Skull and bones10/3/2023 ![]() When measuring the anterior part, it was measured on the back of the head, and when measuring the occipital part, it was measured with the forehead in contact with the surface (bed) made of soft cloth. Measurements were made by placing a wooden support on the neck. Thawing of the cadaver was done at room temperature for approximately three days before the study. The cadaver was not exsanguinated but was washed with an antiseptic soap before frozen at − 20 ☌ within a week of procurement. The investigation was conducted using the head of a fresh human cadaver cut from the body at the neck without any history of head trauma (male aged 54). The aim of this study was to investigate the dominant pathway of contralateral sound transmission, including the anterior of the skull, using a freshly frozen cadaver to collect data under more realistic conditions. Above 2 kHz, the primary longitudinal wave transmission is primarily in the skull base and involves a mixed mode with a bending wave motion. At 1000–2000 Hz, there is a transition from a mass-spring system to a wave transmission. For frequencies between 3 Hz, the dynamics of the skull are a mass-spring system. At around 300 Hz or below, the skull moves in a rigid body motion. The nature of cranial vibration modes varies according to the frequency range 13. ![]() Stimulation of the mastoid initiates a vibration journey that can take various paths through the thin bony shell of the skull vault, thick skull base, or interior of the skull to reach the opposite ear 12. The dominant mechanism for contralateral bone conduction (BC) occurs through the skull bone when sound vibrations travel to the opposite side 10, 11. The contralateral bone conduction (BC) occurs through four different sound wave propagation mechanisms: (1) tangential and (2) normal to the skull bone surface, (3) rigid-body motion, and (4) direct propagation through the cerebrospinal fluid and brain tissue 9. To optimize the effectiveness of BAHAs, understanding how sound reaches the contralateral ear is essential. Moreover, soft tissue in the skull also plays a significant role in bone conduction 5, 6, 7, 8. Ossicles play a role in bone conduction through piston or hinge movement, depending on the sound level 4. The suture of the skull can cause deformation of vibration patterns 2, while bone thickness and density can impact sound propagation direction and vibration amplitude 3. Bone conduction mechanisms are complex and influenced by several factors, including signal frequencies. ![]() BAHAs transmit sound to the contralateral ear, which helps overcome the head shadow effect and improves speech understanding 1. Understanding the complex mechanisms of bone conduction is crucial in improving the efficacy of bone-anchored hearing aids (BAHAs) for patients with unilateral hearing loss. The thesis suggests that signal transmission from the specific midline to the mastoid can be more efficient than the conventional configuration of BC from the mastoid to the mastoid. Within this range, a significant amplitude of acceleration response is measured at the face-side points and the back and upper parts of the head. The study finds that the range showing the highest contralateral transmission efficiency of bone vibration is the intermediate frequency range with contralateral direction. BC stimulation is applied to the mastoid using a bone vibrator, and acceleration responses are observed on the contralateral mastoid bone and seven midline points of skull bones using triaxial accelerometers. The realistic contralateral transmission pathway of bone conduction (BC) vibrations is investigated through each osseous structure in the midlines of the fresh-frozen whole head. The study aimed to investigate the efficient pathway for BC sound transmission by measuring vibrations on the opposite side of the skull bone, referred to as the mastoid position.
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