Uniform Threads Research Articles

Analysis of the Effect of Thread Depth in Four Different Thread Designs on the Stress Distribution at the Implant-bone Interface Using Finite Element Analysis – A Comparative Three-Dimensional In vitro Study

ABSTRACT Statement of Problem: Treatment with dental implants owes much of its success to the development and maintenance of an osseointegrated bone-implant interface. The development of this interface is influenced by various factors, of which implant thread design plays a dominant role. Purpose: The purpose of this study is to analyze the effect of thread depth in four different thread designs on the stress distribution at the implant-bone interface using three-dimensional finite element analysis. Materials and Methods: Four implant models with different thread shapes, namely V thread, square thread, buttress thread, and reverse buttress thread with an uniform thread depth of 0.4 mm were designed. These models were then placed in the mandibular first molar region. Force of 100 N was applied axially and at 45°angle to the implant. Von Mises stress was measured at the implant – Bone interface area and compared for the different designs. Results: The color plots obtained were studied and the maximum Von Mises stress was noted and tabulated for each condition. Stress distribution in the finite element models comes in the numerical values and in color coding. Maximum values of Von Mises stress are denoted by red color and minimum value by blue color. In between, the values are represented by bluish green, green, greenish yellow, and yellowish red in the ascending order of stress distribution. Conclusion: Thread design plays an important role in stress distribution in implant and bone. Varying Von Mises stress is seen at the cortical bone-implant and cancellous bone-implant interface. Clinical Implication: Successful osseointegration is necessary for implant success and thread design plays a very important role in osseointegration. Therefore, the selection of implants with proper thread design contributes greatly to the success of an implant-retained prosthesis.

MH cortical screws, a revolutionary orthodontic TADs design.

MH cortical screws were designed to combine the advantages of thick mini-implants with the versatility of micro-screws while avoiding the disadvantages of both. An MH cortical screw (MH is an abbreviation for the author's name) was made from titanium material. The screw has a 3 mm-long amphora-shaped shank of 2 mm thickness at its thinnest and 3 mm at its thickest part. Uniform 4 mm diameter threads blend into a 1 mm cutting tip. An external hexagonal head with side retentive ligature holes and a central hole for attachments was fabricated on a saucer-shaped gingival collar. Multiple attachments have been prepared for amending to the central hole. The shank design allowed cortical plate retention. The uniform threads and the amphora design provided maximum primary and secondary stability, respectively. The self-drilling tip allowed for a flapless technique, while the hexagonal head with side holes facilitated screwdriver control and allows for ligature wire anchorage. Cleats and buttons facilitated the use of elastics and springs, together with bracket-heads and eyelets for titanium molybdenum alloy and nickel-titanium wires inclusion. Adjustable hooks and chains provided versatility of line of action. Cover screws to retain extra-tissue mini-plates applied skeletal anchorage and long-term retention with flapless manipulations. MH cortical screws are a novel and important introduction to orthodontic anchorage. They combine primary and secondary stability with avoidance of root damage together with insertions into attached gingiva only. Multiple and versatile attachments allow for the application of biomechanical techniques according to the clinician's preferences. Extra-tissue mini-plates facilitate maximum anchorage for skeletal control and long-term retention without surgery.

Legal Intervention in Poverty alleviation

Poverty can be regarded as the single most universal phenomenon forming an unvarying and uniform thread that transcends all boundaries and nations. A whole gamut of complexities is encompassed by the single word ‘poverty’. India’s plunge into mass poverty manifested during the colonial era and markedly accelerated throughout that phase. A poverty alleviation agenda involves several distinct essentials: first, it is crucial to define poverty for a particular region, which can be done only if the specific causative factors are underlined. Based on this understanding, a mode of measurement needs to be devised to identify the poor. Only when these aspects have crystallized, is it possible to design and implement intervention programmes.It is now realized that a collaborative measure of emphasis on accelerated growth and a direct interventionist-safety net procedure is the proper approach to optimize the control strategies. Lastly, it needs to be ensured that the institutions executing these measures complement the policy stance. India as a welfare state is committed to the development of its people. The constitutional responsibility is reflected via legislations and development policies. During the last five decades, India’s tryst with poverty has met with chequered responses. It would, however, be incorrect to say that all poverty reduction programmes have failed.

