Surface Protection of Quaternary Gold Alloys by Thiol Self-Assembled Monolayers.

This work deals with a physical and chemical surface characterization of quaternary 18K, 14K, and 9K gold alloys and pure polycrystalline gold substrates. Surface microstructure and composition are evaluated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray fluorescence spectroscopy. Corrosion resistance of 18K gold alloys is explored by potentiodynamic polarization showing the influence of the manufacturing process on materials fabricated as plates and wires. The research is also in the framework of one of the most common strategies on the modification of metallic surface properties, i.e., the building of self-assembled monolayers (SAM) from organic thiols. The metal affinity of the head group to produce the coating of the substrate by covalent binding is approached by using thiol compounds with different molecular structures and functional group chemistries exposed to an electrolyte solution. Therefore, a comparative study on the surface protection of a quaternary 18K gold alloy and pure gold substrates by SAMs of 6-mercaptopurine (6MP), 1-decanethiol (DT), and 11-mercaptoundecanoic acid (MUA) has been carried out. Surface modification and SAM organization are followed by cyclic voltammetry (CV), and the behavior of the double layer of the electrode-electrolyte interface is evaluated by electrochemical impedance spectroscopy (EIS). The study of these materials allows us to extract fundamental knowledge for its potential application in improving the bioactive properties of different jewelry pieces based on 18K gold alloys.

Observable but Not Isolable: The RhAu24 (PET)181+ Nanocluster.

The synthesis and characterization of RhAu24 (PET)18 (PET = 2-phenylethanethiol) is described. The cluster is cosynthesized with Au25 (PET)18 and rhodium thiolates in a coreduction of RhCl3 , HAuCl4 , and PET. Rapid decomposition of RhAu24 (PET)18 occurs when purified from the other reaction products, precluding the study of isolated cluster. Mixtures containing RhAu24 (PET)18 , Au25 (PET)18 , and rhodium thiolates are therefore characterized. Mass spectrometry, X-ray photoelectron spectroscopy, and chromatography methods suggest a combination of charge-charge and metallophilic interactions among Au25 (PET)181- , rhodium thiolates and RhAu24 (PET)18 resulting in stabilization of RhAu24 (PET)18 . The charge of RhAu24 (PET)18 is assigned as 1+ on the basis of its stoichiometric 1:1 presence with anionic Au25 (PET)18 , and its stability is contextualized within the superatom electron counting rules. This analysis concludes that the Rh atom absorbs one superatomic electron to close its d-shell, giving RhAu24 (PET)181+ a superatomic electron configuration of 1S2 1P4 . Overall, an updated framework for rationalizing open d-shell heterometal dopant electronics in thiolated gold nanoclusters emerges.

A prospective interventional study to examine the effect of a silver alloy and hydrogel-coated catheter on the incidence of catheter-associated urinary tract infection.

INTRODUCTION: Catheter-associated urinary tract infection is a major hospital-acquired infection. This study aimed to analyse the effect of a silver alloy and hydrogel-coated catheter on the occurrence of catheter-associated urinary tract infection. METHODS: This was a 1-year prospective study conducted at a single centre in Hong Kong. Adult patients with an indwelling urinary catheter for longer than 24 hours were recruited. The incidence of catheter-associated urinary tract infection in patients with a conventional latex Foley catheter without hydrogel was compared with that in patients with a silver alloy and hydrogel-coated catheter. The most recent definition of urinary tract infection was based on the latest surveillance definition of the National Healthcare Safety Network managed by Centers for Disease Control and Prevention. RESULTS: A total of 306 patients were recruited with a similar ratio between males and females. The mean (standard deviation) age was 81.1 (10.5) years. The total numbers of catheter-days were 4352 and 7474 in the silver-coated and conventional groups, respectively. The incidences of catheter-associated urinary tract infection per 1000 catheter-days were 6.4 and 9.4, respectively (P=0.095). There was a 31% reduction in the incidence of catheter-associated urinary tract infection per 1000 catheter-days in the silver-coated group. Escherichia coli was the most commonly involved pathogen (36.7%) of all cases. Subgroup analysis revealed that the protective effect of silver-coated catheter was more pronounced in long-term users as well as female patients with a respective 48% (P=0.027) and 42% (P=0.108) reduction in incidence of catheter-associated urinary tract infection. The mean catheterisation time per person was the longest in patients using a silver-coated catheter (17.0 days) compared with those using a conventional (10.8 days) or both types of catheter (13.6 days) [P=0.01]. CONCLUSIONS: Silver alloy and hydrogel-coated catheters appear to be effective in preventing catheter-associated urinary tract infection based on the latest surveillance definition. The effect is perhaps more prominent in long-term users and female patients.

