University of Twente Student Theses


Optimized and user-friendly workflow for the fabrication of 3D printed maxillary hollow closed surface model obturator using CT, intraoral scanning technology, and computer aided/manufacturing

Ooms, A. (2022) Optimized and user-friendly workflow for the fabrication of 3D printed maxillary hollow closed surface model obturator using CT, intraoral scanning technology, and computer aided/manufacturing.

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Abstract:An oronasal defect created by the surgical resection of the palate and maxilla can be directly obturated by a hand-kneaded maxillofacial prosthesis, the so-called immediate surgical obturator (ISO). The ISO consists of a transparent baseplate and silicon putty obturator. The obturator replaces hard and soft tissue, thereby improving deglutition and mastication, speech enhancement, avoiding contamination, and improving the overall quality of life [1], [2]. Besides the advantages of the maxillary prosthesis, the ISOs are, on the other hand, large, high-weighted, and unstable, especially in large defects. The hand-kneaded silicone putty obturator is also porous and susceptible to fluid and bacterial uptake, which further increases the weight, and results in a foul smell [3]. These disadvantages often reduce the patient’s function and comfort. Creating a hollow maxillary obturator could reduce the weight of the prosthesis by 7 – 33 %, depending on the size of the defect [4]. Computer-aided design and manufactured (CAD/CAM) designed obturators may overcome the limitations of the conventional method. This thesis aimed to investigate the shape, volume, clinical fit, weight reduction, and material properties of a novel designed CAD/CAM prosthesis, the so-called closed surface model (CSM) obturator. In this study, CT and intraoral scanning technology were used for the image acquisition of the novel CAD/CAM ISOs. An existing CAD/CAM workflow was optimized and used to design and print different scaled CSM obturators around the segmented bone and soft tissue, in Clear resin. The clinical fit of the prostheses was evaluated in a clinical trial study with four included maxillectomy patients in the Netherlands Cancer Institute—Antoni van Leeuwenhoek Hospital (NKI-AVL). In addition, the CSM obturators were evaluated with a retrospective study of maxillectomy patients from 2010 to 2020 in the NKI-AVL (n = 17). The criteria included patients with a pre-and postoperative CT scan, in which the conventional obturator could be segmented from the postoperative scan based on greyscale thresholding. The skulls of both scans were also segmented and registered to obtain the resection margins, which were classified according to the novel Ooms’ classification system. The CSM obturators were then designed according to this classification system and compared with the conventional and theoretical reference obturators by weight reduction and Hausdorff Distances (HD). Furthermore, this study investigated whether the material of the CAD/CAM ISOs was stable in a simulated oral cavity environment of 37°C heated water. In addition, the fracture mechanic performance during the removal of the prosthesis in the patient’s mouth was researched by a compressive resistance test. The outcome of the maximal fracture load was used for a digital Finite Element Analysis to study the tensile stress and deformation in Ansys. Our clinical results showed that the shape and volume of the conventional obturator depend on the height of the resection and whether the canine was resected. This resulted in different CSM design choices per Ooms’ class. The 0.8 scaled CSM around segmented resection margins showed the overall best clinical fit with a clinical weight reduction between 36 – 39%. In the retrospective study, the average weight reduction of the CSM obturator was about 47%, which was similar to the theoretical clinical reference. In the material property study, the prosthesis had a water absorption of 2%, and material deformation occurred at the thinnest, lateral side of the baseplate. The fracture load during the prosthesis removal was 25 N which indicated that the prosthesis was safe for usage. Future studies should focus on the improvement of the final workflow and prosthesis design to enable the clinical implementation of the CAD/CAM obturators. The improvements should include a more automated workflow, integrated into a user interface, and adjustments in the baseplate design to gain retention o to the remaining bone structures and teeth. Furthermore, the finalized designs should be evaluated within a large cohort clinical-trial study, comparing the conventional obturator with the novel CSM obturators. The clinical-trial findings will gain insight into the impact of the amount of weight reduction on the patient’s comfort improvement.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Programme:Technical Medicine MSc (60033)
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