An often-heard axiom in dispensing is that a good fitting hearing aid begins with the impression-taking process. The use of more viscous impression materials, long canal lengths, and open-jaw impressions are the key to impressions that work, according to the authors. In this article, four AuD candidates/graduates share their experiences after adopting this impression-taking technique.

There is general agreement that accurate ear impressions are critical for the manufacturing of comfortable and feedback-free hearing instruments. Unfortunately, there is also broad disagreement on how impressions should be taken. Earmold labs and hearing instrument manufacturers consider impressions to be satisfactory if they show a complete imprint of the ear concha and canal, and concern themselves little with which technique or material was employed to make the impression.

The audiologists enrolled in the doctoral level program at the PCO School of Audiology established that not all impression techniques and materials would produce equally good ear imprints. In fact, they found that ear impressions were the most suitable for manufacturing properly fitting earmolds and hearing aid shells when the following steps were employed:

  1. Taking a long canal impression;
  2. Using a higher viscosity (as opposed to a soft) silicone;
  3. Taking the impression with the patient’s mouth wide open; and
  4. Using a mouth prop inserted at the corner of the patient’s mouth on the side the impression was made.

This impression-taking technique and topics related to creating a good earmold have been explored in several journal and Web site articles.1-5

The following information has been derived from research assignments submitted by the AuD students during the authors’ teaching of “Earmold Techniques/Technology” (Course ACD602) at the Pennsylvania College of Optometry (PCO) School of Audiology in Philadelphia. Findings reported by other students were consistent with those presented below. All patient names cited in the articles have been changed to protect their identities.

An Astonishing Finding
By Kathy Pfouts, Asheboro, NC
Throughout this course, I was determined to find out if the recent increase of hearing aid and earmold remakes in my office might be related to my impression-taking technique. I have dealt with the same earmold lab and hearing aid manufacturer for several years, and remakes were never a problem until the recent introduction of a new economical DSP instrument. The remake problem was serious enough that I had stopped ordering earmolds from that lab for patients with severe to profound hearing losses, previous users, and eventually anyone I considered to be a difficult fit.

As it pertains to hearing aids, I felt relatively certain that, since the higher-end digital hearing aids had not required remakes, the fault must be at the lab—especially since my technique and type of impression material had not changed.

I talked with the hearing aid manufacturer and questioned them as to why the economy line of digital hearing aids required remakes when the higher-end digitals did not. Their response astounded me: I was told that, most likely, all of my impressions had resulted in loose fitting hearing aids due to the combination of the soft material and closed-jaw technique. It had not posed a problem in the past because the higher-end digital hearing aids had a feedback management system. Therefore, the feedback problem was managed—or concealed—and was not a problem for the patients. Since the economy digitals do not have a feedback management system, the looser-fitting hearing aids resulted in feedback and unhappy patients.

To determine the accuracy of this idea, a total of 14 patients that had previous fitting problems were scheduled for new impressions/remakes. As recommended in the course, impressions for all remakes were made using a more viscous impression material. All impressions were made using a bite block to ensure uniform, open-jaw impressions.

Hearing aids: A total of 10 hearing aid remakes were made for the 7 subjects: 3 binaural sets (6 remakes) and 4 monaural. In all cases, the new hearing aids fit well, were comfortable, and had an adequate acoustic seal to prevent feedback, even in cases of exaggerated jaw movement. The hearing aids were relatively easy to insert and remove, with the exception of one set that require buffing due to problems with insertion. The patients with in-the-canal hearing aids were pleased with the size and cosmetic appearance, as they fit more flush with the ear canal and were less noticeable than their previous hearing aids. All subjects were pleased with the fit/feel of their hearing aids at delivery and at their follow-up visit, one week post delivery.

Earmolds: Fourteen earmold remakes were made for seven subjects, all binaural sets, all for children, cases in which rapid growth is often a fitting issue. All remade earmolds (including 2 sets of swim molds) fit well at delivery and at the one week follow-up appointment. Feedback was no longer an issue with the earmolds, and retention and comfort had also improved. The parents of two of the children commented that their child appeared to be hearing better with the new earmolds than with the previous earmolds. The swim molds provided the tight seal necessary to prevent water leakage.

These field studies convinced me that the low-viscosity (soft) silicone material and closed-jaw impression technique were the most likely causes of the poorly fitting aids. No remakes have been required with any type of earmold or hearing aid from any manufacturer since employing the new material and technique. This not only significantly reduced the level of frustration felt by my patients and myself, but also saved time.

