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

4D Printing in Biomedical Engineering: Advancements, Challenges, and Future Directions

4D printing has emerged as a transformative technology in the field of biomedical engineering, offering the potential for dynamic, stimuli-responsive structures with applications in tissue engineering, drug delivery, medical devices, and diagnostics. This review paper provides a comprehensive analysis of the advancements, challenges, and future directions of 4D printing in biomedical engineering. We discuss the development of smart materials, including stimuli-responsive polymers, shape-memory materials, and bio-inks, as well as the various fabrication techniques employed, such as direct-write assembly, stereolithography, and multi-material jetting. Despite the promising advances, several challenges persist, including material limitations related to biocompatibility, mechanical properties, and degradation rates; fabrication complexities arising from the integration of multiple materials, resolution and accuracy, and scalability; and regulatory and ethical considerations surrounding safety and efficacy. As we explore the future directions for 4D printing, we emphasise the need for material innovations, fabrication advancements, and emerging applications such as personalised medicine, nanomedicine, and bioelectronic devices. Interdisciplinary research and collaboration between material science, biology, engineering, regulatory agencies, and industry are essential for overcoming challenges and realising the full potential of 4D printing in the biomedical engineering landscape.

Trueness of cone-beam computed tomography-derived skull models fabricated by different technology-based three-dimensional printers

BACKGROUND

Three-dimensional (3D) printing is a novel innovation in the field of craniomaxillofacial surgery, however, a lack of evidence exists related to the comparison of the trueness of skull models fabricated using different technology-based printers belonging to different cost segments.

METHODS

A study was performed to investigate the trueness of cone-beam computed tomography-derived skull models fabricated using different technology based on low-, medium-, and high-cost 3D printers. Following the segmentation of a patient's skull, the model was printed by: (i) a low-cost fused filament fabrication printer; (ii) a medium-cost stereolithography printer; and (iii) a high-cost material jetting printer. The fabricated models were later scanned by industrial computed tomography and superimposed onto the original reference virtual model by applying surface-based registration. A part comparison color-coded analysis was conducted for assessing the difference between the reference and scanned models. A one-way analysis of variance (ANOVA) with Bonferroni correction was applied for statistical analysis.

RESULTS

The model printed with the low-cost fused filament fabrication printer showed the highest mean absolute error ([Formula: see text]), whereas both medium-cost stereolithography-based and the high-cost material jetting models had an overall similar dimensional error of [Formula: see text] and [Formula: see text], respectively. Overall, the models printed with medium- and high-cost printers showed a significantly ([Formula: see text]) lower error compared to the low-cost printer.

CONCLUSIONS

Both stereolithography and material jetting based printers, belonging to the medium- and high-cost market segment, were able to replicate the skeletal anatomy with optimal trueness, which might be suitable for patient-specific treatment planning tasks in craniomaxillofacial surgery. In contrast, the low-cost fused filament fabrication printer could serve as a cost-effective alternative for anatomical education, and/or patient communication.

Effect of internal structures on the accuracy of 3D printed full-arch dentition preparation models in different printing systems

PURPOSE

The objective of this study was to investigate how internal structures influence the overall and marginal accuracy of full arch preparations fabricated through additive manufacturing in different printing systems.

MATERIALS AND METHODS

A full-arch preparation digital model was set up with three internal designs, including solid, hollow, and grid. These were printed using three different resin printers with nine models in each group. After scanning, each data was imported into the 3D data processing software together with the master cast, aligned and trimmed, and then put into the 3D data analysis software again to compare the overall and marginal deviation whose results are expressed using root mean square values and color maps. To evaluate the trueness of the resin model, the test data and reference data were compared, and the precision was evaluated by comparing the test data sets. Color maps were observed for qualitative analysis. Data were statistically analyzed by one-way analysis of variance and Bonferroni method was used for post hoc comparison (α = .05).

RESULTS

The influence of different internal structures on the accuracy of 3D printed resin models varied significantly (P < .05). Solid and grid models showed better accuracy, while the hollow model exhibited poor accuracy. The color maps show that the resin models have a tendency to shrink inwards.

CONCLUSION

The internal structure design influences the accuracy of the 3D printing model, and the effect varies in different printing systems. Irrespective of the kind of printing system, the printing accuracy of hollow model was observed to be worse than those of solid and grid models.

Mechanical Properties of Three-Dimensional Printed Provisional Resin Materials for Crown and Fixed Dental Prosthesis: A Systematic Review

The emergence of digital dentistry has led to the introduction of various three-dimensional (3D) printing materials in the market, specifically for provisional fixed restoration. This study aimed to undertake a systematic review of the published literature on the Mechanical Properties of 3D- Printed Provisional Resin Materials for crown and fixed dental prosthesis (FDP). The electronic database on PubMed/Medline was searched for relevant studies. The search retrieved articles that were published from January 2011 to March 2023. The established focus question was: "Do provisional 3D-printed materials have better mechanical properties than conventional or milled provisional materials?". The systematically extracted data included the researcher's name(s), publication year, evaluation method, number of samples, types of materials, and study outcome. A total of 19 studies were included in this systematic review. These studies examined different aspects of the mechanical properties of 3D-printed provisional materials. Flexural Strength and Microhardness were the frequently used mechanical testing. Furthermore, 3D-printed provisional restorations showed higher hardness, smoother surfaces, less wear volume loss, and higher wear resistance compared to either milled or conventional, or both. 3D-printed provisional resin materials appear to be a promising option for fabricating provisional crowns and FDPs.

Dental Materials Applied to 3D and 4D Printing Technologies: A Review

As computer-aided design and computer-aided manufacturing (CAD/CAM) technologies have matured, three-dimensional (3D) printing materials suitable for dentistry have attracted considerable research interest, owing to their high efficiency and low cost for clinical treatment. Three-dimensional printing technology, also known as additive manufacturing, has developed rapidly over the last forty years, with gradual application in various fields from industry to dental sciences. Four-dimensional (4D) printing, defined as the fabrication of complex spontaneous structures that change over time in response to external stimuli in expected ways, includes the increasingly popular bioprinting. Existing 3D printing materials have varied characteristics and scopes of application; therefore, categorization is required. This review aims to classify, summarize, and discuss dental materials for 3D printing and 4D printing from a clinical perspective. Based on these, this review describes four major materials, i.e., polymers, metals, ceramics, and biomaterials. The manufacturing process of 3D printing and 4D printing materials, their characteristics, applicable printing technologies, and clinical application scope are described in detail. Furthermore, the development of composite materials for 3D printing is the main focus of future research, as combining multiple materials can improve the materials' properties. Updates in material sciences play important roles in dentistry; hence, the emergence of newer materials are expected to promote further innovations in dentistry.

