Titanium as a biomaterial for ossicular replacement: results after implantation in the middle ear of the rabbit

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 and, hence, its greater exposure to infectious agents. In this study, the biocompatability of titanium was examined in the middle ear of rabbits by using light and scanning electron microscopy. Implants were placed as middle ear prostheses or as free implants. These were inspected at 28 days, 84 days, 168 days, 336 days and 504 days following implantation for mucosal coverage, percent epithelization and any sign of foreign-body reaction. After 28 days, the prostheses were covered by regular mucosa. Although a majority of the free implants took up to 336 days for complete epithelialization, some of the free implants were not epithelialized even at day 504. There were no inflammatory cells observed on the surface of the material, nor were unusual amounts of fibrous tissue seen. In addition, the titanium material exhibited an affinity toward bone. The results of this animal experiment indicate that titanium is a favorable material for ossicular replacement prostheses.     

Acute respiratory distress syndrome in children

In 1991, the Dental Implant Clinical Research Group initiated a long-term clinical study in cooperation with the Department of Veterans Affairs to investigate the influence of implant design, application, and site of placement on clinical performance and crestal bone height. As part of this investigation, Periotest values for 2,212 root from implants were determined at second-stage surgery and during a 24-month follow-up period. Mean Periotest values decreased for implants placed in quality 1 and 2 bone, did not change for implants in quality 3 bone, and increased for implants in quality 4 bone. Implants in the posterior maxilla and single implants in the anterior maxilla had increasing mean Periotest values as compared with decreasing values for implants in other regions. Mean Periotest values for uncoated implants decreased gradually to approach those of hydroxyapatite-coated implants.     

Replacement of ear ossicles with titanium prostheses

BACKGROUND: Titanium has been a well established implant material for many years. New material processing techniques now permit the manufacture of small implants for ossicular chain reconstruction. METHODS: Between November 1994 and September 1995, 100 titanium middle ear implants (55 PORP, 45 TORP) were used for reconstruction of the ossicular chain. A range of five different sizes for partial and total protheses suits all implantation needs. The shape of the implants can be altered by bending. Time consuming intraoperative shaping and trimming is avoided. RESULTS: At a follow-up time of three months (33 patients) and six months (17 patients), no adverse reactions or extrusions occurred. Biologic fixation between the foot of the partial prothesis and the head of the stapes was found eight months after implantation. A hearing result of 0-20 dB residual air-bone gap was achieved in 79%. CONCLUSION: Titanium middle ear implants show good bio-compatibility and are readily integrated into the ossicular chain. Although delicate in shape, they offer excellent mechanical properties in respect to sound conduction and implantation. Initial results show Titanium to be a perfect implant material for middle ear prostheses, although long-term results are not yet available.     

Evaluation of expanded polytetrafluoroethylene as a soft-tissue filling substance: an analysis of design-related implant behavior using the porcine skin model

Soft-tissue augmentation using the synthetic nonfluid biomaterial expanded polytetrafluoroethylene (ePTFE) has been supported by number of recent reports citing the favorable characteristics of biocompatibility, soft and natural feel, ease of use, and permanent augmentation. Concern has been expressed about this application for ePTFE material because of the proximity of the implants to the skin surface and potential problems with infection and extrusion. We evaluated the behavior of a series of specific ePTFE implant designs using a long-term subcutaneous augmentation model. By using a porcine model, 466 implants of ePTFE in the form of strips, rolls, or tubes were placed using a percutaneous insertion device subcutaneously over the dorsum and face. The animals were divided into three study groups by length of implantation (3 weeks, control; 6 months, intermediate term; and 12 months, long-term) and en-bloc tissue specimens, including skin, implants, and underlying soft tissue, were harvested for gross and histologic examination. Implants were removed at the earliest sign of infection, exposure, or extrusion and the difficulty of removal was ascertained and recorded. These data reveal that ePTFE material elicits acceptable levels of tissue activity with low extrusion rates over the short and long term supporting its use for soft-tissue augmentation. The data show a clear difference, however, in the host response and behavior of the implants for this application based on shape or design. A statistically significant difference in the low, but measurable, extrusion rates was observed amongst these implant designs. ePTFE tubes showed greater stability and predictable augmentation over other implant designs for soft-tissue augmentation and seem to represent a substantial improvement for this application.     

