Additive Manufacturing Technologies Used for 3D Metal Printing in Dentistry

Surface characteristics of additively manufactured CoCr and Ti6Al4V dental alloys: The effects of carbon and gold thin film coatings, and alkali-heat treatment

This study investigates the impact of surface modifications on additively manufactured CoCr and Ti6Al4V dental alloys, focusing on surface properties. Thin film carbon (C) and gold (Au) coatings, as well as alkali-heat treatment, were applied to the high- and low-polished specimens. Scanning electron microscopy (SEM) showed that thin film coatings retained the underlying surface topography, while the alkali-heat treatment induced distinct morphological changes. Energy-dispersive x-ray spectroscopy (EDS) analysis revealed that C-coating enriched surfaces with C, and Au-coating introduced detectable amounts of Au. Nevertheless, signs of coating delamination were observed in the high-polished specimens. Alkali-heat treatment led to the formation of a sodium titanate layer on Ti6Al4V surfaces, confirmed by sodium presence and Fourier transform infrared spectroscopy (FTIR) results showing carbonate bands. Surface roughness measurements with atomic force microscopy (AFM) showed that C-coating increased surface roughness in both high- and low-polished alloys. Au-coating slightly increased roughness, except for low-polished Au-coated Ti6Al4V, where a decrease in roughness was observed compared to low-polished bare Ti6Al4V, likely due to surface defects present in the latter resulting from the additive manufacturing process. Alkali-heat treatment led to a pronounced increase in roughness for both alloys, particularly for Ti6Al4V. Both thin film coatings decreased the water contact angles in all specimens in varying magnitudes, indicating an increase in wettability. However, the alkali-heat treatment caused a substantial decrease in contact angles, resulting in a highly hydrophilic state for Ti6Al4V. These findings underscore the substantial impact of surface modifications on additively manufactured dental alloys, potentially influencing their clinical performance. RESEARCH HIGHLIGHTS: Thin film coatings and chemical/heat treatment modify the surface properties of additively manufactured dental alloys. The surfaces of the alloys get rougher and more hydrophilic after alkali-heat treatment. Thin gold coatings exhibit potential adhesion challenges.

Reconstruction of Maxillary Defects Using Virtual Surgical Planning and Additive Manufacturing Technology: A Tertiary Care Centre Experience

Introduction

Maxillary reconstruction is often a challenging task for the surgeons because of the complex anatomy. However, with the advances in virtual surgical planning (VSP) and 3D printing technology there is a new avenue for the surgeons which offers a suitable alternative to conventional flap-based reconstructions.

Patients and Methods

In this article, we have described 4 case scenarios which were managed with the help of VSP and additive manufacturing technology for complex maxillary reconstruction procedures. Use of the technologies aided the clinician in achieving optimal outcomes with regards to form, function and esthetics.

Discussion

Virtual surgical planning (VSP) has gained a lot of impetus in past 1 decade. These aides the surgeon in determining the extent of disease and also carry out the treatment planning. In addition to VSP, the concept of additive manufacturing provides a viable alternative to the conventional reconstruction modalities for maxillary defect rehabilitation. Increased accuracy, rehabilitation of normal anatomical configuration, appropriate dental rehabilitation, decreased intra-operative time and post-operative complications are some of the advantages. In addition, patient-specific implants eliminate the need for a separate donor site. Apart from the treatment of pathologies, they also can be used for reconstruction of post-traumatic defect, where endosteal implant placement is not possible.

Conclusion

These modalities show promising results for reconstruction of complex maxillary defects.

Materials and Applications of 3D Printing Technology in Dentistry: An Overview

PURPOSE

This narrative review aims to provide an overview of the mechanisms of 3D printing, the dental materials relevant to each mechanism, and the possible applications of these materials within different areas of dentistry.

METHODS

Subtopics within 3D printing technology in dentistry were identified and divided among five reviewers. Electronic searches of the Medline (PubMed) database were performed with the following search keywords: 3D printing, digital light processing, stereolithography, digital dentistry, dental materials, and a combination of the keywords. For this review, only studies or review papers investigating 3D printing technology for dental or medical applications were included. Due to the nature of this review, no formal evidence-based quality assessment was performed, and the search was limited to the English language without further restrictions.

RESULTS

A total of 64 articles were included. The significant applications, applied materials, limitations, and future directions of 3D printing technology were reviewed. Subtopics include the chronological evolution of 3D printing technology, the mechanisms of 3D printing technologies along with different printable materials with unique biomechanical properties, and the wide range of applications for 3D printing in dentistry.

