4,709 research outputs found

    NASA SBIR abstracts of 1990 phase 1 projects

    Get PDF
    The research objectives of the 280 projects placed under contract in the National Aeronautics and Space Administration (NASA) 1990 Small Business Innovation Research (SBIR) Phase 1 program are described. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses in response to NASA's 1990 SBIR Phase 1 Program Solicitation. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 280, in order of its appearance in the body of the report. The document also includes Appendixes to provide additional information about the SBIR program and permit cross-reference in the 1990 Phase 1 projects by company name, location by state, principal investigator, NASA field center responsible for management of each project, and NASA contract number

    ADDITIVE MANUFACTURING AND 3D PRINTING IN DENTISTRY

    Get PDF
    CAD / CAM techniques applied to solving dental problems demonstrate that there are many solutions available on the market to help the dentist individually perform the rehabilitation of a dental element to meet the specific needs of each patient. These manufacturing technologies close a digital workflow, potentially managed entirely by the dentist, which involves taking the impression of the oral cavity and the dental elements present through an intraoral scanner with the generation of a file on which to create the CAD project and to start extrapolating the file of the final work to be produced by subtractive or additive CAM. The 3D printing techniques allow to work easily with polymeric and ceramic materials, in order to create dental crowns that can satisfy practically all the needs encountered in the dental field. Leaving aside the techniques applied to polymers, this PhD project focuses on the applications of ceramic materials. This PhD thesis focuses on the design, study and implementation of 3D printing of ceramic supports specifically dedicated to the stabilization of dental implants. Through the development of a prototype of a 3D printer, it was possible to obtain the printing of ceramic products useful for the intended purpose

    FABRICATION OF CERAMIC MICROPATTERNS AND THEIR IMPACT ON BONE CELLS

    Get PDF
    The main objective of this study is to elucidate possible methods of producing ceramic calcium phosphate micropatterns ranging from 5 to 100 µm. Today, micropatterned ceramic surfaces are of great interest for fundamental materials research as well as for high-end industrial processes, whereas the fabrication of these patterns in the sub-100 µm range is still a challenge. Therefore, six different patterning techniques have been applied in order to generate ceramic patterns: Microtransfer molding (µTM), modified micromolding (m-µM), Aerosol-Jet® printing, CNC-micromachining, laser ablation and direct laser interference patterning (DLIP). The patterning techniques have been evaluated concerning their capability of fabricating ceramic patterns smaller than 100 µm. Another objective of this study has been the investigation of the influence of ceramic patterns on human osteoblasts (HOB). This investigation has revealed that ceramic hydroxyapatite-based patterns ranging from 16 to 77 µm in widths have a strong influence on the contact guidance of the HOB, whereas the cells showed distinct orientations between 0°-15° in reference to the pattern direction

    Ceramic Brackets Revisited

    Get PDF
    Increasing demand for esthetics during fixed appliance therapy has led to a significant increase in the demand for and use of ceramic brackets. This comprehensive review covers the physical properties as well as rebonding and debonding of polycrystalline and monocrystalline ceramic brackets. Furthermore, this review aims to present the advantages and disadvantages as well as the refinements these brackets underwent since their introduction in the late 1980s. Interestingly, the introduction and development of these brackets were a part of a quickly expanding ceramic technology in many industries. The authors strongly believe that the novice will particularly benefit from this review presenting up-to-date knowledge

    Bonding of orthodontic brackets to enamel: Studies on the clinical outcome of bracket bonding and approaches to increase the bond strength of the adhesive interface