Accelerated Discovery of Ternary Gold Alloy Materials with Low Resistivity via an Interpretable Machine Learning Strategy.

New ternary gold alloys with low resistivities (ρ) were screened out via an interpretable machine learning strategy by using the support vector regression (SVR) model integrated with SHAP analysis. The correlation coefficient (R) and the root mean square error (RMSE) of test set were 0.876 and 0.302, respectively, indicating the strong generalization ability of the model. The average ρ of top 10 candidates was 1.22×10-7 â€…Ω m, which was 41% lower than the known minimum of 2.08×10-7 â€…Ω m. The outputs of SVR model were analyzed with the critical SHAP values including first ionization energy of C-site (584 kJ ⋅ mol-1 ), electronegativity of C-site (1.72) and the second ionization energy of B-site (1135 kJ ⋅ mol-1 ), respectively. Moreover, an online web server was developed to share the model at http://materials-data-mining.com/onlineservers/wxdaualloy.

The Effect of Different Foundation Materials on the Color of Monolithic Zirconia at Different Thicknesses.

STATEMENT OF THE PROBLEM: Monolithic zirconia restoration has been introduced to overcome the porcelain chipping. Different factors can affect the color of monolithic zirconia, so achieving the desired color in the restorations is considered as a challenge. PURPOSE: The purpose of this in vitro study was to determine the effect of different foundation materials on the color of monolithic zirconia at different thicknesses. MATERIALS AND METHOD: In this experimental study, thirty ceramic disks in three thicknesses (i.e. 0.6mm, 1.1mm and 1.5mm) were fabricated from high translucency shade A2 monolithic zirconia block. Disk shaped foundation materials were fabricated from nickel chromium alloy (Ni-Cr), non-precious gold alloy (NPG), zirconia, and shade A2 composite resin. The color was measured by a spectrophotometer. The color differences (∆E) in the control and the test groups were calculated. The data were analyzed using two way ANOVA and compared with the posthoc Tukey test (a=0.05). RESULTS: Ceramic thickness and foundation materials had a significant effect on the mean values of ∆E of monolithic zirconia ceramics (p= 0.001). The highest amount of ∆E value was observed in NPG, while Ni-Cr resulted in the lowest ∆E. Unacceptable results (∆E>2.25) were observed for monolithic zirconia ceramics on NPG foundation material with a thicknesses of 0.6 and 1.1mm. The mean L* values of all foundation materials were higher than those of the control group except for Ni-Cr. The highest a* was seen in NPG and the mean b* values of all tested foundation materials were higher than those of the control group except for Ni-Cr. CONCLUSION: Increasing the thickness of monolithic zirconia decreased the color mismatch. High translucent monolithic zirconia could mask the color of Ni-Cr and zirconia in all three thicknesses (∆E<2.25), while it could not mask the color of NPG under thickness of 1.5mm.

Robust Colloidal Synthesis of Palladium-Gold Alloy Nanoparticles for Hydrogen Sensing.

Metal nanoparticles are currently used in a variety of applications, ranging from life sciences to nanoelectronic devices to gas sensors. In particular, the use of palladium nanoparticles is gaining increasing attention due to their ability to catalyze the rapid dissociation of hydrogen, which leads to an excellent response in hydrogen-sensing applications. However, current palladium-nanoparticle-based sensors are hindered by the presence of hysteresis upon hydride formation and decomposition, as this hysteresis limits sensor accuracy. Here, we present a robust colloidal synthesis for palladium-gold alloy nanoparticles and demonstrate their hysteresis-free response when used for hydrogen detection. The obtained colloidal particles, synthesized in an aqueous, room-temperature environment, can be tailored to a variety of applications through changing the size, ratio of metals, and surface stabilization. In particular, the variation of the viscosity of the mixture during synthesis resulted in a highly tunable size distribution and contributed to a significant improvement in size dispersity compared to the state-of-the-art methods.

