No abstract

To rehabilitate most cases of conductive hearing loss closure of ear drum perforations and rebuilding of the ossicular chain can be performed. Due to the great number of biocompatible bone substitute materials available it is occasionally difficult for the surgeon to choose the most favorable substitute. Autogenous structures (ossicles, cortical bone, cartilage) and allogenous tissues (ossicles, cortical bone, cartilage, dentin) are possible bone replacement materials. Xenogenic tissue is currently not used in middle ear surgery. Ionomer cement is a hybrid material for replacement of bone but does not fit direct classification of the various classes of alloplastic materials in current use: that is, metals (gold, steel wire, platinum, titanium), plastics (polyethylene, polytetrafluorethylene) and ceramics (ceramic oxide, carbon, calcium-phosphate ceramic, vitreous ceramic). For restoration of the sound conductive apparatus preference is given to autogenous ossicles because cortical bone is resorbed and cartilage weakens over time. Most surgeons do not use allogenous tissue, because of the possible transmission of such infectious disease as immunodeficiency syndrome or Creutzfeldt-Jakob disease. Only dentin deserves special attention as a possible bone substitute in the middle ear because its form can be preserved during sterilization. Based on the observations available to date, it becomes apparent that titanium implants hold greater promise than gold. Form-stable synthetic materials are not generally recommended due to foreign body reactions which have been confirmed by many investigators. Ceramic materials (e.g. ceramic oxide, carbon, calcium-phosphate ceramic, glass ceramic) are well tolerated in the middle ear and have also proved to be useful over time. Hybrid bone substitute ionomer cement is easily workable and well integrated, showing a good functional outcome. For many years good results in otosclerosis surgery have been achieved with a prosthesis made of platinum-wire and Teflon. Short-term follow-up periods hold great promise with pistons made of gold. Autogenous ossicles, ionomer cement and recently titanium protheses--as far as usable--are employed by the author for reconstructing the middle ear. For the time being platinum-Teflon prostheses and gold are used in otosclerosis surgery.

During post-set hardening the self-curing bone substitute Ionocem develops a solid bond with the adjacent bony tissue, leaving no empty spaces. The fully matured material can be fixed to bone with freshly mixed cement or it may be used as a blank, e.g. an ossicular implant (Ionos ossicle). After insertion of 945 alloplastic middle ear prostheses over a period of 4.5 years, the take-rate was 94%. In some patients revision surgery became necessary, in 50% of cases because of prosthesis dislocation. A granular version of the cement (Ionogran) was implanted in 46 ears for obliteration of mastoid cavities and showed complete mucosal overgrowth within a maximal period of 3 months. Posterior canal wall reconstruction with the self-curing bone substitute was done in 74 patients, with revisions required in 12 cases because of persistent epithelial deficits in the external ear canal or epitympanic retraction. Overall results showed that the ionomer-based cement was a useful substitute for bone in reconstructive otologic surgery.

The middle ear poses unique challenges when finding suitable materials for ossicular reconstruction, primarily because of its link to the external environment via the eustachian tube, which leads to a greater potential for exposure to infectious agents. In this animal study, the biocompatibilities of titanium and glass-ionomer cement were assessed in the middle ear of the rabbit after being implanted as total ossicular replacement prostheses (TORPs) or as free pins. Animals were sacrified after 28, 84, 168, 336, or 504 days or 2 years, and a cutting saw technique was used to prepare slides for light microscopy. Slides were examined for mucosal coverage and any sign of foreign body reaction. Both materials showed good acceptance in the middle ear. After 28 days, the TORPs were covered by middle ear mucosa. As expected, it took a longer time (up to 504 days) to cover the free implants. An interesting finding was the growth of new bone on both the surface of the titanium implants and the glass-ionomer prostheses. The results of this animal study indicate that both titanium and glass-ionomer cement are favorable materials for ossicular replacement prostheses.

Ionomer-based cements are obtained by the reaction of an aluminum-fluoro-silicate glass with a polyalcenoic acid. During setting and hardening the cement bonds closely with adjacent hard tissue. The previous implantation of this material in the baboon tibia has held great promise as a possible use in bone replacement. In the present study the cement was tested concerning its biocompatibility and biostability in the middle ears of 64 rabbits. Viscid cement paste was inserted into the epitympanic space of each animal. A preformed cement strut was then placed to serve as a columella between the eardrum and stapes footplate. During a subsequent interval of 28 days up to 2 years middle ear specimens were evaluated under a surgical microscope, following which histologic sections were studied under light microscopic conditions. Findings demonstrated that after insertion of freshly mixed cement a firm adhesion to bone developed that proved to be biocompatible and biostable over time. After 28 days the preformed and fully hardened implants were overgrown by a delicate mucosa normally present in the middle ear. No evidence for any rejection of the implants could be found. The experience available to date indicates that ionomer cement is biocompatible and biostable, easy to handle and workable without splintering. With appropriate use it represents a useful implant material in surgery of the head and neck.