The Influence of Polishing and Artificial Aging on BioMed Amber® Resin's Mechanical Properties

Currently, 3D print is becoming more common in all branches of medicine, including dentistry. Some novel resins, such as BioMed Amber (Formlabs), are used and incorporated to more advanced techniques. The aims of the study were to check whether or not polishing and/or artificial aging influences the properties of the 3D-printed resin. A total of 240 specimens of BioMed Resin were printed. Two shapes (rectangular and dumbbell) were prepared. Of each shape, 120 specimens were divided into four groups each (with no influence, after polishing only, after artificial aging only, and after both polishing and artificial aging). Artificial aging took place in water at the temperature of 37 °C for 90 days. For testing, the universal testing machine (Z10-X700, AML Instruments, Lincoln, UK) was used. The axial compression was performed with the speed of 1mm/min. The tensile modulus was measured with the constant speed of 5 mm/min. The highest resistance to compression and tensile test were observed in the specimens that were neither polished nor aged (0.88 ± 0.03 and 2.88 ± 0.26, respectively). The lowest resistance to compression was observed in the specimens that were not polished, but aged (0.70 ± 0.02). The lowest results of the tensile test were observed when specimens were both polished and aged (2.05 ± 0.28). Both polishing and artificial aging weakened the mechanical properties of the BioMed Amber resin. The compressive modulus changed much with or without polishing. The tensile modulus differed in specimens that were either polished or aged. The application of both did not change the properties when compared to the polished or aged probes only.

In situ evaluation of microbial profile formed on Ti-6Al-4V additive manufacturing disks: 16S rRNA sequencing

STATEMENT OF PROBLEM

Dental implants obtained by additive manufacturing may present changes in the microbiome formed. However, studies profiling the microbial communities formed on Ti-6Al-4V are lacking.

PURPOSE

The purpose of this in situ study was to characterize the profile of the microbial communities formed on Ti-6Al-4V disks produced by additive manufacturing and machining.

MATERIAL AND METHODS

Titanium disks produced by additive manufacturing (AMD) and machining (UD) were housed in the buccal region of removable intraoral devices. These devices containing both disks were used by eight participants for 96 hours. After every 24 hours of intraoral exposure, the biofilm that had formed on the disks was collected. The 16S rRNA genes from each specimen were amplified and sequenced with the Miseq Illumina instrument and analyzed. Total microbial quantification was evaluated by analysis of variance-type statistics using the nparLD package. The Wilcoxon test was used to evaluate alpha diversity (α=.05).

RESULTS

A difference was found in the microbial communities formed on additively manufactured and machined disks, with a reduction in operational taxonomic units (OTUs) for the AMD group compared with the UD group. Firmicutes and Proteobacteria were the most abundant phyla. Of the 1256 genera sequenced, Streptococcus predominated on both disks.

CONCLUSIONS

The microbiome of the biofilm formed on the Ti-6Al-4V disks was significantly influenced by the fabrication method. The AMD disks showed lower total microbial counts than the UD disks.

Design and Implement Strategy of Wireless Bite Force Device

Abnormal bite force is an important risk factor for oral and maxillofacial disorders, which is a critical dilemma that dentists face every day without effective solutions. Therefore, it is of great clinical significance to develop a wireless bite force measurement device and explore quantitative measurement methods to help find effective strategies for improving occlusal diseases. This study designed the open window carrier of a bite force detection device through 3D printing technology, and then the stress sensors were integrated and embedded into a hollow structure. The sensor system mainly consisted of a pressure signal acquisition module, a main control module, and a server terminal. A machine learning algorithm will be leveraged for bite force data processing and parameter configuration in the future. This study implemented a sensor prototype system from scratch to fully evaluate each component of the intelligent device. The experimental results showed reasonable parameter metrics for the device carrier and demonstrated the feasibility of the proposed scheme for bite force measurement. An intelligent and wireless bite force device with a stress sensor system is a promising approach to occlusal disease diagnosis and treatment.

Sports mouthguard overview: Materials, fabrication techniques, existing standards, and future research needs

Sports mouthguards are proven devices that reduce both the probability of and damage to orofacial tissues. While commonly used, clinicians may be unaware of the different sports mouthguard materials, proposed fabrication techniques, design recommendations, and newer digital fabrication methods. An overview of existing sports mouthguard standards is presented. It identifies that identify that the present requirements, while historically chosen in good faith, appear to be arbitrarily selected and not from clinical evidence-based derived data. In addition, identified sports mouthguard heterogeneous testing and data acquisition methods distinguishes that little possibility is afforded for the correlation of results. Furthermore, updated evidence with concussion prevention and/or alleviation is presented with evidence provided by sports mouthguard imbedded technology. The need for continued research is stressed to provide evidence-based data for concussion alleviation/prevention, digital fabrication methods and materials, and clinically based information for the revision of existing standards.

Polymer/Graphene Nanocomposites via 3D and 4D Printing—Design and Technical Potential

Graphene is an important nanocarbon nanofiller for polymeric matrices. The polymer–graphene nanocomposites, obtained through facile fabrication methods, possess significant electrical–thermal–mechanical and physical properties for technical purposes. To overcome challenges of polymer–graphene nanocomposite processing and high performance, advanced fabrication strategies have been applied to design the next-generation materials–devices. This revolutionary review basically offers a fundamental sketch of graphene, polymer–graphene nanocomposite and three-dimensional (3D) and four-dimensional (4D) printing techniques. The main focus of the article is to portray the impact of 3D and 4D printing techniques in the field of polymer–graphene nanocomposites. Polymeric matrices, such as polyamide, polycaprolactone, polyethylene, poly(lactic acid), etc. with graphene, have been processed using 3D or 4D printing technologies. The 3D and 4D printing employ various cutting-edge processes and offer engineering opportunities to meet the manufacturing demands of the nanomaterials. The 3D printing methods used for graphene nanocomposites include direct ink writing, selective laser sintering, stereolithography, fused deposition modeling and other approaches. Thermally stable poly(lactic acid)–graphene oxide nanocomposites have been processed using a direct ink printing technique. The 3D-printed poly(methyl methacrylate)–graphene have been printed using stereolithography and additive manufacturing techniques. The printed poly(methyl methacrylate)–graphene nanocomposites revealed enhanced morphological, mechanical and biological properties. The polyethylene–graphene nanocomposites processed by fused diffusion modeling have superior thermal conductivity, strength, modulus and radiation- shielding features. The poly(lactic acid)–graphene nanocomposites have been processed using a number of 3D printing approaches, including fused deposition modeling, stereolithography, etc., resulting in unique honeycomb morphology, high surface temperature, surface resistivity, glass transition temperature and linear thermal coefficient. The 4D printing has been applied on acrylonitrile-butadiene-styrene, poly(lactic acid) and thermosetting matrices with graphene nanofiller. Stereolithography-based 4D-printed polymer–graphene nanomaterials have revealed complex shape-changing nanostructures having high resolution. These materials have high temperature stability and high performance for technical applications. Consequently, the 3D- or 4D-printed polymer–graphene nanocomposites revealed technical applications in high temperature relevance, photovoltaics, sensing, energy storage and other technical fields. In short, this paper has reviewed the background of 3D and 4D printing, graphene-based nanocomposite fabrication using 3D–4D printing, development in printing technologies and applications of 3D–4D printing.

