Toxicity of Earmold Tubing Adhesives and Recommended Precautions

Question

I am opposed to using glues, even tubing glue, to secure tubing in an earmold due to possible harmful effects to the ear skin and canal. Most often when an earmold is retubed the mold goes directly into the ear, with no time for the glue to dry. If the tubing is loose, simply using a tighter fitting tube will provide a snug fit that will not slip out. I have talked with other audiologist about this, some agree and some disagree. What is the best procedure to secure the tube in the mold? To glue or not to glue? Are there any articles on this subject?

Answer

I, too, share your concern for skin sensitivity issues arising from common earmold/tubing servicing practices plus a host of other common practices that can make wearing an earmold an unhappy experience for the user. As you might be aware, we have been involved in research into the neurophysiology of the external ear for some years now. Consequently, we have discovered critical areas of concern that should garner the attention of all hearing health practitioners and manufacturers.

In addressing the toxicity issue of resins, monomers, and adhesives that can be used with earmolds and earmold tubing, it must first be noted that some of these are only toxic before they are cured into inactive states. For instance, monomers used for gluing earmold tubing are usually non-toxic to the skin after being UV-cured, while uncured monomer can cause instant acute dermatitis (and closure of the EAC) upon contact. Certainly, adhesives such as rubber cement, plastic cement, and all two-part epoxies--wet or dry--have potentially troubling effects on human skin.
Surprisingly, however, some of the newer medical-grade cyanoacrylate "super glues", while toxic in liquified form, become fairly innocuous within a short curing time. These are commonly used in suturing procedures. The larger danger in using these with earmold tubing is the possibility of binding the earmold to the skin.

In a day and age when many patients come in with ears that have been traumatized with cotton swabs, we often find the critical corneum stratum (keratin layer) of the EAC has been removed and the ear ultra sensitive to anything touching underlying (and unprotected) epithelium. Likewise, the use of hydrogen peroxide and/or boric acid solutions pose serious challenges to earmold comfort and hearing aid adaptation, even without an adhesive-inspired dermatitis issue. When a healthy layer of keratin is not intact, many if not all, hearing users experience earmold discomfort over time. Even open-ear and RITE users report itching and distracting sensations when the keratin layer is missing.

For these reasons, I suggest the following cautions and instructions for hearing health professionals to consider:

1. First, all hearing professionals should become well versed in EAC neurophysiology. This means understanding and recognizing what EAC keratin is, its desquamation pathway, and why it is absolutely necessary for user comfort. Furthermore, one should have an intimate knowledge of the neuroreflexes, including the mechanoreceptors that activate sensitive reflexes when hearing aids and earmolds are inserted. A good primer on all of this topic can be found at www.hearingreview.com/issues/articles/2006-03_14.asp.
   
   
2. During the video otoscopy examination it is imperative that the dispensing professional note the presence or absence of EAC keratin. Such can be identified by desquamation "lines" in the shiny surface of the keratin. Grainy or closely spaced lines, or keratin that peeling up off the EAC may be the result of dehyrdration, diabetes mellitus II, or medication side-effects. If the keratin is absent, it is important to inquire if the patient used cotton swabs or any offending solutions to "clean" their ears. In such cases, patients should be instructed in appropriate and safe ear care practices that can be found at www.digicare.org/ExternalEarCare.asp.
   
   
3. By slightly reducing the size of the tubing opening in the earmold, tubing can be pressure-fitted without glue. If adhesive is still needed for retention, be sure to UV or White-light cure monomer or if one of the medical grade cyanoacrylate "super glues" is used, make sure that any excess is cleaned from the earmold surface that comes into contact with the skin, and that it has adequate time to completely dry before insertion. I note that these adhesives are still caustic to human skin in until they are dried. Some useful information about impressions and earmold care can be found at www.audiologyonline.com/articles/pf_article_detail.asp?article_id=299.
   
   
4. When inserting a freshly retubed and.or cleaned earmold, I recommend a small amount of MiraCell solution be applied to the surface of the earmold as a lubricant and to minimize contact dermatitis. More information about this may be found at www.miracell.com/earcare.html.

Of course, there may be other considerations. Especially, one should avoid any adhesive, safe or toxic, from having direct contact with the skin. Taking an extra bit of time and precaution will not only exhibit professionalism, but will also assure a more comfortable wearing experience for hearing aid users.

Dr. Chartrand serves as Director of Research at DigiCare Hearing Research & Rehabilitation in Colorado City, Colorado, and is an adjunct assistant professor at Northcentral University. His areas of research interest are psychosocial effects of hearing impairment, neurophysiology of the ear, and auditory rehabilitation. For contact: www.digicare.org or chartrandmax@aol.com.