title: Ultra-small-angle X-ray scattering-X-ray photon correlation spectroscopy studies of incipient structural changes in amorphous calcium phosphate-based dental composites.
abstract: The local structural changes in amorphous calcium phosphate (ACP)-based dental composites were studied under isothermal conditions using both static, bulk measurement techniques and a recently developed methodology based on combined ultra-small angle X-ray scattering-X-ray photon correlation spectroscopy (USAXS-XPCS), which permits a dynamic approach. While results from conventional bulk measurements do not show clear signs of structural change, USAXS-XPCS results reveal unambiguous evidence for local structural variations on a similar time scale to that of water loss in the ACP fillers. A thermal-expansion-based simulation indicates that thermal behavior alone does not account for the observed dynamics. Together, these results suggest that changes in the water content of ACP affect the composite morphology due to changes in ACP structure that occur without an amorphous-to-crystalline conversion. It is also noted that biomedical materials research could benefit greatly from USAXS-XPCS, a dynamic approach.
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA. fan.zhang@nist.gov
authors.forename: Fan
authors.initials: F
authors.lastname: Zhang
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Allen
authors.forename: Lyle E
authors.initials: LE
authors.lastname: Levine
authors.forename: Laura
authors.initials: L
authors.lastname: Espinal
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Antonucci
authors.forename: Drago
authors.initials: D
authors.lastname: Skrtic
authors.forename: Justin N R
authors.initials: JN
authors.lastname: O'Donnell
authors.forename: Jan
authors.initials: J
authors.lastname: Ilavsky
mesh_terms: D001272:Atmosphere / Q000737:chemistry; D002130:Calcium Phosphates / Q000737:chemistry*; D003198:Computer Simulation; D003764:Dental Materials / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D017785:Photons; D012031:Refractometry; D053838:Scattering, Small Angle; D012822:Silicon Dioxide / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013057:Spectrum Analysis; D013818:Thermogravimetry; D014961:X-Ray Diffraction; D014965:X-Rays
chemical_list: D002130:Calcium Phosphates; D003764:Dental Materials; C519480:amorphous calcium phosphate; D012822:Silicon Dioxide