Best Earmold Impression Method? Open Mouth, Closed Mouth, or Relaxed Mouth?


I would be interested in hearing from fitters and users of earmolds as to what methods for making an impression works best. From what I can see the common methods are:

  1. Closed Mouth
  2. Open Mouth - potentially with a brace to keep your mouth open
  3. Relaxed Mouth - Mouth/jaw moved, and talking allowed during the time the impression sets up.

I just got molds that were done with the relaxed mouth method, and quite frankly they are not very good – unacceptable. They seem to move in my ear and make noise every time I move my jaw. The noise sounds like Velcro being pulled apart. The interesting part is that I hear the noise at about the same volume regardless of whether the HA’s are turned on or off. The sound must be coming from the molds moving in the ear canal, not from the HA receiver.

I found this article which is a bit dated, but seems pretty thorough:

Impression-Taking Techniques that Result in Fewer Remakes

It is long article, but I would suggest the conclusion of it is that using the open mouth technique results in the best fit. I realize it is controversial, but is that the best current thinking? The argument is made that an open mouth increases the diameter and length of the ear canal, and if you don’t want it to be loose when you open your mouth, you need to take the impression with an open mouth.


The other issue is that the critical gain test did not show much of an improvement over the closed click sleeves for feedback prevention, although she said she got my gain up to the full target. Feedback is still a bit of an issue.

A second question would be the depth of the mold. If loose fit is an issue, is it better to ask for a deeper mold? Potential to get better acoustic isolation?

I’ve got to get these molds remade, and would really like to get a good fit this time. I’ve lost count of the number of times I have been back to the fitter for changes. Seems like I am going in circles. These molds are far inferior to the off the shelf click sleeves.



I was always told to move my mouth around like I was chewing, and it has always gotten me very comfortable ITE hearing aids

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Sorry to be dogging your posts here, @Sierra . But I do remember a previous thread somewhere on this forum where there was discussion of how ear canal shape may change or not with mouth/jaw movement and what mold fitting technique worked best/mattered most in such situations. Seems to me, rather than just going ahead and making an experimental impression, etc., that if there were some quick and easy way to evaluate your ear canal shape in various states of mouth openness, that would give you a head-start on deciding what you need to do.

My molds were made by ReSound, presumably using their 16:4 mm philosophy and the outside face of the mold is just even with the interior base of my tragus in each ear. According to ReSound, the mold should go no more than 4 mm past the first second(edited) bend in the ear canal. Pehaps I am misinterpreting the depth of insertion from your diagram above, but it looks like more than 1/2 the length of the mold is inserted beyond the first bend of the ear canal. If your present molds are inserted to such a depth and it’s just a question of in what mouth position your mold should be taken, maybe the difference in relative position of the mold in the ear canal explains a very large part of the difference in mold sound/mold sensation between you and me. I wonder if your provider has something like a foam plug that could be reliably position at different depths in your ear canal and by which you could test the sound effects of opening/closing your mouth, chewing, etc. Or if there is something like a tulip dome or power dome that could be inserted to various depths that would provide a decent mold stand-in. Even if you didn’t get the “full-mold” sound effect, by relative chewing sound, etc., you might be able to gauge at what depth your mold sound problem arises.

I vaguely remember, perhaps from a ReSound impression-making Audiology Online course, that the first bit of your ear canal, running to the first bend, is pretty well-cushioned material, fatty tissue lining, etc. Further on into the ear, the ear canal lining is much closer to the bone or harder tissue structures. If my molds sit “outside” in the more cushy area of the canal and yours are more connected to bony/hard structures further along in the canal, that may be the source of your annoying sound problems. As I’ve pointed out in other posts, perhaps because of the structure of my ear canals, the undulations, the arc helicis lock on the top of the mold, I have zero problems with slippage. Perhaps going for a mold that’s designed to be inserted to a good depth to avoid slippage is just inviting other problems…

Edit_Update: Guess I’m misreading, the ReSound blog post says the 16:4 rule is 4 mm beyond the 2nd bend! At any rate, it might be worth a forum survey: who made your molds and are you happy with the result?! Perhaps just as some folks here brag about HA’s and some OEM’s in their perception are better than others, maybe some mold-making companies (associated with OEM’s or not) are better than others in average customer satisfaction - along with a provider’s impression making skills, etc.

2nd Edit_Update: Further point (and a clarification in my own understanding) is the 16:4 rule applies to EAR CANAL LENGTH THAT IMPRESSION CAPTURES and is not necessarily the length used in making the mold itself, which may be only some smaller fraction of the length used in making the actual mold - which the designers chose from the 3D scan of the impression mold. So in my case, the mold actually made to wear begins near the outside of the ear canal opening and runs 15 to 16 mm into my ear - and so it seems compared to the diagram Sierra offered as OP in this thread, my actual mold is much more in the outer portion of my ear canal, lined with softer tissue.



From the ReSound blog referenced in my last post above:

In some cases it’s recommended to do an open jaw impression.

• When ear geometry lacks retention
• When patient has severe Temporomandibular Joint (TMJ) movement
• When device has tendency to work out of ear
• When patient has feedback or loose fit issues

So seems like all of the above might apply but for starters, I wonder if there is a very easy way to evaluate if you have severe TMJ?



I wonder if it’s possible to do all three - closed mouth, open mouth and chewing.

I’m sure doing that then scanning those into 3D software to evaluate changes in the shape would provide enough information to work out where the fit issue lies.

Wouldn’t be the most cost effective but in problem cases, I’d expect it to yield results.



Yes, my understanding is that the outer part of the canal has cartilidge around it and will give some if the mould is larger. The inner part is close to the bone, and does not give so much. But, it should not change shape either.

