Measurement Accuracy in Cone Beam Computed Tomography in the Presence of Metal Artifact

Cone beam computed tomography (CBCT) image quality is known to be affected by artifacts produced by metal restorations, causing image deterioration via bright streaks and loss of gray values in the vicinity of the metallic structure. The aim of the study was to determine the impact of progressively increasing metal artifacts on the measurement accuracy of commonly evaluated points in implant treatment planning.

Holes were drilled into porcine mandibles at known distances from the alveolar crest on the buccal and lingual surfaces and filled with gutta-percha. Repeated CBCT images were taken, with progressively increasing amalgam restorations and stainless steel crowns (up to a total of eight restorations per jaw). The imaging field of view (FOV) was of a single site (5 × 5 cm²) in two different locations in the mandible, as well as a full-arch FOV (10 × 5 cm²). Images were taken using clinical settings, and with increased kVp and exposure time, without metal artifact reduction (MAR) corrections. Measurements between the buccal and lingual gutta-percha points on the mandible were performed using a digital caliper and compared to the same measurements taken digitally on the CBCT images. Measurements were obtained with no restorations (baseline) and compared with increasing number of restorations.

Comparison between caliper measurements and baseline CBCT with no metal artifact demonstrated differences ranging from 0 to 1.7 mm, with no clear detectable pattern of change related to the restorations. Compared to baseline measurements, scans with amalgam and stainless steel restorations showed a maximum difference of 0.54 ± 0.64 mm and 0.62 ± 0.64 mm, respectively, with no significant differences with increasing metal restorations.

There may be a variation of up to 1.7 mm between measured anatomical points and CBCT imaging under commonly used settings. While this result may be clinically important, it does not appear to be affected by increasing metal artifact due to amalgam restorations or stainless steel crowns. The findings of this study support current clinical practices accounting for a safety margin of up to 2 mm with any CBCT image, and not limiting CBCT scans for patients with multiple metal restorations.