Osteogenesis at the dental implant interface: high-voltage electron microscopic and conventional transmission electron microscopic observations

Three Dimensional Printing and Biomaterials in the Repairment of Bone Defects; Hydroxyapatite PLA Filaments

Background/aim

Application fields of bone tissue engineering studies continue to expand. New biocompatible materials aimed to improve bone repairment and regeneration of implants are being discovered everyday by scientists, engineers, and surgeons. Our objective in this study is to combine polylactic acid which is a polymer with hydroxyapatite in the repairment of bone defects considering the increased need by medical application fields.

Materials and methods

After 750 g of PLA with a diameter of 2.85 mm was granulated into minimum particles, these particles were homogenously mixed with hydroxyapatite prepared in laboratory environment. Using this mixture, HA-PLA filament with a diameter of 2.85 mm was prepared in the extrusion device in Kütahya Medical Sciences University Innovative Technology Laboratory. The temperature was 250 °C and the gearmotor speed was 9 rpm during extrusion. X-ray diffraction (XRD) analysis was made for crystal phase analyses of the produced hydroxyapatite powder, to determine the produced main phase and examine whether a minor phase occurred. Vickers microhardness test was applied on both samples to measure the endurance levels of the samples prepared with HA-PLA filament. A loading force of 10 kg was applied on the samples for 10 s.

Results

Hydroxyapatite peaks in XRD spectrum of the sample presented in figures are concordant with Joint Committee on Powder Diffraction Standards, JCPDS - File Card No. 01-075-9526 and no significant minor phase was observed. For both samples, hardness value was observed to increase between 3 and 5 mm.

Conclusion

Surfacing hydroxyapatite on metallic materials is possible. By similar logic, to increase durability with low cost, characteristics of biomaterials can be improved with combinations such as hydroxyapatite PLA. Thus, we found that while these materials have usage limitations due to present disadvantages when used alone, it is possible to increase their efficiency and availability through different combinations.

Osseointegration and current interpretations of the bone-implant interface

Complex physical and chemical interactions take place in the interface between the implant surface and bone. Various descriptions of the ultrastructural arrangement to various implant design features, ranging from solid and macroporous geometries to surface modifications on the micron-, submicron-, and nano- levels, have been put forward. Here, the current knowledge regarding structural organisation of the bone-implant interface is reviewed with a focus on solid devices, mainly metal (or alloy) intended for permanent anchorage in bone. Certain biomaterials that undergo surface and bulk degradation are also considered. The bone-implant interface is a heterogeneous zone consisting of mineralised, partially mineralised, and unmineralised areas. Within the meso-micro-nano-continuum, mineralised collagen fibrils form the structural basis of the bone-implant interface, in addition to accumulation of non-collagenous macromolecules such as osteopontin, bone sialoprotein, and osteocalcin. In the published literature, as many as eight distinct arrangements of the bone-implant interface ultrastructure have been described. The interpretation is influenced by the in vivo model and species-specific characteristics, healing time point(s), physico-chemical properties of the implant surface, implant geometry, sample preparation route(s) and associated artefacts, analytical technique(s) and their limitations, and non-compromised vs compromised local tissue conditions. The understanding of the ultrastructure of the interface under experimental conditions is rapidly evolving due to the introduction of novel techniques for sample preparation and analysis. Nevertheless, the current understanding of the interface zone in humans in relation to clinical implant performance is still hampered by the shortcomings of clinical methods for resolving the finer details of the bone-implant interface. STATEMENT OF SIGNIFICANCE: Being a hierarchical material by design, the overall strength of bone is governed by composition and structure. Understanding the structure of the bone-implant interface is essential in the development of novel bone repair materials and strategies, and their long-term success. Here, the current knowledge regarding the eventual structural organisation of the bone-implant interface is reviewed, with a focus on solid devices intended for permanent anchorage in bone, and certain biomaterials that undergo surface and bulk degradation. The bone-implant interface is a heterogeneous zone consisting of mineralised, partially mineralised, and unmineralised areas. Within the meso-micro-nano-continuum, mineralised collagen fibrils form the structural basis of the bone-implant interface, in addition to accumulation of non-collagenous macromolecules such as osteopontin, bone sialoprotein, and osteocalcin.

