Hot isostatic pressing as an alternative thermo-mechanical treatment for metallic full-arch implant-supported frameworks obtained by additive and subtractive manufacturing technology: Vertical and horizontal fit, screw removal torque, and stress analysis

PURPOSE

To assess vertical and horizontal fit, screw removal torque, and stress analysis (considered biomechanical aspects) of full-arch implant frameworks manufactured in Ti-6Al-4V through milling, and additive manufacturing Direct Metal Laser Sintering (DMLS) and Electron Beam Melting (EBM), and the effect of the thermo-mechanical treatment Hot Isostatic Pressing (HIP) as a post-treatment after manufacturing.

MATERIAL AND METHODS

Maxillary full-arch implant frameworks were made by milling, DMLS, and EBM. The biomechanical assessments were screw removal torque, strain-gauge analyses, and vertical and horizontal marginal fits. The vertical fit was assessed by the single-screw test and with all screws tightened. All frameworks were submitted to a standardized HIP cycle (920°C, 1000 bar pressure, 2 h), and the tests were repeated (α = 0.05).

RESULTS

At the initial time, milled frameworks presented higher screw removal torque values, and DMLS and EBM frameworks presented lower levels of strain. Using the single-screw test, milled and DMLS frameworks presented higher vertical fit values, and with all screws tightened and horizontally, higher fit values were found for milled frameworks, followed by DMLS and EBM. After HIP, milling and EBM frameworks presented higher screw removal torque values; the lowest strain values were found for EBM. Using the single-screw test, milled and DMLS frameworks presented higher vertical fit values, and with all screws tightened and horizontally no differences were found.

CONCLUSIONS

DMLS and EBM full-arch frameworks presented adequate values of screw removal torque, strain, and marginal fit, although the worst values of marginal fit were found for EBM frameworks. The HIP cycle enhanced the screw removal torque of milled and EBM frameworks and reduced the strain values of milled frameworks. The HIP represents a reliable post-treatment for Ti-6Al-4V dental prostheses produced by milling and EBM technologies.

3D Printing of Ti-6Al-4V-Based Porous-Channel Dental Implants: Computational, Biomechanical, and Cytocompatibility Analyses

Objective: Loosening of dental implants due to resorption of the surrounding bone is one of the challenging clinical complications in prosthetic dentistry. Generally, stiffness mismatch between an implant and its surrounding bone is one of the major factors. In order to prevent such clinical consequences, it is essential to develop implants with customized stiffness. The present study investigates the computational and experimental biomechanical responses together with cytocompatibility studies of three-dimensional (3D)-printed Ti-6Al-4V-based porous dental implants with varied stiffness properties. Methods: Additive manufacturing (direct metal laser sintering, DMLS) was utilized to create Ti-6Al-4V implants having distinct porosities and pore sizes (650 and 1000 μm), along with a nonporous (solid) implant. To validate the compression testing of the constructed implants and to probe their biomechanical response, finite element models were employed. The cytocompatibility of the implants was assessed using MG-63 cells, in vitro. Results: Both X-ray microcomputed tomography (μ-CT) and scanning electron microscopy (SEM) studies illustrated the ability of DMLS to produce implants with the designed porosities. Biomechanical analysis results revealed that the porous implants had less stiffness and were suitable for providing the appropriate peri-implant bone strain. Although all of the manufactured implants demonstrated cell adhesion and proliferation, the porous implants in particular supported better bone cell growth and extracellular matrix deposition. Conclusions: 3D-printed porous implants showed tunable stiffness properties with clinical translational potential.

A Sustainability-Based Expert System for Additive Manufacturing and CNC Machining

The objective of this research study is to develop a set of expert systems that can aid metal manufacturing facilities in selecting binder jetting, direct metal laser sintering, or CNC machining based on viable products, processes, system parameters, and inherent sustainability aspects. For the purposes of this study, cost-effectiveness, energy, and auxiliary material usage efficiency were considered the key indicators of manufacturing process sustainability. The expert systems were developed using the knowledge automation software Exsys Corvid®V6.1.3. The programs were verified by analyzing and comparing the sustainability impacts of binder jetting and CNC machining during the fabrication of a stainless steel 316L component. According to the results of this study, binder jetting is deemed to be characterized by more favorable indicators of sustainability in comparison to CNC machining, considering the fabrication of components feasible for each technology.

