3D printing in dentistry

Comparative analysis of intaglio surface trueness of cement-retained implant-supported prostheses generated by a cast-free digital workflow and a three-dimensionally printed cast workflow

STATEMENT OF PROBLEM

Comparative analysis of the accuracy of the prostheses produced by a cast-free digital workflow and 3-dimensional (3D) printing cast workflow is lacking.

PURPOSE

The purpose of the present investigation was to compare the intaglio surface trueness of implant-supported prostheses fabricated by using 3 different digital workflows: cast-free computer-aided design (CAD), 3D printed cast CAD (direct insert), and 3D printed cast CAD (indirect insert).

MATERIAL AND METHODS

The laboratory data of 11 partially edentulous arches for prosthetic implant treatment were obtained. Three different workflows were tested to produce the cement-retained prostheses: cast-free CAD (Group CF), 3D printed cast CAD with direct insert (Group PD), and 3D printed cast CAD with indirect insert (Group PI). The intaglio surfaces of the prosthesis CAD data from Groups CF, PD, and PI were superimposed with 3D printed prosthesis scan data from Group CF to measure 3D surface deviation. Using the prosthesis CAD data from Group CF as a reference, those from Groups PD and PI were compared by superimposition analysis. The root mean square (RMS) estimates, positive average deviations, and negative average deviations were measured. The Kruskal-Wallis test and Dunn test with Bonferroni correction, and the Wilcoxon rank sum test were used for statistical analyses (α=.05).

RESULTS

Significant differences were found among the 3 groups when the 3D printed prosthesis scan data were referenced (P<.05). Group CF showed the lowest RMS, positive average deviation, and negative deviation values, while Group PI showed the highest values. Significant differences in the RMS, positive average deviation, and negative average deviation values were found between Groups PD and PI when the prosthesis CAD data (Group CF) were referenced (P<.05).

CONCLUSIONS

Among the 3 different workflows tested, the prostheses generated from the cast-free CAD flow showed significantly lower intaglio surface deviation than those generated from the 3D printed cast CAD flows, regardless of the insertion method of the implant replicas.

Development and In-Silico and Ex-Vivo Validation of a Software for a Semi-Automated Segmentation of the Round Window Niche to Design a Patient Specific Implant to Treat Inner Ear Disorders

The aim of this study was to develop and validate a semi-automated segmentation approach that identifies the round window niche (RWN) and round window membrane (RWM) for use in the development of patient individualized round window niche implants (RNI) to treat inner ear disorders. Twenty cone beam computed tomography (CBCT) datasets of unilateral temporal bones of patients were included in the study. Defined anatomical landmarks such as the RWM were used to develop a customized 3D Slicer™ plugin for semi-automated segmentation of the RWN. Two otolaryngologists (User 1 and User 2) segmented the datasets manually and semi-automatically using the developed software. Both methods were compared in-silico regarding the resulting RWM area and RWN volume. Finally, the developed software was validated ex-vivo in N = 3 body donor implantation tests with additively manufactured RNI. The independently segmented temporal bones of the different Users showed a strong consistency in the volume of the RWN and the area of the RWM. The volume of the semi-automated RWN segmentations were 48 ± 11% smaller on average than the manual segmentations and the area of the RWM of the semi-automated segmentations was 21 ± 17% smaller on average than the manual segmentation. All additively manufactured implants, based on the semi-automated segmentation method could be implanted successfully in a pressure-tight fit into the RWN. The implants based on the manual segmentations failed to fit into the RWN and this suggests that the larger manual segmentations were over-segmentations. This study presents a semi-automated approach for segmenting the RWN and RWM in temporal bone CBCT scans that is efficient, fast, accurate, and not dependent on trained users. In addition, the manual segmentation, often positioned as the gold-standard, actually failed to pass the implantation validation.