Biocompatibility of Titania Nanotube Coatings Enriched with Silver Nanograins by Chemical Vapor Deposition

Bioactivity investigations of titania nanotube (TNT) coatings enriched with silver nanograins (TNT/Ag) have been carried out. TNT/Ag nanocomposite materials were produced by combining the electrochemical anodization and chemical vapor deposition methods. Fabricated coatings were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The release effect of silver ions from TNT/Ag composites immersed in bodily fluids, has been studied using inductively coupled plasma mass spectrometry (ICP-MS). The metabolic activity assay (MTT) was applied to determine the L929 murine fibroblasts adhesion and proliferation on the surface of TNT/Ag coatings. Moreover, the results of immunoassays (using peripheral blood mononuclear cells-PBMCs isolated from rats) allowed the estimation of the immunological activity of TNT/Ag surface materials. Antibacterial activity of TNT/Ag coatings with different morphological and structural features was estimated against two Staphylococcus aureus strains (ATCC 29213 and H9). The TNT/Ag nanocomposite layers produced revealed a good biocompatibility promoting the fibroblast adhesion and proliferation. A desirable anti-biofilm activity against the S. aureus reference strain was mainly noticed for these TiO₂ nanotube coatings, which contain dispersed Ag nanograins deposited on their surface.

Biomechanical and histological evaluation of the osseointegration capacity of two types of zirconia implant

The purpose of this study was to evaluate the biomechanical and histological behavior of a ceria-stabilized zirconia-alumina nanocomposite (NanoZr) in comparison with that of 3 mol% yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) in Sprague Dawley rats. Cylindrical NanoZr and 3Y-TZP implants (diameter 1 mm, length 2 mm) were used. Implant-surface morphology and surface roughness were determined by scanning white-light interferometry and scanning electron microscopy, respectively. The cylindrical zirconia implants were placed at the distal edge of the femur of Sprague Dawley rats. At weeks 2, 4, and 8, the interfacial shear strength between implant and bone was measured by push-in test. Histological analysis was performed using hard-tissue sections. Bone-implant contact (BIC), the thickness of new bone around the implant within the bone marrow area, and osteoclast numbers were evaluated. The average surface roughness of 3Y-TZP (Sa 0.788 μm) was significantly higher than that of NanoZr (Sa 0.559 μm). The shear strengths of 3Y-TZP and NanoZr were similar at 2 weeks, but at 4 and 8 weeks the shear strength of NanoZr was higher than that of 3Y-TZP. The average BIC values within the bone marrow area for 3Y-TZP and NanoZr were 25.26% and 31.51% at 2 weeks, 46.78% and 38% at 4 weeks, and 47.88% and 56.81% at 8 weeks, respectively. The average BIC values within the cortical area were 38.86% and 58.42% at 2 weeks, 66.82% and 57.74% at 4 weeks, and 79.91% and 78.97% at 8 weeks, respectively. The mean BIC value did not differ significantly between the two zirconia materials at any time point. The NanoZr implants were biocompatible, capable of establishing close BIC, and may be preferred for metal-free dental implants.

Characteristics of Micro-Arc Treated Osseointegrated Porous Hydroxyapatite/Titanium Dioxide Coatings on Titanium Metal

A rapid and sufficient osseointegrating functions is obviously essential to the patients who suffered the bone reconstruction period. In order to perfectly target this issue, a single-stage micro-arc treated (MAT) coating beneficial from its inherent porous morphologies with controllable pore sizes, strong adhesive force between coatings and substrate and wide selections in electrolytes, is considered. Hydroxyapatite is extensively utilized and identified as mimic composition to human bone and an active bone ingrowth function. However, a controllable high-purity HAp phase via one-stage MAT has not yet been achieved. This study therefore prepares high-purity HAp coatings using one-stage MAT with the electrolyte combination of Calcium acetate and sodium biphosphate dihydrate on a titanium surface through a systematical evaluation of various MAT parameters, including Ca/P ratios of the electrolyte, electrolyte concentrations, working voltages, and treatment periods. Analytical results show that high-purity HAp can grow at a relatively high Ca/P ratio and electrolyte concentration when combined with a relatively high working voltage and long treatment time, which would otherwise grow with CaTiO3 and/or anatase TiO2 and/or rutile TiO2 simultaneously. Additionally, CaTiO3 acts a precursor phase for HAp formation. Ultimately, the highest purity of HAp coating is obtainable on metal titanium using a Ca/P ratio = 2.16 and applying a working voltage of 450 V for 10 min using one-stage MAT. This highest purity of HAp coating also presents excellent level of Ecorr than that on raw Ti alloys. The high Ecorr of HAp coating contributed from its thick and dense oxide layer by working voltage via one-stage MAT, consequently promises its satisfactory protection. The HAp coating demonstrated in this study not only provides the effective approach to produce the desired purity of HAp coatings but compromises its resistance to SBF. The bioactive HAp coating on Ti alloys via one-stage MAT, thus, considers as one significant surface modification for artificial hip joints and dental implants.

