Search

The aim of this work was to analyze the properties and shear bond strength (SBS) of lithium disilicate to resin cement before and after etching the glass-ceramic surfaces. Lithium-metasilicate samples were heat treated and characterized by Scanning Electron Microscopy, X-ray diffraction and roughness measurement. For the analysis of the shear bonding strength (SBS) of lithium disilicate to dental resin cement, three groups (n = 12) of Li2Si2O5 were prepared: 1°)without treatment (NT); 2°)surface etching with hydrofluoric acid(HF), followed by silane agent and adhesive treatment; 3°) surface treatment with a self-etching ceramic primer (SECP). After the heat-treatment, the samples had Li2Si2O5 crystalline phase dispersed in a residual amorphous phase. Roughness of the NT and SECP samples was smaller that of the HF samples. Samples without surface treatment (NT) had the lowest SBS (5.5MPa). HF(24.2MPa) and SECP(24.8MPa) samples has similar SBS. Weibull statistics showed that HF-samples are more reliable than NT and SECP. The SBS was significantly increased by either HF etching and SECP surface treatment. While the chemical characteristics of the surface submitted to SECP treatment are considered to be responsible for the SBS increase, the main adhesion mechanism after HF etching is the increase in surface roughness.

The Cr-Co-Mo alloys are commonly used in dentistry for prosthetic components and dental implant supported prosthesis. These alloys present high corrosion resistance owing to a passive oxide film on the surface. However, the oral environment is an aggressive system, due to pH variation, chloride and fluoride ions presence, that can decrease the metal alloy corrosion resistance. Although Cr-Co-Mo alloys have been used for a long time, their electrochemical properties on different pH have not been studied yet. This study aimed to evaluate the electrochemical properties of Cr-Co-Mo alloy in NaCl 0.9% solution in different pH and mouthwash solution. To imitate the oral environment, electrolytes with a pH equal to 2, 3, and 6 were used. Corrosion studies were performed by open circuit potential observation, potentiodynamic polarization curve, chronoamperometry and electrochemical impedance. The results showed that the analyzed alloy has good corrosion resistance under experimental conditions, although the acidified NaCl 0.9% solution increased the corrosion current, particularly in cathodic potentials.

Two distinct AISI type 316 stainless steels, of Brazilian and Swedish origins, were compared regarding their creep fracture mechanisms at 600, 700 and 800°C. The possible mechanisms associated with the creep fracture strength were identified by means of fracture maps proposed either by Ashby and collaborators or by Miller and Langdon. Experimental creep results were consistent with the general Ashby and collaborators map for face centered cubic alloys. By contrast, the two different 316 steel displayed significant differences in the model-based map of Miller and Langdon. In the present work, changes in the maps frontier are proposed as well as the introduction of a new field in the map related to grain boundary precipitation. These propositions allowed the Miller and Langdon map to be coherent with the experimental creep fracture results of both 316 stainless steels.

O titânio comercialmente puro (Ti cp) e o principal material usado na fabricacao dos implantes dentarios osseointegraveis. Para melhorar os indices de sucesso do tratamento odontologico e reduzir o tempo de osseointegracao dos implantes, foram desenvolvidas varias metodologias de tratamento da superficie dos implantes. Para caracterizar as morfologias das superficies dos implantes sao usadas as analises no microscopio eletronico de varredura (MEV), rugosidade, molhabilidade, identificacao de possiveis contaminantes, ensaios in-vitro de culturas de celulas e in-vivo com animais. Entre as tecnicas citadas, as mais usadas sao as analises no MEV, as medidas dos parâmetros da rugosidade e da molhabilidade. Alguns trabalhos disponiveis na literatura sugerem a caracterizacao somente do valor de Ra sem apresentar uma explicacao para a escolha deste parâmetro. No presente trabalho e feita a proposta de um modelo matematico para quantificar a relacao entre os varios parâmetros da rugosidade 3D (Ra, Rq, Rz, Rms, Pico, Vale, PV, R3z e Smax) com a molhabilidade e a energia de superficie do Ti cp com dois tamanhos de grao (micrometricos e sub-micrometricos) e submetidos ao tratamento com acido. Os resultados mostraram que para o nivel de confianca de 95%, as propriedades das superficies do Ti cp tratados com acido sao mais influenciadas pelos parâmetros de rugosidade Ra e Rms. Palavras-chave: titânio, rugosidade, molhabilidade, metodologia de LASSO

Over the last decades, much research has been done to improve the surface quality of dental implants, but there was no change in the materials used to manufacture the implants. The purpose of the present work is to compare the compressive strength and fatigue failure of dental implants made with a new material, nanocrystalline Ti grade 4 fabricated by Equal Channel Angular Pressing (ECAP) (Ti Hard) with a traditional material, microcrystalline Ti grade 4 (Ti G4). Machined screw-shaped implants with three different designs (Easy, Torq and Flash) made with the two materials were subjected to static and dynamic compressive loads. Implants made with Ti Hard showed higher static compressive strength (Easy: 889.9 ± 79.4 N, Flash: 588.9 ± 74.7 N, Torq: 498.3 ± 54.6 N) than implants made with TiG4 (Easy: 776.4 ± 74.5 N, Flash: 308.8 ± 15.2 N, Torq: 410.3 ± 25.2 N) and higher fatigue strength for 5 106 cycles (Easy: 400 N, Flash: 280 N, Torq: 260 N) than implants made with TiG4 (Easy: 300 N, Flash: 200 N, Torq: 200 N). The higher fatigue strength of nanocrystalline Ti G4 is attributed to a delay in crack initiation.

