In vitro and in vivo evaluation of the effects of demineralized bone matrix or calcium sulfate addition to polycaprolactone–bioglass composites

The objective of this study was to improve the efficacy of polycaprolactone/bioglass (PCL/BG) bone substitute using demineralized bone matrix (DBM) or calcium sulfate (CS) as a third component. Composite discs involving either DBM or CS were prepared by compression moulding. Bioactivity of discs was evaluated by energy dispersive X-ray spectroscopy (ESCA) and scanning electron microscopy (SEM) following simulated body fluid incubation. The closest Calcium/Phosphate ratio to that of hydroxyl carbonate apatite crystals was observed for PCL/BG/DBM group (1.53) after 15 day incubation. Addition of fillers increased microhardness and compressive modulus of discs. However, after 4 and 6-week PBS incubations, PCL/BG/DBM discs showed significant decrease in modulus (from 266.23 to 54.04 and 33.45 MPa, respectively) in parallel with its highest water uptakes (36.3 and 34.7%). Discs preserved their integrity with only considerable weight loss (7.5–14.5%) in PCL/BG/DBM group. In vitro cytotoxicity tests showed that all discs were biocompatible. Composites were implanted to defects on rabbit humeri. After 7 weeks, new tissue formation and mineralization at bone-implant interface were observed for all implants. Bone mineral densities at interface were higher than that of implant site and negative controls (defects left empty) but lower than healthy bone level. However, microhardness of implant sites was higher than in vitro results indicating in vivo mineralization of implants. Addition of DBM or CS resulted with higher microhardness values at interface region (ca. 650 μm from implant) compared to PCL/BG and negative control. Histological studies revealed that addition of DBM enhanced bone formation around and into implant while CS provided cartilage tissue formation around the implant. From these results, addition of DBM or CS could be suggested to improve bone healing efficacy of PCL/BG composites.     

Preliminary<Emphasis Type="Italic">in vitro</Emphasis> and<Emphasis Type="Italic">in vivo</Emphasis> characterizations of a sol-gel derived bioactive glass-ceramic system

This study investigates quantitatively and qualitatively the sol-gel derived bioactive glass-ceramic system (BGS)—apatite-wollastonite (AW) type granules in the size range of 0.5–1 mm, as an effective graft material for bone augmentation and restoration. Scanning electron micrographs (SEM) of the sintered granules revealed the rough material surface with micropores in the range 10–30 μm. X-ray diffraction (XRD) pattern of the granules revealed the presence of crystalline phases of the hydroxyapatite and wollastonite, and the functional groups of the silicate and phosphates were identified by Fourier transform infrared spectroscopy (FT-IR). Thein vitro cell culture studies with L929 mouse fibroblast cell line showed very few cells adhered on the BGS disc after 24 h. This could be due to the highly reactive surface of the disc concomitant with the crystallization but not due to the cytotoxicity of the material, since the cellular viability (MTT assay) with the material was 80‰ Cytotoxicity and cytocompatibility studies proved that the material was non-toxic and biocompatible. After 12 weeks of implantation of the BGS granules in the tibia bone of New Zealand white rabbits, the granules were found to be well osteointegrated, as observed in the radiographs. Angiogram with barium sulphate and Indian ink after 12 weeks showed the presence of microcapillaries in the vicinity of the implant site implicating high vascularity. Gross observation of the implant site did not show any inflammation or necrosis. SEM of the implanted site after 24 weeks revealed good osteointegration of the material with the newly formed bone and host bone. New bone was also observed within the material, which was degrading. Histological evaluation of the bone healing with the BGS granules in the tibial defect at all time intervals was without inflammation or fibrous tissue encapsulation. After 2 weeks the new bone was observed as a trabeculae network around the granules, and by 6 weeks the defect was completely closed with immature woven bone. By 12 weeks mature woven bone was observed, and new immature woven bone was seen within the cracks of the granules. After 24 weeks the defect was completely healed with lamellar bone and the size of the granules decreased. Histomorphometrically the area percentage of new bone formed was 67.77% after 12 weeks and 63.37% after 24 weeks. Less bone formation after 24 weeks was due to an increased implant surface area contributed by the material degradation and active bone remodeling. The osteostimulative and osteoconductive potential of the BGS granules was established by tetracycline labelling of the mineralizing areas by 2 and 6 weeks. This sol-gel derived BGS granules proved to be bioactive and resorbable which in turn encouraged active bone formation.     

