|
 
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| REVIEW ARTICLE |
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| Year : 2023 | Volume
: 15
| Issue : 1 | Page : 15-27 |
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3D printing in orthodontics: A narrative review
Sruthi Harikrishnan, Aravind Kumar Subramanian
Department of Orthodontics, Saveetha Dental College and Hospital, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai, India
| Date of Submission | 18-Apr-2022 |
| Date of Decision | 01-Oct-2022 |
| Date of Acceptance | 16-Nov-2022 |
| Date of Web Publication | 28-Feb-2023 |
Correspondence Address:
Dr. Aravind Kumar Subramanian
Department of Orthodontics, Saveetha Dental College and Hospital, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai 600077, Tamil Nadu
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/jioh.jioh_83_22
Aim: Digital technology profoundly impacts every aspect of orthodontics, from diagnosis and treatment planning to appliance fabrication. Integrating computer-aided designing tools and rapid prototyping hardware has allowed orthodontic practices and laboratories worldwide to revolutionize their workflows. This narrative review aims to consolidate literature findings regarding the use of three-dimensional (3D) printing technology in orthodontics in terms of its current state of development and availability while also exploring the type of printing technology used, accuracy, and efficiency of its potential use in clinical orthodontics. Materials and Methods: 3D printing in orthodontics has been the subject of a comprehensive electronic literature search from 2010 to 2020 using PubMed and Google Scholar databases with relevant MeSH terms and keywords. Orthodontics, 3D printing, 3D-printing processes, accuracy, precision, and efficiency were used to identify studies for this review. Two calibrated reviewers separately applied inclusion and exclusion criteria to each article. Selected article references were checked to expand the article search. Types of 3D printers, assessment techniques, and examined parameters were considered for data extraction, and qualitative analysis was done for evidence synthesis. Results: The search strategy yielded 108 titles. Thirty-six articles that met our inclusion criteria were included in the qualitative analysis: 20 articles were about cast models, seven about indirect bonding, three about aligners, and six about surgical splint fabrication. The most common 3D-printed device types were models. The most commonly used 3D-printing techniques are stereolithography and digital light processing for orthodontic applications. 3D-printed clear aligners are more precise than thermoformed clear dental aligners. Digital occlusal splint and surgical templates increase accuracy, reliability, and efficiency than a conventional one. Conclusions: A 3D printer can be used by the orthodontist to create an entirely digital workflow. Although the 3D-printing technologies used for orthodontic appliance fabrication have demonstrated equal or superior accuracy to conventional models, there is insufficient evidence to conclude that one type of printing is more accurate and efficient than the others. These findings suggest that conventional impressions and stone models can be eliminated, reducing the amount of storage required in the office and improving practice efficiency, appliance fit, and model reuse. Digital 3D-printed appliances are more accurate, reliable, and efficient than conventional ones. Future research must identify potential 3D-printing technology specific to various orthodontic procedures. Keywords: 3D Printing, CAD-CAM, Digital Orthodontics, Orthodontics
How to cite this article:
Harikrishnan S, Subramanian AK. 3D printing in orthodontics: A narrative review. J Int Oral Health 2023;15:15-27 |
| Introduction | |  |
Orthodontics is currently benefiting from increased precision and accuracy using computer-aided design and manufacturing (CAD/CAM) in practice. The CAD-CAM paradigm necessitates using three functional elements: a data acquisition digitalization instrument, digital data editing, and processing software, and a method for manufacturing a final product from digital data. Three-dimensional (3D) printing can either be done subtractively or additively. Subtractive manufacturing comprises cutting or removing material from a block to obtain a particular shape. Contrarily, additive manufacturing (AM) refers to a technology that involves layering a raw material in a specified pattern to create the desired object.
