Preliminary experience with a novel model assessing In vivo mechanical strength of bone grafts and substitute materials

A novel canine tibia model was used to evaluate four bone graft materials: autologous cortical bone, allograft cortical bone, hydroxyapatite/tricalcium phosphate (HA/TCP) ceramic granules, and a HA/TCP and collagen composite. Mechanical material properties were assessed using custom-designed stainless steel plugs for control of graft volume and interface surface area. These plugs held the bone graft materials in the cortex of the tibia shaft and allowed in vivo mechanical testing. After 6 months of ad lib weight bearing, the grafts were harvested and tested in torsion. The samples in each animal were compared with the test plugs into which new bone had grown without the addition of graft. Control bone peak shear strength averaged 47 (±8.3) MPa (6.78±1.2 kpsi). Compared on the basis of peak torque, stiffness, and energy to peak torque, no significant differences were found among any of the graft materials or control bone. Histologic examination revealed the materials to be osteoconductive with the extensive formation of dense, compact cancellous bone. The new bone in the autograft and allograft samples completely filled the available space, whereas gaps persisted in the synthetic ceramics.     

Zirconia Phase Transformation in Zirconia-Toughened Alumina Ceramic Femoral Heads: An Implant Retrieval Analysis

BackgroundZirconia-toughened alumina ceramic was introduced as a femoral head material for total hip arthroplasty. The material combines the stability of alumina with the toughness of zirconia. Despite inherent benefits for bearing surfaces, concern exists in the medical field that phase transformation of the zirconia grains could worsen wear resistance and lower the strength of the head. We examined these concerns in retrieved and artificially aged ceramic heads.MethodsTwenty-eight ceramic composite heads retrieved at revision surgery were combined with 5 pristine heads (as negative controls for phase transformation) and 5 artificially aged pristine heads (as positive controls). The extent of zirconia phase transformation at the bearing surfaces was examined through confocal Raman spectroscopy and X-ray diffraction. Burst testing was conducted on all pristine and aged heads and the 4 retrieved implants with the longest lengths of implantation.ResultsRetrieved heads had higher maximum average volume fractions of the monoclinic phase compared to pristine or aged heads. Length of implantation was not correlated to the volume fraction of the monoclinic phase. All the heads achieved a burst load far above the 46 kN Food and Drug Administration acceptance criterion; 3 of the 4 retrieved heads had burst strengths exceeding 100kN.ConclusionOur results showed that phase transformation occurs in vivo in ceramic composite femoral heads, but the amount transformed did not increase with the length of time the head had been implanted. The negligible effect upon burst strength of the retrieved and artificially aged heads is reassuring. These results support continued clinical use of this alumina-zirconia composite material as a head material.     

Biomechanical comparison of the strength of adhesion of polymethylmethacrylate cement to zirconia ceramic and cobalt–chromium alloy components in a total knee arthroplasty

Purpose The purpose of this study was to clarify the biomechanical characteristics of cement–material interfaces for the zirconia ceramic and cobalt–chromium (Co–Cr) alloy femoral components used for total knee arthroplasty.Methods In the first sub-study, we compared the strength of adhesion of the cement to flat plates, by tensile testing under dry and moistened conditions. In the second sub-study, we compared the maximum load of the cement–component complex by tensile testing. In the third sub-study, we compared the fatigue characteristics of the cement–component complex by use of a dynamic tensile testing machine.Results Under dry conditions, the maximum strength of adhesion to the zirconia ceramic plate was the same as that to the Co–Cr alloy plate. Under moistened conditions, however, the strength of adhesion to the zirconia ceramic plate was significantly lower (p = 0.0017) whereas the strength of adhesion to the Co–Cr alloy plate was not reduced. Maximum load for the cement–component complexes for zirconia ceramic and Co–Cr alloy was no different under both dry and moistened conditions. Fatigue testing showed that cement–zirconia adhesion was stronger than cement–Co–Cr alloy adhesion (p = 0.0161).Conclusions The strength of adhesion of cement to zirconia ceramic is substantially weaker under wet conditions than under dry conditions. The mechanical properties of cement–zirconia ceramic component complexes and cement–Co–Cr alloy component complexes are equivalent.     