This work evaluated the mechanical strength and surface roughness of MgZn30Ca5ribbon manufactured via a melt spinning technique for applications in the biomedical field. Annealing was performed at 280°C. The inner side (in contact with the wheel) and the outer side (not in contact with the wheel) of the ribbons were mechanically evaluated using nanoindentation, and its surfaces were analyzed by an optical profilometer. Differential scanning calorimeter (DSC) and X-ray diffraction (XRD) analyses were also performed to identify the structure and devitrification of the magnesium metallic glass (MgMG). The nanohardness and elastic modulus increased after annealing (p 0.05). Although both sides of the ribbons showed different surface profiles (p

The present work presents an experimental study on the behavior of ceramic tile rendering build on concrete block masonry walls loaded to compression failure. The walls were tested considering two different coating systems: a) direct application of adhesive mortar and lastly the ceramic tile; b) with cement plaster followed by the adhesive mortar and finally the ceramic tile. Four events were recorded: noise emission, plaster detachment, ceramic tile detachment and wall rupture. For both coating systems, the fracture loads were similar and ceramic tile detachment occurring at loads above expected service for residential buildings.

Objective Commercially pure titanium (cp Ti) and Ti–6Al–4V (Ti G5) alloy have limitations for biomedical application, due to lower mechanical strength and the possibility of ion release, respectively. The purpose of this work was to compare the properties of a modified cp Ti grade 4 (Ti G4 Hard) with those of available cp Ti and Ti G5 alloys. Methods Bars, discs and dental implants made with Ti G2, G4, G5 and G4 Hard were used. Mechanical tests (tension, compression, hardness and torque) and roughness measurements were performed. Clinical trials were used to evaluate the biological behavior of dental implants made with Ti G4 Hard and Ti G4. Results The results of the mechanical tests showed that the mechanical strength of modified Ti G4 is higher than that of Ti G2, G4 and G5. Scanning electron microscopy analysis showed that modified Ti G4 after etching has better surface morphological features than conventional cp Ti and Ti G5. The clinical performances of Ti G4 and Ti G4 Hard were similar. Significance The improvement of the mechanical properties of modified Ti G4 means that Ti G5 can be safely replaced by Ti G4 Hard without compromising the fracture resistance, with the advantage of not releasing toxic ions.

The objective of this study was to assess the influence of cortical thickness and bone density on the insertion torque of a mini-implant (MI) with microthreads. Mini-implants with lengths of 6 and 8 mm in the active part were inserted into synthetic bone blocks (polyurethane resin). The density of these blocks was 20 pounds per cubic foot (pcf), simulating bone marrow, and that of blocks 1, 2, and 3-mm-thick blocks was 40 pcf, simulating cortical bone. Blocks with uniform density of 40 pcf were also used to simulate bone areas of greater density. Insertion torque was quantified with a universal testing machine (EMIC). For both MIs, increasing insertion torque was associated with increasing cortical bone thickness. For the same MI length, significant differences were observed among all assessed groups. The insertion torque of the 6-mm-long MI inserted in a 3-mm-thick cortical bone was equivalent to that of the 8-mm-long MI inserted in a 1-mm-thick cortical bone. MIs inserted in bone blocks of greater density presented insertion torque values almost twice as high as those in other groups. The shorter MI, the lower the insertion torque, and the greater the cortical bone thickness, the greater the insertion torque. To minimize fracture risk, the size of MI should be selected according to the insertion site. Refereed/Peer-reviewed