CONCLUSIONS

This review article gives an overview of the history and evolution of 3D printing technology, as well as its associated advantages and disadvantages. Current 3D printing technologies include stereolithography, digital light processing, fused deposition modeling, selective laser sintering/melting, photopolymer jetting, powder binder, and 3D laser bioprinting. The main categories of 3D printing materials are polymers, metals, and ceramics. Despite limitations in printing accuracy and quality, 3D printing technology is now able to offer us a wide variety of potential applications in different fields of dentistry, including prosthodontics, implantology, oral and maxillofacial, orthodontics, endodontics, and periodontics. Understanding the existing spectrum of 3D printing applications in dentistry will serve to further expand its use in the dental field. Three-dimensional printing technology has brought about a paradigm shift in the delivery of clinical care in medicine and dentistry. The clinical use of 3D printing has created versatile applications which streamline our digital workflow. Technological advancements have also paved the way for the integration of new dental materials into dentistry.

3D Printing Technologies for Fabrication of Magnetic Materials Based on Metal-Polymer Composites: A Review

Additive manufacturing is a very rapidly developing industrial field. It opens many possibilities for the fast fabrication of complex-shaped products and devices, including functional materials and smart structures. This paper presents an overview of polymer 3D printing technologies currently used to produce magnetic materials and devices based on them. Technologies such as filament-fused modeling (FDM), direct ink writing (DIW), stereolithography (SLA), and binder jetting (BJ) are discussed. Their technological features, such as the optimal concentration of the filler, the shape and size of the filler particles, printing modes, etc., are considered to obtain bulk products with a high degree of detail and with a high level of magnetic properties. The polymer 3D technologies are compared with conventional technologies for manufacturing polymer-bonded magnets and with metal 3D technologies. This paper shows prospective areas of application of 3D polymer technologies for fabricating the magnetic elements of complex shapes, such as shim elements with an optimized shape and topology; advanced transformer cores; sensors; and, in particular, the fabrication of soft robots with a fast response to magnetic stimuli and composites based on smart fillers.

The impact of print orientation on the fracture resistance and failure patterns of additively manufactured cobalt-chromium post and cores

PURPOSE

The aim of this study was to evaluate the impact of the print orientation of direct metal laser sintering (DMLS) posts and cores on the fracture resistance and failure patterns of endodontically treated mandibular premolar teeth.

MATERIALS AND METHODS

Sixty intact human mandibular premolars were endodontically treated. The teeth were then randomly divided into four groups (n = 15). Cobalt-chromium (Co-Cr) metal posts were fabricated by traditional casting (Group C), and DMLS method in 0-, 45-, and 90-degree print orientations (Group DMLS 0, Group DMLS 45, and Group DMLS 90). The posts and cores were cemented with composite resin cement and subjected to compression test at a crosshead speed of 1 mm/min. Data was analyzed by using one-way analysis of variance ANOVA and multiple comparison post hoc Tukey tests (α = 0.05). Specimens were viewed under a stereo microscope with x20 magnification to evaluate the fracture types.

RESULTS

No significant differences were found among the groups tested in terms of fracture resistance (p > 0.05). Group C and Group DMLS 0 group exhibited similar fracture patterns.

CONCLUSIONS

It is possible to produce post and core restorations with the DMLS technique and use them clinically.  Print orientation did not influence the fracture resistance. However, fracture patterns were different. Group C outperformed all DMLS groups in terms of fracture patterns.

Research on the Quality of Partially Removable Skeletal Prostheses Made Using Classical Versus Modern Sintering Techniques

Conventional partially removable skeletal dentures are one of the most common therapeutic solutions offered to edentulous patients worldwide. The present study aims to compare the skeleton of removable dentures realized via classical techniques to that realized via modern techniques, represented by the laser sintering technique, with the comparative aspects being realized through the evaluation of atomic force microscopy (AFM). A total of 20 metal frameworks made of Co-Cr were sectioned, representing the infrastructure of partially removable skeletal dentures, developed using the classical technique versus the laser sintering technique. The infrastructures of partially removable skeletal dentures were designed for both the maxilla and the mandible, with the design of each type of denture being identical, and were developed using both techniques. The roughness values are different depending on the technological method used; for the conventional casting technique, we have higher roughness for the component elements of the partially removable skeletal denture that have more stretch, e.g., the major connector, and for the 3D laser sintering technique, lower roughness is obtained for the component elements that have a lower stretch, e.g., the clasp arms, the minor connector, or the junction between the saddles and the major connector. The clinical implications of the presence of roughness at the level of the active arms or at the level of the connector saddle junction are represented by the risk of fracture, which confers real discomfort to the patient.

