Diagnostic performance of clinical photon-counting CT in the assessment of peri-implantitis – an ex vivo diagnostic accuracy study

Purpose To evaluate the diagnostic performance of photon-counting computed tomography (PCCT) for the assessment of peri-implant bone defects and to compare it with cone-beam computed tomography (CBCT) at comparable radiation doses. Methods Circular peri-implant defects were artificially created around 27 titanium implants placed in nine porcine mandibles. Defect morphology was digitized using an intraoral scanner (STL, stereolithography file format) as reference standard. Specimens were imaged with high-resolution CBCT (HD-CBCT) and PCCT at clinically commonly used dose levels, which were nearly identical for both modalities to ensure comparability. Vertical defect depth and horizontal defect width were measured at predefined locations by two calibrated readers. Agreement with the reference standard was assessed using paired statistical testing, Bland-Altman analysis, mean absolute error (MAE), relative error metrics, and intraclass correlation coefficients (ICC). Results For vertical defect depth (mean reference 4.68 ± 2.20 mm), PCCT demonstrated significantly lower MAE than CBCT (0.14 mm vs. 0.67 mm; p < 0.001) and narrower limits of agreement. Relative absolute error was 4.3% for PCCT and 17.4% for CBCT. For horizontal defect width (mean reference 0.99 ± 0.39 mm), both modalities slightly underestimated the defect width compared to the reference standard of the oral scanner. However, PCCT showed lower MAE (0.077 mm vs. 0.18 mm; p < 0.001) and reduced proportional variability. Intra- and inter-reader reliability were consistently higher for PCCT (ICC up to 0.994) compared with CBCT. Conclusions Within the limitations of this ex vivo model, PCCT provided more accurate and reproducible three-dimensional measurements of standardized peri-implant bone defects than CBCT. These findings need to be confirmed by further in vivo studies to determine its clinical diagnostic value and potential impact on treatment planning.