Implant Material Tolerance

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Abstract
After surgical and antibiotic destruction of guinea pig cochleas non specific lesions appear which seem more due to this destruction than to the electrode implantation or chronic stimulation. Moreover, despite these lesions, the electrical threshold level value necessary to elicit brain stem evoked responses in these implanted animals does not vary in time. The electrical chronic stimulation of the newborn deafened guinea pigs cochlea prevents the cochlear nucleus atrophy observed in the non stimulated animals. In man the implanted material tolerance is perfect provided this material is covered by a Silastic or teflon sheet and is located far from the skin incision. Degradation of isolating material occurred only in case of chronic movements. For this reason device and electrodes must be placed above and behind the ear. The waterproofness of the implanted receptor is indispensable to avoid physiological liquid penetration inside the electronic device. High level voltage stimulation may involve bubble formation responsible for temporary system failure; this drawback is suppressed by enlarging the electrode tip surface allowing low level stimulation. The threshold level and the frequency discrimination of the implanted electrodes did not change for more than 6 years. Post-operative infection occurred especially in case of pre-operative chronic otitis; it may be due also to the large use of "Histoacryl". However, these infections, which never affected the threshold level voltage of the implanted electrodes, are no longer encountered since we use "Tissucol", exclude the middle ear closing the Eustachian tube, and employ our electrode bearer.

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