Earmold Impressions Flashcards
Does the valley of the ear become a helix lock for retention?
Yes
What is the valley?
The area right behind the crus
Does the crus align with tube orientation?
Yes
Does the concha bowl provide stability and/or retention?
Yes
Does the antitragus provide retention?
Yes
It keeps the earmold from coming out
Where is the isthmus?
Before the 2nd bend
About 10 mm into the canal
Where does cartilage change to bone in the ear canal?
At and past the 2nd bend
Is the isthmus placement consistent in all people?
Yes
How far do we want to go past the 2nd bend?
2 mm
Why do we want to go 2 mm past the 2nd bend?
For retention
What is aperture?
Acoustic seal area
Do we need to stretch the aperture to create the proper fit?
Yes
A loose hearing aid is actually more uncomfortable
Do you choose what kind of impression material to use based on how much you want to stretch the aperture?
Yes
Some stretch it more than others
What are the three kinds of impression material?
Addition-cured silicone
Condensation-cured silicone
Methyl-methacrylate
What is addition-cured silicone?
Combines 1:1 polyvinyl-siloxane parts of paste
This is the one we use in class
What is condensation-cured silicone?
Dimmethyl-siloxane paste mixed with hardener
Not as commonly used
What is methyl-methacrylate?
Powder and liquid
Pre-measured acrylic powder and liquid formulas are rapidly mixed together
Mainly used when someone has silicone allergies
What is viscosity?
Refers to how easily material flows before it cures
What is high viscosity?
Thick
Resistant to flow
Condensation-cured silicone
Stretches the aperture of the canal
What is medium viscosity?
Provides some stretch to aperture
Addition-cured or methyl-methacrylate
What is low viscosity?
Runny and loose
Flows easily
Will not alter the anatomical structure of the ear canal
Most suitable for devices requiring deep insertion
Addition-cured silicone
Doesn’t stretch the aperture very much
Is aperture stretching important for attenuation products and deep in canal impressions?
No
What is stress relaxation?
Materials ability to return to its shape after removal
What material is superior for stress relaxation?
Silicone
Methyl-methacrylate’s shape can distort during removal (low stress relaxation)
What is contraction ratio?
It refers to shrinkage over a 7-day period
How much will silicone shrink (contraction ratio)?
0.1-0.7%