Plasma electrolytic oxidation of titanium and improvement in osseointegration

Reducing the osseointegration time for biomedical titanium implants in surgical patients is an important goal. However, a huge controversy exists over the effectiveness of osseointegration of the surface layer by plasma electrolytic oxidation (PEO), which is a widely favored surface modification for titanium-based implants. In this study, various surface coatings, including anatase-TiO2 (A-TiO2 ), rutile-TiO2 (R-TiO2 ), hydroxyapatite (HAp), strontium-containing hydroxyapatite (Sr-HAp), and dual-phase HAp-TiO2 were synthesized on titanium implants by PEO. A comparative study of osseointegration performance (both in vitro and in vivo) and bone/implant adhesion strength conducted using push-out thrust tests were demonstrated. The in vitro experimental test results agree strongly with the in vivo test results: the dual-phase HAp-TiO2 coating exhibits the superior cell adhesion and differentiation condition among all of the coatings in the in vitro tests and therefore has the highest push-out bonding strength of 5.37 MPa after 12 wk of implantation in the in vivo test. The HAp-containing coatings benefit from its bioactivity and therefore perform the others in terms of long-term osteocyte growth (from the in vitro results) and the extent of osseointegration (from the in vivo results). The dual-phase HAp-TiO2 coating provides the advantages of both the bioactive HAp and structural enhancement by the TiO2 , effectively promoting osseointegration.

TiO2 nanotubes on Ti: Influence of nanoscale morphology on bone cell-materials interaction

Ti being bioinert shows poor bone cell adhesion with an intervening fibrous capsule. Ti could be made bioactive by several methods including growing in situ TiO2 layer on Ti-surface. TiO2 nanotubes were grown on Ti surface via anodization process and the bone cell-material interactions were evaluated. Human osteoblast cell attachment and growth behavior were studied using an osteoprecursor cell line for 3, 7, and 11 days. An abundant amount of extracellular matrix (ECM) between the neighboring cells was noticed on anodized nanotube surface with filopodia extensions coming out from cells to grasp the nanoporous surface of the nanotube for anchorage. To better understand and compare cell-materials interactions, anodized nanoporous sample surfaces were etched with different patterns. Preferential cell attachment was noticed on nanotube surface compare to almost no cells in etched Ti surface. Cell adhesion with vinculin adhesive protein showed higher intensity, positive contacts on nanoporous surface and thin focal contacts on the Ti-control. Immunochemistry study with alkaline phosphatase showed enhanced osteoblastic phenotype expressions in nanoporous surface. Osteoblast proliferation was significantly higher on anodized nanotube surface. Surface properties changed with the emergence of nanoscale morphology. Higher nanometer scale roughness, low contact angle and high surface energy in nanoporous surface enhanced the osteoblast-material interactions. Mineralization study was done under simulated body fluid (SBF) with ion concentration nearly equal to human blood plasma to understand biomimetic apatite deposition behavior. Although apatite layer formation was noticed on nanotube surface, but it was nonuniform even after 21 days in SBF.

Maxillary sinus augmentation with Bio-Oss particles: a light, scanning, and transmission electron microscopy study in man

Biological interactions occurring at the bone-biomaterial interface are critical for long-term clinical success. Bio-Oss is a deproteinized, sterilized bovine bone that has been extensively used in bone regeneration procedures. The aim of the present study was a comparative light, scanning, and electron microscopy evaluation of the interface between Bio-Oss and bone in specimens retrieved after sinus augmentation procedures. Under light microscopy, most of the particles were surrounded by newly formed bone, while in a few cases, at the interface of some particles it was possible to observe marrow spaces and biological fluids. Under scanning electron microscopy, in most cases, the particle perimeter appeared lined by bone that was tightly adherent to the biomaterial surface. Transmission electron microscopy showed that the bone tissue around the biomaterial showed all the phases of the bone healing process. In some areas, randomly organized collagen fibers were present, while in other areas, newly formed compact bone was present. In the first bone lamella collagen fibers contacting the Bio-Oss surface were oriented at 243.73 +/- 7.12 degrees (mean +/- SD), while in the rest of the lamella they were oriented at 288.05 +/- 4.86 degrees (mean +/- SD) with a statistically significant difference of 44.32 degrees (p < 0.001). In the same areas the intensity of gray value was 172.56 +/- 18.15 (mean +/- SD) near the biomaterial surface and 158.71 +/- 21.95 (mean +/- SD) in the other part of the lamella with an unstatistically significant difference of 13.79 (p = 0.071). At the bone-biomaterial interface there was also an electron-dense layer similar to cement lines. This layer had a variable morphology being, in some areas, a thin line, and in other areas, a thick irregular band. The analyses showed that Bio-Oss particles do not interfere with the normal osseous healing process after sinus lift procedures and promote new bone formation. In conclusion, this study serves as a better understanding of the morphologic characteristics of Bio-Oss and its interaction with the surrounding tissues.