A biocompatible silicon nitride dental implant material prepared by digital light processing technology

For decades, titanium has been the preferred material for dental implant fabrication. However, metallic ions and particles can cause hypersensitivity and aseptic loosening. The growing demand for metal-free dental restorations has also promoted the development of ceramic-based dental implants, such as silicon nitride. In this study, silicon nitride (Si₃N₄) dental implants were fabricated for biological engineering by photosensitive resin based digital light processing (DLP) technology, comparable to conventionally produced Si₃N₄ ceramics. The flexural strength was (770 ± 35) MPa by the three-point bending method, and the fracture toughness was (13.3 ± 1.1) MPa · m^1/2 by the unilateral pre-cracked beam method. The elastic modulus measured by the bending method was (236 ± 10) GPa. To confirm whether the prepared Si₃N₄ ceramics possessed good biocompatibility, in vitro biological experiments were performed with the fibroblast cell line L-929, and preferable cell proliferation and apoptosis were observed at the initial stages. Hemolysis test, oral mucous membrane irritation test, and acute systemic toxicity test (oral route) further confirmed that the Si₃N₄ ceramics did not exhibit hemolysis reaction, oral mucosal stimulation, or systemic toxicity. The findings indicate that Si₃N₄ dental implant restorations with personalized structures prepared by DLP technology have good mechanical properties and biocompatibility, which has great application potential in the future.

A completely digital workflow to fabricate a double-layered template for anterior esthetic veneers

In the esthetic restoration of anterior teeth, trial restorations are an efficient way of communicating among patients, doctors, and dental laboratory technicians. Although the development of digital technologies has made it popular to design digital diagnostic waxing in a software program, problems such as the polymerization inhibition of silicone materials and time-consuming trimming remain. The silicone mold based on a 3-dimensionally printed resin cast still has to be transferred to the digital diagnostic waxing and to the patient's mouth to generate a trial restoration. A digital workflow is proposed to fabricate a double-layer guide to reproduce the digital diagnostic waxing in the patient's mouth. This technique is suitable for esthetic restorations of anterior teeth.

In-vitro performance of subtractively and additively manufactured resin-based molar crowns

PURPOSE

To compare the in-vitro performance and wear behavior of additively or subtractively fabricated resin-based composite molar crowns for temporary and permanent application.

MATERIALS AND METHODS

Identical molar crowns (n = 8 per group) were manufactured from materials for temporary or permanent application (3x temporary additive fabrication, 3x additive permanent fabrication, 1x temporary subtractive fabrication, 1x permanent subtractive fabrication). All crowns were adhesively bonded (Calibra Universal, Dentsply Sirona, USA) on standardized resin-based composite molars (FDI 46, P Pro temporary Crown & Bridge). Thermal cycling and mechanical loading (2 × 3000 × 5°C/55 °C, 2min, H₂0 dist., 1.2 × 10⁶ force 50N) were performed and fracture force was determined (v = 1 mm/min, Z010, Zwick, Germany). Mean wear, maximum wear, and roughness were investigated on polished (P1200) specimens (n = 8 per group, d = 8 mm) in a pin-on-block test (50N; 120000 cycles; 1.6Hz; H₂O). Statistics were performed by using one-way ANOVA, Bonferroni post-hoc-tests, and Pearson-correlation (α = 0.05).

RESULTS

All crowns survived TCML without failures. Fracture forces ranged from 1362.4 ± 182.4N to 2354.1 ± 373.3N for the additive temporary crowns, from 1680.4.4 ± 525.1N to 2601.6 ± 403.7N for the additive permanent crowns, and reached values of 2988.5 ± 604.7N for subtractive temporary crowns and 3092.0 ± 307.6 N for subtractive permanent crowns. Significant (p < 0.001) differences were identified between the various additively manufactured systems, but not for the subtractively fabricated systems (p = 0.673). Mean wear of the additive temporary crowns ranged between 114.5 ± 25.8 μm and 163.8 ± 21.4 μm without significant differences (p = 0.061). Mean wear of the additive permanent crowns ranged between 120.0 ± 27.5 μm and 171.3 ± 31.8 μm with significant differences (p = 0.004). No statistically significant differences were identified between temporary and permanent subtractively manufactured specimens, with mean wear ranging between 140.5 ± 51.1 μm and 176.6 ± 26.8 μm (p = 0.673). Maximum wear of additive temporary specimens ranged between 221.4.5 ± 53.3 μm and 322.1 ± 50.6 μm; significant differences were identified between the groups (p = 0.016). Maximum wear of additive permanent specimens ranged between 246.3 ± 47.3 μm and 337.4 ± 61.4 μm, and significant differences were identified between the groups (p = 0.006). Mean wear of the subtractive group (permanent and temporary) showed no differences in maximum wear from 277.9 ± 79.7.1 μm to 316.4 ± 58.1 μm (p = 0.288). Ra roughness ranged from 0.7 ± 0.2 μm to 3.6 ± 1.3 μm with significant differences (p < 0.001) and Rz reference between 65.9 ± 26.2 μm and 16.8 ± 6.3 μm.

CONCLUSION

Temporary and permanent molar crowns provided at least acceptable in-vitro performance and fracture force for clinical mid-term application. Laboratory wear stability of the resin-based materials appeared sufficient, but should be verified under clinical conditions.

(Bio)printing in Personalized Medicine—Opportunities and Potential Benefits

The global development of technologies now enters areas related to human health, with a transition from conventional to personalized medicine that is based to a significant extent on (bio)printing. The goal of this article is to review some of the published scientific literature and to highlight the importance and potential benefits of using 3D (bio)printing techniques in contemporary personalized medicine and also to offer future perspectives in this research field. The article is prepared according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Web of Science, PubMed, Scopus, Google Scholar, and ScienceDirect databases were used in the literature search. Six authors independently performed the search, study selection, and data extraction. This review focuses on 3D bio(printing) in personalized medicine and provides a classification of 3D bio(printing) benefits in several categories: overcoming the shortage of organs for transplantation, elimination of problems due to the difference between sexes in organ transplantation, reducing the cases of rejection of transplanted organs, enhancing the survival of patients with transplantation, drug research and development, elimination of genetic/congenital defects in tissues and organs, and surgery planning and medical training for young doctors. In particular, we highlight the benefits of each 3D bio(printing) applications included along with the associated scientific reports from recent literature. In addition, we present an overview of some of the challenges that need to be overcome in the applications of 3D bioprinting in personalized medicine. The reviewed articles lead to the conclusion that bioprinting may be adopted as a revolution in the development of personalized, medicine and it has a huge potential in the near future to become a gold standard in future healthcare in the world.

