Non-PRO English to Italian Medical Medical: Instruments

A good ear impression needs to include all of the contours of the pinna as well as the ear canal.
But how long does the canal portion need to be to provide the production lab with sufficient information to properly build the custom device/earmould?
We recommend following the 16/4 rule.
The 16/4 rule ensures that the canal portion of the impression is at least 16mm from the aperture of the canal to the tip of the impression.