Lost-wax Research Articles

Effect of different digital technology on the adaptation and retention of Co-Cr partial denture frameworks.

To evaluate the overall adaptation and retention of class I cobalt-chromium (Co-Cr) removable partial denture (RPD) frameworks using three different computer-aided design and computer-aided manufacturing (CAD-CAM) technologies: Indirect wax milling with lost wax technique (LWT), direct milling, and selective laser melting (SLM) technique. An educational maxillary stone model (Kennedy class I) was scanned after preparing rest seats to create a resin model. The resin model was scanned, and the RPD framework was digitally designed and saved as a standard tessellation language (STL) file. Twenty-four Co-Cr RPD frameworks were then constructed and divided into three groups (n = 8) based on fabrication technique: Group A (indirect wax milling with LWT), Group B (direct milling), and Group C (selective laser melting). In Group A, the STL file was used to mill the design from castable resin blanks which were then cast by the LWT. In Group B, the STL file was used to mill the design from the Co-Cr blank directly. Finally in Group C, the STL file was used to print the design from Co-Cr powder using SLM 3D printed technique. Geomagic Control X software was used to measure the overall adaptation of the fabricated RPD frameworks, Retention was also tested using a universal testing machine. One-way Analysis of Variance (ANOVA) test was used to compare the three groups then the Tukey HSD post-hoc test was used for pair-wise comparisons. The significance level was set at p ≤ 0.05. Regarding the overall adaptation, Group B (0.71±0.02mm) showed significantly higher adaptation than Group A (0.96±0.06mm) and Group C (1.05±0.16mm). Regarding retention, Group B (2.03±0.34 N) showed significantly higher retention than Group A (1.00±0.13 N) and Group C (0.78 ±0.17 N). Based on the findings of this in vitro study, Co-Cr RPD frameworks fabricated by direct milling technique revealed the best adaptation and retention.

Fit accuracy in the rest region of RPDs fabricated by digital technologies and conventional lost-wax casting: a systematic review and meta-analysis

BackgroundDigital technologies have recently been introduced into the fabrication of removable partial dentures (RPDs). However, it is still unclear whether the digitally fabricated RPDs fit better than conventionally cast ones in the rest region. The aim of this study was to evaluate the fit accuracy in the rest region of RPDs fabricated by digital technologies and compare it to those made by conventional lost-wax (CLW) technique.MethodsA comprehensive search was conducted in Cochrane Library, PubMed, EMbase, Web of Science and SpringerLink. Studies published up to August 2022 were collected. Two authors analyzed the studies independently and assessed the risk of bias on the modified methodological index for non-randomized studies (MINORS) scale. The mean values of gap distance between rests and corresponding rest seats of each study were extracted as outcome. A random-effects model at a significance level of P < 0.05 was used in the global comparison and subgroup analysis was carried out.ResultsOverall, 11 articles out of 1214 complied with the inclusion criteria and were selected, including 2 randomized controlled trials (RCTs), 1 non-randomized clinical trial and 8 in vitro studies. Quantitative data from Meta-analysis revealed that fit accuracy in the rest region of RPDs fabricated with CLW showed no statistically significant difference with digital techniques (SMD = 0.33, 95%CI (-0.18, 0.83), P = 0.21). Subgroup analysis revealed a significantly better fit accuracy of CLW-fabricated RPDs in the rest region than either additive manufacturing (AM) groups or indirect groups (P = 0.03, P = 0.00), in which wax or resin patterns are milled or printed before conventional casting. While milled RPDs fit significantly better than cast ones in the rest region (P = 0.00). With digital relief and heat treatment, hybrid manufactured (HM) clasps obtained better fit accuracy in the rest region (P < 0.05). In addition, finishing and polishing procedure had no significant influence in the fit accuracy in all groups (P = 0.83).ConclusionsRPDs fabricated by digital technologies exhibit comparable fit accuracy in rest region with those made by CLW. Digital technologies may be a promising alternative to CLW for the fabrication of RPDs and additional studies are recommended to provide stronger evidence.Trial registrationCRD42020201313.

