Conventional 3D Printing Research Articles

Assessing cytotoxicity: a comparative analysis of biodegradable and conventional 3D-printing materials post-steam sterilization for surgical guides

Abstract Introduction:
Ecological concerns and diminishing petroleum resources have prompted the exploration of biodegradable 3D-printing materials derived from bio-renewable sources, such as polylactide acid (PLA) or polyhydroxyalkanoates (PHA). This study aimed to compare the potential cytotoxic effects of a biodegradable PLA/PHA blend filament, a conventional photopolymer (MED610), and a combination of MED610 with a support material (SUP705) before and after steam sterilization in vitro.
Materials and Methods:
PLA/PHA, MED610, and SUP705 (both in their pure and steam-sterilized forms; n=6 per group) were assessed for their cytotoxic effects on human fibroblasts using the neutral red uptake assay. Positive controls included zinc diethyldithiocarbamate (ZDEC) and zinc dibutyldithiocarbamate (ZDBC), whereas high-density polyethylene served as a negative control. A stock solution of the extraction medium was used as the vehicle control.
Results:
Significant differences in cell viability were observed between pure PLA/PHA (1.2 ± 0.24) and MED610 (0.94 ± 0.08) (p=0.005). However, both materials exhibited non-cytotoxicity, with cell viability exceeding 70% compared to vehicle controls. SUP705 (0.58 ± 0.42) demonstrated significantly reduced cell viability compared to PLA/PHA (p=0.001) and MED610 (p=0.007). After steam sterilization, no significant difference in cell viability was noted between MED610 (1.0 ± 0.08) and PLA/PHA (1.2 ± 0.25) (p=0.111). While both materials remained non-cytotoxic after sterilization, SUP705 (0.60 ± 0.45) exhibited cytotoxic effects compared to MED610 (p=0.006) and PLA/PHA (p<0.001). Steam sterilization did not induce significant cytotoxic effects in the investigated materials (p=0.123).
Conclusion:
Pure and steam-sterilized PLA/PHA and MED610 were not cytotoxic. The observed cytotoxicity of SUP705 suggests caution in scenarios requiring sterile conditions, as the removal of support material from complex printed parts may be challenging. The consideration of PLA/PHA is recommended in such settings to ensure biocompatibility.

Influence of robot-guide strategies on the geometry of directed energy deposition components

Directed energy deposition (DED) for additive manufacturing applications is commonly realized by the usage of industrial robots. The DED processing end effectors are usually mounted on industrial robot systems and can, therefore, be moved and oriented in up to many degrees of freedom. However, the design of the powder nozzle and the programming of the robot can limit the movement options. For this reason, translational movements, as with conventional 3D printers, are still common today. The end effector is usually guided horizontal over the component surface although welding in position (PA) is preferred in general. It may be necessary to tilt the end effector in order to gain advantages during processing due to the constrained position. This is particularly advantageous for overhang structures and is often realized with the help of a turn-tilt positioning table in combination with an industrial robot. However, this approach is, in some cases, not possible due to geometrical constrains. To extend applications in this direction, advanced methods for slicing the components and programming the robot movements are necessary. The main aspect of this work is the development, testing, and evaluation of a multidimensional DED manufacturing approach. This is tested on a thin-walled component with defined overhang areas and compared with conventional approaches. Different strategies are assessed in terms of the geometrical match of the target geometry. Influences of strategies on the results are evaluated. It can be shown that multidimensional path planning approaches lead to a better match of the target geometry.

Experimental investigations on the formation of boundary layers in glass-based additive manufacturing of fused silica fibers by Laser Glass Deposition

Laser glass deposition is an additive manufacturing method to produce individualized glass components. This process uses a CO2 laser with a defocused beam as a heat source to additively melt-fused silica filaments. The fiber filament is fed laterally in the process zone and is deposited layer-by-layer to form 3D structures. The formation of boundary layers in conventional 3D-printing methods is a usual byproduct of the process. In this paper, the boundary layer formation of deposited fused silica filaments is investigated in detail by means of varying different process parameters such as, laser power, feed rate, laser spot diameter, and printing strategy. This involves examining both thin-walled and thick-walled test specimens. Quality characteristics like the surface roughness and the optical transmission are analyzed for the printed specimen. Finally, fully transparent structures with surface roughness below 100 nm and a transparency of 90% could be printed boundary layer-free and without post-processing.

