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

Controlling Cellular Behavior by Surface Design of Titanium-based Biomaterials

BACKGROUND/AIM

Titanium alloys, especially Ti6Al4V, are widely used in orthopedic and dental implants. Additive manufacturing has emerged as an innovative fabrication technique for titanium implants, gradually replacing traditional machining methods. A notable feature of additively manufactured medical devices is their considerable surface heterogeneity and roughness. Coating these materials to achieve physical and chemical uniformity is essential for enhancing biocompatibility. This study evaluates the combined effect of surface roughness (ranging from sub-micrometer to micrometer scale) and three nanometer-thick polyelectrolyte multilayer coatings on protein adsorption, as well as the adhesion and proliferation of normal human osteoblasts.

MATERIALS AND METHODS

The adhesion of human osteoblasts to various substrates (either uncoated or coated) was quantified using a lactate dehydrogenase assay and scanning electron microscopy. The surface density of adsorbed human serum albumin was analyzed by the Bradford assay.

RESULTS

Application of polyelectrolyte multilayer coatings significantly increased the hydrophilicity of titanium substrates without altering their sub-micrometer and micrometer roughness or topography. The coatings rich in reactive amino groups were found to enhance the adsorption of human serum albumin and promote the adhesion of osteoblasts.

CONCLUSION

The chemical composition of the surface, particularly the presence of free primary amino groups, significantly affects cellular behavior in machined, sand-blasted, and additively manufactured titanium materials, while the impact of surface roughness appears secondary. No correlation was observed between surface hydrophilicity and protein adsorption or cell attachment.

Current Trends and Innovations in Oral and Maxillofacial Reconstruction

This review examines the latest advancements in maxillofacial reconstruction, focusing on transformative innovations in dentistry. Traditional surgical techniques, although effective, are accompanied by challenges such as inherent risks, complications, and inconsistent outcomes that can be influenced by variations in surgeon skill. To address these drawbacks, cutting-edge technologies have emerged, emphasizing enhanced precision, safety, and efficiency in treatment modalities. Key innovations in this field include 3-dimensional printing (additive manufacturing), virtual surgical planning, computer-aided design/computer-aided manufacturing (CAD/CAM) technology, and tissue engineering. These advancements not only revolutionize diagnostics but also streamline workflow processes, offering sustainable, timely treatments while improving therapeutic results and aesthetic outcomes. The integration of CAD/CAM technology enhances workflow efficiency by simplifying complex processes in dental prosthetic design. Simultaneously, additive manufacturing facilitates the creation of intricate dental implants with superior accuracy. Virtual surgical planning provides clinicians with valuable preoperative insights, enabling tailored surgical interventions, while tissue engineering presents regenerative solutions to complex reconstructive challenges. Despite these technological breakthroughs, the adoption of these innovations requires significant initial investments and extensive training for healthcare professionals. While logistical and financial obstacles can arise, the long-term benefits, such as enhanced patient care and superior aesthetic results, are considerable. In conclusion, this article aims to evaluate the transformative impact of digital and additive manufacturing technologies on maxillofacial reconstruction and to underscore their crucial role in advancing modern dentistry.

Compression and bending performance of selective laser melted Ti6Al4V porous structures with cylindrical thin walls for dental implants

Titanium alloy dental implants play a crucial role in the field of oral rehabilitation. However, the use of solid designs can give rise to mechanical problems such as mismatched compressive elastic modulus with the host bone tissue, resulting in stress shielding and stress concentration. These problems have been a persistent bottleneck in their application effectiveness. To overcome this challenge, this study creatively designed five types of porous structures with cylindrical thin wall based on the Gibson-Ashby theoretical model. The aim is to optimize the mechanical performance of dental implants, enhance their compatibility with the host bone tissue, and utilize selective laser melting technology for precise fabrication of porous structures using Ti6Al4V material. Through a combination of simulation analysis and compression experiments, the stress and strain distributions of the five structures are systematically investigated under different bite conditions. The experimental results demonstrate that all five porous structures designed in this study effectively alleviate stress shielding phenomenon in dental implants, significantly improving the bonding performance between the implants and bone tissue. This meets the clinical implantation requirements and provides strong theoretical support for the application of dental implants in clinical settings.

Conventional vs. 3D printed band and loop space maintainers: a fracture strength analysis

Premature loss of primary teeth is a common occurrence in pediatric dentistry and often necessitates the use of space maintainers to prevent complications. Traditional space maintainers, such as band and loop space maintainers (BLSM), have been widely used, but are fabricated using conventional methods. With advancements in technology, three-dimensional (3D) printing has emerged as a promising alternative for fabricating dental appliances including space maintainers. This study aimed to evaluate and compare the fracture strengths of conventional band and loop space maintainers (C-BLSMs) fabricated using stainless steel with that of 3D printed BLSMs manufactured using additive manufacturing techniques. Fifteen C-BLSM and fifteen 3D printed BLSMs were fabricated and subjected to fracture-strength testing using a universal testing machine. The maximum occlusal bite force in the mixed dentition was determined based on established literature. Statistical analysis was performed to compare the mean fracture resistance between the two groups. The mean fracture resistance of the 3D printed BLSMs was significantly higher (308.53 N) than that of C-BLSMs (130.85 N). This difference was statistically significant (p < 0.05), highlighting the superior mechanical properties of 3D printed BLSMs. Three-dimensional printing technology offers significant advantages in terms of fracture strength compared with conventional fabrication methods for BLSMs.