RESUMO O óxido de zircônio (ZrO2) policristalino parcialmente estabilizado com 3%mol de óxido de ítrio (Y2O3), ou 3Y-TZP, é usado como biomaterial nas restaurações protéticas odontológicas. Esta indicação possui limitação devido à coloração branca e alta opacidade da zircônia. Para melhorar a estética sem comprometer o desempenho funcional são adicionados outros óxidos à zircônia. Esta adição modifica a coloração da zircônia para tonalidades próximas a dos dentes naturais. Este trabalho avaliou o efeito da adição do Fe2O3 na microestrutura, nas propriedades mecânicas e nas propriedades ópticas da 3Y-TZP. Foram preparados cinco grupos de amostras com diferentes percentuais de Fe2O3. A caracterização química dos grupos foi realizada por fluorescência de raios-X (FRX). As propriedades mecânicas foram determinadas em ensaios de dureza e de resistência a flexão em quatro pontos. A análise quantitativa de transformação de fases foi realizada pelo método de Rietveld dos dados dos ensaios de difração de raios-X (DRX). O MEV foi usado para caracterizar a morfologia da superfície antes e após o ensaio de flexão. Os resultados mostraram que a adição do Fe2O3 influencia na transformação de fase, aumenta a dureza e a resistência à fratura por flexão quando sua concentração se encontra entre 0,02% e 0,17% do peso total. Acima dessa faixa de concentração, as amostras apresentaram perdas no desempenho mecânico. A adição de Fe2O3 não induziu mudanças significativas na densidade e no tamanho médio de grão. ABSTRACT The zirconium oxide (ZrO2) polycristaline partially stabilized by yttrium oxide (Y2O3) at 3mol%, 3Y-TZP, has its use been increased as a biomaterial. However, as dental prosthetics, its indication is still limited because of its white color and high opacity. Seeking improvements regarding aesthetics without compromising its functional performance, oxides such as iron oxide (Fe2O3) has been added to the microstructure of zirconia in order to provide a yellow-brownish color similar to natural teeth. This study evaluated the effect of adding Fe2O3 on the microstructure and mechanical and optical properties of 3Y-TZP. Five groups were investigated containing different concentrations of Fe2O3. Firstly, a chemical characterization of each group was carried out through X-ray fluorescence test (XRF). Microstructural characterization was performed by density and average grain size measurements. Mechanical properties were evaluated by performing hardness and four points flexural strength tests. Quantitative analysis of phase transformation was done using the Rietveld method, for each group submitted to the test of X-ray diffraction (XRD). Fractography by SEM analysis were also made on the fracture surface of the samples from tensile test. The results showed that the Fe2O3 addition influenced the phase transformation process, and proportionally increased the samples hardness and flexural strength when their concentrations varied from 0.02% to 0.17% of the total weight. Above this range, the samples showed losses in their mechanical performance. The Fe2O3 additions showed no significant changes in the density and average grain size of 3Y-TZP.

The mechanical, chemical, roughness and wettability properties of 70/30 poly (L,DL-lactide acid) three-dimensional (3D)-printed surgical plates made with extruded polymer filaments developed in the first part of this work were investigated. The plates were printed with horizontal (HRZ) and vertical (VRT) running layer orientations and evaluated by tensile, Fourier transform infrared (FTIR), optical perfilometry and wettability tests before and after degradation in simulated body fluid (SBF) for 21 days. The results show that the ultimate tensile strength (UTS) of HRZ plates before immersion in SBF was higher (34.1 MPa) than that of VRT plates (31.8 MPa). The Young’s modulus (E) of HRZ plates and VRT plates are similar (4 GPa). After immersion in SBF, the UTS of HRZ plates dropped to 20.5 MPa and E decreased to 3.3 GPa. VRT were not tested after SBF immersion due to the large degradation. FTIR analysis showed no evidence of chemical change in the plates after immersion in SBF. The roughness parameter R3z of VRT surfaces (19.54 µm) was higher than that of the HRZ surfaces (12.80 µm). The roughness parameters increased after degradation in SBF (p = 0.7048). The contact angles of HRZ surfaces before immersion in SBF (66.28°) were higher than after immersion in SBF (18.12°); the same behavior was also observed in VRT plates. Refereed/Peer-reviewed

The aim of this work was to manufacture 70/30 poly-l-dl-lactic acid (PLDLLA) filaments for three-dimensional (3D) printers by using the extrusion technique and to study the properties of filaments and printed plates for surgical fracture stabilization. Different extrusion methodologies were tested and filaments were analyzed in terms of homogeneity, accuracy diameter, finishing surface morphology, and chemical degradation. X-ray diffraction and differential scanning calorimetry showed that the filaments have less crystallinity than does the raw material. Infrared and thermogravimetric analysis showed no evidence of chemical degradation. Surgical plates made with the filaments revealed small changes in the material properties after the printing process. PLDLLA filament extrusion and 3D printing are a promising way to satisfy the demand of implantable bioabsorbable products. Refereed/Peer-reviewed

Os tratamentos das superfícies dos implantes dentários osseointegráveis sofreram modificações significativas com o objetivo de melhorar a estabilidade primária e secundária. Entre as modificações destaca-se a deposição de íons, como flúor, cálcio e magnésio. Estes íons possuem baixa taxa de degradação no meio corpóreo e ótima interação biológica com as células e com os tecidos ósseos. No presente trabalho, para avaliar os efeitos do F, Ca e do Mg na osseointegração foram realizados ensaios in vitro e in vivo. Implantes foram inseridos em tíbias de coelhos e determinou-se os torques de inserção e remoção após 2, 4 e 8 semanas. Os ensaios in vivo foram complementados pela medida da rugosidade, molhabilidade e análise da superfície em microscopia eletrônica de varredura. Os resultados foram comparados com os obtidos com implantes com a superfície tratada com ácido (superfície Porous) e com deposição de flúor (superfície Porous Nano). Os resultados obtidos mostraram que o torque para remover os implantes Porous 8 semanas após a cirurgia foi de 16,96 + 1,32 N.cm, o tratado com flúor apresentou melhores resultados (17,93 ± 4,47 N.cm) e a superfície com Ca e Mg foi a que apresentou a interface osso-implante com menor resistência (10,83 + 1,20 N.cm). O maior torque indica que a adição de flúor facilita os mecanismos envolvidos na osseointegração dos implantes e permite o carregamento da prótese em tempos menores. Surfaces treatments improve the primary and secondary stability of dental implants. Among surfaces modifications the deposition of ions, such as fluorine, calcium and magnesium has been studied. These ions have low degradation rate in the body environment and great biological interaction with the cells and bone tissue. In the present work, in vitro and in vivo test evaluated the effects of F, Ca and Mg in osseointegration. Implants were inserted into the tibia of rabbits, insertion and removal torque was measured after 2, 4 and 8 weeks. In vivo testing was complemented by measuring the roughness, wettability and surface analysis in scanning electron microscopy. The results were compared with those obtained with implants with the acid treated surface (Porous surface) and fluoride deposition (Porous Nano surface). The results showed that the group treated with fluoride showed better results on the removal torque (17.93 ± 4.47 N.cm) and the surface with Ca and Mg (10,83 + 1,20 N.cm) ) showed the lowest bone-interface implant resistance. The higher torque indicates that the addition of fluoride facilitates the mechanisms involved in the dental implant osseointegration and allows the loading of the prosthesis in early time.

