Question
An excellent impression is critical for a well fitting hearing instrument. The following tips will help insure a good fit, either for a new custom instrument or a remake.
Answer
An excellent impression is critical for a well fitting hearing instrument. The following tips will help insure a good fit, either for a new custom instrument or a remake.
Using a silicone impression material will yield more accurate ear impressions. The use of powder/liquid materials contributes to an increase in the need for remakes because these materials continue to alter their shape long after they have been removed from the ear. Silicone is more durable and tolerates shipping and ''rough'' handling best. The Silhouette™ Plus system by Siemens uses advanced gun geometry and the latest silicone impression material technology to create an optimum impression.
Before beginning an ear impression, examine the outer ear and ear canal for signs of irritation, infection, discharge, excessive cerumen and hair.
An otoblock should be placed in the canal at a point deeper than the intended canal length of the hearing instrument, usually past the second bend. A vertically placed otoblock will ensure that the block will not cut into the impression. If an otoblock inadvertently twists horizontally, the impression will have a noticeable void once the block is removed. The canal length can be marked with a permanent marker to the desired length of the hearing instrument. It is always worth the extra time to place the otoblock perfectly!
When ordering an ITC, MC, or CIC instrument, a ''complete'' impression is necessary. This includes the concha bowl and the helix, as these are important for component orientation.
While taking an impression with a syringe or gun delivery system, slowly pull away from the canal, keeping the tip completely surrounded by impression material as the silicone material fills the canal. This will reduce the likelihood of distortions and air pockets or ''voids'' in the impression. Allow material to set for approximately five minutes. Do not apply any pressure to the material by hand, such ''hand packing'', will often distort the impression.
Provide the hearing instrument manufacturer with any special instructions or considerations necessary, such as reduced helix or post-op surgical ear, etc. If you send open-and closed-mouth impressions, mark them clearly, as the manufacturer will need to evaluate both impressions before making the custom shell.
If a remake is needed for any reason (such as the instrument not fitting comfortably, slipping, or causing feedback) a new impression is advised. The more information marked on the repair form and/or the impression, the better! For example, instead of just checking ''too loose'' on the repair form it is helpful to also mark where it is loose on the impression or instrument. The bottom line is that the more information you can give the lab the better chance you will get back an instrument that fits well.
Author: Siemens Audiology Staff
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