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| REVIEW ARTICLE |
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| Year : 2022 | Volume
: 8
| Issue : 1 | Page : 31 |
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Application progress of three-dimensional printing technology in orthodontics
Tingwu Su1, Hongqi Zhang2, Ting Kang1, Mengqi Zhou1, Jie Han1, Nan Ning3, Hai Lin4, Xuepeng Chen1, Qianming Chen1
1 Stomatology Hospital, School of Stomatology, Zhejiang University School of Medicine, Clinical Research Center for Oral Diseases of Zhejiang Province, Key Laboratory of Oral Biomedical Research of Zhejiang Province, and Cancer Center of Zhejiang University, Hangzhou, Zhejiang, China
2 Department of Prosthodontics, Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China
3 Center of Medical Department, Meiqi Technology, Hangzhou, Zhejiang, China
4 College of Computer Science and Technology, State Key Lab of CAD and CG, Zhejiang University, Hangzhou, Zhejiang, China
| Date of Submission | 19-Sep-2022 |
| Date of Decision | 16-Oct-2022 |
| Date of Acceptance | 17-Oct-2022 |
| Date of Web Publication | 15-Dec-2022 |
Correspondence Address:
Qianming Chen
Stomatology Hospital, School of Stomatology, Zhejiang University School of Medicine, Clinical Research Center for Oral Diseases of Zhejiang Province, Key Laboratory of Oral Biomedical Research of Zhejiang Province and Cancer Center of Zhejiang University, Hangzhou, Zhejiang, 310006
China
Xuepeng Chen
Stomatology Hospital, School of Stomatology, Zhejiang University School of Medicine, No. 166 Qiutao Road, Shangcheng District, Hangzhou, Zhejiang, 310006
China
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/digm.digm_36_22
Three-dimensional (3D) printing technology, known as additive manufacturing, is an advanced technology that rapidly developed in the late 20th century. In the medical field, 3D printing technology has achieved breakthrough progress in medical model manufacturing, implant placement, and prosthodontics and orthodontics. In this paper, the application of 3D printing technology from the perspective of orthodontics, such as dental models, clear aligners, orthodontic brackets, transfer trays, and removable appliances, is reviewed. The application of 3D printing technology is increasingly used in the orthodontic field due to its advantages of high accuracy, high efficiency, simple operation and personalization, and an increasing number of economic applications in the medical field are worth the wait.
Keywords: Clinical application, Orthodontics, Three-dimensional printing technology
How to cite this article:
Su T, Zhang H, Kang T, Zhou M, Han J, Ning N, Lin H, Chen X, Chen Q. Application progress of three-dimensional printing technology in orthodontics. Digit Med 2022;8:31 |
How to cite this URL:
Su T, Zhang H, Kang T, Zhou M, Han J, Ning N, Lin H, Chen X, Chen Q. Application progress of three-dimensional printing technology in orthodontics. Digit Med [serial online] 2022 [cited 2023 Jun 8];8:31. Available from: http://www.digitmedicine.com/text.asp?2022/8/1/31/363935 |
| Introduction | |  |
Three-dimensional (3D) printing technology, known as additive manufacturing, is an advanced technology that rapidly developed in the late 20th century. 3D printing does not need to manufacture entity models, reduces staff involvement, simplifies the production process, improves production efficiency, and can also allow personalized designs and wholesale production. In the medical field, 3D printing has been widely used and has made breakthrough progress in medical model manufacturing, implant placement, and prosthodontics and orthodontics. This paper reviews the application of 3D printing technology from the perspective of orthodontics.
Three-dimensional printing technology
3D printing technology is currently applied in many fields[1],[2] due to the rapid development of computer technology. In the 1970s, Charlie Shull proposed the idea of 3D printing by selective solidification of continuous layers. In the 1980s, his company established the world's first printing equipment production company and 3D system and the first 3D printer stereolithography appearance (SLA-250), which also announced the birth of 3D printing technology.[3] Fused deposition modeling (FDM) and selective laser sintering (SLS) were invented one after another. In 1996, the name "3D printer" was formally used in production. After 2000, with the rapid development of computer technology, the application of 3D printing technology has become increasingly widespread.[4] It has been applied in the fields of automobile manufacturing, biomedicine, architecture, etc., 3D printing technology has gradually developed in the direction of specialization and standardization of printing equipment and materials.
