamethylene diisocyanate. The resulting diisocyanates were subsequently end-capped with a free-radically polymerizable monomer bearing a hydroxy group. UMs1-8 were combined with the monofunctional monomer (octahydro-4,7-methano-1H-indenyl)methyl acrylate and a poly(ε-caprolactone)-polydimethylsiloxane-poly(ε-caprolactone) (PCL-PDMS-PCL) triblock copolymer (BCP1) as a toughening agent. The double-bond conversion, glass transition temperature (T_g), and mechanical properties (flexural strength/modulus, fracture toughness) of corresponding light-cured materials were measured (cured in a mold using a light-curing unit). The results showed that the incorporation of BCP1 was highly efficient at significantly increasing the fracture toughness, as long as the obtained networks exhibited a low crosslink density. The structure of the urethane macromonomer (nature of the rigid group in the spacer; nature and number of polymerizable groups) was demonstrated to be crucial to reach the desired properties (balance between flexural strength/modulus and fracture toughness). Amongst the evaluated macromonomers, UM1 and UM2 were particularly promising. By correctly adjusting the BCP1 content, light-cured formulations based on those two urethane dimethacrylates were able to fulfill ISO20795-1:2013 standard requirements regarding high-impact materials. These formulations are therefore suitable for the development of 3D printable high-impact denture bases.