Effect of Depth of Conical-Shaped Tympanic Membrane on Middle-Ear Sound Transmission

The shape of the tympanic membrane(TM) is often changed due to middle-ear diseases or middle-ear surgery. Although it is assumed that this change in shape affects the sound transmission of the middle ear, the degree of this effect remains unclear. In this study, three-dimensional finite-element models of the middle ear with different depths of the conical-shaped portion of the TM were established, and the effects of the depth, Young’s modulus and thickness of the TM on middle-ear sound transmission were analyzed. The efficiency of sound transmission was found to decrease when the depth of the conical-shaped portion of the TM decreased because of a decline in the efficiency of transmission of the vibration of the TM to the ossicles. The transfer function was also influenced by the Young’s modulus and thickness of the TM. Thus, when substitutional materials, whose Young’s modulus or thickness was appropriately greater than those of the normal TM, were used in TM reconstruction, the efficiency improved, even if its shape was flat.