Design of dental implants,influence on the osteogenesis and fixation

The fixation and the bone ingrowth at the interface of porous cylindrical implants (total porosity of 37% and average pores diameter of 480 microm) were compared in vivo to rough cylindrical implants (R (a) = 5.3 microm), both of commercially pure titanium, made by powder metallurgy. The implants were inserted into the tibias of 20 rabbits and the animals were sacrificed 4 and 8 weeks after surgery. The percentage of bone-implant contact observed in porous implant was significantly larger than in the rough ones for all of sacrifice periods, respectively, 57% vs. 46% after 4 weeks, and 59% vs. 50% after 8 weeks. The mechanical tests showed a significant increase in the shear strength of the porous implants for the two analyzed periods, 4 and 8 weeks (14 and 20 MPa), when compared with rough ones (4 and 13 MPa). These results suggest that porous implants improve the contact at the implant-bone interface and increase the fixation to the bone, improving the osseointegration. Thus, the porous implant might be an alternative to dental implant in less favorable conditions, and appear to be better fixed to bone, offering promising alternatives.     

Bone ingrowth potential of electron beam and selective laser melting produced trabecular-like implant surfaces with and without a biomimetic coating

The bone ingrowth potential of trabecular-like implant surfaces produced by either selective laser melting (SLM) or electron beam melting (EBM), with or without a biomimetic calciumphosphate coating, was examined in goats. For histological analysis and histomorphometry of bone ingrowth depth and bone implant contact specimens were implanted in the femoral condyle of goats. For mechanical push out tests to analyse mechanical implant fixation specimens were implanted in the iliac crest. The follow up periods were 4 (7 goats) and 15 weeks (7 goats). Both the SLM and EBM produced trabecular-like structures showed a variable bone ingrowth after 4 weeks. After 15 weeks good bone ingrowth was found in both implant types. Irrespective to the follow up period, and the presence of a coating, no histological differences in tissue reaction around SLM and EBM produced specimens was found. Histological no coating was detected at 4 and 15 weeks follow up. At both follow up periods the mechanical push out strength at the bone implant interface was significantly lower for the coated SLM specimens compared to the uncoated SLM specimens. The expected better ingrowth characteristics and mechanical fixation strength induced by the coating were not found. The lower mechanical strength of the coated specimens produced by SLM is a remarkable result, which might be influenced by the gross morphology of the specimens or the coating characteristics, indicating that further research is necessary.     

In vivo osseointegration of dental implants with an antimicrobial peptide coating

This study aimed to evaluate the in vivo osseointegration of implants with hydrophobic antimicrobial GL13K-peptide coating in rabbit femoral condyles by micro-CT and histological analysis. Six male Japanese Rabbits (4 months old and weighing 2.5?kg each) were included in this study. Twelve implants (3.75?mm wide, 7?mm long) were randomly distributed in two groups, with six implants in the experimental group coated with GL13K peptide and six implants in the control group without surface coating. Each implant in the test and the control group was randomly implanted in the left or right side of femoral condyles. On one side randomly-selected of the femur, each rabbit received a drill that was left without implant as control for the natural healing of bone. After 3?weeks of healing radiographic evaluation of the implant sites was taken. After 6?weeks of healing, rabbits were sacrificed for evaluation of the short-term osseointegration of the dental implants using digital radiography, micro-CT and histology analysis. To perform evaluation of osseointegration, implant location and group was double blinded for surgeon and histology/radiology researcher. Two rabbits died of wound infection in sites with non-coated implants 2?weeks after surgery. Thus, at least four rabbits per group survived after 6?weeks of healing. The wounds healed without suppuration and inflammation. No implant was loose after 6?weeks of healing. Radiography observations showed good osseointegration after 3 and 6?weeks postoperatively, which proved that the tissues followed a natural healing process. Micro-CT reconstruction and analysis showed that there was no statistically significant difference (P?>?0.05) in volume of bone around the implant between implants coated with GL13K peptide and implants without coating. Histomorphometric analysis also showed that the mineralized bone area was no statistically different (P?>?0.05) between implants coated with GL13K peptide and implants without coating. This study demonstrates that titanium dental implants with an antimicrobial GL13K coating enables in vivo implant osseointegration at similar bone growth rates than gold-standard non-coated dental implants up to 6?weeks of implantation in rabbit femurs.     