Successful chemotherapy in a patient with recurrent carcinoma of the urachus

OBJECTIVE: Titanium in other parts of the body, well known for its biocompatibility, was examined in an animal model for its use as an ossicular replacement material. STUDY DESIGN: The biocompatibility of titanium was studied in the middle ear of rabbits using light and scanning electron microscopy. Titanium pins were placed as middle ear prostheses or as free implants and were examined after 28, 84, 168, and 336 days. RESULTS: After 28 days, the prostheses were covered by regular mucosa. The free implants took up to 336 days to be totally epithelialized. There were no inflammatory cells observed on the surface of the material nor were unusual amounts of fibrous tissue seen. In addition, the titanium material exhibited an affinity toward bone. CONCLUSIONS: The results of this animal experiment indicate that titanium is a useful material for ossicular replacement prostheses.     

Interaction between bile salts and beta-adrenoceptor antagonists

Chronic suppurative otitis media (CSOM) in profoundly deaf patients is a contraindication for cochlear implantation. Eight (6%) of the 126 patients referred to cochlear implantation at this center between 1986 and 1992 became deafened as a result of bilateral CSOM but were otherwise suitable candidates. This study details the methods used in four patients to prepare the septic ear for a sterile device. Two patients had wet radical cavities with residual cholesteatoma, and two had discharging safe perforations resistant to surgical repair. Obliteration of the middle ear cleft with blind pit closure of the ear canal was attempted in all four patients, and cochlear implants were installed at a second operation 3 to 6 months later. The hearing results were as good as in implanted patients without CSOM, and the only complication has been the finding of a cholesteatoma pearl at the second operation in one patient. Fat obliteration of the mastoid and middle ear with blind pit closure of the ear canal can be adapted to make most chronic ears fit for implantation, if the patient is prepared to undergo two operations.     

Indications for middle ear obliteration within the scope of cochlear implant management

BACKGROUND: Cochlear implants have gained worldwide acceptance as a reliable method of rehabilitation of profoundly hearing-impaired patients. Due to thorough patient selection major postoperative complications rarely occur and are flap related in most cases. Deafness can develop during chronic suppurative otitis media, either coincidentally or secondary to the medical treatment; normally this condition is regarded as a contraindication for cochlear implantation. In cases with a mastoid cavity after surgical treatment for cholesteatoma, the electrode covered only by the epithelial lining will likely become exposed or extruded. Therefore we suggest the obliteration of the middle ear cleft with abdominal fat and the blindsac closure of the external ear canal before cochlear implantation in these conditions. PATIENTS: The average age of our 12 patients was 48 years, whereas the youngest was 2 1/2 years of age. Due to chronic inflammatory ear disease. 11 patients had a mastoid cavity on both ears. Eight patients had a cholesteatoma, the chronic bone destroying process in the temporal bone of two female patients was considered as a fibroinflammatory pseudotumor. The child had a congenital deafness in both ears with a Mondini dysplasia in CT scan. She had already developed two episodes of pneumococcal meningitis which was caused by a defect in the stapes footplate through which a liquor-filled cystic sac herniated in the middle ear. Because of a massive liquorrhoea after opening of the sac, we decided to obliterate the middle ear cleft after successful insertion of the electrode array. RESULTS: All active electrodes of 10 Nucleus implants (Cochlear) and two Clarion devices (Advanced Bionics Corp.) were successfully inserted in the cochlea of the 12 patients. After an average follow-up of 15 months, a temporary facial palsy in one patient and an insufficient closure of a retroauricular fistula over the mastoid cavity in two cases were observed as postoperative complications. One patient with a fibroinflammatory pseudotumor developed a massive inflammatory reaction in the implanted ear two months after cochlear implantation, which could not be controlled by conservative treatment. The implant had to be removed and local conditions settled after administration of immunosuppressive treatment with cyclophosphamide. The patient received a new implant seven months ago. CONCLUSIONS: Implantation of a foreign body in a potentially infected space which communicates intracranially means a surgical challenge which can be managed by obliteration of the middle ear after subtotal petrosectomy with abdominal wall fat combined with a reliable closure of the external ear canal. In case of massive inflammation we would prefer a two-stage procedure.     