The state of additive manufacturing in dental research - A systematic scoping review of 2012-2022

Background/purpose

Additive manufacturing (AM), also known as 3D printing, has the potential to transform the industry. While there have been advancements in using AM for dental restorations, there is still a need for further research to develop functional biomedical and dental materials. It's crucial to understand the current status of AM technology and research trends to advance dental research in this field. The aim of this study is to reveal the current status of international scientific publications in the field of dental research related to AM technologies.

Materials and methods

In this study, a systematic scoping review was conducted using appropriate keywords within the scope of international scientific publishing databases (PubMed and Web of Science). The review included related clinical and laboratory research, including both human and animal studies, case reports, review articles, and questionnaire studies. A total of 187 research studies were evaluated for quantitative synthesis in this review.

Results

The findings highlighted a rising trend in research numbers over the years (From 2012 to 2022). The most publications were produced in 2020 and 2021, with annual percentage increases of 25.7% and 26.2%, respectively. The majority of AM-related publications in dentistry research originate from Korea. The pioneer dental sub-fields with the ost publications in its category are prosthodontics and implantology, respectively.

Conclusion

The final review result clearly stated an expectation for the future that the research in dentistry would concentrate on AM technologies in order to increase the new product and process development in dental materials, tools, implants and new generation modelling strategy related to AM. The results of this work can be used as indicators of trends related to AM research in dentistry and/or as prospects for future publication expectations in this field.

Feasibility study and material selection for powder-bed fusion process in printing of denture clasps

BACKGROUND AND OBJECTIVE

The retention of selective laser melting (SLM)-built denture clasps is inferior to that of cast cobalt-chromium (Co-Cr) clasps engaging 0.01-in undercuts, which are commonly used in clinical practice. Either the clasps engage in excessively deep undercuts or inappropriate printing process parameters are applied. With appropriate undercut engagement and levels of process parameters, the retention of SLM-built clasps (including Co-Cr, commercially pure titanium [CP Ti], and Ti alloy [Ti-6Al-4V] ones) may be comparable to that of cast Co-Cr clasps. Therefore, this feasibility study aimed to evaluate their retention to guide dentists during material selection for the powder-bed fusion process during the printing of denture clasps.

METHODS

We engaged the clasp arm at an appropriate undercut depth (0.01 or 0.02 in), built clasps at the orientation of their longitudinal axes approximately parallel to the build platform, generated square prism support structures at a critical overhang angle of 30°, applied optimized laser parameters (laser power, scan speed, and hatch space), and adopted annealing treatment for Co-Cr, CP Ti, and Ti-6Al-4V clasps. After postprocessing and accuracy measurement, an insertion/removal test of the clasps for 15,000 cycles was performed to simulate 10 years of clinical use, and the retentive force was recorded every 1500 cycles. Permanent deformation of the retentive arms of the clasps was measured. Cast Co-Cr clasps engaging 0.01-in undercuts were designated the control group.

RESULTS

The initial retentive forces of the SLM-built Co-Cr clasps engaging 0.01-in undercuts and CP Ti and Ti-6Al-4V clasps engaging 0.02-in undercuts were comparable to those of the control group. SLM-built Co-Cr clasps engaging 0.01-in undercuts and Ti-6Al-4V clasps engaging 0.02-in undercuts had similar final retentive force and less permanent deformation compared with those of the control group; SLM-built CP Ti clasps engaging 0.02-in undercuts had lower final retentive force and greater permanent deformation.

CONCLUSIONS

Considering the long-term retention and permanent deformation of the retentive arms, Co-Cr and Ti-6Al-4V alloys, except CP Ti, are recommended for printing denture clasps. SLM-built Co-Cr clasps should engage 0.01-in undercuts, and Ti-6Al-4V clasps should engage 0.02-in undercuts.

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.

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.

A Comparative Study of Additive and Subtractive Manufacturing Techniques for a Zirconia Dental Product: An Analysis of the Manufacturing Accuracy and the Bond Strength of Porcelain to Zirconia

This study was aimed at preparing zirconia samples via additive manufacturing (AM) and subtractive manufacturing (SM) and testing the following aspects: (1) the manufacturing accuracy of the zirconia samples and (2) the bond strength of porcelain to zirconia to evaluate the applicability of the zirconia fabricated by AM in dental clinics. We used three milling machines for SM (AR, K5, and UP) and a 3D printer for AM (AO). The manufacturing accuracy of the zirconia specimen in the internal and marginal areas was evaluated by superimposing techniques to calculate the root mean square (RMS) values. The bond strengths of porcelain to zirconia prepared via SM and AM were measured using a universal testing machine. The internal and marginal RMS values of the zirconia prepared by AM (AO) were within the range of those of the zirconia prepared by SM (AR, K5, and UP). Moreover, the bond strength value of the zirconia prepared by AM (35.12 ± 4.09 MPa) was significantly higher than that of the zirconia prepared by SM (30.26 ± 5.20 MPa). Therefore, AM technology has significant potential for applications in dentistry.