The brittle behavior of ceramics limits the use of these materials under conditions of cyclic loading, as is the case of fixed partial dentures. To improve toughness and biocompatibility of ceramics is necessary to employ powders with better purities, adjust the conditions of compaction and sintering, microstructure control and explore mechanisms for increasing the toughness. Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) is generally used for dental ceramic restorations. The zirconia framework is fabricated using the CAD/CAM system. The ceramic mechanical properties are determined by testing polished sample. Previous work did not analyze the influence of surface defects induced during dentures grinding. Ceramic restorations manufacturing are made with coarse grinding high-speed diamond rotatory cutting instruments. This process induces residual stresses and the high temperature induces surface cracks. Consequently, a lower strength and reliability of the material is observed. In this work the mechanical properties of yttria stabilized zirconia were determined with the use of samples of dental prostheses molded in patients and machined with the use of a dental laboratory CAD/CAM system. The results showed that the mechanical properties of pre-sintered blocks are different from prosthetics machined by CAD/CAM and sintered under the same conditions used in the laboratories of the prosthesis. The defects created during machining reduce the mechanical properties of zirconia.

Several CAD/CAM systems are available to dental prosthesis laboratories that can be used to make all-ceramic copings and frameworks. In Brazil, the use of these systems presents low demand, due principally the high blocks ceramics cost used for theses systems. The ceramic blocks are imported. To increase the dental ceramic CAD/CAM applications is necessary develop and produce the ceramics blocks in Brazil. The purpose of the present work is to compare the mechanical properties of blocks of zirconium developed in the Brazil (ProtMat® Co) and imported (VITA). It was determined the mechanical and physics properties of the two types of blocks of zirconium stabilized with ytria. The blocks have been sinterized at 1530 °C and their mechanical and physics properties were measured. The x-ray diffraction analysis showed only tetragonal phase, which improve the blocks toughness. The Vickers hardness and fracture toughness were 1300HV and 9 MPam1/2, respectively. High bending fracture resistance was obtained for both materials with average values of 910MPa. The Weibull modulus was m=10 for Brazilian and imported blocks. It was not observed an important difference among the microstructures and mechanical properties of the analyzed zirconium blocks.

Osseointegration has been defined as “a direct structural and functional connection between ordered, living bone and the surface of a load-carrying implant”. However, titanium and its alloys cannot directly bond to living bone after being implanted into the body. The osseointegration of titanium dental implants is critically dependent on the implant surface properties. Various surface modifications have been proposed in order to provide commercially pure titanium with bioactive bone bonding ability. In the present work, the titanium dental implant surface morphology was modified by acid etching and electrochemical treatments with the purpose of enhancing tissue response, and decreasing the waiting time for implant loading. The results show that surface morphology, topography, roughness and chemical composition were changed by the treatments and these changes has a significant influence on osseointegration. The best results were observed in the samples submitted to the electrochemical treatment.

The objective of this study was to physico/chemically characterize a commercially available and a newly developed Bioglass and also to evaluate their degradation properties. Materials and Method: Two bioresorbable glasses were utilized, a bioglass synthesized at Chemical Engineering College (University of São Paulo, Lorena, São Paulo) (BG1), and the other bioglass utilized was Biogran (BG2) (3i Implant Innovations, Brazil). Particles size distribution histograms were developed for both materials, and then they were characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) before and after immersion in simulated body fluid (SBF) for 30, 60, and 90 days. Results: The particle size distribution showed that the mean particle diameters at 10%, 50%, and 90% of the total volume were 17.65, 66.18, and 114.71 µm for BG1, and 354.54, 437.5, 525.00 µm for BG2. SEM images of BG1 showed that the as-received material had a rough surface and as the time of degradation elapsed, this surface became smooth. The images of BG2 showed that the as-received material also had a rough surface, and after immersion in SBF, the material’s crystalline content/morphology could be observed. The X-ray diffraction recorded that BG1 showed a silica peak, not seen at BG2. FTIR revealed that both bioglasses were of similar composition, except for the CO3-carbonate minor peak, present at the BG2 sample. Conclusions: 1. The particle size distribution showed a polydispersed pattern for both materials. 2. The material suffered degradation, and the decomposition increased as a function of immersion in SBF. 3. Both bioglasses had similar composition.