Identification of Fazael 2 (4000–3900 BCE) as first lost wax casting workshop in the Chalcolithic Southern Levant

Apart from many lost wax cast metal fragments, crucible fragments and several heated sediment nodules were found at the Chalcolithic site Fazael 2 (central Jordan Valley). Petrographic investigations on the heated sediment nodules revealed many features characteristic of the Chalcolithic Southern Levantine lost wax casting moulds. Heating temperatures were assessed using infrared spectroscopy, showing that casting did not vitrify the clay fraction in the moulds. Consequently, Fazael is the first identified Chalcolithic Southern Levant production site for lost wax cast metal items. These findings confirm the existence of a metallurgical tradition with lost wax casting in the Jordan Valley parallel to the unalloyed copper metallurgy in the Northern Negev. Moreover, crucibles and heated sediment nodules are made of local ferruginous loess, a material not mentioned in previous studies on lost wax casting mould fragments. Therefore, the existence of more than one such production site must be assumed.

First evidence for alloying practices in the Chalcolithic Southern Levant (4500–3800 BCE) as revealed by metallography

Excavations at the Chalcolithic site Fazael in the central Jordan Valley uncovered a large number of metal items, many of them polymetallic copper alloys cast in the lost wax technique. Metallography and SEM–EDS analysis on a subset of the assemblage confirm previous notions of the lost wax metallurgy in the Chalcolithic Southern Levant but extend them significantly in three aspects: The Fazael metal assemblage is slightly depleted in its arsenic content compared to metal assemblages from other sites, silt-sized quartz inclusions in unalloyed and polymetallic copper items, and the presence of unalloyed copper inclusions. These latter provide the earliest direct evidence for mixing of different metal types in West Asia, potentially alloying or recycling.

EMPHASIS ON VISUAL AND TACTILE EXPERIENCES: MECHANICAL TREATMENTS OF BRONZES AND JADES IN ANCIENT CHINA

AbstractThis article presents fresh evidence and arguments regarding the historical study of sensory experience through a focus on the mechanical treatments of bronzes and jades in ancient China. The techniques employed to polish and engrave hard bronze surfaces before the invention of iron tools that are harder than bronze remain a mystery. The article provides new insights into engraved/chiseled bronze inscriptions, which can be too easily dismissed by connoisseurs as fake. Through a focus on post-processing techniques for cast bronze objects made before 1 b.c.e. in China and exchanges of techniques between bronze producers and jade workers, I argue that some of the traces found on bronze objects that may have been left by working with abrasives such as those used in lapidary industry demonstrate that lapidary techniques and post-processing of cast bronze objects were interrelated. Investigations as to how bronze and jade producers interacted show that they aimed to improve the visual and tactile experiences for their customers or patrons. Active and frequent exchanges of ideas and techniques took place between the bronze and jade production communities. Their emphasis on visual and tactile experiences demonstrates how such industrial powers developed in ancient China and how they were sustained throughout the last two millennia b.c.e.

Bronze producing tool of the first half of the 1st century BC from West Georgia

The Article is a discusses of the scientific research process of operating principles of bronze producing tools- crucibles discovered by archeologists in Sachkhere region, village Sairkhe, at Sakhoveli metallurgical spot in 1968. These artefacts always attracted attention due to their original form. But for scientists, it remained a mystery that despite of abundance of crucibles and cast bronze objects of different purposes revealed at Sairkhe site during the archeological excavations, the presence of high temperature producing furnace for metal melting, where these crucibles could have been placed, has never been discovered. As a result of multiple experiments and based on the reliable scientific arguments, we were able to determine that the metallurgists from Sairkhe possessed totally original method of bronze production. They created such type of crucibles that didn’t need big furnaces producing high temperature. Melting and alloying copper for producing bronze was possible with these crucibles themselves, thus making the most complicated and expensive metallurgical cycle, simple and cheap.

Mechanisms of influence of modifiers on crystallization of tin and aluminium bronzes

It has been shown that elementary crystalline cells of α‑phases of tin, aluminum bronzes and main modifying phases do not correspond to the principle of structural and dimensional correspondence of Dankov‑Konobeevsky. Modifying structures in tin and aluminum bronze castings is a nanostructured process. The main role of tin and aluminum bronze modifiers is to significantly reduce the concentration of adsorbed hydrogen, which prevents the formation of crystallization centers of α‑phase microcrystals in castings when they solidify.