Study on hybrid 3D printing and milling process for customized polyether-ether-ketone components.

Polyether-ether-ketone (PEEK) has been widely applied in various fields due to its excellent mechanical properties and biocompatibility. The efficient and high-quality customized manufacturing of PEEK components are investigated in this study by the hybrid 3D printing and milling process. At first, the alternating hybrid process is selected and verified by comparing two typical hybrid process categories and conducting experiments, respectively. Second, a set of procedures are designed to automate the engineering application of the hybrid process trying to avoid the disadvantages of manual programing. Then, considering the tool length and possible interferences during the hybrid process, a model segmentation algorithm, namely, the exchange principle of avoiding interference (EPAI) is proposed. Based on the introduced EPAI and the programing language Python, the additive and subtractive hybrid manufacturing (ASHM) data processing procedure is proposed and realized by post-processing of the conventional 3D printing codes. Finally, the feasibility experiments have been conducted. The experimental results verify the hybrid manufacturing process in the fabrication of parts with complex internal features. The surface roughness Ra and dimensional error L of the parts have been reduced by 75.5% and 85.2%, respectively, while the shear strength τ has been increased by 14.1%. Compared with conventional milling process, the material consumption is reduced by 48.7%.

Effects of Ultrasonic Vibration on 3D Printing of Polylactic Acid/Akermanite Nanocomposite Scaffolds

The mechanical properties of 3D-printed scaffolds for load-bearing implantation are crucial. Although the addition of nanoparticles to polymeric matrix scaffolds can improve their mechanical and biological properties, due to certain limitations in printability, high amounts of reinforcement cannot be used. Therefore, in this study, an attempt was made to use ultrasonic (UT) vibration to inhibit nozzle clogging during fused filament fabrication (FFF) of polylactic acid (PLA) scaffolds including 0, 20, and 40 wt.% Akermanite (Ak). Nozzle clogging happened during the conventional 3D printing of PLA-40wt.%Ak, while that did not occur during UT-assisted 3D printing of PLA-40wt.%Ak. Results of X-ray Diffraction (XRD) analysis and Scanning Electron Microscopy (SEM) indicated that applying ultrasonic (UT) vibration had no negative effect on the phases and morphology of the scaffolds. The results obtained by the compression test indicated that applying UT during 3D-printing resulted in almost 27% increment of elastic modulus and almost 25% increase of the compressive strength of the scaffolds. As the conclusion, this study highlights the effectiveness of ultrasonic-assisted 3D printing in producing nanocomposite scaffolds with significantly higher nanoparticle loadings, as compared to conventional printing methods. By utilizing ultrasonic vibration during the printing process, the study showcases the possibility of overcoming viscosity limitations and optimizing the mechanical performance of scaffolds for various biomedical applications, including bone tissue engineering.

Fabrication of carbon fiber reinforced SiC composites based on laser directed energy deposition

Carbon fiber reinforced silicon carbide ceramic matrix composites (CF/SiC) are widely applied in aerospace and other industries fields for its extraordinary properties. Nevertheless, traditional preparation processes encounter the challenges of long cyclicality, high economic cost due to the increasing requests. Consequently, this work integrates the CF/SiC composites with the novel laser directed energy deposition (L-DED) printing technology, which is differing from conventional 3D printing technology for it omits the post-processing procedure. CF/SiC composites are designed and manufactured efficiently, and the effects of carbon fiber addition are analyzed. Mechanical properties are utilized to characterize the internal bonding strength and the results reveal that the maximum flexural and compressive reach 119.33 ± 4.04 MPa and 396.20 ± 10.21 MPa, respectively, attributed to the enhanced crack propagation resistance caused by the carbon fiber addition. At the same time, this paper not only characterizes the performance through objective experimental data, but also expounds the formation mechanism of pores and cracks through material analysis. In conclusion, this work pioneers the application of L-DED molding technology to CF/SiC composites fabrication and validated its preparation capability, which not only improves the efficiency but also opens up a new path for CF/SiC composites preparation in the field of 3D printing.