Computer-Guided Osteotomy with Simultaneous Implant Placement and Immediately Loaded Full-Arch Fixed Restoration: A Case Report

Aim: This case report aims to illustrate a clinical protocol that allows for the rehabilitation of patients requiring extensive osteotomy, simultaneous implant placement, and full-arch, screwed-in prosthetics in one session. This protocol allows for the improvement of the aesthetics and functionality of the fixed implant-supported prosthesis through the preoperative planning of all surgical procedures, including osteotomy, and of the prosthesis through the application of 3D-printing technology for the creation of surgical templates and prostheses. Methods: This case report concerns a 72-year-old patient, ASA1, who, following diagnosis, the establishment of a treatment plan, and the provision of informed consent, opted for an immediate, full-arch rehabilitation of the lower arch. The digital planning stage started with the correct positioning of the fixtures. The proper bone levels were found and used to guide the creation of the provisional screwed-in prothesis. Two templates with the same supports (landmarks/pins) were then 3D-printed: a positioning template, including a slit to assist the surgeon during the osteotomy, and a surgery template to assist the surgeon during the implants’ positioning. A screwed-in prosthesis encased in resin C&B MFH (NEXTDENT®, Soesterberg, The Netherlands) was delivered. Minimal occlusal adjustments were performed. Results: In a single clinical session, through careful planning and the pre-operative 3D printing of a prosthesis, a temporary implant-supported prosthetic rehabilitation was possible in a case that required an extended osteotomy. Clinically, the correspondence between the virtual design phase and the final realization was consistent. At a functional level, the provisional prosthesis required minimal occlusal adjustments and the DVO values obtained in the immediate post-operative period were found to be comparable to those of the virtual design. By planning the final position of the bone and the implants in advance, it was possible to deliver a full-arch prothesis with proper implant emergence, occlusal vertical dimensions, and occlusal relationship. Conclusion: This fully digital protocol allows the clinician to preview and plan the osteotomy and implant surgery as well as the delivery of the temporary, immediately loaded, complete, fixed prosthesis in patients who are candidates for post-extraction surgery with the need for severe osteotomy.

Wear behavior of materials for additive manufacturing after simulated occlusion of deciduous dentition

OBJECTIVES

To evaluate wear characteristics of materials for additive manufacturing (AM) after a simulated occlusal test in primary teeth. Wear was simulated by means of impacting - sliding wear testing (ISWT) between specimens prepared from materials for AM against enamel derived from deciduous teeth.

METHODS

The prepared hemispherical upper specimens were subjected to impacting-sliding wear test (ISWT) machine against the flattened enamel of deciduous molars on lower specimens. The samples were subjected to 20,000 load cycles using a contact force of 30 N between the opposing surfaces under controlled conditions. In the upper specimens, five groups (n=9): four types of additively manufactured materials Dima, Zenith, Detax, Veltz and a deciduous enamel groups were tested in this study. The enamel-to-enamel group was used as the control. Wear characteristics comprised wear surface area, wear depth, wear volumetric loss, and surface roughness were measured with a confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Data obtained were statistically analyzed by Kruskal-Wallis test and Dunn's test with Bonferroni correction (p < 0.05).

RESULTS

Dima showed significantly higher worn surface area (p = 0.009, 0.001, and < 0.001 for Zenith, Detax, and control enamel, respectively), volumetric loss (p = 0.027, 0.007, and < 0.001 for Zenith, Detax, and control enamel, respectively), and damaged opposing enamel (p = 0.002, 0.001, and 0.01 for Detax, Veltz, and control enamel, respectively). There was no significant difference among the volumetric loss in Zenith and Detax. However, SEM revealed that Zenith showed rough worn surfaces and chipping, Detax showed rather a smooth circular worn surface. The worn area of Veltz was smaller than Detax and Zenith at 5,000 cycles, but higher at 15,000 and 20,000 cycles, and SEM showed detachment.

CONCLUSION

Wear behavior was different among different materials for AM. In the upper specimens, DM and VZ showed large wear. In the lower specimens, DM caused largest enamel wear and damage. In contrast, ZT and DX showed lower wear and caused less damage to the antagonistic primary enamel. SEM image of ZT showed large losses due to chipping, whereas DX showed the rather smooth. DX was confirmed to have lowest wear and caused least damage to the opposing deciduous enamel, which might be applicable as restorative treatments in deciduous dentition.

SIGNIFICANCE

Additive manufactured dental materials could be considered as a treatment modality in deciduous teeth.

Additive manufacturing technologies in the oral implant clinic: A review of current applications and progress

Additive manufacturing (AM) technologies can enable the direct fabrication of customized physical objects with complex shapes, based on computer-aided design models. This technology is changing the digital manufacturing industry and has become a subject of considerable interest in digital implant dentistry. Personalized dentistry implant treatments for individual patients can be achieved through Additive manufacturing. Herein, we review the applications of Additive manufacturing technologies in oral implantology, including implant surgery, and implant and restoration products, such as surgical guides for implantation, custom titanium meshes for bone augmentation, personalized or non-personalized dental implants, custom trays, implant casts, and implant-support frameworks, among others. In addition, this review also focuses on Additive manufacturing technologies commonly used in oral implantology. Stereolithography, digital light processing, and fused deposition modeling are often used to construct surgical guides and implant casts, whereas direct metal laser sintering, selective laser melting, and electron beam melting can be applied to fabricate dental implants, personalized titanium meshes, and denture frameworks. Moreover, it is sometimes required to combine Additive manufacturing technology with milling and other cutting and finishing techniques to ensure that the product is suitable for its final application.

PEEK for Oral Applications: Recent Advances in Mechanical and Adhesive Properties

Polyetheretherketone (PEEK) is a thermoplastic material widely used in engineering applications due to its good biomechanical properties and high temperature stability. Compared to traditional metal and ceramic dental materials, PEEK dental implants exhibit less stress shielding, thus better matching the mechanical properties of bone. As a promising medical material, PEEK can be used as implant abutments, removable and fixed prostheses, and maxillofacial prostheses. It can be blended with materials such as fibers and ceramics to improve its mechanical strength for better clinical dental applications. Compared to conventional pressed and CAD/CAM milling fabrication, 3D-printed PEEK exhibits excellent flexural and tensile strength and parameters such as printing temperature and speed can affect its mechanical properties. However, the bioinert nature of PEEK can make adhesive bonding difficult. The bond strength can be improved by roughening or introducing functional groups on the PEEK surface by sandblasting, acid etching, plasma treatment, laser treatment, and adhesive systems. This paper provides a comprehensive overview of the research progress on the mechanical properties of PEEK for dental applications in the context of specific applications, composites, and their preparation processes. In addition, the research on the adhesive properties of PEEK over the past few years is highlighted. Thus, this review aims to build a conceptual and practical toolkit for the study of the mechanical and adhesive properties of PEEK materials. More importantly, it provides a rationale and a general new basis for the application of PEEK in the dental field.