In the past, resin 3D printers were expensive and bulky, demanding specialized technicians and high-priced maintenance. Desktop printers are now capable of producing an output of an industrial standard at a far lower cost and with unparalleled versatility. By bringing together developmental biology, cell biology, tissue engineering, and regenerative medicine, a slew of new possibilities have been made strategic advantage of 3D bioprinting to fabricate tissue replicas such as blood vessels for patient implantation and medication testing.[1],[2] This narrative review aims to consolidate literature findings regarding the use of 3D-printing technology in orthodontics in terms of its current state of development and availability while also exploring the type of printing technology used, accuracy, and efficiency of its potential use in clinical orthodontics.
| Materials and Methods | | |
Search strategy
3D printing in orthodontics has been the subject of a comprehensive electronic literature search from 2010 to 2020 using PubMed and Google Scholar databases with relevant MeSH terms and keywords. Combinations of the following keywords were used for the identification of the studies to be considered in this review: “Orthodontics,” “3D printing,” “3D printing techniques,” “Accuracy,” “Precision,” and “Efficiency.” Two calibrated reviewers conducted the search, independently applying the inclusion and exclusion criteria to each article with adequate concordance. To broaden the search for relevant articles, selected article references were reviewed.
Eligibility criteria
Inclusion criteria
Following are the inclusion criteria:
Studies involving 3D printing for cast model fabrication
Studies involving 3D printing for aligner fabrication
Studies involving 3D printing for indirect bonding tray fabrication
Studies involving 3D printing for surgical templates for orthognathic surgery (OGS) and mini-implant placement
Studies involving 3D printing for any orthodontic appliance fabrication
Studies reporting accuracy, precision, or efficiency of one type of 3D-printing technique compared with another type of 3D-printing technique or conventional/conventional technique for orthodontic applications.
Exclusion criteria
Following are the exclusion criteria:
No control group
Case reports, case series, review articles, systematic reviews, and meta-analysis.
Data analysis
The following characteristics were considered for data extraction: the type of 3D printers used, method of assessment, and parameter assessed. Qualitative analysis was done for evidence synthesis.
| Results | | |
The flow of records through the reviewing process is shown in [Figure 1]. The search strategy yielded 108 titles. After screening, 72 articles were rejected based on the title and abstract because they did not meet the inclusion/exclusion criteria. The remaining 36 articles were read entirely. Finally, after careful analysis, 36 articles that fulfilled our inclusion criteria were included in the qualitative analysis. The 36 articles were further divided based on the orthodontic application with 20 articles relevant to cast models [Table 1], seven articles on indirect bonding [Table 2], three articles on aligners [Table 3], and six articles on surgical splint fabrication [Table 4]. The results of this review show that a wide range of 3D-printed devices have been clinically trialed, but few articles have rigorously assessed the efficacy or effectiveness of clinical 3D-printed devices. The results of data extraction are summarized below.
Models
Cast models are inextricably linked to orthodontic practice. Conventional models, on the other hand, are oversized, require storage space, and cannot be replicated. Through software programs, digital models assist in arch alignment and idealist tooth movement. Brackets can be successfully debonded using these tools before the final appointment. 3D-printed cast replicas are used to capture precise measurements of teeth and arches. 3D printers have revolutionized conventional stone models. By printing 3D models through intraoral digital scans, patients are more cooperative because the conventional challenges with impression taking are avoided.
It was found by Zhang et al. that the printing accuracy of 3D-printed dental models was higher at 50 μm thickness.[3] 3D-printed models comparing different technologies with differing model base designs showed that regardless of solid or hollow model bases, the printer technology affected the precision of 3D-printed models. Compared with the digital light processing (DLP) printer, the CLIP technology printer had a substantially lower variance from the reference model.[4] Conventional dental casts and 3D-printed models made with three different printer types were compared for their accuracy and reproducibility; the results revealed that the conventional cast’s volumetric changes were less.[5] The precision of linear measurements taken from printed models was slightly lower than that of plaster replicas in a study conducted by Brown et al.[6] A study by Favero et al. examined the effect of print layer height on the accuracy of 3D-printed models. They found that the 25-m and 100-m layer height groups had a more significant and a lesser deviation, respectively.[7] While studying the 3D-printed model’s anterior and posterior dentition print errors, Dong et al. found that the posterior dentition’s average deviation was more significant than the anterior region’s. The pits and fissures of posterior teeth differed much more than in other places.[8],[9] In orthodontics, digital models must take into consideration all of these variances. Perhaps, digital and 3D-printed models have not yet supplanted conventional models to the point where they are entirely obsolete.
