Virtual Prototyping in the Development Process of Customised Hearing Aid Shells.

In the paper the author proposes a novel approach to design customised shells for hearing aids by means of techniques of virtual prototyping, used today in several fields of medicine. Digital technology is providing the technical platform to eliminate the need to take an ear impression, replacing the ear canal of a patient with a digital scan, but at present on the market there are still not systems able to perform in vivo scans of the human ear canal. Starting from CT (Computed Tomography) data of the external ear, adopting the powerful and quite easy to automate NURBS (Non Uniform Rational B-spline) modelling tools available in the commercial Rhinoceros® CAD system, the author uses a straightforward modelling procedure that by means of VBS (Visual Basic Scripting) tools, allows obtaining automatically and quickly the accurate CAD solid model of the customised hearing aid shell. Having the CAD model, then, it is possible to view and modify the shape in the three-dimensional space and so to design innovative acoustic prostheses completely internal to the ear canal to which they perfectly fit. Moreover, the procedure followed in the paper, will allow, analysing the ear canal changes in response to normal jaw motion, to design the best shape of the hearing aid shell.