Pre-treatment of titanium implants with fluoride improves their retention in bone

Fluoride pre-treatment of titanium improved the bone response to this material in the present study. Fluoride pre-treated titanium implants had a four times increased retention in rabbits ulna after four and eight weeks healing periods as measured by a push out technique. Scanning electron microscopic evaluation of the implants revealed that the F-treated implants were partly covered with bone after the push out procedure indicating that an internal fracture had occurred in the bone rather than between the bone and the implant. This was not observed in the titanium control group. It is suggested that the presence of a fluoride coat on the surface of titanium implants stimulates the bone response leading to a connection between titanium and phosphate from tissue fluids. Free fluoride ions will catalyse this reaction and induce the formation of fluoridated hydroxyapatite and fluorapatite in the surrounding bone.     

In vivo study of degradable magnesium and magnesium alloy as bone implant

In order to investigate the in vivo behavior of pure magnesium and AZ31B and the influence of mineralization induction ability, sample rods were implanted intramedullary into the femora of rabbits. After one and nine weeks, six animals from each group were sacrificed, respectively. Undecalcified cross-sections of implant were performed to observe bone-implant by scanning electron microscopy (SEM) and energy dispersive spectromicroscopy (EDS). The SEM/EDS evaluation showed that there is a thin layer of bone around magnesium and its alloy after nine-week implantation. The results further showed that the aluminum-zinc containing magnesium alloys AZ31B provided a slower degradation rate in vivo than the pure magnesium. At the locations where magnesium was resorbed, the deposition of new bone was found. The results indicate that magnesium is biocompatible, osteo-conductive and is a potential material for use as a degradable bone implant.     

No biological advantage with a low temperature curing versus a conventional bone cement: an experimental, mechanical and histomorphometrical study in the rabbit tibia

Both tibial marrow cavities of 12 rabbits were evacuated and filled with curing bone cement. In one of the tibias conventional curing bone cement (Simplex P®) was injected, while the other tibia of the same animal was filled with a low temperature curing bone cement (Boneloc®). Three titanium implants were inserted along the proximal metaphysis of each tibia. Eight weeks after insertion the most distal implant in each tibia was removed while recording the removal torque. The implant was then once again screwed home into its bone bed. The animals were sacrificed 16 weeks after implant insertion. The previously removed implant and another implant in each tibia were then both removed while recording the removal torque. The third implant in each tibia was cut out en bloc with surrounding tissue and processed for ground section. We found no statistical differences in the mechanical or the histomorphometric evaluation of implant integration between the two cements, indicating that the low temperature curing bone cement does not result in a significantly different bone response from that of a conventional acrylic cement. ©©1999©Kluwer Academic Publishers     

Healing of titanium implants in onlay bone grafts: an experimental rabbit model

An experimental rabbit bone graft model for the study of bone formation and remodeling around titanium implants is described. A 2.5-cm long radius bone segment served as an onlay graft. Two commercially pure (c.p.) titanium implants were inserted into the bone graft prior to fixation to the inferior border of the mandibular base with osteosynthesis titanium screws. Each animal was operated twice, allowing follow-up periods of 6 weeks on one side and 6 months on the contralateral side. In order to study bone remodeling by means of fluoroscopy the animals received single injections of tetracyclin and alizarine complexone 2 weeks and 1 week, respectively, prior to sacrifice by perfusion fixation with glutaraldehyde. The bone and implants were excized en bloc, postfixed and embedded in plastic resin. Stained and unstained thin ground sections as well as microradiographed thick sections were produced for light microscopic morphometry and fluoroscopy. After 6 weeks, osteoclastic/osteoblastic activity was primarily observed in the graft-recipient contact area and in the intracortical compartment of the graft bone. New bone formation observed on the implant surface originated from the recipient site. The bone formation was evident also in the implant-graft interface. At 6 weeks the average bone fill of the implant threads was 28.4% which increased to 36.4% after 6 months as measured by morphometry. An average of 17.6% bony contact was measured after 6 weeks which increased to 29.7% 6 months after surgery. The graft bone had reduced in size from an average of 39.5% after 6 weeks down to 24.8% after 6 months (P < 0.05). It is concluded that the described experimental model can serve as a useful method for the study of implant healing in onlay grafts.     

