Forces and moments generated during extrusion of a maxillary central incisor with clear aligners: an in vitro study

3D-Printed Clear Aligners: An Emerging Alternative to the Conventional Thermoformed Aligners? - A Systematic Review

OBJECTIVES

To assess the differences between the traditional thermoformed clear aligners (TFA) and the emerging 3D-printed clear aligners (DPA) by comparing their mechanical and chemical properties, manufacturing process, accuracy trueness and precision, and effect on sustainability. To evaluate whether 3D-printing is more efficient than thermoforming in the manufacturing of clear aligners; Data: Data was collected from scientific articles related to 3D-printed aligners' properties and comparative cross-referenced articles related to the thermoformed aligners' properties; Sources: The sources assessed to retrieve the articles were scientific databases Scopus and PubMed; Study selection: A PICO format research question guided the study selection by both assisting in the formulation of keyword combinations and establishing a set of inclusion and exclusion criteria to meet this review's objectives; Results: The results indicate that both aligners have good mechanical properties, but the DPA distinguished themselves with two novel properties, shape memory and design flexibility. Additionally, they exerted a consistent force profile in contrast to the TFA. The DPA have higher accuracy, trueness and precision than the TFA, however similar to the thermoforming process, direct-printing also varied the thickness of the DPA from the original master STL model. There are limited studies on sustainability and biocompatibility of the DPA; Conclusions: Following this review, it can be concluded that 3D-printed aligners are likely to serve as an alternative to the thermoformed aligners in the near future, seeing their innovative and promising properties. However, further experimental studies with higher quality of evidence and an emphasis on randomization are necessary to confirm current laboratory-based studies' findings and address important limitations before promoting the aligners to a larger audience.

CLINICAL SIGNIFICANCE

Seeing the design flexibility benefits of 3D-printing technology, and the shape memory property of currently marketed 3D-printed aligners, this could positively impact the accomplishment of precise, desired orthodontic outcomes, also while potentially reducing clinical treatment time.

A study on the compressive strength of three-dimensional direct printing aligner material for specific designing of clear aligners

BACKGROUND

The demand for orthodontic treatment using clear aligners has been gradually increasing because of their superior esthetics compared with conventional fixed orthodontic therapy. This study aimed to evaluate and compare the compressive strength of three-dimensional direct printing aligners (3DPA) with that of conventional thermo-forming aligners (TFA) to determine their clinical applicability. In the experimental group, the 3DPA material TC-85 (TC-85 full) was used to create angular protrusions called rectangular pressure areas (RPA). A protrusion akin to the power ridge typically employed in conventional TFAs was created using glycol-modified polyethylene terephthalate (PETG; Control 1). RPA was created using the same TC-85 without filling the protrusions (TC-85 blank; Control 2). Compression cycle tests were conducted on an LTM 3 h electrodynamic testing machine (Zwick Roell, Germany), with 500 cycles and compression depths of 100, 300, 500, and 700 µm. Twenty specimens were tested for PETG, 17 for the TC-85 blank, and 19 for the TC-85 full.

RESULTS

Changes in the compressive force were assessed based on the material and thickness. The results indicated significantly higher and broader ranges of compressive strength for specimens fabricated with the 3DPA material TC-85 compared with those fabricated using PETG. Among the TC-85 specimens, TC-85 full demonstrated the highest statistically significant compressive strength .

CONCLUSIONS

3DPA technology enables precise modifications in the shape and inner thickness at specific dental sites, including the creation of ridges in targeted areas, of aligners. These alterations enhance the biomechanical capability of aligners to exert selective forces necessary for desired tooth movement while reducing the number of attachments, thereby demonstrating the clinical potential of 3D-printed aligners in orthodontic treatment.

Directly printed aligner therapy: A 12-month evaluation of application and effectiveness

INTRODUCTION

Directly printed aligners (DPAs) are gaining in popularity, potentially streamlining manufacturing, decreasing environmental waste, and offering enhanced adaptation and tailoring. This transition has been facilitated by advances in materials, software, and production. Although DPAs may have enhanced versatility and application in the management of more complex malocclusions, there is little research evaluating their effectiveness.

METHODS

A total of 54 patients undergoing treatment with DPAs were evaluated for occlusal improvement, overall treatment duration, and adverse effects. Regression models were fit to evaluate the association between the need for refinement, final peer assessment rating (PAR) score, and independent variables, including the total number of aligners and treatment indications.