Extrusion-Based Bioprinting in a Cost-Effective Bioprinter

Three-dimensional (3D) bioprinting has emerged as a revolutionary approach in the life sciences, combining multiple disciplines such as computer engineering, materials science, robotics, and biomedical engineering. This innovative technology enables the production of cellular constructs using bio-inks, and differs from conventional 3D printing by incorporating living cells. The present work addresses the conversion of a commercial thermoplastic 3D printer into a low-cost bioprinter. The modification addresses the challenges of the high cost of commercial bioprinters, limited adaptability, and specialized personnel requirements. This modification uses an extrusion-based bioprinting method that is particularly popular in research due to its viscosity tolerance and versatility. The individual steps, including replacing the extruder with a syringe pump, rebuilding the electronic motherboard, and configuring the firmware, are explained in detail. The work aims at providing access to bioprinting technology so that laboratories with modest resources can take advantage of the immense potential of this technology. This modification resulted in improved resolution, allowing submicron movements, which is comparable to some of the commercially available bioprinters. The accuracy of the modified printer was validated using hydrogel bioprinting tests, suggesting that it is suitable for broader applications in regenerative medicine.

Enhancement of Overlimiting Current in a Three-Dimensional Hierarchical Micro/Nanofluidic System by Non-uniform Compartmentalization

Overlimiting current (OLC) is a non-linear current response that occurs related to an ion concentration polarization (ICP) phenomenon in micro/nanofluidic systems and holds great importance since it represents the rate of selective ion transportation through perm-selective structure. For last two decades, numerous studies of OLC have been reported about understanding the fundamentals of nanoelectrokinetics and enhancing ion transportation through perm-selective membranes. Recent study reported that the alignment of non-uniform microspace near the perm-selective membranes in two-dimensional micro/nanofluidic systems can significantly enhance OLC, i.e., overlimiting conductance (σOLC). This is attributed to recirculation flow induced by combination of unbalanced electroosmosis and induced pressure driven flow among non-uniform microspaces. However, 2D micro/nanofluidic systems have limited practicality due to their small volume and low throughput. Herein, we tested the OLC enhancement using 3D-printed hierarchical micro/nanofluidic systems with respect to the non-uniformity of microspaces. The 3D microspaces were fabricated as a mesh structure using a conventional 3D printer. By comparing current–voltage measurement with each type of mesh, we experimentally confirmed the generation of recirculation flow among non-uniform meshes and ionic current enhancement in 3D hierarchical micro/nanofluidic system. Also, we further investigated the enhancement of overlimiting conductance depending on the mesh pattern. Furthermore, we validated that this effect of microscale non-uniform compartmentalization, both increasing surface area and aligning non-uniform spaces, appears not only at low molar concentration but at high molar concentrations. This demonstration can offer a strategy to design optimal electrochemical systems where a perm-selective ion transportation is crucial.

Research progress of three-dimensional bioprinting technology in auricle repair and reconstruction

To review the research progress on the application of three-dimensional (3D) bioprinting technology in auricle repair and reconstruction. The recent domestic and international research literature on 3D printing and auricle repair and reconstruction was extensively reviewed, and the concept of 3D bioprinting technology and research progress in auricle repair and reconstruction were summarized. The auricle possesses intricate anatomical structure and functionality, necessitating precise tissue reconstruction and morphological replication. Hence, 3D printing technology holds immense potential in auricle reconstruction. In contrast to conventional 3D printing technology, 3D bioprinting technology not only enables the simulation of auricular outer shape but also facilitates the precise distribution of cells within the scaffold during fabrication by incorporating cells into bioink. This approach mimics the composition and structure of natural tissues, thereby favoring the construction of biologically active auricular tissues and enhancing tissue repair outcomes. 3D bioprinting technology enables the reconstruction of auricular tissues, avoiding potential complications associated with traditional autologous cartilage grafting. The primary challenge in current research lies in identifying bioinks that meet both the mechanical requirements of complex tissues and biological criteria.

