Clinical trials with a polycrystalline alumina dental implant.

The Tübingen polycrystalline alumina implant utilizes bony apposition as the method of stabilization. Its cylindrical configuration allows the implant site to be prepared by use of ultra-low-speed drills. This study focused on the use of the implant as a single-tooth, free-standing device. Thirty patients were selected. Devices were followed for five years. The implants were placed in one of two applications: immediate extraction site or healed edentulous ridge. A simple purse-string suture technique was used for closure. Periodic observations were recorded. Of the 30 planned implants, all have been completed to date. Twenty-five of the 30 have been considered successful. Twenty-three of the 25 successes were from the immediate extraction group. Only 2 of 5 were successful in the healed ridge group. Due to the structural requirements of the Tübingen implant, its size makes it usable only in wider-than-average edentulous ridges. The success rate was 83.3%, and for those devices placed in immediate extraction sites, a success rate of 92% was recorded.

An investigation of skin deformation around percutaneous devices.

According to the literature one of the primary failure models of percutaneous devices (PDs) in soft tissue implantation sites is that of mechanically induced trauma along the implant/tissue interface. In order to avoid such avulsion, subcutaneous flanges have been incorporated into PD designs to provide a better distribution of stresses along the implant/tissue interface. Tissue necrosis and inflammation were then observed to be most pronounced around the rim of the subcutaneous flange. It was the goal of this study to develop and test PDs with subcutaneous flanges of varying stiffnesses in order to allow the flange to distribute stresses into the surrounding tissues more evenly, thereby reducing the likelihood of failure due to avulsion. PDs were tested with flanges of constant thickness or varying linearly, reducing toward the flange rim. They were evaluated using an in-vitro testing method which was designed to simulate the situation of an implanted PD subjected to external loading. The results indicated that the stiffness characteristics of the subcutaneous flange had a substantial effect on the behavior of the devices under loading. A PD having a radial stiffness decrease would improve the likelihood of implant survival in the clinical situation due to the reduction of mechanically induced trauma along the implant/tissue interface.

Biomechanical considerations on some postoperative problems of directly anchored total hip replacements.

Uncemented total hip replacements have resulted in a higher incidence of postoperative complaints than cemented ones. The theoretical explanation of these not well defined discomforts is based on the differences of the stress and strain fields around the distal portions of the femoral components. While the noncemented stems are press-fitted and most of them tapered distally, thus creating hoop stresses and strains in the surrounding cortical bone, the shrinkage of the cement prevents these mechanical irritations. The relatively sudden disappearance of these discomforts within the first 2 postoperative years is attributed to the shift of the main zone of load transmission from the distal to the proximal portion of the stems following bone remodeling.

[Postoperative pain in cement-free femur shaft prosthesis]. / Zur Frage postoperativer Schmerzen bei zementfreien Hüftschaftprothesen.

With practically all hip endoprosthesis systems the femoral components of which are implanted cement-free irritations in the femoral region persisting for up to two years p.o. have been reported significantly more frequently than with cemented shafts. The discussion of this observation is based on the fact that stems inserted cement-free are mostly press-fitted into the surrounding bone, thus, creating a completely different stress and strain field as compared to cemented shafts. The usually spontaneous disappearance of these initial irritations is attributed to remodelling reactions which, controlled by the load distribution in the surrounding bony tissue which, in turn, is mainly controlled by the shape of the prosthesis, results in the formation of well load bearing bony structures along steps and other surface undulations along the proximal part of the prosthesis.

[Experimental results of stepped titanium shafts for hip endoprostheses]. / Experimentelle Ergebnisse an Stufenschäften aus Titan für Hüftendoprothesen.

Among the materials which can be used for hip prostheses to be implanted without bone cement, ceramics and titanium possess the best overall properties for insuring long-term stability in the light of present knowledge. However, considered separately, the two materials are most suitable for different special requirements. Results of long-term animal experiments conducted by different working groups on functionally stressed hip and tooth-root implants made of bio-inert Al2O3 ceramic and titanium have furnished knowledge of the possibilities and limitations of the adaptation reaction of the bone tissue. The present authors investigated whether, by combining Al2O3 ceramic and titanium, a cement-free total hip replacement can be adapted to specific local stresses, taking biomechanical rules and anatomical factors into account. In recent experimental series it proved possible to limit the problems which had occurred in previous series, reported elsewhere. Positive results in dogs led to a human implant which has so far been used 15 times, with Al2O3 (FRIALIT) acetabula and heads, which have been implanted successfully for a number of years, in combination with the new stepped titanium shaft. In addition to a short review of follow-up findings thus far, the results of the experimental investigations are presented.