In vitro investigations on retention force behavior of conventional and modern double crown systems.

OBJECTIVE: This study aimed to investigate the effects of long-term use on the retention force and wear behavior of double crown systems. METHODS: Based on a common double crown design sixty pairs of telescopic crowns were fabricated and divided into six groups, each consisting ten samples: "Gold standard" cast gold alloy primary and secondary crown (GG) and cast non-precious alloy (NN), computer-aided design (CAD)/computer-aided manufacturing (CAM)-milled zirconia primary crown and galvanoformed secondary crown (ZG), CAD/CAM-milled non-precious alloy primary and secondary crown (CC NN), CAD/CAM-milled zirconia primary crown and non-precious alloy secondary crown (CC ZN) and CAD/CAM-milled zirconia primary crown and polyetheretherketone (PEEK) secondary crown (CC ZP). In the constant presence of artificial saliva, all samples were subjected to 10,000 joining-separation cycles at a velocity of 120 mm/min. Wear was analyzed by reflected light microscopy and confocal microscopy before and after artificial aging. RESULTS: Retention force losses were observed in each group after long-term use, with significant losses in the groups ZG and CC ZP (pZG = 0.01, pCC ZP = 0.049). During artificial aging, no significant differences in pull-off force were recorded for groups GG, NN and CC ZN. Regarding wear, merely the Y-TZP primary crowns of the CC ZP group displayed no surface changes. SIGNIFICANCE: All tested production methods and material combinations seem to be suitable for clinical practice. CAD/CAM technology allows similarly predictable results to be achieved as the gold standard. Confocal microscopy is recommended for surface examinations of double crowns.

Evaluating the Wear of Resin Teeth by Different Opposing Restorative Materials.

The aim of this study was to evaluate the wear properties of resin teeth with different opposing dental restorative materials. One type of resin tooth (Trubyte Biotone) was tested against six types of restorative materials including type III gold alloy (GO), monolithic zirconia (MZ), lithium disilicate glass ceramic (LD), nickel-chromium alloy (NC), feldspathic ceramic (FC), and steatite (ST). Two-body wear tests were performed under a vertical load of 5 kgf and thermo-cycling at 5/55 °C with a total of 120,000 cycles. The wear amount was quantified by measuring the volume loss of the resin teeth and the vertical substance loss of the opposing materials using three-dimensional images. The FC group showed a significantly greater amount of wear of the resin teeth, followed by the ST, NC, LD, MZ, and GO groups. The GO group showed significantly less wear of resin teeth than the other groups. There were no statistically significant differences in the wear of opposing restorative materials between groups. Within the limits of this study, it is recommended that zirconia, rather than feldspathic ceramic, should be used for restorations in the esthetic zone, and gold alloy should be used for areas with little or no esthetic demand.

High hardness in the biocompatible intermetallic compound ß-Ti3Au.

The search for new hard materials is often challenging, but strongly motivated by the vast application potential such materials hold. Ti3Au exhibits high hardness values (about four times those of pure Ti and most steel alloys), reduced coefficient of friction and wear rates, and biocompatibility, all of which are optimal traits for orthopedic, dental, and prosthetic applications. In addition, the ability of this compound to adhere to ceramic parts can reduce both the weight and the cost of medical components. The fourfold increase in the hardness of Ti3Au compared to other Ti-Au alloys and compounds can be attributed to the elevated valence electron density, the reduced bond length, and the pseudogap formation. Understanding the origin of hardness in this intermetallic compound provides an avenue toward designing superior biocompatible, hard materials.

Role of Small Pd Ensembles in Boosting CO Oxidation in AuPd Alloys.