Influence of Ion Nitriding on Microstructure and Properties of Haynes 282 Nickel Superalloy Specimens Produced Using DMLS Technique

The paper investigates the influence of the ion-nitriding process on the microstructure, corrosion resistance, and tensile strength at elevated temperatures of Haynes 282 nickel superalloy specimens produced by the Direct Metal Laser Sintering (DMLS) technique. The study was performed for two conditions, i.e., as-built by DMLS method and as-built by DMLS method + covered by a layer containing CrN + Cr₂N phases. An analysis of the surface morphology revealed that the ion-nitriding process significantly affects the physical and chemical phenomena occurring on the specimen's surface. The XRD measurement of the specimens showed that preparing them with the DMLS method as well as following a nitriding process produced residual tensile stresses. Based on the measurement of the nanohardness distribution through the layer approximatively of 7 μm in width and the superalloys substrate, the results of the nanohardness showed the maximum values of 27 GPa and 13.5 GPa for the nitrided layer and the substrate, respectively. The surface protection from the nitrided layer proved a positive effect on the corrosion resistance of the DMLS specimens in the solution of 0.1 M Na₂SO₄ + 0.1 M NaCl at room temperature. The results of the tensile tests at 750 °C showed that the ion-nitriding process did not significantly affect the elevated-temperature tensile strength of the superalloy specimens produced with the DMLS technique.

Comparative Analysis of Bone Ingrowth in 3D-Printed Titanium Lattice Structures with Different Patterns

In this study, metal 3D printing technology was used to create lattice-shaped test specimens of orthopedic implants to determine the effect of different lattice shapes on bone ingrowth. Six different lattice shapes were used: gyroid, cube, cylinder, tetrahedron, double pyramid, and Voronoi. The lattice-structured implants were produced from Ti6Al4V alloy using direct metal laser sintering 3D printing technology with an EOS M290 printer. The implants were implanted into the femoral condyles of sheep, and the animals were euthanized 8 and 12 weeks after surgery. To determine the degree of bone ingrowth for different lattice-shaped implants, mechanical, histological, and image processing tests on ground samples and optical microscopic images were performed. In the mechanical test, the force required to compress the different lattice-shaped implants and the force required for a solid implant were compared, and significant differences were found in several instances. Statistically evaluating the results of our image processing algorithm, it was found that the digitally segmented areas clearly consisted of ingrown bone tissue; this finding is also supported by the results of classical histological processing. Our main goal was realized, so the bone ingrowth efficiencies of the six lattice shapes were ranked. It was found that the gyroid, double pyramid, and cube-shaped lattice implants had the highest degree of bone tissue growth per unit time. This ranking of the three lattice shapes remained the same at both 8 and 12 weeks after euthanasia. In accordance with the study, as a side project, a new image processing algorithm was developed that proved suitable for determining the degree of bone ingrowth in lattice implants from optical microscopic images. Along with the cube lattice shape, whose high bone ingrowth values have been previously reported in many studies, it was found that the gyroid and double pyramid lattice shapes produced similarly good results.

Efficiency Research of Conformal Channel Geometries Produced by Additive Manufacturing in Plastic Injection Mold Cores (Inserts) Used in Automotive Industry

In the production of geometries that traditional methods cannot produce, it is seen that additive manufacturing (AM) technology, which has come to the fore, has been used extensively in conformal cooling channel (CCC) applications in recent years. This study, conducted within the scope of CCC's use of applied mold cores in automotive industry plastic part production, aimed to reduce the cycle time in the injection printing process. The v1 geometry, which gives the analysis results for ideal printing quality from the channel geometries developed with three different design approaches, is produced with direct metal laser sintering, which is an AM laser sintering technology, and the injection printing cycle time has been reduced by 38%. CCC applied the study's primary motivation to develop duct geometry to provide balanced cooling in the automotive industry's mold cores produced with AM. It is known that the Computer Numerical Control machining process in traditional mold methods does not allow the processing of the channels in the internal geometries, and the deep areas where the heat is concentrated cannot be cooled sufficiently. In the study, CCC geometries where AM design parameters are used effectively and the balanced cooling performance expected from the die core can be achieved. The effects of different geometries on production are discussed.