Tensile, flexural, and mode-I cracking behavior of interpenetrating phase composites (IPC), developed using additively manufactured PLA-based structures with different infill densities and epoxy resin polymer as matrix

Interpenetrating phase composites (IPC) materials are designed to combine the advantages of made-from materials or develop an intended behavior. Recently, the use of 3D printed structures has received attention due to advantages, such as the rapid and cheap prototyping techniques of complex structures. However, most materials, such as polylactic acid (PLA) used for conventional 3D printing, have low strength and insignificant durability. To overcome these issues, the excellent characteristics of polymer adhesives, such as epoxy resin, can be used to increase their strength and durability. In this paper, PLA-based 3D printed samples and epoxy resin adhesive were merged to develop an interpenetrating phase composite. The samples were printed with 25, 50, 75, and 100 infill percentages and tested in direct tensile, bending, and mode-I fracture. From the results, it can be seen that reducing the infill percentage to 75, 50, and 25 % reduces the tensile strength to 16, 9, and 3 MPa (−40 %, −66 %, and −90 % compared to the sample with 100 % infill with 26 MPa strength), adding epoxy resin to develop an IPC, results in 24, 29 and 32 MPa tensile strength. Compared to 3D-printed parts with the same infill percentages, the IPCs have 150, 320, and 1140 % higher tensile strengths, respectively. Also, the failed samples were reviewed by scanning electron microscope.

Low-cost automated flat-sheet membrane casting: An open-source, advanced manufacturing approach

Novel membrane materials developed in research labs struggle to gain widespread industrial adoption due in part to insufficient reproducibility and unreliable performance data. Open-source hardware approaches, especially 3D printing, enable the democratization of automation within a laboratory setting, and in the context of membranes, can minimize the inherent variability associated with manual methods of membrane casting. In this study, the native hardware and firmware of an inexpensive, conventional 3D printer was extensively modified for the purpose of flat-sheet membrane casting. Replicate poly (ether-ether ketone) (PEEK) membranes were cast with a thickness coefficient of variation of ∼10 % using the modified device. Cast membranes were used to assess the importance of controlling shear rate by characterizing both intra- and inter-film variability. Statistical differences in pure water permeability were observed across tested shear rates, with distinct morphological changes occurring to the membrane substructure. Overall, the technology developed in this study is shown to be an extremely useful approach for improving the process of developing membranes at the bench-scale.

A novel pellet-based 3D printing of high stretchable elastomer

Elastomers, known for their high stretchability and flexibility, are widely used in high-tech applications. However, traditional manufacturing methods for elastomeric part production have limitations. 3D printing, particularly fused deposition modeling (FDM), offers a promising alternative by allowing the fabrication of customized elastomers with desired shapes and properties. Conventional filament-based FDM techniques struggle to print elastomers. This article presents a novel approach for 3D printing polyolefin elastomer (POE) using a direct pellet printing technique. A customized pellet printer with a pneumatic pressure feeding system was used that eliminates filament buckling issues commonly associated with conventional filament-based 3D printing methods. The mechanical properties and microstructure of the printed parts were analyzed to evaluate the suitability of the technique for producing high-quality elastomeric components. SEM images indicated a high-quality and accurate printing method; however, there are micro-holes between the raster due to the high shrinkage rate of POE and increasing the nozzle temperature improves the print quality. The mechanical properties of the printed samples exhibited remarkable formability, with elongation reaching up to 1965%. It is also found that as the nozzle temperature increased, the strength, elongation, and bonding between layers improved significantly. This innovative 3D printing technique has the potential for various applications such as soft robotics and wearable electronics.

Marginal fit of 3-unit implant-supported fixed partial dentures: Influence of pattern fabrication method and repeated porcelain firings.