[Resorbable, porous tricalcium phosphate ceramic in middle ear surgery. Initial clinical results]. / Resorbierbare, poröse Trikalziumphosphat-Keramik in der Mittelohrchirurgie. Erste klinische Ergebnisse.

In our experimental study in the pig we could demonstrate that resorbable, porous tricalcium phosphate ceramic material is suitable for an obliteration of mastoid cavities (respectively the hypotympanon of the pig) or for the reconstruction of bony wall. To examine this material in a clinical study for middle-ear surgery, we chose 2 mm thick ceramic plates and segments of truncated cones. With the aid of a diamond drill and irrigation this ceramic can be treated easily. In 25 middle ears, the following reconstructive surgeries were performed with these ceramic implants: in 22 cases a partial replacement of the lateral attic wall, in one case a replacement of the total lateral attic wall, in one case a reconstruction of the canal wall after radical mastoidectomy, and in one case an obliteration of the mastoid cavity. These 25 ears have been followed up for 2-11 months with an average of 7,1 months. In 19 cases the implants showed no sign of any complication. In four cases, however, a dehiscence of the skinny covering (outer ear canal) was observed during the post-operative healing period. In one case this dehiscence closed spontaneously, in the other case we recovered the implant by surgery. In one patient we had to remove the implant, in another one the implant is uncovered and still under observation. An inflammation of the implant bed occurred once. One implant sank down into the middle ear cavity.

Experiences with Al2O3--ceramic middle ear implants.

The excellent tolerance of bio-inert aluminium oxide ceramic after being implanted into the middle ear has been shown by our electron microscopic studies and clinical experience over 4 years. Our implants developed for ossicular chain reconstruction were covered by a delicate middle ear mucosa within a few weeks. We have observed no foreign body reactions. The ceramic implants are distinguished by the almost unlimited number of forms or shapes into which they can be ground quickly and precisely during operation. We value Al2O3 ceramic implants because there is no bony fixation with the surrounding bone but rather a joint-like connection with the remaining parts of the ossicular chain.

[Obliteration of the mastoid cavity with porous tricalcium phosphate ceramic. Results 12 and 18 months after ceramic implantation in the hypotympanon of the pig]. / Verödung des Warzenfortsatzes mit poröser Trikalziumphosphat-Keramik. Ergebnisse 12 und 18 Monate nach Keramik-Implantation in das Hypotympanon des Hausschweines.

The paper reports on the obliteration of mastoid cavities with resorbable tricalcium phosphate ceramic. As a model, we chose the pneumatic air cell system of the pig's hypotympanon, which resembles the human mastoid. At the time of surgery, the specimens were 10-12 weeks old. In a first group the cells of the hypotympanon were totally removed and the operation cavity was obliterated with adjacent layers of porous tricalcium phosphate ceramic. In a second group of specimens the air cell system was partly removed, leaving the apical part of the hypotympanon intact; the operation cavity was obliterated again with porous tricalcium phosphate ceramic. After 12 and 18 months survival the hypotympanons were removed and prepared for histological investigations. Those ceramic plates, lying close to the bony shell were strongly resolved and replaced by new bone. Other ceramic plates, however, especially those in the center of the implant, showed few signs of resorption and bony remodelling. Inside the ceramic implant there was hardly connective tissue. The space between the still unsolved ceramic plates was filled up with new bony tissue. This bone was partly structured and adjoined directly to the ceramic. The ceramic was integrated into the new bony tissue without any sign of an inflammation.

The influence of fine surface structures on the osseo-integration of implants.