Fit and Retention of Cobalt-Chromium Removable Partial Denture Frameworks Fabricated with Selective Laser Melting.

To evaluate fit and retention of cobalt-chromium removable partial denture (RPD) frameworks fabricated with selective laser melting (SLM). Three types of framework for clasp-retained RPDs were virtually designed and fabricated using SLM (n = 30). For comparison, 30 additional frameworks were produced using conventional lost-wax casting. A biomechanical model was created, incorporating extracted teeth mounted on flexible metal posts. Using this model, horizontal constraint forces resulting from a misfit were measured using strain gauges, while vertical forces were not recorded. The constraint force components and resultant forces were determined for all abutment teeth, and the maximum retention force during RPD removal from the model was also assessed. For statistical evaluation, the two fabrication methods were analyzed by calculating the means and standard deviations. The average horizontal constraint forces showed similar values for both fabrication methods (SLM: 3.5 ± 1.0 N, casting: 3.4 ± 1.6 N). The overall scatter of data for cast RPDs was greater compared to those fabricated using SLM, indicating a better reproducibility of the SLM process. With regard to retention, the intended retention force of 5-10 N per abutment tooth was not attained in one of the cast groups, while it was consistently achieved in all SLM groups. This in vitro study found that SLM is a promising option for the manufacture of cobalt-chromium RPD frameworks in terms of fit and retention.

Частично разрушенные сарматские погребения Есауловского Аксая (ограбление или ритуальное осквернение?)

Introduction. The article is devoted to the problem of the partial robbery of the high-status Middle Sarmatians burials analyzed in the Esaulovsky Aksai River floodplain. The analysis of the burial complexes near the village named Kovalevka revealed an interesting feature. There was partial destruction of the buried Sarmatians bones, but, at the same time, the parts of the bones and accompanying burial equipment remained undisturbed. Typically, these burials had some status artifacts like bronze cast and forged cauldrons, weapons and horse harness items, and ceramics from the Central Caucasus, Kuban, and Lower Don Valley. Methods and materials. The objects of research were not only burials from Kovalevka but also synchronic burial complexes from Zhutovo, Aksai, Peregruznoe, and Oktyabrsky. The research involves using both traditional general scientific methods, including chronological and spatial analysis, and special archaeological research methods, including formal typological, cartographic, and analogy methods, which describe the scientific facts and reconstruct ethnocultural processes. Analysis. These burials are characterized not only by dead-drops under an individual mound but also by a special inventory, where, except for the swords and arrows, there were also spearheads, two-part bits with rodshaped psalms, and horse bones. At the same time, the synchronic Early Sarmatian complexes found in the burial mounds were left intact. Such partial robbery of the high-status Middle Sarmatians burials is also fixed when expanding the area of the neighboring burial grounds of the Esaulovsky Aksai River basin. This observation suggests that a group of well-armed nomads with slightly different traditions characteristic of the Middle Sarmatian culture appeared on the studied territory occupied by the Early Sarmatian population at the turn of the era. Migrants who founded their cemeteries in the floodplain of the Esaulovsky Aksai River aroused the anger of the local Sarmatian groups, which led to the burials desecration of the aliens. Results. We can assume that at the end of the 1st century BC and the beginning of the 1st century AD, in the Don-Volga interfluve, there was a struggle for control over an important transit zone, as indirectly evidenced by a significant number of prestigious imported items discovered in the burials of the investigated territory. Key words: Early Sarmatians, Middle Sarmatians, burial, robbery of burials, Don-Volga interfluve.