A comparison of trueness and precision of 12 3D printers used in dentistry

Introduction

Judging the dimensional accuracy of the resulting printed part requires comparison and conformity between the 3D printed model and its virtual counterpart. The resolution and accuracy of 3D model samples are determined by a wide array of factors depending on the technology used and related factors such as the print head/laser spot size/screen resolution, build orientation, materials, geometric features, and their topology.

Aims

The aim of this manuscript is to present a literature review on 12 3D printers, namely the Ackuretta Sol, Anycubic Photon and Photon S, Asiga Max UV, Elegoo Mars, Envisiontec Vida HD, Envisiontec One, Envisiontec D4K Pro, Formlabs Form 2 and Form 3, Nextdent 5100, and Planmeca Creo, studying the accuracy of these printers that are of a wide variety of budgets.

Design

The present study involves some of the recently released 3D printers that have not yet been studied for their accuracy. Since these new printers will replace current models that may have been included in the previous studies in the literature, it is important to study whether they are statistically more or less accurate and to discuss whether these results are clinically relevant. For the purposes of this study, the use of a standardised printable object was used to measure the accuracy of these recent 3D printers.

Materials and methods

In total, 12 3D printers produced test blocks. All test blocks were printed using the same settings with 100 micron Z layer thickness and the print time set to standard where applicable. To measure the resulting blocks a digital measurement was taken using a Dentsply Sirona Ineos X5 lab scanner to measure the XYZ dimensions of each block produced on each printer using CloudCompare to measure the deviation compared to the Master STL. Each measurement was taken from the central axis of that dimension.

Results

When grouped into homogenous subsets, the cheapest 3D printers in the group, namely the Anycubic printers and the Elegoo Mars, are statistically not dissimilar to the higher priced Asiga Max UV or even the mid-priced Formlabs printers in the X and Z dimensions. However, the Envisiontec One and D4K Pro, Ackuretta Sol and Asiga Max UV were statistically superior in terms of consistently accurate Y dimension. Although these printers use different technologies to print, no specific type of printer technology is more accurate than the others.

Discussion

The null hypothesis was proved to be true, in that no significant differences were found among the various technologies of 3D printing regarding trueness and precision. The evolution of 3D printers that leads to budget printers being as statistically accurate, for at least two of the dimensions of data recorded, as expensive printers is remarkable. Whilst clear differences in the mean error between the printers were found, the performance of these printers is considered exceptional. Albeit, the Envision One, Envision D4K, Ackuretta Sol and Asiga Max UV printers performed the best with overall trueness under 35 μm.

Conclusion

This study shows that the current range of 3D printers can produce clinically acceptable levels of accuracy. The present study also shows that there is no statistical difference in the results of budget printers and more expensive printers for the X and Z dimensions but this was not the case for the measurements in the Y dimension. This study confirms that all of the 3D printers can produce a reliable, reproducible model.

3D Printing: An Emerging Technology for Biocatalyst Immobilization

Employment of enzymes as biocatalysts offers immense benefits across diverse sectors in the context of green chemistry, biodegradability, and sustainability. When compared to free enzymes in solution, enzyme immobilization proposes an effective means of improving functional efficiency and operational stability. The advance of printable and functional materials utilized in additive manufacturing, coupled with the capability to produce bespoke geometries, has sparked great interest towards the 3D printing of immobilized enzymes. Printable biocatalysts represent a new generation of enzyme immobilization in a more customizable and adaptable manner, unleashing their potential functionalities for countless applications in industrial biotechnology. This review provides an overview of enzyme immobilization techniques and 3D printing technologies, followed by illustrations of the latest 3D printed enzyme-immobilized industrial and clinical applications. The unique advantages of harnessing 3D printing as an enzyme immobilization technique will be presented, alongside a discussion on its potential limitations. Finally, the future perspectives of integrating 3D printing with enzyme immobilization will be considered, highlighting the endless possibilities that are achievable in both research and industry. This article is protected by copyright. All rights reserved.

Additively Manufactured Surgical Implant Guides: A Review

Static computer assisted implant surgery (s-CAIS) is an integral part of the digital workflow in implant dentistry and provides the link between the virtual planning environment and surgical field. The accuracy of s-CAIS is influenced by many cumulative factors including the fit of the template which is related to the manufacturing process. This critical review provides an overview of the current research on additively manufactured surgical implant guides.