A Critical Systematic Scoping Review on the Applications of Additive Manufacturing (AM) in the Marine Industry

(1) Background: Additive manufacturing (AM), which has also become known as 3D printing, is rapidly expanding its areas of use in the marine industry. This study undertakes a historical development of AM in the marine industry. The study also criticises these developments to date and the future technological applications they will lead to, while considering the benefits for the industry and its segments. (2) Methods: This review followed the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and was registered in the Open Science Framework. The personalized search strategy was applied to Scopus, and Web of Science databases. The core emphasis was placed on two eligibility criteria throughout the evaluation process. Firstly, Criteria 1 sought to determine the paper's relevance to AM. Secondly, Criteria 2 aimed to assess whether the paper delves into the implementation of AM or provides valuable insights into its utilisation within the marine industry. The risk of bias was analysed using a checklist of important parameters to be considered. (3) Results: In recent years, there has been a growing trend in studies related to the application of AM in the marine industry. While AM is widespread in industries such as automotive, aviation, and healthcare, it is relatively new for the marine industry. Almost only 5% of publications related to AM are related to the marine industry. There is a need for extensive research in many areas. It has been observed that classification societies and approval institutions, which largely drive the marine industry, have not yet taken AM into consideration sufficiently. (4) Conclusions: The studies show that AM is very promising for the marine industry. However, there are new studies at the experimental and theoretical level that need to be carried out to determine the right materials and AM methods to establish the quality control methodology and the necessary classification rules. This review also emphazises AM's pivotal role in reshaping the marine industry, addressing the potential environmental and occupational safety effects of AM.

Three-Dimensionally-Printed Polymer and Composite Materials for Dental Applications with Focus on Orthodontics

Three-dimensional printing has transformed dentistry by enabling the production of customized dental restorations, aligners, surgical guides, and implants. A variety of polymers and composites are used, each with distinct properties. This review explores materials used in 3D printing for dental applications, focusing on trends identified through a literature search in PubMed, Scopus, and the Web of Science. The most studied areas include 3D-printed crowns, bridges, removable prostheses, surgical guides, and aligners. The development of new materials is still ongoing and also holds great promise in terms of environmentally friendly technologies. Modern manufacturing technologies have a promising future in all areas of dentistry: prosthetics, periodontology, dental and oral surgery, implantology, orthodontics, and regenerative dentistry. However, further studies are needed to safely introduce the latest materials, such as nanodiamond-reinforced PMMA, PLA reinforced with nanohydroxyapatite or magnesium, PLGA composites with tricalcium phosphate and magnesium, and PEEK reinforced with hydroxyapatite or titanium into clinical practice.

Trueness of the apical and middle root portion segments of 3D-printed removable die and alveolar cast designs manufactured using stereolithographic 3D printing

PURPOSE

The present study evaluated the effects of the root portion design, segment (middle vs. apical), and part (die vs. cast) on the trueness of three-dimensional (3D)-printed removable die-cast complex.

MATERIAL AND METHODS

The trueness of apical and middle segments of the root portion of 45 3D-printed removable dies and casts with three different root portion designs (n = 15) was assessed using a metrology-grade computer program. The three removable dies and cast designs (root form [RF], conical [CON], and cylindric [CYL]) were created using professional computer-aided manufacturing computer programs (DentalCAD 3.1 Rijeka, and InLab CAD 22.0), and manufactured using stereolithographic 3D printer (Form3; FormLabs, Somerville, MA). Subsequently, the 3D-printed removable dies and casts were scanned by a single operator with an intraoral scanner (PrimeScan; Dentsply Sirona, Charlotte, NC), and their respective standard tessellation language files were aligned and compared to master reference files in a metrology-grade computer program (Geomagic Control X; 3D systems, Rock Hill, NC). The root mean square (RMS) values of the middle and apical segments for each removable die and cast were calculated and analyzed using a mixed model including a repeated measure 3-way analysis of variance (ANOVA) and post-hoc stepdown Bonferroni-corrected pairwise comparisons (α = 0.05).

RESULTS

A statistically significant 3-way interaction between factors was detected, suggesting that the part (removable die or alveolar cast) and their design affected the RMS values of their apical and middle root portion segment. (p = 0.045). The post-hoc analysis identified significant differences between RMS values of the apical segments of the CON and CYL removable dies (p = 0.005). Significant differences were observed between the middle and apical segments of the CON (p < 0.001) and RF removable die designs (p = 0.004). No statistically significant differences were noticed between the RMS of the different alveolar cast designs (p > 0.05). Significant differences were detected between the apical and middle segments of the same alveolar cast design (p < 0.05).