Biodegradable implants for the delivery of veterinary vaccines: design, manufacture and antibody responses in sheep

Biodegradable implants made from cholesterol and lecithin (C:L) were used to deliver a recombinant antigen (recombinant Dichelobacter nodosus pili) and adjuvant (Quil A) to sheep. Implants (5.5- x 1.8-mm) were placed subcutaneously and compared to a conventional vaccination regime (2 injections, 4 weeks apart) for antibody responses and tissue compatibility. Release profiles of antigen and adjuvant were also studied in vitro and in vivo. The presence of Quil A in vaccine implants had a marked effect on the rate at which antigen was released with 29 and 44% being released in the first 24 h from implants containing pili alone and pili with Quil A, respectively. Sheep produced significant levels of antibody when immunized with implants, however the response was short-lived and of significantly lower intensity than the response stimulated by two injections of antigen with Quil A (P < 0.01). A second implant system was developed where implants coated with C:L to delay antigen release, were used in combination with uncoated implants to deliver a priming dose and boosting dose of antigen. Antibody titres stimulated by the 4 double implant system were equivalent to those stimulated by a conventional regime of two injections (four weeks apart) for the first six weeks of the experiment. After this time, antibody levels in the groups which received implants dropped significantly. In vitro studies revealed that some of the implant coatings had caused a delay in the release of antigen (the rate of release peaked at 72 h), however this was not long enough to provide a significant boosting effect. In all cases, implants were well tolerated by sheep and caused less local reaction than injected vaccines.     

Superiority of the ear pinna over muscle tissue as site for DNA vaccination

Three different vaccination sites were compared for efficiency of immunization with naked DNA. Using the bacterial lacZ gene as a model, all three sites of the mouse (skeletal muscle, dermis of abdominal skin or of the ear pinna) could express the gene product beta-gal but varied in expression time with muscle tissue showing the longest expression. Expression time, however, did not correlate with immune response intensity. The ear pinna was by far the most effective and muscle the least effective priming site for specific humoral and cytotoxic T cell-mediated immune responses. Following intra-pinna DNA inoculation, beta-gal expressing cells were detectable around the injection site and in the major draining lymph node. Efficiency of immunization was also dependent on the promoter and expression vector used. The cytomegalus virus promoter driven pCMV beta vector was superior to the Moloney murine leukemia virus LTR driven BAG vector. LacZ DNA immunization was also compared with cell-based vaccination with lacZ-transfected tumor cells, in which case again the pinna was the best site for inducing strong immune responses. Tumor-specific T cell responses could also be well induced in the pinna, leading to cytotoxic T lymphocyte induction and protective antitumor immunity. Thus, the pinna was found to be a privileged site for induction of antitumor responses and for genetic immunization, an important finding of immediate practical and potential future clinical implications.     

Mechanical and histological evaluation of amorphous calcium phosphate and poorly crystallized hydroxyapatite coatings on titanium implants