Marginal fit significantly impacts the long-term success of dental restorations. Different pattern fabrication methods, including hand-waxing, milling, or 3D printing, may affect restorations accuracy. The effect of porcelain firing cycles on the marginal fit of metal-ceramic restorations remains controversial, with conflicting findings across studies. The aim was to evaluate the potential effects of multiple porcelain firings (3, 5, 7 cycles) as well as pattern fabrication method (conventional hand-waxing, milling, and 3D printing) on the marginal adaptation of 3-unit implant-supported metal-ceramic fixed partial dentures. It was hypothesized that neither the wax pattern fabrication method nor repeated ceramic firings would significantly affect the marginal adaptation of metal-ceramic crowns. In this in-vitro study, 30 Cobalt-Chromium alloy frameworks were fabricated based on pattern made through three techniques: conventional hand-waxing, CAD-CAM milling, and CAD-CAM 3D printing (n = 10 per group). Sixteen locations were marked on each abutment to measure the vertical marginal gap at four stages: before porcelain veneering and after 3, 5, and 7 firing cycles. The vertical marginal gap was measured using direct microscopic technique at ×80 magnification. Mean vertical marginal gap values were calculated and two-way ANOVA and Tukey's post hoc tests were used for inter-group comparisons (α = 0.05). The 3D printing group showed significantly lower (P<0.001) mean vertical marginal gaps (60-76 μm) compared to the milling (77-115 μm) and conventional hand-waxing (102-110 μm) groups. The milling group exhibited a significant vertical gap increase after 3 firing cycles (P<0.001); while the conventional (P = 0.429) and 3D printing groups (P = 0.501) showed no significant changes after 7 firing cycles. Notably, the vertical marginal gap in all groups remained below the clinically acceptable threshold of 120 μm. CAD-CAM 3D printing provided superior marginal fit compared to CAD-CAM milling and conventional hand-wax pattern fabrication methods. The impact of porcelain firing on the mean marginal gap was significant only in the milling group. All three fabrication techniques yielded clinically acceptable vertical marginal adaptation after repeated firings. Additive manufacturing holds promise to produce precise implant-supported prostheses.

Development of a 3D Microfluidic Analytical Device for the Detection of Pathogenic Bacteria in Commercial Food Samples with Loop-Mediated Isothermal Amplification

Traditional methods of detecting foodborne pathogens take several days to produce the required results. Furthermore, various molecular techniques (e.g., PCR) that also produce reliable results in the detection of pathogenic bacteria have been introduced, but the cost–time ratio required does not allow them to be considered a substantial solution to this specific problem. Three-dimensional (3D) printing technology provides the ability to design and manufacture microfluidic analytical devices using conventional 3D printers, which, in combination with colorimetric loop-mediated isothermal amplification (LAMP), may further simplify the process. The overall reduction in time and cost may provide the opportunity to upscale this diagnostic modality. Moreover, unlike most microfluidic analytical devices, this technique is simpler and more user-friendly, as it does not require any expertise or additional equipment apart from a conventional oven. A 3D-printed microfluidic analytical device in combination with LAMP was developed and tested for the simultaneous detection of foodborne pathogens in food samples. A total of 150 commercial food specimens (50 milk, 50 chicken, 50 lettuce samples) were analyzed for possible contamination with Salmonella typhimurium, Listeria monocytogenes and Escherichia coli. The 3D-printed microfluidic device was 100% precise for both negative (80 samples) and positive samples (7 samples were positive for S. typhimurium, 28 for L. monocytogenes, and 35 for E. coli) for all pathogens. Overall, the amount of data analyzed led to a high level of confidence in the precision of this device. As such, this new 3D device in combination with LAMP provides a precise detection method for food pathogens with a low detection limit.

