title: Polymerization behavior of hydrophilic-rich phase of dentin adhesive.
abstract: 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.
authors.affiliation: Bioengineering Research Center, University of Kansas, Lawrence, KS, USA Bioengineering Graduate Program, University of Kansas, Lawrence, KS, USA.
authors.forename: F
authors.initials: F
authors.lastname: Abedin
authors.affiliation: Bioengineering Research Center, University of Kansas, Lawrence, KS, USA yeq@ku.edu.
authors.forename: Q
authors.initials: Q
authors.lastname: Ye
authors.affiliation: Bioengineering Research Center, University of Kansas, Lawrence, KS, USA.
authors.forename: R
authors.initials: R
authors.lastname: Parthasarathy
authors.affiliation: Bioengineering Research Center, University of Kansas, Lawrence, KS, USA Department of Civil Engineering, University of Kansas, Lawrence, KS, USA.
authors.forename: A
authors.initials: A
authors.lastname: Misra
authors.affiliation: Bioengineering Research Center, University of Kansas, Lawrence, KS, USA Department of Mechanical Engineering, University of Kansas, Lawrence, KS, USA.
authors.forename: P
authors.initials: P
authors.lastname: Spencer
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D002164:Camphor / Q000031:analogs & derivatives / Q000737:chemistry; D002626:Chemistry, Pharmaceutical; D003432:Cross-Linking Reagents / Q000737:chemistry; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D017666:Deuterium Oxide / Q000737:chemistry; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D058567:Photoinitiators, Dental / Q000737:chemistry; D058105:Polymerization; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013997:Time Factors; D014783:Viscosity; D014867:Water / Q000737:chemistry; D062366:para-Aminobenzoates / Q000737:chemistry
chemical_list: D003432:Cross-Linking Reagents; D017220:Dentin-Bonding Agents; D008689:Methacrylates; D058567:Photoinitiators, Dental; D000644:Quaternary Ammonium Compounds; C523330:ethyl 4-N,N-dimethylaminobenzoate; D062366:para-Aminobenzoates; D014867:Water; D017438:Bisphenol A-Glycidyl Methacrylate; C005044:hydroxyethyl methacrylate; D002164:Camphor; D017666:Deuterium Oxide; C553149:camphorquinone
keywords: hydrophobic/hydrophilic components; phase separation; photoinitiator; polymerization kinetics; postpolymerization; water