Achieving uniform thread load distribution in bolted joints using different pitch values

Bolted joints are a critical component of machines and structures under cyclic loading. Bolt fatigue failure usually takes place in the first engaged thread for being the most loaded one. In this sense, a uniform thread load distribution improves its mechanical response and consequently the reliability of the joint. For this purpose, different thread pitch values can be used in the bolt and the nut, and there is an optimum value that leads to the most uniform load distribution for each particular joint configuration (geometry, preload level, materials and boundary conditions). Sopwith developed an analytical model to calculate this value, but no validation was carried out. This work presents a semianalytical model to estimate the load distribution for any differential thread spacing, which can also be used to calculate the optimum value. The results of this model are nearly coincident with Finite Element results and more accurate than those obtained from Sopwith model.

Facial fat grafting with a prototype injection control device

ObjectiveTo evaluate the initial clinical performance of a prototype injection control device (ICD) to facilitate fat grafting by injection.MethodsAn ICD, which mechanically couples the act of withdrawing the cannula with the act of depressing the plunger, was fabricated for the purpose of facial fat grafting. The action of the device results in deposition of consistent threads of fat having a volume of approximately 33 uL per cm that the cannula is withdrawn, which is slightly less than the internal volume of a 12-gauge cannula. A total of 26 patients underwent 30 procedures, and the results were subjectively evaluated using pre- and postoperative photographs, with a minimum follow-up of 4 months.ResultsThe desired degree of correction was more consistent, recovery was faster, and procedural efficiency was improved when performing the procedure with the ICD compared to historical use of the manual method of injection. Minor irregularities were the only complications encountered.ConclusionThe ICD optimally distributes fat as a uniform thread along the withdrawal tract of the cannula, thereby eliminating clumping and minimizing tissue trauma, resulting in reduced recovery time as well as more consistent and predictable clinical results. Since the ICD automates the injection process, it provides a notable and easily attainable efficiency in procedural time and minimal learning curve for the user.

Zebra mussel adhesion: Structure of the byssal adhesive apparatus in the freshwater mussel, Dreissena polymorpha

The freshwater zebra mussel (Dreissena polymorpha) owes a large part of its success as an invasive species to its ability to attach to a wide variety of substrates. As in marine mussels, this attachment is achieved by a proteinaceous byssus, a series of threads joined at a stem that connect the mussel to adhesive plaques secreted onto the substrate. Although the zebra mussel byssus is superficially similar to marine mussels, significant structural and compositional differences suggest that further investigation of the adhesion mechanisms in this freshwater species is warranted. Here we present an ultrastructural examination of the zebra mussel byssus, with emphasis on interfaces that are critical to its adhesive function. By examining the attached plaques, we show that adhesion is mediated by a uniform electron dense layer on the underside of the plaque. This layer is only 10-20 nm thick and makes direct and continuous contact with the substrate. The plaque itself is fibrous, and curiously can exhibit either a dense or porous morphology. In zebra mussels, a graded interface between the animal and the substrate mussels is achieved by interdigitation of uniform threads with the stem, in contrast to marine mussels, where the threads themselves are non-uniform. Our observations of several novel aspects of zebra mussel byssal ultrastructure may have important implications not only for preventing biofouling by the zebra mussel, but for the development of new bioadhesives as well.