Advances in powder bed fusion 3D printing in drug delivery and healthcare

Powder bed fusion (PBF) is a 3D printing method that selectively consolidates powders into 3D objects using a power source. PBF has various derivatives; selective laser sintering/melting, direct metal laser sintering, electron beam melting and multi-jet fusion. These technologies provide a multitude of benefits that make them well suited for the fabrication of bespoke drug-laden formulations, devices and implants. This includes their superior printing resolution and speed, and ability to produce objects without the need for secondary supports, enabling them to precisely create complex products. Herein, this review article outlines the unique applications of PBF 3D printing, including the main principles underpinning its technologies and highlighting their novel pharmaceutical and biomedical applications. The challenges and shortcomings are also considered, emphasising on their effects on the 3D printed products, whilst providing a forward-thinking view.

Thin Films Deposition of Ta2O5 and ZnO by E-Gun Technology on Co-Cr Alloy Manufactured by Direct Metal Laser Sintering

In recent years in the dental field, new types of materials and techniques for the manufacturing of dental crowns and analog implants have been developed to improve the quality of these products. The objective of this article was to perform the surface characterization and determine the properties of Co-Cr alloy samples fabricated by the direct metal laser sintering (DMLS) process and coated by e-gun technology with thin films of Ta₂O₅ and ZnO. Both oxides are frequently used for dental products, in pharmacology, cosmetics, and medicine, due to their good anticorrosive, antibacterial, and photo-catalytic properties. Following the deposition of thin oxide films on the Co-Cr samples fabricated by DMLS, a very fine roughness in the order of nanometers was obtained. Thin films deposition was realized to improve the hardness and the roughness of the Co-Cr parts fabricated by the DMLS process. Surface characterization was performed using SEM-EDS, AFM, and XRD. AFM was used to determine the roughness of the samples and the nanoindentation curves were determined to establish the hardness values and modulus of elasticity.

Mechanical Properties and Corrosion Resistance of TiAl6V4 Alloy Produced with SLM Technique and Used for Customized Mesh in Bone Augmentations

Bone augmentation procedures represent a real clinical challenge. One option is the use of titanium meshes. Additive manufacturing techniques can provide custom-made devices in titanium alloy. The purpose of this study was to investigate the material used, which can influence the outcomes of the bone augmentation procedure. Specific test samples were obtained from two different manufacturers with two different shapes: surfaces without perforations and with calibrated perforations. Three-point bending tests were run as well as internal friction tests to verify the Young’s modulus. Test samples were placed in two different buffered solutions and analyzed with optical microscopy. A further SEM analysis was done to observe any microstructural modification. Three-point flexural tests were conducted on 12 specimens. Initial bending was observed at lower applied stresses for the perforated samples (503 MPa) compared to non-perforated ones (900 MPa); the ultimate flexural strength was registered at 513 MPa and 1145 MPa for perforated and non-perforated samples, respectively. Both microscopic analyses (optical and SEM) showed no significant alterations. Conclusions: A normal masticatory load cannot modify the device. Chemical action in the case of exposure does not create macroscopic and microscopic alterations of the surface.

Mechanical Properties of Dental Alloys According to Manufacturing Process

The purpose of this study is to investigate the effect of the fabrication method of dental prosthesis on the mechanical properties. Casting was produced using the lost wax casting method, and milling was designed using a CAD/CAM program. The 3D printing method used the SLS technique to create a three-dimensional structure by sintering metal powder with a laser. When making the specimen, the specimen was oriented at 0, 30, 60, and 90 degrees. All test specimens complied with the requirements of the international standard ISO 22674 for dental alloys. Tensile strength was measured for yield strength, modulus of elasticity and elongation by applying a load until fracture of the specimen at a crosshead speed of 1.5 ± 0.5 mm/min (n = 6, modulus of elasticity n = 3). After the tensile test, the cross section of the fractured specimen was observed with a scanning electron microscope, and the statistics of the data were analyzed with a statistical program SPSS (IBM Corp. Released 2020. IBM SPSS Statistics for Windows, Version 27.0. Armonk, NY, USA: IBM Corp.) and using Anova and multiple comparison post-tests (scheffe method). The yield strength was the highest at 1042 MPa at an angle of 0 degrees in the specimen produced by 3D printing method, and the elongation was the highest at 14% at an angle of 90 degrees in the specimen produced by 3D printing method. The modulus of elasticity was the highest at 235 GPa in the milled specimen. In particular, the 3D printing group showed a difference in yield strength and elongation according to the build direction. The introduction of various advanced technologies and digital equipment is expected to bring high prospects for the growth of the dental market.