Enhanced bone integration of implants with increased surface roughness: a long term study in the sheep

OBJECTIVES

This study evaluated the quality and the remodeling of bone around commercially pure titanium implants after 3, 6, 12 and 18 month implantation periods in the sheep.

METHODS

Twelve animals were implanted in the cortico-trabecular areas of both femurs. Each femur received four implants with a rough surface (type 1) in the right femur and four with a smooth surface (type 2) in the left one. Bone blocks containing the implants were studied by histomorphometry on undecalcified specimens. The amount of bone around implants was measured (bone volume, fractional woven bone volume, bone thickness, contact interface) together with osteoblastic activity (mineral apposition rates, bone formation rates) and resorption activity (eroded surfaces).

RESULTS

No significant differences could be observed for the two types of implants between 3 and 6 months. At 12 and 18 months, bone volume and contact interface were still increasing and there was always a tendency for type 1 implants to be associated with higher values. On the contrary, mineral apposition rate, bone formation rates and eroded surfaces decreased in the referent area in contact with the implant; this phenomenon of 'return to the normal' was more evident with type 1 implants. The remodeling process appears to increase bone quality and bone-titanium interface around implants in long term periods.

CONCLUSIONS

The net bone quantity necessary to immobilize implants is obtained rapidly but the adapting process to mechanical strength can lead to a small but persistent increase in bone volume around implants. Although the differences between type 1 and type 2 implants were often small or statistically insignificant, the rougher type 1 implants seemed to be associated with stronger bone response.

Improvement of bioactivity of H(2)O(2)/TaCl(5)-treated titanium after subsequent heat treatments

Commercially pure titanium was treated with a H(2) O(2)/3mM TaCl(5) solution at 80 degrees C for various periods and a titania gel layer was formed on the surface. This gel remained amorphous when heating for 1 h below 200 degrees C and transformed to anatase after heating between 300 degrees and 600 degrees C. The anatase titania gel layers were found to be bioactive as to deposit carbonate ion-incorporated apatite within 1 day of immersion in the Kokubo solution, whereas the amorphous layers did not deposit apatite within 7 days. The apatite particles were found to nucleate preferentially inside the cracks prevailing in the thicker gel layers of 1-h chemically treated specimens. After immersing for 2 days, the titanium specimens were almost completely covered by apatite. Elimination of peroxide radicals from the titania gel and formation of anatase upon subsequent heating are considered to be responsible for the enhanced ability of apatite deposition.

Surface roughness parameters as predictors of anchorage strength in bone: a critical analysis

The surface roughness of a bone implant was defined parametrically. The values of the parameters defining the surface were varied. Some traditionally used surface roughness parameters were calculated. By means of a theoretical model the bone-implant interfacial shear strength was estimated. No simple correlation between the values of the surface roughness parameters and the estimated interfacial shear strength was found. It was concluded that the value of the traditional surface roughness parameters as predictors of interfacial shear strength is limited. If however a change of the surface topography of an implant is restricted to scale a positive correlation was found between the theoretical interfacial shear strength and some surface roughness parameters. It is suggested that the bone-implant interfacial shear strength in the general case be estimated by means of strength analyses based upon a study of the size, shape and density of the individual elements constituting the rough surface.

Tissue response to titanium implants in the rat maxilla: ultrastructural and histochemical observations of the bone-titanium interface

BACKGROUND

The detailed mechanism of osseointegration, the most appropriate implant-bone interface, remains unclear in jaw tissues at the ultrastructural level in contrast to the many reports using long bones. The present study reports on tissue response to titanium-implantation on an animal model using rat maxilla.

METHODS

Animals were sacrificed at 1 to 28 days post-implantation and prepared tissue specimens, freed from implants by a cryofracture technique, were processed for transmission electron microscopy and histochemistry for tartrate resistant acid phosphatase activity (TRAPase).