Load Redistribution on Lead Screw Threads Wearing Under Varying Operating Conditions

The load applied to a lead screw assembly is distributed amongst the engaged threads of its wearing nut in a manner that can range from highly nonuniform to nearly uniform. Nonuniform load distributions can arise when new or unworn threads are initially placed into service or, alternatively, in worn threads whereupon the operating conditions are changed from pre-existing conditions at steady-state wear. In threads wearing under constant conditions, nonuniform load distributions evolve to uniform load distributions with sufficient continued sliding as the most heavily loaded threads wear most rapidly, causing their loads to be redistributed to those threads less heavily loaded. Using a newly implemented discrete-thread numerical approach, an example lead screw with rigid nut and elastic screw body having flexible meshed thread pairs is modeled here to demonstrate the broad distribution of thread loads on a new lead screw assembly that gradually evolves toward uniformity as the coupled consideration of thread loading and wear depth approaches a steady-state of equal rates of thread wear. Thread load redistributions brought about by linear ramp changes in applied load, or temperature in the case of a nut/screw pair of dissimilar materials, are predicted at various rates of ramp between prior and future steady operating conditions. While showing the expected maintenance of uniform thread loading under slowly ramped conditions, this numerical approach was verified in cases of rapid ramps approaching step changes, for which existing closed-form analytical models provide agreement. At intermediate rates, this numerical model is complemented by newly expanded closed-form analytical models of both discrete- and continuous-thread types that describe asymptotic behavior during extended ramps.

Resistência mecânica às forças de tração e flexão: proposta de novo desenho para os pinos de Schanz dos fixadores externos monolaterais

OBJETIVO: Determinar a resistência mecânica à tração e à flexão de três modelos de pinos de Schanz, dois disponíveis no Brasil e o proposto neste estudo: o cônico com 4,0 a 5,0mm de diâmetro máximo, o pino com diâmetro de 5,0mm, comprimento de rosca de 40mm e alma de 3,2mm e o proposto neste trabalho, com 5,0mm de diâmetro, alma de 3,2mm e comprimento de rosca de 15mm, com o propósito de apontar o mais eficaz. MÉTODOS: Foram construídos 48 corpos de provas, distribuídos em seis grupos com oito corpos cada. A resistência à tração foi testada nos grupos 1, 2 e 3 utilizando-se uma máquina de tração de fabricação ITM®. Para verificar a resistência à flexão, nos grupos 4, 5 e 6, foram usados um perfurador de bancada, marca Cardoso® FFC-20 na instalação do pino e, em seguida, a máquina universal de ensaios ZD100PU. RESULTADOS: Nos testes de tração os pinos cônicos suportaram a tração média de 98,462kgf; os de rosca uniforme longa (40mm), 283,70kgf; e os pinos propostos com rosca uniforme de 15mm, a força média de 116,947kgf. A diferença estatística não foi significante entre os grupos. Nos testes de flexão, os pinos cônicos resistiram à força de 6,563kgf; os pinos com rosca uniforme de 40mm, à força média de 6,177kgf; e os pinos propostos, à força média de 30,275kgf, existindo diferença significativa com os grupos anteriores. CONCLUSÕES: Os três modelos de pinos de Schanz apresentaram resistência equivalente à tração e o modelo proposto - comprimento de rosca de 15mm - é significativamente mais resistente às forças de flexão.

The beads-on-string structure of viscoelastic threads

By adding minute concentrations of a high molecular weight polymer, liquid jets or bridges collapsing under the action of surface tension develop a characteristic shape of uniform threads connecting spherical fluid drops. In this paper, high-precision measurements of this beads-on-string structure are combined with a theoretical analysis of the limiting case of large polymer relaxation times, for which the evolution can be divided into two distinct regimes. This excludes the very late stages of the evolution, for which the polymers have become fully stretched. For times smaller than the polymer relaxation time, over which the beads-on-string structure develops, we give a simplified local description, which still contains the full complexity of the problem. At times much larger than the relaxation time, we show that the solution consists of exponentially thinning threads connecting almost spherical drops. Both experiment and theoretical analysis of a one-dimensional model equation reveal a self-similar structure of the corner where a thread is attached to the neighbouring drops.

