Mapping morphologic change in the external ear

The movement of the external ear canal, associated with jaw motion, relative to the concha region of the pinna has been studied. This issue is most relevant to the fitting and function of In-The-Ear hearing-aids. Pairs of open-jaw and closed-jaw silicone impressions were taken of 14 ears from 10 subjects. 3D coordinate data was obtained from the concha region and the anterior surface of the canal using a reflex microscope. The canal regions were plotted via an optical flat mirror. Proprietary area-based matching software was used to verify the stability of the concha region and evaluate distortion of the canal during jaw motion. The canal data from each pair was placed into the same coordinate system with their respective concha regions aligned using the areamatching software. Contour and difference maps of the canal data were used to demonstrate the amount of anterior-posterior (A-P), superior-inferior (S-I), and medial-lateral (M-L) movement that occurred between the open and closed-jaw impressions. Rotations were also evaluated. Analysis confirmed that the concha regions did not undergo significant deformation during jaw movement. The canal regions underwent varying amounts of internal deformation with the majority of canals conforming within an RMS of 400 pm across the entire surface. The majority of canals underwent significant morphologic change relative to the concha. Movement of the canal in the M-L plane ranged from 0 to 3.8 mm with a mean of 1.4 mm; 8 canals moved laterally, 5 canals moved medially and 2 ears did not move in the M-L plane. Movement in the S-I plane ranged from 0 to 3.7 mm with a mean of 1.3 mm; 9 canals moved inferiorly, 2 canals moved superiorly and 3 canals did not moved in the S-I plane. Movement in the A-P plane ranged between +3.5 mm and -3 mm, with 5 canals moving anteriorly, 3 ears moved posteriorly, and 4 ears moving in a mixed fashion. The geometry of the external ear has created difficulties in acquiring accurate surface maps for analysis. The study has focused on the key areas of the pinna and canal previously reported to undergo significant change. This study does not support previous reports that suggest that the ear canal only widens with jaw opening. This study gives insights into the variability in the movements of the ear canal relative to the concha region of the pinna and will be of interest to clinicians involved in the fitting of hearing-aids.