    Get PDF
    ABSTRACT An extensively used form of orthodontic treatment is the use of fixed appliances, where brackets are attached to the teeth for the duration of the treatment, often with light curing adhesives. The adhesion between the brackets and enamel must withstand the forces generated during the treatment, but on the other hand, an easy removal of the appliances at the end of the treatment without causing damage to dental hard tissues is desirable. Sometimes bracket failure occurs during the treatment, in which case a new bracket must be bonded on the tooth, and here the changes in enamel surface after initial bonding procedures may influence the rebonding. In the studies presented in this thesis, the failure rate of brackets in clinical practice and certain methods to improve the bonding and rebonding of brackets were investigated. The failure rate of orthodontic brackets in this study cohort was 7.9%. More brackets were debonded from mandibular teeth than from maxillary teeth, and the selected bonding system and the operator’s bonding technique had an effect on the bonding success. A glass fiber weave placed in the adhesive interface improved the degree of cure of the adhesive under metal brackets, and transillumination through teeth was possible, but the irradiance diminished quickly as the thickness of the tooth slices increased. Ceramic brackets yielded highest bond strengths (21.9 MPa) compared to metal (8.14 MPa) and polycarbonate brackets (10.47), and a silane based primer improved the bond strength of ceramic brackets even further (26.45 MPa). However, this improvement of bond strength was associated with enamel fractures. To achieve adequate bond strength values after bracket failure, a small amount of enamel needed to be ground off before rebonding. It can be concluded, that a clinically significant number of brackets fail during the treatment, and therefore these methods that improve bonding are of importance. Yet a higher bond strength must not come at the detriment of intact dental hard tissues. KEYWORDS: orthodontic bracket, bond strength, dental bonding, bracket failureTIIVISTELMÄ Oikomishoidossa paljon käytetty hoitomuoto on kiinteä kojeistus, jossa kaarilankojen kiinnikkeet, braketit, kiinnitetään hammaskiilteeseen. Kiinnityksessä käytetään useimmiten valokovetteisia kiinnitysmuoveja. Sidoksen täytyy kestää hoidon aikaiset voimat, joten sidoslujuuden parantaminen on tärkeää. Toisaalta liian vahva kiinnitys saattaa johtaa hammaskudoksen vaurioihin hoidon päättyessä, kun braketit irrotetaan hampaista. Jos braketti irtoaa kesken hoidon, täytyy hampaaseen kiinnittää uusi braketti ja tällöin ensimmäisen sidostuksen aikaansaamat muutokset hammaskiilteessä saattavat vaikuttaa uudelleensidostamiseen. Näissä tutkimuksissa selvitettiin brakettien irtoamisfrekvenssiä, sekä pyrittiin parantamaan brakettien sidoslujuutta erilaisin keinoin. Tutkitussa potilasaineistossa 7,9 % braketeista irtosi ennenaikaisesti kesken hoidon. Irtoaminen oli yleisempää alaleuan hampaissa kuin yläleuassa. Valittu kiinnitysmuovi ja sidosaine, sekä operaattorin sidotustekniikka vaikuttivat sidostuksen onnistumiseen. Lasikuituverkko braketin alla paransi kiinnitysmuovin kovettumisastetta metallisten brakettien ja suurempien kojeiden alla. Kiinnitysmuovin valokovetus oli mahdollista dentiinin läpi, mutta vain alle 4 mm paksuuteen asti. Vertailtaessa erityyppisten brakettien sidoslujuuksia, keraamisten brakettien sidoslujuus oli korkeampi (21,9 MPa) kuin polykarbonaatti- (10,47 MPa) tai metallibrakettien (8,14 MPa). Silaanipohjainen esikäsittelyaine braketin pohjassa paransi keraamisten brakettien sidoslujuutta (26,45 MPa), mutta vahvempi sidos johti kiillevaurioihin kiinnikkeitä irrotettaessa. Braketin ennenaikaisen irtoamisen jälkeen pieni määrä kiillettä täytyi hioa pois, jotta uutta brakettia kiinnitettäessä saavutettiin alkuperäiseen sidostukseen verrattavissa oleva sidoslujuus. Yhteenvetona voidaan todeta, että kliinisesti merkittävä osa braketeista irtoaa hoidon aikana, joten kiinnitystä on tärkeää parantaa, mutta toisaalta voimakas sidostuminen ei saa johtaa hampaan kovakudosten vaurioihin. AVAINSANAT: braketti, sidosulujuus, sidostaminen, brakettien irtoamine

    Analysis of accuracy and precision of optical 3D digitisation devices in dental computer-aided-design and computer-aided-manufacturing systems