3D printing enables the manufacturing of pieces layer by layer instead of common manufacturing methods that rely on machining, molding, and subtractive methods.[5] At present, the main technical forms of 3D printing include[6] SLS, SLA, selective laser melting (SLM), laminated object manufacturing, FDM, and inkjet printing. At present, 3D printing technology is applied to orthodontics, including SLA, SLS, and SLM. The differences among these methods are summarized in [Table 1].[7],[8] | Table 1: The different characteristics of stereolithography appearance, selective laser sintering, and selective laser melting.
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The types of printing materials mainly include the following: (1) thermoplastic materials, (2) photosensitive resin materials, (3) powdery material, (4) metallic materials, (5) ceramic, (6) graphene, and (7) poly ether-ether-ketone (PEEK) and other nanometer materials. At present, many printing materials have been applied in stomatology. 3D printing technology for photosensitive resin materials and metallic materials is relatively mature. The printing technology of ceramic and PEEK materials is also under exploration. The application of 3D-printed photosensitive resin materials is widely used in the fabrication of orthopedics and prostheses, such as dental models, surgical guides, and prostheses. At present, the photosensitive resin materials used for printing are mainly liquid photosensitive resins. On the premise of high precision, some complex structures can be printed as well. Metal is easily seen as a printing material, such as Ti, Ti6A14V (TC4), Ti6A17Nb, and Co-Cr alloys. Printed metal materials are mostly produced in the form of powder, and the properties of the product are closely related to the metal powder. 3D printing metal materials have been widely used in the fabrication of metal crowns, porcelain fused to metal crown bases, removable denture brackets, and personalized lingual orthodontic brackets. This technology, which greatly shortens the average production cycle, improves the production accuracy, and reduces the cost, is gradually replacing the traditional casting process. 3D printing technology of ceramic has the advantages of high manufacturing accuracy, high efficiency, and personalized customization, but there are also problems such as delamination, easy-to-produce microcracks, and insufficient density. As a result of the ceramic powder deficiency, the application of 3D printing ceramic products is relatively limited.
However, due to the consideration of biological safety, biocompatibility and biological function, the materials that can be used in stomatology are relatively limited, such as dental material developed by Formlabs, which is biocompatible and has passed CE certification. This material can be used for desktop 3D printers. Envision Tec company has two materials, e-guard and e-dent, certified by Food and Drug Administration FDA, which can be used to manufacture dental crowns. The ortho-rigid base, C and B, which was developed by Vertex Dental Company, has passed CE Class IIa and can be worn orally for approximately 1 month.[9]
3D printing relies on the cross-development of digital technology, precision machinery, and materials science and is increasingly widely used in integrated 3D printing, 3D scanning technology, medical image processing technology, and 3D model building technology. Scottish scholars completed the first 3D printing of artificial liver tissue in 2012.[10] In 2019, 3D printing of bone tissue, heart, and other human tissues and organs was also successfully completed.[11] 3D printing has great value for research and prospects in medical model manufacturing, tissue and organ regeneration, and bone reconstruction, especially in prosthodontics and orthodontics. This paper focuses on the application of 3D printing in orthodontics.
Digitization plays an increasingly important role in orthodontic treatment. Multisource data information matching is carried out by using software such as Dolphin, Mimics, and Hyper Work through accurate and rapid intraoral scanning,[12] condylar movement trajectories, medical radiological images, cone-beam computed tomography (CBCT), and magnetic resonance imaging. A patient's dentition information, soft and hard tissue characteristics, personalized mandibular movement, and jaw position relationship are reconstructed three-dimensionally, and then an orthodontic plan is developed comprehensively and precisely.[13] The function of 3D printing technology in clinical work should not be underestimated. Currently, 3D printing has been gradually used in digital dental models, clear aligners, personalized labial brackets and lingual brackets, removable appliances, transfer trays, personalized skeletal expanders, implant anchors, occlusal splints, and other aspects. It has consistently provided convenience for clinical operations in orthodontics.[14]
| Dental Model | | |
Model analysis is very important in orthodontics, where dental models can clearly display malocclusion. The model plays a vital role in orthodontic treatment plans, brace bonding, and clear aligners. However, the traditional plaster model is vulnerable to damage. It requires a large space to store in quantity, is difficult to transport, and has low copying accuracy. The model easily causes discomfort when taking impressions, and the fear and resistance of children may affect the accuracy of the model. Intraoral digital scanning is applied in dentistry.[15] The model collected is converted into a 3D digital model online and can be layered and sliced into a real model by 3D printing technology anywhere and anytime. Gholinia et al.[16] conducted a comparative study between the digital model and plaster model constructed from 22 patients, which confirmed that the accuracy of the digital model was definitely better. Tomassetti et al.[17],[18],[19] obtained digital information after scanning the plaster model, constructed a digital model, and compared them. They found that the digital model has better accuracy, feasibility, and economy.[2] Jiang[20] used CBCT to scan a plaster model and built a digital model to store it. In addition, Kau[21],[22] and other scholars also constructed a digital model by combining CT data and image superimposition technology.