RESULTS

The mean number of aligners in the initial plan was 7.1 ± 2.9 and 5.1 ± 4.3 in maxillary and mandibular arches. Refinement was required in 40.8% (n = 20). The pretreatment PAR score of 17.01 ± 7.93 showed a significant improvement (86.6%), with a final PAR score of 2.25 ± 1.15. Minor complications were noted in 3 participants. The need for refinement was unrelated to the total number of aligners (odds ratio, 1.05; 95% confidence interval, 0.94-1.18; P = 0.36). There was weak evidence of an association between the final PAR score and the total number of aligners (odds ratio, -0.03; 95% confidence interval, -0.07 to 0.003, P = 0.07).

CONCLUSIONS

On the basis of this preliminary retrospective evaluation, DPAs may be used to manage mild-moderate malocclusion, producing a significant reduction in PAR score. Nevertheless, additional prospective research is required to confirm these findings and compare the relative merits of DPAs to alternatives.

Efficacy of microchips and 3D sensors for orthodontic force measurement: A systematic review of in vitro studies

OBJECTIVE

To evaluate the efficacy of microchips and 3D microsensors in the measurement of orthodontic forces.

METHODS

Through September 2023, comprehensive searches were conducted on PubMed/MEDLINE, SCOPUS and SCIELO without restrictions.

RESULTS

After removing duplicate entries and applying the eligibility criteria, 23 studies were included for analysis. All the studies were conducted in vitro, and slightly more than half of them were centred on evaluating orthodontic forces exerted by aligners. Eight utilized microchips as measurement tools, while the remaining studies made use of 3D microsensors for their assessments. In the context of fixed appliances, key findings included a high level of agreement in 3-dimensional orthodontic force detection between simulation results and actual applied forces. Incorporating critical force-moment combinations during smart bracket calibration reduced measurement errors for most components. Translational tooth movement revealed a moment-to-force ratio, aligning with the bracket's centre of resistance. The primary findings in relation to aligners revealed several significant factors affecting the forces exerted by them. Notably, the foil thickness and staging were found to have a considerable impact on these forces, with optimal force transmission occurring at a layer height of 150 μm. Furthermore, the type of material used in 3D-printing aligners influenced the force levels, with attachments proving effective in generating extrusive forces. Deliberate adjustments in aligner thickness were observed to alter the forces and moments generated.

CONCLUSIONS

Microchips and 3D sensors provide precise and quantitative measurements of orthodontic forces in in vitro studies, enabling accurate monitoring and control of tooth movement.

Evaluation of different designs of 3D printed clear aligners on mandibular premolar extrusion using force/moment measurement devices and digital image correlation method

Objective

This study aimed to investigate the effect of three-dimensional (3D) printed clear aligners (CA) with different designs on the extrusion of mandibular premolars using a force/moment measurement system and digital image correlation (DIC).

Methods

The forces and moments applied to the mandibular canines, first and second premolars were measured using a multi-axis force/moment transducer when an extrusion of 0.5 mm was planned, assuming the mandibular first premolars were intruded by 1 mm. In addition, displacement and strain changes in the CA were analyzed using the DIC method. CA designs were categorized based on the presence of first premolar attachment and subdivided into equigingival margins, 1-mm extended margins, equi-margins with 1-mm thickness and height, and equi-margins with 1-mm reduced buccolingual width. The CA was printed directly at a thickness of 0.5 mm, and the experiments were conducted at 37°C.

Results

The results showed that attachment played an important role in the extrusion of first premolars in both the force/moment measurement system and the DIC method. Intrusion was observed without attachment, even though extrusion was planned. CA designs apply greater force to the cervical region by extending the margin or reducing the buccolingual width, thereby improving extrusion efficiency.

Conclusions

Force and moment changes in direct 3D printed CA are complex and difficult to predict; however, modifying aligner designs, such as extending the margin or reducing buccolingual width, and using appropriate attachments could minimize unwanted tooth movement, optimize planned treatment, and increase treatment predictability.

In Vitro Comparison of Direct Attachment Shape and Size on the Orthodontic Forces and Moments Generated by Thermoplastic Aligners During Expansion

OBJECTIVE

To evaluate the effects of varying direct attachment shape and size on the forces and moments generated by thermoplastic aligners during simulated expansion.

MATERIALS AND METHODS

An in vitro orthodontic force tester (OFT) was used to measure the forces and moments from a typodont where the buccal teeth were translated lingually 0.2 mm to simulate expansion. Hemi-ellipsoid and rectangular attachments with either 0.5 or 1.0 mm thickness were added on upper right first premolar (UR4), second premolar (UR5) and first molar (UR6). Analysis of variance (ANOVA) was used to determine two-way interactions among the factors on the outcomes.

