Polymerization behavior of hydrophilic-rich phase of dentin adhesive

The 2-fold objectives of this study were 1) to understand whether model hydrophobic- and hydrophilic-rich phase mimics of dentin adhesive polymerize similarly and 2) to determine which factor,the dimethacrylate component,bisphenol a glycerolate dimethacrylate (bisgma) or photoinitiator concentration,has greater influence on the polymerization of the hydrophilic-rich phase mimic. current dentin adhesives are sensitive to moisture,as evidenced by nanoleakage in the hybrid layer and phase separation into hydrophobic- and hydrophilic-rich phases. phase separation leads to limited availability of the cross-linkable dimethacrylate monomer and hydrophobic photoinitiators within the hydrophilic-rich phase. model hydrophobic-rich phase was prepared as a single-phase solution by adding maximum wt% deuterium oxide (d2o) to hema/bisgma neat resins containing 45 wt% 2-hydroxyethyl methacrylate (hema). mimics of the hydrophilic-rich phase were prepared similarly but using hema/bisgma neat resins containing 95,99,99.5,and 100 wt% hema. the hydrophilic-rich mimics were prepared with standard or reduced photoinitiator content. the photoinitiator systems were camphorquinone (cq)/ethyl 4-(dimethylamino)benzoate (edmab) with or without [3-(3,4-dimethyl-9-oxo-9h-thioxanthen-2-yloxy)-2-hydroxypropyl]trimethylammonium chloride (qtx). the polymerization kinetics was monitored using a fourier transform infrared spectrophotometer with a time-resolved collection mode. the hydrophobic-rich phase exhibited a significantly higher polymerization rate compared with the hydrophilic-rich phase. postpolymerization resulting in the secondary rate maxima was observed for the hydrophilic-rich mimic. the hydrophilic-rich mimics with standard photoinitiator concentration but varying cross-linker (bisgma) content showed postpolymerization and a substantial degree of conversion. in contrast,the corresponding formulations with reduced photoinitiator concentrations exhibited lower polymerization and inhibition/delay of postpolymerization within 2 h. under conditions relevant to the wet,oral environment,photoinitiator content plays an important role in the polymerization of the hydrophilic-rich phase mimic. since the hydrophilic-rich phase is primarily water and monomethacrylate monomer (e.g.,hema as determined previously),substantial polymerization is important to limit the potential toxic response from hema leaching into the surrounding tissues. © international & american associations for dental research 2015.