Evolution and new application of the alumina ceramics in joint replacement

Alumina and zirconia are the structural ceramics used in orthopedics. Alumina offers better tribological characteristics and high chemical–physical stability, but poor toughness. For this reason it is not used for complex shape and thin ceramic components. On the opposite, zirconia is tougher and less stable. A new alumina matrix composite material, called Biolox^® Delta (CeramTec AG, Plochingen, Germany), has been obtained in order to mix and enhance positive characteristics of both materials.     

Reactions and complications after the implantation of Endobon including morphological examination of explants

In the study described here, the integration of hydroxyapatite (HA) ceramic implants (Endobon) was investigated. These implants have an interconnecting system of pores and are free from foreign protein. The material is not toxic, genotoxic, nor zytotoxic, and it is biocompatible. The progress of integration was investigated by means of clinical and radiological check-ups. From 10 patients, it was possible to obtain samples for histological analysis during a second operation (e.g., metal explantation). Microscopic examination showed bony integration with newly formed bone in direct contact with the HA ceramic; it also showed osteoblasts and osteoid seams. No second operation took place earlier than 4 months after the first operation, yet even after this relatively short period, bony integration was already evident. Clinical observation (based on X-rays, reports of pain, signs of inflammation) showed that in most cases healing was taking place without complications. More general operational complications such as thrombosis or nerve injury were observed in 4 patients. If the implant is not sufficiently protected from mechanical stress, bony integation will not take place, and the implant may fracture. HA ceramic, with a porosity between 30% and 80%, is not comparable to cortical bone but only to spongy bone. This factor must be taken into account when deciding whether a HA ceramic implant is indicated. Received: 13 March 1997     

Self-hardening calcium phosphate composite scaffold for bone tissue engineering.

Calcium phosphate cement (CPC) sets in situ to form solid hydroxyapatite, can conform to complex cavity shapes without machining, has excellent osteoconductivity, and is able to be resorbed and replaced by new bone. Therefore, CPC is promising for craniofacial and orthopaedic repairs. However, its low strength and lack of macroporosity limit its use. This study investigated CPC reinforcement with absorbable fibers, the effects of fiber volume fraction on mechanical properties and macroporosity, and the cytotoxicity of CPC-fiber composite. The rationale was that large-diameter absorbable fibers would initially strengthen the CPC graft, then dissolve to form long cylindrical macropores for colonization by osteoblasts. Flexural strength, work-of-fracture (toughness), and elastic modulus were measured vs. fiber volume fraction from 0% (CPC Control without fibers) to 60%. Cell culture was performed with osteoblast-like cells, and cell viability was quantified using an enzymatic assay. Flexural strength (mean+/-SD; n=6) of CPC with 60% fibers was 13.5+/-4.4 MPa, three times higher than 3.9+/-0.5 MPa of CPC Control. Work-of-fracture was increased by 182 times. Long cylindrical macropores 293+/-46 microm in diameter were created in CPC after fiber dissolution, and the CPC-fiber scaffold reached a macroporosity of 55% and a total porosity of 81%. The new CPC-fiber formulation supported cell adhesion, proliferation and viability. The method of using large-diameter absorbable fibers in bone graft for mechanical properties and formation of long cylindrical macropores for bone ingrowth may be applicable to other tissue engineering materials.     

The use of hydroxyapatite in orthopaedic surgery: A ten-year review

Summary Hydroxyapatite (HA), which constitutes 65% of the mineral component of human bone, is a crystalline structure whose synthesis was achieved at the beginning of the century. The development of the technology of coating metals with a ceramic material stimulated extensive research throughout the world leading to the use of implants coated with HA in maxillofacial surgery. The application to ostearticular implants was preceded by rigorous and prolonged experimentation, which demonstrated that implants of titanium coated with HA were devoid of risk and made it possible to secure excellent bony fixation. With a follow-up well in excess of 10 years the published results are evidence of considerable improvement and confirm that articular implants coated with HA represent a major advance. However, HA is only involved in bony fixation and cannot compensate for inadequate design of the implants as regards their shape or surface state.     