Between piece molds and lost wax: the casting of a diatrete ornamentation in early China rethought

For a long time, research on the pre-Han (before 202 BCE) Chinese use of the lost-wax process was targeted at demonstrating that it was of no use at all. That position was severely shaken when the zun-pan set of Zeng Hou Yi (“Marquis Yi of Zeng,” d. 433 BCE) was unearthed at Hubei Suizhou in 1978, along with subsequently excavated finds or rediscovered artifacts carrying similarly interpenetrating openwork. Since the early 2000s, however, there has been a persistent revival of a research orientation against the use of the lost-wax process in Bronze Age China. After surging first in Chinese academia, the new tide took some time to arrive in the West. A response to Donna Strahan’s prestigious lecture, “Debating the Use of Lost-wax Casting in Ancient China,” this article presents my thinking about lost wax versus piece molds in early Chinese casting practices. Strahan’s studied “diatrete” ornamentation in the Metropolitan Museum of Art, to me, can be securely identified as lost-wax cast thanks to some telltale traces. Through this critical investigation, I invite my fellow art historians, archaeologists, and historians of metal technology to emerge from the “doubting of lost wax” era to tackle new challenges in early Chinese archaeo-metallurgy.

Effect of printing parameters on extrusion-based additive manufacturing using highly filled CuSn12 filament

Typical additive manufacturing (AM) processes for producing metal and ceramic parts are highly energy-consuming and expensive to install and maintain. On the other hand, material extrusion AM (MEAM) technologies are conventionally used to produce polymeric parts but only marginally to process metallic materials. A feasible alternative is to process polymeric filaments loaded with metal particles. Debinding and sintering processes are then required to join the metal particles and obtain the final parts. In recent years, highly filled metal filaments consisting of a polymer loaded with a high concentration of metal powder have been commercialized for this purpose. In this study, the printability of a commercial CuSn12 filament was investigated by evaluating the influence of the process parameters on the density, shrinkage, porosity, and mechanical properties of the additively manufactured samples using a low-cost desktop 3D printer. Parameters such as the flow rate and ironing had the greatest influence on the density of the green samples. The correct selection of these parameters may reduce shrinkage after sintering. Furthermore, the obtained bronze had a notable ultimate tensile strength (mean value of 107 MPa), high stiffness (E values range from 38 to 50 GPa), and a greater elongation at break (mean value of 13%) than that of cast bronze of the same CuSn12 type. In this case, the extrusion pattern and ironing had the most significant influence on the final mechanical performance. The study provides insights into the use of highly filled bronze filaments combined with MEAM to produce functional parts for engineering applications.

Materials and manufacturing techniques for occlusal splints: A literature review.

To review the materials and fabrications methods of occlusal splints with their advantages and shortcomings and to clarify the indications for each. Temporomandibular joint disorders (TMDs) encompass a range of conditions affecting the masticatory system. Occlusal splints are currently recognized as a viable option for the management of TMDs when they are adopted in conjunction with additional approaches varying from conservative procedures (counseling, biofeedback, physical therapy, pharmacotherapy) to irreversible and less conservative ones (occlusal adjustments, orthodontics, arthroscopy, and surgery). These splints can vary in design, function, and material. The components used to fabricate the splints must withstand occlusal forces, be aesthetically pleasing, comfortable, and minimally interfering with function and phonetics. Traditional methods for fabricating splints include sprinkle-on, thermoforming, and lost wax techniques. However, with the advancement of CAD/CAM technology, additive (3D printing) and subtractive (milling) manufacturing methods expand the range of possibilities by introducing novel solutions for elaborating splints. An electronic search was conducted on PubMed using the following keywords: "occlusal splint", "guard and "materials", and "manufacturing". Thirteen in vitro publications were screened and they consisted of four clinical studies, nine reviews (three of them were systematic reviews), and five case reports. The choice of material is crucial for the success of splint therapy. Factors such as biocompatibility, ease of fabrication, adjustability, cost, and patient preference should be considered. Newer materials and techniques are emerging because of advancements in material science and manufacturing techniques. However, it should be noted that most of the evidence is based on in vitro studies with different methodologies, limiting their validity in daily practice.

