## 2 Materials and Methods  
### Patients  
All patients visited our hospital to fit the CC hearing devices. The inclusion criteria were as follows: CT was performed for the diagnosis and evaluation of ear malformation before fitting, hearing loss was predominantly derived from aural atresia or severe stenosis, and CC hearing devices were fitted to the atretic ear to compensate for hearing loss. Three patients participated in the study (Table 1).  
Patient 1 was a woman with bilateral microtia and congenital aural atresia. She had previously undergone bilateral otolplasty without any surgical repair of congenital aural  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Age (Years)**} & \multirow{2}{*}{**Sex**} & \multirow{2}{*}{**Ear**} & \multicolumn{2}{c}{**Averaged Hearing Level (dB)**} & \multicolumn{2}{c}{**CT Slice**} & \multicolumn{2}{c}{**Mass of the Transducer (g)**} \\ \cline{5-8}  & & & **AC** & **BC** & **Width (mm)** & **Impression** & **CT Images** \\ \hline \multirow{2}{*}{1} & \multirow{2}{*}{25} & \multirow{2}{*}{F} & Left & 75 & 18.3 & \multirow{2}{*}{0.4} & 2.7 & 3.6 \\ \cline{3-4} \cline{6-8}  & & & Right & 93.3 & 20 & & 2.8 & 3.0 \\ \hline
2 & 9 & M & Right & 56.7 & 8.3 & 1.0 & 6.3 & 4.9 \\ \hline
3 & 5 & M & Left & & 1.0 & 4.0 & 4.7 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Patients’ characteristics and transducer properties.  
Figure 1: Cartilage conduction hearing aids (HB-J1 CC, Rion Co Ltd., Kokubunji, Tokyo, Japan) have three transducer types: (**a**) simple-attachment, (**b**) ear-chip attachment, and (**c**) ear-chip embedded (cited by [14]). Ear chip is ordinarily designed based on ear impression to allow a tight attachment to ear. Ear-chip types can be used through inserting them into ear. In contrast, simple-type transducer requires a double-sided tape for fixation.  
atresia. She had used conventional BC hearing aids, the transducers of which induced the hollow of the skull bone and local pain. She visited our hospital to fit CC hearing devices instead of BC hearing aids. Her right ear canal showed severe stenosis, and CT findings revealed that the ear canal occluded completely with soft tissue density. Her left ear was closed completely, and CT findings revealed no existence of the ear canal.  
Patient 2 was a man with right severe stenosis of the ear canal, accompanying mild anomaly of the auricula. The diameter of the entrance of the ear canal was approximately 1 mm, and CT found that the ear canal was completely occluded with soft tissue density. His left ear was normal. He had tried to use an AC hearing aid on his right ear. However, the hearing aid was not stably fixed, and he gave up on its continuous use. He visited our hospital to fit a CC hearing device into his right ear.  
Patient 3 was a man with right microtia and bilateral severe stenosis. No cavity in the ear canal was observed from the outside, and CT findings revealed that the ear canal was completely occluded with soft tissue density. Although he had used an AC hearing aid on his left ear, sufficient benefits were not obtained. He visited our hospital to fit CC hearing devices into both ears. Due to severe microtia, a simple transducer type was fitted to the right ear. Thus, solely the left ear was a subject of this study.  
This study was approved by the Ethics Committee of Nara Medical University (No. 1981). Participants (or their parents if the participant's age was <20 years) provided written informed consent before enrollment.