Bone regeneration potential of a soybean-based filler: experimental study in a rabbit cancellous bone defects

Autologous and allogenic bone grafts are considered as materials of choice for bone reconstructive surgery, but limited availability, risks of transmittable diseases and inconsistent clinical performances have prompted the development of alternative biomaterials. The present work compares the bone regeneration potential of a soybean based bone filler (SB bone filler) in comparison to a commercial 50:50 poly(d,l lactide–glycolide)-based bone graft (Fisiograft^® gel) when implanted into a critical size defect (6-mm diameter, 10-mm length) in rabbit distal femurs. The histomorphometric and microhardness analyses of femoral condyles 4, 8, 16 and 24 weeks after surgery showed that no significant difference was found in the percentage of both bone repair and bone in-growth in the external, medium and inner defect areas. The SB filler-treated defects showed significantly higher outer bone formation and microhardness results at 24 weeks than Fisiograft^® gel (P < 0.05). Soybean-based biomaterials clearly promoted bone repair through a mechanism of action that is likely to involve both the scaffolding role of the biomaterial for osteoblasts and the induction of their differentiation.     

Assessment of bone ingrowth potential of biomimetic hydroxyapatite and brushite coated porous E-beam structures

The bone ingrowth potential of biomimetic hydroxyapatite and brushite coatings applied on porous E-beam structure was examined in goats and compared to a similar uncoated porous structure and a conventional titanium plasma spray coating. Specimens were implanted in the iliac crest of goats for a period of 3 (4 goats) or 15 weeks (8 goats). Mechanical implant fixation generated by bone ingrowth was analyzed by a push out test. Histomorphometry was performed to assess the bone ingrowth depth and bone implant contact. The uncoated and hydroxyapatite-coated cubic structure had significantly higher mechanical strength at the interface compared to the Ti plasma spray coating at 15 weeks of implantation. Bone ingrowth depth was significantly larger for the hydroxyapatite- and brushite-coated structures compared to the uncoated structure. In conclusion, the porous E-beam surface structure showed higher bone ingrowth potential compared to a conventional implant surface after 15 weeks of implantation. Addition of a calcium phosphate coating to the E-beam structure enhanced bone ingrowth significantly. Furthermore, the calcium phosphate coating appears to work as an accelerator for bone ingrowth.     

磷灰石陶瓷的制备、性能及其应用

本文探讨了以两种磷酸三钙为原料、采用简便的制陶工艺制成的磷灰石。研究结果表明,原料的分散细度对制品的各项性能有重要的影响。其次,选择适当的烧成温度亦是关健之一。在动物实验中,对六条狗进行了皮下、骨膜下及骨内种植实验,所得结论认为磷灰石是一种生物可容性种植材料,促进骨质生长和新骨形成。在动物实验的基础上对30名重症牙周炎患者作植入手术,并与单纯采用翻瓣手术的作了比较,结果表明,磷灰石植入手术显然比单纯牙龈翻瓣手术优越。     

In vivo study of degradable magnesium and magnesium alloy as bone implant

In order to investigate the in vivo behavior of pure magnesium and AZ31B and the influence of mineralization induction ability, sample rods were implanted intramedullary into the femora of rabbits. After one and nine weeks, six animals from each group were sacrificed, respectively. Undecalcified cross-sections of implant were performed to observe bone-implant by scanning electron microscopy (SEM) and energy dispersive spectromicroscopy (EDS). The SEM/EDS evaluation showed that there is a thin layer of bone around magnesium and its alloy after nine-week implantation. The results further showed that the aluminum-zinc containing magnesium alloys AZ31B provided a slower degradation rate in vivo than the pure magnesium. At the locations where magnesium was resorbed, the deposition of new bone was found. The results indicate that magnesium is biocompatible, osteo-conductive and is a potential material for use as a degradable bone implant.     