The improvement of operational properties of the parts of means of transport by applying regular reliefs

Problem. Specially created regular surface reliefs strongly influence the reliability and operational properties of machine parts. One of the effective methods of obtaining reliefs is cold plastic deformation (CPD). This method of modification does not lead to the occurrence of significant stresses in the material of the part and can be form-forming. The latter is important in repair production. However, to date, there is no systematic study of the formation of reliefs by CPD methods, especially with the use of linear indenters. Goal. To improve the operational properties of the parts of means of transport by applying regular micro- and macro-reliefs of technological and operational purposes by deepening linear indenters. Methodology. Press hydroficated equipment was used to create a normal indenter penetration force. The brands of typical structural materials are defined: steel, gray cast iron, bronze, brass, aluminum and titanium alloys. A linear indenter made of high-speed steel with angles at the top of 60° - 90° and a radius at the base of 0.005 - 0.5 mm was created. Methods of microstructural analysis and microhardness, standard and original instruments and devices were used. The range of groove depths was 0.02-0.5 mm. A lubricating-cooling liquid based on rapeseed oil was used. Results. It was hypothesized that when the indenter is immersed in the material of the part, the factors that have the greatest influence on the depth and other parameters of the relief groove are the normal strength, hardness, and relative elongation of the material under study. These theoretical principles formed the basis of the mathematical model of the indentation process. Originality. It was created a classification of regular reliefs by purpose: for preliminary division of the allowance during cutting; for preparing the surfaces of parts for applying coatings, including anti-friction films; to create labyrinths on the surface of parts for lubricants; for preliminary separation of fragmentary ammunition cases; to create strengthened new load-bearing surfaces, in particular, discrete when restoring worn parts; to obtain complex profiles on the surfaces of the holes of the parts. The calculation of the impact of the indentation force and the geometric parameters of the linear indenter on the shape and dimensions of the relief groove has been developed. Theoretical propositions about the influence of the embedment force, hardness and plasticity of the material of the part on the parameters of the relief groove were experimentally confirmed. These factors affect the optimization parameter both directly and through intermediate factors: the radius of rounding and the angle at the top of the indenter and the composition of the lubricating and cooling liquid and the speed of immersion. The interrelationship of phenomena during the formation of reliefs and the dependence of the depth of the groove on the process factors are constructed. Practical value. The method of restoring worn parts by indenting a linear indenter was developed, the principle of obtaining discrete surfaces of machine parts by alternating relief grooves with flat areas within a discreteness of 5-50% and methods of obtaining shaped surfaces in the holes of hollow parts by copying were developed.

Analytische Methode zur Berechnung der Nennspannungen im Zahnfuß von Schneckenwellen

AbstractAccording to the state of the art, worm gears are designed due to the softer bronze-material of the worm wheel primarily against damage of the wheel because of wear, pitting or breakage of the teeth. The aim of research in the last decades is to optimize the load capacity on the worm wheel by using higher-strength bronze alloys, cast iron or steel to increase the transmission capacity of worm gears. This development may lead to an increased number of damage cases on the worm shaft. In literature, documented cases of tooth segment fractures of the worm shaft can already be found. Since the worm is only designed against deflection according to the state of the art, there is a need for a method to calculate the material stress in worm shafts. This paper presents an analytical method based on the nominal stress approach for calculating bending, compression, and shear stresses in the tooth root of worm shafts to close this gap. The stresses resulting from different load distributions in the tooth contact due to assembly deviations are calculated with the presented method and compared with results from the Finite Element Method.

Digital Evaluation of Trueness and Fitting Accuracy of Co-Cr Crown Copings Fabricated by Different Manufacturing Technologies.

The dentistry industry has seen a number of exciting new advancements in recent years, many of which have been made possible by the introduction of automated technologies such as computer-aided design and computer-aided manufacturing (CAD/CAM). Despite the fact that these new approaches simplify the fabrication process in favor of decreased material consumption and improved time efficiency, it is possible that they may have an effect on the prosthesis's fitness, which in turn may affect how long they will last. The purpose of this in vitro study was to evaluate the trueness and fitness of cobalt-chromium (Co-Cr) crown copings fabricated by selective laser melting (SLM), milling, and conventional casting methods. A zirconium die was fabricated and scanned with a laboratory scanner to manufacture the Co-Cr metal copings for three groups (n = 12). In group A, the copings were fabricated by a 3D printing technique called SLM; in group B, the copings were fabricated by the milling technique; and in group C, the copings were fabricated by the conventional lost-wax method. After fabrication, the trueness and the internal fitness of the copings were evaluated using a metrology software program (Geomagic Control X, 3D Systems Inc., Rock Hill, SC). The one-way ANOVA and Tukey's honestly significant difference test were used to statistically analyze the data. The highest root mean square (RMS) value of trueness was for CAD/CAM milling, and the highest mean of horizontal gaps was for the casted (lost-wax technique) group. There were highly significant differences in the mean RMS value of trueness and the mean horizontal gaps between the three groups. The fabrication method of Co-Cr crown copings has an effect on the trueness and fitness of the copings.

