Background: Poly-ether-ether-ketone(PEEK) has been introduced to many dental fields. Recently it was tested as a retainer wire‎ following orthodontic treatment. This study aimed to investigate the effect of changing the bonding spot size and location on the performance of PEEK retainer wires. Methods: A biomechanical study involving four three-dimensional finite element models was performed. The basic model was with a 0.8 mm cylindrical cross-section PEEK wire, bonded at the center of the lingual surface of the mandibular incisors with 4 mm in diameter composite spots. Two other models were designed with 3 mm and 5 mm composite sizes. The last model was created with the composite bonding spot of the canine away from the center of the crown, closer to the lateral incisor. The linear displacement of the teeth, strains of the periodontal ligament, and stresses in PEEK wire and composite were evaluated. The data was numerically produced with color coded display by the software. Selected values were tabulated and compared among models. Results: The amount of linear displacement and strain was very low. Stresses in the wire and composite were affected by the size and position of the composite bonding spot. The safe limits were identified at 235 MPa for PEEK and 100 MPa for composite. The basic model had a von Mises stress in the PEEK wire of 122.09 MPa, and a maximum principal stress in the composite of 99.779 MPa. Both stresses were within the safe limits, which means a lower risk of failure in PEEK and composite. All other models had stresses that exceeded the safe limit of the composite. The 3 mm composite model was the only one that developed stresses in the wire more than the safe limits of PEEK. Conclusions: Within the limitations of this study, bonding PEEK wires with 4 mm bonding spots to the clinical crown center provided the best mechanical performance of the wires and spots; otherwise, the mechanical properties of the wire and composite would be affected and, therefore, might affect the retention process. Keywords: Retention, PEEK, Finite element analysis
The ceramic compound Mg1-xSixAl2O4 (x= 0, 0.1, 0.2, 0.3, 0.4) was prepared from nano powder of Al2O3 and MgO doped with Nano powder of SiO2 at different molar ratios. The specimens were prepared by standard chemical solid reaction technique and sintered at 1450 oC. Structure of the specimens was analyzed by using X-ray diffraction (XRD). The X-ray patterns of the specimens showed the formation of pure simple cubic spinel structure MgAl2O4 phase with space group of ̅ . The average grain size and surface topology were studied by atomic force microscopy. The results showed that the average grain size was about 73-90 nm. The DC electrical properties of the specimen were measured. The apparent density was found to increase and the porosity a
... Show MoreOil is considered the most important source for providing the funds for the national economic sectors. The revenues of oil constitute %95 of the GPD. Therefore, the development of the remaining sectors depend on oil..
The Iraqi Oil Marketing Organization (SOMO) depended on the a unified price for all the buyers, That may not reflect the real value of market and did not contribute in marketing the type of heavy oil. Then, to what extent had SOMO been able to market the light and heavy crude oil in a way that contains the expected increase in the crude oil production.
When sites of new communication occurs which represents the merit of the development of communication technology which is characterized by the services of ( facebook-twiter-corapora-youtube-mass space-friendster-flicker-willnecked in addition to the direct services for viber-whatsup-telgram-and chat on) play important role in changing the infrastructure of Arabic societies which are consideredas closed and not changeable societies during near period and the significance of this study comes from the importounce of this subject which is considered as anew trend of the age on the field of media and public response and acceptance inspite of what is known about Arabic society-it doesn’t accept change-this occurance is associated with terms
... Show MoreThe purpose of this research is to identify
the effect of the translation of poetic poem into an artistic picture in the achievement of retention among fifth grade students.
In order to verify the research goal, the first two hypotheses were determined. There are no statistically significant differences between the average scores of the experimental group who study (according to the technical picture) ) And the control group (according to the traditional method of art education) at the level of significance (0,05). The second is that there are no statistically significant differences between the average of the experimental group who study (according to the technical picture) and the control group who study (On According to the trad
The following dilutions -710X46, -610X46, -510X46 of Bacillus thuringiensis were used for bioassay against the different larval instar of the potato tuber moth Phthorimaea operculella by the spraying method, the results showed that there was no significant influence in the percentage of egg hatching in comparison with the control. The sensitivity of larval stages was reduced with the increasing the age and exposure period. The study also showed that the larvae infected with B.t. stopped feeding, movement and a general paralysis causing the death of larva after (24-48) hours , and the larva color was changed from the natural waxy colour to brown finally to the black after death.
The following dilutions -710X46, -610X46, -510X46 of Bacillus thuringiensis were used for bioassay against the different larval instar of the potato tuber moth Phthorimaea operculella by the spraying method, the results showed that there was no significant influence in the percentage of egg hatching in comparison with the control. The sensitivity of larval stages was reduced with the increasing the age and exposure period. The study also showed that the larvae infected with B.t. stopped feeding, movement and a general paralysis causing the death of larva after (24-48) hours , and the larva color was changed from the natural waxy colour to brown finally to the black after death.
The present study aims at answering the following questions:.
1-Which is more effective in enriching students. Vocabulary ,the use of short stories or the traditional way?
2-What extent has the use of short stories an effect upon the students. achievement in vocabulary test?
3- Is there any significant difference between the male and female student of the experimental group in vocabulary achievement test?
 
... Show MoreIn this study, some attenuation parameters of gamma shields were studied. This shields consisting of composite materials of Unsaturated polyester as a base material and Nano iron oxide (Fe2O3) and, micro iron (Fe) as reinforcement materials at different percentages (1, 3,5,7and 9)wt%, and with different thickness (1, 1.5, 2, 2.5, 3, 3.5and 4) cm. The results showed that the use of nanoparticles is better than the microparticales in the field of radiation shielding. It has been shown that the values of attenuation parameters of gamma it bitter in the case of nanoparticles than case of the use of micro material.
Abstract
Should be the goal of Government controls, including environmental controls and safety laws to protect citizens from the harmful effects of negative secreted by human's additions and changes in the environment. and perhaps the protection aspects of the protection of citizens from the adverse effects of communications towers, including those produced by towers of health effects. The people the right to choose the nature of the physical environment, which should not be imposed on them by others. Communications towers are one of the main problems that have been
... Show MoreThis Investigation aims to study the effect of adding Steel fibers with different volume fractions Vf (o.5, 0.75, and 1% by volume of concrete) with aspect ratio 100 on mechanical properties of concrete, and also
finding the influence of petroleum products (Kerosene and Diesel) on mechanical properties of Steel Fiber Reinforced Concrete (SFRC).
The experimental work consists of two groups: group one consists of specimens (cubes and prisms) plain and concrete reinforced with steel fiber exposed to continuous curing with water. Group two consists of
specimens (cubes and prisms) plain and concrete reinforced with steel fiber exposed to kerosene and diesel after curing them in water for 28 days before exposure. The results of all te