Take a peek at any hearing-related journal or attend a hearing care convention and you may note the lack of discussion when it comes to earmold selection and modification issues. Based on the paucity of current information on this topic, one would think all earmold selection issues are either solved or just plain dead. Nothing could be further from the truth.
First, there are a growing number of behind-the-ear (BTE) users. Although much of this growth can be attributed to the proliferation of the open fit, some of the growth in BTE use can be explained by the fact that advanced features, like directional microphones, can be purchased as a standard option in a BTE device. Second, according to MarkeTrak VII,1 8% of hearing aid users are dissatisfied with fit and/or comfort of their hearing aids. With a nearly 10% failure rate, and over one-quarter of users dissatisfied with the whistling and buzzing of their hearing aids, it might be wise to revisit the lost art of earmold selection and modification.
The focus of this paper is to review the evolution of earmold technology, and its practical application to hearing aid selection and modification. Although some peer-reviewed evidence on the proper selection of earmold material and style does exist and will be reviewed here, it is scarce. Therefore, we include the opinion of two earmold lab experts in our review of earmold selection and modification issues.
When a first-time user of hearing instruments orders BTEs from you, several choices need to be made. One of the most important choices involves the type of earmold your patient will use with the instrument. In nearly all cases, you will base your decision on the degree of hearing loss, skin texture, anatomy of the external ear, and other issues that play a role in the selection process. For the busy dispensing professional, it really comes down to accounting for two major issues:
- Selecting of the correct earmold material.
- Ordering the correct earmold style.
According to experts closely involved in the manufacturing of custom earmolds, choosing the incorrect material and style are the top reasons for earmold remakes. We will examine each of these issues separately.
Selecting the Right Earmold Material
To effectively select earmold material for your patients, it is important to become familiar with the common materials used in todays earmolds. Every manufacturer has its own unique name for each type of material, but most fall into three categories: acrylic/lucite, polyvinyl chloride (vinyl/PVC), and silicone. Of course, each of these materials brings along a list of pros and cons to the hearing aid fitting.
Table 1 details the various types of earmold materials along with advantages and disadvantages for each using universally accepted terms instead of the manufacturers jargon or trademarked names.
|Acrylic||Regular||Allows for delicate earmolds that will keep their shape, good for mild to moderately-severe hearing losses, easy to modify||Should not use for active children for fear of ear injury, prone to feedback with more severe hearing losses|
|Body Temperature Reactive||Extends acrylic fitting range into the severe range and increases comfort, retains shape for more delicate earmolds, easy to modify||Should not use for active children for fear of ear injury, prone to feedback with more severe hearing losses|
|Polyvinyl chloride||High Durometer (firmer)||Used for moderate to severe range, skeleton and canal lock style, not as grabby as silicone, more comfortable than acrylic||Susceptible to body chemistryreduced life span (4 months-2 years), difficult to modify|
|Low Durometer (softer)||Used for moderate to severe range, half shell and full shell, not as grabby as silicone, more comfortable than acrylic, better for active children||Susceptible to body chemistryreduced life span (4 months-2 years), difficult to modify|
|Silicone||High temperature, high pressure cure||More resistant to feedback due to grabbiness, good for severe to profound hearing losses, hypoallergenic||No tubing adhesives (tubes come out easily), more expensive, difficult to insert due to grabbiness, difficult to modify|
|Low pressure, low pressure cure||More resistant to feedback due to grabbiness, the most effective earmold in reduction of feedback, great for severe to profound hearing losses, hypoallergenic||No tubing adhesives (tubes come out easily), more expensive, difficult to insert due to grabbiness, difficult to modify, can cause skin abrasion due to extreme grabbiness|
When selecting earmold material, it is important to take several factors into consideration. Many hearing care professionals are aware that the severity of the hearing loss is an important consideration. For instance, a patient with a greater than 70 dB hearing loss at 1000 Hz is a candidate for a softer material such as silicon.2 However, this is not the only issue at hand. Age, ear tissue, and the activity level of the patient should also be considered. As we age, our ear tissue becomes softer and more mobile (or flabby), causing softer materials to rub and grab at the skin in the ear canal. This can cause soreness and blistering, making it extremely difficult to insert the hearing instrument. This set of conditions can also make it uncomfortable to wear soft, silicon earmolds. For patients with severe hearing losses and skin that is no longer as firm as it once was, an earmold made of vinyl material may be the better option.
