Clinically Relevant Properties of 3D Printable Materials for Intraoral Use in Orthodontics: A Critical Review of the Literature

Biocompatibility of 3D-printed vs. thermoformed and heat-cured intraoral appliances

Objectives

The development of additive manufacturing has the potential to revolutionize the fabrication of medical devices. This technology, also known as 3D printing, offers precise, cost-effective, and personalized approaches, which could be particularly beneficial in the production of intraoral appliances. Despite its promise, research on the biocompatibility of 3D-printed intraoral devices is still limited. Our study aims to address this gap.

Methods

We examined the cytotoxicity of materials processed via three techniques commonly used for the fabrication of different intraoral appliances: 3D printing (Dental LT Clear), thermoforming (Duran adjusted with Durasplint LC), and conventional heat-curing (Villacryl H Plus). We also investigated the impact of chemical or UVC disinfection on the biocompatibility of these materials. We assessed the biological effects induced in human gingival fibroblasts (HGFs) through both direct contact tests (MTT and LDH assays) and extract tests (PrestoBlue, DCF, and cell death type assays). Additionally, we observed changes in cellular morphology and migration rate under an inverted light microscope. The surface roughness of materials was evaluated using contact profilometry. Statistical analysis was conducted using two-way analysis of variance.

Results

Our findings suggest that all three fabrication techniques induced a slight cytotoxic effect in HGFs, as evidenced by both direct contact and extract tests. However, these materials could be considered nontoxic according to the ISO 10993-5:2009 norm, as the decrease in metabolic activity observed was always less than 30% compared to the untreated control.

Conclusion

This novel study confirms that 3D printing may be a safe alternative to conventional methods for fabricating intraoral appliances. However, further tests assessing the long-term intraoral usage are still needed.

A fully digital workflow for the design and manufacture of a class of metal orthodontic appliances

Background

Traditional working procedures requires a lot of clinical processes and processing time.

Methods

The orthodontic metal appliances were made by applying oral scanners, digital images, computer-aided design and computer-aided manufacturing (CAD-CAM) printers.

Results

The computer digital technology simplified the manufacturing process for dental appliances and shorten the duration for clinical operation and technical processing.

Conclusions

The technique described in this paper can guarantee the accuracy of orthodontic appliances and bring revolution the field.

Clinical significance

The CAD-CAM technology provides a fully digital workflow for manufacturing metal orthodontic appliances, which saves a considerable amount of labor and material costs, and significantly reduces heavy metal pollution in the working environment of dental technicians.

Functional Biomaterials and Digital Technologies in Dentistry: From Bench to Bedside

This Special Issue, "Functional Biomaterials and Digital Technologies in Dentistry: From Bench to Bedside", highlights the integration of advanced materials science and digital technologies in dental and maxillofacial applications [...].

Design, Stereolithographic 3D Printing, and Characterization of TPMS Scaffolds

Anatomical and functional tissue loss is one of the most debilitating problems and involves a great cost to the international health-care sector. In the field of bone tissue, the use of scaffolds to promote tissue regeneration is a topic of great interest. In this study, a combination of additive manufacturing and computational methods led to creating porous scaffolds with complex microstructure and mechanical behavior comparable to those of cancellous bone. Specifically, some representative models of triply periodic minimal surfaces (TPMSs) were 3D-printed through a stereolithographic technique using a dental resin. Schwarz primitive and gyroid surfaces were created computationally: they are characterized by a complex geometry and a high pore interconnectivity, which play a key role in the mechanism of cell proliferation. Several design parameters can be varied in these structures that can affect the performance of the scaffold: for example, the larger the wall thickness, the lower the elastic modulus and compressive strength. Morphological and mechanical analyses were performed to experimentally assess the properties of the scaffolds. The relationship between relative density and elastic modulus has been analyzed by applying different models, and a power-law equation was found suitable to describe the trend in both structures.