Engineering Dental Tissues Using Biomaterials with Piezoelectric Effect: Current Progress and Future Perspectives

Dental caries and traumatic injuries to teeth may cause irreversible inflammation and eventual death of the dental pulp. Nevertheless, predictably, repair and regeneration of the dentin-pulp complex remain a formidable challenge. In recent years, smart multifunctional materials with antimicrobial, anti-inflammatory, and pro-regenerative properties have emerged as promising approaches to meet this critical clinical need. As a unique class of smart materials, piezoelectric materials have an unprecedented advantage over other stimuli-responsive materials due to their inherent capability to generate electric charges, which have been shown to facilitate both antimicrobial action and tissue regeneration. Nonetheless, studies on piezoelectric biomaterials in the repair and regeneration of the dentin-pulp complex remain limited. In this review, we summarize the biomedical applications of piezoelectric biomaterials in dental applications and elucidate the underlying molecular mechanisms contributing to the biological effect of piezoelectricity. Moreover, we highlight how this state-of-the-art can be further exploited in the future for dental tissue engineering.

Advances in orthodontic clear aligner materials

Rapid technological improvements in biomaterials, computer-aided design (CAD) and manufacturing (CAM) have endorsed clear aligner therapy (CAT) as a mainstay of orthodontic treatment, and the materials employed for aligner fabrication play an all-important role in determining the clinical performance of clear aligners. This narrative review has attempted to comprehensively encompass the entire gamut of materials currently used for the fabrication of clear aligners and elucidate their characteristics that are crucial in determining their performance in an oral environment. Historical developments and current protocols in aligner fabrication, features of contemporary bioactive materials, and emerging trends related to CAT are discussed. Advances in aligner material chemistry and engineering possess the potential to bring about radical transformations in the therapeutic applications of CAT; in the absence of which, clear aligners would continue to underperform clinically, due to their inherent biomechanical constraints. Finally, while innovations in aligner materials such as shape memory polymers, direct three-dimensional (3D) printed clear aligners and bioactive materials combined with clear aligner materials are essential to further advance the applications of CAT; increased awareness of environmental responsibilities among aligner manufacturers, aligner prescribing clinicians and aligner users is essential for better alignment of our climate change goals towards a sustainable planet.

Mohan D, Karganroudi SS. The Unprecedented Role of 3D Printing Technology in Fighting the COVID-19 Pandemic: A Comprehensive Review

The coronavirus disease 2019 (COVID-19) rapidly spread to over 180 countries and abruptly disrupted production rates and supply chains worldwide. Since then, 3D printing, also recognized as additive manufacturing (AM) and known to be a novel technique that uses layer-by-layer deposition of material to produce intricate 3D geometry, has been engaged in reducing the distress caused by the outbreak. During the early stages of this pandemic, shortages of personal protective equipment (PPE), including facemasks, shields, respirators, and other medical gear, were significantly answered by remotely 3D printing them. Amidst the growing testing requirements, 3D printing emerged as a potential and fast solution as a manufacturing process to meet production needs due to its flexibility, reliability, and rapid response capabilities. In the recent past, some other medical applications that have gained prominence in the scientific community include 3D-printed ventilator splitters, device components, and patient-specific products. Regarding non-medical applications, researchers have successfully developed contact-free devices to address the sanitary crisis in public places. This work aims to systematically review the applications of 3D printing or AM techniques that have been involved in producing various critical products essential to limit this deadly pandemic's progression.

Dental 3D Printing Design Based on Neurodegeneration and Virtual Reality Imaging Technology

Objective

To model and compare the stress variation and distribution of the implant and its supporting components under two types of loading with the abutment in the axial and coronal lingual augmentation positions by means of the 3D finite element method.

Method

15 all-ceramic crowns completed by the same technician between the years 2014 and 2015 were randomly selected. A high precision laser scanner was used to scan the specimen models of all-ceramic crowns and then converted and imported into the promapping software to create 15 solid models each in the axial position of the crown and the lingual augmentation position of the crown.