Effect of ceramic layering on the fit of cobalt-chromium alloy 3-unit fixed dental prostheses fabricated by additive, soft milling, and casting technologies

STATEMENT OF PROBLEM

The change in fit after ceramic layering of additively manufactured cobalt-chromium alloy frameworks has not been evaluated extensively.

PURPOSE

The purpose of this in vitro study was to compare the fit of cobalt-chromium alloy fixed dental prostheses fabricated by different techniques before and after ceramic layering.

MATERIAL AND METHODS

A cobalt-chromium alloy master model was prepared to receive a 3-unit fixed dental prosthesis. Sixty cobalt-chromium alloy frameworks (N=60) were manufactured by using 3 manufacturing techniques (n=20): selective laser melting (Mediloy S-Co), soft milling (Ceramill Sintron), and conventional casting as the control group (Girobond NB). The replica technique was used to measure the marginal and internal discrepancies. The frameworks were then layered with ceramic, and the same fit measuring procedure was repeated. The results were compared before and after ceramic layering within each group. The data were analyzed using the Levene, ANOVA, and paired-samples t tests (α=.05).

RESULTS

A significant difference was found within groups before and after ceramic layering for selective laser melting (P=.006) and soft milling (P=.009) but not for conventional casting (P>.05). No statistical difference was reported in the marginal region for conventional casting group (P=.155) in contrast with the soft milling and selective laser melting groups (P=.003). Soft milling showed increased gap values in the marginal (P=.006) and occlusal regions (P=.004).

CONCLUSIONS

Ceramic layering increased the discrepancy of the laser-sintered and milled frameworks, increasing the marginal discrepancy.

Effect of Fabrication Technique on the Microgap of CAD/CAM Cobalt-Chrome and Zirconia Abutments on a Conical Connection Implant: An In Vitro Study

The aim of this in vitro study was to investigate the microgaps at the implant-abutment interface when zirconia (Zr) and CAD/CAM or cast Co-Cr abutments were used.

METHODS

Sixty-four conical connection implants and their abutments were divided into four groups (Co-Cr (milled, laser-sintered and castable) and Zirconia (milled)). After chewing simulation (300,000 cycles, under 200 N loads at 2 Hz at a 30° angle) and thermocycling (10,000 cycles, 5 to 50 °C, dwelling time 55 s), the implant-abutment microgap was measured 14 times at each of the four anatomical aspects on each specimen by using a scanning electron microscope (SEM). Kruskal-Wallis and pair-wise comparison were used to analyze the data (α = 0.05).

RESULTS

The SEM analysis revealed smaller microgaps with Co-Cr milled abutments (0.69-8.39 μm) followed by Zr abutments (0.12-6.57 μm), Co-Cr sintered (7.31-25.7 μm) and cast Co-Cr (1.68-85.97 μm). Statistically significant differences were found between milled and cast Co-Cr, milled and laser-sintered Co-Cr, and between Zr and cast and laser-sintered Co-Cr (p < 0.05).

CONCLUSIONS

The material and the abutment fabrication technique affected the implant-abutment microgap magnitude. The Zr and the milled Co-Cr presented smaller microgaps. Although the CAD/CAM abutments presented the most favorable values, all tested groups had microgaps within a range of 10 to 150 μm.

3D printing parameters, supporting structures, slicing, and post-processing procedures of vat-polymerization additive manufacturing technologies: A narrative review

OBJECTIVE

To review the elements of the vat-polymerization workflow, including the 3D printing parameters, support structures, slicing, and post-processing procedures, as well as how these elements affect the characteristics of the manufactured dental devices.

DATA

Collection of published articles related to vat-polymerization technologies including manufacturing workflow description, and printing parameters definition and evaluation of its influence on the mechanical properties of vat-polymerized dental devices was performed.

SOURCES

Three search engines were selected namely Medline/PubMed, EBSCO, and Cochrane. A manual search was also conducted.

STUDY SELECTION

The selection of the optimal printing and supporting parameters, slicing, and post-processing procedures based on dental application is in continuous improvement. As well as their influence on the characteristics of the additively manufactured (AM) devices such as surface roughness, printing accuracy, and mechanical properties of the dental device.

RESULTS

The accuracy and properties of the AM dental devices are influenced by the technology, printer, and material selected. The printing parameters, printing structures, slicing methods, and the post-processing techniques significantly influence on the surface roughness, printing accuracy, and mechanical properties of the manufactured dental device; yet, the optimization of each one may vary depending on the clinical application of the additively manufactured device.

CONCLUSIONS

The printing parameters, supporting structures, slicing, and post-processing procedures have been identified, but additional studies are needed to establish the optimal manufacturing protocol and enhance the properties of the AM polymer dental devices.