Application of computer-aided design and 3D-printed template for accurate bone augmentation in the aesthetic region of anterior teeth

PURPOSE

To explore the outcomes of bone augmentation in the aesthetic zone of the anterior teeth using computer-aided design and a 3D-printed template.

METHODS

Ten patients with severe bone defects in the aesthetic zone of anterior teeth were included in the study; CT data were collected before surgery. The design of the osteotomy line in the bone defect area was determined under computer simulation. The position parameters and osteotomy line of the free bone were determined via virtual surgery. A 3D-printed template was prepared to guide the accurate placement of the bone graft. Reexamination was conducted to evaluate the position of the bone graft immediately after the operation and the resorbed capacity of the bone graft before implant restoration.

RESULTS

The position of the bone graft was consistent with the preoperative design. The amount of bone graft resorbed was within the acceptable range three months after the operation, and the effect of implant restoration was satisfactory.

CLINICAL SIGNIFICANCE

Use of computer-aided design and a 3D-printed template can be an effective approach for accurate bone augmentation in the aesthetic zone of the anterior teeth.

Advanced materials and technologies for oral diseases

Oral disease, as a class of diseases with very high morbidity, brings great physical and mental damage to people worldwide. The increasing burden and strain on individuals and society make oral diseases an urgent global health problem. Since the treatment of almost all oral diseases relies on materials, the rapid development of advanced materials and technologies has also promoted innovations in the treatment methods and strategies of oral diseases. In this review, we systematically summarized the application strategies in advanced materials and technologies for oral diseases according to the etiology of the diseases and the comparison of new and old materials. Finally, the challenges and directions of future development for advanced materials and technologies in the treatment of oral diseases were refined. This review will guide the fundamental research and clinical translation of oral diseases for practitioners of oral medicine.

Four-Dimensional Printing and Shape Memory Materials in Bone Tissue Engineering

The repair of severe bone defects is still a formidable clinical challenge, requiring the implantation of bone grafts or bone substitute materials. The development of three-dimensional (3D) bioprinting has received considerable attention in bone tissue engineering over the past decade. However, 3D printing has a limitation. It only takes into account the original form of the printed scaffold, which is inanimate and static, and is not suitable for dynamic organisms. With the emergence of stimuli-responsive materials, four-dimensional (4D) printing has become the next-generation solution for biological tissue engineering. It combines the concept of time with three-dimensional printing. Over time, 4D-printed scaffolds change their appearance or function in response to environmental stimuli (physical, chemical, and biological). In conclusion, 4D printing is the change of the fourth dimension (time) in 3D printing, which provides unprecedented potential for bone tissue repair. In this review, we will discuss the latest research on shape memory materials and 4D printing in bone tissue repair.

Bioprinting and biomaterials for dental alveolar tissue regeneration

Three dimensional (3D) bioprinting is a powerful tool, that was recently applied to tissue engineering. This technique allows the precise deposition of cells encapsulated in supportive bioinks to fabricate complex scaffolds, which are used to repair targeted tissues. Here, we review the recent developments in the application of 3D bioprinting to dental tissue engineering. These tissues, including teeth, periodontal ligament, alveolar bones, and dental pulp, present cell types and mechanical properties with great heterogeneity, which is challenging to reproduce in vitro. After highlighting the different bioprinting methods used in regenerative dentistry, we reviewed the great variety of bioink formulations and their effects on cells, which have been established to support the development of these tissues. We discussed the different advances achieved in the fabrication of each dental tissue to provide an overview of the current state of the methods. We conclude with the remaining challenges and future needs.

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.

Three-dimensional printing and 3D slicer powerful tools in understanding and treating neurosurgical diseases

With the development of the 3D printing industry, clinicians can research 3D printing in preoperative planning, individualized implantable materials manufacturing, and biomedical tissue modeling. Although the increased applications of 3D printing in many surgical disciplines, numerous doctors do not have the specialized range of abilities to utilize this exciting and valuable innovation. Additionally, as the applications of 3D printing technology have increased within the medical field, so have the number of printable materials and 3D printers. Therefore, clinicians need to stay up-to-date on this emerging technology for benefit. However, 3D printing technology relies heavily on 3D design. 3D Slicer can transform medical images into digital models to prepare for 3D printing. Due to most doctors lacking the technical skills to use 3D design and modeling software, we introduced the 3D Slicer to solve this problem. Our goal is to review the history of 3D printing and medical applications in this review. In addition, we summarized 3D Slicer technologies in neurosurgery. We hope this article will enable many clinicians to leverage the power of 3D printing and 3D Slicer.

Comparison in Terms of Accuracy between DLP and LCD Printing Technology for Dental Model Printing

Background: The aim of this study is to evaluate the accuracy of a Liquid Crystal Display (LCD) 3D printer compared to a Direct Light Processing (DLP) 3D printer for dental model printing. Methods: Two different printers in terms of 3D printing technology were used in this study. One was a DLP 3D printer and one an LCD 3D printer. The accuracy of the printers was evaluated in terms of trueness and precision. Ten STL reference files were used for this study. For trueness, each STL file was printed once with each 3D printer. For precision, one randomly chosen STL file was printed 10 times with each 3D printer. Afterward, the models were scanned with a model scanner, and reverse engineering software was used for the STL comparisons. Results: In terms of trueness, the comparison between the LCD 3D printer and DLP 3D printer was statistically significant, with a p-value = 0.004. For precision, the comparison between the LCD 3D printer and the DLP 3D printer was statistically significant, with a p-value = 0.011. Conclusions: The DLP 3D printer is more accurate in terms of dental model printing than the LCD 3D printer. However, both DLP and LCD printers can accurately be used to print dental models for the fabrication of orthodontic appliances.

A Novel Approach to Guided Implant Surgery: A Technical Note

Computer-guided software and kits have significantly improved the clinical applications of implant surgery. Nonetheless, some technical problems are still in evidence during clinical procedures because of cumbersome surgical tools that can limit access to implant sites, mainly in posterior areas of the mouth in the presence of bulky anatomical structures and in patients with reduced mouth-opening capacity. The present paper aimed to present a novel approach to guided implant surgery, describing the technical characteristics of an innovative guided surgical kit made up of modified sleeves and modular surgical drills. The proposed guided surgical kit is based on a novel patented system of sleeves and modular burs, with an increased length of the metal sleeves and a reduced height of the drills. The innovative design of the proposed system would allow the clinician to position guided fixtures in all clinical situations; the reduced encumbrance would be particularly helpful to gain access to the posterior areas of both maxilla and mandible, which have limited inter-arch space, with an easy and user-friendly approach. The modular system could overcome anatomical limitations, such as reduced mouth-opening capacity, and permit clinicians to maintain the stability and integrity of the surgical templates, even in cases where there is very limited intermaxillary space.