We present a theoretical explanation on how PdAu alloy catalysts can enhance the oxidation of CO molecules based on density functional theory calculations of CO adsorption and oxidation on AuPd/Pd(111) surfaces. Our study suggests that the enhanced activity is largely attributed to the possible existence of "partially-poisoned" Pd ensembles that accommodate fewer CO molecules than Pd atoms. Whereas the oxidation of preadsorbed CO is likely governed by O2 trapping, our study shows that small Pd ensembles such as dimers and compact trimers tend to provide more active sites than larger ensembles; CO adsorbed on a Pd monomer is found to react hardly with O2 to form CO2. In addition, we find the tendency of CO-induced Pd agglomeration, which may in turn facilitate CO oxidation by creating more dimers and compact trimers as compared with the adsorbate-free surface where monomers are likely prevailing.

The effect of copper alloy scaler tip on the surface roughness of dental implant and restorative materials / 대한치과보철학회지

PURPOSE: This study is designed to investigate the various impacts of different types of scaler tips such as cooper alloy base tip and the others on the surface roughness of teeth and implant by the method which is currently in clinical use. MATERIALS AND METHODS: Four different types of disc shaped porcelain, titanium, zirconia, and Type III gold alloy dental materials sized 15 mm diameter, 1.5 mm thickness were used for the experiment. Plastic hand curette (Group PS), cooper alloy new tip (Group IS), and stainless steel tip (Group SS) were used as testing appliances. A total of 64 specimens were used for this study; Four specimens for each material and appliance group. Surface roughness was formed with 15 degree angle in ultrasonic scaler tip and with 45 degree angle in hand curette of instrument tip and the specimen surface with 5 mm long, one horizontal-reciprocating motion per second for 30 seconds by 40 g force. To survey the surface roughness of each specimen, a field emission scanning electron microscope, an atomic force microscope, and a surface profiler were used. (Ra, microm). RESULTS: According to SEM, most increased surface roughness was observed in SS group while IS groups had minimal roughness change. Measurement by atomic force microscope presented that the surface roughness of SS group was significantly greater than those of PS, IS and control groups in the type III gold alloy group (P<.05). IS group showed lesser surface roughness changes compared to SS group in porcelain and gold alloy group (P<.05). According to surface profiler, surface roughness of SS group showed greater than those of PS, IS and control groups and IS group showed lesser than those of SS group in all specimen groups. Type III gold alloy group had large changes on surface roughness than those of porcelain, titanium, zirconia (P<.05). CONCLUSION: The result of this study showed that newly developed copper alloy scaler tip can cause minimal roughness impacts on the surface of implant and dental materials; therefore this may be a useful alternative for prophylaxis of implant and restored teeth.

Bond strength of gold alloys laser welded to cobalt-chromium alloy.

The objective of this study was to investigate the joint properties between cast gold alloys and Co-Cr alloy laser-welded by Nd:YAG laser. Cast plates were fabricated from three types of gold alloys (Type IV, Type II and low-gold) and a Co-Cr alloy. Each gold alloy was laser-welded to Co-Cr using a dental laser-welding machine. Homogeneously-welded and non-welded control specimens were also prepared. Tensile testing was conducted and data were statistically analyzed using ANOVA. The homogeneously-welded groups showed inferior fracture load compared to corresponding control groups, except for Co-Cr. In the specimens welded heterogeneously to Co-Cr, Type IV was the greatest, followed by low-gold and Type II. There was no statistical difference (P<0.05) in fracture load between Type II control and that welded to Co-Cr. Higher elongations were obtained for Type II in all conditions, whereas the lowest elongation occurred for low-gold welded to Co-Cr. This study indicated that, of the three gold alloys tested, the Type IV gold alloy was the most suitable alloy for laser-welding to Co-Cr.

Monte Carlo dosimetry for I125 and Pd103 eye plaque brachytherapy.