Results

We showed that the abutments were significantly more stressed in the bone cortex than in the bone cancellous under both loads when the abutments were in the long axis position and in the lingual ridge position of the dentition. The distribution of stresses in the bone tissue was mainly concentrated in the cortical bone. The stresses induced by oblique forces were greater than those induced by vertical forces. When comparing the abutment in the long axis position of the dentition with the lingual ridge position of the dentition, the peak stresses obtained from the stress analysis of the abutment in the lingual ridge position were all increased to different degrees under both loads, and the differences were statistically significant (p < 0.05) suggesting that the design of the abutment in the direction of the long axis of the dentition is less stressful than that of the crown in the lingual augmentation position, and the risk of alveolar ridge resorption and screw fracture is less.

Conclusion

In this paper, we proposed a dental 3D scanning system, which is less stressful based on a 3D reconstruction algorithm using Fourier transform contouring that achieved a speed dental 3D scanner with Fourier transform contouring by projecting a raster pattern onto a dental impression.

Corrosion properties of low carbon CoCrMo and additively manufactured CoCr alloys for dental applications

OBJECTIVES

Additive manufacturing (AM) is being applied to metallic biomaterials and dental alloys, including CoCrMo. CoCrMo mechanical properties and corrosion resistance are vital to the structural integrity of implants and dental appliances. The goal of this work is to assess the resistivity of AM cobalt chromium alloys by comparing them with traditional CoCrMo, regarding electrochemical properties resulting from microstructural and oxide film differences.

METHODS

In this work, selective laser melting (SLM), was used to manufacture CoCrMoW. The corrosion characteristics of AM alloy were compared to that of wrought LC CoCrMo (ASTM F-1537) in both phosphate buffered saline (PBS) and PBS with 10 mM H₂O₂ to simulate increased inflammatory conditions. Anodic polarization and electrochemical impedance spectroscopy (EIS) were performed.

RESULTS

Both alloys were substantially similar in corrosion behavior in both solutions. They exhibited changes with the different solutions. Polarization resistances were statistically lower (R_p^AM = 1.4 MΩcm² (PBS) vs. 0.72 MΩcm² (H₂O₂), R_p^LC = 1.86 MΩcm² (PBS) vs. 0.55 MΩcm² (H₂O₂)), and open circuit potentials (OCP's) were statistically higher in 10 mM H₂O₂ for both alloys (0.20 V (in H₂O₂) vs. - 0.09 V in PBS). Chemistry variations were revealed by the corrosion tests indicating that wrought LC CoCrMo retained its casting-based chemical heterogeneity, while AM CoCrMoW had sub-cell structures within the solidified grains.

SIGNIFICANCE

As novel production methods like AM arise, it is necessary to understand any microstructural differences that may diminish the corrosion resistance properties. AM CoCrMoW alloys hold significant promise for use in dentistry where complex geometries are required.

Patient Awareness of Additive Manufacturing in Dentistry – A Survey

Introduction: Additive manufacturing or 3D printing technology creates the object layer by layer. Its development in dentistry has been particularly rapid over the last ten years and covers more and more dental fields. The aim of this article is to demonstrate the patient’s awareness of additive manufacturing and their opinion about the price and application of 3D printed products in dentistry. Materials and methods: The survey was distributed to a total of 111 patients, of whom 49.5% were men and 50.5% were women. The majority of respondents have higher education. Their age varies from 34 to 76. Students do not participate in the survey. More than half of the respondents (55.5%) are retired. Results and conclusion: Patients are mainly informed by dentists but consider themselves insufficiently informed. 3D printed versions are rarely offered, especially for temporary constructions. Patients rate the price as too high, but would not give up treatment only for that reason. They are hesitant in their choice for treatment with a classic or 3D printed technique.

