Comfort and Retention: Why Ear Canal Dynamics Matter and How Technology Can Improve It

Discomfort and poor retention are among the most common hidden causes of reduced wearing time, compromised outcomes, and ultimately increased refit and remake rates.

The effectiveness of any hearing aid depends less on its electronics and more on how consistently it seals within a dynamic canal. Even the most advanced hearing device will fail to deliver its benefits if the user finds it uncomfortable or if it slips out of place. Understanding why this happens and how new technologies can help can significantly improve patient outcomes.

The human ear: A dynamic and highly individual structure

No two ears are the same. Anatomically, the ear canal varies between individuals in curvature, diameter, softness, and how it responds to jaw movement. 

One of the most underestimated factors in achieving a stable, comfortable earpiece fit is the natural variability and movement of the ear canal itself.

Research by Pirzanski and Berge has shown that ear canals differ not only in shape and softness but also in how they dynamically respond to jaw movement, such as speaking or chewing. These mandibular actions can compress or expand the canal and, in some individuals, change its diameter by more than 2 mm -enough to significantly affect both retention and acoustic sealing. In practice, this means that when the canal expands during jaw motion, the earmold may temporarily lose its seal, creating an unintended “dynamic vent.” The larger this temporary vent becomes, the more likely it is that low frequency sound will escape or that external noise will enter the canal without passing through the hearing aid’s processing path. Even minor canal widening can create a dynamic vent, leading to low‑frequency leakage, increased feedback risk, and perceptible intermittency (“on–off” sensation) during jaw movement.

Another important factor is the stiffness of the ear canal, which strongly influences both sealing and retention. Clinicians often try to estimate canal firmness during examination, yet studies show these predictions are usually inaccurate – only 34% of assessments correctly identified canal softness levels. Older adults typically have softer, more compliant canals, while children’s ear canals are unexpectedly firm, a pattern opposite of common assumptions. This stiffness matters because softer canals in seniors tend to deform more during jaw movements, increasing the likelihood of leakage, feedback, or loosening, whereas the firmer canals of children maintain a more stable seal but can create comfort challenges if not designed carefully.

Additionally, the ear canal changes dynamically with age. Voss et al. (2025) have recently published their results exploring how the ear canal geometry changes across the lifespan. The group of researchers made use of a large dataset of Computerized Tomography (CT) scans and measured individuals from 0.7 to 91 years old.

Figure 2 shows how the cross sectional area of the ear canal changes with depth across four age groups: children (<10 years), younger individuals (10–20 years), adults (20–60 years), and older adults (>60 years). A clear age related pattern emerges; children consistently display the smallest and narrowest canals, especially in the mid canal region between 10–20 mm from the entrance. Younger individuals have a more uniform canal area (around 40 mm2), though still smaller than that of adults. Adults exhibit a broader canal throughout, while older adults show the largest canal areas overall, with a pronounced widening near the aperture (15mm from the entrance). Notably, the figure also highlights that older adults have wider canals in the cartilage portion yet converge to dimensions very similar to adults past the bony–cartilage junction.

Together, these trends underscore how canal size and stiffness evolve with age and affects the size of the canal, and why a “perfect fit” today may not remain optimal over time without thoughtful, adaptable design choices.

Why comfort matters - more than we think

If an earmould causes discomfort, even slightly, users often stop wearing their hearing aids altogether. Pressure points, poor venting, or a shape that doesn’t accommodate natural jaw motion quickly turn a medically necessary device into a daily frustration. In cases where the ear canal has sharp bends or the patient has dexterity problems, it is also important that the earpiece can be introduced and removed comfortably. 

Retention issues pose an equally significant challenge. If an earmould slips out, it may get lost or cause acoustic feedback. The leakage also leads to inconsistent hearing performance. A comfortable, secure fit isn’t just a matter of user satisfaction, it directly impacts the success of hearing-aid fitting.
 

Two main challenges: Improving retention and acoustic sealing the canal by maintaining comfort 

Retention challenges tend to arise when the ear canal provides insufficient natural locking points or when mandibular movement widens the canal enough to loosen the fit. Modern digital design workflows - like those available in 3Shape EarmouldDesigner - allow clinicians and labs to simulate and visualize these pressure zones and insert features such as canal locks, concha locks, or sculpted transitions with far greater precision.

The second challenge is achieving an optimal acoustic seal without compromising comfort. The region between the first and second bend of the ear canal is particularly critical; careful sculpting in this area can significantly enhance stability while maintaining wearer comfort. Ultimately, effective sealing depends on maintaining a consistent seal despite dynamic ear canal movement and anatomical changes that may affect insertion and fit.