The effect of amorphous calcium phosphate (Ca/P) and poorly crystallized (60% crystalline) hydroxyapatite (HA) coatings on bone fixation to "smooth" and "rough" (Ti-6A1-4V powder sprayed) titanium-6Al-4V (Ti) implants was investigated. Implants were evaluated histologically, mechanically, and by scanning electron microscopy (SEM) after 4 and 12 weeks of implantation in a rabbit transcortical femoral model. Histological evaluation of amorphous vs. poorly crystallized HA coatings showed significant differences in bone apposition (for rough-coated implants only) and coating resorption (for smooth- and rough-coated implants) that were increased within cortical compared to cancellous bone. The poorly crystallized HA coatings showed most degradation and least bone apposition. Mechanical evaluation, however, showed no significant differences in push-out shear strengths between the two types of coatings evaluated. Differences between 4 and 12 weeks were significant for coating resorption and push-out shear strength but not for bone apposition. Significant enhancement in interfacial shear strengths for bioceramic coated as compared to uncoated implants were seen for smooth-surfaced implants (3.5-5 times greater) but not for rough-surfaced implants at 4 and 12 weeks. Rough implants showed greater mean interfacial strengths than uncoated smooth implants at 4 and 12 weeks (seven times greater) and to coated smooth implants at 12 weeks only (two times greater). Mechanical failure of the bone/coating/implant interface consistently occurred within the bone, even in the case of the poorly crystallized HA coatings, which had almost completely resorbed on rough implants. These results suggest that once early osteointegration is achieved biodegradation of a bioactive coating should not be detrimental to the bone/coating/implant fixation.     

Configuration of experimentally produced cholesteatoma by transplantation of a free skin graft

Residual cholesteatoma was experimentally produced in guinea pigs by transplanting a free skin graft into the middle ear bulla. In group A, the graft was placed on the mucosa after scratching the surface with a pick, while in group B, it was placed on the bone surface following removal of the mucosa and drilling with a diamond burr. The group A procedure was conducted on the left ear and the group B procedure on the right ear in 12 guinea pigs. The animals were sacrificed at two, four and eight weeks after transplantation. In all 12 ears of group A, the graft kept its original flat shape, resembling an open type residue. In eight of 12 ears of group B, the graft grew forming a squamous pearl, while in the remaining four ears it retained a flat shape. The difference in configuration is thought to be due to the amount of granulation around the graft.     

Paranasal implants for correction of midface concavity

Central midface concavity was corrected with the placement of porous polyethylene implants in the paranasal area. This simulated the effect of skeletal osteotomies and advancement without altering dental occlusion. Implants were placed to correct congenital, posttraumatic, and cleft-related skeletal midface retrusion in nine patients. In seven of the patients, paranasal augmentation was performed in conjunction with rhinoplasty. There have been no implant-related complications during a mean 33-month follow-up (range 5 to 83 months). Screw fixation of these implants ensures stable positioning and allows precise final contouring during surgery.     

Histologic evaluation of osseointegrated implants restored in nonaxial functional occlusion with preangled abutments

Of concern with the use of preangled abutments on implants is the transmission of masticatory forces and the angle at which they occur. Nineteen endosseous implants were placed in two subhuman primates. After 6 months, to allow for osseointegration, the implants were fitted with preangled abutments of various degrees and restored with type IV alloy castings. Straight abutments were used as control. Histologic evaluation revealed that, after 1 year of service, the implants exhibited complete osseointegration. Implants, whether restored with straight or preangled abutments, had no adverse effect on the surrounding bone. Soft tissue pockets measured, on average, from 2.2 to 2.6 mm; acute and chronic inflammatory cells were present. When crown loss was observed, it was caused by mechanical failure of components, such as gold screws and the screws used to secure the preangled abutments to the implants. Preangled abutments appear to be a valuable adjunct in implant dentistry, although long-term studies are needed for confirmation.     

Hypothalamic areas involved in prostaglandin (PG)-induced gonadotropin release. I: effects of PGE2 and PGF2alpha implants on luteinizing hormone release