Tissue reaction to collagen-coated porous hydroxyapatite

To give tenacity to high porosity (80%-90%) hydroxyapatite (HA) and to make a stronger bone substitute, a collagen-coated porous HA (C-HA) was prepared, and its compressive strength was examined. By implanting C-HA into the femoral condyle of adult rabbits, the capacity for new bone formation and foreign-body reactivity were quantitatively compared with those of HA alone. The compressive strength of C-HA was 4.3 times greater than HA. At four weeks after implantation, the mean areal ratio of the newly formed bone in the C-HA block in each rabbit was 9.9%, which was somewhat less than the 13.7% in the HA block; the mean number of multinucleated giant cells (MGC) per visual field at x25 in the C-HA-implanted specimens in each rabbit was 14.4, significantly larger than the 6.1 in the HA specimens. However, 12 weeks after C-HA implantation, the areal ratio of new bone increased to 32.7%, the number of MGC decreased to 9.4, and the differences compared to the values in HA cases, 31.5% and 6.8, disappeared. These results showed that C-HA is mechanically stronger than HA and that there is no difference between HA and C-HA in capacity for new bone formation or foreign-body reaction.     

Development of a hydroxyapatite/collagen nanocomposite as a medical device

The effect of cross-linking of a hydroxyapatite/collagen (HA/Col) nanocomposite, in which HA nanocrystals and collagen fibers are aligned like natural bone by a self-organization mechanism between HA and collagen in vitro, on mechanical properties was examined. The influence of degree of cross-linking, as well as rhBMP-2 preadsorption to the composite on the substitution pattern and rate with bone, was examined. In Experiment 1, anterior fusion was carried out at the C3-C4 vertebrae on 10 dogs and they were implanted as follows: without cross-linking and without adsorbed rhBMP-2 (three dogs), with cross-linking and without adsorbed rhBMP-2 (three dogs), without cross-linking and with adsorbed rhBMP-2 (two dogs), and with cross-linking and adsorbed rhBMP-2 (two dogs). Implants were removed from each dog for histology determinations after 12, 16, and 24 weeks in the non-rhBMP-treated groups, and after 16 and 24 weeks in the rhBMP-treated groups. In Experiment 2, the HA/Col composites with cross-linking and both with and without rhBMP-2 pretreatment were implanted into a bone defect of 20 mm made in the central part of tibiae in dogs (N = 3 in each group). As a control, bone defects of 20 mm remained without implantation (N = 3). The dogs were allowed to walk using an Ilizarov extra skeletal fixator. The implants were removed after 12, 16, and 24 weeks from one dog in each group. The cross-linking of the HA/Col composite was effective in controlling both the mechanical strength and bioresorbability. A "self-organization process" on the HA/Col implant surface resulted in the formation of bone remodeling units in and around the implant. Radiographic and histological findings suggest that a combined treatment of cross-linking of the HA/Col composite with preadsorption of rhBMP-2 molecules may be a very suitable replacement of existing ceramic systems in the anterior fusion of the cervical spine, as well as inlay grafting of bone defects in weight-bearing sites.     

Wear-Resistant, Hemocompatible Ti-Nb-Zr and Zr-Nb Alloys to Improve Blood Pump Design and Performance

Abstract Over the past several years, we have developed novel titanium-niobium-zirconium (Ti-Nb-Zr) alloys to address the long-term performance needs of orthopedic implants. The unique properties of these alloys also render them promising candidates for blood pumps. These properties include excellent biocompatibility in combination with high strength and toughness, and low elastic modulus (low stiffness). Additionally, these metal alloys are readily hot or cold worked into complex shapes including wire, foil, tubing, and bar. They are readily machined and polished, and they can be surface oxidized to form a hard, wear-resistant, low-friction ceramic surface layer. In this diffusion-hardened condition, oxygen also hardens the underlying metal to optimize the bone between the ceramic oxide surface and the tough metal substrate. Unlike metal surfaces, oxidative wear, which can alter surface energy, friction, and hemocompatibility, does not occur. Consequently, the combined benefits of a stable, wear-resistant, low-friction ceramic surface layer with the toughness, strength, formability, and thermal conductivity of metal may provide improvements in the design and performance of blood pumps and peripheral graft and percutaneous (power) components of the pump.     

Clinical result of sintered bovine hydroxyapatite bone substitute: analysis of the interface reaction between tissue and bone substitute

Background  

Autogenic bone graft is the first choice for managing bone defects. However, donor site-associated morbidity and limited bone volume are constraints in clinical applications. Allografts can provide sufficient amounts for bone defects but have a high risk of infection. Bone substitute composed of hydroxyapatite (HA) is an alternative material for avoiding the aforementioned risks. Sintered bovine bone is a naturally occurring HA that has been proved to have excellent bioactivity for inducing osteoblastic expression and new bone formation in animal studies. The objective of this study was to evaluate the interactions between the tissue and the bone substitute composed of HA (sintered from bovine bone) in the human body.     