Bioactive TiOB‐Coating on Titanium Alloy Implants Enhances Osseointegration in a Rat Model

The surface properties of titanium alloy implants for improved osseointegration in orthopaedic and dental surgery have been modified by many technologies. Hydroxyapatite coatings with a facultative integration of growth factors deposited by plasma spraying showed improved osseointegration. Our approach in order to enhance osseointegration was carried out by a surface modification method of titanium alloy implants called plasma chemical oxidation (PCO). PCO is an electrochemical procedure that converts the nm‐thin natural occurring titanium‐oxide layer on an implant to a 5 µm thick ceramic coating (TiOB‐surface). Bioactive TiOB‐surfaces have a porous microstructure and were loaded with calcium and phosphorous, while bioinert TiOB‐surfaces with less calcium and phosphorous loadings are smooth. A rat tibial model with bilateral placement of titanium alloy implants was employed to analyze the bone response to TiOB‐surfaces in vivo. 64 rats were randomly assigned to four groups of implants: (i) pure titanium alloy (control), ii) titanium alloy, type III anodization, (iii) bioinert TiOB‐surface, and (iv) bioactive TiOB‐surface. Mechanical fixation was evaluated by pull out tests at 3 and 8 weeks. The bioactive TiOB‐surface showed significantly increased shear strength at 8 weeks compared to all other groups.     

Tissue reaction against a self-setting calcium phosphate cement set in bone or outside the organism

Calcium phosphate cements are able to set in situ when injected into bone tissue. We evaluated the tissue reaction occurring when a DCPD-based calcium phosphate cement was either set within the bone or implanted when already set. The samples were implanted in rabbit condyles and examined histologically after 8 and 16 weeks. The relative bone surface, the fibrous capsule around the implants and the implant section surface were measured. Solid material seemed to be better tolerated than paste implants. More bone was found at the solid implant contact whatever the implantation time and the solid material degraded much less rapidly. In conclusion, the physico-chemical modification of the biological environment occurring during setting increases the foreign body reaction against the material.     

An animal study on the bone behaviour of Ca–P-coated implants: influence of implant location

Four different implant materials were installed into the mandibular corner of goats to investigate the trabecular bone response in a mainly unloaded model. The implants were installed using a standardized technique and were left in situ for 12 weeks. One goat had to be sacrificed after surgery because of a broken rib; the other animals healed uneventfully. After sacrifice of the animals, the bone response to the uncoated and the three different Ca–P implants was evaluated histologically and histomorphometrically. Four sections of each implant were evaluated; two were located in the cortical and two in the trabecular bone. Of the 44 retrieved implants, 20 implants appeared to be installed partially in the mandibular canal, as clearly visible on the X-rays. These implants were not used in the histomorphometrical measurements. Histological evaluation showed that the trabecular and cortical bone reactions were similar; there was no significant difference in the percentage of bone contact nor in the amount of bone in contact with the implants. In conclusion this study showed that the mandibular corner is an unsatisfactory model for the installation of implants because of anatomical restrictions. Also, the experiment remained inconclusive about the influence of loading conditions on bone behaviour. Nevertheless, the histological results confirmed the bioactive properties of Ca–P coatings.     

Evaluation of the biocompatibility of two magnesium alloys as degradable implant materials in comparison to titanium as non‐resorbable material in the rabbit

The aim of this study is to compare the biocompatibility of the two magnesium based alloys LAE442 and LANd442 with that of titanium. For this purpose, cylindrical implants were introduced into the medullary cavity of rabbit's tibiae for 4 and 8 weeks. Animals without any implant served as a control. In the follow-up, clinical, X-ray and μCT-investigations were performed to evaluate the reactions of the bone towards the implanted materials. After euthanasia, ex vivo μCT- and histological investigations were performed to verify the results of the in vivo tests. It could be shown that all materials induce changes in the bone. Whereas LANd442 caused the most pronounced reactions, such as increasing bone volume and bone porosity and decreasing bone density, titanium showed the most bone–implant contact by forming trabeculae. The tibiae of rabbits without implants also reacted by forming cavities, it is therefore assumed that the surgery method itself influences the bone.     

