Search results for "Steel"
showing 10 items of 338 documents
Biomarker responses of the earthworm Aporrectodea tuberculata to copper and zinc exposure: differences between populations with and without earlier m…
2003
Biomarkers in the earthworm Aporrectodea tuberculata (Eisen) were measured to find out their possible induction under Cu and Zn exposure and differences in the responses between two populations with different exposure history. The biomarkers applied were concentration of metallothioneins (MT), and cytochrome P4501A (CYP1A) monooxygenase and glutathione-S-transferase (GST) activities. These were measured from earthworms sampled at three distances from a steel smelter in Finland and from the individuals from two populations, one with and another without earlier metal exposure, exposed to three combined Cu/Zn concentrations in the laboratory. In the field, MT concentration, and cytochrome CYP1…
In vitro comparison of the retention capacity of new aesthetic brackets.
1999
Tensile bond strength and bond failure location were evaluated in vitro for two types of aesthetic brackets (non-silanated ceramic, polycarbonate) and one stainless steel bracket, using bovine teeth as the substrate and diacrylate resin as the adhesive. The results show that metallic bracket had the highest bond strength (13.21 N) followed by the new plastic bracket (12.01 N), which does not require the use of a primer. The non-silanated ceramic bracket produced the lowest bond strength (8.88 N). Bond failures occurred mainly between bracket and cement, although a small percentage occurred between the enamel-cement interface with the metal and plastic brackets and within the cement for the …
Shaping ability of nickel-titanium rotary instruments in simulated S-shaped root canals.
2009
Objective The aim of this study was to compare the shaping ability of 4 nickel-titanium rotary techniques and 1 hand technique in simulated S-shaped curved root canals. Study design Seventy-five simulated double-curved resin root canals were divided into 5 groups (n = 15). The canals were compared at 12 different levels and at 3 different times: before preparation and after preparation to master apical 25 and 35. Data were statistically analyzed by performing 2-by-2 comparisons with the Tukey parametric test of variance analysis using a confidence interval of 95%. Results All of the 75 resin blocks presented transportation of the root canals by transforming the apical curvature into a strai…
Influence of prefabricated post material on restored teeth: fracture strength and stress distribution.
2006
This work studied how prefabricated intraradicular post material affects the mechanical performance of restored teeth. The effect of using two different materials (glass fiber and stainless steel) with significantly different elastic moduli was studied.A combined theoretical and experimental method was used: first, an experimental fracture strength test was performed on 60 extracted human maxillary central incisors. The teeth were decoronated, treated endodontically and restored, 30 with glass fiber posts and 30 with stainless steel posts. The data were recorded and the results compared using an ANOVA test. Then, the finite element technique was used to develop a model of the restored tooth…
Comparative fracture behavior of monolithic and veneered zirconia posterior fixed dental prostheses
2017
The purpose of this study was to evaluate and to compare the fracture load and the fracture pattern of monolithic and veneered zirconia posterior fixed dental prostheses (FDPs). Twenty standardized steel dies were prepared to receive posterior 3-unit FDPs. Specimens were randomly divided into 2 groups (n=10): (1) Lava Zirconia, and (2) Lava Plus. All FDPs were cemented using glass ionomer cement and subjected to thermal and mechanical cycling at 5-55ºC with a 30-s dwell time for 120,000 masticatory cycles. All specimens were subjected to a three-point bending test until fracture. Data were statistically analyzed using Student's t test, paired t-test and Weibull statistics (α=0.05). No diffe…
Effect of Thermomechanical and Static Loading on the Load to Fracture of Metal‐Ceramic, Monolithic and Veneered Zirconia Posterior Fixed Partial Dent…
2018
PURPOSE To evaluate the influence of static (not preloaded) and thermomechanical loading on the load to fracture of metal-ceramic, monolithic and veneered zirconia computer-aided design/computer-aided manufacturing (CAD/CAM) posterior fixed partial dentures (FPDs). MATERIALS AND METHODS One hundred standardized specimens with 2 abutments screwed onto a platform were prepared from stainless steel to receive a posterior 3-unit FPD with an intermediate pontic. Specimens were randomly divided into 5 groups (n = 20): Metal-ceramic (control group), Lava Zirconia system, Vita In-Ceram YZ, IPS e.max ZirCAD, and Lava Plus. Half of the specimens of each group (n = 10) underwent no preloading, and the…
Influence of prefabricated post dimensions on restored maxillary central incisors
2007
summary The aim of this study was to test the following hypothesis: biomechanical performance (fracture strength and stress distribution) of restored teeth is less sensitive to post diameter and post length when using glass fibre posts than when using stainless steel posts. First, an experimental fracture strength test was performed on 80 extracted human maxillary central incisors. Teeth were decoronated, treated endodontically and restored (40 with glass fibre posts and 40 with stainless steel posts), and the length and diameter of the posts varied uniformly. Failure loads were recorded and results were compared using an ancova analysis. Secondly, the finite element technique was used to …
Premolars restored with posts of different materials: fatigue analysis
2011
Previous works studied the effect of the material and the dimensions of the post on the biomechanical performance (fracture strength and stress distribution) of restored teeth, under static loads. The aim of this work was to study the effect of the post material (glass fibre and stainless steel) on restored teeth, which have the final crown, under dynamic conditions. The use of a biomechanical model, including a fatigue analysis from FEA, is presented as a powerful method to study the effect of the material of the intraradicular post. The inclusion of the fatigue analysis allows for a more realistic study that takes into account the dynamic nature of masticatory forces. At the same time, th…
Influence of design mistakes and material degradation on the collapse of a long-span RC roof in South Italy
2020
Abstract In 2004, during ordinary maintenance work, consisting in the waterproofing of a building located in the South of Italy, the long-span (14.50 m) in situ cast reinforced concrete (RC) roof partially collapsed. The building, constructed in 1950, was in service as a cinema up to 1967 and utilized as a school up to 1985. Finally, it was a hotel up to 2000. In 2004, when the building was not in service and underwent maintenance work, it partially collapsed under the dead load. After the collapse, which involved a large portion of the roof, several beams and two columns, the Court nominated a first Official Technical Consultant in order to investigate on the causes of failure and related …
Mechanical Behavior of Steel Fiber-Reinforced Concrete Beams Bonded with External Carbon Fiber Sheets
2017
This study investigates the mechanical behavior of steel fiber-reinforced concrete (SFRC) beams internally reinforced with steel bars and externally bonded with carbon fiber-reinforced polymer (CFRP) sheets fixed by adhesive and hybrid jointing techniques. In particular, attention is paid to the load resistance and failure modes of composite beams. The steel fibers were used to avoiding the rip-off failure of the concrete cover. The CFRP sheets were fixed to the concrete surface by epoxy adhesive as well as combined with various configurations of small-diameter steel pins for mechanical fastening to form a hybrid connection. Such hybrid jointing techniques were found to be particularly adva…