title: Determination of the depth of cure for VLC composites by nuclear magnetic resonance microimaging.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the potential of nuclear magnetic resonance microimaging (NMRM) for investigating the depth of cure for visible light curing of dental composite materials.
  
  
  METHODS
  Cylindrical composite specimens were light-cured within the NMRM instrument for predetermined times. Vertical slice, mid-resolution, spin-echo images were acquired using a Bruker AM300WB instrument with a Bruker microimaging attachment. Images were digitized and intensity profiles generated using deuterium oxide/water as a reference intensity. Separate specimens were made to obtain Vickers microhardness values as a function of depth to compare an established method for determining depth of cure with NMRM.
  
  
  RESULTS
  A difference in NMR image intensity between uncured and cured composite resin has been detected. Values for integrated intensities were obtained at 150 microns intervals over the mid-fifth of the total image width. An abrupt transition was not seen at the cure front which advances with cumulative exposure time. NMRM produced similar data trends to microhardness measurement.
  
  
  CONCLUSIONS
  NMRM produces three-dimensional images of "mobile" hydrogen nuclei to a resolution of 10(-5) mm3. It is non-invasive, non-destructive and able to selectively image protons in different chemical environments. It can be used to investigate depth of cure for light curing materials, but must be regarded as a research technique and not one for routine measurement. Refinement is necessary, possible, and in progress to improve resolution from the present 10(-2) mm3 towards the limit, and to reduce noise.
authors.affiliation: Department of Dental Prosthetics and Gerontology, University of Dundee, Scotland, UK.
authors.forename: C H
authors.initials: CH
authors.lastname: Lloyd
authors.forename: S N
authors.initials: SN
authors.lastname: Scrimgeour
authors.forename: J A
authors.initials: JA
authors.lastname: Chudek
authors.forename: R L
authors.initials: RL
authors.lastname: Mackay
authors.forename: G
authors.initials: G
authors.lastname: Hunter
authors.forename: D
authors.initials: D
authors.lastname: Pananakis
authors.forename: E W
authors.initials: EW
authors.lastname: Abel
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D006245:Hardness Tests; D008027:Light; D009682:Magnetic Resonance Spectroscopy; D008422:Materials Testing / Q000379:methods; D013997:Time Factors; D014520:Urethane / Q000737:chemistry*
chemical_list: D003188:Composite Resins; C056413:Occlusin; D014520:Urethane