Several CAD/CAM systems are available to dental prosthesis laboratories which can be used to fabricate all-ceramic copings and frameworks. The use of these systems presents low demand, due principally the high blocks ceramics cost used for theses systems. Usually, these ceramic blocks are sintered at high temperatures, between 1450 and 15500C, resulting in micrometric ZrO2 microstructure. A considerable innovation in these ceramics systems used in CAD/CAM applications was introduced by the use of nanometric-tetragonal ZrO2 blocks, which are sintered at low sintering temperatures resulting in nanometric grains morphology and improved mechanical properties. The purpose of the present work is to characterize the mechanical properties of nanoparticled zirconium oxide blocks comparing with commercial micrometric ceramic parts. XRD patterns showed that the blocks have only the tetragonal-ZrO2 as crystalline phase. The tetragonal-monoclinic transformation phase was responsible for the excellent mechanical properties. Nanometric blocks presented hardness of 13GPa, fracture toughness of 11MPam1/2 , bending strength of 1020MPa and Weibull modulus, m=14, while micrometric ZrO2 blocks similar hardness, fracture toughness 8.5MPam1/2, bending strength of 850MPa and Weibull modulus of 10.

Yttria stabilized tetragonal zirconia (Y-TZP) ceramics were sintered by liquid phase sintering at low temperatures using bioglass as sintering additive. ZrO2–bioglass ceramics were prepared by mixing a ZrO2 stabilized with 3 mol%Y2O3 and different amounts of bioglass based on 3CaO·P2O5–MgO–SiO2 system. Mixtures were compacted by uniaxial cold pressing and sintered in air, at 1200 and 1300 °C for 120 min. The influence of the bioglass content on the densification, tetragonal phase stability, bending strength, hardness and fracture toughness was investigated. The ceramics sintered at 1300 °C and prepared by addition of 3% of bioglass, exhibited the highest strength of 435 MPa, hardness of 1170 HV and fracture toughness of 6.3 MPa m1/2. These results are related to the low monoclinic phase content, high relative density and the presence of the thermal residual stress generated between the ZrO2-matrix and bioglass grain boundary, contributing to the activation of the toughening mechanisms.

Titanium alloys are considered to be the most attractive metallic materials for biomedical applications. Ti-6Al-4V has long been favored for biomedical applications. However, for permanent implant applications the alloy has a possible toxic effect resulting from released vanadium and aluminum. For this reason, vanadium-and aluminum-free alloys have been introduced for implant applications.

In this work, the static mechanical properties and cyclic fatigue life of 3 mol. (%) Y2O3-stabilized tetragonal zirconia polycrystalline (3Y-TZP) ceramics were investigated. Pre-sintered samples were sintered in air at 1600 °C for 120 minutes, and characterized by X ray diffraction and scanning electronic microscopy. Hardness and fracture toughness were determined by Vicker's indentation method, and Modulus of Rupture was determined by four-point bending testing. Fully dense sintered samples, near to 100% of theoretical density, presented hardness, fracture toughness and bending strength of 13.5 GPa, 8.2 MPa.m½ and 880 MPa, respectively. The cyclic fatigue tests were also realized using four-point bending testing, within a frequency of 25 Hz and stress ratio R of 0.1. The increasing of load stress lead to decreasing of the number of cycles and the run-out specimens number. The tetragonal-monoclinic (t-m) ZrO2-transformation observed by X ray diffraction contributes to the increasing of the fatigue life. The 3Y-TZP samples clearly presents a range of loading conditions where cyclic fatigue can be detected.

The purpose of this study was to evaluate the fracture resistance and the fracture surface of NiTi SMA engine-driven endodontics files submitted to clockwise torsion. The maximum angular deflection and the maximum torque were analyzed without axial loading. The helical plastic deformations and the fracture surface morphology were evaluated by Scanning Electron Microscopic. The results showed that there was a significant statistical difference in the maximum fracture torque and no statistical difference for the angular deflection for the analyzed files. In relation to the maximum torque at the instant of the fracture, one of the brand presented better performance than the other. According to Scanning Electron Microscopic evaluation, all the files showed ductile fracture morphology.

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T19:05:37Z No. of bitstreams: 1 S1516-14392007000100011.pdf: 1230549 bytes, checksum: 4852a7a3e94a624d9987724c612c883f (MD5) Made available in DSpace on 2013-08-22T19:05:37Z (GMT). No. of bitstreams: 1 S1516-14392007000100011.pdf: 1230549 bytes, checksum: 4852a7a3e94a624d9987724c612c883f (MD5) Previous issue date: 2007-03-01 Made available in DSpace on 2013-09-30T20:09:31Z (GMT). No. of bitstreams: 2 S1516-14392007000100011.pdf: 1230549 bytes, checksum: 4852a7a3e94a624d9987724c612c883f (MD5) S1516-14392007000100011.pdf.txt: 15810 bytes, checksum: eac5a94e2e92abeed52708937a4b5001 (MD5) Previous issue date: 2007-03-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:17:43Z No. of bitstreams: 2 S1516-14392007000100011.pdf: 1230549 bytes, checksum: 4852a7a3e94a624d9987724c612c883f (MD5) S1516-14392007000100011.pdf.txt: 15810 bytes, checksum: eac5a94e2e92abeed52708937a4b5001 (MD5) Made available in DSpace on 2014-05-20T15:17:43Z (GMT). No. of bitstreams: 2 S1516-14392007000100011.pdf: 1230549 bytes, checksum: 4852a7a3e94a624d9987724c612c883f (MD5) S1516-14392007000100011.pdf.txt: 15810 bytes, checksum: eac5a94e2e92abeed52708937a4b5001 (MD5) Previous issue date: 2007-03-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) InCeram (Vita Zahnfabrik- Germany) is known as a high strength ceramic being used for core crowns and for fixed partial denture frameworks. InCeram system consists of slip-casting technique which is used for to build the framework, which is then pre-sintered obtaining an open-pore microstructure. The material gains its strength by infiltration of the lanthanum glass into the porous microstructure. In this work, commercial alumina (Al2O3), alumina-zirconia (Al2O3-ZrO2) and glasses lanthanum oxide-rich powders, used in InCeram system, were characterized, using x ray diffraction, dilatometry and scanning electron microscopy. The characteristics of these powders were related aiming to consider their substitution for new ceramic materials. Universidade de São Paulo Escola de Engenharia de Lorena Departamento de Engenharia de Materiais Universidade Estadual de São Paulo Faculdade de Odontologia de São José dos Campos Instituto Militar de Engenharia