Thread Friction Torque in Bolted Joints

Abstract In this paper, formulas are developed for the calculation of the effective thread friction radius in fasteners, in order to determine the thread friction torque component. Due to the lack of exact formulas in the literature, current practice uses the average value of the minor and major thread radii, as an approximation, for determining the thread friction torque component. Results provided by these formulas are compared with those given by the current practice that uses the average value of the minor and major thread radii, instead of the exact value. It is well known that the torque-tension relationship in threaded fastener applications is highly sensitive to the friction torque components: between threads, and under the turning fastener head or nut. Even moderate variations or inaccuracies in determining the friction torque components would significantly impact the fastener tension and the joint clamp load. High accuracy in the estimation of the friction torque components is critical, as it directly affects the reliability, safety, and the quality of bolted assemblies. This analysis focuses on the thread friction torque component. The new formulas for the thread friction radius are developed for a mathematical model of a bolted joint using five assumed scenarios of the contact pressure between male and female threads. Because of the fact that the variation in the sliding speed of various points on a thread surface is insignificant, a uniform thread friction coefficient is used in the analysis. However, a contact area weighted average value is used for the thread friction coefficient. Numerical results and error analysis are presented in terms of a single nondimensional variable, namely, the ratio between the major and minor thread radii.

Mechanical Properties of Bacterial Fibres

AbstractBacterial thread is the name given to a fibrillar fiber produced from cell-separation-suppressed mutants of Bacillus subtilis. which grow in long cellular filaments and produce in cultures aggregates that resemble randomly-laid textile webs. Threads are produced by steady withdrawal at the end of a sterile toothpick - for all the world like Carothers, 50 years ago! Individual filaments are drawn radially into the forming thread and adhere strongly to each other with axial alignment. Uniform threads up to 1 meter in length and 180 μm in diameter can be produced. Such threads contain about 50,000 filaments and upwards of 1010cells Tests on thread show that peptidoglycan, which is the load-bearing polymer of the bacterial cell wall, behaves mechanically like other visco-elastic polymers. When dry its behavior is glassy, with high modulus; when wet, it is relatively weak and of low initital modulus. Relaxation data indicate a very wide spectrum of relaxation times. All the mechanical properties depend strongly on the RH of the test environment; they are also influenced by the ionic environment at the time threads are drawn. Available evidence indicates that peptidoglycan is not crystaline. Nonetheless there is some degree of orientation in the bacterial cell wall. This is shown by the effect of enzyme attack on mechanical properties and by the twisted growth pattern of bacteria.

THE EFFECTS OF ACTINOMYCIN D ON THE ULTRASTRUCTURE OF THE NUCLEUS OF THE AMPHIBIAN EMBRYONIC CELL.

Observations have been made of ultrastructural modifications induced in the nuclei of differentiating amphibian embryonic cells cultured in the presence of Actinomycin D. Of particular interest are regions within the nucleus (regions otherwise rather empty) containing loose groupings of uniform threads having a diameter of around 200 A. These threads have been observed in continuous lengths up to 0.5 micro, and appear to be composed of subfilaments. It is suggested, after taking account of some recent work on lampbrush chromosomes, that these threads are lengths of uncoiled chromosome in a condition of heterosynthetic inhibition. It is further suggested that active and inactive portions of the genome may be distinguishable by the facility with which they can be induced to undergo this ultrastructural modification.