| Clear Aligners | | |
Clear orthodontics is based on the development of computer science technology and 3D printing technology. The clear aligner is usually made by digital flow as follows:[23] intraoral scanning, digital model manipulation, 3D printing, postprint processing, and appliance fabrication. Moreover, clear orthodontics significantly improves the fabrication efficiency and avoids the positioning and adhesion of brackets and metal archwires and the continuous replacement of metal archwires. Instead, it is replaced regularly to achieve the goal of arrangement, which improves the experience and esthetics of patients and decreases the risk of periodontal diseases.
The material of the clear aligners includes various thermoplastic materials or combinations of materials. Its mechanical properties are changed by many factors, such as the characteristics of the material, the homogeneity of the thickness of the aligner, and the displacement of the appliance. Ryu et al.[24] studied changes in four types of thermoforming materials after the thermoforming process. The study showed that thermoforming decreases the transparency of thicker material and can also modify the surface hardness of some plastics. Thermoformed clear aligners have been observed to have different thicknesses, ranging from 0.5 to 1.5 mm, which can certainly affect their properties and clinical performance while inducing dental movement by pressure on the tooth surfaces.[25] However, due to the elastic deformation of this material, irreversible deformation often occurs after repeated wear, which influences the strength of the force.[26] In addition, the performance of the material will also be affected during thermoforming or vacuum forming, such as the decrease in accuracy and the change in transparency.[24] Therefore, some scientists applied 3D printing materials to solve these problems.[27],[28],[29] A study conducted by Prashant et al.[27] reported a successful 3D-printed 0.75 mm thick clear aligner using Dental LT® (Long Term) clear resin (Form Labs, Somerville, MA, USA) and compared it to a conventionally manufactured thermoformed dental clear aligner. The results showed that the precision of the appliance made by 3D printing was higher than that of the traditional method (2.55% < 4.41%). In addition, dental LT resin is an approved Class II a biocompatible material with high resistance to breaking and is ideal for gnathological splints, dental retainers, and other rigid direct-printed orthodontic appliances.[25] However, some problems remain, such as the unstable color of materials and biological safety,[27] which impact their widespread application in clinical practice.
| Orthodontic Bracket | | |
Krey et al.[30] proposed using a digital process and 3D printing technology to design personalized labial resin brackets for orthodontics. The results showed no significant difference between the dentition after 3 months and an ideal occlusal model of 3 months, and the patients were satisfied with the treatment effect. Although personalized customization is realized through this system, some problems remain, such as the sharp edge formed by printing causing gingivitis; the bracket wing is too large and easy to bend or crack.[31] For material selection for brackets, compared with that of resin materials and metal materials, the esthetic performance of ceramic materials is more prominent. Therefore, research on labial ceramic bracket-related 3D printing is increasing. Yang et al.[32] described the process of 3D printing to create personalized ceramic brackets for the first time: intraoral scanning, virtual diagnosis alignment, design for personalized brackets, 3D printing, sandblasting and embedding, polishing and glazing, sintering and polishing. Compared with other preformed ceramic brackets,[33] the color of 3D-printed ceramic brackets is deeper, as is the color of teeth. The brackets have better integrity, friction, and shear strength. Due to the change in processing technology and manufacturing methods, although the time for bracket design and manufacturing is prolonged, it can reduce the chairside time, avoid patient discomfort, and achieve better treatment effects.[34],[35]
Moreover, a greater demand for personalized design for lingual brackets is evident. Insufficient operation space may contribute to adhesive strength and oral retention, ultimately affecting the patient's pronunciation, tongue movement, periodontitis, and other adverse effects.[36] The 3D printing technology of lingual brackets has attracted increasing attention from scientists. Wiechmann et al.[37] took the lead in applying SLM technology to the design and production of a personalized lingual bracket. The thickness of the bracket base is only 0.4 mm, which has little impact on tongue movement and uncomfortable sensations, especially pronunciation. The 3D-printed metal lingual bracket with a free-form surface design is more suitable for the lingual shape of teeth. In addition, direct molding of personalized brackets results in better adhesion and less periodontal irritation. In contrast, the brackets are thinner, the area of the bracket base is larger, and the adhesive force is better.[38]
| Transfer Tray | | |
