REASURCH THE WORK OF THE TRADITIONAL CIRCULAR ARCH OF TIMBER JAMBS WITH AN OPTION OF ITS STRENGTHENING

The article discussesthe research of the traditional circular archs of timber jambs, designedin the 16-th century by the French architectPhilibert Delorme, with an option of its strengthening, which make this arch comparable to the glued timber one. The experimental research of a flat arch, made of small wooden bricks strung on a steel rope and prestressed from the foundationzone, was carried out in the NRU MGSU. According to the results, it was found, that the arch has a low carrying capacity and can work only on compression. However, by strengthening the arch by using a steel band along its upper face and thus moving to the truss structure, it is possible to increase significantly its carrying capacity and bring it closer to the glued timber arch. During tests, it was noted that by the character of its work this arch is close to the circular arch of timber jambs. In the LIRA-CAD PC a computer simulationwas carried out of the traditional and the strengthened by a steel band along its upper face circular arches of timber jambs, as well as the glued timber arch. The following results were obtained.During the deformation process, the deflection of the strengthened circular arch decreased by 31%, and the stresses in it decreased by 26% compared to the traditional one, and according to the carrying capacity the arch has become comparable to the glued timber one. On this basis the conclusions were obtained, that it is possible to create non-linear form constructions, inherent to the natural objects, using the strengthened circular arch.

Evaluation of Antibacterial Effect of Silver Nanoparticle Coated Stainless Steel Band Material – An In vitro Study

Correction: On 23rd April 2020, corrections were made to page 16: The caption of Figure 6 (p.16) was changed FROM Figure 4: Petridishes showing Lactobacillus colonies of control samples at (a) 24 hours, (b) 48 hours and (c) 1 week TO Figure 6: Petridishes showing streptococcus mutans colonies of control group at (a) 24 hours, (b) 48 hours and (c) 1 week. The caption of Figure 7 (p.16) was changed FROM Figure 5: Petridishes showing Lactobacillus colonies of test samples at (a) 24 hours, (b) 48 hours and (c) 1 week TO Figure 7: Petridishes showing Streptococcus mutans colonies of test samples at (a) 24 hours (b) 48 hours and (c) 1 week. AbstractIntroduction: Decalcification, caries, inflammatory periodontal disease are the most common iatrogenic effects of orthodontic treatment because of failure to maintain proper oral hygiene. Although various methods have been tried to minimize the incidence of white spot lesions, none of them proved to be effective. The purpose of this study was to develop a hard coating of silver nanoparticles on stainless steel band material and to evaluate the antibacterial efficacy against most common cariogenic pathogens. Materials & Method: Stainless steel band material was cut into 45 pieces of about 0.5 x 1 cm in dimension, of these 25 band material strips were coated with silver nanoparticles using thermal evaporation technology in a Vacuum coating unit (Indovision, India) at a vacuum of 4.5 ×10−5 millibar at 961°C for 5 minutes and remaining strips served as control. Scanning electron microscopy (SEM) study of coated band material showed a uniform deposition of silver nanoparticles of about 18.63 percent by weight. Five coated and five uncoated band material strips were utilized for each test to evaluate the antibacterial effect of the coated band material against Streptococcus mutans, Lactobacillus acidophilus using zone of inhibition and direct contact test. In zone of inhibition test, the bacterial growth inhibition zone was measured after a period of 24-48 hours, where as in direct contact test, the number of bacterial colonies were counted after 24 hours, 48 hours and 1 week. Five coated band materials were immersed separately in a container having 5 ml of artificial saliva and the amount of silver nanoparticles released from coated samples was evaluated after 24 hrs, 48 hrs, and 1 week using atomic absorption spectrophotometer. Result: A stable uniform coating of silver nanoparticles on the band material was obtained by physical vapor deposition. The coated band material showed a potent antibacterial activity against L.acidophilus and S.mutans. The maximum amount of silver nanoparticles released from the silver nanoparticle coated band material was 0.0236 ± 0.0067 ppm, which is below the maximum permissible level set by WHO [0.1 mg /l], proving it as biocompatible. Conclusion: Silver nanoparticle coating on orthodontic band surfaces can provide suitable antimicrobial activity during active orthodontic treatment.