The Impact of Plastic Deformation on the Microstructure and Tensile Strength of Haynes 282 Nickel Superalloy Produced by DMLS and Casting

The article presents the results of research on the influence of plastic deformation on the microstructure and tensile strength of Haynes 282 nickel superalloy produced by direct metal laser sintering (DMLS) and a conventional technique (casting). Samples were tested for dimensional accuracy using a 3D scanner. Then, the samples were subjected to plastic deformation by rolling. The microstructures of the DMLS and the as-cast samples were analysed using a scanning electron microscope. The strength properties of the samples were determined in a static tensile test. Microhardness measurements of the samples were also performed. Based on the analysis of the dimensional accuracy, it was found that the surface quality of the components produced by DMLS is dependent on the input parameters of the 3D printing process. Using the DMLS method, it is possible to produce Haynes 282 with a fine-crystalline microstructure containing dendrites. The fine-crystalline dendritic microstructure and low porosity showed very good tensile strength compared to the as-cast material. It was also found that the increase in the degree of plastic deformation of the as-cast Haynes 282 and the samples produced by the DMLS technique resulted in an increase in the strength of the tested samples, with reduced ductility.

Investigation of the Performance of Ti6Al4V Lattice Structures Designed for Biomedical Implants Using the Finite Element Method

The development of medical implants is an ongoing process pursued by many studies in the biomedical field. The focus is on enhancing the structure of the implants to improve their biomechanical properties, thus reducing the imperfections for the patient and increasing the lifespan of the prosthesis. The purpose of this study was to investigate the effects of different lattice structures under laboratory conditions and in a numerical manner to choose the best unit cell design, able to generate a structure as close to that of human bone as possible. Four types of unit cell were designed using the ANSYS software and investigated through comparison between the results of laboratory compression tests and those of the finite element simulation. Three samples of each unit cell type were 3D printed, using direct metal laser sintering technology, and tested according to the ISO standards. Ti6Al4V was selected as the material for the samples. Stress-strain characteristics were determined, and the effective Young's modulus was calculated. Detailed comparative analysis was conducted between the laboratory and the numerical results. The average Young's modulus values were 11 GPa, 9 GPa, and 8 GPa for the Octahedral lattice type, both the 3D lattice infill type and the double-pyramid lattice and face diagonals type, and the double-pyramid lattice with cross type, respectively. The deviation between the lab results and the simulated ones was up to 10%. Our results show how each type of unit cell structure is suitable for each specific type of human bone.

Microstructure and Properties of Additively Manufactured AlCoCr0.75Cu0.5FeNi Multicomponent Alloy: Controlling Magnetic Properties by Laser Powder Bed Fusion via Spinodal Decomposition

A non-equiatomic AlCoCr_0.75Cu_0.5FeNi alloy has been identified as a potential high strength alloy, whose microstructure and consequently properties can be widely varied. In this research, the phase structure, hardness, and magnetic properties of AlCoCr_0.75Cu_0.5FeNi alloy fabricated by laser powder bed fusion (LPBF) are investigated. The results demonstrate that laser power, scanning speed, and volumetric energy density (VED) contribute to different aspects in the formation of microstructure thus introducing alterations in the properties. Despite the different input parameters studied, all the as-built specimens exhibit the body-centered cubic (BCC) phase structure, with the homogeneous elemental distribution at the micron scale. A microhardness of up to 604.6 ± 6.8 HV0.05 is achieved owing to the rapidly solidified microstructure. Soft magnetic behavior is determined in all as-printed samples. The saturation magnetization (M_s) is dependent on the degree of spinodal decomposition, i.e., the higher degree of decomposition into A2 and B2 structure results in a larger M_s. The results introduce the possibility to control the degree of spinodal decomposition and thus the degree of magnetization by altering the input parameters of the LPBF process. The disclosed application potentiality of LPBF could benefit the development of new functional materials.