Some electron-microscopical observations on bacterial cytology

Some micrographs from bacteria taken with the Delft electron microscope are reproduced. The text is principally confined to a discussion of some cytological characteristics as shown by these micrographs. 1. a. Although it is questionable whether micrographs of bacteria prepared in a primitive way are apt to furnish useful information regarding the cell shape, the electron micrographs obtained werer in satisfactory agreement with the current conceptions as based on light microscopical observations (Fig. 9 and 10). Pseudomonas fluorescens (Fig. 5) was found to be slightly bent like a spirillum, which tends to confirm Pijper's recently advanced theory, however. Fig 2 of Bacillus subtilis shows a perfectly straight rod. Pseudomonas fluorescens (Fig. 5 and 6) often shows characteristic cell wall bladders. Coccoid cells opften assume hexagonal shape (Fig. 12 and 13). 2. b. A distinct cell wall was clearly perceptible in all investigated Eubacteria. Special attention has been paid to the appearance in conglomerates of coccoid cells of structures reminiscent of “middle lamellae” and “triangular spaces” in tissues of higher plants. 3. c. With regard to cell wall formation there is reason to conclude that the initial phenomenon is the appearance of a dark “lamella” in the central part of the cytoplasm (Fig. 13). In bacteria usually designated as rods, this phenomenon is accompanied by a notch in protoplasm and original cell wall, as a first indication of the progressing cell constriction, ultimately leading to cell division (Fig. 14). 4. d. Micrographs of some strains of bacteria ( Serratia marcescens and Pseudomonas fluorescens) show characteristic differences in cytoplasm which support a subdivision into primary and secondary cell types as proposed by Piekarski and Ruska. 5. e. The frequent occurence of distinct globular bodies in many bacterial cells which become clearly visible only at 75–110 kv has tempted us to make a few remarks regarding the nucleus problem. Noteworthy is the fact in case of occurrence of primary and secondary cell types these bodies were exclusively found in the very opaque protoplasma concentration of the latter type. In Fig. 7 and 8 of Pseudomonas fluorescens the bodies seem mutually connected by threads, suggesting a recently accomplished division. 6. f. The problem of flagellation is mainly considered in the light of Pijper's recent studies. Bacill subtilis micrographs (Fig. 2 and 3) show a striking number of perfectly uniform threads, a great number of which is evidently broken off from the cells. Several micrographs (especially Fig. 11 of Spirillum serpens and Fig. 9 of Vibrio metchnikovii) are strongly suggestive of a protoplasmatic origin of the flagella. Taking together all micrographic evidence it is hard to accept Pijper's thesis that flagella are mere “products of motility”, originating from a twisting of mucous polysaccharides.

THE STRUCTURE OF MEIOTIC CHROMOSOMES IN THE GRASSHOPPER AND ITS BEARING ON THE NATURE OF "CHROMOMERES" AND "LAMP-BRUSH CHROMOSOMES"

1. Chromomeres do not exist as definite structures. What has been described as chromomeres are (a) misinterpretations of gyres of the chromonematic helix (leptotene, somatic prophase); (b) points of overlap of chromonemata (diplotene); (c) heterochromatic sections consisting of more tightly coiled regions of the chromonema. The fundamental unit of the chromosome is a microscopically uniform thread. The longitudinal differentiation of the chromosome is due to differential coiling of this chromonema.2. Lamp-brush chromosomes are typical diplotene chromosomes, but with tremendously enlongated chromonemata. The side branches are the gyres of the major coils of the individual chromonemata, which have laterally separated from each other.

A METHOD FOR MEASURING THE SOFTENING TEMPERATURE OF GLASSES1

For the purpose of measurement the softening point of glasses is defined as that temperature at which a uniform thread of glass .65 mm to 1 mm in diameter suspended in a vertical position in an electric furnace of specified characteristic will elongate at the rate of 1 mm per minute. The measurements on a given glass are reproducible to within 1 to 2°C. This method has been found useful as control of glass composition in melting units as well as a point of reference to distinguish between different glasses. Data are given showing the variation in softening point of a tank glass and a pot glass over an interval of time.

Spermatogenesis in Blasia

1. Centrosomes are present in Blasia at all stages of the mitosis which differentiates the androcytes, and in the androcytes they persist and function as the blepharoplasts. 2. In the transformation of the androcyte into the spermatozoid, the blepharoplast fragments repeatedly by simple fission, forming a number of distinct granules which coalesce to form a short lumpy rod. This rod elongates and becomes a more uniform thread bearing two cilia, while the nucleus also elongates in intimate union with it to form the body of the spermatozoid. The present instance is the first in which blepharoplast fragmentation has been reported in a bryophyte. 3. It is possible that the fission of the Blasia blepharoplast, and therefore the more complex fragmentation of the blepharoplasts of Equisetum, Marsilia, and the cycads, may be homologized with the normal division exhibited by ordinary centrosomes.