Effect of the CAD-CAM and lost-wax framework fabrication techniques on the fracture strength of porcelain in metal-ceramic restorations.

Ceramic fracture is a common problem in metal-ceramic restorations (MCRs). The advent of computer-aided design and computer-aided manufacturing (CAD-CAM) technology eliminated the lost-wax technique, which was responsible for many of the problems associated with framework fabrication. However, the role of the CAD-CAM technology in decreasing porcelain fracture is not yet known. The aim of the present in vitro study was to compare the fracture strength of porcelain in MCRs with metal frameworks fabricated with the use of the lost-wax and CAD-CAM techniques. Twenty metal dies were prepared with a deep chamfer finish line, with a depth of 1.2 mm and the occlusal taper of the walls of 8°, a 2-millimeter occlusal reduction of the functional cusp, a 1.5-millimeter occlusal reduction of the nonfunctional cusp, and the functional cusp bevel. Ten frameworks were fabricated using the CAD-CAM system and 10 with the lost-wax technique. After porcelain veneering, the specimens underwent thermocycling and cyclic loading to simulate the aging process. The load test was then performed. The fracture strength of porcelain was compared between the 2 groups, and the mode of failure was also determined using a stereomicroscope. Two specimens were excluded from the CAD-CAM group. Thus, 18 specimens were statistically analyzed. The results revealed no significant difference in fracture strength between the 2 groups (p > 0.05). The mode of failure was mixed in all specimens from both groups. Our results indicated that the fracture strength of porcelain and the mode of failure did not depend on the metal framework fabrication technique (lost-wax or CAD-CAM).

Decontamination of lithium disilicate ceramics using various photosensitizers, herbal and chemical disinfectants, and the effect of surface conditioners on bond strength values

AimTo assess and compare the antimicrobial efficacy of disinfectants on lithium disilicate ceramic (LDC) used in dental applications and shear bond strength (SBS) of LDC after using different conditioners hydrofluoric acid (HF), self-etching ceramic primers (SECP) and Neodymium-doped yttrium orthovanadate (Nd: YVO4). Materials and methodsOne hundred and twenty LDC discs were fabricated by auto-polymerizing acrylic resin using the lost wax technique. S. aureus, S. mutans, and C. albican were inoculated on thirty discs (n = 30 each). Each group was further divided into three subgroups based on different disinfecting agents used (n = 30) Group 1: Garlic extract, Group 2: Rose Bengal (RB) activated by PDT, and Group 3: Sodium hypochlorite (NaOCl). An assessment of the survival rate of microorganisms was performed. The remaining thirty samples were surface treated using three different LDC surface conditioners (n = 10) Group 1: HF + Silane (S), group 2: SECP, and Group 3: Nd: YVO4 laser+S. SBS and failure mode analysis were performed using a universal testing machine and stereomicroscope at 40x magnification, The statistical analysis was conducted using one-way ANOVA and Post Hoc Tukey test. ResultsGarlic extract, RB, and 2% NaOCl sample displayed comparable outcomes of antimicrobial potency against C. albicans, S aureus, and S. mutans (p > 0.05). Furthermore, SBS analysis showed HF+S, SECP, and Nd: YVO4+S exhibited comparable outcomes of bond strength (p > 0.05). ConclusionGarlic extract and Rose bengal activated by PDT can be contemplated as alternatives to the chemical agent NaOCl used for LDC disinfection. Similarly, SECP and Nd: YVO4 possess the potential to be used for the surface conditioning of LDC to improve the bond integrity with resin cement.

Hydrogel-Assisted Double Molding Enables Rapid Replication of Stereolithographic 3D Prints for Engineered Tissue Design.

