Photon-counting CT outperforms dental CBCT in detecting small accessory canals in root-filled teeth in a phantom study.

Accurate visualization of dental structures in root-filled teeth is critical for endodontic assessment but challenging due to artifacts from root canal (RC) fillings. This study compares photon-counting-detector CT (PCD-CT) and cone-beam CT (CBCT) for detecting small accessory canals in the presence of RC fillings. A phantom model with four bovine teeth containing RC fillings and five artificial accessory canals (1000-200 μm) per tooth was embedded in a bovine rib. The phantom was scanned with clinical PCD-CT (ultra-high-resolution protocol) and dental CBCT (endodontic protocol). Canal visibility was evaluated using signal-to-noise criteria, and canal diameters were compared with micro-CT measurements, serving as the reference. Blooming artifacts from RC fillings were quantified using the full width at half maximum (FWHM) of attenuation profiles. PCD-CT detected all canals down to 400 μm and 81.5% at 200 μm, while CBCT reliably detected canals ≥ 800 μm, with detection dropping to 47.2% at 400 μm and none at 200 μm. Measurement errors for canal diameters were lower with PCD-CT. Artifact widths varied between modalities, with no clear superiority. PCD-CT provided higher detectability and measurement fidelity for small accessory canals in root-filled teeth compared to a dental CBCT, with similar filling-related blooming, supporting the potential of PCD-CT in post-treatment endodontic imaging.