BackgroundAngulated implants may result in inaccurate impressions, and the impression technique may affect the accuracy of the definitive cast. This study was designed to compare the dimensional accuracy of casts obtained from three impression techniques for three definitive lower casts with implants at different angulations.MethodsThree Osseolink implants were placed in three reference models with different angles (parallel, 15° and 30°). Impressions of each model were made with three techniques (n = 10 per group): indirect, unsplinted direct, and acrylic resin-splinted direct technique. Impressions were poured with type IV dental stone. Inter-implant distances were measured for casts using a coordinate measuring machine, and the deviations from the reference models (Δr) were calculated. Data were analyzed using one-way ANOVA followed by post hoc tests to detect significance between groups (α = 0.05).ResultsThis study showed that the deviations in micrometers from the reference model were the least for acrylic resin-splinted direct technique (Δr1 = 49.96, Δr2 = 50.36) versus indirect (Δr1 = 93.8, Δr2 = 90.9) and unsplinted direct techniques ((Δr1 = 67.07, Δr2 = 68.66) in 30° angulated implant situation (p value < 0.0001* for both Δr1 and Δr2). In 15° angulated implants, both the acrylic resin-splinted direct (Δr1 = 44.64, Δr2 = 45.58) and unsplinted direct techniques (Δr1 = 47.39, Δr2 = 55.28) were more accurate than indirect technique (Δr1 = 64.8, Δr2 = 68.3) (p value < 0.0001* for both Δr1 and Δr2). While in parallel condition, no difference was found between all three techniques (p value = 0.085, 0.056 for Δr1 and Δr2, respectively).ConclusionsThe impression technique affected the accuracy of definitive casts. The acrylic resin splinted direct technique produced the most accurate casts, followed by direct unsplinted and indirect techniques. Furthermore, implant angulation affected the impression accuracy. When implant angulation increased from parallel implants to 30°, the forces of deformation increased, which resulted in increased distortion.

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Glass ionomers (GICs), because of their qualities, are in a good position to be modified to resist masticatory stresses as permanent posterior restoration and prevent recurrent caries. The purpose of the present study was to evaluate the effect of adding quaternized chitosan-coated mesoporous silica nanoparticles (HTCC@MSNs) to conventional GIC on its mechanical properties, antimicrobial activity and fluoride release and the effect of 1- and 3-month water aging on the studied properties. HTCC@MSNs was synthesized, added to commercially available conventional GIC at 1%, 3%, and 5% by weight forming three experimental groups and compared with plain GIC as a control group. Flexural strength, modulus, Vickers microhardness and wear volumes were evaluated. Antibacterial activity was tested against Streptococcus mutans and fluoride release in de-ionized water was measured. All properties were evaluated before and after one- and three-month aging (n = 10 specimens per test/per time). Two-way ANOVA was used for statistical analysis. Characterization confirmed successful preparation of HTCC@MSNs. The flexural strength, modulus, hardness and wear resistance of the GICs improved significantly by adding 1–3% HTCC@MSNs, while 5% HTCC@MSNs group showed no significant difference compared to control group. Bacterial inhibition zones and fluoride release increased proportionally to the amount of filler added. Mechanical properties were improved by artificial aging. Fluoride release values, and bacterial inhibition zones decreased with aging for all groups. HTCC@MSNs as a filler with the optimized proportion provides strengthening and antibacterial effect. In addition, aging is an important factor to be considered in evaluating experimental fillers.

The cycle-to-cycle variation in the fiow field inside a four stroke ignition engine has been studied. The particle image velocimetry (PIV) technique has been used to measure the flow field inside the engine. Tlie measurements have been carried out in a motored engine equipped with suhable access. The measurements have been carried out in both the sectional and the planar directions such that the necessary data for calculating the swirl ratio and turnble motions becornes available, Tlie staridard deviations from the ensemble averaged rneasurements for these two motions have been used as indicators for the cyclic variations in the fiow field, The effect of the engine speed, inlet valve shrouding and piston geometry on the cyclic variations in the flow has been assessed. According to the analysis of the measurements, it has been found that increasing the engine speed increases both the swirl ratio as well as the cycle-to-cycle variation, The cyclic variability in the swirl ratio decreases when 120e shrouded inlet valve is used. This trend is reverted when the shroud is increased to 1800. Also the cyclic variability in the tumble ratio increases when using the 120e and 180e shrouded inlet valves. The cyclic variability based on the swirl ratio decreases with wider and less deep piston bowei. On the contrary, the cyclic variability in the tumble motion increases with shallow and wider piston bowel, Also the cyclic varial)ility in the swirl ratio increases as the compression ratio increases. EXPERIMENTAL WORK Particle Image Velocimetry is a well-established technique for the measurements of irtstantaneous plariar velocity fields and has been reviewed by a number of

Recently, wall climbing robots have attracted much attention because of its importance in many applications such as cleaning, painting, fire fighting, tanks and walls inspection. This paper presents the design, modeling and control of a wall climbing robot, crossing over obstacles with heights more than the current ones. The proposed climbing robot consists of two mobile robots connected with a link and two revolute joints. The climbing robot is designed in a way that during crossing over obstacles, one of the mobile robots adheres to the wall while the other mobile robot with its connected link forms a 2 DOF arm crossing over obstacles. An impeller based vacuum is generated giving the adhering capability to each mobile robot. The model of the climbing robot is presented in both stationary and motion modes. A PIDcomputed torque controller is designed to the 2 DOF arm for crossing over obstacles and the presented simulation results show the validity of the proposed controller.