In Vivo Evaluation of Zirconia Ceramic in the DexAide Right Ventricular Assist Device Journal Bearing

Zirconia is a ceramic with material properties ideal for journal bearing applications. The purpose of this study was to evaluate the use of zirconium oxide (zirconia) as a blood journal bearing material in the DexAide right ventricular assist device. Zirconia ceramic was used instead of titanium to manufacture the DexAide stator housing without changing the stator geometry or the remaining pump hardware components. Pump hydraulic performance, journal bearing reliability, biocompatibility, and motor efficiency data of the zirconia stator were evaluated in six chronic bovine experiments for 14–91 days and compared with data from chronic experiments using the titanium stator. Pump performance data including average in vivo pump flows and speeds using a zirconia stator showed no statistically significant difference to the average values for 16 prior titanium stator in vivo studies, with the exception of a 19% reduction in power consumption. Indices of hemolysis were comparable for both stator types. Results of coagulation assays and platelet aggregation tests for the zirconia stator implants showed no device‐induced increase in platelet activation. Postexplant evaluation of the zirconia journal bearing surfaces showed no biologic deposition in any of the implants. In conclusion, zirconia ceramic can be used as a hemocompatible material to improve motor efficiency while maintaining hydraulic performance in a blood journal bearing application.     

Low-intensity pulsed ultrasound increases bone ingrowth into porous hydroxyapatite ceramic

Synthetic porous ceramic made of hydroxyapatite (HA) has been used as a bone graft substitute. In the present study we investigated whether low-intensity pulsed ultrasound (LIPUS) accelerates bone ingrowth into the pores of HA ceramic. Application of LIPUS did not mechanically weaken porous ceramic that was immersed in water in vitro. In vivo experiments using rabbits showed that LIPUS application for 2 weeks significantly increased osteoblast number and bone area in the central part of the porous HA ceramic implanted in the femoral condyle in comparison with similarly implanted HA ceramic that was not exposed to LIPUS. LIPUS application for 3 weeks significantly increased mineralized tissue volume and mineral content in the porous HA ceramic. Wound healing assays revealed increased migration of MC3T3-E1 cells as a result of LIPUS treatment, partly accounting for the increased osteoblast number. Use of porous HA ceramic combined with LIPUS may be a promising treatment for filling large bone defects in a clinical setting.     

Understanding Bone Strength Is Not Enough

Increases in fracture risk beyond what are expected from bone mineral density (BMD) are often attributed to poor “bone quality,” such as impaired bone tissue strength. Recent studies, however, have highlighted the importance of tissue material properties other than strength, such as fracture toughness. Here we review the concepts behind failure properties other than strength and the physical mechanisms through which they cause mechanical failure: strength describes failure from a single overload; fracture toughness describes failure from a modest load combined with a preexisting flaw or damage; and fatigue strength describes failure from thousands to millions of cycles of small loads. In bone, these distinct failure mechanisms appear to be more common in some clinical fractures than others. For example, wrist fractures are usually the result of a single overload, the failure mechanism dominated by bone strength, whereas spinal fractures are rarely the result of a single overload, implicating multiple loading cycles and increased importance of fatigue strength. The combination of tissue material properties and failure mechanisms that lead to fracture represent distinct mechanistic pathways, analogous to molecular pathways used to describe cell signaling. Understanding these distinct mechanistic pathways is necessary because some characteristics of bone tissue can increase fracture risk by impairing fracture toughness or fatigue strength without impairing bone tissue strength. Additionally, mechanistic pathways to failure associated with fracture toughness and fatigue involve multiple loading events over time, raising the possibility that a developing fracture could be detected and interrupted before overt failure of a bone. Over the past two decades there have been substantial advancements in fracture prevention by understanding bone strength and fractures caused by a single load, but if we are to improve fracture risk prevention beyond what is possible now, we must consider material properties other than strength. © 2017 American Society for Bone and Mineral Research.     