A Monte Carlo study of dosimetry for eye plaque brachytherapy is performed. BrachyDose, an EGSnrc user code which makes use of Yegin's multi-geometry package, is used to fully model I125 (model 6711) and Pd103 (model 200) brachytherapy seeds and the standardized plaques of the Collaborative Ocular Melanoma Study (COMS). Three-dimensional dose distributions in the eye region are obtained. In general, dose to water is scored; however, the implications of replacing water with eye tissues are explored. The effect of the gold alloy (Modulay) backing is investigated and the dose is found to be sensitive to the elemental composition of the backing. The presence of the silicone polymer (Silastic) seed carrier results in substantial dose decreases relative to water, particularly for Pd103. For a 20mm plaque with a Modulay backing and Silastic insert, fully loaded with 24 seeds, the dose decrease relative to water is of the order of 14% for I125 and 20% for Pd103 at a distance of 1cm from the inner sclera along the plaque's central axis. For the configurations of seeds used in COMS plaques, interseed attenuation is a small effect within the eye region. The introduction of an air interface results in a dose reduction in its vicinity which depends on the plaque's position within the eye and the radionuclide. Introducing bone in the eye's vicinity also causes dose reductions. The dose distributions in the eye for the two different radionuclides are compared and, for the same prescription dose, Pd103 generally offers a lower dose to critical normal structures. BrachyDose is sufficiently fast to allow full Monte Carlo dose calculations for routine clinical treatment planning.

Misfit profile of dental bridges

Ante la evidencia de que los puentes odontológicos (PO) desadaptan más que las restauraciones individuales y que la desadaptación en prótesis fija es un factor determinante del fracaso, se llevóa cabo un estudio comparativo del perfil de desadaptación de los PO más utilizados en rehabilitación bucal: el PO colado en oro y el colado en aleación no preciosa y porcelana fundida.A partir de este, podemos trasladar al clínico las ventajas y debilidades de un tipo de estructura con respecto a la otra. Los resultados obtenidos muestran dos perfiles diferentes, presentandoel PO ceramometálico un comportamiento más desordenado que el colado en oro, la restauración del pilarposterior se separa de la pieza dentaria por distal, se acerca por mesial y mantiene esta separación en distal y mesial del pilar anterior. El PO colado en oro se separa en los extremos, distal del molar y mesial del premolar y se acerca marcadamente en las caras vecinas al tramo, distal del premolar y mesial del molar. Ha quedado también demostrado que el comportamiento adaptativo,a pesar de ser diferente, es menor en las aleaciones no nobles con porcelana fundida con respecto a la aleación de oro, relegadas estas últimas, a un bajo porcentaje en su uso clínico en rehabilitación, debido a la demanda estética y los altos costos. El impacto de este trabajo en la clínica consiste en que el PO ceramometálico ha desadaptado más en las áreas donde su confección en boca es más dificultosa por su visión e inaccesibilidad (AU)

Misfit profile of dental bridges

Ante la evidencia de que los puentes odontológicos (PO) desadaptan más que las restauraciones individuales y que la desadaptación en prótesis fija es un factor determinante del fracaso, se llevóa cabo un estudio comparativo del perfil de desadaptación de los PO más utilizados en rehabilitación bucal: el PO colado en oro y el colado en aleación no preciosa y porcelana fundida.A partir de este, podemos trasladar al clínico las ventajas y debilidades de un tipo de estructura con respecto a la otra. Los resultados obtenidos muestran dos perfiles diferentes, presentandoel PO ceramometálico un comportamiento más desordenado que el colado en oro, la restauración del pilarposterior se separa de la pieza dentaria por distal, se acerca por mesial y mantiene esta separación en distal y mesial del pilar anterior. El PO colado en oro se separa en los extremos, distal del molar y mesial del premolar y se acerca marcadamente en las caras vecinas al tramo, distal del premolar y mesial del molar. Ha quedado también demostrado que el comportamiento adaptativo,a pesar de ser diferente, es menor en las aleaciones no nobles con porcelana fundida con respecto a la aleación de oro, relegadas estas últimas, a un bajo porcentaje en su uso clínico en rehabilitación, debido a la demanda estética y los altos costos. El impacto de este trabajo en la clínica consiste en que el PO ceramometálico ha desadaptado más en las áreas donde su confección en boca es más dificultosa por su visión e inaccesibilidad

Comparación In Vitro de la adaptación marginal entre incrustaciones MOD maquinadas con el sistema IPS e: max CAD y restauraciones MOD en oro colado tipo III / valuation of marginal adaptation In Vitro of MOD fillings with an enamel finish manufactured with IPS e: max CAD (computer assisted design) and with gold type III

