ABSTRACT
BACKGROUND AND OBJECTIVES: Although the necessity of hearing aids as one of the rehabilitation methods is increasing, many hearing impaired persons are avoiding the use of behind-the-ear (BTE) hearing aids and prefer the complete-in-the-canal (CIC) hearing aids. CIC hearing aids have cosmetic and acoustic advantages but have problems of acoustic feedback and discomfort in wearing. Changes in the external auditory canal (EAC) by mandibular movements are a primary factor for the acoustic feedback and discomfort. The purpose of this research is to study the pattern of changes in the EAC by mandibular movement using the Korean population as subjects and to get basic data concerning the manufacture of impressions and shells for CIC hearing aids. MATERIALS AND METHODS: Subjects were 19 men with a fit external ear diameter to make CIC hearing aid. Impressions were made by taking 5 different conditions of jaw into consideration : fully opened state, 1/2 opened state, biting state, chewing state and resting state. Impressions were scanned at intervals of O.1mm using a 3D Laser digitizing system. We measured anterior to posterior (AP) width and superior to inferior (SI) height of each impression at the first bend, interbend and the 2nd bend of 5 conditions. RESULTS: Compared with the resting state, statistically significant changes in the AP width of the ear canal were observed at the interbend in the following order : fully opened jaw, 1/2 opened jaw (p <0.05), at 1st bend: 1/2 opened jaw (p<0.05). The 2nd bend biting state showed maximal AP width of the ear canal (p<0.05). The SI height of ear canal revealed statistically insignificant changes. CONCLUSION: We recommend making of ear impressions in the chewing state and shells to be supported at the interbend of the ear canal. The SI dimension of a shell tip should be more ground than AP dimension.