A Brief Review on Factors Affecting the Tribological Interaction between Human Skin and Different Textile Materials

The application of tribology is not just limited to mechanical components of engineering systems. As a matter of fact, the understanding of friction and wear can be applied to everyday life. One of the important fields is skin tribology, as human skin interacts with various surfaces of different materials. This paper focuses on the friction behavior of the skin when in contact with the fabric and other materials in relative motion. The excessive friction at the fabric-skin interface may lead to discomfort, blistering, chafing, and pressure ulcers especially in athletes who experience higher friction due to rapid movement for an extended period. Other than understanding the fabric properties, it is equally important to understand the structure and properties of the skin to evaluate its function and interaction with the different fabric materials. The identification of the contributing factors of skin friction can help to design suitable fabric materials. An overview of skin functions and the factors that affect the friction on the skin-textile material interface are presented in this review article.

Application and Development of Modern 3D Printing Technology in the Field of Orthopedics

3D printing, also known as additive manufacturing, is a technology that uses a variety of adhesive materials such as powdered metal or plastic to construct objects based on digital models. Recently, 3D printing technology has been combined with digital medicine, materials science, cytology, and other multidisciplinary fields, especially in the field of orthopedic built-in objects. The development of advanced 3D printing materials continues to meet the needs of clinical precision medicine and customize the most suitable prosthesis for everyone to improve service life and satisfaction. This article introduces the development of 3D printing technology and different types of materials. We also discuss the shortcomings of 3D printing technology and the current challenges, including the poor bionics of 3D printing products, lack of ideal bioinks, product safety, and lack of market supervision. We also prospect the future development trends of 3D printing.

Evaluating the Three-Dimensional Printing Accuracy of Partial-Arch Models According to Outer Wall Thickness: An In Vitro Study

The printing accuracy of three-dimensional (3D) dental models using photopolymer resin affects dental diagnostic procedures and prostheses. The accuracy of research into the outer wall thickness and printing direction data for partial-arch model printing has been insufficient. This study analyzed the effects of wall thickness and printing direction accuracy. Anterior and posterior partial-arch models were designed with different outer wall thicknesses. After 3D printing, a trueness analysis was performed. Those with full-arch models were the control group. The full-arch model had an error value of 73.60 ± 2.61 µm (mean ± standard deviation). The error values for the partial-arch models with 1-, 2-, and 3-mm thick outer walls were 54.80 ± 5.34, 47.58 ± 7.59, and 42.25 ± 9.19 μm, respectively, and that for the fully filled model was 38.20 ± 4.63 μm. The printing accuracies differed significantly between 0 degrees and 60 degrees, at 49.54 ± 8.16 and 40.66 ± 6.80 μm, respectively (F = 153.121, p < 0.001). In conclusion, the trueness of the partial-arch model was better than that of the full-arch model, and models with thick outer walls at 60 degrees were highly accurate.

Direct 3D Printing of Clear Orthodontic Aligners: Current State and Future Possibilities

The recent introduction of three-dimensional (3D) printing is revolutionizing dentistry and is even being applied to orthodontic treatment of malocclusion. Clear, personalized, removable aligners are a suitable alternative to conventional orthodontic appliances, offering a more comfortable and efficient solution for patients. Including improved oral hygiene and aesthetics during treatment. Contemporarily, clear aligners are produced by a thermoforming process using various types of thermoplastic materials. The thermoforming procedure alters the properties of the material, and the intraoral environment further modifies the properties of a clear aligner, affecting overall performance of the material. Direct 3D printing offers the creation of highly precise clear aligners with soft edges, digitally designed and identically reproduced for an entire set of treatment aligners; offering a better fit, higher efficacy, and reproducibility. Despite the known benefits of 3D printing and the popularity of its dental applications, very limited technical and clinical data are available in the literature about directly printed clear aligners. The present article discusses the advantages of 3D printed aligners in comparison to thermoformed ones, describes the current state of the art, including a discussion of the possible road blocks that exist such as a current lack of approved and marketed materials and limited existence of aligner specific software. The present review suggests the suitability of 3D direct printed aligners is superior to that of thermoformed manufactured aligners because of the prior’s increased accuracy, load resistance, and lower deformation. It is an overall more stable way to produce an aligner where submillimeter movements can make a difference in treatment outcome. Direct 3D printing represents a complex method to control the thickness of the aligner and therefore has a better ability to control the force vectors that are used to produce tooth movement. There is currently no other approved material on the market that can do this. The conclusion of this article is that we encourage further in vitro and in vivo studies to test these new technologies and materials.