Nine Case Studies
By Theresa Shevetz, Columbus, Ohio
I fit hearing aids every day, all day, and I have found that there are many things that can go wrong with a hearing aid fitting. Having the aid stay in place and be comfortable to the patient can be problematic, especially when fitting completely-in-the-canal (CIC) instruments. These instruments are fit deep within the ear canal, and jaw movement always presents the potential for soreness and/or the shell rubbing against the wall of the ear canal.

Like most hearing care professionals, I like to think of myself as compassionate and determined—but my job can also make me crazy with frustration. Feedback is my biggest pet peeve. Now, for the first time since I began dispensing hearing aids, I am confident that I can make a comfortable and well-fitting hearing aid on a consistent basis. Prior to my coursework, I used a liquid and powder impression material. For the purpose of this study, a higher viscosity (firmer) silicone was ordered. In all the cases below, a syringe was used to inject the impression material, with the patient keeping their mouth open.

Case 1. Rachel, 32, has been, by far, my most challenging fit. She has worn in-the-canal (ITC) analog aids for 7 years. Her ears are very small, and the canal portions on her most recent hearing aids were almost non-existent. Fit with new mini-canals, she reported that the hearing aids would “plug off” every 10 seconds, with or without jaw movement. Even inserting the aids would make them sound “plugged.” She was ready to quit trying because she was so frustrated.

I requested that the hearing aids be remade because I was convinced it was due to the vents located at the top of the aids; the new aids had the vents at the bottom. She tried them faithfully, but no matter what she did, the aids kept “plugging off.” Comparing the old aids with the new, I was now convinced that the sound was being blocked off by her narrow ear canals. I tried opening up the vents and shortening the canal length as much as I could. The results were better, but the “plugging off” phenomenon was still happening. Now, with trench-like vents almost up the entire length of the aids, I was worried, but she said she’d give it another try.

At this point, my coursework started. I read the lecture and my eyes widened with relief: The jaw’s downward movement can cause the instrument’s sound to cut off. Open-jaw impressions were taken and remakes requested for the third time. The aids were sent directly to her home because she lives 90 minutes away.

She sounded so excited when she called. She wasn’t experiencing any “plugging off” effect. She hasn’t called with a problem since that time.

Case 2. Betty, an 80-year-old woman, had been fit with CIC hearing aids after losing a significant amount of hearing following radiation treatment. The aid in the right ear was very susceptible to feedback caused by substantial jaw movement.

Her tiny ear canals made it difficult for a good fit without making her ears sore. After many months of buffing down the aid and three remakes, I made the impression following the new protocol and had a successful fit. I was able to increase the high frequencies without the threat of feedback and, as a result, her word understanding was much improved. Her husband called to tell me that it is working so well and feels so comfortable that she’s considering having the left aid done the same way!

Case 3. Tim, 34, was originally fit with binaural CIC hearing aids. We were juggling fit and feedback issues for both instruments. I tried to increase the higher frequencies, only to be greeted with feedback with every movement of his jaw. I encouraged him to stay on course and not get discouraged.

An open-jaw impression using the higher viscosity silicone was taken. He came in to pick up the hearing aid, and I had it programmed to where we had wanted it to be prior to the remake. It felt and sounded great, without a hint of feedback. Next objective: his left ear.

Case 4. Martin, a 64 year-old man was fit with binaural CIC hearing aids. He has a severely sloping high frequency hearing loss. Fit with digitals and doing well, he returned because the aids had “loosened up” in his ears and were causing feedback when he moved his head. The canals on the aids were very short, so I recommended remaking the aids with longer canals. Open jaw impressions were taken. The hearing aids that were returned were twice as long as the originals. I was worried that they wouldn’t fit properly, especially in the bony portion of the canal. He loved the fit of the hearing aids, saying, “Now they feel like they belong there.” I turned up the high frequencies and he was thrilled!

Case 5. Jimmy, 14, was born with mild cerebral palsy. He was fit with CICs. His mother wanted Jimmy to try the aids during summer vacation so he would get accustomed to them before school started. Jimmy, who has tiny ear canals, was carefully instructed to leave his jaw open while the impression material set. He has had his aids for 3 weeks now and the fit seems to be working well. Good thing; I believe he may have given up on amplification if the aids hadn’t fit well.

Case 6. Stan is a first time hearing aid user. His left CIC would not stay in his ear canal so it was remade. It was very tight and I was skeptical, but I let him try it. He called saying that he was still having trouble with retention. This time it was coming out not because it was too loose, but rather, it was too large: a poor fit the second time. With the impression-taking technique recommended above, a remake was done. He picked up the aid. The faceplate was recessed and it fit beautifully—even better than I had anticipated. There was no movement of the aid with his jaw opening and closing. He was very pleased.

