November 8, 2005 Feature

Stick It in Your Ear

A Systematic Approach to Earmold Selection

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Total hearing aid sales have remained flat for more years than anyone in the industry would like to admit. Recently, however, there has been quite a bit of movement in the distribution of styles of instruments sold. According to The Hearing Review 2005 Dispensers Survey, 33% of hearing aid fittings performed by audiologists in 2004 were Behind-the-Ear (BTE) instruments. That means that BTE's now account for a larger percentage of hearing aids sold than Completely-in-the-Canal (CIC) aids.

Almost since their introduction into the market, CICs have been such a challenge that their selection and fitting has generated a significant number of publications. In looking at CICs as an option for my patients, it always intrigued me that all the acoustic benefits and preparation precautions for CICs were identical to making a good earmold for a BTE instrument. At that time, however, BTEs represented only a small percentage of sales, so the minimal coverage of earmolds in the journals seemed reasonable.

This recent Hearing Review Survey data should cause audiologists to re-think their interest in earmolds. If more than one out of five hearing aids sold is a BTE, understanding how to plan and execute good, logical earmold selections and fitting is very important.

Prior to my transition to the manufacturing side of the industry in 2001, I dispensed roughly 2,100 hearing aids. Of those, the best estimate I can come up with is around 50 In The Ear (ITE) hearing aids. My fittings during that time included losses from mild to profound. After making over 2,000 earmolds, I have come to the conclusion that they represent a frustrating paradox: Earmolds are not inherently difficult to do well, but they are very easy to mess up.

Don't Roll the Dice-Plan

When I was in graduate school I thought earmolds were simply a way for the sound to get from a BTE into the ear. My clinical fellow supervisor and mentor, Jim Gahn, taught me that the earmold was the "make it or break it" part of the hearing aid fitting. In trying to figure this whole thing out, I was reminded, strangely enough, of my youth.

Growing up in my father's drug store I watched my uncle Angelo, a retired piano player, full-time hearing aid user and part-time hearing aid dealer, perform what seemed almost like Voodoo on other people's hearing aids. They came into the store grumpy, frustrated, and despondent. After 15 minutes of grinding, funny smells, and laughter in the mysterious "consultation room," they left happy. When I questioned my uncle about what he had done, the word "earmold" was always in his answer.

Later Uncle Angelo allowed me to peer into the vault of acoustic and musical knowledge he called his head. Over the years he reminded me that recalling my musical training could solve all my earmold problems. More importantly, he instilled in me the need to approach earmolds with as much thought and planning as I do hearing aid selection and fitting.

Many years after that, I had the pleasure and honor to meet Mark Ross. He and I have shared more than a few conversations on the importance of earmolds and the necessity for all audiologists to dust off their notes and re-visit this absolutely critical component of the amplification system.

In selecting the right hearing aid and assistive technology solutions for patients, audiologists study audiometric data, lifestyle information, target gain rules, and research into the efficacy of certain algorithms. After all that careful planning, it seems a shame to roll the dice with the earmold. What follows is a suggested process for thinking through the design of the appropriate earmold to complement those carefully selected and programmed hearing aids.

A Few Interesting Cases

One of the reasons I really like earmolds is that I am inherently a cheapskate. In my personal life, I'm always looking for ways to solve problems with a $1.49 roll of duct tape and a few wood screws. In my professional life, this "low-tech/low-cost" approach comes in the form of re-designing or tweaking earmolds. Here are a few examples of how a $25 earmold can provide a big payoff to the patient.

In 1996, I spoke about earmolds at the National Convention of Self Help for Hard of Hearing People (SHHH). After the talk, a woman in her early 40s came to the podium and told me that she had recently lost all but a scrap of her hearing to meningitis. She was wearing the highest technology hearing aids available at the time, but was still not hearing well. Due to ossification and other health issues, she was not a candidate for a cochlear implant. Recalling one of Uncle Angelo's tricks, I cupped my hand behind her pinna and spoke loudly and directly into her unaided ear.