3D and 4D printing in dentistry and maxillofacial surgery: Printing techniques, materials, and applications

3D and 4D printing are cutting-edge technologies for precise and expedited manufacturing of objects ranging from plastic to metal. Recent advances in 3D and 4D printing technologies in dentistry and maxillofacial surgery enable dentists to custom design and print surgical drill guides, temporary and permanent crowns and bridges, orthodontic appliances and orthotics, implants, mouthguards for drug delivery. In the present review, different 3D printing technologies available for use in dentistry are highlighted together with a critique on the materials available for printing. Recent reports of the application of these printed platformed are highlighted to enable readers appreciate the progress in 3D/4D printing in dentistry.

Evaluation of the 3D Printing Accuracy of a Dental Model According to Its Internal Structure and Cross-Arch Plate Design: An In Vitro Study

The amount of photopolymer material consumed during the three-dimensional (3D) printing of a dental model varies with the volume and internal structure of the modeling data. This study analyzed how the internal structure and the presence of a cross-arch plate influence the accuracy of a 3D printed dental model. The model was designed with a U-shaped arch and the palate removed (Group U) or a cross-arch plate attached to the palate area (Group P), and the internal structure was divided into five types. The trueness and precision were analyzed for accuracy comparisons of the 3D printed models. Two-way ANOVA of the trueness revealed that the accuracy was 135.2 ± 26.3 µm (mean ± SD) in Group U and 85.6 ± 13.1 µm in Group P. Regarding the internal structure, the accuracy was 143.1 ± 46.8 µm in the 1.5 mm-thick shell group, which improved to 111.1 ± 31.9 µm and 106.7 ± 26.3 µm in the roughly filled and fully filled models, respectively. The precision was 70.3 ± 19.1 µm in Group U and 65.0 ± 8.8 µm in Group P. The results of this study suggest that a cross-arch plate is necessary for the accurate production of a model using 3D printing regardless of its internal structure. In Group U, the error during the printing process was higher for the hollowed models.

3D Printing of Clear Orthodontic Aligners: Where We Are and Where We Are Going

Clear orthodontic aligners were developed at the end of the 1990s [...].

Additive manufacturing of ceramics for dental applications: A review

OBJECTIVE

The main goal of this review is to provide a detailed and comprehensive description of the published work from the past decade regarding AM of ceramic materials with possible applications in dentistry. The main printable materials and most common technologies are also addressed, underlining their advantages and main drawbacks.

METHODS

Online databases (Web of knowledge, Science Direct, PubMed) were consulted on this topic. Published work from 2008 to 2018 was collected, analyzed and the relevant papers were selected for inclusion on this review.

RESULTS

Ceramic materials are broadly used in dentistry to restore/replace damaged or missing teeth, due to their biocompatibility, chemical stability and mechanical and aesthetic properties. However, there are several unmet challenges regarding their processing and performance. Due to their brittleness nature, a very tight control of the manufacturing process is needed to obtain dental pieces with adequate mechanical properties. Additive manufacturing (AM) is an emerging technology that constitutes an interesting and viable manufacturing alternative to the conventional subtractive methods. AM enables the production of customized complex 3D parts in a more sustainable and less expensive way. AM of ceramics can be achieved with an extensive variety of methods.

SIGNIFICANCE

There is no perfect technology for all materials/applications, capable alone of fulfilling all the specificities and necessities of every patient. Although very promising, AM of ceramic dental materials remains understudied and further work is required to make it a widespread technology in dentistry.