Plaster Molds Research Articles

Determinación de un eje hipotético en registros incompletos. Su utilidad para la individualización de las marcas de mordeduras humanas

The purpose of the present work was to analyse the possibility of identifying human teeth marks from a measurement analysis based on the angles formed by the incisors in relation to a hypothetical intercanine axis. The analysis of the validity of this method uses the previously mentioned traces, taking into account the different anatomical areas and the different photographic projections. For the study, the normal bite impression using wax was recorded in fifty student volunteers. This impression was used to make plaster moulds in an articulator. Using this articulator, three bites were inflicted on different areas (shoulder, forearm and hand) of a dummy covered with Plasticine and photographs were taken at different angles (test). The results were analysed statistically to establish a relationship with the real measurement values of each plaster model (control). The application of the so-called “incisal edge method” for the study of the different photographic projections of the teeth marks made in the different anatomical areas gave results with a minimal variation between the control and test values (95% confidence interval). Significant differences were only seen with the lateral incisors (42 and 22).

Properties of Slip‐Cast and Pressureless‐Sintered ZrB2–SiC Composites

In view of the perspective to produce near‐net shapes of ultra‐refractory ceramics, ZrB2–SiC composite were produced by slip casting on plaster mould and pressureless sintered at 2150°C with a holding time of 120 min, using silicon nitride as a sintering aid. After sintering, slip‐cast samples reached a very high relative density over 98%, while for comparison, the density of cold isostatic pressed samples was about 94%. Traces of the formation of secondary phases such as B4C, graphite, and BN were found in all samples, while no grain boundary phases were revealed. RT flexural strength of as‐sintered slip cast bars was affected by the presence of an external porous layer of coarse ZrB2particles, while at 1500°C the flexural strength increased, as a glassy layer sealed the superficial defects. Because of the absence of softening grain boundary phases, subcritical crack growth did not occur during high‐temperature strength tests.

Dimensional Changes of Casting by Lost Foam Casting Process Using Plaster Mold and Sheet Lamination Model

Dimensional Changes of Casting by Lost Foam Casting Process Using Plaster Mold and Sheet Lamination Model

The Initial Practice on Electro-Modification Processes to Al-12Si Alloys

The modification of Si-flakes from coarse acicular to fine fibrous is a common issue in Al-Si alloys casting products. The one of aims of this work is to practice the probability of applying the pulsed electric discharge (PED) to modify the morphology of Si-flakes. In the experiment, the Al-12Si alloy cast in plaster mold was treated with high voltage pulse electric discharge during the solidification. The combined effects of strong pulse electric current and chemical additives of refiner/modifier on solidification structure of eutectic silicon and tensile properties were studied. The experimental results indicated that the eutectic silicon flakes can be fragmentized by high-density pulse electric current. The best tensile properties were obtained when pulse electric discharge was used and combined with a trifle addition of refiner/modifier into the molten metal.

Improvement on the Manufacturing Process of the Dental Surgical Guide Made by a 5-Axis CNC Drill Press

Traditionally, three CT markers are attached to a surgical guide of dental implant surgery to correlate the implant positions in CT images and the drill positions of a drill press. To allow the drill press to know the positions of the CT markers, users need to use the press to probe the positions of them manually. This process is inaccurate and time-consuming. The objective of this research was to develop a new process to eliminate the traditional probing process. This new process uses two identical pairs of locating pins both in the plaster mold cavity and on the fixture of a CNC drill press, respectively. Since the position of the drill bit relative to the locating pins and the positions of the locating pins relative to the CT markers are designed by us, the drill press knows the positions of the CT markers without probing them. According to the preliminary evaluation results, the mean errors of the location and angle of the drilled holes were 0.696 mm and 1.23°, which indicate that this innovative idea presented in this paper is feasible and promising.

