Introduction: Stainless Steel crowns (SSCs) are widely used in restoring severely damaged primary molar teeth. Since these crowns do not adapt ideally to tooth substance, they may lead to some changes in surrounding gingiva. This clinical study was performed to evaluate the effect of stainless Steel crowns placed on primary molars on gingival structures. Materials & Methods: In this retrospective study, 117 crowns in eighty four 4-11 year old children attended to pediatric department of Zahedan dental school were evaluated. Convenience sampling method was done. Some clinical factors such as gingival index, tooth type, state of being either right or left molar, or upper or lower molar, time elapsed after cementation, crown marginal adaptation, excessive cementation around the margin of crown and the oral hygiene level were examined. Kruskal-Wallis and Mann-Whitney tests were used for data analysis through SPSS 15 software (P<0.05). Results: In our study only 11.1% of the evaluated crowns demonstrated clinically healthy gingiva, and there was a significant correlation between upper and lower molar, crown marginal adaptation and oral hygiene level with gingival index (P<0.05), while gingival index was not significantly affected by tooth type, tooth side, time elapsed after cementation and presence of excessive cement around the margin of crown and sex (P>0.05).Conclusion: Stainless Steel crowns had no harmful effect on the gingiva provided performing standard preparation procedures especially in upper molars and stablishing proper marginal adaptation and good oral hygiene level.

Introduction: The bonding process of the brackets to enamel has been a critical issue in orthodontic research. The purpose of this study was to evaluate the shear bond strength of 3 lightcured adhesives (transbond XT, Z250, light bond).Materials & Methods: In this study sixty extracted human premolars were collected and randomly divided into 3 test groups. All teeth were etched by 37% phosphoric acid. In first group brackets were bonded by Transbond XT adhesive, in group two brackets were bonded by Light bond adhesive and in third group were bonded by filtek Z250 composite. All of them were cured with Ortholux xt for 40 seconds.24 hours after thermocycling, Shear Bond Strength (SBS) values of these brackets were recorded using a Universal Testing Machine. Adhesive Remnant Index (ARI) scores were determined after the failure of the brackets, using Stereo Microscope the data were analyzed using ANOVA and Chi-square tests.Results: Mean shear bond strength of Transbond XT, light bond and Z250 were 28.9±2.25 MPa, 25.06±1.98 MPa and 26.8±2.57 MPa, respectively. No significant difference was observed in the SBS among the groups and a clinically acceptable SBS was found for the three adhesives. ARI scores were not significantly different between the various groups (P>0.05).Conclusion: This study showed that the Z250 can be used as light bond and transbond xt to bond orthodontic brackets and ARI and SBS scores were not significantly different.

Progressive collapse studies generally assess the performance of the structure under gravity and blast loads, while earthquakes may also lead to the progressive collapse of a damaged structure. In this study, the progressive collapse response of concentrically braced dual systems with Steel moment-resisting frames was assessed under seismic loads through pushover analysis using triangular and uniform lateral load patterns. Two different bracing types (X and inverted V braces) were considered, and their performances were compared under different lateral load patterns using the nonlinear static alternate path method recommended in the Unified Facilities Criteria (UFC) guideline. Eventually, the seismic progressive collapse resistance of models was compared to their progressive collapse response under gravity loads. These studies showed that models under the seismic progressive collapse loads satisfied UFC acceptance criteria and limited rehabilitation objective. The structures had better performance under seismic progressive collapse than models under gravity loads because of more resistance, ductility, suitable load redistribution, and more structural elements that participated in load redistribution. Furthermore, despite studies on progressive collapse under gravity loads, the dual system with X braces showed better progressive collapse performance (more resistance, residual reserve strength ratio and ductility) under seismic loads than the model with inverted V braces.

Background and Objective: Denture fracture due to excessivethickness, malocclusion or other traumas during sneezing or washingare disadvantages of acrylic prosthetics and PMMA resin. So furthermethods are needed to increase their transverse strength. Althoughthere are many studies on reinforcing and modifying withcopolymers, cross–linking or use of metallic or fibric strengtheners toenhance mechanical properties, There are limited studies withparadoxical results. The aim of this study was to compare thetransverse strength between reinforcement with polyethylene fiberand two older methods (stainless Steel, metallic mesh).Subjects and Methods: In this study 40 PMMA resin samples (65x12x3 mm) were made and categorized in 4 groups: With noreinforcing agent (control group); with metal wire (diameter 1.0mm); with metal mesh (diameter 0.3 mm) and with polyethylene fiber (Fibre–braid). These samples were put to 3-point loading test byInstron universal testing machine.Results: The average transverse strength in control group was 78.37MPa and for three other groups: metallic wire, mesh and polyethylenefibers, in sequence, were 80.25 MPa, 9 MPa and 78.56 MPa. Theresults were not statistically significant (P>0.05).Conclusion: Reinforcing the acrylic resin using different techniquesdo not produce increases in transverse strength in comparison withthe conventional acrylic resin with no reinforcement. Therefore, noneof the tested techniques are recommended.

In this paper, effect of standoff distance parameter on morphology and mechanical properties of explosively bonded AlMg5-AI-Steel is being studied. Results have shown that by changing standoff distance and loss of kinetic energy, the shape of interface is transited from Smooth-wavy to Wavy and wavy in a vortex way. With increasing of the standoff distance due to the loss of kinetic energy also local melted zone has been created in front of vortices. Chemical composition of local melting zone was mixed of parent and flyer plates due to circular movement of jet. These areas have reduced bonding strength due to stress concentratio; results also have shown that strength level of all weldment was above standard level .The sample without local melting zone and wavy interface has the highest strength.

The use of cold rolling, is one of the methods of producing multilayer clad sheets. The advantages of this method over other methods of producing multilayer clad sheets have led to its widespread use in recent years. Existence of several parameters affecting the mechanical properties and bond strength of multilayer sheets produced by cold roll bonding, has made research in this field important. In this paper, using experimental method, the effect of several effective parameters such as temperature and time of thermal operation and type of sheet surface preparation on the mechanical properties of AA5456 / AA1020 / St321 three-layer sheet produced by cold rolling has been investigated. In this regard, two sanding methods including flap disc and Cylindrical Sandpaper have been used to prepare the surface of the sheets and heat treatment has been performed at three temperature levels of 310, 355 and 400 ° C for three periods of 30, 60 and 90 minutes. The results of these tests showed that the highest increase in tensile strength was obtained in the sample of heat treatment at a temperature of 400 ° C for 60 minutes and surface preparation by Cylindrical Sandpaper.

Protective Steel doors are widely used in buildings due to their high resistance against the impact loads. However, its heavy weight has been always considered as a major drawback for these doors. In this paper, a new optimized stiffened impact-protective Steel door incorporating sandwich panel with aluminum foam core (OSSA) is examined. This door consists of two face sheets, main and secondary stiffeners, and aluminum foam as the inner core. In order to optimize the door, at first the rigidity and weight functions of the stiffened Steel door were extracted. Then an optimal door weighing 42% less than the primary door was obtained. Due to the high energy absorption capacity of the combined foam core and stiffened Steel door structure, the use of aluminum foam core in the optimized Steel door was proposed. By doing numerical analysis, and depending on the thickness of the face sheet of OSSA, 20 to 32% reduction in the maximum displacement was observed. The results also showed that, with 67% increase in the peak overpressure, OSSA has kept almost the same maximum displacement as that of the Steel door without an aluminum foam. In other words, by using aluminum foam core in the optimized stiffened door, the door will resist 67% more impact load.