RESULTS

Different patterns in bone formation were recognized between lateral and base areas of implant cavities. In the lateral area with narrow gaps, bone deposition took place from the pre-existing bone towards the implant after active bone resorption by osteoclasts reactive to TRAPase. However, no distinct bone formation appeared in the lateral area where the implant had been installed close to the osteotomy margin. On the other hand, new bone formation was found at the base area without any apparent bone resorption. Interestingly, mononuclear cells reactive to TRAPase, presumably preosteoclasts, frequently occurred near preosteoblasts. Osseointegration around the implants was obtained in this model by 28 days post-implantation except for the lateral area with complete contact with implants, where the thin layer remained in contact with the implant surface.

CONCLUSIONS

These findings indicate that ossification proceeds at different modes around the titanium implant in rat maxilla, depending on the nature of the recipient bones and the dimension of the gap between the implant and osteotomy margin.

The relation between surface roughness and interfacial shear strength for bone-anchored implants. A mathematical model

A rough bone implant surface was conceptualized as being built up of pits of different sizes and of different shapes. Hypotheses were formulated regarding the mechanical strength of the interfacial bone based upon the present knowledge of the character of the tissues adjacent to endosseous implants and the mechanical characteristics of different bone constituents. A surface roughness parameter was derived, the pit effectivity factor (fpe), which describes how effective the individual pits of the rough surface are as retention elements with regard to shear. Another surface roughness parameter was defined, the pit density factor (fpd), the value of which depends upon how densely packed the pits are. The interfacial shear strength of a rough implant surface with known microgeometry can be estimated by means of these two surface roughness parameters. The effectiveness of pits of different sizes and of different shapes was investigated using this model.

The biologic tissue responses to uncoated and coated implanted biomaterials

Ultrastructural examination of the morphology and morphometry of the bone supporting uncoated titanium and ceramic implants was assessed in an experimental animal model involving 120 implants placed into the mandibles of 30 adult mongrel dogs. Further, preliminary morphologic and morphometric observations of the bone supporting uncoated and hydroxylapatite-coated endosteal titanium implants was evaluated in a second investigation involving 72 implants placed into the mandibles and maxillae of 6 additional dogs. A densely mineralized collagen fiber matrix was observed directly interfacing with uncoated implants. The only material interposed between the implant and bone matrix was a 20- to 50-nm electron-dense material suggestive of a proteoglycan. Also seen in these same osseointegrated implants were narrow unmineralized zones interposed between the implant and bone matrix. In these zones of remodeling bone, numerous osteoblasts were observed interacting with the collagen fiber matrix. It was shown that a normal homeostasis of anabolic osteoblastic activity and catabolic osteoclastic activity resulted in bone remodeling and the resultant osseointegration of the implants. Hydroxylapatite-coated implants intimately interfaced with healthy bone. The mineralized matrix extended into the microporosity of the HA coating. This matrix contained viable osteocytes.

Proteoglycans at the bone-implant interface

The widespread success of clinical implantology stems from bone's ability to form rigid, load-bearing connections to titanium and certain bioactive coatings. Adhesive biomolecules in the extracellular matrix are presumably responsible for much of the strength and stability of these junctures. Histochemical and spectroscopic analyses of retrievals have been supplemented by studies of osteoblastic cells cultured on implant materials and of the adsorption of biomolecules to titanium powder. These data have often been interpreted to suggest that proteoglycans permeate a thin, collagen-free zone at the most intimate contact points with implant surfaces. This conclusion has important implications for the development of surface modifications to enhance osseointegration. The evidence for proteoglycans at the interface, however, is somewhat less than compelling due to the lack of specificity of certain histochemical techniques and to possible sectioning artifacts. With this caveat in mind, we have devised a working model to explain certain observations of implant interfaces in light of the known physical and biological properties of bone proteoglycans. This model proposes that titanium surfaces accelerate osseointegration by causing the rapid degradation of a hyaluronan meshwork formed as part of the wound-healing response. It further suggests that the adhesive strength of the thin, collagen-free zone is provided by a bilayer of decorin proteoglycans held in tight association by their overlapping glycosaminoglycan chains.