CLINICAL SIGNIFICANCE

The understanding of the factors involved in the additive manufacturing workflow leads to a printing success and better outcome of the additively manufactured dental device.

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.

The Concept of Sustainable Development of Modern Dentistry

This paper concerns the assessment of the current state of dentistry in the world and the prospects of its sustainable development. A traditional Chinese censer was adopted as the pattern, with a strong and stable support on three legs. The dominant diseases of the oral cavity are caries and periodontal diseases, with the inevitable consequence of toothlessness. From the caries 3.5–5 billion people suffer. Moreover, each of these diseases has a wide influence on the development of systemic complications. The territorial range of these diseases and their significant differentiation in severity in different countries and their impact on disability-adjusted life years index are presented (DALY). Edentulousness has a significant impact on the oral health-related quality of life (OHRQoL). The etiology of these diseases is presented, as well as the preventive and therapeutic strategies undertaken as a result of modifying the Deming circle through the fives’ rules idea. The state of development of Dentistry 4.0 is an element of the current stage of the industrial revolution Industry 4.0 and the great achievements of modern dental engineering. Dental treatment examples from the authors’ own clinical practice are given. The systemic safety of a huge number of dentists in the world is discussed, in place of the passive strategy of using more and more advanced personal protective equipment (PPE), introducing our own strategy for the active prevention of the spread of pathogenic microorganisms, including SARS-CoV-2. The ethical aspects of dentists’ activity towards their own patients and the ethical obligations of the dentist community towards society are discussed in detail. This paper is a polemic arguing against the view presented by a group of eminent specialists in the middle of last year in The Lancet. It is impossible to disagree with these views when it comes to waiting for egalitarianism in dental care, increasing the scope of prevention and eliminating discrimination in this area on the basis of scarcity and poverty. The views on the discrimination of dentistry in relation to other branches of medicine are far more debatable. Therefore, relevant world statistics for other branches of medicine are presented. The authors of this paper do not agree with the thesis that interventional dental treatment can be replaced with properly implemented prophylaxis. The final remarks, therefore, present a discussion of the prospects for the development of dentistry based on three pillars, analogous to the traditional Chinese censer obtaining a stable balance thanks to its three legs. The Dentistry Sustainable Development (DSD) > 2020 model, consisting of Global Dental Prevention (GDP), Advanced Interventionist Dentistry 4.0 (AID 4.0), and Dentistry Safety System (DSS), is presented.

Challenges of Co-Cr Alloy Additive Manufacturing Methods in Dentistry-The Current State of Knowledge (Systematic Review)

Complex dental components which are individually tailored to the patient can be obtained due to new additive manufacturing technology. This paper reviews the metallic powders used in dental applications, the fabrication process (build orientation, process parameters) and post-processing processes (stress relieving, surface finishing). A review of the literature was performed using PubMed, ScienceDirect, Mendeley and Google Scholar. Over eighty articles were selected based on relevance to this review. This paper attempts to include the latest research from 2010 until 2020, however, older manuscripts (10 articles) were also selected. Over 1200 records were identified through the search; these were screened for title and/or summary. Over eighty articles were selected based on relevance to this review. In order to obtain a product which can be used in clinical applications, the appropriate manufacturing parameters should be selected. A discussion was made on optimal selective laser melting (SLM) parameters in dentistry. In addition, this paper includes a critical review of applied thermal treatment methods for Co-Cr alloys used in dentistry.

Chemical composition, surface roughness, and ceramic bond strength of additively manufactured cobalt-chromium dental alloys

STATEMENT OF PROBLEM

Selective laser melting (SLM) additive manufacturing (AM) technology is a current option to fabricate cobalt-chromium (Co-Cr) metal frameworks for dental prostheses. However, the Co-Cr alloy composition, surface roughness, and ceramic bond strength values that SLM metals can obtain are not well-defined.

PURPOSE

The purpose of this in vitro study was to compare the chemical composition, surface roughness, and ceramic shear bond strength of the milled and SLM Co-Cr dental alloys.

