###### Abstract  
In cranioxillofacial surgical procedures, an emerging practice adopts the preoperative virtual planning that uses medical imaging (computed tomography), 3D thresholding (segmentation), 3D modeling (digital design), and additive manufacturing (3D printing) for the procurement of an end-use implant. The objective of this case study was to evaluate the cumulative spatial inaccuracies arising from each step of the process chain when various computed tomography protocols and thresholding values were independently changed. A custom-made quality assurance instrument (Phantom) was used to evaluate the medical imaging error. A sus domesticus (domestic pig) head was analyzed to determine the 3D thresholding error. The 3D modeling error was estimated from the computer-aided design software. Finally, the end-use implant was used to evaluate the additive manufacturing error. The results were verified using accurate measurement instruments and techniques. A worst-case cumulative error of 1.7 mm (3.0%) was estimated for one boundary condition and 2.3 mm (4.1%) for two boundary conditions considering the maximum length (56.9 mm) of the end-use implant. Uncertainty from the clinical imaging to the end-use implant was 0.8 mm (1.4%). This study helps practitioners establish and corroborate surgical practices that are within the bounds of an appropriate accuracy for clinical treatment and restoration. 3D printing; cranioxillofacial surgery; medical imaging; computed tomography (CT); segmentation; digital design; CAD; implants; cumulative error; error propagation; standard uncertainty; spatial accuracy; quality control; quality assurance +
Footnote †: journal: Medical Imaging  
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Footnote 1: Department of Mechanical Engineering, Aalto University, Otakaari 4, 02150 Espoo, Finland  
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Footnote 2: MIKES-National Metrology Institute of Finland, VTT Technical Research Centre of Finland, Tekniikantie 1, 02150 Espoo, Finland  
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Footnote 3: Department of Radiology, Medical Imaging Center, University of Helsinki and Helsinki University Hospital, P.O.Box 263, HUS, 00029 Helsinki, Finland  
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Footnote 4: Correspondence: [EMAIL_ADDRESS]; Tel. : +358-50-566-2207  
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Footnote 4: Correspondence: [EMAIL_ADDRESS]; Tel. : +358-50-566-2207  
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Footnote 4: Correspondence: [EMAIL_ADDRESS]; Tel. : +358-50-566-2207  
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Footnote 5: Correspondence: [EMAIL_ADDRESS]; Tel. : +358-50-566-2207  
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Footnote 6: Correspondence: [EMAIL_ADDRESS]; Tel. : +358-50-566-2207
replacement system from the United States Food and Drug Administration (FDA) [2]. Substantial AM growth is enabled by its economical lot-size-one that allows for unprecedented geometrical freedom [5] in one build cycle using minimal set-up because it is a general-purpose digital technology which is not constrained by patient-specific tooling [6; 7; 8]. Further, it enables a unique supply chain with increased communication and responsiveness [9] that complements the state of urgency in the medical field. The powder bed fusion (PBF) technique is one of the seven AM processes in which thermal energy is used to selectively fuse regions of the powder bed [1]. When this method is applied to fabricate metallic parts, it is typically known as direct metal laser sintering (DMLS), selective laser melting (SLM), and electron beam melting (EBM) depending on the power source and the machine manufacturer. This method has been widely implemented to manufacture custom-made and patient-specific implants from metal alloys, particularly titanium [10; 11; 12; 13; 14; 15; 16; 17]. Implants seem to be one of the most utilized applications of additive manufacturing in the head and neck area in hospitals [18]. Further, it is increasingly fulfilling the demand for porous titanium that can facilitate osseointegration through the independent adjustment of the mechanical properties and porosity in terms of size and distribution [19; 20; 21; 22; 23]. A classification for medical applications of AM was established by [PERSON] et al.