Mini-implantes ortodônticos de Ti-6Al-4V podem liberar íons metálicos devido à corrosão in vivo da liga em fluidos corporais. Os produtos de corrosão liberados podem favorecer a ocorrência de efeitos indesejáveis no corpo humano. O objetivo deste estudo foi determinar as concentrações de titânio, alumínio e vanádio nos órgãos de coelhos (rins, fígado e pulmões), após a inserção de mini-implantes ortodônticos fabricados a partir da liga Ti-6Al-4V. Dezoito coelhos da raça Nova Zelândia tiveram quatro mini-implantes inseridos em sua tíbia esquerda e cinco coelhos foram usados como controle. Após 1, 4 e 12 semanas os coelhos foram submetidos à eutanásia, os tecidos selecionados foram removidos e preparados para análise por espectroscopia de absorção atômica com forno de grafite. Quantidades variadas Ti, Al e V foram detectadas nos grupos testados comprovando que existe liberação de íons metálicos por mini-implantes ortodônticos de Ti-6Al-4V. Apesar da tendência de liberação de íons pela liga de titânio, as quantidades de metais detectadas foram extremamente baixas. Sendo assim, mini-implantes ortodônticos de Ti-6Al-4V podem ser usados com segurança como dispositivos auxiliares de ancoragem ortodôntica.

Mini-implantes têm sido utilizados com sucesso como elemento de ancoragem ortodôntica, mas a diminuição do tamanho e a aplicação precoce da carga são requisitos importantes para a otimização da metodologia. A proposta deste trabalho foi avaliar a evolução da fixação óssea de mini-implantes de titânio carregados imediatamente. Nove coelhos da raça Nova Zelândia foram utilizados neste estudo. Em cada animal foram inseridos 4 mini-implantes de titânio grau 5 (liga Ti-6Al-4V) , dos quais 2 foram carregados imediatamente com 1 N. Os animais foram eutanasiados após 1, 4 e 12 semanas e as amostras foram divididas em seis grupos, sendo 3 grupos carregados e 3 grupos sem carga. O ensaio de torque de remoção dos implantes foi realizado e os resultados tratados estatisticamente com o módulo ANOVA e pós-teste de Tukey. Após 1 e 4 semanas de cicatrização não foi detectada diferença estatisticamente significativa nos valores de torque de remoção, independente do carregamento. Entretanto, após 12 semanas, tanto o grupo carregado quanto o não carregado apresentaram aumento significativo no torque de remoção e os maiores valores foram atribuídos ao grupo sem carregamento. O carregamento imediato resultou em menor fixação óssea dos mini-implantes após 12 semanas de cicatrização, contudo não comprometeu a estabilidade dos implantes.

The use of materials for biomedical applications has become vital to enhance the quality of life and longevity of human beings. Commercially pure titanium (cpTi) and titanium alloys are the most adequate materials for some biomedical applications, but cpTi and the Ti-6Al-4V alloy (Ti G5) have limitations for biomedical application due to low mechanical strength and the possibility of ion release, respectively. In order to address this problem, commercially pure ultrafine grained titanium (UFG Ti) obtained by severe plastic deformation (SPD) has been suggested as a promising alternative for biomedical applications. This thermomechanical process is able to improve the strength of cpTi and titanium alloys while keeping their excellent biocompatibility. The purpose of this review was to compare the mechanical strength of UFG Ti, cpTi and a Ti G5 alloy. In addition, the biological performance of UFG Ti was also evaluated by in vivo testing. Prodigious improvements were seen in surface topography, wettability and in homogeneity of oxide layer. The overall improvements in microstructure provided by ECAP technique coupled with surface etching resulted in a remarkable performance of cpTi alloy for biomedical applications. Refereed/Peer-reviewed

The purpose of this work was to study the influence of screw length and bone thickness on the stability of temporary implants. A total of 96 self-drilling temporary screws with two different lengths were inserted into polyurethane blocks (n = 66), bovine femurs (n = 18) and rabbit tibia (n = 12) with different cortical thicknesses (1 to 8 mm). Screws insertion in polyurethane blocks was assisted by a universal testing machine, torque peaks were collected by a digital torquemeter and bone thickness was monitored by micro-CT. The results showed that the insertion torque was significantly increased with the thickness of cortical bone from polyurethane (p &lt, 0.0001), bovine (p = 0.0035) and rabbit (p &lt, 0.05) sources. Cancellous bone improved significantly the mechanical implant stability. Insertion torque and insertion strength was successfully moduled by equations, based on the cortical/cancellous bone behavior. Based on the results, insertion torque and bone strength can be estimate in order to prevent failure of the cortical layer during temporary screw placement. The stability provided by a cortical thickness of 2 or 1 mm coupled to cancellous bone was deemed sufficient for temporary implants stability.

