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Objective: To compare the softening efficacy of synthetic D-limonene in various concentration levels on gutta-percha at different contact times.
Methods: The bottom of 165 plastic molds was filled with Cavit and thermoplasticized gutta-percha, respectively. The molds were stored in an incubator at 37oC to simulate oral temperature and were divided into five experimental and two control groups according to the type of solvents used for softening effect and its concentration, and the contact times were varied at one, three, and five minutes. 0.2 ml of the solvent was added to the surface of all of the samples with the use of calibrated droppers and then the samples were left for one, three, and five minutes. A No.30 finger spreader moved downward with a constant speed of 5 mm/min by Universal Testing Machine EZ-S (SHIMADZU, Japan). The force was recorded in Newton, and data were recorded as numbers and graphs. Statistical analysis was performed by using IBM SPSS statistics 20 (New York, USA by the Kruskal-Wallis) at 95% confidence level.
Results: In each experimental group, the force required to move the finger spreader increased as the contact time increased. In the one-minute contact time group of samples, there was no statistically significant difference among different types of solvents except between chloroform and normal saline, chloroform and ethanol, 97% D- limonene and normal saline solution, and 97% D-limonene and ethanol (p <0.05).
Conclusion: This study revealed that the loaded force was less in the one-minute contact time group when compared to that in its three- and five-minute counterparts. The one-minute contact time is the optimum contact duration to soften gutta-percha. The least concentration of synthetic D- limonene that yielded the same gutta-percha-softening efficacy as chloroform was 60% synthetic D-limonene.
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