A Comparative Study on the Effect of Two Different Investing Mediums on the Movement of Artificial Teeth during the Fabrication of Complete Denture: An in vitro Study

ABSTRACT Purpose Acrylic processing of waxed-up dentures is considered to be a crucial and technique-sensitive procedure. Even after investing a lot of time and clinical skill a definitive movement of teeth during and after processing has long been observed which lead to occlusal discrepancies and disturb the harmonious occlusal scheme achieved earlier. Shifting of the teeth can occur as a result of the investing procedures and investing materials. The objective of this study was to evaluate and compare the movement of artificial teeth in two-dimensions of space (anteroposterior and mediolateral) during processing of the waxed-up dentures using two different gypsum materials for investing. Methods Two groups of 15 waxed-up maxillary dentures were processed using two different investing mediums (a) dental plaster and (b) combination of dental stone core and plaster mold. The artificial teeth movement was measured in the mediolateral and the anteroposterior directions between predetermined reference points before and after processing with the aid of a traveling microscope. The findings were statistically analyzed using parametric t-tests and ANOVA F-test. Results Artificial teeth movement in both the anteroposterior and mediolateral direction was less with the use of investment combination of dental stone core and plaster mold when compared to the conventional method of investing with dental plaster. Conclusion The dental stone core method is superior in view of the fact that it produces significantly less artificial teeth movement than the conventional method. However, neither of the investing methods is successful in completely preventing artificial teeth movement.

Curing Characteristics of Natural Rubber Filled with Gypsum

Abstract This research aims at reutilizing discarded plaster molds by using waste gypsum obtained from these molds as an inert filler in natural rubber. Its effects on curing characteristics were investigated in comparison with commercial gypsum and calcium carbonate. These fillers were characterized by an X-ray diffractometer before being mixed with natural rubber at various amounts. Several ingredients necessary for curing via sulfur system were also incorporated. The rubber compounds were then tested for their curing behaviors using a moving die rheometer to investigate the effects of the fillers. The results show that when filler loadings increased the maximum and minimum torques of the compounds increased accordingly while the scorch time and 90% cure time steadily decreased. The cure rate index of the NR-filled compounds was clearly affected by the filler especially when commercial and waste gypsums were used.

Plaster Mold Process Using Pattern Produced by Laser Beam Stereolithography

Plaster Mold Process Using Pattern Produced by Laser Beam Stereolithography

Influence of the mode of nutritive and non-nutritive sucking on the dimensions of primary dental arches

Sucking is innate in both infants and young children. It is termed nutritive when referring to suckling from the breast or bottle-feeding and non-nutritive when applied to sucking of a digit or pacifier. Few studies have attempted to assess the impact of the type of sucking on the size of the dental arches. The aim of this study was to quantify the influence of the mode of nutritive suckling and non-nutritive sucking habits (NNSH) on the measurements of the dental arches. This was a transverse descriptive study involving 226 Senegalese children. The mode of feeding and the presence or not of a NNSH (digit or pacifier) were gathered from parents of all children using a structured questionnaire. Quantitative variables regarding intra- and inter-arch relationships were recorded using plaster moulds taken from the children. Statistical analyses were used to compare the different variables according to gender, the mode of feeding and the presence or not of a NNSH. The subjects in the study (123 boys and 103 girls) were aged between 5 and 6years old. The children who had enjoyed mixed feeding (breast/bottle combination) had a great length of the anterior maxillary arch and a significantly greater depth of the palatal arch than children receiving breast-feeding alone. The children with antecedents or a current NNSH had a longer anterior maxillary arch than subjects with no NNSH (P=0.01). Regarding inter-arch relationships, the children with antecedents or a current digit-sucking habit had less overbite than their peers who had no NNSH (P=0.04). The results of this study show that bottle-feeding, even partial, as well as NNSH are associated with changes in certain dimensions of the maxillary dental arch and in inter-arch relationships. Longitudinal studies are required to investigate further the nature of this association.