RESULTS

The interactions between group and tooth were significant for all outcomes (p < 0.001). The greatest buccal forces (Fy) were observed with 1 mm rectangular attachment on the UR4 (0.78 ± 0.29 N), with 1 mm hemi-ellipsoid attachment on UR5 (0.28 ± 0.21 N) and with 0.5 mm rectangular attachment on UR6 (1.71 ± 0.18 N). The greatest buccolingual moments (Mx) were obtained with 1 mm rectangular attachment on UR4 (5.61 ± 1.43 Nmm), without any attachments on UR5 (3.33 ± 1.73 Nmm) and with 1 mm hemi-ellipsoid attachment on UR6 (4.18 ± 4.31).

CONCLUSION

Direct attachment shape and size had a significant effect on the orthodontic forces and moments generated by thermoplastic aligners during simulated expansion. Although loads varied significantly by tooth morphology and its location in the arch, best forces and moments for expansion were obtained with 1 mm rectangular attachments on UR4s, 1 mm hemi-ellipsoid attachments on UR5s and 0.5 mm rectangular attachments on UR6s.

Prospects for 3D-printing of clear aligners—a narrative review

Clear aligner therapy is a rapidly developing orthodontic treatment. 3D-printing technology, which enables the creation of complex geometric structures with high precision, has been used in dentistry. This article aims to summarize the various aspects of 3D-printing clear aligners and give an outlook on their future development. The traditional thermoforming technology is introduced and the principle and application of 3D-printed clear aligners and materials are introduced, as well as the application prospects of 3D-printed clear aligners. According to PRISMA statement, the relevant literature of 3D-printing clear aligner was searched in PubMed, Web of Science, Embase and other databases. We searched the related words in the MESH database and then carried out advanced searches. We read systematic review and conference papers to find the articles related to the subject and manually added and excluded articles by reading the title and abstract. The production of clear aligners combines computer-aided 3D analysis, personalized design and digital molding technology. The thickness and edges of the 3D-printed clear aligner can be digitally controlled, which allows appliance more efficiently fitted. Presently, the array of clear resins suitable for 3D-printing include photo polymeric clear methacrylate-based resin (Dental LT) (Form Labs, Somerville, Mass), aliphatic vinyl ester-polyurethane polymer (Tera Harz TC-85) (Graphy, Seoul, South Korea). They all have good biocompatibility. But no such material is currently approved on the market. Developing biocompatible resins and further improving the material’s mechanical properties will be critical for the combination of 3D-printing and clear aligners. However, the literature on 3D-printed clear aligners is limited and lacks clinical application. Further in vivo and in vitro tests, as well as additional exploration in conjunction with corresponding cytological tests, are required for the research on available materials and machinery for 3D-printing clear aligners.

Application of Robotics in Orthodontics: A Systematic Review

Robotics has various applications in dentistry, particularly in orthodontics, although the potential use of these technologies is not yet clear. This review aims to summarize the application of robotics in orthodontics and clarify its function and scope in clinical practice. Original articles addressing the application of robotics in any area of orthodontic practice were included, and review articles were excluded. PubMed, Google Scholar, Scopus, and DOAJ were searched from June to August 2023. The risk of bias was established using the risk of bias in non-randomized studies (ROBINS) and certainty assessment tools following the grading of recommendations, assessment, development, and evaluation (GRADE) guidelines. A narrative synthesis of the data was generated and presented according to its application in surgical and non-surgical orthodontics. The search retrieved 2,106 articles, of which 16 articles were selected for final data synthesis of research conducted between 2011 and 2023 in Asia, Europe, and North America. The application of robotics in surgical orthodontics helps guide orthognathic surgeries by reducing the margin of error, but it does not replace the work of a clinician. In non-surgical orthodontics, robotics assists in performing customized bending of orthodontic wires and simulating orthodontic movements, but its application is expensive. The articles collected for this synthesis exhibited a low risk of bias and high certainty, and the results indicated that the advantages of the application of robotics in orthodontics outweigh the disadvantages. This project was self-financed, and a previous protocol was registered at the PROSPERO site (registration number: CRD42023463531).

Orthodontic Aligners: Current Perspectives for the Modern Orthodontic Office

Orthodontic aligners are changing the practice of orthodontics. This system of orthodontic appliances is becoming the mainstay appliance of choice for orthodontic offices in many countries. Patient preferences and lifestyle needs have made this appliance the primary choice when seeking care. In the early days, appliances lacked the efficiency and effectiveness of traditional bracket-wire systems, but modern systems are now able to handle a more comprehensive orthodontic caseload. Current systems provide newer biomechanical strategies and artificial intelligence-driven tooth movements for better outcomes. These improvements now mean that an orthodontist can be better prepared to manage a larger number of orthodontic malocclusions. This paper aims to discuss some of the evolution of orthodontic aligners and to describe to orthodontists the fundamentals of aligner therapy. In addition, it will provide an evidence-based outcome to the existing treatment outcomes in the current literature.