Effect of Multi-Variant Thermal Treatment on Microstructure Evolution and Mechanical Properties of AlSi10Mg Processed by Direct Metal Laser Sintering and Casting

This article presents a study on the influence of temperature and time of multi-variant heat treatment on the structure and properties of materials produced in direct metal laser sintering (DMLS) and casting technology. The materials were manufactured in the form of cuboidal elements with a cross-section of 1.5 mm × 15 mm and a length of 60 mm. The samples prepared in this way had a similar volume, but due to the production technology the metal crystallization took place at different rates and directions. In the cast, the direction of heat transfer was toward the mold, and the DMLS was directed locally layer by layer. The small thickness of the cast material allowed reaching conditions similar to the DMLS cooling process. Both DMLS and cast samples show similar mechanical properties (hardness) achieved after long ageing time, i.e., 16 h at 170 °C. The maximum hardness was observed for 8 h. In the DMLS samples, in contrast to cast samples, no lamellar precipitates of silicon were observed, which indicates their better resistance to cracking

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.

A Comparative Study between Polymer and Metal Additive Manufacturing Approaches in Investigating Stiffened Hexagonal Cells

Recent polymer and metal additive manufacturing technologies were proven capable of building complex structures with high accuracy. Although their final products differ significantly in terms of mechanical properties and building cost, many structural optimization studies were performed with either one without systematic justification. Therefore, this study investigated whether the Direct Metal Laser Sintering (DMLS) and Fused Deposition Modelling (FDM) methodologies can provide similar conclusions when performing geometrical manipulations for optimizing structural crashworthiness. Two identical sets of four shapes of stiffened hexagonal cells were built and crushed under quasi-static loading. The results were compared in terms of collapsing behavior, load-carrying performance, and energy-absorption capability. Although the observed failure modes were different since the base-materials differ, similar improvement trends in performance were observed between both fabrication approaches. Therefore, FDM was recommended as a fabrication method to optimize thin-walled cellular hexagonal parameters since it was 80% more time-efficient and 53.6% cheaper than the DMLS technique.

Evaluation of Dislocation Densities in Various Microstructures of Additively Manufactured Ti6Al4V (Eli) by the Method of X-ray Diffraction

Dislocations play a central role in determining strength and flow properties of metals and alloys. Diffusionless phase transformation of β→α in Ti6Al4V during the Direct Metal Laser Sintering (DMLS) process produces martensitic microstructures with high dislocation densities. However, heat treatment, such as stress relieving and annealing, can be applied to reduce the volume of these dislocations. In the present study, an analysis of the X-ray diffraction (XRD) profiles of the non-heat-treated and heat-treated microstructures of DMLS Ti6Al4V(ELI) was carried out to determine the level of defects in these microstructures. The modified Williamson–Hall and modified Warren–Averbach methods of analysis were used to evaluate the dislocation densities in these microstructures. The results obtained showed a 73% reduction of dislocation density in DMLS Ti6Al4V(ELI) upon stress relieving heat treatment. The density of dislocations further declined in microstructures that were annealed at elevated temperatures, with the microstructures that were heat-treated just below the β→α recording the lowest dislocation densities.

Effect of Various Peening Methods on the Fatigue Properties of Titanium Alloy Ti6Al4V Manufactured by Direct Metal Laser Sintering and Electron Beam Melting

Titanium alloy Ti6Al4V manufactured by additive manufacturing (AM) is an attractive material, but the fatigue strength of AM Ti6Al4V is remarkably weak. Thus, post-processing is very important. Shot peening can improve the fatigue strength of metallic materials, and novel peening methods, such as cavitation peening and laser peening, have been developed. In the present paper, to demonstrate an improvement of the fatigue strength of AM Ti6Al4V, Ti6Al4V manufactured by direct metal laser sintering (DMLS) and electron beam melting (EBM) was treated by cavitation peening, laser peening, and shot peening, then tested by a plane bending fatigue test. To clarify the mechanism of the improvement of the fatigue strength of AM Ti6Al4V, the surface roughness, residual stress, and surface hardness were measured, and the surfaces with and without peening were also observed using a scanning electron microscope. It was revealed that the fatigue strength at N = 10⁷ of Ti6Al4V manufactured by DMLS was slightly better than that of Ti6Al4V manufactured by EBM, and the fatigue strength of both the DMLS and EBM specimens was improved by about two times through cavitation peening, compared with the as-built ones. An experimental formula to estimate fatigue strength from the mechanical properties of a surface was proposed.

