Evaluation of one-month earplug fitting practice

Introduction
Education and practice are essential to achieve appropriate fitting of earplugs. We examined the fitting performance before and after the one-month earplug fitting practice by measuring the sound attenuation levels and also by evaluating the location and the compressed form of earplugs in the external auditory meatus using the computed tomograph (CT).

Methods
Subjects were twelve volunteers with normal hearing. Foam earplugs were used. First, we delivered plain instruction how to insert earplugs and let them practice for ten days, followed by the first Real-Ear Attenuation at Threshold test (REAT test) and CT scanning of subject's external auditory meatus with earplugs. The three-dimensional images of the earplugs were processed with the image processing workstation and personal computer. Second, we ask them to receive one month regimented education: a) verbal and documented instruction every week, b) self-checking with "Earplug Checker" every week. Then, the second REAT test and CT scanning were performed.

Results
The sound attenuation level significantly increased about 5 dB after the one-month earplug fitting practice (Paired t-test; P < 0.05), except at 250 Hz and 500 Hz. The distance between tympanic membrane and earplug was significantly shortened after the one-month earplug fitting practice (Paired t-test; P< 0.002).

Discussion
Since the standard deviation of the improvement of sound attenuation levels at 250 Hz and 500 Hz were larger than those at the other frequencies, these frequencies were considered to be most affected by the fitting performance of this type of earplugs. The CT scanned image of the subjects with low levels of attenuation demonstrated the strongly compressed earplugs around the entrance of external auditory meatus. On the contrary, those with proper levels demonstrated the deeply inserted and compressed earplugs in the external auditory meatus.