Individual Earmuff During Reconstruction of the Auricle

Auricular reconstruction represents one of the most demanding challenges in craniofacial surgery. But some of the complications may be stimulated by trauma or continuing pressures. Therefore, earmuff is important to the reconstructed ears as a protective guard. The widely used traditional earmuff was designed by Tanzer and Chaisson. We renovated a more comfortable and much safer individual earmuffs using a low-temperature thermoplastic splint. The low-temperature thermoplastic splint was softened by hot water at 60°C to 70°C. Afterward, the low-temperature thermoplastic splint was stretched over an oval plaster mold. Then, it was fabricated, followed by trimming of the excess material, leaving a quarter-inch flange attached to the cup. Individualized adjustment of the earmuff was performed by immersing in hot water at 60°C to 70°C. When intenerated, it was placed around the reconstructed ear for 10 to 15 minutes until completion of shaping could be achieved. Finally, the earmuff was fixed with elastic band, which was based on the size of child's head circumference and could be adjusted for the patient's comfort. The individualized earmuff was applied in more than 400 patients after surgery of microtia reconstruction. Such individualized earmuffs are proved to provide sufficient protection, while leaving no major problems. The individual earmuff provides effective protection, secure fit, and comfort for the reconstructed ear.

The Development of a Rapid Prototyping Prosthetic Socket Coated with a Resin Layer for Transtibial Amputees

This article proposes a type of transtibial socket composed of an inner layer fabricated by a rapid prototyping (RP) machine and an outer layer coated with unsaturated polyester resin. This work integrates contemporary technologies including a handheld scanner and CAD systems, to design a thin primary socket shape and then manufactures the socket using a fused deposition-modeling machine. To prevent breakage caused by the layer-based forming process and to reinforce flexural strength, the current research coats the preliminary RP socket with a layer of unsaturated polyester resin. After shaping the proximal brim of the resin-reinforced RP socket to match the specific stump, this study assembles and aligns a shank and a prosthetic foot to form a prosthesis set. After completing a trial safety walk wearing the prosthesis, which is satisfactory to the amputee and a registered prosthetist, this research measures interface pressures between the stump and the resin-reinforced RP socket. Experiment results demonstrate that the resin-reinforced RP socket is applicable for transtibial amputees. In addition to strengthening the FDM socket and producing consistent socket fit, this study also demonstrates a feasible procedure that employs current technologies to design and manufacture transtibial sockets without plaster moulds.

Slip Casting of ZrB2–SiC Composite Aqueous Suspensions

AbstractSlip casting of concentrated aqueous suspensions was set up as forming technique for the production of crucibles from ZrB2–SiC composite powder. The dispersion effectiveness and the effect on the final microstructures of two commercial ammonium polyacrylates (Duramax D3005 and Dolapix PC33) used as dispersants were investigated. The first goal was pursued by evaluating the zeta potential of the powders in water at different concentrations of additives, while the second one was assessed by analyzing the microstructure. Duramax D3005 resulted more effective than Dolapix PC33 in electrostatically stabilize the suspensions. Correspondently, almost homogeneous microstructures and lower final porosity of the sintered crucibles were obtained with Duramax D3005, while ZrB2 layers on the vertical surfaces initially in contact with the plaster molds were observed using Dolapix PC33. Moreover, the use of this latter dispersant did not allow the preparation of thick crucible walls due to the sample rupture during the binders pyrolysis stage.

S0402-1-5 窒化アルミニウムの泥しょう鋳込み成形とミリ波焼結([S0402-1]粉末成形とその評価(1))

Aluminum nitride powder is dispersed non-aqueous slurry systems and casted on plaster molds. The compacts are de-binded in vacuum at 823 K, then sintered 28GHz milli-wave sintering furnace at 2023 to 2148K for 60mim. Sintered compacts reach almost full density, but there are several defects in appearances (cracks) and microstructures (white layer parallel to casting direction, and convection mark). Cracks and convection mark may be introduced by unstable heating of the furnace and temperature gradient in the specimen during heating.