She said, "Oh, that sounds pretty good!" I've found this to be true with patients with severe cochlear distortion. I made her a pair of earmolds that acoustically functioned like my hand (a continuous flow adapter bore #5). When I fit the earmolds, I made one of my typical boneheaded moves. Forgetting that she needed to speechread me to understand speech at all, I stood behind her and asked, "So Beth, what do you think?"

She turned around, and with tears running down her face, said, "You just said my name and asked what I think!" That was a very inexpensive change to a very expensive hearing aid that made a big difference. Sometimes that's all we have to do.

The following year, I was doing another earmold talk at the SHHH convention and another woman came up to me with the following report:

"When I replaced my earmolds, I asked my audiologist to order the ones you talked about (continuous flow adapter bore #2). It made a huge difference-many people thought I had gotten new hearing aids! I was able to understand people from further away and I could hear the difference between F's and S's better."

In 2000, I filled a prescription from a children's hospital for a little girl with a shallow cookie bite hearing loss between 50 dB and 30 dB. The audiologist prescribed a programmable analog aid with a "standard" earmold with a #13 medium tube. The office where I worked didn't have Real Ear, but the functional gain on this girl looked great until she got to about 4000 Hz where it actually was worse than her unaided responses. Otoscopy and Tympanometry confirmed that she had patent PE tubes with volumes over 3 cc.

Thinking back to my anatomy and acoustics coursework, I realized that these ears wouldn't have a nice 4000 Hz resonance the prescription would have needed to really work. I pulled the tube out, drilled the bore to create a 3 mm horn, and inserted a continuous flow adapter. When we repeated the functional gain measurements, the lost gain was restored and all was well.

This case illustrates the absolute necessity to design each and every earmold according to the physical characteristics of each and every ear. This includes the possibility that there may need to be two different earmold configurations on the same head. When I make an earmold, I follow a very methodical and anatomy-driven process that keeps me both honest and on the right track.

Evaluating the External Ear

When I begin planning an earmold, the very first thing I look at is the pinna. Actually I look at as many pinnae as the patient has (usually two). I start watching how the patient's ears move during the case history. I look to see if the person's massiter muscle is clearly defined when she closes her jaw. I tell a few corny jokes so I can see what happens when she smiles. I take inventory of all the expected landmarks and make a mental note of any departures from average. Quite often, I will either draw or photograph pinnae that are really interesting.

The pinna also gives us a lot of information regarding which style of earmold might be the most appropriate. The firmness of the pinna, particularly in the concha and helix areas, should be evaluated and be taken into consideration. The only way I know to do this is to take the pinna between my fingers, and bend the helix and the concha. If the pinna is very stiff, I will usually lean toward a half shell or canal-lock earmold rather than a shell or skeleton.

If I notice a great deal of pinna movement or massiter muscle flexion when patients talk I put on gloves and put my pinky fingers in their ear canals and ask them to open and close their jaw. If the mandibular condyle protrudes into the canal at or lateral to the first bend of the canal, I use a modified open-jaw impression technique. This begins by filling the ear canal with the jaw relaxed and then about 1/3 of the way through the set time of the material I'm using, I have patients open their jaw for about 30 to 45 seconds and then relax again. If the condyle makes an indentation in the impression, I circle it with a red marker and indicate that the lab should not fill that void. If this recess doesn't end up in the finished earmold, the mandibular movement will likely displace the mold enough to allow for feedback.

After evaluating and documenting the characteristics of the pinna, I begin a careful otoscopic exam. My goal is not merely to confirm the absence of cerumen, but to take a "walk-through" of the canal. I memorize the color of the skin, any existing scratches or abrasions, and the shape and depth of the two turns. Finally, I carefully examine the tympanic membrane and make a mental image of the landmarks in the canal just lateral to the annular ring. This area will be my target for otoblock placement, so I want to be familiar enough with it to know, not guess, that I am in the right spot.