For patients with mild to moderately severe hearing losses, a harder materialsuch as acrylicis appropriate. Acrylic earmolds tend to be less abrasive to the tissue in the ear canal and are easier to maintain and modify. When selecting acrylic as an earmold material, the activity of your patient should be considered. Children, teens, and active adults have the possibility of ear injury with a harder material. Again, a softer material such as vinyl or silicone should be considered for these active patients.
Conventional wisdom suggests that softer earmolds are more effective in ensuring an acoustic seal in the ear canal, thus minimizing feedback; however, this result has not been supported by the clinical research.3 In one study, four earmolds of varying softness from a single ear impression were made, and no differences in acoustic seals were found. Based on these results, soft and hard earmolds appear to provide the same acoustic seal while being rated similarly in terms of comfort.
Selecting the Correct Earmold Style
One of the challenges of selecting the most appropriate earmold style is related to sifting through the myriad style options. Some styles are given a descriptive name, some are named after the inventor, and others are named after the application in which they are used. Because each earmold manufacturer might use slightly different terminology, Dillon4 has summarized a number of standard styles most commonly used today in his excellent book, Hearing Aids. Still others have recommendations for the most appropriate tubing and bore as it relates to high fidelity performance.5
Lets turn our attention to the clinical selection of the correct earmold style. Conventional wisdom would suggest bulkier earmolds should be selected for patients with moderate-to-severe losses or greater. However, bulkier earmolds do not guarantee greater insertion gain than earmolds that are less bulky. In fact, Kuk6 has shown that less bulky canal and skeleton earmolds permit as much insertion gain as shell earmolds. His work provides clinical evidence that the canal portion of the earmold contributes the most to the maximum gain requirements of a BTE hearing aid, and further reinforces the importance of an accurate earmold impression.
Earmold Modification Tips from the Experts
Jim Kuznar, lab manager at Great Lakes Earmold Laboratory, has 35 years of experience with earmold technology. In his nearly four decades of manufacturing custom earmolds, he has seen many changes in the industry and has gained a lot of insight relative to selecting and fitting earmolds. In recent years, he has noticed a higher percentage of bad fits due to changes in impression material and the cartridge system. He attributes the low viscosity of the material in the cartridge system to an increase in the number of remakesespecially for severe-to-profound hearing losses. His advice for taking earmold impressions is to use a thicker viscosity material when taking impressions for severe-to-profound hearing losses. He reports that he sees more remakes when a hearing care professional changes material from the syringe to the cartridgeor at least until the person acquires a little more experience with the new system.
According to Dave Prahl, shell process manager at MEMSI, Plymouth, Minn, a firm that is involved in manufacturing 400,000 hearing aids per year, The most common problems are associated with a fit that is either too loose or too tight. For the acrylic earmold that is too tight and causing a pressure sore, he recommends the use of a carbide bit to remove 1-2 mm of earmold material around the area causing the problem, then polishing the earmold before placing it back on the patient. For earmolds made of soft material that are too tight, he recommends using a razor blade to remove excess material and smoothing the rough edge with a detailing stone before placing it back on the patients ear.
An earmold fitting too loosely and causing feedback is the other common problem that can be readily fixed by the hearing care professional. For acrylic earmolds, applying a UV compatible build-up material on the tragus area, or in between the first and second bend on the posterior side of the canal, will solve most problems associated with a loose fit.
The Bottom Line
In an era in which professionals should be more concerned about evidence-based practices, there are very few controlled studies6,7 and other high levels of evidence to rely on when making earmold selection decisions.8,9 The professional must look to case studies2 and expert opinion10 as the only types of evidence available to them when making these important clinical decisions.
It should be noted that, although attention to this subject in peer-reviewed journals is relatively scarse, many researchers, authors, and earmold manufacturers have contributed significantly in clarifying techniques involved in the selection of earmold materials, impression-taking, and modification.11-19 According to expert opinion in this area, it is critical for the dispensing professional to hone the seemingly lost art of proper earmold impression technique and scientific breakthroughs in earmold technology.
Relying on the expert opinion of your favorite earmold lab manager, and sorting through the scientific evidence, is the first step in making more effective earmolds for your patients.
|Brian Taylor, MA, is director of continuing education, and Rebecca Younk, MS, is regional trainer, for Amplifon USA, Plymouth, Minn.|
Correspondence can be addressed to HR or Brian Taylor, MA, Amplifon USA, 5000 Cheshire Ln, Plymouth, MN 55446; email: [email protected].
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