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Cr Alloy (cr + alloy)
Selected AbstractsStress distribution associated with loaded acrylic,metal,cement crowns by using finite element methodJOURNAL OF ORAL REHABILITATION, Issue 11 2002M. Toparli SUMMARY, The axisymmetrical finite element method (FEM) was used to compare stress distribution in a maxillary second premolar restored tooth. The three models were evaluated by crowning the tooth with Au,Pd alloy, Ni,Cr alloy and Ti alloy with acrylic. A longitudinal static force, 200 N in magnitude at an angle of 45° was applied on the occlusal margin of each model. The tooth was assumed isotropic, homogenous and elastic. This numerical study was carried out using axisymmetric finite element models and calculation programmes were prepared by the authors using FORTRAN 77. Comparison of stress distributions was made in four regions of apex, cole, dentin,metal interface and metal,acrylic interface. The highest stress values were obtained when NiCr alloy with acrylic was used. [source] Dimensional measurement and finite element analysis of I-bar clasps in clinical useJOURNAL OF ORAL REHABILITATION, Issue 11 2000Y. Sato An I-bar clasp is a popular retainer for distal-extension removable partial dentures. However, there have been almost no evidence-based criteria on the mechanically preferable shape. The present study aimed to investigate the variations of dimension in I-bar clasps used in patients, and to clarify the effect of the variations on stiffness and stress of I-bar clasps by finite element analysis. Dimensions (thickness, width, taper, radius of curvature, length, relation to oral structures) of 23 I-bar clasps were measured. A three-dimensional finite element model was made for each measured I-bar clasp with vertical and horizontal straight sections connected with a curved section. A concentrated load of 5 N was applied at the lowest point of the tip that contacted the abutment in the buccal direction. Maximal equivalent stress and stiffness of each clasp were evaluated. The measured dimension, stiffness, and maximum stress showed wide variations. Mean stiffness was far from the proper one, and mean stress was near the proportional limit of Co,Cr alloy. Considering the stiffness and stresses in this study, only six clasps out of 23 were appropriate. These results suggest that evidence-based criteria of preferable shape of I-bar clasps should be determined. [source] Fracture Resistance of Endodontically Treated Teeth: Three Walls versus Four Walls of Remaining Coronal Tooth StructureJOURNAL OF PROSTHODONTICS, Issue 1 2009Siriporn Arunpraditkul DDS Abstract Purpose: The purpose of this study was to evaluate the fracture resistance of endodontically treated teeth between those with four walls and those with three walls of remaining coronal tooth structure and the effect of the site of the missing coronal wall. Materials and Methods: Thirty-two endodontically treated second mandibular premolars were decoronated, leaving 3 mm above the cementoenamel junction (CEJ). A 0.5-mm-wide chamfer was prepared 1 mm above the CEJ. The teeth were randomly divided into four groups. Group 1 had four walls of coronal tooth structure, whereas groups 2, 3, and 4 had only three walls, missing the buccal, lingual, and mesial wall, respectively. The cast dowel and cores and crowns (Ni,Cr alloy) were cemented with zinc phosphate cement. A compressive load was applied 45° to the long axis, 2 mm below the buccal cusp, with an Instron machine until failure at a crosshead speed of 5 mm/min. Failure load (kg) and mode of failure were recorded. Data were analyzed with one-way ANOVA and Scheffé tests (p < 0.05). Results: Group 1 had the highest fracture resistance (1190.3 ± 110.5 kg), significantly different from the other groups (p < 0.05) (group 2: 578.5 ± 197.4 kg; group 3: 786.6 ± 132.8 kg; group 4: 785.4 ± 289.9 kg). There were no significant differences among the test groups. The mode of failure in group 1 was a horizontal root fracture, whereas that of the other groups was either vertical or oblique fracture. Conclusions: Teeth with four walls of remaining coronal dentine had significantly higher fracture resistance than teeth with only three walls. The site of the missing coronal wall did not affect the fracture resistance of endodontically treated teeth. [source] Corrosion of some selected ceramic alloys used in fixed partial dentures and their postsolder joints in a synthetic neutral salivaEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2009Pascal De March The electrochemical behavior of several alloys used in the frameworks of fixed partial dentures and their corresponding postsolders was studied in artificial saliva as a function of chemical composition. Open circuit potentials and polarization resistances were measured. The general electrochemical behaviors between the cathodic domain and the oxidation of solvent were characterized using cyclic polarization. The possible galvanic corrosion of coupled parent and postsolder alloys was also studied. The polarization resistances were high or very high. During immersion, the noblest alloys stayed in the immunity domains of their base elements, whereas Ni,Cr alloys were quickly passivated. The oxidation of the noble elements occurred only when the alloys were exposed to very high potentials solely achievable by artificial means. However, problems of galvanic corrosion may occur between an alloy and its postsolder joint if they are both exposed to saliva. Such corrosion may lead to a weakening of the framework. The parent alloy was often potentially affected by such corrosion but with low exchange currents. [source] | ||||||||||