CONCLUSIONS

For the manufacturing trinomial and 3D printing strategy used in the present study, the interaction of the part, design, and segment affected the trueness of removable dies and alveolar casts. The trueness was higher on the middle segment on removable dies and alveolar casts in all designs used, except for CYL removable dies, where the trueness difference between segments was small. Higher trueness values may be achieved with designs with simple apical segment geometries.

Evaluation of stress distribution on an endodontically treated maxillary central tooth with lesion restored with different crown materials: A finite element analysis

Objectives

The biomechanical response of teeth with periapical lesions that have been restored using various substructure materials, as well as the stress mapping in the alveolar bone, has not been thoroughly described. In this context, the objective of this study is to investigate the structural stress distributions on root canal-treated maxillary right central incisors with lesions restored using different crown materials under linear static loading conditions through finite element analysis (FEA).

Methods

In the study, five FEA models were utilised to represent healthy teeth and teeth restored with different substructure materials: (A) a healthy tooth, (B) a lesioned, root canal-treated, composite-filled tooth, (C) a lesioned, fiber-posted, zirconia-based crown, (D) a tooth with lesions, a fiber post, and Ni-Cr infrastructure crown, (E) a tooth with a lesion, a fiber post, and an IPS E-max infrastructure crown. A force of 100 N was applied at an angle of 45° to the long axis of the tooth from 2 mm cervical to the incisal line on the palatal surface. Deformation behaviour and maximum equivalent stress distributions on the tooth sub-components, including the bony structure for each model, were simulated.

Results

Differences were observed in the stress distributions of the models. The maximum stress values of the models representing the restorations with different infrastructures varied, and the highest value was obtained in the model of the E-max crown (Model E: 136.050 MPa). The minimum stress magnitudes were obtained from Model B the composite-filled tooth (80.39 MPa); however, it was observed that the equivalent stresses in all the models showed a similar distribution for all components with varying magnitudes. In periapical lesion areas, low stresses were observed. In all models, the cervicobuccal collar region of the teeth had dense equivalent stresses.

Conclusion

Different restorative treatment methods applied to root canal-treated teeth with periapical lesions can impact the stress in the alveolar bone and the biomechanical response of the tooth. Relatively high stress values in the cortical bone at the cervical line of the tooth have been observed to decrease towards the apical region. This observation may suggest a potential healing effect by reducing pressure in the periapical lesion area.

Clinical significance

Composite resin restorations can be considered the first-choice treatment option for the restoration of root canal-treated teeth with lesions. In crown restorations, it would be advantageous to prefer zirconia or metal-supported prostheses in terms of biomechanics.

Biomaterials Adapted to Vat Photopolymerization in 3D Printing: Characteristics and Medical Applications

Along with the rapid and extensive advancements in the 3D printing field, a diverse range of uses for 3D printing have appeared in the spectrum of medical applications. Vat photopolymerization (VPP) stands out as one of the most extensively researched methods of 3D printing, with its main advantages being a high printing speed and the ability to produce high-resolution structures. A major challenge in using VPP 3D-printed materials in medicine is the general incompatibility of standard VPP resin mixtures with the requirements of biocompatibility and biofunctionality. Instead of developing completely new materials, an alternate approach to solving this problem involves adapting existing biomaterials. These materials are incompatible with VPP 3D printing in their pure form but can be adapted to the VPP chemistry and general process through the use of innovative mixtures and the addition of specific pre- and post-printing steps. This review's primary objective is to highlight biofunctional and biocompatible materials that have been adapted to VPP. We present and compare the suitability of these adapted materials to different medical applications and propose other biomaterials that could be further adapted to the VPP 3D printing process in order to fulfill patient-specific medical requirements.

The Utility of 3D Printing for Surgical Planning and Patient-Specific Implant Design in Maxillofacial Surgery: A Narrative Review

Maxillofacial reconstructive implants are typically created in standard shapes and have a widespread application in head and neck surgery. During surgical procedures, the implant must be correctly bent according to the architecture of the particular bones. Bending takes practice, especially for untrained surgeons. Furthermore, repeated bending may increase internal stress, resulting in fatigue in vivo under masticatory loading and an array of consequences, including implant failure. There is a risk of fracture, screw loosening, and bone resorption. Resorption, infection, and displacement are usually associated with the use of premade alloplastic implants and autogenous grafts. Recent technological breakthroughs have led to the use of patient-specific implants (PSIs) developed by computer-designed additive manufacturing in reconstructive surgery. The use of computer-designed three-dimensional (3D)-printed PSI allows for more precise restoration of maxillofacial deformities, avoiding the common difficulties associated with premade implants and increasing patient satisfaction. Additive manufacturing is something that refers to a group of additive manufacturing methods. This technique has been quickly used in a variety of surgical procedures. The exponential expansion of this technology can be attributed to its enormous surgical value. Adding 3D printing to a medical practice can be a rewarding experience with stunning results.