A dental implant: aluminium trioxide exhibited no effect on mouse reproductive and mutanogenic potential

Several diseases as well as trauma can affect the composition and integrity of periodontal tissues leading eventually to the destruction of connective tissue matrix and cells, loss of attachment and resorption of alveolar bone, often followed by tooth loss. Replacement of the missing tooth could then be provided by endosseous dental implants healing in a form of osseo- or fibrosteal integration to the alveolar bone. Aluminium oxide ceramics, a form of endosseous implant, allows osseointegration type of healing and has demonstrated excellent biocompatibility. However, potential aluminium toxicity has been implicated in the pathogenesis of a number of clinical disorders and for this reason we examined the reproductive and mutagenic effect of aluminium trioxide ceramic implant in experimental mice. 720 female and 45 fertile male BALB-cAn NCR mice were included in the study. 3 experimental groups of fertile male mice (15 for each group) were treated with an intraperitoneal injection of aluminium trioxide (1 g/ kg of body weight, group I), with ethyl-methane-sulphonate as a positive control (200 mg/kg, group II) and with Tween-80 (10 mg/kg as a negative control, Group III). Each of the labeled male mice fertilized previously uncoupled female mice during 8 weeks (a pair per week) to facilitate appropriate pre- and post-meiotic conditions of spermatogenesis to occur. Female mice were sacrificed with cervical dislocation at day 13 after fertilization. Immediately upon sacrifice the uterus was removed and the number of alive and healthy, or alive but mutated and/or dead embryos was computed to determine the dominant lethal or mutagenic effect. Animals treated with aluminium trioxide demonstrated similar effects on the reproductive and mutagenic capacity as the negative control, whereas the animals treated as positive controls exhibited significantly reduced reproductive and mutagenic capacity. Collectively, we concluded that aluminium trioxide has a very low rate of embryonal mortality and mutagenicity in mice. This finding is in general agreement with the biocompatibility of aluminium trioxide as an implant material.

Quasi-biological apatite film induced by titanium in a simulated body fluid

Commercially pure titanium (c.p.Ti) is capable of inducing the formation of a carbonated apatite onto its surface in a simulated body fluid (SBF) comprised of calcium ions, phosphate ions, and other inorganic species present in the body fluid. In addition to the incorporation of carbonate ions, such formed apatite has other important characteristics of the bone mineral phase, such as a small crystal size and ionic substitution by Mg2+ and Cl-. Thus, we call this apatite a quasi-biological apatite. The formation of the quasi-biological apatite is proposed to be related to TiOH groups that develop on the titanium surface through interaction with the SBF. The results suggest that titanium implants may be activated such that they can form a strong bond with bone tissue through the in vivo formation of apatite. Since the solution can reach any open space, the process discussed in this study is very suitable for coating porous titanium implants with a quasi-biological apatite film.

Ultrastructural analyses of the attachment (bonding) zone between bone and implanted biomaterials

This report presents transmission electron and high voltage transmission electron microscopic observations of bone and associated remodeling tissues directly interfacing with endosteal dental implants. Undecalcified interfacial tissues were serially sectioned from mandibular samples encasing 60 implants placed into 30 dogs. Two-dimensional ultrastructural analyses and three-dimensional stereology showed that osteogenesis adjacent to dental implants is a dynamic interaction of osseous cells and a collagenous fiber matrix. This study showed that the interfacial bone consists of a mineralized collagen fiber matrix associated with an inorganic (hydroxylapatite) matrix. This study suggested that an unmineralized collagen fiber matrix initially is laid down directly at the implant surface, and that this matrix then is mineralized. Osteoblasts interacted with this matrix, eventually becoming encased within developing lacunae during the remodeling process. This process formed the cellular (osteocyte) aspects of the developed bone. Osteocyte processes extended through canaliculi directly to the implant surface. Apparently, these processes also were entrapped within canaliculi during the mineralization events. At times, these processes paralleled the implant surface. The bone-implant interfacial zone was primarily fibrillar (both mineralized and unmineralized) in morphology, with an electron-dense, ruthenium positive deposition. This electron-dense material was approximately 20 to 50 nanometers in thickness, and only this thin layer separated the remodeled mineralized bone from the implant.

Effect of serum proteins and osteoblasts on the surface transformation of a calcium phosphate coating: a physicochemical and ultrastructural study

Changes occurring at the surface of a calcium phosphate coating when in contact with osteoblasts versus those in acellular solutions were analyzed. The coating studied is one with a well-documented extensive effect on short-term bone growth stimulation. Precipitates associated with original crystals and organized in a weblike structure were observed after a 3-week culture with osteoblasts. The precipitates were identified as carbonated hydroxyapatite (c-HA). In contrast, no significant surface changes were detected after immersion in an acellular serum-containing solution. However, in an acellular serum-free solution simulating the ionic composition of plasma, precipitates, identified as c-HA, were abundantly formed. Dissolution of the original coating preceded precipitation. The data support the hypothesis that dissolution of synthetic calcium phosphate ceramics is an initial step in their transformation to a biologically equivalent apatite, and suggest that both solution-mediated (dissolution-precipitation) and cell-mediated mechanisms are involved in the surface transformation.

