Introduction: Considering the importance of microleakage in posterior composite restorations for recurrent caries and pulpitis in formerly repaired teeth, this study aimed to evaluate and compare the microleakage rate of class II composite restorations in two methods: Open sandwich and Snowplow. Materials and Methods: In this study, a total of 64 premolar teeth with a class II cavity whose margins were extended 1 mm below dentin and cement joint were prepared and divided into two groups. In the first group, a layer of 1 mm thick resinmodified glass ionomer (RMGI Fuji II LC) was placed on the gingival floor and cured. The cavity was then etched with phosphoric acid gel, washed, and a bonding agent was applied. Then resin composite (Z250 3M ESPE) was incrementally applied in the cavities. In the second group, the cavity preparation was performed in the same way as that in group A. Afterward, 1 mm thick flowable composite (Filtek Z350 3M) was placed on the gingival floor, without curing. A layer of 1 mm thick resin composite was then added and packed. Both layers were then cured at once. The prepared teeth underwent 3000 times thermocycling and were placed in methylene blue for 72 h for evaluation of microleakage rate. The teeth were then cut mesiodistally. The samples of both groups were examined under a stereomicroscope, and the mean microleakage in both groups was compared using the Mann-Whitney test. Results: In the first group, based on the degree of dye penetration, the average amount of microleakage was observed in 10. 66% of the samples. In the second group, the average amount of microleakage was 5. 25%, using the Snowplow technique. Moreover, in the Open sandwich technique, dye penetration level in 34. 4%, 12. 5%, 34. 4%, and 18. 8% of samples was zero, one, two, and three, respectively. Moreover, in the Snowplow group, dye penetration level in 46. 9%, 25%, 25%, and 3. 1% of samples was zero, one, two, and three, respectively. The level of significance was set at 0. 05. Conclusion: Based on the obtained results, Snowplow and Open sandwich techniques are not effective for complete elimination of the microleakage of posterior composite restorations. The rate of microleakage in tooth restoration interface in class II restorations using the Snow-plow technique was more compared to the Open sandwich technique.

Introduction: Adaptation of posterior composites to dental walls has been questioned for various reasons and polymerization shrinkage is one example. Thus, the present study investigated microleakage ocurring from different class II composite restorations techniques. Materials & Methods: In this in-vitro study class II cavities with cervical margins 1 mm below the CEJ (Cementoenamel junction) were prepared in 64 extracted human premolars. The teeth were randomly divided into two groups. Group 1 (open sandwich): Glass ionomer was injected on the floor of the cavity and the rest of the cavity was restored using composite resin using incremental technique. Group 2 (Snowplow) one layer of flowable composite was placed in the bottom of the cavity and was co-cured with the first layer of composite resin. The rest of the cavity was restored the same as group 1. To evaluate the microleakage, the specimens were thermocycled for up to 3000 cycles and immersed in 1% methylene blue solution for 72 hours. Then they were sectioned mesiodistally and evaluated under a stereomicroscope. Data were analyzed via MannWhitney and Fishers exact test and p value < 0. 05 was considered significant. Results: The mean value for microleakage in group 1 (795. 74 ±,494. 04 mμ, ) was lower than group 2 (972. 99 ±,457. 8 mμ, ), but the results were not statistically significant (p value = 0. 117). Conclusion: It appears that microleakage in both open sandwich technique and Snowplow technique did not portray statistical significance, so both of them can be used.

Background: This study aimed to compare the efficacy of the snowplow, open sandwich with resin-modified glass ionomer (RMGI), and flowable composite liner techniques for the reduction of cervical microleakage of posterior Class II composite restorations. Materials and Methods: In this in vitro study, 60 class II cavities were prepared in 30 sound extracted premolars. The gingival floor of the cavities was placed 1 mm below the dentin-enamel junction. The teeth were randomly assigned to four groups (n=15). The enamel margin was etched, and SE Bond was applied. The teeth were restored with x-tra fil in group 1 (control), x-tra base + x-tra fil (snowplow technique) in group 2, RMGI + x-tra fil (open sandwich technique) in group 3, and x-tra fil + x-tra base (flowable composite liner) in group 4. After thermocycling, the teeth were immersed in 2% Fuchsin for 24 hours, and were then sectioned. Cervical microleakage of restorations was scored under a stereomicroscope at 20X magnification, and analyzed using the Kruskal-Wallis and Mann-Whitney tests (α=0. 05).   Results: The microleakage of the snowplow (P<0. 001), open sandwich (P=0. 003), and flowable composite liner (P=0. 05) groups were significantly higher than that of the control group. The microleakage of the snowplow technique was also significantly higher than that of the flowable composite liner (P=0. 047). No other significant differences were found (P>0. 05). Conclusion: Within the study limitations, the results indicated that the snowplow, open sandwich with RMGI, and flowable composite liner techniques were not effective in reducing cervical microleakage of class II composite restorations.

Introduction: One of the main disadvantages of composites is marginal microleakage; using flowable composites as a liner beneath composite restorations has been recommended to reduce microleakage. The aim of this study was to assess the microleakage of class II restorations with different flowable composites liners.Materials & Methods: 45 extracted premolars teeth with class II cavity preparation (90 cavities) were divided into five groups and filled as follows: 1.control group: hybrid composite (Z250) 2. Z250+surefil SDR flow 3.Z250+filtek supreme xt flow composite 4.Z250+Grandio flow 5.Z250+Tetric flow. Mesial and distal cavities were filled using snowplow and layering technique, respectively. After that, the samples were immersed in 0.5% fuchsin solution and sectioned. Gingival microleakage was then graded. Data were analyzed using Kruskal Wallis and Mann Whitney U test.Results: There was no significant difference between the snowplow and layering methods. Microleakage of Tetric flow and Grandio flow liners was significantly higher than the control group. Other flowable composites showed no significant difference in comparison with the control group.Conclusion: In the present study, the results indicated that the flowable composites were not effective on reducing gingival microleakage.

Space engines are used for missions such as altitude change, position control, position maintenance, landing, and orbit change. In recent decades, the use of plasma thrusters as a space propulsion system has been considered, one of which is the pulsed plasma thrusters. In this paper, a quasi-experimental electromechanical model for rectangular flat plate electrodes has been developed using two different approaches: slug and snowplow. By equating the whole physical process as a one-dimensional electrical circuit and in the next step, coupling it with the force equation as well as using some experimental parameters, the electromechanical model is obtained. The results of this semi-empirical model are compared and evaluated with the basic experimental parameters for pulsed plasma thrusters used in two satellites. According to the positive results of the evaluations, using this semi-empirical model, the basic parameters of a pulsed plasma thruster such as impulse bit and plasma exhaust velocity can be calculated and some geometric parameters and capacitor parameters of a thruster can be optimized and controlled. The two approaches of slug and snowplow in this model are also compared with experimental results.