The purpose of this study was to evaluate the effect of different bench time on surface hardness of the composite resin after being stored in the refrigerator at 4°C. Before used in this study, the composite resin was refrigerated at 4°C for the test group and kept at 25°C for the control group. The specimens were divided into control group (I) and five experimental groups according to the bench time before polymerization, 0 (II); 15 (III); 30 (IV); 45(V); and 60 (VI) minutes. Sixty specimens with 10 mm diameter and 2 mm thickness were made by using nanofiller composite resin. The material was filled into stainless steel mold and curing for 20 s. After kept in a dark box for 24 hours, the surface hardness of all specimens were tested using Microhardness Tester. The data were analyzed with one-way ANOVA (p≤0.05) and LSD's post hoct test. The results showed that the 60 minute bench time group presented the highest surface hardness value followed by 45, 30, 15 and 0 minutes bench time group. Moreover, the hardness value of 60 min group was almost similar with the control group. Statistical analysis showed no significant differences (p>0.05) between groups. It concluded, bench time has an effect on the surface hardness of composite resin but no significant differences statistically.
Stainless steel orthodontic wire is one of the wires used in orthodontic treatment. This wire is subject to corrosion. One of the efforts to inhibit corrosion is the addition of corrosion inhibitors. Guava leaves can be used as corrosion inhibitors because they contain active tannin compounds that can inhibit corrosion. This study aimed to analyze the effectiveness of guava leaf extract as a corrosion inhibitor for stainless steel orthodontic wire.This research used 0.16x0.22” stainless steel orthodontic wire from Ormco brand which was cut 40 mm long. 20 pieces of stainless steel wire were divided into 4 groups, namely the group that was soaked in saliva without guava leaf extract (control), saliva, and guava leaf extract 200 ppm, 600 ppm, and 1000 ppm. All wires were weighed before and after immersion. The wire immersion was carried out in an incubator at a temperature of 370 C for 10 days. The corrosion rate of the wire is calculated by the weight loss method. Then proceed with calculating the value of the effectiveness of the inhibitor.The results of this study showed the average corrosion rate of the saliva-soaked group was 0.159 mpy, the saliva-soaked group and guava leaf extract 200 ppm 0.037 mpy, the saliva-soaked group and guava leaf extract 600 ppm 0.033 mpy, and the saliva-soaked and guava leaf extract group guava leaf extract 1000 ppm 0.023 mpy. The results of the kruskal-wallis analysis showed that there was a difference in the corrosion rate between the groups soaked in saliva and guava leaf extract (p<0.05).The effectiveness value of guava leaf extract is effective in inhibiting the corrosion rate with the highest effectiveness of 85.53% Keywords: Corrosion Inhibitor, Stainless Steel Orthodontic Wire, Guava Leaf Extract.
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