Ovariectomized rats had a cannula inserted unilaterally within various hypothalamic areas. Several days later they were primed with a sc dose of 10 microng of estradiol benzoate (Eb). Two days after priming they were etherized and an initial blood sample was drawn from the external jugular vein. An inner cannula containing PGE2 or PGF2alpha at its tip was inserted into the previously implanted outer cannula. Blood samples were drawn at 20, 40, 60, and 120 min following the implantation. PGE2 induced a 4-5-fold increase in plasma LH 40 to 60 min following its implantation in the arcuate nucleus-median eminence region (ARH-ME). Levels were already significantly elevated at 20 min. When PGE2 was placed slightly more dorsally, close to the ventromedial nucleus (VMH), LH titers rose to comparable levels but only after a delay of 120 min. PGE2 implanted in the caudal portion of the ARH-ME or dorsally in the VMH-dorsomedial nuclei, barely increased plasma LH, whereas its placement in the anterior portion of the ARH-ME clearly elevated LH titers. PGE2 implants located more than 1 mm lateral from the midline or outside the hypothalamus were ineffective. When PGE2 was placed in the preoptic area (POA) or anterior ventral portion of the anterior hypothalamic area (AHA), plasma LH levels rose strikingly, the first significant increase being observed at 20 min. PGE2 implants located in the vicinity of the paraventricular nucleus-dorsal portion of AHA were much less effective. PGF2alpha implanted in the ARH-ME or POA induced a small increase in plasma LH and the implantation of empty cannulae in the same areas was ineffective. Intrapituitary implants of PGE2 failed to alter plasma LH significantly. The results indicate that PGE2 acts at the ARH-ME region to induce LH release and that an even more effective site of action seems to be located in the POA-AHA. Since these are areas which contain LHRH, the results support the view that PGs can activated LHRH-secreting neurons in these regions.     

Tissue culture of middle ear epithelium using fibroblast-reorganized collagen gels

The middle ear epithelium of the guinea pig has been cultured on a modified floating collagen matrix. Fibroblasts harvested from abdominal skin dermis of allogenic animals were used to reorganize hydrated collagen gels into a dermal-like matrix. Within two days, the explants placed on the surface of these matrices showed proliferation of polygonal "outgrowth cells" which could be maintained for up to one month. During the first two weeks of the culture period, dividing cells were frequently identified. These cells were especially abundant in the marginal area of the explants and consisted of pseudostratified columnar cells. The reorganized collagen gel matrix was stable and did not dissolve even after the "outgrowth cells" became confluent. The present system should allow further elucidation of the growth and differentiation mechanisms of middle ear epithelial cells.     

Transfer to a nitrocellulose membrane allows of the bone forming activity of bone morphogenetic protein

When we purify bone morphogenetic protein (BMP), its activity diminishes, and the quantity we are able to extract decreases. It is difficult to evaluate the effects of each of the processes involved in BMP purification because it is unstable. In order to resolve the problem, a modified bioassay method using only slight quantities of BMP which do not decrease its bone-forming activity, is needed. We transferred BMP separated by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) onto nitrocellulose membranes (NC) and cut out the bands. Then we used each band as implanted material. The NC membrane firmly bound the BMP activity fraction and held it in the implantation area of the mouse thigh. No formation of bone-like tissue was detected histologically at 14 days after the implantation, but, by 21 days after implantation, cartilage like tissue had clearly formed and newly formed bone was seen by 28 days. By implanting BMP transferred to individual NC membranes, we could perform a bioassay easily with small amounts of BMP without any reduction in activity.     

Cochlear implantation in children with inner ear malformations

We performed a case study and intervention study, with follow-up of 1 to 5 years, in 4 children with inner ear malformations who underwent implantation of a multichannel cochlear implant (Nucleus, Cochlear Corporation) at ages 3 to 12 years. Malformations included a common cavity deformity, 2 incomplete partitions, and 1 case of isolated bilateral vestibular aqueduct enlargement. One child had a single-channel implant placed at 3 years of age, and this was exchanged for a 22-channel implant at age 9. One child had her implant placed at age 4.5 years, but due to complications from a cerebrospinal fluid (CSF) leak had the initial implant removed and replaced at age 5 years during repair of the CSF leak. Intraoperative findings included a CSF leak at the time of surgery in 3 patients. One patient contracted bacterial meningitis 7 months postimplantation that was thought to be secondary to acute otitis media in the unoperated ear. Bilateral CSF leaks were noted in the middle ear by a lumbar puncture radionuclide and fluorescein dye study. Successful repair of the CSF leaks and reimplantation of the cochlear implant was carried out in this patient. Mapping and programming of the implant was found to be challenging in each of these patients. All patients demonstrated improved performance after implantation. Two patients demonstrated some open-set speech perception. One patient demonstrates improved use of temporal cues in a structured closed set. One patient has achieved no significant speech recognition at this time, but does have improved sound detection and awareness. Cochlear implantation in children with congenital inner ear abnormalities can be a successful method of rehabilitation. It should be recognized that the postoperative speech perception results may be highly variable among patients, and that intraoperative complications may occur.     

