Lecture 3: Ear Impressions, Ear molds, and Hearing Aid Styles Flashcards
Label the pinna.
See diagram
What steps do you need to take to make ear impressions?
1) Wash hands
2) Perform otoscopic inspection
3) Insert foam or cotton block
4) Check to make sure the foam is sealed properly
5) Mix the silicone impression materials
6) Inject material into the ear
7) Wait 4-5 minutes for the silicone impression to dry
8) Remove the silicone impression
9) Look at the impression and critique
10) Perform otoscopy and make sure no foreign objects are left in the ear
What are otoscopic findings and considerations for taking impressions?
- Atresia or stenosis
- Impacted cerumen
- Aural discharge
- Bony growths
- Inflammatory conditions
- Prolapsed canal
- Enlarged canal
- Foreign objects
- Ear drum distention
- Ear drum retraction
- Ear drum perforation
What are the purposes for using ear molds?
- Ear molds seal the canal
- Ear molds help hold hearing aids in place
- Couples the hearing aid to the ear
- Provide acoustic modification of the amplified signal
What are the key characteristics of ear molds?
- Be comfortable over time
- Should be cosmetically appealing
- Should be easily handled by the patient
What are the different styles of ear molds?
1) Regular
- Used for body aids
- Not typically used anymore
2) Shell (AND micro-shell)
- Concha area is shelled out
- Not as bulky as the regular style
3) Skeleton
- Follows the contour of the ear and hollows out at the middle section
- Reduces overall bulk but keeps the frame of the ear
4) Semi-skeleton
5) Canal (AND micro-canal and canal-lock)
- Most cosmetically appealing option
- Needs a long canal portion to retain retention in the ear
6) Canal Shell
- Half of the concha bowl
- Works with patients with curvy ear canals
7) Non-occluding
- Cross hearing aid fitting
- Solution for people with normal low frequency hearing with loss in the high frequencies
- General rule: the greater the hearing loss, the more material is used to fill the ear canal
What are the different kinds of materials used in ear molds?
1) Acrylic- HARD
- Easy to modify and clean
- Most likely to leak amplified sound; may not have as tight of a seal
- Greater potential for injury if someone strikes the head
- Not recommended for children
2) Vinyl
- Soft plastic
- Comfortable over time
- Good when a tight fit is needed
- Shrinks, hardens, and discolors over time
- Harder to replace the tubing; harder to modify
3) Rubber
- Used for swim plugs
4) Poly-ethylene
- Hard material
- Very unlikely to cause an allergic reaction
5) Combination ear mold
- Canal portion is soft and outer portion is hard
What is venting?
- A column of air surrounded by the walls of the tubing
- A hole or trench in the ear mold or custom hearing aid that allows communication (air & sound) from the residual ear canal space to the outside world
What are the different kinds of venting?
Size
- Small, medium, large
Direction
- Parallel, diagonal, external
What are the effects of venting on gain?
- Acoustic mass of a vent decreases as vent length is shortened and vent diameter is increased (increases the venting effect)
- Acoustic mass of a vent increases as the vent length is lengthened and vent diameter is decreased (decreases the venting effect)
- Vents release low-frequency amplification
- Amount of low-frequency gain released depends on the size of vent
- Increase in vent diameter, decrease in low frequency SPL at the TM
- Decrease in vent diameter, increase in low frequency SPL at the TM
What effects does venting have on the following: occlusion effect, feedback, directivity, internal noise, and amplified sound path?
Occlusion Effect
- Give venting for patients with thresholds greater than 30 dB
- Varies by frequency and by individual
- Reduce the OE by doing a deeper fitting
Feedback
- As we increase the vent size, we increase the possibility of feedback
Directivity
- The more venting you have, the less directivity you have
Internal noise
- Patients with enough low frequency hearing loss can’t hear the internal noise
Amplified Sound path
What are the purposes of venting?
1) Reduce fullness or pressure
2) Reduce occlusion effect
3) Reduce low frequency gain at the eardrum
4) Aerate the ear canal
What is the purpose of damping?
- Dampers are used to decrease gain and maximum output at frequency corresponding to sound bore resonances
- Placement of the damper (between receiver & sound bore tip) affects effectiveness of frequency damping
- Damping creases natural sound quality
What are the different kinds of tubing?
Internal diameter
- Wide I.D. (#9, #12)
- Narrow I.D. (#14, #15, #16)
External diameter
- Thin
- Standard
- Medium
- Thick
- Double-walled
Higher #= Lower internal diameter
Standard size = #13
What are the effects of tubing on the acoustics of an earmold?
Longer tubing
- Increases gain <750 Hz
- Shifts peak to lower frequency
- Slightly decreases gain in area > 3000 Hz
Shorter tubing
- Shifts 1st and 2nd peaks to higher frequencies
- Increases mid- and high-frequency gain
- Decrease in low frequency gain