Objetivo: comparar la adaptación marginal In Vitro de incrustaciones MOD con terminación en esmalte fabricadas con IPS e.max CAD (Computer Asisted Desing) y fabricadas en oro tipo III. Materiales y métodos: En este estudio experimental exploratorio se uso una muestra no probabilística de 15 premolares sanos por cada uno de los dos grupos; IPS e.max CAD y oro tipo III.A todos los premolares se les realizó cavidades MOD estandarizadas para los 2 grupos. Los dientes preparados fueron asignados aleatoriamente a cada grupo. Las incrustaciones del grupo IPS e.max CAD fueron elaboradas con el sistema CEREC 3 y las incrustaciones en oro fueron elaboradas por los investigadores. Se tomaron estereo microfotografías de todas las muestras sobre papel milimetrado, y las imágenes fueron analizadas mediante el programa ImageTool. Se tomaron tres medidas adaptación marginal en el área proximal mesial o distal de cada muestra, que fueron promediadas y reportadas en micras. Los datos fueron analizados mediante ANOVA y Test de Mann-Whitney. Resultados: el 98% del total de las incrustaciones en oro y el 47% del total de las incrustaciones de IPS e.max CAD presentaron una adaptación marginal < a 120 micras. El promedio de desadaptación marginal del grupo IPS e.max CAD fue 122.8 μ + 44.1, mientras que para el grupo oro fue de 75.3 μ+42,6 encontrándose diferencias estadísticamente significativas entre los dos. Conclusiones: El oro reporta mejor adaptación marginal en restauraciones inlays MOD que los sistemas maquinados como el sistema IPS e.max CAD.

Objective: To compare In Vitro, the marginal adaptation of MOD fillings with an enamel finish manufactured with IPS e.max CAD (Computer Assisted Design) and those manufactured with gold type III. Materials and methods: In this exploratory experimental study, a non-probabilistic sample of 15 healthy premolars for each of the two groups (IPS e.max CAD and gold type III) was used. Standardized MOD cavities were made in all the premolars for both groups. The prepared teeth were randomly assigned to each group. The IPS e.max CAD fillings were made using the CEREC 3 system and the gold fillings were made by the researchers. Stereo microphotographs of all the samples were taken on millimeter paper and the images were analyzed using the Image Tool software. Three marginal adaptation measurements in the mesial proximal or distal area were taken for every sample; they were averaged and reported in microns. The data was analyzed using ANOVA and the Mann-Whitney test. Results: 98% of all the gold fillings and 47% of all the IPS e.max CAD fillings showed a marginal adaptation of less than or equal to 120 microns. The marginal unfitness average for the IPD e.max CAD group was 122.8 + 44.1 μm, and for the gold fillings group it was 75.3 + 42.6 μm. There was a statistically significant differences between the groups. Conclusions: Gold reports a better marginal adaptation for inlay MOD fillings than manufactured systems like IPS e.max CAD system.

A morphologic evaluation of defects created by a piezoelectric ultrasonic scaler on casting gold alloy / 대한치주과학회지

PURPOSE: In this study we evaluated the morphologic aspects of defects created by a piezoelectric ultrasonic scaler with scaler tip on casting gold alloy using scanning electron microscope (SEM) images and defect surface profiles. METHODS: 54 blocks of type III casting gold alloy (Firmilay, Jellenko Inc, CA, USA) were scaled by a piezoelectric ultrasonic scaler (P-MAX, Satelec, France) with scaler tip (No. 1 tip) on a sledge device. 2-dimensional profiles of defects on all samples were investigated by a surface profilometer (a-Step 500, KLA-Tencor, CA, USA). The selected working parameters were lateral force (0.5 N, 1.0 N, 2.0 N), mode (P mode, S mode), and power setting (2, 4, 8). SEM images were obtained. Defect surface profiles were made on Microsoft Excel program using data obtained by a surface profilometer. RESULTS: Among P mode samples, there were similarities on defect surface profiles and SEM images regardless of lateral force. The defects created in P mode were narrow and shallow although the depth and the width increased as power setting changed low (2) to high (8). In P mode samples, the defect depth was the greatest when lateral force of 0.5 N was applied. However all the depths were smaller than 1 m. SEM images of Lateral force of 0.5 N, S mode, power setting 2 and 4 were similar to that of P mode, but the other SEM images of S mode showed discernible changes. Defect depth of S mode samples was the greatest when lateral force of 1.0 N was applied. CONCLUSIONS: Within the limitations of this study, it can be concoluded that removing capability of piezoelectric scaler with scaler tip becomes maximized as power level becomes higher but the capability is restricted when excessive lateral force is applied on scaler tip.