Bone tissue engineering using novel interconnected porous hydroxyapatite ceramics combined with marrow mesenchymal cells: quantitative and three-dimensional image analysis

We developed fully opened interconnected porous calcium hydroxyapatite ceramics having two different pore sizes. One has pores with an average size of 150 microm in diameter, an average 40-microm interconnecting pore diameter, and 75% porosity (HA150). The other has pores with an average size of 300 microm in diameter, an average 60-100-microm interconnecting pore diameter, and 75% porosity (HA300). Because of its smaller pore diameter, HA150 has greater mechanical strength than that of HA300. These ceramics were combined with rat marrow mesenchymal cells and cultured for 2 weeks in the presence of dexamethasone. The cultured ceramics were then implanted into subcutaneous sites in syngeneic rats and harvested 2-8 weeks after implantation. All the implants showed bone formation inside the pore areas as evidenced by decalcified histological sections and microcomputed tomography images, which enabled three-dimensional analysis of the newly formed bone and calculation of the bone volume in the implants. The bone volume increased over time. At 8 weeks after implantation, extensive bone volume was detected not only in the surface pore areas but also in the center pore areas of the implants. A high degree of alkaline phosphatase activity with a peak at 2 weeks and a high level of osteocalcin with a gradual increase over time were detected in the implants. The levels of these biochemical parameters were higher in HA150 than in HA300. The results indicate that a combination of HA150 and mesenchymal cells could be used as an excellent bone graft substitute because of its mechanical properties and capability of inducing bone formation.     

Bioactive ceramic prosthetic coatings.

The concept of bioactive ceramic coatings on macroscopically smooth prostheses tries to reconcile opposing principles: the ceramic with beneficial bone tissue growth effects is used as a coating since it does not have sufficient strength and toughness to be used by itself as a prosthesis material. But strength is still an issue since the coating is the primary means of transferring stresses from prosthesis to surrounding tissues. The interface between the metal core and ceramic surface is then critical, since it essentially depends on the strength characteristics of the ceramic. Conversely, when the ceramic coating is used as a means to enhance bone-tissue formation around and into the prosthesis surface, thereby helping to establish a mechanical form of retention, the adhesion of ceramic coating to metallic substrate is not critical. The optimum characteristics of the ceramic are then those that produce the highest effect on bone-tissue growth rates immediately after surgery. The rate of bioactivity is related to the chemical reactivity of the material causing interfacial dissolution, precipitation, and ion exchange reactions. Furthermore, it also appears to depend on a substratum function affecting mineral precipitation, collagen deposition, and cellular differentiation and proliferation.     

Hydroxyapatite-coated titanium for orthopedic implant applications

The interface mechanical characteristics and histology of commercially pure (CP) titanium- and hydroxyapatite- (HA) coated Ti-6Al-4V alloy were investigated. Interface shear strength was determined using a transcortical push-out model in dogs after periods of three, five, six, ten, and 32 weeks. Undecalcified histologic techniques with implants in situ were used to interpret differences in mechanical response. The HA-coated titanium alloy implants developed five to seven times the mean interface strength of the uncoated, beadblasted CP titanium implants. The mean values for interface shear strength increased up to 7.27 megaPascals (MPa) for the HA-coated implants after ten weeks of implantation, and the maximum mean value of interface shear strength for the uncoated CP titanium implants was 1.54 MPa. For both implant types there was a slight decrease in mean shear strength from the maximum value to that obtained after the longest implantation period (32 weeks). Histologic evaluations in all cases revealed mineralization of interface bone directly onto the HA-coated implant surface, with no fibrous tissue layer interposed between the bone and HA visible at the light microscopic level. The uncoated titanium implants had projections of bone to the implant surface with apparent direct bone-implant apposition observed in some locations. Measurements of the HA coating material made from histologic sections showed no evidence of significant HA resorption in vivo after periods of up to 32 weeks.     

The effect of different mineral frames on ectopic bone formation in mouse hind leg muscles induced by native reindeer bone morphogenetic protein

