Ultrasonic Evaluation of Anterior Restorative Materials

A non-destructive technique for the evaluation of the elastic properties of anterior restorative materials utilizing longitudinal waves has been developed, employing a liquid immersion cell to provide coupling between transducers and specimen (Melchor and Petrauskas, Ind. and Eng. Chem. 44:716, 1952; McSkimmin and Andreatch, J. Acous. Soc. Amer. 49:713, 1971). The advantages of immersion techniques as applied to the study of dental restorative materials include: (1) a specimen size approximating those produced by clinical mixes; (2) acoustical coupling to the specimen surface without use of intermediate solids; (3) possible utilization of a wide variety of immersion media, i.e., water, Ringer's, pooled saliva, oils, etc. Sound speed measurements are made by measuring the change in time of flight of an ultrasonic pulse when the specimen is removed from the path of the sound beam. The difference in time of flight is due to the difference in sound speed between liquid and specimen. In addition, the attenuation may be directly measured. A detailed description of the instrumentation and the measuring techniques has been presented recently (Greener, et al., J Dent Res 57, Spec. Issue A, 296, 1978, also DMG Microfilm, Abstr. 887). The measured longitudinal velocity at 5 MHz of six anterior restorative materials and a Plexiglass control after water immersion at 370C for 72 hours and one week are given in the table. The specimens are grouped according to longitudinal velocity as follows: PMMA and Isopast are at one end of the velocity scale, and ASPA and Silicap cements at the other, with composites TD-71 and Cosmic intermediate. Agreement between measured longitudinal velocities of cold cure PMMA and Plexiglass with published values for PMMA (Melchor and