Accurate positioning of brackets is key for ideal orthodontic treatment. If the deviation is large, it may affect the root-bone relationship, axial inclination, crown torque, fenestration, and dehiscence. For lingual brackets, most of the direct bonding is difficult to achieve. Indirect bonding (IDB) bracket positioning measures the manual position on the plaster model, resulting in the transfer tray after the bracket is prebonded to reduce the limitation of intraoral operation, saliva moisture during the direct bonding process, and the influence of inaccurate tooth surface positioning. However, inevitable errors still occur during the transfer process because of the resin elasticity of the transfer tray. Ciuffolo et al.[39] designed a personalized labial bracket transfer tray. By oral scanning and CBCT, virtual tooth arrangement and bracket positioning, he reconstructed the 3D structure and finally designed a transfer tray for the lingual bracket. Some scholars[40] evaluated the accuracy of bracket position using thermoplastic and 3D-printed IDB trays, and the results showed that a 3D-printed IDB tray showed accuracy similar to that of conventional methods for bracket placement, with slightly greater bracket height accuracy. Moreover, another study[41] showed that both vacuum-formed trays and 3D-printed trays had better linear control than angular control of brackets. Furthermore, some scholars[42] investigated the transfer accuracy of two different design versions for 3D-printed IDB trays. The transfer accuracies of the investigated design versions for 3D-printed IDB trays show good and comparable results despite their different retention mechanisms for the attachments and are therefore both suitable for clinical practice. Whether it is applied to a single tooth or a segmented guide plate, it has outstanding advantages in accuracy and operability.[39],[43] Moreover, a whole-segment transfer tray can be used for mild malocclusion without obvious torsion, which markedly improves clinical efficiency and patient comfort.
| Removable Appliance | | |
Removable appliances play an important role in orthodontics, especially for pediatric patients. The inlab manufacturing process is relatively complicated and takes a long time, including taking impressions, using a plaster model, bending the retaining ring, filling the lip guard or tongue plate base, and grinding after the trial. The 3D-printed personalized appliance substantially shortens the production time, reducing the chairside time with high efficiency and accuracy. Relevant scholars[44] designed a digital mobile appliance combined with 3D printing. The retention meets the need for clinical use, which also dramatically promotes the development of personalized diagnosis and digital orthodontic treatment. A study proposed a new clear removable appliance to provide preschool-age children with an improved experience of early occlusal interference treatment. Appliances were designed with the help of 3D dental models and fabricated by 3D printing technology. The mechanical properties of the original dental coping sheet and thermoformed aligners were assessed in a simulated intraoral environment, demonstrating that a new clear removable appliance can correct early-stage anterior crossbite in a safe, comfortable, convenient and efficient manner.[45] In addition, eruption guidance appliances (EGAs) cannot meet all the specific needs of patients, especially for single tooth misalignment or dental asymmetry. A study showed a computer-aided design-based methodology for the design and manufacturing of a patient-specific EGA based on the 3D printing technique.[46] With low-cost procedures and customized shapes, this approach provides new design opportunities for applications.
| Three-Dimensional Printed Anchorage Devices And Palate Expander | | |
In the process of orthodontic treatment, orthodontic force inevitably produces a reaction force with the same size and opposite direction. Anchorage in orthodontics refers to a device that resists the reaction force.[47] Many methods can strengthen anchorage in clinical practice, such as the extraoral arch, lingual arch, transverse palatal bar,[48] Nance arch, and absolute anchorage-micro-implant methods.[49] At present, some scholars use 3D printing technology to simplify the production of Transpalatal Arch, (TPA) and obtain data from intraoral scanning or plaster model scanning, followed by digital TPA designed by software. This method saves patients' time for appointments. Digital data can be reused repeatedly and are convenient to store. Some scholars have tried to explore various anchorage systems to correct buccally flared maxillary 2nd molars and to provide vertical control, such as mini-screws and modified TPAs, while reducing the side effects and other disadvantages of traditional TPAs, such as gingivitis and arteriovenous mini-screws. From the results of 3D finite element models, a study showed that 3D TPA might be better than a 3D splint as an anchor to correct buccally flared maxillary 2nd molars. A 3D finite element analysis found that 3D TPA was better than 3D splint as an anchor to correct buccally flared 2nd molars.[50] However, the material is also limited because of biocompatibility requirements for the long term.