Influência do tipo de pilar de resistência mecânica pré-ciclagem, quantidade de toque retido e desajuste vertical pré e pós-ciclagem, com análise estrutural em MEV / Influence of abutment type in mechanical strength before cyclic loading, retained torque and vertical misfit before and after cyclic loading with structural analysis by SEM

Problemática: De ocorrência clínica comum, o afrouxamento dos parafusos que compõe uma prótese sobre implante é uma complicação que traz transtornos tanto para o profissional quanto para o paciente. Entre os fatores que interferem na estabilidade da união parafusada destaca-se a pré-carga gerada durante o torque do parafuso, as formas como as forças se dissipam através do conjunto implante/pilar/parafuso e as características dos componentes utilizados. Proposição: O objetivo deste estudo foi analisar comparativamente três tipos de pilares sobre implantes, quanto a resistência mecânica previamente ao ensaio de carga cíclica; a porcentagem de torque retido na união parafusada e os níveis de desajuste vertical entre o pilar e o implante antes e após ciclagem; e alterações estruturais na base de assentamento dos pilares através de microscopia eletrônica de varredura (MEV). Material e método: Quarenta e cinco implantes, com conexão tipo hexágono externo foram incluídos em cilindros de PVC utilizando-se resina epóxica com módulo de elasticidade semelhante à estrutura óssea. Os grupos foram estabelecidos de acordo com o tipo de pilar utilizado (n=15): Titânio (pré-fabricado), Ouro (com cinta metálica pré-fabricada e sobre fundido) e Zircônia (pré-fabricado). Cinco pilares de cada grupo foram submetidos a teste de resistência estática para estabelecimento do valor da força a ser utilizada no ensaio de carga cíclica. Os outros 10 pilares de cada grupo foram fixados sobre os respectivos implantes através de parafuso de titânio, sob torque e retorque de 32 Ncm (pilares metálicos) e 20 Ncm (pilar de zircônia). Os corpos de prova foram submetidos à aferição do torque retido (précarga) e dos níveis de desajuste vertical antes e após ensaio de carga cíclica. Os testes foram realizados de acordo com a norma ISO 14801, onde uma força variando entre 11 - 211 N foi aplicada com 30º de inclinação em relação ao longo eixo do implante por 500.000 ciclos e frequência de 15 Hz. Imagens em MEV foram realizadas antes e após os testes a fim de identificar alterações estruturais nos componentes. Quando efeitos significativos entre os grupos foram encontrados pelo teste ANOVA o teste de Tukey, com significância de 5% foi aplicado para identificar as diferenças. Resultado: Com relação à resistência mecânica, os pilares de ouro demonstraram os maiores valores médios com diferenças estatisticamente significantes em relação aos outros pilares (titânio e zircônia), não havendo diferenças estatisticamente significantes entre esses. Quanto à porcentagem de torque retido, previamente a ciclagem não houve diferença entre os grupos. Após a ciclagem, a porcentagem de torque retido diminuiu significativamente para todos os grupos. Os pilares de titânio apresentaram a maior retenção de torque, enquanto os pilares de zircônia a menor, com diferença estatisticamente significante entre os grupos. Os pilares de ouros apresentaram uma retenção de torque intermediaria, sem diferenças estatisticamente significante para os demais grupos. Com relação aos níveis de desajuste vertical, os pilares de ouro foram os que apresentaram as maiores médias, seguido pelo grupo titânio e zircônia respectivamente com diferenças estatisticamente significantes entre todos os grupos. Não foram encontradas diferenças nas análises pré e pós ciclagem, assim como entre as diferentes faces de medição. Imagens em MEV demonstraram alterações estruturais em todos os tipos de pilares após aplicação de carga cíclica, tais como desgastes, amassamento se perda de estrutura. Conclusão: A resistência mecânica dos pilares de zircônia foi considerada igual a dos pilares de titânio. Quanto à porcentagem de torque retido, em todos os grupos houve uma diminuição significativa após a aplicação de carga cíclica. Pilares obtidos através de procedimentos laboratoriais (sobre-fundição) apresentaram os piores níveis de desajuste vertical. Imagens em MEV demonstraram alterações evidentes na base de assentamento dos pilares após aplicação de carga cíclica