Mechanical Properties and Microstructure of DMLS Ti6Al4V Alloy Dedicated to Biomedical Applications

The aim of this work was to investigate the microstructure and mechanical properties of samples produced by direct metal laser sintering (DMLS) with varied laser beam speed before and after heat treatment. Optical analysis of as-built samples revealed microstructure built of martensite needles and columnar grains, growing epitaxially towards the built direction. External and internal pores, un-melted or semi-melted powder particles and inclusions in the examined samples were also observed. The strength and Young's modulus of the DMLS samples before heat treatment was higher than for cast and forged samples; however, the elongation at break for vertical and horizontal orientation was lower than required for biomedical implants. After heat treatment, the hardness of the samples decreased, which is associated with the disappearance of boundary effect and martensite decomposition to lamellar mixture of α and β, and the anisotropic behaviour of the material also disappears. Ultimate tensile strength (UTS) and yield strength(YS) also decreased, while elongation increased. Tensile properties were sensitive to the build orientation, which indicates that DMLS generates anisotropy of material as a result of layered production and elongated β prior grains. It was noticed that inappropriate selection of parameters did not allow properties corresponding to the standards to be obtained due to the high porosity and defects of the microstructure caused by insufficient energy density.

Augmentation of DMLS Biomimetic Dental Implants with Weight-Bearing Strut to Balance of Biologic and Mechanical Demands: From Bench to Animal

A mismatch of elastic modulus values could result in undesirable bone resorption around the dental implant. The objective of this study was to optimize direct metal laser sintering (DMLS)-manufactured Ti₆Al₄V dental implants' design, minimize elastic mismatch, allow for maximal bone ingrowth, and improve long-term fixation of the implant. In this study, DMLS dental implants with different morphological characteristics were fabricated. Three-point bending, torsional, and stability tests were performed to compare the mechanical properties of different designs. Improvement of the weaker design was attempted by augmentation with a longitudinal 3D-printed strut. The osseointegrative properties were evaluated. The results showed that the increase in porosity decreased the mechanical properties, while augmentation with a longitudinal weight-bearing strut can improve mechanical strength. Maximal alkaline phosphatase gene expression of MG63 cells attained on 60% porosity Ti₆Al₄V discs. In vivo experiments showed good incorporation of bone into the porous scaffolds of the DMLS dental implant, resulting in a higher pull-out strength. In summary, we introduced a new design concept by augmenting the implant with a longitudinal weight-bearing strut to achieve the ideal combination of high strength and low elastic modulus; our results showed that there is a chance to reach the balance of both biologic and mechanical demands.

Comparative Evaluation of Marginal Accuracy of Metal Copings Fabricated using Direct Metal Laser Sintering, Computer-Aided Milling, Ringless Casting, and Traditional Casting Techniques: An In vitro Study

Purpose:

The purpose of the study is to determine the amount of marginal discrepancy produced by Co-Cr copings fabricated using various fabrication methods which include direct metal laser sintering (DMLS), computer-aided milling, traditional casting, and ringless casting and compare the values obtained between each fabrication technique and to evaluate if the fabrication technique can produce prosthesis that is within the standards of clinical acceptance of marginal discrepancy.

Materials and Methods:

Ten metal copings were fabricated by DMLS, computer-aided milling, traditional casting, and ringless casting. Marginal gap at the buccal, lingual, mesial, and distal areas was measured using silicone replica technique. A digital microscope was used to measure the silicone layer. Statistical analysis was done using one-way ANOVA test and post hoc Bonferroni test to test the difference between the fabrication method and categories of measured points, respectively.