Introduction Bone morphogenetic proteins (BMPs) require carrier material for slow release and framing material for osteoconduction.Materials and methods The effect of a frame on early bone formation induced by partially purified native reindeer BMP in composite implants containing 3 mg of BMP, type IV collagen and tricalcium phosphate (TCP/Col/BMP) or hydroxyapatite (HA/Col/BMP) or biphasic tricalcium phosphate-hydroxyapatite (TCP/HA/Col/BMP) or biocoral (NC/Col/BMP) was evaluated using a mouse hind leg muscle pouch model. Collagen with native reindeer BMP (Col/BMP) and corresponding implants without native reindeer BMP served as controls. Evaluation was done by incorporation of ⁴⁵Ca, radiographically and histologically 3 weeks after the implantation.Results None of the implants without native reindeer BMP were able to induce new bone visible on radiographs. The area of new bone formation in the Col/BMP (p=0.026) and TCP/HA/Col/BMP (p=0.012) groups was significantly greater than in the TCP/Col/BMP group. The optical density of the new bone area was significantly greater in the TCP/HA/Col/BMP group than in the TCP/Col/BMP (p=0.036) or Col/BMP (p=0.02) groups. ⁴⁵Ca incorporation was many times greater in all the groups containing native reindeer BMP than in the corresponding groups without BMP. In the Col/BMP (p=0.046) and TCP/HA/Col/BMP (p=0.046) groups, ⁴⁵Ca incorporation was significantly greater than in the TCP/Col/BMP group. No significant differences were found in any parameters between HA/Col/BMP and NC/Col/BMP groups and the other BMP-containing groups.Conclusions Hydroxyapatite, biocoral and biphasic tricalciumphosphate-hydroxyapatite are equally good as framing material for native reindeer BMP, while tricalciumphosphate is somewhat worse. Osteoinduction of native reindeer BMP works well with collagen alone.     

Age-related changes in the fracture resistance of male Fischer F344 rat bone

In addition to the loss in bone volume that occurs with age, there is a decline in material properties. To test new therapies or diagnostic tools that target such properties as material strength and toughness, a pre-clinical model of aging would be useful in which changes in bone are similar to those that occur with aging in humans. Toward that end, we hypothesized that similar to human bone, the estimated toughness and material strength of cortical bone at the apparent-level decreases with age in the male Fischer F344 rat. In addition, we tested whether the known decline in trabecular architecture in rats translated to an age-related decrease in vertebra (VB) strength and whether non-X-ray techniques could quantify tissue changes at micron and sub-micron length scales. Bones were harvested from 6-, 12-, and 24-month (mo.) old rats (n = 12 per age). Despite a loss in trabecular bone with age, VB compressive strength was similar among the age groups. Similarly, whole-bone strength (peak force) in bending was maintained (femur) or increased (radius) with aging. There was though an age-related decrease in post-yield toughness (radius) and bending strength (femur). The ability to resist crack initiation was actually higher for the 12-mo. and 24-mo. than for 6-mo. rats (notch femur), but the estimated work to propagate the crack was less for the aged bone. For the femur diaphysis region, porosity increased while bound water decreased with age. For the radius diaphysis, there was an age-related increase in non-enzymatic and mature enzymatic collagen crosslinks. Raman spectroscopy analysis of embedded cross-sections of the tibia mid-shaft detected an increase in carbonate subsitution with advanced aging for both inner and outer tissue.     

Die Regenerationsfähigkeit des Beckenkammes nach Spongiosaentnahme beim Menschen—Induktion durch Phosphatkeramiken?

The starting point for the investigation of calciumphosphate ceramics is given by the bone regeneration, including osteoconduction, osteostimulation and osteoinduction. The amount of the autogenious bone, which can be used for transplantation to induce the organo typical regeneration, is a small one. Based on animal experiments we created a standardized model for investigation of bone regeneration, using the human iliac, crest. The empty iliac crest was filled by hydroxylapatite, tricalciumphosphate, Kiel bone or it remained empty as a control group. Clinical examination, X-ray control, blood chemistry and documentation were done with 104 patients devided in these four groups. Radiography, histological examination and morphometry were done with biopsies of 40 patients. The results show a bony ingrow into the ceramic material. The pores were filled by lamellar bone with new grown osteons. The ceramic granules are complete integrated. The ceramic blocks are only fixed at the edges and at the surface by bone trabeculae. The Kiel bone is surrounded by fibrous tissues without any contact to new built bone. It doesn't act as a bone substitute. The bone regeneration in the not fullfiled iliac crest was fast and of a hard quality of lamellar bone and of big amount. Both ceramics show remarkable degradation. The tricalciumphosphate brakes into pieces and shows dissolution. The hydroxylapatite in smaller particles. The degradation stopped, if the particles were surrounded by new bone. These ceramics can be used as augmentation material in combination with autogenious bone. They act as bone substitutes. The integration and bonding to new bone is complete and can be loaded by mechanical strength.