Effects of surface roughness of titanium implants on bone remodeling activity of femur in rabbits

We investigated the bone remodeling activity on titanium implants with different surface roughnesses using a confocal laser scanning microscope (CLSM). Two kinds of implants were used, the machined smooth-surfaced titanium and the plasma-sprayed rough-surfaced titanium. These implants were randomly inserted in a rabbit's femur from the lateral aspect of the diaphysis bicortically. Rabbits were killed at 6, 16, and 42 weeks after surgery. The implant-bone blocks were embedded in polyester resin, and were prepared to make undecalcified ground sections. Histomorphometric analyses were performed at the cortical bone-implant interface using the image obtained by CLSM. Percentages of direct bone-implant contact and bone volume (BV/TV) around the implant was greater in rough-surfaced titanium compared with the smooth-surfaced titanium at 42 weeks after implantation. On the contrary, the eroded surface (ES/BS) appeared to be less in the rough-surfaced titanium than in the smooth-surfaced titanium at 6 weeks after implantation, but thereafter, no difference was found between the two kinds of implants. Mineralizing surface (MS/BS) and mineral apposition rate (MAR) showed no significant differences throughout the experimental period. These results indicate that increased bone volume in the rabbits of rough-surfaced titanium implants is due to less remodeling activity during the early stage after implantation compared with the smooth-surfaced implants. The surface roughness of titanium is one factor which helps in determining the balance between bone formation and resorption of remodeling at the interface of the bone implants.

Long-term evaluation of bone-titanium interface in rat tibiae using light microscopy, transmission electron microscopy, and image processing

We conducted a 2-year histologic and histometric evaluation of the tibial bone-titanium (Ti) implant interface in male rats. Thirty male 6-week-old rats were used in this study. They were divided into two groups: 15 for day 28 and 15 for day 730. Microscopic observation at day 28 revealed that the newly formed bone around the implant almost surrounded the implant, but fibroblastlike cells were interposed in some histologic sections. At day 730, in contrast, such cells were rarely seen, and the bone around the implant presented a lamellar structure. Transmission electron microscopic observation at day 28 disclosed mature or poorly mineralized bone near the implant; however, an electron-dense amorphous zone about 50 nm in thickness was interposed between the bone and Ti. In places slender cells were interposed between the bone and Ti. The amorphous zone was also observed at the cell-Ti interface. At day 730, a poorly mineralized layer remained in some areas between the mature bone and the titanium, and the interposed amorphous zone was still observed. Occasionally, a 200-nm-thick layer, thought to be cell remnant, was seen. As calculated in an image-processing, system analysis, the percent bone contact and the thickness and area of the surrounding bone for the Ti implant at day 28 were 43.6%, 30.4 microns, and 0.10 mm2, respectively, and those at day 730 were 89.9%, 53.5 microns, and 0.19 mm2, respectively. In summary, although the passage of time may affect bone maturity, interfacial cells remain at the bone-Ti interface as a uniform layer together with unmineralized bone.

Ultrastructural aspects of the intact titanium implant-bone interface from undecalcified ultrathin sections

An osseointegrated oral implant with surrounding bone was used for electron microscopical analyses of the implant-bone interface. The bulk metal was removed by sawing and grinding techniques, leaving only the plasma-sprayed titanium coating anchored in mineralized bone. Ultrathin sections were realized from these reduced interface areas and underwent ultrastructural and crystallographic assessments. The microscopical observations showed that ultramicrotomy was suitable for producing such interface sections. Two different, concomitant, interfacial structures were noticed. On the one hand it was possible to observe bone crystals directly apposed on the implant surface; on the other, a granular electron-dense substance was interposed between the plasma-sprayed coating and the bone. The applied technical approach allows one to study the osseointegration process, at high resolution levels, of intact interfaces from complete osseointegrated implants.