Wide polytef (Gore-Tex) implants in lip augmentation and nasolabial groove correction

OBJECTIVE: To describe a new technique of polytef (Gore-Tex) implantation into the upper and lower lips and nasolabial grooves by using large implants as a method that achieves effective cosmetic improvement. SETTING: A private cosmetic surgery center. PARTICIPANTS: Thirty-three (female) patients who desired fuller lips and 62 patients (52 female and 10 male) who requested less prominent cheek lip grooves. MAIN OUTCOME MEASURE: Significant patient satisfaction after 12 to 54 months. RESULTS: Conspicuous aesthetic effect that related to both lip and nasolabial groove correction was documented. All patients but 4 (2 in each group) were pleased with the final outcome of the treatment. CONCLUSIONS: In the opinion of the authors, the threading technique of polytef implantation creates inconspicuous improvement-both in lip augmentation and nasolabial groove correction. Large polytef implants that were inserted through a tunneling technique produced consistently good results. Implants (lip augmentation: width, < or = 10 mm, and thickness, 4 mm; nasolabial groove correction: width, 8 mm, and thickness, < or = 8 mm) were found to be safe, simple, and effective.     

Functional alveolar ridge reconstruction with prefabricated iliac crest free flap and osseointegrated implants after hemimaxillectomy

We achieved functional alveolar ridge reconstruction after hemimaxillectomy using a prefabricated iliac crest flap. The iliac crest was vascularized secondarily by a long rectus abdominis muscle flap with its inferior epigastric vessels intact to obtain an ideal anatomic location between the maxillary defect and microvascular anastomosis site. The iliac crest was tightly resurfaced with a split-thickness skin graft as well. After a bony surgical delay, the prefabricated iliac crest flap was microsurgically transferred to the face. Three osseointegrated implants were placed in the prefabricated iliac crest, and a dental prosthesis was worn with immobilization and stability. Our procedure enabled recovery of a satisfactory facial appearance and excellent masticatory function.     

Effect of sucralfate and basic fibroblast growth factor on fibrovascular ingrowth into hydroxyapatite and porous polyethylene alloplastic implants using a novel rabbit model

This study investigated the effects of sucralfate and basic fibroblast growth factor (bFGF) on fibrovascular ingrowth into porous implant materials. Seven white female New Zealand rabbits underwent bilateral abdominal incisions through which porous orbital spherical or and disc-shaped implants were inserted between their abdominal muscles. Eighty hydroxyapatite (HA) and porous polyethylene (PP) implants, each material of different pore sizes, were implanted. These implants were either uncoated or coated with suspensions of polyhydroxymethylmethacrylate (hydron); hydron and sucralfate; or hydron, sucralfate, and bFGF. Implants were harvested after 1, 3, or 6 weeks. Observers classified the extent of fibrovascular ingrowth in a blind manner using light microscopy. All discs and spheres showed fibrovascular ingrowth; at 6 weeks, almost all implants were fully vascularized. Although demonstrating different degrees of fibrovascular maturity, all 3- and 6-week discs showed complete cellular ingrowth. Overall, the most extensive and mature fibrovascularization was found in HA implants, regardless of shape, duration of implantation, or angiogenic enhancing agent used. Thus, this study indicates that fibrovascular ingrowth into porous implants is more greatly affected by implant porosity and composition than by addition of angiogenic enhancing agents. Further in vivo study, using other potential angiogenesis-promoting agents as well as implants with different pore characteristics, is warranted using this reliable and predictable animal model.