Eco-friendly 3D Printing Mortar with Low Cement Content: Investigation on Printability and Mechanical Properties

The conventional approach to achieving optimal printability and buildability in 3D printing mortar relies heavily on cement, which is both costly and environmentally detrimental due to substantial carbon emissions from its production. This study aims to mitigate these issues by investigating the viability of slag as a partial substitute for cement, with the goal of developing an eco-friendly alternative. The newly formulated mortar, featuring a 30% reduction in cement content (from 830 to 581 kg/m3) and the inclusion of 0.10% micro-fibers, exhibits properties comparable to conventional 3D printing mortar. The research is structured into two parts: Part 1 focuses on determining the optimal fiber content, while Part 2 delves into the investigation of fiber-reinforced mortar with reduced cement content for 3D printing. Criteria were established to ensure mortar flow at 115%, initial printable time below 60 minutes, and 7-day compressive strength exceeding 28 MPa. Part 1 results indicate that a fiber content of 0.1% by volume meets the specified requirements. In Part 2, it was observed that increasing the slag replacement percentage extended the initial printable time and time gap. However, even at a 30% replacement rate, the initial printable time remained within the acceptable range, partially attributed to the presence of fibers in the mix. Additionally, higher slag content led to increased flow and reduced filament height in the mixes. Notably, all formulations surpassed the 7-day compressive strength threshold. These findings underscore the potential of slag as a sustainable alternative to cement in 3D printing fiber-reinforced mortar, offering promising prospects for environmentally friendly construction practices. Doi: 10.28991/CEJ-2024-010-03-010 Full Text: PDF

Positional Trueness with Different Titanium Base Bonding Techniques for Single Implant Crowns: In Vitro Evaluation of Model-Free Workflow Versus Additively Manufactured Models.

To compare the positional trueness of implant-crown bonding to titanium bases (Ti-bases) using different bonding protocols. A nonprecious alloy model with a single implant at the mandibular right first molar site was digitized, then a single implant crown was designed. The crown was milled, adhesively cemented on a Ti-base, and screw-retained on the implant in the master model to obtain a reference scan. Forty PMMA implant crowns were subtractively manufactured and allocated to one of four study groups (n = 10 crowns per group) based on the bonding protocol on Ti-bases: Group 1 = modelfree bonding; Group 2 = bonding on the master model (control); Group 3 = bonding on a model from an industrial-grade 3D printer (Prodways); Group 4 = bonding on a model from a conventional 3D printer (Asiga). To assess the positional trueness of crowns, the scans of crowns when on the model were superimposed over the reference scan. Median distance and angular deviations were analyzed using Kruskal-Wallis and Mann- Whitney tests (α = .05). Mesial and distal contacts of crowns were assessed by two independent clinicians. The control group (Group 2) resulted in the smallest distance deviations (0.30 ± 0.03 mm) compared to model-free (0.35 ± 0.02 mm; P = .002; Group 1) and conventional 3D printer (0.37 ± 0.01 mm; P = .001; Group 4) workflows. Buccolingual (P = .002) and mesiodistal (P = .01) angular deviations were higher in the conventional 3D printer group than in the control group (P = .002). Proximal contact assessments did not show any differences among groups. While bonding crowns to Ti-bases on a master model created with an industrial-grade 3D printer resulted in the highest positional trueness, model-free workflows had a similar positional trueness to those manufactured with a conventional 3D printer.

Effect of Aging on the Mechanical Properties of CAD/CAM-Milled and 3D-Printed Acrylic Resins for Denture Bases

The purpose of this study was to investigate the mechanical properties of acrylic resins at different aging times for denture bases manufactured using the conventional method, microwave processing, milling, and 3D printing. A total of 160 rectangular samples (64 Å~ 10 Å~ 3.3 ± 0.03 mm) were prepared, divided among the four main resin groups, and subdivided into four analysis times (T0, T1, T2, and T3), resulting in 10 samples per subgroup. The samples were stored in distilled water at 37° ± 2°C for 24 hours (T0), then subjected to thermocycling at temperatures of 5° ± 1°C and 55° ± 1°C in different numbers of cycles: 5,000 (T1); 10,000 (T2); and 20,000 (T3). The mechanical properties evaluated were surface microhardness, flexural strength, and modulus of elasticity. Statistical differences between resin groups and aging time were evaluated using two-way analysis of variance (P < .05). The 3D-printed resin showed the significantly lowest values of microhardness, flexural strength, and modulus of elasticity compared to other resins (P < .001). The CAD/CAM-milled denture resin showed mechanical properties similar to those of traditional resins (conventional and microwave-processed). The 3D-printing resin did not show adequate mechanical properties for long-term clinical use. Despite this, new studies are developing better properties of this resin for long-term use.