In this work, the effects of alumina additions on the properties of the ZrO2-Al2O3 ceramic composites were investigated. Samples of ZrO2 with Al2O3 additions varying between 0 and 30wt-% were prepared. The powder mixtures were milled, compacted by uniaxial cold pressing and sintered at 16000C, in air, for 2 hours. The sintered samples were characterized by their relative density, phase composition and microstructure. As mechanical properties at room temperature, their Vickers hardness and fracture toughness were determined: In all sintering conditions and Al2O3 amounts, the samples presented relative density higher that 99%. The Al2O3 addition produces a linear increase of the hardness, reaching values between 1350 and 1610 HV for the addition of 0 and 30% of alumina, respectively. The fracture toughness was near to 8 MPam1/2 in all conditions. The phase composition, microstructure and relative density were correlated in order to interpret the mechanical properties obtained.

In this work the influence of isothermal sintering time on the microstructural development of ZrO2-Al2O3 composite was studied. Powder mixture of ZrO2 containing 20 wt% Al2O3 was prepared by milling, compaction and sintering at 16000C, in air. The isothermal sintering time at 16000C was varied between 0 and 1440 min. The sintered samples were characterized in terms of phase composition and relative density. Their microstructures were characterized by grain size distributions and average grain size. These results were evaluated using the classic grain growth equation as a function of time, determining the grain growth exponent of these materials. Furthermore, the microstructural aspects were related to the mechanical properties (Vicker’s hardness and fracture toughness) of these composites.

The purpose of the present work is to compare the mechanical properties of commercially available NiTi orthodontic archwires lots. Superelastic (SE) and heat-activated (HA) NiTi archwires from two lots of six manufacturers (3M, GAC, Tp, Orthosource, Orthometric and Morelli) were partitioned into eleven groups (n=132) and tested under three-point benDing tests. The difference between the highest (151.35 gf, Tp) and lowest (98.43 gf, 3M) unloaDing stresses among SE groups was 53.77% (p.05), whereupon there are equivalences in wires commercial offered at different costs. Refereed/Peer-reviewed

The objective was to analyze the influence of dentary and orthopedic forces under static and dynamic loads in temporary screw stability. Self-drilling titanium (Ti6Al4V) screws (6 × 1.5 mm) were inserted and removed from pig ribs. Screws were loaded by static loads of 2 N and 5 N for 5 weeks. Dynamic force was applied during 56,000 cycles for simulations of a patient’s opening–closing mouth movements. Dynamic applied loads ranged from 2 to 5 N and from 5 to 7 N under a frequency of 1 Hz. Torque peak values at placement and removal were measured before and after static and dynamic cycles. Similarities in torque peaks (p = 0.3139) were identified at placement (12.54 Ncm) and removal (11.2 Ncm) of screws after a static load of 2 N. Statistical comparisons showed significant stability loss after dynamic cycles under loads of 2 N (64.82% at p = 0.0005) and 5 N (64.63% at p = 0.0026). Limited stability loss occurred in temporary screws submitted to 2 N static forces (p = 0.3139). The detrimental effects of dynamic cycles in temporary screws stability was attested after the simulation of dentary and skeletal forces, being intermittent forces more relevant in the loss of mechanical stability. Refereed/Peer-reviewed

Cylindrical dental implants made of commercially pure titanium were analysed in four different surface finishes: as-machined, Al2O3 blasted with Al2O3 particles, plasma-sprayed with titanium beads and electrolytically coated with hydroxyapatite. Scanning electron microscopy (SEM) with Energy Dispersive X-ray Analysis (EDX) revealed the topography of the surfaces and provided qualitative results of the chemical composition of the different implants. X-ray Photoelectron Spectroscopy (XPS) was used to perform chemical analysis on the surface of the implants while Laser Scanning Confocal Microscopy (LSM) produced topographic maps of the analysed surfaces. Optical Profilometry was used to quantitatively characterise the level of roughness of the surfaces. The implant that was plasma-sprayed and the hydroxyapatite coated implant showed the roughest surface, followed by the implant blasted with alumina and the as-machined implant. Some remnant contamination from the processes of blasting, coating and cleaning was detected by XPS.