3D Printed and Bioprinted Membranes and Scaffolds for the Periodontal Tissue Regeneration: A Narrative Review

Numerous technologies and materials were developed with the aim of repairing and reconstructing the tissue loss in patients with periodontitis. Periodontal guided bone regeneration (GBR) and guided tissue regeneration (GTR) involves the use of a membrane which prevents epithelial cell migration, and helps to maintain the space, creating a protected area in which tissue regeneration is favored. Over the time, manufacturing procedures of such barrier membranes followed important improvements. Three-dimensional (3D) printing technology has led to major innovations in periodontal regeneration methods, using technologies such as inkjet printing, light-assisted 3D printing or micro-extrusion. Besides the 3D printing of monophasic and multi-phasic scaffolds, bioprinting and tissue engineering have emerged as innovative technologies which can change the way we see GTR and GBR.

Mechanical and electrochemical characterization of 3D printed orthodontic metallic appliances after in vivo ageing

OBJECTIVES

Three-dimensional (3D) printing technology is a promising technique for fabricating custom orthodontic metallic appliances. Aim of this study was to assess the effect of intraoral aging on the mechanical / electrochemical properties of 3D-printed orthodontic metallic appliances.

METHODS

Twelve molar orthodontic distalization appliances 3D-printed from cobalt chromium (Co-Cr) alloy were retrieved after intraoral use and twenty blocks fabricated under similar conditions were used as control. The samples' microstructural / elemental composition assessment was assessed with SEM/EDS, while their mechanical properties (modulus of elasticity [E_IT], Martens hardness [HM] and the elastic index [η_IT]) were measured by instrumented indentation testing. Finally, the samples' electrochemical features were assessed with a potentiostat-connected cell arrangement in terms of open circuit potential (OCP), corrosion potential (E_z), current density (I₃₀₀) and breaking potential (E_pit). Results were analyzed by t-test / Mann-Whitney test (α = 0.05).

RESULTS

The used Co-Cr alloy was found to have a highly homogenous structure with no significant differences between retrieved and new specimens in HM (4037.7 ± 215.6 vs 4090.9 ± 259.8 N/mm²), E_IT (120.0 ± 13.2 vs 123.8 ± 12.9 GPa), or n_IT (28.4 ± 2.6 vs 28.6 ± 2.9 %) (P > 0.05 in all instances). Metallic surfaces retained the same oxidation tendency and oxide dissolution rate in passive region in both groups (P > 0.05 for OCP, E_z, and I₃₀₀). However, intraorally-aged specimens had a significantly lower breakdown potential due to degraded protection efficacy of surface oxide (P = 0.003 for E_pit).

SIGNIFICANCE

The tested 3D-printed Co-Cr orthodontic appliances present clinically-acceptable mechanical properties that remained unaffected by intraoral ageing, which however degraded the protection of surface oxide against pitting corrosion.

Additive Manufactured Polymers in Dentistry, Current State-of-the-Art and Future Perspectives-A Review

3D-printing application in dentistry not only enables the manufacture of patient-specific devices and tissue constructs, but also allows mass customization, as well as digital workflow, with predictable lower cost and rapid turnaround times. 4D printing also shows a good impact in dentistry, as it can produce dynamic and adaptable materials, which have proven effective in the oral environment, under its continuously changing thermal and humidity conditions. It is expected to further boost the research into producing a whole tooth, capable to harmoniously integrate with the surrounding periodontium, which represents the ultimate goal of tissue engineering in dentistry. Because of their high versatility associated with the wide variety of available materials, additive manufacturing in dentistry predominantly targets the production of polymeric constructs. The aim of this narrative review is to catch a glimpse of the current state-of-the-art of additive manufacturing in dentistry, and the future perspectives of this modern technology, focusing on the specific polymeric materials.

Harnessing 4D Printing Bioscaffolds for Advanced Orthopedics

The development of programmable functional biomaterials makes 4D printing add a new dimension, time (t), based on 3D structures (x, y, z), therefore, 4D printed constructs could transform their morphology or function over time in response to environmental stimuli. Nowadays, highly efficient bone defect repair remains challenging in clinics. Combining programmable biomaterials, living cells, and bioactive factors, 4D bioprinting provides greater potential for constructing dynamic, personalized, and precise bone tissue engineering scaffolds by complex structure formation and functional maturation. Therefore, 4D bioprinting has been regarded as the next generation of bone repair technology. This review focuses on 4D printing and its advantages in orthopedics. The applications of different smart biomaterials and 4D printing strategies are briefly introduced. Furthermore, one summarizes the recent advancements of 4D printing in bone tissue engineering, uncovering the addressed and unaddressed medical requirements. In addition, current challenges and future perspectives are further discussed, which will offer more inspiration about the clinical transformation of this emerging 4D bioprinting technology in bone regeneration.

Porous construction and surface modification of titanium-based materials for osteogenesis: A review

Titanium and titanium alloy implants are essential for bone tissue regeneration engineering. The current trend is toward the manufacture of implants from materials that mimic the structure, composition and elasticity of bones. Titanium and titanium alloy implants, the most common materials for implants, can be used as a bone conduction material but cannot promote osteogenesis. In clinical practice, there is a high demand for implant surfaces that stimulate bone formation and accelerate bone binding, thus shortening the implantation-to-loading time and enhancing implantation success. To avoid stress shielding, the elastic modulus of porous titanium and titanium alloy implants must match that of bone. Micro-arc oxidation technology has been utilized to increase the surface activity and build a somewhat hard coating on porous titanium and titanium alloy implants. More recently, a growing number of researchers have combined micro-arc oxidation with hydrothermal, ultrasonic, and laser treatments, coatings that inhibit bacterial growth, and acid etching with sand blasting methods to improve bonding to bone. This paper summarizes the reaction at the interface between bone and implant material, the porous design principle of scaffold material, MAO technology and the combination of MAO with other technologies in the field of porous titanium and titanium alloys to encourage their application in the development of medical implants.

