Quantitative analysis of zirconia and titanium implant artefacts in three-dimensional virtual models of multi-slice CT and cone beam CT: does scan protocol matter?

Abstract

Objectives: Artefacts from dental implants in three-dimensional (3D) imaging may lead to incorrect representation of anatomical dimensions and impede virtual planning in navigated implantology. The aim of this study was quantitative assessment of artefacts in 3D STL models from cone beam CT (CBCT) and multislice CT (MSCT) using different scanning protocols and titanium-zirconium (Ti-Zr) and zirconium (ZrO₂) implant materials.

Methods: Three ZrO₂ and three Ti-Zr implants were respectively placed in the mandibles of two fresh human specimens. Before (baseline) and after implant placement, 3D digital imaging scans were performed (10 repetitions per timepoint: voxel size 0.2 mm³ and 0.3 mm³ for CBCT; 80 and 140 kV in MSCT). DICOM data were converted into 3D STL models and evaluated in computer-aided design software. After precise merging of the baseline and post-op models, the surface deviation was calculated, representing the extent of artefacts in the 3D models.

Results: Compared with baseline, ZrO₂ emitted 36.5-37.3% (±0.6-0.8) artefacts in the CBCT and 39.2-50.2% (±0.5-1.2) in the MSCT models. Ti-Zr implants produced 4.1-7.1% (±0.3-3.0) artefacts in CBCT and 5.4-15.7% (±0.5-1.3) in MSCT. Significantly more artefacts were found in the MSCT vs CBCT models for both implant materials (p < 0.05). Significantly fewer artefacts were visible in the 3D models from scans with higher kilovolts in MSCT and smaller voxel size in CBCT.

Conclusions: Among the four applied protocols, the lowest artefact proportion of ZrO₂ and Ti-Zr implants in STL models was observed with CBCT and the 0.3 mm³ voxel size.

Keywords: artifact; computed tomography; cone-beam computed tomography; dental implant; three-dimensional imaging; titanium; zirconium.

Figure 1.

Step-by-step overview of the study design and workflow. 3D, three-dimensional; CBCT, cone beam CT; DICOM, Digital Imaging and Communications in Medicine; MSCT, multislice CT; STL, standard tessellation language.

Figure 2.

(a) Two-dimensional sectional view of the baseline and post-op scans with ZrO₂ and Ti-Zr implants in the mandible in MSCT and (b) in CBCT. (c) Merging process of the corresponding STL models with 3D representation of the baseline models (green) and the artefact containing post-op models (red) for MSCT and (d) for CBCT. CBCT, cone beam CT; MSCT, multislice CT; STL, standard tessellation language.

Figure 3.

Boxplots displaying the summarized artefact quantity in MSCT and CBCT tested on ZrO₂ and Ti-Zr implants with different acquisition settings. CBCT, cone beam CT; MSCT, multislice CT.