Synchrotron-based phase contrast-enhanced micro-computed tomography reveals delaminations and material tearing in water-expandable root fillings ex vivo

Introduction: This study evaluated the integrity of calcium silicate sealer–based fillings made with hygro-expandable cones (HEC) that are commercially known as CPoint or Smartpoint.
Methods: Fourteen human canines were prepared according to a standardized, conventional endodontic treatment protocol and filled with the HEC/calcium silicate sealer. Three-dimensional imaging was performed with laboratory micro–computed tomography (μCT) at its highest resolution and was compared with synchrotron phase contrast-enhanced μCT (PCE-CT) scans of the treatment extending 1–7 mm from the apex. Conventional destructive optical microscopy validated observations by comparison with virtual slices in the tomographic data.
Results: Conventional laboratory μCT at 10-μm resolution did not reveal the existing voids and defects within the root canal fillings. PCE-CT revealed elongated interfacial delamination localized mainly at the HEC-sealer interface forming extended through-and-through gaps along the root canal filling.
Conclusions: Endodontic studies that use conventional laboratory μCT may underestimate thin defects and delamination within root canal fillings made with HEC because of limited resolution and contrast of laboratory-based broad-spectrum low intensity x-ray sources. These limitations favor use of high-brilliance, monochromatic synchrotron-based PCE-CT to reveal the important micrometer details within large (millimeter sized) samples. PCE-CT revealed the existence of a range of significant structural defects in recently placed HEC fillings, confirmed by optical microscopy after physical sectioning. Substantial delamination spanning 20%–40% of the circumferential interface as well as other structural defects were identified within root canal fillings made of HEC and calcium silicate sealer.