I do seem to fit some the cases listed where an open jaw impression is recommended. So far it seems to stay inserted, but it sure feels like I have TMJ movement and that the mold is loose with some feedback.

I am not sure I totally follow all of those measurements, but here are a couple of pics of what my left mold looks like:

That Resound article is helpful. Thanks for that.



I have thought about doing that. The fitter has said they will make as many molds as I need to get a solution.



I thought the mouth open impression was best for a seal for when your mouth is usually closed. I had
CICs before and they were without issue. They also went past the second bend.



At least in theory a mouth open impression should fit tight with the mouth open, and tighter still with the mouth closed. Again in theory where it fits tighter is the part of the canal that has some flexibility, so it SHOULD not cause discomfort. At least that is the best I can make of it all. The proof is always in the pudding though. I’m still waiting for a good pudding!

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Your left mold seems very smoothly and evenly shaped - no undulations in the shape of your ear canal that would help keep the mold in place - just my naïve and untutored opinion.



Yes, that is what I noticed too. The right one does seem to have more of a shape to it, especially near the inside end where the receiver is. It gets a little larger and has a bit of a hook shape to it. I’m thinking there might be some benefit if they were longer. The left one is the one that moves the most, but the right one does also, but to a lesser degree.



I struggled, for nearly 6 months, to adjust to molds made with the closed mouth method. They didn’t hurt. They stayed put. Boy did they stay put. Every chew, every word, every facial movement tugged at both my ears. I hated the sensation and could not adjust to it. That seemed to be the only type of mold my audiologist would consider. It was get used to it or go back to some type of dome…and those hadn’t worked for me. I changed audiologists and he had me talk while the gel was setting. The resultant molds are tons more comfortable and don’t tug at my ears with every movement of my mouth or face.

As for my hearing, I haven’t noticed any difference in the quality of my hearing as between the 2 molds. For me, the change to the relaxed mold (using the term of the opening article) has been a matter of comfort.

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@Sierra - Sorry if I missed it but what’s the latest on the remake of your molds and are the replacements working out for you?



They replaced the first custom molds almost immediately because they messed the venting up. The replacements are better but do not fit well. Left one has feedback, and the right one slips out. Went on vacation and will have another appointment for new impressions first week in August. This is a long slow process.

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I had my followup appointment today for the molds, and got the open mouth impressions made. The fitter seemed a little skeptical that was going to change anything, but was certainly willing to give it a try. Should have the new ones in 10 days or so. I sure hope they are an improvement. Currently the molds are really no better than the non vented sleeves.

I also found out today that I only have two weeks to make a final decision on KS8’s on whether or not to keep them. It seems to have something to do with our healthcare system and the amount they refund.

I had a good talk about alternatives. She tried a slightly different gain curve adjustment that was recommended by her Rexton support person. It was a change in 1.5 to 2 kHz range where my loss curve is steep. Didn’t help and was in fact probably worse. She also gave me a ReSound aid to try, and did the REM adjustment on it. At first I thought it was better with quieter sounds, but the longer I wore it the more I concluded the ReSound was no better, and probably even a bit worse. So I think I am going to keep the KS8’s. Certainly going to the KS9’s would be an option, but I really don’t think they would be better other than being $100 or so cheaper.

So, I guess I will ride the mold fine tuning option to the end and call it quits on expecting any better. She admitted they could just turn down the gain on the left ear to the point it stops being annoying. I guess it gets back to the early warnings about hearing aids. They are a partial solution to hearing loss, but a far from perfect one…



Would have figured you would have given the KS9 aids a try. Sure wouldn’t cost you anything.
I suspect the KS9 aids are really good aids, not that the KS8 aids aren’t.



To get there, I believe I would have had to return my KS8 aids, then go with no aids until the KS9’s are released in Canada (6 weeks or so in her opinion), then start this whole merry go around process all over again. To date I have used two brand new pairs of KS8’s, the fitter’s demo pair of KS8’s, plus the ReSound ones today, and they all have been essentially the same. I think it is probably time to admit it is my left ear that cannot be fully corrected, unless I get a magic breakthrough with the molds. To be frank I am getting a little tired of them. I tried with just a left ear correction, and that was terrible. I tried just the right ear, and that is better, but probably not as good as the right ear along with a gain reduced left ear. If the molds don’t work any better than they have so far, I will probably go back to just the non vented sleeves, and return the molds.



I had flat forgot about Canada not having the KS9 aids yet, sorry about that.

Does your left ear actually hear sounds in the upper frequencies? If not you could be dealing with frequencies that can not be helped. If you can then the right aids and fitting will help you.

No trying to push but Phonaks have a good reputation for feedback control. I was pretty impressed with the KS9 aids the other day at Costco. Almost enough to sell what I have and do the Costco thing.



The one slightly uncontrolled variable - tough to find out if it makes a difference -is that, as you have pointed out, each HA brand gets a different mold custom-made for its receiver. So there might be the slight possibility that if you switch to another roughly equivalent performance HA, you’d get a better mold somehow.

Is there any way of doing something additional - just joking a bit here - like stuffing “putty” in your left ear with the receiver and the mold in your canal. If the additional material cut out the feedback, then you’d know that the mold you have now for that ear is just not good enough - and couldn’t you just keep pushing Costco to make a better mold, change material, or whatever, until they find a way to get a decent, comfortable seal with a mold that blocks feedback? Sorry, this is just off the top of my head.



What my left ear sounds like to me is a fairy faint replication of a clean signal like I should be hearing, with an overlay, potentially with a slight delay, of a sound that is being produced by a $5 AM radio. “S” sounds in particular seem to get turned to garbage. Today the fitter used a stethoscope with an adapter that let her listen to my hearing aids. She said it was loud, but the left or the right did not sound abnormal to her. One would have to think it is some combination of my ear and the HA’s.