Indirect bonding
Precision bracket placement has been a significant aspect in establishing an ideal tooth location. The introduction of straight-wire orthodontic bracket location is critical to achieving the optimum treatment outcome in a short period, with the least amount of additional arch wire bending and repositioning of brackets. Conventional indirect bonding, on the other hand, involves placing shelves directly onto a patient’s model and creating custom trays using silicone-based and vacuum-formed materials in a laboratory environment.
For orthodontic indirect bonding trays that were digitally and conventionally created, Plattner et al. showed that the active working period was much shorter in 3D-printing technology than in conventionally produced trays.[10] 3D transfer trays printed using polyvinyl siloxane (PVS) and vacuum-formed indirect bonding trays were evaluated by Chaudhary et al. and Niu et al., respectively. Except for vertical transfers, they discovered that 3D-printed trays were more precise than conventional transfer method PVS trays.[11],[12] By utilizing CAD-CAM, Xue et al. came up with a unique and innovative guided bonding tool. They observed that the approach was able to transfer the planned bracket position from the digital setup to the patient’s dentition with a high degree of accuracy.[13] For linear measurements, such as mesiodistal, buccolingual, and occlusal gingival dimensions, a study by Bachour et al. indicated that 3D-printed trays had a high degree of positioning accuracy.[14] However, the precision of angular measurement transfer (torque, tip, and rotation) remains under dispute [Table 2].
Aligners
In recent years, as people have become more conscious of the need for good dental hygiene, the demand for high-quality orthodontic treatment has skyrocketed. Orthodontists often employ transparent dental aligners to straighten out crooked or mismatched teeth because of the large variety of aligner models available. Aligners are conventionally made by obtaining a patient’s impression of their teeth on plaster models and then vacuum thermoforming a biocompatible thermoplastic clear sheet. By utilizing digital technology, 3D modeling techniques, and rapid prototyping, it is possible to eliminate geometrical mistakes during impression collecting and thermoforming. In order to achieve optimal occlusion, dental arches can be aligned virtually using a variety of programs that are now on the market. Complex malocclusion cases can be easily planned using laboratory-created tooth movement. Several phases of alignment can be prepared from scanned plaster models. These stages can subsequently be 3D printed more.
Precisely, aligners with low geometric defects can be constructed using a thermoformed aligner sheet. A clear biocompatible aligner might be 3D printed directly for patient use to reduce these errors further, eliminating any intermediate stages that lead to inaccuracy. Furthermore, direct aligner printing saves money in terms of time, labor, and knowledge. Because the variations between sequential aligners are only 0.2–0.3 mm, errors greater than 0.3 mm have been proven to alter tooth movement expression.
Researchers found that 3D-printed clear aligners are more precise than thermoformed clear dental aligners.[15] According to Ahn et al., multihybrid materials with a three-layer combination of polyethlene glycol, thermoplastic polyurethane, and reinforced resin core could be developed to address the inherent limits of thermoplastic polymer materials currently employed in orthodontics.[16] By comparing the thickness of a digitally developed aligner to its 3D-printed counterpart, Edelmann et al. found that clear aligners created by the 3D printer had wall thicknesses that exceeded those predicted. It was observed that print orientation had no significant effect on the overall accuracy of the 3D-printed aligners in a similar study by McCarty et al.[17] [Table 3].
Surgical templates for orthognathic surgery and mini-implant placement
OGS is used to address facial deformities, particularly ones caused by dental malocclusion, diseases, traumas, and birth defects. Recent developments in dentomaxillofacial imaging with computed tomography (CT) and cone-beam CT (CBCT) have made it possible for CAD/CAM software to construct various algorithms—software for virtual 3D planning of OGS (CBCT). Orthognathic operations to treat craniofacial and maxillomandibular abnormalities and anomalies can be performed correctly with the use of 3D-printed templates. To achieve better results during surgery, surgeons are now using patient-specific 3D-printed models and guides to transfer the plans for the surgical procedure into the operating theater, resulting in a better outcome. Osteotomy/cutting guides, repositioning aids, spacers, fixation plates/implants, and 3D-printed models are OGS’s most frequent 3D-printing applications [Table 4].