The availability of inert materials like dense, pure Al2O3-ceramic or titanium allows the study of purely biomechanical influences of surface modulations or lacune on the osseo-integration of implants at different locations of the skeleton. The discovery of the "load-line-shadow" phenomenon in lacune of dental implants and the observation of the same effect in the grooves of hip sockets (Lindenhof type) indicate the general validity of the rules controlling the remodelling ability of bony tissue. Their application to the problems concerned with load transmission via surfaces which are mainly loaded by shear can contribute to achieve a well defined anchorage of implants.

[Obliteration of the mastoid air cell system with porous tricalcium phosphate ceramic. An animal experiment of the bulla tympanica of the pig (author's transl)]. / Verödung des Warzenfortsatzes mit poröser Trikalzium-phosphat-Keramik. Eine tierexperimentelle Studie an der Bulla tympanica des Schweines.

The paper reports on an animal experiment on the obliteration of mastoid cavities with tricalcium phosphate ceramic. The pneumatic air cell system of the bulla tympanica of pigs of 11-12 weeks of age was totally removed in one group of animals and partially removed in the second group. In this second group, apical part of the bulla was left intact. The operation cavity was then obliterated with adjacent layers of porous tricalcium phosphate ceramic. Histological sections wee evaluated for both groups of animals after survival time of 1, 3 and 6 months. Initially, an ingrowth of granulated tissue between the ceramic layers and into the porous surface can be observed. This dissolves the ceramic material, which is substituted by bony tissue. Pneumatic cells in the apical part of the bulla, which were left intact in the second group of animals, do not obliterate after the air supply has been cut off by sealing the basal part. Cystic cavities remain which contain a serous exudate. After 6 months, the mucous membrane of such cells shows signs of "sclerosis". Formation of spongy bony tissue with marrow spaces can be seen in most of the apical areas of the growing bulla. There is no formation of air-containing cells. It appears from our preliminary results obtained from animal experiments that porous tricalcium phosphate ceramic may be a suitable material for the obliteration of mastoid cavities.

The effects of mechanical factors on bio-compatibility tests.

Evaluation of materials for bone and joint replacement has led to contradictory results in a number of cases: some researchers have reported the formation of good load-bearing bone structures along the surface of a particular material, e.g. dense, high strength Al2O3-ceramics, others found the same material encapsulated by soft tissue. Considering the results of various animal experiments and the evaluation of clinical follow-up studies, it can be shown that many of these conflicting observations are due to different biomechanical conditions at the site of examination. Failure to consider the local load situation at the interface between the implanted specimen and the bone tissue can lead to misleading statements about the possible applications of a material.

Comparative histocompatibility testing of seven calcium phosphate ceramics.

Five hydroxyapatite and two tricalcium phosphate ceramics were implanted in rat femora for one to six months. They were compared with each other in regard to biocompatibility and bone induction. After one month bone had grown directly on to the surface of all implants. After six months the on-growth of bone had increased with the exception of two dense HA materials. In these materials some bio-degradation had occurred with subsequent formation of a wide macrophage interlayer. Bio-degradation and biocompatibility of calcium phosphate ceramics seem to depend not only on density but also on other factors. Induction of bone could not be observed in soft tissue environment.

Five years experience with ceramic-metal-composite hip endoprostheses. I. clinical evaluation.

Clinical experience with 130 endoprostheses, entirely made of ceramic, having an average 5 year follow-up is reported. Excellent to sufficient results were seen in 84% of all cases. A number of particular matters of interest (operative technique, radiological morphology of the bone/ceramic bone interface etc.) are discussed in detail. Complications (loosening of components: 2%; component fracture: 6%, wear phenomena etc.) are described and documented including histological observations from capsular tissue of total ceramic hip joints. The whole system has basically stood the test, during the implantation period, modifications to improve the function of the system will be described in another publication.

Five years experience with ceramic-metal-composite hip endoprostheses. II. Mechanical evaluations and improvements.

The results of the complete and detailed clinical evaluation are compared with the original design criteria. It is shown that most of them stood the test. Those aspects which did not meet the expectations are discussed in detail: The occurrence of very little and biologically tolerable wear during the initial running-in period will be further reduced by a considerable improvement of the material properties. The few cases of severe wear had been associated with clinically exceptional situations, the analysis of which allows for suggestions to avoid such situations. The material improvements and all other steps taken to increase the safety margin considerably against fractures of the ceramic ball are described in detail. In addition, the attention is paid to some necessary clinical precautions.