Effect of 9-BBN on Cure and Hydrophobicity of OASys Composites

Objectives: An Oxirane-Acrylate interpenetrating network composite System (OASys) is being developed to combat composite degradation and polymerization shrinkage stress and double the clinical lifetime of dental composites. Objective: To determine the effect of 9-borabicyclo[3.3.1]nonane (9-BBN) on OASys composite degree of cure and hydrophobicity. 9-BBN is a cationic redox monomer-initiator that will potentially reduce the need for producing toxic free radicals through more traditional polymerizing initiator-monomer complexes.
Methods: Methods: A superhydrophobic OASys composite was developed containing the following monomers in a 25:15:30:30 weight ratio: a multifunctional oxirane (Epalloy 8370), a multifunctional acrylate (Dipentaerythritol Hexaacrylate, DPHA), urethane dimethacrylate (UDMA) and fluorinated acrylate (2-(Perfluorooctyl)ethyl acrylate, C10). This resin system was filled to 70% w/w with acrylate-silanated 0.7 um barium glass filler. The initiator system used was 9% w/w Borate (4-Isopropyl-4'-methyldiphenyliodonium Tetrakis(pentafluorophenyl)borate), 0.1875% w/w CQ (Camphorquinone) and 0.75% w/w HMDA (Hexamethylenediamine). To this, 9-BBN was added in different concentrations (0%, 0.25%, 0.5%) and its effect on degree of cure (Rockwell_15T hardness), hydrophobicity (contact angle measurements), and mechanical properties (three-point bending) was determined.
Results: Results: Addition of 9-BBN did not increase Rockwell_15T hardness (~78 RHN) but contact angles increased from 102°±15° to 109°±15° with 0.5% 9-BBN. However, Rockwell_15T hardness were lower than those of 70:30 bisGMA:triethyleneglycol dimethacrylate (TEGDMA) controls (82±2 RHN) and contact angles remained higher than those of controls (74°±3°). Three point bend tests showed that adding 9-BBN lowered modulus (4387±1238 vs 3896±648 MPa) and ultimate transverse strength (UTS; 61±11 vs 49±6 MPa). BisGMA:TEGDMA controls had modulus and UTS of 5985±922 MPa and 97±20 MPa.
Conclusions: Conclusions: 9-BBN, at the concentrations used, did not significantly increase degree of cure but it did increase hydrophobicity of OASys composites. However, it also decreased modulus and UTS.