Plaster models, a face-bow, and an articulator are used in the conventional means of producing an occlusal splint. Better quantitative control and efficiency are provided by the digital occlusal splint. It is more accurate, reliable, and consistent than a conventional mechanical device.[18],[19],[20],[21] Splints with guidance ramps that are flat and cover the entire occlusal area were originally developed by Gander et al.[22] Osteotomy guides, like the computerized planning repositioning guide, are used to guarantee that the osteotomy cuts are in the correct position. According to numerous research, 3D-printed repositioning guides can be used in place of intermediate wafers for translating virtual surgical designs into the intraoperative context.[23],[24] 3D-printed spacers can be used when the maxilla’s vertical dimension is lengthened, in the bilateral sagittal split osteotomy procedure when the mandible is rotated, or increase the space in symmetry or revision of the chin’s contours and genioplasty. These spacers are maintained in their intended configuration during plate and screw fixation. 3D-printed templates for fabricating precontouring fixation plates in managing craniofacial fractures and orthopedic correction of jaw defects predisposing to malocclusion are useful adjuncts to modern orthodontic and maxillofacial surgery practice.
The temporary anchorage devices is becoming more viable as an exceptional alternative to conventional orthodontic anchorage systems as the requirement for maximum therapeutic results with minimal patient compliance intensifies. The location of the mini-screw insertion is crucial, and it must be carefully examined in terms of soft tissue, biomechanics, accessibility, and patient comfort. Mini-implant alignment and miniscrew assisted rapid palatal expander placement can be accomplished using 3D-printed surgical guides.[25],[26] For a range of clinical diseases, including canine autotransplantation, 3D surgical templates were developed digitally. Customizing the fit and positioning of orthodontic microplates have been made possible by using CAD and 3D-printing technologies. CBCT scans were used to build a 3D-printed model of the patient’s bone, which is then used as a template to position and modify the miniplate to the bone’s shape.[27]
Other orthodontic appliances
Most orthodontic appliances were made by conventional means by orthodontists till the late 1970s. For faster patient treatment, 3D printing allows for the direct fabrication of unique designs. Using 3D printing, orthodontists have greater control over their treatment plans, leading to a more efficient, safe, and comfortable experience for their patients. Biocompatibility and cytotoxicity testing are required for all resin-based intraoral appliances before they may be used for manufacturing. As a result, these materials should be dimensionally and color-stable, as well as resistant to oral degradation. Newly printed appliances must be washed and postcured in order to ensure quality and avoid contamination with nonintraoral resins.
Laser metal sintering or selective laser sintering can be used to create metallic appliances from 3D printed. Orthodontists may now design and construct metal orthodontic appliances more quickly and easily than in the past. The typical process of constructing an appliance comprises separator placement, impression taking, separator replacement, and final appliance delivery. These steps are reduced to scanning the patient’s mouth with intraoral scanners and delivering the finished product in digital appliance fabrication. Metal “bands” manufactured via AM overlay the occlusal surfaces, eliminating the need for separators. Most commonly 3D-manufactured metal appliances are hyrax-style rapid palatal expansion. In addition to Hawley’s retainer and diagnostic settings, this cutting-edge additive printing technique allows for the virtual creation of other removable appliances. Sassani et al. demonstrated the first CAD-CAM removable acrylic orthodontic appliances.[28] Using CAD and AM, Al Moradi et al. developed an Andresen activator and sleep apnea equipment. Recently, a series of 3D-printed molding plates are effective in nasoalveolar molding.[29],[30]
With tailored patient-specific orthodontic brackets, treatment efficiency takes a giant leap forward. To design the optimal physical qualities for moving teeth into the required alignment, intraoral scans and orthodontic simulator software are used. Light-force orthodontics pioneered the use of 3D printing to build custom braces for each patient. 3D-printing polycrystalline alumina ceramic into optimized twin bracket geometries allows for extremely efficient tooth movement. 3D workflow can be used in the future to create innovative ideas such as an attachment for impacted teeth-fixed twin block fabrication, etc.