Zirconia toughening of mullite–zirconia–zircon composites obtained by direct sintering

Although multi-phase ceramic materials were always used, nowadays composite materials have an important industrial and technological role, because they enlarge the design capability of the manufacturer in properties and behaviors. Some mullite–zirconia–zircon composites were recently processed and characterized which presented satisfactory properties for structural applications under severe chemical and thermomechanical conditions. The objective of the present work is to study the influence of the starting composition in the mechanical and fracture properties of mullite–zirconia–zircon composites, with different microstructures, obtained by direct sintering of binary mixtures of electrofused mullite–zirconia (MZ) and micronized zircon. The materials were consolidated by slip casting of concentrated aqueous suspensions in plaster molds from a wide range of powder compositions (between 15–85 wt% and 85–15 wt% of the two raw materials used). Flexural strength ( σ f), dynamic elastic modulus ( E), toughness ( K IC) and fracture surface energy ( γ NBT) were evaluated. The results were explained by microstructure and the XRD-Rietveld analysis. At low proportion, the zircon was thermally dissociated. The ZrO 2 was a product of this reaction and also influenced the mechanical and fracture properties of these materials through several combined mechanisms, principally as a result of the development of microcracks due to the volume change of the zirconia grains caused by the martensitic transformation during the cooling of these composites from sintering temperature. Composites prepared with higher MZ in the starting powders showed a higher fracture toughness and initiation energy. Microstructure consisting of mullite as a continuous predominant phase in which zircon and zirconia grains were distributed showed better mechanical and fracture properties.

Rhinoplasty: A Hands-On Training Module

Rhinoplasty is a complex surgical procedure with a steep learning curve and a small margin for error. The authors present a hands-on, anatomically correct, silicone training model designed specifically for learning the technical aspects of rhinoplasty. Computed tomographic data were acquired and used to create a plaster mold. Silicone was cast into this mold to create an operable, realistic, three-dimensional silicone model. The prototype created an anatomically accurate rhinoplasty training model. The silicone materials simulate the properties and behavior of the anatomical structures of the nose. A realistic three-dimensional silicone nasal model has the potential to be used as a hands-on training module for learning rhinoplasty and assessing surgical competency.

Thermal expansion of zirconia–zirconium titanate materials obtained by slip casting of mixtures of Y-TZP–TiO 2

The objective of this work was to establish the optimum conditions to get zirconia materials with different proportions of zirconium titanate by reaction sintering of ZrO 2 stabilized with 3 mol% of Y 2O 3 (Y-TZP) and TiO 2. The green bodies were fabricated from stable colloidal suspensions of the powders by slip casting in plaster moulds. The rheological characterization of the suspensions allowed the establishment of the optimum green processing conditions. Reaction sintering was performed at 1500 °C during 2 h, and the obtained materials have been characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy with energy dispersive X-ray microanalysis (FE-SEM-EDX). Under these conditions, zirconium titanate materials with tetragonal zirconia could not be obtained because a solid solution of cubic zirconia with titania and yttria is formed at 1500 °C. The thermal expansion of the materials was determined by differential dilatometry from room temperature up to 850 °C, demonstrating that the incorporation of zirconium titanate reduces the thermal expansion of zirconia.

Mechanical and fracture properties of zircon–mullite composites obtained by direct sintering

