Determination of bond strength of impregnating materials: A reevaluation of test methods

Bond strength is one of the most important properties of an impregnating material. This property can be measured by a number of test methods. The main question needing to be answered is which method provides the most accurate values in the most reasonable amount of test time. This paper is a reevaluation of three methods which have moved into the foreground as being the best methods for testing this property. The methods are: 1.) The Helical Coil Method 2.) The Twisted Coil Method, and 3.) The Bundle Method Each method was analyzed for consistency of data and time requirements for performing the test. Results show that the Helical Coil and the Twisted Coil methods were equal in almost all areas of comparison. There was one area, identification of solventless materials, which shows a preference for the twisted coil method. The bundle method showed poor correlation to either of the other methods. The information presented in this paper will identify the similarities and differences between the methods. The conclusions will show the reasons for support of the Helical Coil and the Twisted Coil Methods.