Factors affecting 3D-printing accuracy
Dimensional errors are frequently caused by resin shrinkage during 3D printing. Several variables may influence the precision of 3D-printed objects. These include the speed and intensity of the polymerizing energy source, the direction and orientation of the build, the positioning of 3D objects on the build platform, the amount and configuration of supporting structures, the number of layers, and material shrinkage between layers, and postprocessing procedures.
Build orientation
Product accuracy and biocompatibility can all be affected by the build orientation. For the most precise 3D-printed dentures, Gao et al. tested mandibular copulate dentures made at various angles and found that 45° was the best orientation for the build.[31] Research by Quintana et al. found that the tensile stress and elasticity modulus of stereolithography (SLA)-fabricated samples can be affected by the construction orientation.[32] In terms of tensile strength and elasticity modulus, the axis and location had no effect, but the layout parameters were. Another investigation found that the material’s compressive strength was higher when printing layers perpendicular to the load direction were more efficient than parallel.[33],[34] According to Edelmann et al., the overall precision of the 3D-printed aligner is unaffected by print orientation or postprint curing period.[17] There is a statistically significant interaction between 3D-printed model precision and build angle and layer height, as discovered by Ko et al. This interaction shifts as layer height varies and vice versa.[35]
Layer thickness
For each printing method, the ideal layer thickness may vary. It is faster to build with fewer slices (a thicker layer), but the precision is reduced as the layer thickness increases. According to some reports, the sample’s strength rises when printed using SLA technology with a smaller thickness. The ideal layer thickness was determined by Chockalingam et al. to be 100 m for a posturing time of 60 min and vertical construction.[34] Final orthodontic samples were examined by Loflin et al. using different layer thicknesses, and the results showed that 100 m was the optimum option.[36]
Infill ratio
This is a measure of the amount of solid material in the final printed object. The printer obtains the optimal infill ratio by changing the air gap between the produced lines. It is more crucial for fused deposition modeling (FDM) technology than others.[37] Filling percentage is the most critical element affecting FDM’s compressive strength, according to Milde et al.[38] Increasing the filling rate also enhances strength. When the filling rate is modest, proper design and construction of the structure might yield a greater ultimate power.[37],[39]
Postprocessing
Postprocessing can significantly increase the performance of printed samples, but it comes at a cost and takes time. SLA advancement has been hampered by shrinkage and distortion of resin materials; however, the postcuring approach resolves this problem. Microwave and UV postcuring can increase the modulus of elasticity and the ultimate strength of many materials. Enhanced laser power can simultaneously improve the sample’s strength.
Circular economy in 3D printing
Although 3D printing is all about accuracy and minimization of waste formation, during dental 3D printing, there is a certain amount of waste that cannot be avoided. The amount of 3D-printing waste generated in dentistry has not yet been established as it is upcoming technology. Some examples are the support structures that most printers have as built-in features to avoid deflection and the creation of n numbers of 3D-printed models representing each level of alignment during the virtual planning on which thermoforming aligners are made. It is imperative to limit the amount of scrap and develop a circular economy in the future. One way to accomplish this is by recycling. However, data available on the recycling of 3D-printing wastes are minimal. Physical recycling processes, such as shredding and reprocessing after melting or high-temperature deterioration, are typically used to treat 3D-printing waste. Recycling efficiently while also being environmentally friendly is difficult with these approaches. The development of biodegradable polymer or catalysts/solvents that can promote the degradation of 3D-printed dental products becomes necessary in the future.
