A Hydrophobic Composite Based on an Oxirane/Acrylate Interpenetrating Network

Objectives: To determine the effect of urethane dimethacrylate (UDMA), hexamethylene diamine (HMDA), and 2-(perfluorooctyl)ethyl acrylate (PFOEA) on the degree of cure and hydrophobicity of an Oxirane/Acrylate interpenetrating network composite System (OASys).
Methods: Multifunctional acrylate, dipentaerythritol penta/hexaacrylate (DPHA) and a multifunctional epoxy phenol Novolac oligomer (Epalloy 8730 (EP)), were used to synthesize composites with interpenetrating networks. 4-isopropyl-4’-methyl-diphenyliodonium tetrakis(pentafluorophenyl)borate and camphorquinone served as the photo-initiator system. To this HMDA, UDMA and PFOEA were added in varying concentrations and filled with 70wt% acrylate-silanated barium glass (0.7µm). Samples (n=5) were tested for degree of cure (Rockwell_15T hardness), hydrophobicity (contact angle measurements), and mechanical properties (three-point bending). Polymerization shrinkage stress and volumetric shrinkage were also measured. A 70:30 BisGMA:triethyleneglycol dimethacrylate (TEGDMA) composite was used as controls.
Results: Addition of HMDA (25%EP:75%DPHA+0.75wt%HMDA), UDMA (25%EP:25% DPHA:50%UDMA+0.75%HMDA) and PFOEA (25%EP:15%DPHA:30%UDMA:30%PFOEA+0.75%HMDA) increased hardness from ~68 RHN to 76±4, 81±1, and 75±2 RHN, respectively, and contact angles from 54.3±6.9° to 55.0±6.2°, 74.5±4.5° and 108±12°, respectively. Control composites had a hardness of 82±2 RHN and a contact angle of 74.3±3.4°. Moduli with addition of HMDA, UMDA and PFOEA were 5617±883, 5698±814, and 5244±1373 MPa, respectively, and ultimate transverse strengths (UTS) were 70±12, 73±11 and 70±15 MPa, respectively. Modulus and UTS of control composites were 5985±992 MPa and 97±18 MPa, respectively. OASys with PFOEA had a shrinkage stress and volumetric shrinkage of 0.5±0.27 MPa and 1.69±0.2% respectively. BisGMA:TEGDMA composite had significantly higher shrinkage stress (1.55±0.06 MPa) and volumetric shrinkage (3.67±0.76%).
Conclusions: A hydrophobic composite was developed with adequate mechanical properties and reduced shrinkage stress, and thus shows promise for increasing clinical restoration lifetime. Further improvements are needed to improve mechanical properties.