Chemistry and Rheology of Otoplastic Materials

ABSTRACT

Knowledge of ear impression compounds, as well as earmold materials, is important to provide quality-hearing solutions to hearing-impaired people using BTE hearing aids. This article offers a chemist's and a rheologist's review of earmold materials. The sound attenuation properties of silicones, acrylates, and polyurethane foams have been measured using a novel Acoustic Test Fixture (ATF). The authors conclude that of these three polymeric materials, compliant viscoelastic polyurethane foam provides the best current earmold material solution for hearing-impaired individuals. It overcomes the fundamental limitations of shrinkage and mechanical compatibility to the dynamic ear canal. Also, compliant foam provides an ultra soft modulus at body temperature and superior energy dissipation capability in the audible acoustic range of frequencies.

KEYWORDS

Earmold materials - impression compounds - silicone - acrylates - polyvinylchloride - viscoelastic foam - polyurethane foam - rheology - acoustic test fixture - foam earmolds - otoplastics

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