| Discussion | | |
The results of this review show that a wide range of 3D-printed devices has been clinically trialed, but few articles have rigorously assessed the efficacy or effectiveness of clinical 3D-printed devices. Various studies retrieved for qualitative analysis in this review used different 3D-printing techniques, including SLA, DLP, FDM, selective laser sintering, and binder jetting. The most commonly used 3D-printing techniques were SLA and DLP [Figure 2]. The most common 3D-printed device types were models (55.5%), followed by indirect bonding trays (19%), surgical splints for OGS (16%), and direct printed aligners (8%). 5.5% of the detailed studies accessed the time efficiency of the different printers in printing the same appliances. About 91% of the studies involved access accuracy of the various types of printers. Most studies assessed accuracy through trueness and precision by superimposing STL data of reference and experimental models. The root means square (RMS) value and color difference map were used for quantitative and qualitative analysis between the reference and experimental objects. Other methods used for accuracy assessment are model analysis and conventional linear and angular measurement and occlusal fit. | Figure 2: (A) Stereolithography—a laser beam selectively cures the liquid resin spot by spot; (B) digital light processing—a projector cast light over the entire layer to cure it all at once
Click here to view |
Analysis revealed that the use of 3D printing, orthodontic appliances can be made easily and more accurately. Most commonly 3D-manufactured metal appliances are hyrax-style rapid palatal expansion. The accuracy of models can be affected by the type of printer or the technology used. A study done by Tsolakis et al. also found the same, and according to them, polyjet photo polymer is the most accurate technology. According to this study, layer height and model positioning do not affect the accuracy of appliance.[40] The data in our study suggest that there is no clear relationship between positioning and accuracy. The continuous liquid interface production printer found to have a lower variance as compared to DLP printer. 3D-printed clear aligners are more precise than thermoformed clear dental aligners. A similar study suggests that 3D direct printed aligners are superior to those of thermoformed manufactured aligners because of the prior’s increased accuracy, load resistance, and lower deformation.[29] Digital occlusal splint and surgical templates increase accuracy, reliability, and efficiency than a conventional ones. Other reviews done on similar topics also conclude that the technology aids in better understanding of diagnosis and treatment planning and provides more accurate results.[30] Only in case of models, both linear and volumetric changes were less in the conventional casts, and digital and 3D-printed models have not yet supplanted conventional models to the point where they are entirely obsolete.
Several variables may influence the precision of 3D-printed objects. These include the speed and intensity of the polymerizing energy source, the amount and configuration of supporting structures, the number and thickness of layers, material shrinkage between layers, and postprocessing procedures. Proper designing and postprocessing procedure increase the strength. Ideal layer thickness is found to be 100 m.
This review gives comprehensive coverage of 3D-printing techniques used in orthodontics. Initial scoping revealed that qualitative research literature was too heterogeneous to permit a systematic review of qualitative studies. As this is not a systematic review and there were few articles found, evaluations of methodological quality were not used to exclude articles from the study.
| Conclusions | | |
Orthodontists are increasingly relying on 3D printing, and the technology’s potential applications are rapidly expanding. A 3D printer can be used by the orthodontist to create an entirely digital workflow. SLA, DLP, FDM, and polyjetting (PJ) are the most commonly used 3D-printing technologies for orthodontic applications. Although all of these 3D-printing technologies have demonstrated equal or superior accuracy to conventional models, there is insufficient evidence to conclude that one type of printing is more accurate and efficient than the others. These findings suggest that conventional impressions and stone models can be eliminated, reducing the amount of storage required in the office and improving practice efficiency, appliance fit, and model reuse. Digital 3D-printed appliances increase accuracy, reliability, and efficiency than conventional ones. Future research must identify potential 3D-printing technology specific for various orthodontic procedures. Recycling efficiently while also being environmentally friendly is a major challenge with these approaches. The development of biodegradable polymer or catalysts/solvents that can promote the degradation of 3D-printed dental products becomes necessary in the future.
Acknowledgements
The authors would like to thank Saveetha Dental College and Hospitals, SIMATS, and Saveetha University for their constant support.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
Authors’ contributions
AKS: conceptualization, methodology validation, writing—review and editing, supervision, project administration; SH: conceptualization, methodology, software, investigation, resources, writing.
Ethical policy and institutional review board statement
Nil.
Patient declaration of consent
Nil.
Data availability statement
Data available on request.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]
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