Results:

The values indicate that the marginal gap was least for the copings fabricated using ringless casting followed by traditional casting and DMLS. The widest gap was seen in copings fabricated using computer-aided milling. Analysis of results showed statistically significant difference between copings fabricated using computer-aided milling and traditional casting (P = 0.029 and 0.043 – mesial and distal, respectively) and computer-aided milling and ringless casting (P = 0.002 and 0.001 – mesial and distal, respectively).

Conclusion:

Even though the marginal gap was found to vary with the fabrication method, all measurements of marginal gap of all groups were well within the standard clinical acceptance of 120 μ.

Immunohistochemical Evaluation of Peri-Implant Soft Tissues around Machined and Direct Metal Laser Sintered (DMLS) Healing Abutments in Humans

Background: Direct metal laser Sintering (DMLS) is an additive manufacturing technique that allows fabrication of dental implants and related components with a highly porous surface. To date, no human studies have investigated the soft tissue adhesion and presence of inflammatory infiltrate with porous DMLS healing abutments (HAs), nor have they compared these with the classic machined ones. Purpose: To evaluate the degree of cell adhesion (integrin expression) and the quantity/quality of inflammatory infiltrate, on HAs with different surfaces; full DMLS, full machined, and hybrid (half DMLS and half machined). Methods: Fifty implant patients were randomly assigned to receive one of these different Has: T1, full DMLS (11 subjects); T2, machined in the upper portion and DMLS in the lower one (10 subjects); T3, DMLS in the upper portion and machined in the lower one (19 subjects); T4, full machined (10 patients). Thirty days after placement, circular sections of soft tissues around HAs were retrieved for immunohistochemical evaluation. Results: With regard to the adhesion molecules, the samples showed different intensity of integrin expression, with a statistically significant difference (p < 0.001) between T1 and the other groups. All the samples were positive for the different clusters related to the inflammatory infiltrate (T lymphocytes, CD3; B lymphocytes, CD20; and macrophages, CD68), but a lower infiltrate was found in T1, with statistically significant differences (p < 0.001) among the groups. Conclusions: The HA surface seems to influence the degree of cell adhesion and the inflammatory infiltrate of the surrounding soft tissues.

Design, Development and FE Thermal Analysis of a Radially Grooved Brake Disc Developed through Direct Metal Laser Sintering

The present research work analyzed the effect of design modification with radial grooves on disc brake performance and its thermal behavior by using additive manufacturing based 3D printed material maraging steel. Temperature distribution across the disc surface was estimated with different boundary conditions such as rotor speed, braking pressure, and braking time. Design modification and number of radial grooves were decided based on existing dimensions. Radial grooves were incorporated on disc surface through Direct Metal Laser Sintering (DMLS) process to increase surface area for maximum heat dissipation and reduce the stresses induced during braking process. The radial grooves act as a cooling channels which provides an effective means of cooling the disc surface which is under severe condition of sudden fall and rise of temperatures during running conditions. ANSYS software is used for transient structural and thermal analysis to investigate the variations in temperatures profile across the disc with induced heat flux. FE based thermo-structural analysis was done to determine thermal strains induced in disc due to sudden temperature fluctuations. The maximum temperature and Von Mises stress in disc brake without grooves on disc surface were observed which can severely affect thermal fatigue and rupture brake disc surface. It was been observed by incorporating the radial grooves that the disc brake surface is thermally stable. Experimental results are in good agreement with FE thermal analysis. DMLS provides easy fabrication of disc brake with radial grooves and enhancement of disc brake performance at higher speeds and temperatures. Therefore, DMLS provides an effective means of implementing product development technology.

Comparative Evaluation of Effects of Laser Modalities on Shear Bond Strengths of Veneering Porcelains to Laser Sintered Substructures: An In Vitro Study

OBJECTIVE

Laser modalities and direct metal laser sintering (DMLS) have a potential to enhance micromechanical bonding between dental super- and infrastructures. However, the effect of different manufacturing methods on the metal-ceramic bond strength needs further evaluation. We investigated the effect of surface treatment with Er:YAG, Nd:YAG, and Ho:YAG lasers on the shear bond strength (SBS) of high-fusion dental porcelains (Vita and G-Ceram) to infrastructures prepared with DMLS in vitro settings.

