Creating customized oral stents for head and neck radiotherapy using 3D scanning and printing

Worldwide, head and neck cancer (HNC) accounts for more than 830,000 new cases per year with a mortality rate exceeding 430,000 [1]. A multidisciplinary approach is required for an optimal therapeutic strategy, and radiation therapy (RT) has demonstrated significant benefits in local tumor control and patient survival [2]. However, RT is challenged by its inherent toxicity, notably radiation induced oral mucositis (RIOM) [3]. In a systematic review, 80% of 6181 HNC patients who received RT developed RIOM, half of which were of severe forms (grade III and IV) [4]. RIOM significantly detracts from patients’ quality of life, and may result in unplanned treatment breaks or a change in the therapeutic regimens [5, 6]. Therefore, therapeutic modalities and devices have been developed to tackle RIOM, and one of the most utilized devices is the oral radiation stent. They effectively displace and immobilize healthy tissue away from the radiation path, thereby improving the therapeutic index [7‐12]. However, the workflow for stent fabrication and the degree of customization varies. Previously, we demonstrated the feasibility of utilizing computer-aided-designing (CAD) and 3D-printing to create oral stents using routine diagnostic CT imaging studies [13]. However, this method is limited by availability of high quality scans, absence of dental artifacts, subjectivity in delineation of the dental anatomy, and bite registration inaccuracy, as the mandible is rotated around an anatomical average rather than a patient specific axis. These limitations lead to inaccurate and ill-fitting oral stents. Here, we introduce a novel workflow for the design and fabrication of customized oral stents using 3D-scanning technology. We investigated the utility and limitations in acquiring accurate and reproducible teeth impressions, and subsequent performance of 3D printed customized MOTD stents.

In this study, we explored the utility and limitations of 3D-scanning and 3D-printing technologies to design and fabricate custom mouth opening tongue-depressing (MOTD) stents for HNC radiotherapy. The combination of 3D-scanning, CAD, and 3D-printing showed a significant impact on the workflow and efficiency of the design and fabrication processes, which would help broaden their availability. When compared to a previously published CT imaging-based method [13], the 3D-scanning workflow with automatic registration described in this study required significantly less time and efforts. Our new 3D-scanning and printing method has demonstrated a clear advantage in terms of accuracy, reproducibility, and trueness of fit into the stone models.

Radiation stents have been utilized for decades with variable degrees of customization. The conventional customized radiation stents are made by an oral-maxillofacial surgeon from patient's dental impressions, by first making stone models with an appropriate maxillo-mandibular jaw relation record. These models are then used to hand sculpt a wax-pattern stent, which is subsequently used to make the definitive stent made from polymethyl methacrylate (PMMA) resin. This conventional workflow is often challenged by the multiple appointments, intensive labor, time, and experience it dictates. To overcome these limitations, Wilke et al. [13] proposed a novel workflow for radiation stent fabrication through utilizing CAD and 3D-printing from routine diagnostic CT imaging. However, relying on CT imaging to acquire dental anatomy has its limitations. Images are susceptible to various artifacts, notably, metallic and motion artifacts [17‐19], and the segmentation process is limited by the time, skill, accuracy, and reproducibility factors. Even with the semi-automated and automated segmentation methods, it is challenging to evaluate the accuracy without a known ground truth, such as impression casts or intraoral scanner (IOS) images. [20, 21]. Hence, CT imaging and segmentation are more prone to inaccurate representations compared to the 3D scanning method. To our knowledge, the workflow described in this study is the first to objectively remedy the addressed concerns. Additionally, it overcomes the challenges associated with anatomical and pathological variabilities such as edentulous patients and those with severe malocclusions. We utilized reliable and validated commercially available equipment and created an efficient workflow widely applicable in practice.

This study exhibits a few limitations. First, the reliance on the stone models to acquire dental anatomy which requires an extra visit to the oral-maxillofacial surgeon. We are investigating the incorporation of IOS to acquire the oral anatomy at the patient’s point of care. IOS has demonstrated superiority over traditional methods of dental impression making in terms of accuracy, dimensional change, retrieval, storage and safety in patients with aspiration risks (cleft-lip and palate) or respiratory distress [22‐24]. Another limitation is the reliance on the stone models for outcome evaluation instead of assessing the fit of stents in patients’ mouth and their feedback. Currently, we are conducting a clinical trial to comprehensively assess the efficiency of the proposed workflow in terms of time, labor, and patient-reported-outcomes (PROs). We also plan to apply our digital workflow to other stent designs such as the tongue lateralizing, mouth opening tongue-elevating, and lip protruding stents, which simply require swapping out digital components of the stent design. The tongue lateralizing stent is useful for treating unilateral tonsil cancers, and the mouth opening tongue-elevating stent is useful in treatment of floor of the mouth cancers. The lip protruding stent design is utilized in the treatment of oral cavity cancers such as malignant lesions in the buccal mucosa. We also anticipate that our digital and 3D workflow will lead to economic benefits, and we plan a detailed cost analysis of our method as compared to traditional hand-crafted methods. We acknowledge that lack of complete automation may lead to design variability and delay. Future studies will investigate an automated workflow and personalized design algorithms. Additionally, it is imperative to compare the 3D-printed resin with standard materials like PMMA in mechanical and surface microscopic properties, and radiation sensitivity.

We have outlined an improved workflow for designing and fabricating a 3D-printed radiation stent for HNC patients using the mouth opening tongue-depressing model. Our results demonstrated the potential advantages of utilizing the 3D-scanning technology to overcome the inherent limitations associated with CT diagnostic imaging. The proposed workflow can be conveniently incorporated into radiation oncology practices, and future studies aiming to evaluate the clinical benefits of customized 3D-printed stents are warranted.