MATERIAL AND METHODS

A total of 50 disks of 5 mm in diameter and 1 mm in thickness were fabricated by using subtractive (control group) and AM with each of following SLM providers: SLM-1 (EOS), SLM-2 (3D systems), and SLM-3 (Concept Laser). The milled disks were airborne-particle abraded with 100-μm aluminum oxide particles. All the specimens were cleaned before surface roughness (Ra), weight (Wt%), and atomic (At%) percentages were analyzed. Three-dimensional profilometry was used to analyze the topographical properties of the surface parameters Ra (mean surface roughness). The chemical composition of Co-Cr alloy specimens was determined by using energy dispersive X-ray (EDAX) elemental analysis in a scanning electron microscope (SEM). Thereafter, the specimens were bonded to a ceramic (Dentine A3 and Enamel S-59; Creation CC) interface. Specimens were stored for 24 hours at 23 °C. The bond strength of the SLM-ceramic interface was measured by using the macroshear test (SBT) method (n=10). Adhesion tests were performed in a universal testing machine (1 mm/min). The Shapiro-Wilk test revealed that the chemical composition data were not normally distributed. Therefore, the atomic (At%) and weight percentages (Wt%) were analyzed by using the Kruskal-Wallis test, followed by pairwise Mann-Whitney U tests between the control and AM groups (AM-1 to AM-4). However, the Shapiro-Wilk test revealed that the surface roughness (Ra) and ceramic bond strength data were normally distributed. Therefore, data were analyzed by using 1-way ANOVA, followed by the post hoc Sidak test (α=.05).

RESULTS

Significant differences were obtained in Wt%, At%, and Ra values among the Co-Cr alloys evaluated (P<.05). Furthermore, the control group revealed significantly lower mean ±standard deviation Ra values (0.79 ±0.11 μm), followed by AM-3 (1.57 ±0.15 μm), AM-2 (1.80 ±0.43 μm), AM-1 (2.43 ±0.34 μm), and AM-4 (2.84 ±0.27 μm). However, no significant differences were obtained in the metal-ceramic shear bond strength among the different groups evaluated, ranging from mean ±standard deviation 75.77 ±11.92 MPa to 83.65 ±12.21 MPa.

CONCLUSIONS

Co-Cr dental alloys demonstrated a significant difference in their chemical compositions. Subtractive and additive manufacturing procedures demonstrated a significant influence on the surface roughness of the Co-Cr alloy specimens. However, the metal-ceramic shear bond strength of Co-Cr alloys was found to be independent of the manufacturing process.

The potential of additive manufacturing technologies and their processing parameters for the fabrication of all-ceramic crowns: A review

OBJECTIVE

This article aims to provide a review of the additive manufacturing technologies and the processing parameters that have been investigated for the fabrication of all ceramic crowns.

OVERVIEW

Additive manufacturing has crept its way into the field of dentistry for the fabrication of resin and metal prosthesis. To evaluate the current status of additive manufacturing for the fabrication of all ceramic crowns, literature review was targeted to include publications pertaining to the fabrication of dental ceramics and all ceramic crowns. With respect to the additive manufacturing of dental ceramics, five technologies have been investigated to date: stereolithography, material extrusion, powder based fusion, direct inkjet printing, and binder jetting. The processing parameters and experimental outcomes were collated and described for each of the aforementioned technologies.

CONCLUSION

Additive manufacturing has demonstrated promising experimental outcomes and corroborated to the fabrication all ceramic crowns. However, the technology is yet to witness a commercial breakthrough within this domain.

CLINICAL SIGNIFICANCE

Additive manufacturing mitigates raw material wastage and tooling stresses that are associated with milling of ceramics. Continued research and development can lead to its approbation as an alternate technology for manufacturing all ceramic restorations.

An update on applications of 3D printing technologies used for processing polymers used in implant dentistry

Polymer additive manufacturing (AM) technologies have been incorporated in digital workflows within implant dentistry. This article reviews the main polymer AM technologies in implant dentistry, as well as their applications in the field such as manufacturing surgical guides, custom trays, working implant casts, and provisional restorations.

In Situ Controlled Surface Microstructure of 3D Printed Ti Alloy to Promote Its Osteointegration

It is well known that three-dimensional (3D) printing is an emerging technology used to produce customized implants and surface characteristics of implants, strongly deciding their osseointegration ability. In this study, Ti alloy microspheres were printed under selected rational printing parameters in order to tailor the surface micro-characteristics of the printed implants during additive manufacturing by an in situ, controlled way. The laser path and hatching space were responsible for the appearance of the stripy structure (S), while the bulbous structure (B) and bulbous⁻stripy composite surface (BS) were determined by contour scanning. A nano-sized structure could be superposed by hydrothermal treatment. The cytocompatibility was evaluated by culturing Mouse calvaria-derived preosteoblastic cells (MC3T3-E1). The results showed that three typical microstructured surfaces, S, B, and BS, could be achieved by varying the 3D printing parameters. Moreover, the osteogenic differentiation potential of the S, B, and BS surfaces could be significantly enhanced, and the addition of nano-sized structures could be further improved. The BS surface with nano-sized structure demonstrated the optimum osteogenic differentiation potential. The present research demonstrated an in situ, controlled way to tailor and optimize the surface structures in micro-size during the 3D printing process for an implant with higher osseointegration ability.