Monday, April 21, 2014

Your Audiology Tutorial: Earmold Impressions

Earmold impressions are silicone casts of the external auditory meatus (canal) taken either for the formation of custom hearing aids, specialized molds for hearing protection, or to keep water out of the ear. They are usually comprised of a two part material such as vinyl polysiloxane mixed together and inserted via a plastic syringe or device that resembles a caulking gun. A powder and water mixture is sometimes used, though it is reputed to be less stable. A foam dam is placed somewhere between the first and second bend of your ear canal before the material is placed to prevent it from going too deep/far (a "blow-by" - bad news). Don't be alarmed if you feel the need to cough as the material goes in (a normal reflex).

Three to five minutes later, after the silicone hardens, the fitter removes (hopefully gently) the impression with a slight clockwise rotation. During this, he or she may ask you to lower your jaw (for your comfort).  The impression is examined for smoothness. "Weld marks" or lines on the canal or helix portions of the impression may lead to a poor fit of the device. For hearing aids, it may not just mean discomfort, but also nonstop feedback, the kind you may have heard bleeding out of retirees' devices while in line at the Early Bird Special or at church.

Impressions are usually kept by the hearing aid or specialty mold manufacturers for a few years. 360 degree images are saved to mainframes/clouds and can be accessed for reproduction later. For at least a decade, Siemens has offered a specialty device to hearing aid dispensers and audiologists - a rotating carousel on which the impression is scanned and the image sent right to the home office.  This certainly saves postage and FedEx fees.

Impressions may need to be retaken if a patient gains or loses a significant amount of weight, which yes, can change the diameter of your ear canal.

Most patients have no difficulties with this procedure, though I did hear about one lady who ran screaming into the waiting room with an ear filled with impression material as she apparently had some sort of highly unfavorable tactile response. She downed a Valium prior to her next attempt and made it through.

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