MATERIALS AND METHODS

Study specimens (n = 128) were randomly divided into study subsets (n = 8), considering treatment types applied on the surface of infrastructures, including sandblasting and selected laser modalities; infrastructure types as direct laser sintered (DLS) and Ni-Cr based; and superstructure porcelains as Vita and G-Ceram. The SBS test was performed to assess the effectiveness of surface modifications that were also examined with a stereo microscope.

RESULTS

Considering laser procedure types, the highest SBS values were obtained by Er:YAG laser, followed by, with a decreasing efficiency, Ho:YAG laser and sandblasting procedures, and Nd:YAG laser procedure (p < 0.05). Nd:YAG laser decreases the bonding of Vita and G-Ceram in all the infrastructures compared with sandblasting. Considering porcelains, the highest SBS values were obtained by Vita (p < 0.05). Considering infrastructures, the highest SBS values were obtained by DMLS procedure (p < 0.05). The laser procedures caused surface irregularities as revealed by the stereo microscopic examination.

CONCLUSIONS

In current experimental settings, Er:YAG laser applied to DLS infrastructure veneered with Vita porcelain increases bonding strength more distinctly, and Nd:YAG laser applied to Ni-Cr-based infrastructure veneered with G-Ceram porcelain alters bonding strength unfavorably.

Osseointegration of Coarse and Fine Textured Implants Manufactured by Electron Beam Melting and Direct Metal Laser Sintering

Osseointegrated implants transfer loads from native bone to a synthetic joint and can also function transdermally to provide a stable connection between the skeleton and the prostheses, eliminating many problems associated with socket prostheses. Additive manufacturing provides a cost-effective means to create patient-specific implants and allows for customized textures for integration with bone and other tissues. Our objective was to compare the osseointegration strength of two primary additive manufacturing methods of producing textured implants: electron beam melting (EBM) (mean Ra = 23 μm) and direct metal laser sintering (DMLS) (mean Ra = 10 μm). Due to spatial resolution, DMLS can produce surfaces with a roughness comparable to EBM. Two cohorts of Sprague-Dawley rats received bilateral, titanium implants in their distal femurs and were followed for 4 weeks. The first-cohort animals received EBM implants transcortically in one femur and a DMLS implant in the contralateral femur. The second cohort received DMLS implants (either fine textured or coarse textured to mimic EBM) in the intramedullary canal of each femur. Osseointegration was evaluated through mechanical testing and micro-computed tomography (bone volume fraction [BV/TV] and bone-implant contact [BIC]). The fixation strength of coarse textured implants provided superior interlocking relative to fine textured implants without affecting BV/TV or BIC in both cohorts. Coarse EBM implants in a transcortical model demonstrated an 85% increase in removal torque relative to the fine DMLS textured implants. The thrust load in the intramedullary model saw a 35% increase from fine to coarse DMLS implants.

Enhanced Injection Molding Simulation of Advanced Injection Molds

The most time-consuming phase of the injection molding cycle is cooling. Cooling efficiency can be enhanced with the application of conformal cooling systems or high thermal conductivity copper molds. The conformal cooling channels are placed along the geometry of the injection-molded product, and thus they can extract more heat and heat removal is more uniform than in the case of conventional cooling systems. In the case of copper mold inserts, cooling channels are made by drilling and heat removal is facilitated by the high thermal conductivity coefficient of copper, which is several times that of steel. Designing optimal cooling systems is a complex process; a proper design requires injection molding simulations, but the accuracy of calculations depends on how precise the input parameters and boundary conditions are. In this study, three cooling circuit designs and three mold materials (Ampcoloy 940, 1.2311 (P20) steel, and MS1 steel) were used and compared using numerical methods. The effect of different mold designs and materials on cooling efficiency were examined using calculated and measured results. The simulation model was adjusted to the measurement results by considering the joint gap between the mold inserts.