The aim of this study was to compare the surface morphology and fracture torque resistance of as-received, sterilized and retrieved mini-implants in order to evaluate the fracture risks of re-using orthodontic mini-implants after sterilization. Thirty mini-implants retrieved from 19 patients, twenty as-received and twenty autoclaved mini-implants from the same manufacturer were used in this study. Ten samples from each group were analyzed by scanning electron microscopy and the remaining specimens were tested for their fracture torque resistance. Results were statistically analyzed using one-way ANOVA. No defects or corrosion could be identified in autoclaved and retrieved mini-implants, but a worn surface and scratch marks could be observed on the retrieved ones. A statistical significant difference in the fracture torque was observed between the as-received and the retrieved groups. Re-use of retrieved mini-implants should not be recommended because their torque resistance is reduced. As-received mini-implants submitted to autoclave sterilization can be recommended to be used clinically.

In the present work, the composition of H- 13 tool steel was modified with respect to the vanadium content to include an addition of niobium to obtain improved austenite grain size control without altering the tempering response of the steel. Optical metallography and transmission electron microscopy (TEM) observation of extraction replicas showed that the new steel had a smaller austenite grain size and a finer carbide size distribution than the vanadium steel, which indicates a higher potential toughness.

In the present work the relationship between the microstructure and the hardness of an AISI H-13 tool steel both with and without an addition of niobium was studied. Extensive investigation by direct observation using optical and electron microscopy was carried out. It was found that the deformation during ausforming introduces changes in the microstructure, such as high dislocation density and carbide precipitation, which affect the hardness of the steels. The results show that the partial substitution of vanadium by niobium does not lead to any significant change in the hardness of the hot work tool steels investigated.MST/1559

The purpose of this work is to present a metallographic study of a carbon steel bar perforated by the impulsive loading of a metallic jet. The results show that the passage of shock waves through the material has strong effects on its microstructure. The development of intense twinning, shear bands, grain growth, and recrystallization was observed.

No presente trabalho, a influência da temperatura e do tempo de sinterização no desenvolvimento microestrutural e propriedades de compósitos cerâmicos à base de ZrO2-Al2O3 foram estudados, visando futura aplicação deste material como componente de sistemas de implantes dentários. Compósitos de ZrO2 com adições de 20% de Al2O3 foram misturados/moídos, compactados e, em seguida, sinterizados em temperaturas de 1500 ou 1600°C. Em cada temperatura, os patamares de sinterização, foram variados de 0 a 480 minutos. Os corpos sinterizados foram caracterizados quanto às fases presentes, microestrutura, densidade relativa, além de dureza e tenacidade à fratura. Para uma avaliação biológica primária, testes de citotoxicidade baseados em cultura celular de mamíferos foram realizados. Os resultados indicaram que em todas as condições de sinterização as amostras apresentaram apenas duas fases cristalinas, ZrO2 tetragonal e alfa-Al2O3. É observado um aumento dos valores de propriedades mecânicas em função do aumento da temperatura de sinterização, os quais devem ser relatados ao leve aumento da densificação das amostras. Por outro lado, o aumento do tempo de isoterma de sinterização ocasiona uma redução considerável na dureza e na tenacidade à fratura das amostras que pode ser relacionada ao crescimento de grão da ZrO2 e Al2O3. A avaliação biológica demonstrou que os materiais obtidos são biocompatíveis, devido ao crescimento celular apresentado durante o teste citotoxicológico, indicando que esses compósitos cerâmicos podem ser caracterizados como biomateriais adequados para a aplicação em implantes. In the present work, the influence of the temperature and sintering time on the microstructural development of ZrO2-Al2O3 ceramic composite was studied, aiming at the viability of the application of this material as dental material. Tetragonal ZrO2 powder (Y-TZP) with additions of 20wt.% of Al2O3 were mixed, pressed and sintered at 1500 or 1600°C. In each temperature, the isothermal sintering time varied between 0 and 480 minutes. Sintered samples were characterized by crystalline phases, microstructure, relative density, hardness and fracture toughness. For primary biological evaluation, cytotoxicity tests based on cellular culture of mammals were carried through. The results indicated that in all sintering conditions the samples presented only two crystalline phases, tetragonal -ZrO2 e alpha-Al2O3. An increase of the mechanical properties values as a function of the sintering temperature increase was observed, due to the increase on the densification. On the other hand, the increase of the isothermal sintering time causes a considerable reduction in the hardness and fracture toughness, which can be related to the ZrO2 and Al2O3-grain growth. The biological evaluation demonstrated that these bioceramics are biocompatible, presenting cellular growth during the cytotoxic test, indicating that these ceramic composite can be characterized as biomaterials adjusted for the application in implantations.

The need for new materials to substitute injured or damaged parts of the human body has led scientists of different areas to investigate bioceramics since the 70's, when other materials in use started to show rejection problems. Ceramics show some advantages like being the material that best mimics the bone tissue, although present low toughness when compared with the metallic materials. As patients have become more and more demanding regarding esthetic and biocompatibility aspects of their dental restorations, ceramic material has become a main object of scientific interest especially from the material point of view. The alumina-zirconia composites are one of the relatively good and promising candidate for biomaterials application, due to biocompatibility and their mechanical properties that combines high flexural strength with a high toughness. The aim of the present work is to analyze the mechanical properties of these composites, where Y-TZP zirconia content was varied from 5 to 80 wt.% These systems can achieve a flexural strength 93 % and fracture toughness 29 % superior when compared to the pure alumina ceramics. These results showed that ceramic abutments components can be prepared for prosthetic rehabilitations with dental implants.