    Get PDF
    The implementation of intraoral and extraoral computer-aided-design and computer-aided-manufacturing (CAD/CAM) systems in prosthetic dentistry has simplified the procedure, shortened the period of design and manufacture and improved accuracy and aesthetic properties of dental restorations. Three-dimensional (3D) digitisation has become an adequate replacement for conventional dental impressions. The market offers a variety of diverse optical intraoral and extraoral CAD/CAM systems equipped with digitisation devices that are based on different working principles. The main goal of this research is to determine whether precision and accuracy differ among optical digitisation devices. The research includes five high-end devices: Cerec AC, Cerec InEos, Trios, KaVo Everest and Sinergia Scan. The evaluation methodology of the experiment is based on CAD inspection. The results, obtained from accuracy and precision measurements with tolerance levels of 0.01, 0.25 and 0.05 mm, indicate that there is a difference in accuracy and precision between optical digitisation devices based on different working principles

    Laser Surface Structuring of Alumina

    Get PDF
    Alumina ceramic is an important abrasive material for grinding wheels used for rough grinding/machining of materials in manufacturing industry. Purpose of this work is to explore laser surface structuring of alumina grinding wheels for precision machining/grinding of materials by modifying surface microstructure of wheels. Major objective of this work is to study the evolution of surface microstructure and depth of modification such that microstructures/properties of modified wheels can be efficiently tailored based on fundamental understanding of physical processes taking place during laser surface structuring. Surface structuring of alumina using a continuous wave Nd:YAG laser resulted in significant surface melting and subsequent rapid solidification. The surface modified alumina consisted of microstructure characterized by regular polygonal and faceted surface grains with well defined edges and vertices. Such multifaceted grains act as micro-cutting tools on the surface of grinding wheels facilitating micro-scale material removal during precision machining. The formation of faceted morphology is explained on the basis of evolution of crystallographic texture in laser modified alumina. Furthermore, complete crystallographic description of multifaceted morphology of surface grains is provided based on detailed analysis of surface micro-texture. Due to complexity of microstructure formed during laser surface structuring, a fractal analysisbased approach is suggested to characterize surface microstructures. Detailed analysis of the effects of laser interaction with porous alumina ceramic indicated that melt surface undergoes rapid evaporation resulting in generation of high (\u3e105 Pa) evaporationinduced recoil pressures. These pressures drive the flow of melt through underlying porous alumina during modification extending the depth of modification. An integrative modeling approach combining thermal analysis and fluid flow analysis resulted in better agreements between predicted and experimental values of depths of melting. Finally, improvements in microindentation fracture toughness of alumina ceramic are reported with increasing laser fluence. Such improvements in the fracture toughness seem to be derived from better surface densification and coarsening of grain structure. The understanding of the evolution of faceted morphology, depth of surface modifications and improvements in fracture properties in laser surface microstructured alumina ceramic reached in this work provides the foundation for tailoring of surface microstructures/properties of alumina grinding wheels for precision machining applications

    Design and implementation of sensor systems for control of a closed-loop life support system

    Get PDF
    The sensing and controlling needs for a Closed-Loop Life Support System (CLLSS) were investigated. The sensing needs were identified in five particular areas and the requirements were defined for workable sensors. The specific areas of interest were atmosphere and temperature, nutrient delivery, plant health, plant propagation and support, and solids processing. The investigation of atmosphere and temperature control focused on the temperature distribution within the growth chamber as well as the possibility for sensing other parameters such as gas concentration, pressure, and humidity. The sensing needs were studied for monitoring the solution level in a porous membrane material along with the requirements for measuring the mass flow rate in the delivery system. The causes and symptoms of plant disease were examined and the various techniques for sensing these health indicators were explored. The study of sensing needs for plant propagation and support focused on monitoring seed viability and measuring seed moisture content as well as defining the requirements for drying and storing the seeds. The areas of harvesting, food processing, and resource recycling, were covered with a main focus on the sensing possibilities for regulating the recycling process
    corecore