This whole external ear evaluation takes about three minutes, four if I find something interesting. Readers may be thinking, "Why not just use a video otoscope?" Remember how cheap I said I was? Actually, I prefer to use conventional otoscopy as I can typically get a truer color representation and find it easier to maneuver around in order to see the greatest amount of "ear estate" (I told you my jokes were corny).

Measure Twice, Plug Once

I strongly recommend that if you have access to a probe microphone (real ear) system that you use it and incorporate those data into your earmold decisions. The ideal earmold is acoustically inert to the hearing aid response. If we recall the basics of real ear measurement, we need to collect data about the resonance of the open ear (real-ear unaided response, REUR), how much of that resonance is lost by the occluding effect of the physical presence of the earmold (real-ear occluded response, REOR), and then use these data to modify the hearing aid output (real-ear aided response, REAR) so that the target(s) we selected can be met (see John Pumford and Sheila Sinclair's great primer on real ear measurement at the Audiology Online Web site).

The figure on p. 7 [PDF] shows a summary of how real ear information can be incorporated into planning an earmold. The shaded area is a target output range for a hearing aid (HA) based on the Desired Sensation Level (DSL) i/o algorithm. If we look at the hearing aid response in isolation, it appears to fall right into the target range. If we measure the ear canal resonance (REUR) and add it to the hearing aid response, we could say that we're in really good shape. We might even think that the earmold is pretty inconsequential to the fitting. But unless we also measure the REOR and subtract it from the HA + REUR, we really miss the boat, so to speak. After subtracting the REOR from the HA + REUR, we get the actual aided response or REAR. In this example, the REAR falls short of the target and will need to be adjusted. The tricky thing about REOR is that each time we re-make the earmold, it can, and usually does, change.

Make a Good Impression

Chester Perzanski, a process engineer at Starkey in Ontario, Canada has determined that 50% of hearing aid re-makes are due to poor impressions. Several years ago, I spent the day in an earmold lab and feel that at least that many earmolds are re-made for the same reason.

Taking a pair of accurate ear impressions requires approximately one-sixth of an hour but 100% of your attention. If the impression comes out of the ear and is even a little off, you should do it again. Consider how your patient will interpret the following:

"This impression is quite good, but not quite up to my standards. I know it's not the most comfortable procedure, but I really need to do one more, so we have the best impression possible in order to make the best possible earmold (hearing aid)."

Some may consider that such a blatant admission of imperfection will erode patient confidence. It has my experience that just the opposite is true. Ensuring the impressions are as perfect as possible is critical to the success of the final hearing aid or earmold and should therefore be a requirement for concluding the patient contact.

A Few Final Words

One of the most helpful habits I've developed over the years is to periodically take an additional impression of a patient or of a staff member and send it to my preferred lab for a critique. Even though I'm very tough on myself, it is very helpful to get an objective opinion of my technique.

Throughout my career, I have been fortunate to work in close proximity to some excellent otologists. This has provided me with the opportunity to make impressions of an unusually large number of post-surgical ears as part of my daily practice. Audiologists in more traditional practice settings should seek out these "odd-ball" ears to practice their technique. A relatively inexpensive way to do this is to remark to the owners of these ears how interesting they are and that in exchange for allowing you to practice on them, you'll make them a free cell phone headset or hearing protection earmold.

Brad Ingrao, is the editor-in-chief of the Electronic Deaf Education Network and serves as an advisor for the National Center for Hearing Assistive Technology, Raising Deaf Kids, the Hearing Healthcare Web site, and Audiology Online. Contact him at bingrao@e-audiology.net.

cite as: Ingrao, B. (2005, November 08). Stick It in Your Ear : A Systematic Approach to Earmold Selection. The ASHA Leader.

Acronym Key

BTE = behind-the-ear hearing aid

CIC = completely-in-the canal hearing aid

DSL = Desired Sensation Level

HA = hearing aid

ITE = in-the-ear hearing aid

REAR = real-ear aided response

REOR = real-ear occluded response

REUR = real-ear unaided response



  

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