Fabrication And In Vitro Evaluation Of 3D Printed Porous Silicate Substituted Calcium Phosphate Scaffolds For Bone Tissue Engineering

Silicate-substituted calcium phosphate (Si-CaP) ceramics, alternative materials for autogenous bone grafting, exhibit excellent osteoinductivity, osteoconductivity, biocompatibility and biodegradability; thus, they have been widely used for treating bone defects. However, the limited control over the spatial structure and weak mechanical properties of conventional Si-CaP ceramics hinder their wide application. Here, we used digital light processing (DLP) printing technology to fabricate a novel porous 3D printed Si-CaP scaffold to enhance the scaffold properties. Scanning electron microscopy, compression tests, and computational fluid dynamics simulations of the 3D printed Si-CaP scaffolds revealed a uniform spatial structure, appropriate mechanical properties, and effective interior permeability. Furthermore, compared to Si-CaP groups, 3D printed Si-CaP groups exhibited sustained release of silicon (Si), calcium (Ca) and phosphorus (P) ions. Furthermore, 3D printed Si-CaP groups had more comprehensive and persistent osteogenic effects due to increased osteogenic factor expression and calcium deposition. Our results show that the 3D printed Si-CaP scaffold successfully improved bone marrow mesenchymal stem cell (BMSCs) adhesion, proliferation and osteogenic differentiation and possessed a distinct apatite mineralization ability. Overall, with the help of DLP printing technology, Si-CaP ceramic materials facilitate the fabrication of ideal bone tissue engineering scaffolds with essential elements, providing a promising approach for bone regeneration. This article is protected by copyright. All rights reserved.

Three-Dimensional Visualization of Postsurgical Airway Changes Using 3D Printing Technology in a Patient With Mandibular Prognathism: A 5-Year Follow-up Study

This case-report described the 3-dimensional (3D) evaluation of airway changes using 3D printing technology in a patient with mandibular prognathism, treated via mandibular setback surgery with maxillary posterior impaction. The airway dimensions, following orthognathic surgery, were printed using 3D printing technology and the sequential airway changes were visualized. The patient underwent orthognathic surgery for the correction of mandibular prognathism. Five years later, the airway changes were visualized and evaluated using rapid prototyping. The 3D visualization of the airway changes following surgery alerted clinicians of patients with mandibular prognathism and facilitated effective communication with their patients. This case-report documented the long-term evaluation and visualization of the postoperative airway changes in patients with mandibular prognathism using cone-beam computed tomography and 3D printing technology.

Three-Dimensional Printing Technology in Orthodontics for Dental Models: A Systematic Review

Background: Three-dimensional printing technology is an additive manufacturing technology that is used to reconstruct 3D objects. In the last decade, it has been rapidly involved in dentistry and in orthodontics. This article aims to review the literature and present the accuracy of different 3D printer types and any factors that could affect the 3D printing of dental models in the orthodontic field. Methods: The search strategy of this systematic review included keywords in combination with MeSH terms in Medline, Scopus, and Cochrane Library until June 2022 and only in English. Results: Eleven articles were selected for our study. All the articles were in vitro prospective studies, and they presented a low risk of bias. The results suggested that the accuracy of a printed dental cast can be affected by the different types of 3D technologies, the dental cast’s base design, and the printing materials. The accuracy appears to not be affected by the layer height and the position of the model on the building template. Conclusions: According to this systematic review, all different types of 3D technology can produce clinically accepted results for orthodontic purposes. There is a need for more studies to clarify the accuracy and added value of 3D printing technology in orthodontics.

Three-Dimensional-Printed Customized Orthodontic and Pedodontic Appliances: A Critical Review of a New Era for Treatment

Three-dimensional (3D) designing and manufacturing technology is a direct derivative of digital technology. Three-dimensional volume and surface acquisition, CAD software, and 3D manufacturing are major changes included in daily practice in many orthodontic and pedodontic offices. Customized appliances can be designed using dental CAD software or general-purpose CAD software in the office or a laboratory. Materials that can be used are resins, alloys, or zirconia. Methods: The search strategy of this critical review included keywords in combination with MeSH terms in Medline, Scopus, and Cochrane Library up to June 2022 in the English language without any limit to the publication period. Results: According to our search, 12 articles were selected for our study. All the articles were in vitro prospective studies. Conclusions: The results suggested that almost all the known appliances can be designed and printed in a tailor-made fashion in contrast to the traditional one-size-fits-all approach. Customized appliances should be manufactured according to the patient’s needs, and this is justified by the certainty that this approach will be beneficial for the patient’s treatment. There is a need for more research on all direct 3D-printed appliances.

A Hybrid Capsule Network for Automatic 3D Mandible Segmentation applied in Virtual Surgical Planning

Automatic mandible segmentation of CT images is an essential step to achieve an accurate preoperative prediction of an intended target in three-dimensional (3D) virtual surgical planning. Segmentation of the mandible is a challenging task due to the complexity of the mandible structure, imaging artifacts, and metal implants or dental filling materials. In recent years, utilizing convolutional neural networks (CNNs) have made significant improvements in mandible segmentation. However, aggregating data at pooling layers in addition to collecting and labeling a large volume of data for training CNNs are significant issues in medical practice. We have optimized data-efficient 3D-UCaps to achieve the advantages of both the capsule network and the CNN, for accurate mandible segmentation on volumetric CT images. A novel hybrid loss function based on a weighted combination of the focal and margin loss functions is also proposed to handle the problem of voxel class imbalance. To evaluate the performance of our proposed method, a similar experiment was conducted with the 3D-UNet. All experiments are performed on the public domain database for computational anatomy (PDDCA). The proposed method and 3D-UNet achieved an average dice coefficient of 90% and 88% on the PDDCA, respectively. The results indicate that the proposed method leads to accurate mandible segmentation and outperforms the popular 3D-UNet model. It is concluded that the proposed approach is very effective as it requires more than 50% fewer parameters than the 3D-UNet.

3D Printing of Metal-Organic Framework-Based Ionogels: Wearable Sensors with Colorimetric and Mechanical Responses

Soft ionotronics are emerging materials as wearable sensors for monitoring physiological signals, sensing environmental hazards, and bridging the human-machine interface. However, the next generation of wearable sensors requires multiple sensing capabilities, mechanical toughness, and 3D printability. In this study, a metal-organic framework (MOF) and three-dimensional (3D) printing were integrated for the synthesis of a tough MOF-based ionogel (MIG) for colorimetric and mechanical sensing. The ink for 3D printing contained deep eutectic solvents (DESs), cellulose nanocrystals (CNCs), MOF crystals, and acrylamide. After printing, further photopolymerization resulted in a second covalently cross-linked poly(acrylamide) network and solidification of MIG. As a porphyrinic Zr-based MOF, MOF-525 served as a functional filler to provide sharp color changes when exposed to acidic compounds. Notably, MOF-525 crystals also provided another design space to tune the printability and mechanical strength of MIG. In addition, the printed MIG exhibited high stability in the air because of the low volatility of DESs. Thereafter, wearable auxetic materials comprising MIG with negative Poisson's ratios were prepared by 3D printing for the detection of mechanical deformation. The resulting auxetic sensor exhibited high sensitivity via the change in resistance upon mechanical deformation and a conformal contact with skins to monitor various human body movements. These results demonstrate a facile strategy for the construction of multifunctional sensors and the shaping of MOF-based composite materials.

