Use of CBCT Imaging, Open-Source Modeling Software, and Desktop Stereolithography 3D Printing to Duplicate a Removable Dental Prosthesis—A Proof of Concept
Wei-Shao Lin, DDS; Bryan T. Harris, DMD; and Dean Morton, BDS, MS
This article describes an alternative computer-aided design/computer-aided manufacturing (CAD/CAM) technique that uses cone-beam computed tomography (CBCT) imaging, open-source 3-dimensional (3D) modeling software, and a desktop stereolithography (SLA) 3D printer to duplicate an existing complete removable dental prosthesis (CRDP). Intended to offer a proof of concept, this proposed technique provides dental clinicians who have access to a CBCT imaging unit and a desktop SLA 3D printer an option to manufacture a duplicated prosthesis in-office. The 3D model of the CRDP can be preserved indefinitely, and the CAD/CAM process makes it possible to manufacture the CRDP multiple times with ease, when necessary. Different materials can be selected for the SLA 3D printer, and the duplicated prosthesis could be used for a variety of clinical and laboratory indications, such as a custom tray, a trial prosthesis, a reference record for a definitive prosthesis in laboratory procedures, or a radiographic template. Clinicians should select and use 3D software, printers, and materials with proper biocompatibility and classification and clearance from respective medical device regulatory bodies (such as US Food & Drug Administration) in different intended applications.
Additive manufacturing (AM), often referred to as 3-dimensional (3D) printing, has been considered a disruptive technology and brought significant socio-economic, environmental, geopolitical, security, and intellectual property implications to industry.1,2 Based on the definition from the American Society for Testing and Materials, AM is a process of “joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies.”3 The distinguishing feature of the AM process from both subtractive manufacturing (ie, cutting, milling, and grinding)4 and traditional formative manufacturing (ie, pressing, casting, and forming) is that it enables a layer-wise production and is suitable for manufacturing devices or products with individualized, increased geometric complexity.5
AM encompasses an array of manufacturing technologies, including stereolithography (SLA), selective laser sintering inkjet printing, fused deposition modeling (FDM), selective electron beam melting, etc.6-9 First pioneered by Charles W. Hull in 1986, SLA produces 3D models by constructing successive 2-dimensional (2D) layers of light-polymerizing liquid photopolymer upon each other, with each layer being polymerized by a concentrated beam of ultraviolet light.6,7
First adopted by the automobile and aerospace industries for prototyping, AM has now been used extensively in medicine and dentistry. In dentistry, AM can be used to fabricate dental casts, preproduction wax or polymer patterns for dental prostheses, molds for dental or facial prostheses, and metal or all-ceramic prostheses or their framework.10,11 When used in conjunction with 3D imaging modalities, such as cone-beam computed tomography (CBCT), computed tomography (CT), or magnetic resonance imaging (MRI), and 3D virtual modeling and planning software, AM can create patient-specific craniofacial casts, surgical templates, intraoperative guidance devices, and/or reconstruction plates.12-14
To generate 3D objects with the AM process from a 3D imaging volumetric dataset in the data imaging and communications in medicine (DICOM) file format, two types of software systems are often required.15-18 A 3D modeling software can be used to convert DICOM files into a universally accepted 3D file format, such as standard tessellation language (STL) or wavefront object (OBJ),17,18 and/or to further modify or edit the 3D file.1,5 A 3D slicing software can then alter the orientation of the file in the 3D printer and divide it into thin slice datasets suitable for the subsequent AM process.18 With the increasing accessibility of open-source 3D software and the decreasing cost of desktop 3D printers, clinicians now have opportunities to incorporate 3D design and printing in local dental clinics without having to outsource these tasks to external production manufacturers.19
An acceptable complete removable dental prosthesis (CRDP) or diagnostic tooth arrangement can be duplicated for a variety of clinical indications, such as a custom tray or trial prosthesis or a reference record to facilitate obtaining a definitive impression, maxillomandibular relationship, occlusal vertical dimension, and diagnostic tooth arrangement for a conventional or implant-supported dental prosthesis.20-23 In addition, the duplicated CRDP/diagnostic tooth arrangement can be used in conjunction with radiopaque markers as a radiographic template to indicate the desired position and angulation of the implant during radiographic imaging acquisition. The radiographic template can then be modified and used as a surgical template to allow for a prosthetically driven osteotomy and/or the placement of dental implants.24-26 Different material and technique combinations have been proposed to duplicate the CRDP or the diagnostic tooth arrangement with autopolymerizing acrylic resin, such as creating the mold with irreversible hydrocolloid impression material and impression trays, or using a reline jig and polyvinyl siloxane with dental stone, or polyvinyl siloxane only.27-29 A recent report proposed the use of a handheld optical scanner (Artec Space Spider, Artec 3D, artec3d.com), a custom-made rotary table, proprietary 3D software (Artec Studio 9.0, Artec 3D), and an FDM 3D printer (MakerBot Replicator 5th Generation, MakerBot, makerbot.com) to duplicate the existing CRDP.30
This article describes a proof of concept using an in-office CAD/CAM workflow of CBCT imaging, open-source modeling software, and a desktop SLA 3D printer to duplicate an existing CRDP.