Although the true acoustic seal is formed within the ear canal, retention becomes especially important in open fittings, where even minor loosening can disrupt performance. While open fittings intentionally reduce occlusion, they still rely on stable retention to maintain predictable acoustics and avoid unintentional dynamic venting.

Solutions for comfort and retention

1. Good impression techniques and high-precision ear scanning

If the clinician does not anticipate mandibular movement related expansion, the resulting earmould may fit perfectly when the jaw is at rest but lose effectiveness during everyday activity. This reinforces the value of high viscosity open jaw impressions and high resolution digital ear scanning, which capture the canal in its most expanded, acoustically relevant state - helping ensure consistent retention and a stable seal even during speech and movement. Proper insertion depth, full expansion of the material, and ensuring neutral jaw position (or intentional open jaw impressions) can capture more accurate geometry for a stable fit.

A high resolution ear impression scanner captures small variations in canal geometry with exceptional accuracy. This allows:

• Better modelling of dynamic shapes
• More predictable retention
• Reduced need for remakes

2. Retention modelling

Retention can be enhanced through both design choices and manufacturing techniques. There are several retention strategies available depending on the patient’s anatomy and device type. The most common retention types are depicted in Figure 3. 

The decision of using one or another retention can be anatomical or aesthetical. Some users prefer more discreet designs, choosing smaller or less visible retention elements even if that means accepting slightly less holding force. Balancing these functional and cosmetic priorities allows clinicians to tailor the earpiece to both the physical ear and the user’s personal preferences.

With digital tools, technicians can now iterate multiple retention strategies from the same scan and choose the most suitable one without additional patient appointments. Besides, 3Shape Advance enables automatic insertion of several retention types - reducing manual labour and variation between technicians. In only a few minutes we can obtain different designs (concha lock, helix lock, none, etc.) and send to print. The cost of having these different options is now much more reduced. 

3. Sculpting and visual aids

For areas like the transition between the first and second bend, 3Shape EarmouldDesigner provides visual guides that help technicians sculpt more accurately and consistently, ensuring both comfort and stability.

The software offers visual guides and sculpting tools that help technicians shape critical ear canal areas with greater accuracy, comfort, and stability.
Sculpting tools such as Tube, Paint, Plane Cut, Spray Material, and Spline Cut enable precise smoothing, cutting, and material adjustment directly on the scan.

Digital workflows ensure designs are saved, editable, and repeatable, making future adjustments easier and safer as ear anatomy changes. Besides, dedicated views in the software help to get an understanding of how the material has been removed or added in the earpiece.

4. Streamlined, repeatable production

Overall, digital manufacturing means each iteration is saved, editable, and reproducible. For users whose ear canal changes over time, adjustments become simpler and safer.

Take home message

Comfort and retention may seem like simple concepts, but they depend on a complex combination of anatomy, aging, impression quality, and design. With modern tools like precise ear impression scanning, automated retention features, and intuitive digital sculpting, it’s now easier than ever to create earmoulds that stay in place and feel great throughout the day.

Ultimately, improving retention and comfort helps users wear their devices consistently, leading to better hearing outcomes and higher satisfaction.

5 take-home messages: 

1. The acoustic seal inside the ear canal is the most critical, and most dynamic, zone, largely influenced by jaw movement, canal softness, and anatomy rather than the outer ear alone.
2. Comfort and retention are inseparable: even small pressure points, leakage, or instability can lead to reduced wearing time, feedback, or complete device rejection.
3. Ear canals change across the lifespan, meaning a “perfect fit” today may not remain optimal over time - making adaptability and repeatability essential.
4. High quality impressions and high resolution digital scanning are foundational, as they capture dynamic canal geometry more accurately and reduce remakes and fitting errors.
5. Digital design and manufacturing tools enable better, more consistent outcomes, allowing precise sculpting, automated retention features, and easy future adjustments that improve long term user satisfaction and hearing outcomes.
   
   
   

References

• Pirzanski, C., & Berge, B. (2005). Ear canal dynamics. The Hearing Journal, 58(10), 50.
• Pirzanski, C., & Berge, B. (2004). If you blame buffing for bad fittings, you’ve probably given the wrong impression. The Hearing Journal, 57(2), 40
• Voss, S. E., Remenschneider, A. K., Farrar, R. M., Myoung, S., & Horton, N. J. (2025). Comprehensive Measurements and Analyses of Ear Canal Geometry From Late Infancy Through Late Adulthood: Age-Related Variations and Implications for Basic Science and Audiological Measurements. Trends in Hearing, 29.