Tissue response to hafnium

The aim of the present experimental study was to evaluate the tissue response to hafnium (Hf) a reactive metal closely related to titanium (Ti) and zirconium (Zr). Hf has not been previously evaluated as implant material in a biologic environment. In a first experiment, 21 machined Hf non-threaded implants (test) and 21 similar Ti implants (control) were inserted in the abdominal wall of 21 rats. Animals were sacrificed after 8 days (6 rats), 6 (7 rats) and 12 weeks (8 rats). In a second experiment, 18 rabbits received 18 Hf and 18 Ti threaded implants in their tibiae, one implant in each tibia. The rabbits were sacrificed after 6, 12 and 24 weeks (6 animals/time interval). The bulk metal of the abdominal wall implants, embedded together with the surrounding tissue, was electrolytically dissolved and semithin (1 m) sections of the intact tissue–implant interface were evaluated by light microscopy (morphometry). Bone-implant contact and bone area within threads were evaluated in ground sections. In soft tissues, a fluid space containing predominantly monocytes/macrophages surrounded the abdominal implants at 8 days. At 6 and 12 weeks, a fibrous capsule, consisting of layers of macrophages and fibroblasts, surrounded the implants. Macrophages, including multinuclear giant cells, always formed the innermost layer in contact with the implant surface. No quantitative or qualitative difference in the tissue organization was detected between Ti and Hf implants. In rabbits, 6 weeks after insertion, the proximal two threads located within the cortical bone were filled with bone in contact with Hf and Ti. The distal threads contained bone marrow. After 12 and 24 weeks, mature bone was present in the proximal 3–4 implant threads. No statistically significant difference was found between Hf and Ti implants at any time periods. It is concluded that Hf is an interesting metal for biomedical applications in bone and soft tissue. © 2001 Kluwer Academic Publishers     

In vivo studies of the ceramic coated titanium alloy for enhanced osseointegration in dental applications

This paper reports the effect of the various ceramic coatings viz., hydroxyapatite (HA) and partially stabilized zirconia (PSZ) on the bond strength between the bone and implant, and cell compatibility of screw-shaped Ti-6Al-7Nb dental implants. Electrophoretic deposition technique (EPD) was used to obtain a uniform coating of one of the three types of ceramic layers (HA, PSZ and 50%HA + 50%PSZ) on the screws. Structural investigations were carried out on the prepared HA powder and the modified surfaces of the Ti-6Al-7Nb alloy using different techniques, namely X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The in vivo studies were performed by the implantation of screw-shaped uncoated and coated implants in the tibia of white New Zealand rabbits. To understand the bone-implant interface, biomechanical test was carried out after 2, 6 and 18 weeks healing periods. There was increased mechanical strength (torque value) of bone-implant interface with time, and the highest increment in the bond strength was recorded for implants coated with a 50% HA and 50% PSZ. Histological results show that the coated Ti-6Al-7Nb screws after 18 weeks of the implantation seem to be well-tolerated by the bone since no adverse tissue reaction was evident. However, there was a faster reaction of bone towards the coated implants compared to the uncoated one. The histochemical stain studies shows higher cellular activity and mature bone formation on all the samples.     

Histological and microradiographic appearances of Silicon Nitride and Aluminum Oxide in a rabbit femur implantation model*

Silicon nitride (Si₃N₄) is a ceramic known for its high performance characterized by fracture toughness, high wear resistance and low coefficient of friction. It has therefore been considered as a biomaterial especially for orthopaedic and dental indications. There is a controversy concerning the biocompatibility among the limited number of authors dealing with this material. Own investigations, applying the L929‐fibroblast cell culture model revealed good biocompatibilty. The aim of this study is to verify these findings in the animal model. 36 cylinders of Si₃N₄ and the established biomaterial aluminum oxide (Al₂O₃) were implanted “press fit” into the lateral condyli of the femurs of 6 New Zealand white male rabbits (three implants per condylus, materials randomized). The right femur of each animal was prepared for microradiographs and grounded sections, the left for histological sections, respectively. Animals were divided into 2 groups with 3 rabbits each. One group was sacrificed after a period of 4 weeks and the other after 8 weeks. Morphometric assessment of bone‐implant attachment was performed using a digital image analyzing system. Percentages of bone‐implant attachment ranged from 44 to 82 %. There was no statistically different percentage of bone‐implant attachment between Al₂O₃ and Si₃N₄ after 4 and 8 weeks, except in the histological section after 8 weeks of implantation. During the period of 4 to 8 weeks after implantation there was no significant decrease of bone‐implant contact except for Al₂O₃ in the histological sections. No local or generalized immuno‐inflammatory reactions were observed. The lamellar bone in direct contact to the materials showed no histological evidence of round cell infiltration or giant cell reactions. Our investigations suggest that Si₃N₄ shows good biocompatibility and presumably even better osseointegration than Al₂O₃.