Purpose: The aim of this study was to evaluate comparatively three type of abutment in regard to mechanical resistance before cyclic loading, the maintenance of the applied torque and vertical misfit in abutment/implant interface before and after cyclic loading, and damage surface by SEM. Material and Method: Forty five external hex implants were embedded in an epoxy resin and received your respective abutments, randomly divided in three experimental groups (n=15): (A) machined titanium (Ti) abutments; (B) premachined gold (Au) abutments and (C) machined zirconia (ZrO2) abutments. For all groups, only one type of screw was used. The abutment screws were tightened according to the manufacture's recommended torque. Initially, a static bending test was performed using 5 specimens of each group to determine the load applied in the cyclic loading test. Thus, 10 specimens of each group were used to measure the reverse torque value (preload) of the abutment screw and vertical gap between the abutments and implant, before and after loading. The tests were performed according to ISO norm 14801. A cyclic loading (0,5 x 106 cycles; 15 Hz) between 11 - 211 N was applied at an angle of 30 degrees to the long axis of the implants. Group means were compared using ANOVA and Tukey test. Result: The mechanical strength test showed that the UFL mean for Au abutments was significantly higher than the mean of the other abutments (p<0.001). The analysis of reverse torque (preload) before cyclic loading showed no significant differences among abutment groups. After cyclic loading the lowest decrease in preload was observed in group Ti, whereas the highest was observed in group ZrO2, with significant differences between them. The group Au showed an intermediate decrease, with no significant difference to the other groups. In relation to the vertical misfit, the gold abutments showed the highest values, followed by the titanium and zirconia respectively. SEM images obtained after cyclic loading showed clear changes on the seating surfaces of abutments. Conclusion: The mechanical strength of the zirconia abutments was similar to titanium abutments. The load application on the joint implant/abutment/screw reduced significantly torque values in all groups. Premachined abutments presented the worst levels of vertical misfit. SEM images showed changes evident on the seating surfaces of abutments after cyclic loading application

Effect of five commonly used prosthesis materials on bacterial colonization: An in vivo study / 第二军医大学学报

typeⅢgold alloy. Candida albicans could be found on acrylic resin ,but there was little on the other 4 dental metals. Conclusion: From the perspective of reserving periodontal tissue, pure-Ti and typeⅢgold alloy seem to be the first choice, Co-Cr alloy and Ni-Cr alloy are the second.

Experimental mechanics analysis of posterior galvano-ceramic bridges made by Ni-Cr pontic fired bonding galvano caps / 北京大学学报(医学版)

Objective: To measure the fracture strength of the posterior galvano-ceramic bridges made by Ni-Cr pontic fired bonding galvano caps with highly temperature-resistant adhesive and to provide re-ference data for clinical application. Methods: A standard low dental cast was achieved with 46 missing. Five posterior galvano-ceramic bridges made by Ni-Cr pontic fired bonding galvano caps, with abutments being 47 and 45 . The low dental cast was fixed on the panel of the universal testing machine, vertical load given on the central of the pontic as the velocity of 2 mm/min. Results: The fracture strength of the posterior galvano-ceramic bridges made by Ni-Cr pontic fired bonding galvano caps was (877.00?126.53) N, the fracture strength of the metal frame was (1 448.94?51.02) N. Conclusion: Posterior galvano-ceramic bridges made by Ni-Cr pontic fired bonding galvano caps could endure the normal human occlusal force.