Influence of Motion Mechanism Change in 3D Printers on the Quality of Printed Models

The objective of this study is to compare the quality of 3D printed models manufactured using the Fused Filament Fabrication (FFF) method. The samples were fabricated using a robotic arm with 4 axes and conventional 3D printers. The focus of this experiment lies in assessing the influence of the devices’ structural design on the resulting quality of the 3D printed models. Additionally, the study aims to identify the strengths and limitations of each device and define their respective applicability. The 3D model designed for this investigation comprises intricate geometrical shapes specifically chosen to evaluate the precision and repeatability of layer deposition while establishing geometric tolerances and determining shape deviations. The samples were 3D printed under identical printing conditions and parameters, and subsequently, these produced samples will undergo 3D digitization through an optical scanner, namely ATOS II Triple Scan. The obtained data will then be subjected to a comparative analysis utilizing GOM Inspect software to determine the geometric tolerances. The findings from this analysis will be critically evaluated and serve as a basis for informing and guiding future research endeavors.

Fit and Strength of a Three-Unit Temporary Prosthesis Made by Different Manufacturing Techniques: An In Vitro Study.

To compare the fit and fracture load of temporary fixed partial prostheses fabricated by means of a conventional direct technique, milling, or 3D printing. A maxillary right first premolar and molar were prepared on a Frasaco cast, which was then duplicated 40 times. In total, 10 provisional three-unit fixed prostheses (Protemp 4, 3M) were made using the conventional technique with a putty mold. The 30 remaining casts were scanned to design a provisional restoration using CAD software. A total of 10 designs were milled (CEREC MC X5/shaded PMMA Disk, Dentsply Sirona), while the other 20 were 3D printed with one of the two 3D printers (Asiga UV MAX or Nextdent 5100, C&B, Nextdent). Internal and marginal fit were examined using the replica technique. Next, the restorations were cemented on their respective casts and loaded until fracture using a universal testing machine. The location and propagation of the fracture were also evaluated. 3D printing demonstrated the best internal fit. Nextdent (median internal fit: 132 μm) was significantly better compared to the milled (median internal fit: 185 μm; P = .006) and conventional restorations (median internal fit: 215 μm; P < .001), while the fit of Asiga (median internal fit: 152 μm) was only significantly better than the conventional restorations (P < .012). The lowest marginal discrepancy was found for the milled restorations (median marginal fit: 96 μm), but this was only significant when compared to the conventional group (median internal fit: 163 μm; P < .001). The conventional restorations demonstrated the lowest fracture load (median fracture load: 536 N), which was only significant when compared to Asiga (median fracture load: 892 N; P = .003). Within the present in vitro study's limitations, CAD/CAM demonstrated superior fit and strength compared to the conventional technique.

PHASE SEPARATION AND PARTICULATE LEACHING INTEGRATED 3D PRINTING OF POROUS SCAFFOLDS FOR BONE TISSUE ENGINEERING APPLICATIONS

Conventional 3D printing by itself is incapable of creating pores on a micro scale within deposited filaments throughout 3D scaffolds. These pores and hence larger surface areas are needed for cells to be adhered, proliferated, and differentiated. The aim of this work was to fabricate 3D polycaprolactone (PCL) scaffolds with internal multiscale porosity by using two different 3D printing techniques (ink/pellet of polymer-salt composite in low/high temperature printing) combined with salt leaching to improve cell adhesion, and cell proliferation besides to change degradation rate of PCL scaffolds:1. Non-solvent phase separation integrated 3D printing of polymer-salt inks with various salt content (i.e., low temperature ink-based printing, LT).2. FDM printing of composite polymer-salt pellets which will be obtained by casting and evaporating of prepared ink (i.e., high temperature composite-pellet-based printing, HT).Further, the two approaches were followed by post salt leaching. Stem cells were able to attach on the surface and grow up to 14 days based on increasing cellular activities.