title: Poly(propylene glycol) and urethane dimethacrylates improve conversion of dental composites and reveal complexity of cytocompatibility testing.
abstract: OBJECTIVE
  To determine the effects of various monomers on conversion and cytocompatibility of dental composites and to improve these properties without detrimentally affecting mechanical properties, depth of cure and shrinkage.
  
  
  METHODS
  Composites containing urethane dimethacrylate (UDMA) or bisphenol A glycidyl methacrylate (Bis-GMA) with poly(propylene glycol) dimethacrylate (PPGDMA) or triethylene glycol dimethacrylate (TEGDMA) were characterized using the following techniques: conversion (FTIR at 1 and 4mm depths), depth of cure (BS EN ISO 4049:2009 and FTIR), shrinkage (BS EN ISO 17304:2013 and FTIR), strength and modulus (biaxial flexural test) and water sorption. Cytocompatibility of composites and their liquid phase components was assessed using three assays (resazurin, WST-8 and MTS).
  
  
  RESULTS
  UDMA significantly improved conversion, BFS and depth of cure compared to Bis-GMA, without increasing shrinkage. UDMA was cytotoxic at lower concentrations than Bis-GMA, but extracts of Bis-GMA-containing composites were less cytocompatible than of those containing UDMA. PPGDMA improved conversion and depth of cure compared to TEGDMA, without detrimentally affecting shrinkage. TEGDMA was shown by all assays to be highly toxic. Resazurin, but not WST-8 and MTS, suggested that PPGDMA exhibited improved cytocompatibility compared to TEGDMA.
  
  
  CONCLUSIONS
  The use of UDMA and PPGDMA results in composites with excellent conversion, depth of cure and mechanical properties, without increasing shrinkage. Composites containing UDMA appear to be slightly more cytocompatible than those containing Bis-GMA. These monomers may therefore improve the material properties of dental restorations, particularly bulk fill materials. The effect of diluent monomer on cytocompatibility requires further investigation.
authors.affiliation: Division of Biomaterials & Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK. Electronic address: nick.walters@uta.fi.
authors.forename: Nick J
authors.initials: NJ
authors.lastname: Walters
authors.affiliation: Division of Biomaterials & Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK.
authors.forename: Wendy
authors.initials: W
authors.lastname: Xia
authors.affiliation: Division of Biomaterials & Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK; Plymouth University Peninsula Schools of Medicine and Dentistry, Portland Square, Drake Circus, Plymouth, Devon PL4 8AA, UK.
authors.forename: Vehid
authors.initials: V
authors.lastname: Salih
authors.affiliation: Paediatric Dentistry, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK.
authors.forename: Paul F
authors.initials: PF
authors.lastname: Ashley
authors.affiliation: Division of Biomaterials & Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK. Electronic address: anne.young@ucl.ac.uk.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Young
mesh_terms: D001672:Biocompatible Materials / Q000494:pharmacology*; D017438:Bisphenol A-Glycidyl Methacrylate / Q000494:pharmacology*; D003188:Composite Resins / Q000494:pharmacology*; D055119:Elastic Modulus; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D008689:Methacrylates / Q000494:pharmacology*; D044367:Phase Transition; D011092:Polyethylene Glycols / Q000494:pharmacology*; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000494:pharmacology*; D011140:Polyurethanes / Q000494:pharmacology*; D019946:Propylene Glycol / Q000494:pharmacology*; D013499:Surface Properties; D013718:Tensile Strength
chemical_list: D001672:Biocompatible Materials; D003188:Composite Resins; D008689:Methacrylates; D011109:Polymethacrylic Acids; D011140:Polyurethanes; C029824:urethane dimethacrylate luting resin; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; D019946:Propylene Glycol
keywords: Bis-GMA; Cytocompatibility; Degree of conversion; Dental composite; Dental material; Monomer; PPGDMA; Polymerization shrinkage; TEGDMA; UDMA