Advancements in Clear Aligner Fabrication: A Comprehensive Review of Direct-3D Printing Technologies

Clear aligners have revolutionized orthodontic treatment by offering an esthetically driven treatment modality to patients of all ages. Over the past two decades, aligners have been used to treat malocclusions in millions of patients worldwide. The inception of aligner therapy goes back to the 1940s, yet the protocols to fabricate aligners have been continuously evolved. CAD/CAM driven protocol was the latest approach which drastically changed the scalability of aligner fabrication-i.e., aligner mass production manufacturing. 3D printing technology has been adopted in various sectors including dentistry mostly because of the ability to create complex geometric structures at high accuracy while reducing labor and material costs-for the most part. The integration of 3D printing in dentistry has been across, starting in orthodontics and oral surgery and expanding in periodontics, prosthodontics, and oral implantology. Continuous progress in material development has led to improved mechanical properties, biocompatibility, and overall quality of aligners. Consequently, aligners have become less invasive, more cost-effective, and deliver outcomes comparable to existing treatment options. The promise of 3D printed aligners lies in their ability to treat malocclusions effectively while providing esthetic benefits to patients by remaining virtually invisible throughout the treatment process. Herein, this review aims to provide a comprehensive summary of studies regarding direct-3D printing of clear aligners up to the present, outlining all essential properties required in 3D-printed clear aligners and the challenges that need to be addressed. Additionally, the review proposes implementation methods to further enhance the effectiveness of the treatment outcome.

Influence of Post-Processing on the Degree of Conversion and Mechanical Properties of 3D-Printed Polyurethane Aligners

BACKGROUND

This study explores how different post-processing methods affect the mechanical properties and degree of conversion of 3d-printed polyurethane aligners made from Tera Harz TC-85 resin.

METHODS

Using Fourier-transform infrared (FTIR) spectroscopy, the degree of conversion of liquid resin and post-processed materials was analyzed. This investigation focused on the effects of various post-curing environments (nitrogen vs. air) and rinsing protocols (centrifuge, ethanol, isopropanol, and isopropanol + water). The assessed mechanical properties were flexural modulus and hardness.

RESULTS

The degree of conversion showed no significant variance across different groups, though the polymerization environment influenced the results, accounting for 24.0% of the variance. The flexural modulus varied considerably, depending on both the rinsing protocol and the polymerization environment. The standard protocol (centrifugation followed by nitrogen polymerization) exhibited the highest flexural modulus of 1881.22 MPa. Hardness testing revealed significant differences, with isopropanol treatments showing increased resistance to wear in comparison to the centrifuge and ethanol rinse treatments.

CONCLUSIONS

This study conclusively demonstrates the adverse effects of oxygen on the polymerization process, underscoring the critical need for an oxygen-free environment to optimize material properties. Notably, the ethanol rinse followed by nitrogen polymerization protocol emerged as a viable alternative to the conventional centrifuge plus nitrogen method.

Connecting the dots towards precision orthodontics

Precision orthodontics entails the use of personalized clinical, biological, social and environmental knowledge of each patient for deep individualized clinical phenotyping and diagnosis combined with the delivery of care using advanced customized devices, technologies and biologics. From its historical origins as a mechanotherapy and materials driven profession, the most recent advances in orthodontics in the past three decades have been propelled by technological innovations including volumetric and surface 3D imaging and printing, advances in software that facilitate the derivation of diagnostic details, enhanced personalization of treatment plans and fabrication of custom appliances. Still, the use of these diagnostic and therapeutic technologies is largely phenotype driven, focusing mainly on facial/skeletal morphology and tooth positions. Future advances in orthodontics will involve comprehensive understanding of an individual's biology through omics, a field of biology that involves large-scale rapid analyses of DNA, mRNA, proteins and other biological regulators from a cell, tissue or organism. Such understanding will define individual biological attributes that will impact diagnosis, treatment decisions, risk assessment and prognostics of therapy. Equally important are the advances in artificial intelligence (AI) and machine learning, and its applications in orthodontics. AI is already being used to perform validation of approaches for diagnostic purposes such as landmark identification, cephalometric tracings, diagnosis of pathologies and facial phenotyping from radiographs and/or photographs. Other areas for future discoveries and utilization of AI will include clinical decision support, precision orthodontics, payer decisions and risk prediction. The synergies between deep 3D phenotyping and advances in materials, omics and AI will propel the technological and omics era towards achieving the goal of delivering optimized and predictable precision orthodontics.

What is the current state of artificial intelligence applications in dentistry and orthodontics?

BACKGROUND

The use of Artificial Intelligence (AI) in the medical field has the potential to bring about significant improvements in patient care and outcomes. AI is being used in dentistry and more specifically in orthodontics through the development of diagnostic imaging tools, the development of treatment planning tools, and the development of robotic surgery. The aim of this study is to present the latest emerging AI softwares and applications in dental field to benefit from.

