title: The effect of filler and silane content on conversion of resin-based composite.
abstract: OBJECTIVE
  This study examines the influence of filler loading and silane content on the conversion of photoactivated, resin-based composites as determined using Fourier transform infrared spectroscopy (FTIR).
  
  
  METHODS
  Zirconia/silica filler was processed with a silane coupling agent (gamma-methacryloxypropyltrimethoxysilane) to achieve a range of silane-to-filler compositions. Treated fillers were compounded with a photoactivated BisGMA/TEGDMA resin to yield a series of pastes all containing 72 wt% total solids. Diffuse reflectance FTIR was used to characterize methacrylate unsaturation of the silane on the filler particles while paste conversion was determined using transmission FTIR. A resin matrix conversion was determined by adjusting the paste conversion for silane unsaturation. Two additional series of pastes were compounded to achieve variable filler-to-resin ratios using non-treated filler and filler processed with 8 wt% silane. Paste conversion was determined using transmission FTIR.
  
  
  RESULTS
  Pastes compounded from fillers containing variable percent silane demonstrated linearly decreasing conversion (R(2)=0.986) with increasing silane content and ranged from 52.7 to 62.8%. Adjusting paste conversion for silane unsaturation yielded similar resin matrix conversion for all cured pastes (65.1+/-0.8%). Pastes compounded with increasing filler-to-resin ratios had progressively decreasing conversion. Correcting for silane unsaturation suggests this effect was independent of whether the filler was silane-treated or not.
  
  
  CONCLUSIONS
  Composite resin matrix conversion as determined via FTIR can be underestimated by the presence of unreacted methacrylate from silane on the filler. A corrected resin matrix conversion can be estimated by adjusting for silane unsaturation. Additionally, increasing filler-to-resin ratio progressively decreases conversion independent of the presence of silane on the filler.
authors.affiliation: 3M Dental Products, 3M Center, Building 260-2B-12, St Paul, MN 55144-1000, USA. rhalvorson@mmm.com
authors.forename: Rolf H
authors.initials: RH
authors.lastname: Halvorson
authors.forename: Robert L
authors.initials: RL
authors.lastname: Erickson
authors.forename: Carel L
authors.initials: CL
authors.lastname: Davidson
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects*; D008027:Light; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry; D012821:Silanes / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D015040:Zirconium / Q000737:chemistry
chemical_list: D003188:Composite Resins; D008689:Methacrylates; D011108:Polymers; D011109:Polymethacrylic Acids; D012821:Silanes; C020946:triethylene glycol dimethacrylate; C017492:methacryloxypropyltrimethoxysilane; D011092:Polyethylene Glycols; D012822:Silicon Dioxide; D015040:Zirconium; C028541:zirconium oxide