The process of duplicating an existing CRDP with this technique begins with placing the CRDP on an appliance holder (3D Accuitomo 170, J. Morita USA, global.morita.com) and polystyrene block, and scanning the CRDP with the CBCT imaging scanner (3D Accuitomo 170) at fields of view of 80 mm x 80 mm, 75 kV, and 2.0 mA (Figure 1). The scanned volumetric dataset is then saved in the DICOM file format.
The next step is to download and install the open-source 3D modeling software systems (InVesalius 3.0, CTI Renato Archer, cti.gov.br; and Autodesk Meshmixer 3.2, Autodesk, meshmixer.com).1,5,17,18 After initiating the InVesalius 3.0 software, select “Load data” in the left panel window to import the DICOM volumetric dataset. Then choose “Select region of interest” and select “Soft Tissue” from the dropdown menu of “Set predefined or manual threshold” and click the “Create surface” icon (Figure 2). Next, choose “Export data,” and select “Export 3D surface” from the menu and save the 3D model in an STL format (Figure 3).
At this point, initiate the Meshmixer 3.2 software and, in the left panel window, choose “Select” function to select the entire 3D model. Select the “Deform” and “Smooth” options to create a 3D model with a smoother surface finish (Figure 4). Choose the “Shape Preserving” option under the “Smoothing Type” function and then choose a Smoothing Value of 1, a Smoothing Scale of 4, and Constraint Rings of 3 (Figure 5). Select “Export” from the menu and save the 3D model in an STL format.
Next, import the STL file into the 3D slicing software (PreForm Software, Formlabs, Inc., formlabs.com) of the desktop SLA 3D printer (Form 2, Formlabs, Inc.). In the software, on the left panel menu, select the “Orientation” tab and orient the 3D model with the intaglio surface facing up (Figure 6). Then, select the “Supports” tab on the left panel menu to automatically generate the supporting structures for the subsequent 3D manufacturing process (Figure 7). The complete 3D model file then gets transferred to the desktop SLA 3D printer, and appropriate light-polymerizing liquid photopolymer material (Standard Clear Resin, Formlabs, Inc.) can be used to additively manufacture the 3D object. For intraoral usage, biocompatible light-polymerizing liquid photopolymer material (such as, Dental SG Resin, Formlabs, Inc.) should be selected and used.
After removing the manufactured object and build plate from the printer (Figure 8), take the object from the build plate and place it in a plastic container filled with 91% isopropyl alcohol to rinse off residual light-polymerizing liquid photopolymer (Figure 9). Place the manufactured object in a dental light-polymerizing unit, such as the Enterra™ VLC Curing Unit (Dentsply International, dentsplysirona.com), for 20 minutes (or as per the light-polymerizing material manufacturer’s recommendations) to ensure complete post-manufacture polymerization (Figure 10).
Then, use cutting pliers to separate the supporting structures from the duplicated CRDP (Figure 11), and finish and polish the unit with laboratory instruments (Ultra Denture Kit, Brasseler USA, brasselerusadental.com), as necessary (Figure 12 and Figure 13).
With an appropriate selection of liquid photopolymer material, the duplicated CRDP could then be used for different indications, such as a custom tray for a definitive prosthesis, a trial prosthesis, a reference record for a definitive prosthesis in laboratory procedures, or a radiographic template.