High Precision 3D Printing for Micro to Nano Scale Biomedical and Electronic Devices

Three dimensional printing (3DP), or additive manufacturing, is an exponentially growing process in the fabrication of various technologies with applications in sectors such as electronics, biomedical, pharmaceutical and tissue engineering. Micro and nano scale printing is encouraging the innovation of the aforementioned sectors, due to the ability to control design, material and chemical properties at a highly precise level, which is advantageous in creating a high surface area to volume ratio and altering the overall products’ mechanical and physical properties. In this review, micro/-nano printing technology, mainly related to lithography, inkjet and electrohydrodynamic (EHD) printing and their biomedical and electronic applications will be discussed. The current limitations to micro/-nano printing methods will be examined, covering the difficulty in achieving controlled structures at the miniscule micro and nano scale required for specific applications.

Material Design for Enhancing Properties of 3D Printed Polymer Composites for Target Applications

Polymer composites are becoming an important class of materials for a diversified range of industrial applications due to their unique characteristics and natural and synthetic reinforcements. Traditional methods of polymer composite fabrication require machining, manual labor, and increased costs. Therefore, 3D printing technologies have come to the forefront of scientific, industrial, and public attention for customized manufacturing of composite parts having a high degree of control over design, processing parameters, and time. However, poor interfacial adhesion between 3D printed layers can lead to material failure, and therefore, researchers are trying to improve material functionality and extend material lifetime with the addition of reinforcements and self-healing capability. This review provides insights on different materials used for 3D printing of polymer composites to enhance mechanical properties and improve service life of polymer materials. Moreover, 3D printing of flexible energy-storage devices (FESD), including batteries, supercapacitors, and soft robotics using soft materials (polymers), is discussed as well as the application of 3D printing as a platform for bioengineering and earth science applications by using a variety of polymer materials, all of which have great potential for improving future conditions for humanity and planet Earth.

Additive Manufacturing Technologies for Fabrication of Biomaterials for Surgical Procedures in Dentistry: A Narrative Review

PURPOSE

To screen and critically appraise available literature regarding additive manufacturing technologies for bone graft material fabrication in dentistry.

MATERIAL AND METHODS

PubMed and Scopus were searched up to May 2021. Studies reporting the additive manufacturing techniques to manufacture scaffolds for intraoral bone defect reconstruction were considered eligible. A narrative review was synthesized to discuss the techniques for bone graft material fabrication in dentistry and the biomaterials used.

RESULTS

The databases search resulted in 933 articles. After removing duplicate articles (128 articles), the titles and abstracts of the remaining articles (805 articles) were evaluated. A total of 89 articles were included in this review. Reading these articles, 5 categories of additive manufacturing techniques were identified: material jetting, powder bed fusion, vat photopolymerization, binder jetting, and material extrusion.

CONCLUSIONS

Additive manufacturing technologies for bone graft material fabrication in dentistry, especially 3D bioprinting approaches, have been successfully used to fabricate bone graft material with distinct compositions.

Accuracy of Fixed Implant-Supported Dental Prostheses Additively Manufactured by Metal, Ceramic, or Polymer: A Systematic Review

PURPOSE

Additive manufacturing (AM) in prosthodontics is used as an alternative to casting or milling. Various techniques and materials are available for the additive manufacturing of the fixed and removable tooth-supported restorations, but there is a lack of evidence on the accuracy of AM fixed implant-supported prostheses. Recent studies investigated the accuracy of ceramic AM prostheses. Therefore, the aim of this systematic review was to evaluate the accuracy of additively manufactured metal, ceramic or polymers, and screw- or cement-retained fixed implant-supported prostheses.

MATERIALS AND METHODS

Two calibrated investigators performed an electronic search of relevant publications in the English language following selected PICOS criteria and using a well-defined search strategy (latest search date-1st of June, 2021). Based on the exclusion criteria (no control group, less than five samples per group, 3D printing of the implant abutment part, only subjective evaluation of accuracy, etc.) studies were not included in the review. Quantitative data of accuracy evaluation such as marginal gap, strain analysis, and linear measurements was extracted and interpreted. QUADAS-2 tool was used to assess the risk of methodological bias of all included studies.

RESULTS

Sixteen in vitro studies were selected for the final analysis. Six of the selected studies evaluated screw-retained restorations and 10 cement-retained implant-supported restorations. Only 4 publications concluded that AM restorations were more accurate than conventionally made (cast or milled) ones. The most common finding was that AM restorations were more accurate than cast and demonstrated less or similar accuracy compared to milled ones (n = 10 studies). Detected marginal discrepancies mean values of the AM prosthesis varied from 23 to more than 200 µm, but most of them were categorized as clinically acceptable.

CONCLUSIONS

AM implant-supported fixed prostheses demonstrate similar accuracy compared to conventional and computer-aided design and computer-aided manufacturing techniques in vitro. Detected inaccuracies of AM restorations do not exceed clinically acceptable limits. Clinical studies with longer follow-up periods are needed to show the reliability of AM prostheses.

A new trend of using poly(vinyl alcohol) in 3D and 4D printing technologies: Process and applications

Recently, 3D/4D printing technologies have been the researchers' interest, and they are getting improved more important. They are applicable in various fields like medical fields, pharmaceutics, construction, tissue engineering, dentistry, water treatment, etc. These technologies overcame the difficulty of the conventional methods in producing complicated structures. They can be fed by different materials such as nanomaterials, smart polymers, responsive polymers, metamaterials, synthetic polymers, natural polymers, and so forth. One of the smart and stimuli-responsive polymers is poly(vinyl alcohol) (PVA). In addition to numerous applications of PVA like medicine, environmental fields, etc., researchers are showing a tendency to use PVA in 3D/4D printing technologies. The main reasons for PVA's increased interest in 3D/4D printing technologies are suitable flowability, stimuli-responsivity, extrudability, biocompatibility, biodegradability, cost-effectiveness, and other features. This review aims to introduce the 3D/4D printing technologies' knowledge and then the applications of PVA as a feed in these novel technologies.

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.

Main Applications and Recent Research Progresses of Additive Manufacturing in Dentistry

In recent ten years, with the fast development of digital and engineering manufacturing technology, additive manufacturing has already been more and more widely used in the field of dentistry, from the first personalized surgical guides to the latest personalized restoration crowns and root implants. In particular, the bioprinting of teeth and tissue is of great potential to realize organ regeneration and finally improve the life quality. In this review paper, we firstly presented the workflow of additive manufacturing technology. Then, we summarized the main applications and recent research progresses of additive manufacturing in dentistry. Lastly, we sketched out some challenges and future directions of additive manufacturing technology in dentistry.