Refractory materials based on zircon (ZrSiO 4) are applied in high temperature applications (1400–1500 °C). They are demonstrated to have an excellent chemical attack resistance, such as corrosion or degradation due to molten glass or metals. On the other hand mullite (3Al 2O 3⋅2SiO 2) is important both in traditional and advanced ceramics. Although multi-phase ceramic materials were always used, nowadays composite materials have an important industrial and technological development, to enlarge the designing capability of the manufacturer in properties and behaviors. The objective of the present work is to study the influence of the starting composition on the mechanical and fracture properties of zircon–mullite composites obtained by direct sintering of consolidated samples by slip cast of concentrated aqueous suspensions in plaster molds. Zircon–mullite composites using 15–45 wt% mullite were prepared and compared with pure zircon material obtained in the same conditions. Flexural strength ( σ f), dynamic elastic modulus ( E), toughness ( K IC) and initiation fracture surface energy ( γ NBT) were evaluated. The results were explained by microstructure and the XRD analysis. The presence of mullite increased the zircon thermal dissociation. The ZrO 2 was a product of this reaction and also influence the mechanical and fracture properties of these materials through several combined mechanisms. Zircon composites prepared with 45 wt% of mullite in the starting powder showed a higher fracture toughness and initiation energy than ceramics derived from pure zircon. Microstructure consisting in mullite as a continuous predominant phase in which zircon and zirconia grains were distributed improved almost all the mechanical and fracture properties.

VALORIZATION OF PLASTER MOLDS WASTE FROM FINE CERAMIC INDUSTRY

The Environment Action Program foresees the development of a Thematic Strategy concerning the sustainable use of natural resources and waste management (Report EUR 21002 EN, 2004). In this context, the activities regarding the research and industrial development related to waste valorization through recycling and reusing have been grown. The wastes resulted from the fine ceramic technological process (scraps, used molds etc.) may be valorized. The used molds can be valorized in other technological processes if the content in calcium sulfate semi-hydrate is framed within the limits imposed by the respective technology. The enhancement of the semi-hydrate can be achieved by a dehydration process in accordance with the chemical transformation in the system CaSO4.2H2O CaSO4. In this paper, the thermodynamic potential of dehydration of the used plaster molds resulted from the manufacture of household ceramic products is studied. If a 60 minutes time is considered as an efficient dehydration time, one may observe that regardless the dehydration temperature, the content of semi-hydrate in the obtained plaster is around 86 %. Such a product can be used as plaster for construction, for modeling or for fertilizer conditioning.

Interexaminer Variance of Median Nerve Compound Muscle Action Potential Measurements in Hand Position With and Without Fixation in Plaster

We examined how hand fixation affects interexaminer variance in measuring compound muscle action potential (CMAP) during nerve conduction studies of the median nerve. Subjects comprised 6 experienced examiners [1 woman and 5 men; mean (SD) age, 38.3 +/- 8.5 years; range, 28-46 years]. The standardized median nerve motor conduction setting was used for electromyography. The mean of 5 serial stimulations was taken as 1 examination for each subject. Distal latency, conduction velocity, and peak-to-peak amplitude of CMAP were measured as parameters. Subjects were examined without hand fixation and with hands fixed in prepared plaster molds. Fixation yielded significantly decreased coefficient of variance for CMAP amplitude (5.0% +/- 3.4%) compared with measurement without fixation (8.4% +/- 3.7%; P = 0.028). No differences in distal latencies or conduction velocities were evident between fixation and nonfixation. This study provides quantitative evidence for empirical observations that hand fixation might decrease CMAP variability in median nerve studies.

Manufacture of hydroxyapatite beads for medical applications

Dense, microporous and macroporous hydroxyapatite spherical granules for medical applications were prepared by a new manufacturing procedure. This process is related to a lost wax method and yields beads with a fully controlled porosity, in terms of shape and pore size. A CaCO 3 scaffold exhibiting controlled size spherical cavities is impregnated with an aqueous hydroxyapatite suspension. After drying in a plaster mould, a thermal treatment destroys the carbonate scaffold and makes it possible to release the HA beads. By this process, HA beads with diameters in the range of 300 μm to 3 mm are obtained. A post-thermal treatment of the beads allows the ceramic to be densified at various densification levels. Porous ceramics make it possible to functionalise the hydroxyapatite granules by loading the structure with biologically active substances. Drug releasing kinetics in continuous distilled water flow were analysed as a function of time and ceramic porosity. Spheres continue to release the biological molecules for more than 5 days.