Soft and hard tissue response to endosseous dental implants

The last two decades have seen a remarkable growth in the development of dental implants and their incorporation into the practice of dentistry. This turn of events was made possible by an improved understanding of biological response of living tissues to implants as well as clinical trials that validated the long-term success of these implants. Despite major structural differences between teeth and implants, such as the absence of a periodontal ligament around implants, the latter appear to provide a reliable functional replacement for their natural counterparts. This review briefly summarizes the major structural differences of the interfacial region of teeth and dental implants and their supporting tissues. It focuses on our current understanding of the soft and hard tissue responses to submerged and nonsubmerged root-form dental implants. The influence of a number of factors that affect the tissue response is reviewed, including biomaterials, implant design, surgical technique, and the local microbiota. Our recently acquired ability to modulate wound healing with guided tissue regeneration and growth factors will undoubtedly play an important role in the future utilization and success rates of dental implants.

Light and electron microscopic studies of bone-titanium interface in the tibiae of young and mature rats

Bone-titanium contact was examined in young and mature rats on various days after insertion of pure titanium into the tibia. Under light microscopy, on the 14th day, lamellar mature bone was initially formed, and was seen to make direct contact with the titanium in both groups. In young rats on the 28th day, bone-titanium contact was greater than that in mature animals. On 1-micron sections, an amorphous zone 0.5-1.0 micron thick was found around the titanium, and a slender cell layer lay parallel to the implant, forming the superficial layer of the amorphous zone. Ultrastructurally, these slender cells were identified as osteoblastlike cells and made direct contact with the implant via a 20-50-nm thin amorphous zone. Below this cell layer, a collagen-containing, poorly mineralized zone was present and bordered by lamellar bone with a lamina limitans-like structure. However, this cell layer was absent in places, and therefore the thick amorphous zone without slender cell layer consisted ultrastructurally of a 20-50-nm thin amorphous zone and a poorly mineralized zone bordered by the lamellar bone. Sometimes this poorly mineralized zone was absent, and in such cases, the lamellar bone contacted the titanium by the thin amorphous zone formed on the lamina limitans-like structure. Thus, although bone was seen to make contact with the titanium implant, ultrastructurally a 20-50-nm thin amorphous zone, a slender cell layer, and/or a poorly mineralized zone were interposed between the bone and titanium.

Transmission electron and high-voltage electron microscopy of osteocyte cellular processes extending to the dental implant surface

Examination of the morphology of osteocytes within the bone supporting endosteal dental implants was performed using conventional transmission and high-voltage transmission electron microscopy (HVEM). The in vivo dog model used 72 implants inserted into the premolar region of 18 experimental animals. Forty-eight implants in 12 dogs were used as anterior abutments for fixed bridges for periods up to 12 months. The mineralized matrix of the supporting bone was either directly apposed to the implant surface or was separated from the implant by a narrow region of unmineralized matrix. Osteocytes were routinely observed to be closely associated with the bone-implant interface, as well as at a distance from the implant. Osteocytes were found to extend cellular processes directly to the implant surface through canaliculi. The osteocyte processes contained microfilaments. The three-dimensional capabilities of HVEM elucidated the nature of these cell processes at the point of exit from the osteocyte, as the processes extended through the mineralized matrix, and as the processes terminated at the implant interface. This report suggests that avenues of communication may exist between the implant and the osseous cells, providing intriguing hypotheses regarding biomechanical forces and osteogenesis at the implant interface. Furthermore, an electron-dense deposit was observed upon the inner confines of the canalicular wall, upon the outer aspects of the osteocyte lacuna, and upon the outer aspect of the bone interfacing the implant.

Osteoblast activity at the dental implant-bone interface: transmission electron microscopic and high voltage electron microscopic observations

The purpose of this report is to present transmission electron microscopic and high voltage transmission electron microscopic (HVEM) observations of a longitudinal investigation examining the activities of osteoblasts and associated tissues apposing titanium and alumina oxide ceramic endosteal dental implants. The HVEM permitted 3-dimensional stereologic observations. All observations were obtained from undecalcified interfacial tissues from this in vivo experimental dog model using commercially available implants placed into the mandible. Two similar implants were placed in both sides of the mandible, with implants in 12 of the 18 dogs supporting fixed bridges for either 6 or 12 months. From the study, we observed that a mineralized matrix exists in direct apposition to the implant. Since bone does not interface the entire length of the implant, other interfacial zones were found to exist which consisted of unmineralized tissues. In such zones, we observed that osteoblasts were routinely found directly at the implant interface to the mandibular bone. These interfacial tissues included unmineralized collagen fibers, proteinaceous material, a finely fibrillar matrix, and the osteoblasts. This study has reinforced the concept that the oral tissue-dental implant interface is a dynamic zone consisting of remodeling activities of the osseous cells and extracellular matrices.