بررسي خارج دهاني نيروي كششي و مقايسه ي كاهش نيرو در سه گونه كش ارتودنسي

In Vitro Evaluation of Extension Force and Comparison of Force Degradation in Three Brands of Orthodontic Latex Elastics

Statement of Problem: Elastic made from natural rubber is one of force supplies in orthodontic practice. Using elastic depends on the extension force of its different sizes as announced by the manufacturers. On the other hand, the elasticʹs force is not constant and is decayed gradually. Purpose: The aim of the study was to evaluate and compare three brands of latex orthodontic elastic with respect to initial force and force decay over a 24 hour period. Materials and Method: A sample size of 20 elastic bands from American orthodontics, Dentaurum and Unitek companies was used. Products with identical size were tested (The 3/[6 inch and 4 or 4.5 oz elastic from each company). Two statical tests were employed: A dry test for extension force, and a wet test to evaluate force degradation in artificial saliva used to simulate the oral environment. A Dartec testing machine with load cell capacity of 200 Newton ʹs for testing was used. The extension of the elastic bands was 3 times as much as the marketed internal diameter (standard index). Force measurements were made at 7 time intervals: 0, 1/2, 1. 3, 6, 12 and 24 hours. ANOYA and Duncan tests were used. Results: The results showed a wide range of initial force between the brands at the extension of 3 times of the marketed internal diameter. The elastic bands from American orthodontics and Dentaurum generated a force below their marketed force level at 3 times extension of their internal diameter extension. Unitek elastic bands generated a significantly higher force than that marketed at 3 times internal diameter extension ( p <0.05). The force decay patterns of all brands were very similar. Conclusion: Most of the elastic bands did not match the specified index using the dry tests. There were notable force degradation of all the types of elastic when they were subjected to artificial saliva immersion, approximating %18.64 during the first hour. An average degradation of 4% was observed in a period of up to 24 hours