FLOW OF METHYL METHACRYLATES

¹ Thomas W. Evans Museum and Dental Institute, School of Dentistry, University of Pennsylvania, Philadelphia, Pa.

An analysis of our experimental work to date seems to indicate that properly processed methyl methacrylate tends to behave like an elastic material but undergoes a certain amount of permanent distortion under a constant load maintained for an appreciable time. The rate of change of distortion is retarded, apparently by internal friction, so that it has a logarithmic decrement in both compression and recovery. Furthermore, it exhibits an hysteresis-like effect, recovery not being complete. It remains to be determined whether or not this latter phenomenon is comparable to that occurring in the core of an electromagnet.

Many questions remain unanswered. What brings about the seemingly initial distortion represented by the parabolic curve? Is there an instantaneous compression upon application of the load and/or recovery upon its removal which has not been detected because of inherent difficulties? What effects do pearl size and methods of mixing, packing and processing have on the properties being investigated? And so on ad infinitum. Many of these questions must be answered not only to determine whether methyl methacrylate is suitable for certain types of dental restorations but also to obtain the most desirable physical qualities with the materials available.