Case 7. Helen is an experienced user. She was fit with digital in-the-ear (ITE) hearing aids. She had a sore in the upper concha of her left ear. I aggressively buffed down the helix lock until it was almost gone, but the sore spot persisted. After two remakes, the last of which we could not even get into her ear, I used the new impression-taking technique. She’s been wearing the aid for 2 weeks and it fits wonderfully. She still has a bit of soreness in the upper concha bowl, but it’s much better. I buffed it down the other day and I anticipate that it will be fine.

Case 8. Patrick’s story is not as successful. He is an older gentleman who was wearing an ITE hearing aid. Closed mouth impressions were taken for the first fitting, and the resulting hearing aids were uncommonly short. The faceplates were deep but the aids were about half as long as I had expected. The aids were “walking” out of his ears by the time he arrived home. He returned within hours and open-jaw impressions were taken with silicone material. To my amazement, the new aids had their canals just as short as the first pair, and they were still prone to feedback with jaw movement.

Case 9. George claimed that his new digital ITE hearing aids were the “most comfortable hearing aids” he has ever had, but they seemed to feedback when he walked. (When he walks, he lowers his head.) I initially reduced the high frequencies, but then his intelligibility was poor. I remade both aids with his jaw open and the results were excellent. He reports that the aids are very comfortable and there is no feedback even with the restored high frequencies.

I can’t express how pleased I am with the results from this simple impression technique. I recognize the landmarks of each impression and know what to correct for a second impression if the first isn’t satisfactory. When someone walks into my office with a problem, I now know what to look for. It feels like a whole new door has been opened, and I now have new solutions for the problems of comfort, retention, and feedback.

Dramatically Positive Changes
By Londa Nidiffer, Oxford, Penn
My remake rate tended to be quite high during my first year of practice. About 40% of my patients required a remake, and some patients required more than one. That has changed! The anecdotal reports from patients has been very gratifying. Hearing instruments made using the new technique were reported by patients to be more comfortable, with less occlusion effect, and reduced incidence of feedback.

One patient whose aid has been remade 2 previous times using a closed-jaw technique, was fit via the open-jaw impression technique and a request for a longer canal. The result, as he put it: “This is wonderful.” Two other patients who have had one aid each remade requested that the other aid be remade using this technique, because they found the remade aid to be so comfortable.

In the last 2 months, none of my fittings that utilized a higher viscosity silicone and the open-jaw technique have required a remake due to feedback or comfort. Patients who are long-time users of BTE’s have responded positively as well, remarking on the comfort of their new molds. I have experienced significantly fewer feedback-related adjustments.

We Have the Control
By Jane Laseter, Montgomery, Ala
Having seen good fits with all of my 10 patients used in this assignment, I realize that I do have control over how well an instrument or mold will fit the patient. Particularly with children, getting a better fit initially means that they can wear their earmold for a longer time, even while they’re growing and their ear is changing. I feel that some problems that we’ve managed with frequency response programming and trimpot adjustments won’t be an issue if we modify and improve our impression-taking technique.

In talking with the hearing instrument manufacturers and earmold labs, I realized time and time again that they seemed relatively unimpressed and disinterested in what type of material I was using or what technique I used. They seem to be of the opinion that an aid or mold that fits well is the result of their manufacturing process, their trimming, grinding, and coating. It seems that it would be to their advantage to educate professionals (and/or themselves) about what makes a good impression and share that information with their customers.

Summary
These and other results in hearing instrument fittings documented by the AuD students indicate that ear tissue stretching achieved through employing proper impression techniques and materials creates a desirable effect. The benefits of taking ear impressions as described above include a secure and comfortable fit, reduced or eliminated acoustic feedback, less or no occlusion effect, enhanced retention, and uninterrupted sound propagation.

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Chester Pirzanski, BSc, and Brenda Berge, AuD, are adjunct instructors at the Pennsylvania College of Optometry, School of Audiology, Philadelphia. Pirzanski is process engineer, trainer, and lecturer with Starkey Labs-Canada, Mississauga, Ontario, and Berge is an audiologist in a multi-office private practice in Guelph, Ontario.

References
1. Pirzanski C. An alternative impression taking technique: The open-jaw impression. Hear Jour. 1996; 49(11):30-35.
2. Pirzanski C, Berge B. Ear impressions: Art or science? Available at: www.audiologyonline.com.
3. Pirzanski C. Ear impressions. Available at: www.educationservice.net.
4. Pirzanski C. Factors in earmold selection: starting (and finishing) right. Hearing Review. 2001;8(4): 20-24.
5. Pirzanski C. Communicating with manufacturers: returns and remakes. Hearing Review. 1999;6(10):26-30.

Correspondence can be addressed to HR or Chester Pirzanski, Starkey Labs Canada, Ltd., 7310 Rapistan Ct., Mississauga, Ontario, L5n 6L8, Canada; email: [email protected]