TYPES OF STUDIES REVIEWED

Search strategies were conducted in three electronic databases, with no date limits in the following databases up to April 30, 2023: MEDLINE, PUBMED, and GOOGLE® SCHOLAR for articles related to AI in dentistry & orthodontics. No inclusion and exclusion criteria were used for the selection of the articles. Most of the articles included (n = 79) are reviews of the literature, retro/prospective studies, systematic reviews and meta-analyses, and observational studies.

RESULTS

The use of AI in dentistry and orthodontics is a rapidly growing area of research and development, with the potential to revolutionize the field and bring about significant improvements in patient care and outcomes; this can save clinicians' chair-time and push for more individualized treatment plans. Results from the various studies reported in this review are suggestive that the accuracy of AI-based systems is quite promising and reliable.

PRACTICAL IMPLICATIONS

AI application in the healthcare field has proven to be efficient and helpful for the dentist to be more precise in diagnosis and clinical decision-making. These systems can simplify the tasks and provide results in quick time which can save dentists time and help them perform their duties more efficiently. These systems can be of greater aid and can be used as auxiliary support for dentists with lesser experience.

Perceptions of orthodontic residents toward the implementation of dental technologies in postgraduate curriculum

BACKGROUND

Dental technologies have increasingly been implemented in orthodontic practice to offer better experiences for orthodontists and patients, however, there is no scientific evidence yet whether which technologies should be implemented into the postgraduate programs.

OBJECTIVES

To investigate perceptions of orthodontic residents toward the confidence and importance of dental technologies, as well as to determine their necessity in postgraduate programs.

MATERIALS AND METHODS

The online questionnaire was designed to collect data from residents from all accredited orthodontic postgraduate programs in Thailand. The questionnaire consisted of four sections, which were (1) demographic data, (2) self-perceived importance of orthodontic technologies, (3) self-perceived confidence toward orthodontic technologies, and (4) the necessity of orthodontic technologies in postgraduate programs. The data were analyzed using descriptive statistics, Spearman correlation, and a chi-square test.

RESULTS

Intraoral scanner was found to be an orthodontic technology with the highest scores for both self-perceived importance (4.37 ± 0.59) and confidence (4.23 ± 0.75), followed by cone-beam computed tomography, digital treatment planning software, and lab-produced aligners. These orthodontic technologies were also considered as mandatory in orthodontic postgraduate programs. CAD/CAM technologies appeared to be least important, and their training may be arranged as short course training. There was no significant influence of training locations on the necessity of all orthodontic technologies (P > 0.05), except CBCT. Self-perceived importance and confidence in all technologies were found to have significant positive correlations (P < 0.05), except teledentistry and in-office aligners.

CONCLUSION

Orthodontic technologies were perceived as important in clinical workflow. Intraoral Scanners, CBCT, digital treatment planning software, lab-produced aligners, and digital modeling software appeared to be necessary for clinical practice and should be considered for orthodontic postgraduate programs, while other technologies may be arranged as short course training. Further research should investigate how to arrange and organize training sessions in orthodontic postgraduate programs.

Effects of Polishing and Artificial Aging on Mechanical Properties of Dental LT Clear® Resin

Three-dimensional printing has become incorporated into various aspects of everyday life, including dentistry. Novel materials are being introduced rapidly. One such material is Dental LT Clear by Formlabs, a resin used for manufacturing occlusal splints, aligners, and orthodontic retainers. In this study, a total of 240 specimens, comprising two shapes (dumbbell and rectangular), were evaluated through compression and tensile tests. The compression tests revealed that the specimens were neither polished nor aged. However, after polishing, the compression modulus values decreased significantly. Specifically, the unpolished and nonaged specimens measured 0.87 ± 0.02, whereas the polished group measured 0.086 ± 0.03. The results were significantly affected by artificial aging. The polished group measured 0.73 ± 0.05, while the unpolished group measured 0.73 ± 0.03. In contrast, the tensile test proved that the specimens showed the highest resistance when the polishing was applied. The artificial aging influenced the tensile test and reduced the force needed to damage the specimens. The tensile modulus had the highest value when polishing was applied (3.00 ± 0.11). The conclusions drawn from these findings are as follows: 1. Polishing does not change the properties of the examined resin. 2. Artificial aging reduces resistance in both compression and tensile tests. 3. Polishing reduces the damage to the specimens in the aging process.