An interesting study illustrated the digital process in the custom fabrication of a metallic mini-implant-supported palate expander. After mini-implant insertion into the palate, recording an intraoral digital scan, digital design with incorporation of a scanned expansion mechanism, direct 3D metal printing via laser melting, laser welding of the hyrax mechanism, and insertion, the appliance is produced. 3D metal-printed orthodontic appliances are an efficient and accurate strategy to fabricate palatal mini-implant-borne appliances.[51] A novel methodology has been developed to plan the MSE position using the digital model of dental arches and CBCT. By evaluating the bone morphology of the palate and midface on patient CBCT, the placement of MSE is more accurate in micro-implant insertion sites, and the effect of maxillary expansion is better than that with traditional sites.[52]
| Three-Dimensional-Printed Implant Anchorage Guide | | |
As mentioned above, implant anchorage plays an irreplaceable role in orthodontic anchorage. The traditional method of implant placement is based on dentists' clinical experience. Suitable sites for insertion include the inter-radicular alveolar bone in the upper and lower jaws and the anterior palate in the maxilla. The following factors may compromise the desired performance of the implant: the point of insertion in the mucosa, the angle to the occlusal plane, the length, and the exact position among roots regarding tooth movement.[53]
For some insufficient or relatively limited alveolar bone areas, such as between the maxillary first molar and the second premolar, complications easily occur, such as implant slippage and tooth root injury. With the development of digitization, the implant can be placed accurately and efficiently under the application of digital navigation and digital implant guidance. Then, similar methods were also copied in other fields of orthodontics. Some experts use CBCT to rebuild a 3D jaw on the software and design the position and angle of implant placement virtually in Mimics software. Finally, the 3D-printed implant guide was successfully completed. With a reasonable preoperative design, they not only achieved the ideal implant placement effect but also reduced the probability of complications. Previous studies have also suggested the use of mini-implant guides when implanting between roots.[54] CBCT imaging for exact mini-implant guidance and implementation has been used by several researchers. The digital flow can overcome inaccuracies introduced by designing the guide on plaster models or incorporating elements that compromise the point of insertion, exact pathway and inclination of the mini-implant.[55] Based on technical technology, the digital implant surgical guide is mainly made of metal powder, liquid resin, ABS material, and PEEK material.[56]
| Orthognathic Splints | | |
For some patients with skeletal malocclusion, orthodontic and orthognathic treatment is often needed. After preoperative orthodontic treatment with tooth compensation removed, orthodontic surgical splints (OSS) were designed and manufactured to locate the jaw position during orthognathic surgery. It also helps stabilize the jaw block after the operation. The accuracy of the OSS affects the accuracy of orthognathic surgery.[57],[58] Many scholars have used 3D printing technology in craniomaxillofacial surgery, burn and plastic surgery, etc., 3D printing OSS[59],[60] has gradually replaced manual OSS with its advantages of low cost, high efficiency, and high precision. Studies[61],[62] have shown that the accuracy of 3D printing OSS is superior or equivalent to that of traditional OSS. Song and Baek[63] found that the maximum error of the 3D printing OSS is only 1.00 mm, which is smaller than that of manual splints, but no obvious difference exists between 3D-printed splints and traditional manual splints; this result is similar to the results of Kim (0.18–1.04 mm)[61] and Shaheen (0.12–0.88 mm).[57]
| Conclusion | | |
The application of 3D printing technology is increasingly used in stomatology and is also commonly used in the orthodontic field due to its advantages of high accuracy, high efficiency, simple operation, and personalization.[64],[65] However, 3D printing technology still has some problems, such as biosafety, high technical costs, printing material limitations, and rough and sharp edges during surface treatment, which also hinder its wide application and promotion in oral therapy. Global regulatory bodies have not yet implemented guidance for the use of 3D printing in surgery[66] or in dentistry, but at some stage, regulators will need to set appropriate standards. However, with the continuous updating and upgrading of materials, these problems will be gradually solved. The management and supervision system of 3D printing technology will be improved in the future. Degradable materials and other new materials, such as PEEK, nontoxic antibacterial materials, and hydrogels, have been continuously studied in recent years. Therefore, the application of 3D printing technology in orthodontics is worth exploring in the research and development of new safe biomaterials, orthodontic-related 3D-design-data library updating, and technology and equipment innovation in the 3D printing industry.
Financial support and sponsorship
This work has been supported by the National Natural Science Foundation of China (No. 81400511), Zhejiang Provincial Natural Science Foundation of China (No. LY18H140001).
Conflicts of interest
There are no conflicts of interest.
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[Table 1]
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