The comparison of changes in hearing thresholds and insertion losses due to occlusion induced by ear impression in sound field assessment

The methods of determining the amount of sound attenuation by ear mold, earplug or any other foreign body that placed in or out of the ear canal, is divided in subjective and objective. Due to the contradictory results in the studies in this field, this study aimed to use more audiometric frequencies considering the strengths and weaknesses of previous studies.

This study was conducted on 30 individuals with normal hearing in the age range of 21-26-year-old. First the impression mold was prepared from both ears. The evaluating real ear unaided response and the real ear occluded response. In the next step, hearing thresholds were assessed by sound field with a precision of 1 dB, once in both open ear and once in both closed ears. Finally, the insertion loss due to mold placement at each frequency was compared with the amount of behavioral threshold changes at the same frequency.

By using paired t-test at frequencies of 400, 500, 800, 1000, 1500, 1600, 2000, 2500, 3000, 4000, 5000, 6000, 6300 and 8000 Hz, the difference in behavioral hearing thresholds with and without molding was greater than the amount of the insertion loss (p < 0.001).

The insertion loss due to impression for behavioral assessment at all of the tested frequencies were more than the attenuation in real ear evaluation (p < 0.001). In this regard, consequently the standard deviation of insertion loss due to impression in behavioral threshold condition was more than real ear measurement.