Annotation Ultrasonic Evaluation of Anterior Restorative Materials E. H. GREENER, D. C. WATTS, and E. C. COMBE Northwestern University, Chicago, Illinois, and Turner Dental School, University of Manchester, United Kingdom J Dent Res 58(1):543, January 1979 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

Received for publication May 15, 1978. Accepted for publication June 16, 1978.

Petrauskas, op. cit.) is excellent. The velocity data appear to mirror elastic properties from what is known about the structure of these materials, i.e., Isopast is a low inorganic filled (25 wt. %) system of submicroscopic (0.07 Am) SiO2 in a modified Bowen's resin, TD-71 is a filled conventional PMMA, etc. The product of the square of the longitudinal velocity and the material's density will yield an 'effective elastic modulus' which can be equated with Young's modulus if attenuation and Poisson's ratio are small. Measured attenuations of the dental restoratives are considerably higher than that for Plexiglass and probably represent energy dissipation effects due to macro- and micro-defects associated with porosity, setting chemistry and structure. In this study the highest values of attenuation appear to be associated with systems which maximize SiO2/ matrix interfaces. The major errors in this technique appear to be associated with critical measurement of signal displacement in attenuated specimens. Other sources of error are specimen geometry changes after immersion (warping and swelling). Reproducibility is of the order of ± 5%. Accordingly, the changes in longitudinal velocity occurring after one week water storage appear to be within experimental precision with the exception of cold cure PMMA (9%). This larger change may be associated with possible leaching of monomer and/or water sorption.

Acknowledgment. Partial support for this research is acknowledged from Fogarty Senior International Fellowship, Fogarty International Center, NIH (F06TW



Plexiglass Cold cure PMMA*

2770 2760 2628 Isopast** TD-71+ 3080 Cosmic* 3265 ASPA* 3490 4055 Silicap** *Amalgamated Dental, London **Ivoclar, Lichtenstein +Dental Fillings, Ltd., London

0.93.5 2502 3.5 2566 3.7 2965 6.4 3303 3.0 3268 5.0 4290

4.2 4.6 4.1 5.6 3.0 5.5

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Ultrasonic evaluation of anterior restorative materials.

Annotation Ultrasonic Evaluation of Anterior Restorative Materials E. H. GREENER, D. C. WATTS, and E. C. COMBE Northwestern University, Chicago, Illin...
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