Tissue-engineered in vitro models are an essential tool in biomedical research. Tissue geometry is a key determinant of function, but controlling the geometry of microscale tissues remains challenging. Additive manufacturing approaches have emerged as a promising means for rapid and iterative changes in the geometry of microdevices. However, it has been shown that poly(dimethylsiloxane) (PDMS) cross-linking is often inhibited at the interface of materials printed with stereolithography. While approaches to replica mold stereolithographic three-dimensional (3D) prints have been described, these methods are inconsistent and often lead to print destruction when unsuccessful. Additionally, 3D-printed materials often leach toxic chemicals into directly molded PDMS. Here, we developed a double molding approach that allows precise replication of high-resolution stereolithographic prints into poly(dimethylsiloxane) (PDMS) elastomer, facilitating rapid design iterations and highly parallelized sample production. Inspired by lost wax casting, we used hydrogels as intermediary molds to transfer high-resolution features from high-resolution 3D prints into PDMS, while previously published work focused on enabling direct molding of PDMS onto 3D prints through the use of coatings and post-cross-linking treatments of the 3D print itself. Hydrogel mechanical properties, including cross-link density, predict replication fidelity. We demonstrate the ability of this approach to replicate a variety of shapes that would be impossible to create using photolithography techniques traditionally used to create engineered tissue designs. This method also enabled the replication of 3D-printed features into PDMS that would not be possible with direct molding as the stiffness of these materials leads to material fracture when unmolding, while the increased toughness in the hydrogels can elastically deform around complex features and maintain replication fidelity. Finally, we highlight the ability of this method to minimize the potential for toxic materials to transfer from the original 3D print into the PDMS replica, enhancing its use for biological applications. This minimization of the transfer of toxic materials has not been reported in other previously reported methods describing replication of 3D prints into PDMS, and we demonstrate its use through the creation of stem cell-derived microheart muscles. This method can also be used in future studies to understand the effects of geometry on engineered tissues and their constitutive cells.

Hardness comparison between Co – Cr metal alloy specimens made by different methods

The aim of this study is to compare the hardness of Co–Cr metal alloy specimens made by different methods and how it is influenced by multiple temperature changes. Fifty-four samples are made by three different methods and are accordingly divided in three groups – group M (Milling), group LP (Laser Printing) and group LW (Lost Wax), with 18 samples each. All of them contain three subgroups with six samples – metal samples with no thermal cycles (subgroup 1), metal samples with one thermal cycle (subgroup 2) and metal samples with two thermal cycles (subgroup 3). Their Vickers hardness is evaluated by a weight of 1 kg applied for 20 s. The results are presented in tables. The average hardness is the highest for group LP – 509, followed by group M – 440, and for group LW it is 401. For the subgroups, the best results are exhibited by the samples of subgroup 2 – 430, followed by subgroup 3 – 457, and subgroup 1 – 450.

EFFECT OF REPEATED FIRINGS ON METAL CERAMIC BOND STRENGTH OF CO-CR ALLOY FABRICATED BY DIRECT METAL LASER SINTERING AN IN-VITRO STUDY

Purpose: The bond strength of metal ceramic restorations places a key role for the longevity of the prosthesis which could be affected by the fabrication technique and the number of firings. The current research evaluates the effect of repeated firings on bond strength of metal ceramic systems with copings fabricated from two processing techniques, lost wax technique through induction casting and direct metal laser sintering. Materials and Methods: 21 metal ceramic bars will be fabricated using Direct Metal Laser Sintering (Group DMLS) and 21 using conventional lost wax technique (Group Cast). Each sample will have a dimension of 25x3x0.5mm respectively. In the center of each bar, a 1.1mm thickness of porcelain will be fused onto an 8x3mm rectangular area. Each group is further subdivided into 3 subgroups which are subjected to repeated firings (3, 5, 7) and the bond strength is measured with positioning of the samples on a Universal Testing Machine. Results: Group ANOVA and Post Hoc Tukeys test showed comparison of overall bond strength of ceramic samples fabricated using DMLS &amp; Casting subjected to different Firing was done and the difference in mean was statistically significant (p&lt;0.05). Conclusion: The DMLS group showed slight superior bond strength properties when compared with Cast group.