IHS Earmold and Impression Techniques 4 — Questions and Answers
Question 1: The acoustic bore diameter of an earmold has its greatest effect on which aspect of hearing aid performance?
- Low-frequency output
- High-frequency output and resonance (Correct answer)
- Maximum power output
- Battery drain
Correct answer: High-frequency output and resonance
A larger acoustic bore diameter enhances high-frequency resonance and output, while a smaller bore rolls off high frequencies; bore modifications are a primary acoustic tuning tool.
Question 2: When a patient with a high-gain hearing aid reports persistent feedback even after earmold remake, the clinician should next consider:
- Reducing the hearing aid gain
- Evaluating the acoustic vent size and considering a smaller or occluded vent (Correct answer)
- Switching to an in-the-canal style hearing aid
- Increasing the canal length of the new earmold
Correct answer: Evaluating the acoustic vent size and considering a smaller or occluded vent
Acoustic vents can be a pathway for amplified sound to escape and re-enter the microphone; reducing vent size or occluding it eliminates this feedback path for high-gain fittings.
Question 3: What is the recommended mixing ratio consideration when using two-part silicone impression material?
- More hardener than base produces a softer impression
- Equal parts base and catalyst as specified by the manufacturer ensure proper polymerization (Correct answer)
- A higher base ratio allows more working time
- The ratio only affects color, not setting time or hardness
Correct answer: Equal parts base and catalyst as specified by the manufacturer ensure proper polymerization
Manufacturer-specified equal-parts ratios ensure the correct chemical reaction for complete polymerization and predictable material properties; deviating from this causes incomplete curing.
Question 4: A 'trampoline' earmold is designed primarily for which patient population?
- Adults with severe-to-profound hearing loss requiring maximum gain
- Infants and young children due to its flexible, safe material construction (Correct answer)
- Patients with chronic otitis externa requiring antimicrobial materials
- Elderly patients with reduced dexterity who need easier insertion
Correct answer: Infants and young children due to its flexible, safe material construction
Trampoline or soft, highly flexible earmolds are often recommended for young children because their ear canals change rapidly and the soft material is safer and more comfortable.
Question 5: The 'open jaw' technique for ear impressions is recommended when fitting patients with:
- Severe cerumen impaction
- Telecommunications devices that are worn only in quiet environments
- Behind-the-ear aids used for active individuals who talk frequently (Correct answer)
- In-the-canal aids where retention is the primary concern
Correct answer: Behind-the-ear aids used for active individuals who talk frequently
Patients who talk or chew frequently cause significant TMJ-related ear canal shape changes; the open-jaw technique captures the ear canal in its most displaced state to prevent feedback and discomfort during use.
Question 6: When an earmold is described as having a 'positive pressure vent,' this means the vent:
- Is angled to direct amplified sound toward the tympanic membrane
- Has a valve that allows air to escape outward but not enter (Correct answer)
- Is drilled at an angle that increases canal air pressure
- Provides a pathway for moisture to exit the ear canal
Correct answer: Has a valve that allows air to escape outward but not enter
A positive pressure vent incorporates a one-way valve design that allows trapped canal air to escape to relieve the occlusion effect while preventing amplified sound from leaking back.
Question 7: Libby horns are earmold modifications used to:
- Reduce low-frequency amplification to improve speech clarity
- Enhance high-frequency output by flaring the bore diameter toward the canal tip (Correct answer)
- Increase overall gain across all frequencies for profound hearing loss
- Improve earmold retention in patients with shallow concha bowls
Correct answer: Enhance high-frequency output by flaring the bore diameter toward the canal tip
A Libby horn progressively increases the acoustic bore diameter from the earmold body toward the canal tip, which boosts high-frequency amplification through acoustic resonance.
IHS Earmold and Impression Techniques 4
The acoustic bore diameter of an earmold has its greatest effect on which aspect of hearing aid performance?