Enhanced bone healing around nanohydroxyapatite-coated polyetheretherketone implants: An experimental study in rabbit bone.

OBJECTIVE: To investigate the bone response to threaded polyetheretherketone (PEEK) implants coated with nanohydroxyapatite. MATERIALS AND METHODS: A total of 39 PEEK implants were coated with nanocrystalline hydroxyapatite and 39 uncoated implants were used as controls. The implant surface was characterized by optical interferometry and scanning electron microscope. The implants were inserted in the tibia and femur of 13 rabbits. After 6 weeks of healing, quantitative and qualitative analyses were performed. RESULTS: The test implants showed significantly higher removal torque test values compared with the control group. Histomorphometric evaluation demonstrated higher bone-to-implant contact for the test implants; however, there were no differences in bone area between the groups. Qualitative histological analyses demonstrated inflammatory cellular reactions in close vicinity of both implant surfaces. A two-cell layer of foreign body giant cells was observed irrespective of sample type. CONCLUSION: Our findings demonstrate that implants with a threaded design render good stability to PEEK in both coated and uncoated implants. Nanohydroxyapatite-coated PEEK implants demonstrated improved bone formation compared with uncoated controls.

Early bone formation in human bone grafts treated with platelet-rich plasma: preliminary histomorphometric results.

The aim of this study was to evaluate the effect of platelet-rich plasma (PRP) on early and late bone healing after autogenous maxillary sinus grafting. Eleven patients were subjected to sinus augmentation with particulated autogenous bone bilaterally with the addition of PRP in one side. Platelet counts in baseline whole blood and PRP were registered. Biopsies were taken in the grafted bone of the sinus area with trephine at 3 months (nine patients) and simultaneously a micro-implant was installed in the same region. The micro-implants with surrounding bone were retrieved by biopsy at 6 months (seven patients). Undecalcified cut and ground sections were histomorphometrically analysed. Quantification of new and old bone in all biopsies was performed. The results of this histological study showed that significantly more new bone was formed at PRP-treated sites compared to controls after 3 months of healing. After 6 months, this effect could no longer be observed. This is in accordance with previous studies showing that PRP has a rather low regenerative capacity but may influence the early phase of bone healing. The additional value of PRP in autogenous bone grafts in the maxillary sinus is questionable.

Improved bone ingrowth and fixation with a thin calcium phosphate coating intended for complete resorption.

Bonit is claimed to be a resorbable electrochemically deposited calcium phosphate coating consisting mainly of brushite, which is a hydroxyapatite precursor. This study involved a comparison of Ti6Al4V screw-shaped implants with and without a 15 +/- 5 microm Bonit coating in rabbit tibia and femur, after 6 and 12 weeks of insertion. The biomechanical removal torque test showed significantly increased values for the coated implants after 12 weeks (p < 0.05) but not after 6 weeks of integration. Higher bone-implant contact was found for the coated implants in the tibia after 6 weeks and for both tibial and femoral screws after 12 weeks (p < 0.05). There was no difference in the inflammatory reaction around the implants, and possible grains of the coating could be detected after 6 weeks, but not after 12 weeks of follow-up. This unloaded short-term study has shown promising results for the easily applicable and resorbable coat (Bonit) compared to uncoated titanium-alloy implants.

Tissue reactions adjacent to well-fixed hydroxyapatite-coated acetabular cups. Histopathology of ten specimens retrieved at reoperation after 0.3 to 5.8 years.

Ten acetabular cups coated with hydroxyapatite (HA) had originally been inserted in five primary and five revision total hip replacements. The thickness of the HA was 155 +/- 35 microm. The cups, which were well-fixed, were retrieved, with their adherent tissue, at reoperation after 0.3 to 5.8 years because of infection (five hips), wear of polyethylene (three hips), and instability (two hips). Undecalcified sections showed a direct contact between bone and osteoid-like tissue which had formed directly onto the HA coating. The area within the threads and their mirror images, as well as the implant-tissue interfaces consisted of similar amounts of bone and soft tissue. Degradation of HA was seen in all hips. The mean thickness of the remaining HA coating was 97 microm (95% CI 94 to 101). The metal interface comprised 66% HA. The HA-tissue interface contained more bone than soft tissue (p = 0.001), whereas the metal-tissue interface included more soft tissue than bone (p = 0.019). Soft tissue at the implant interface and poor replacement of HA by bone may interfere with long-term fixation.

Enamel matrix derivative and titanium implants.

AIM: The aim of present study was to evaluate if an enamel matrix derivative (Emdogain) may enhance bone formation and osseointegration of titanium implants, using a well-documented rabbit model. MATERIAL AND METHODS: Thirty-six threaded commercially pure titanium (cp.ti.) implants were inserted in six New Zealand white rabbits. One implant was placed in each femur and two in each tibia. Prior to implant insertion approximately 0.5 mL of Emdogain (EMD) (test) or the vehicle gel (PGA: propylene glycol alginate) (control) was injected into the surgically prepared implant site. The follow-up time was 6 weeks. Biomechanical evaluations by resonance frequency analysis (RFA) and removal torque measurements (RTQ) were performed. Histomorphometrical quantifications were made on ground sections by measurements of the percentage of bone-to-metal contact, bone area inside the threads as well as outside the threads (mirror image). Bone lengths along the implant surface were also measured and used for shear strength calculations. RESULTS: The results demonstrated no beneficial effects from the EMD treatment on bone formation around titanium implants in any of the tested parameters. Significant differences were demonstrated with removal torque test and shear force calculations for the control implants. No other parameter demonstrated a statistically significant difference. CONCLUSION: The results of the present study may indicate that EMD does not contribute to bone formation around titanium implants. This observation may indicate that the bone formation that occurs after EMD treatment in periodontal defects is the result of functional adaptation. However, further research is required to evaluate the effect of EMD treatment on bone formation.

Biological behavior of sol-gel coated dental implants.

The biocompatibility of dental implants coated with titania/hydroxyapatite (HA) and titania/bioactive glass (BG) composites obtained via sol-gel process was investigated using an in vitro and in vivo model. A device for the in vitro testing of screw-shaped dental implants was developed, in order to well compare the two experimental models studying the behavior of human MG63 osteoblast-like cells seeded onto a particular geometry. The expression of some biochemical parameters of osteoblastic phenotype (alkaline phosphatase specific activity, collagen and osteocalcin production) and some indications on cells morphology obtained by scanning electron microscopy were evaluated. The in vitro and in vivo models were compared after implants insertion in rabbit tibia and femur. The removal torque and histomorphometric parameters (percentage of bone in contact with implant surface and the amount of bone inside the threaded area) were examined. A good agreement was found between the in vitro and in vivo models. These experiments showed better performances of HA and BG sol-gel coated dental implants with respect to uncoated titanium; in particular, it was found that in vitro the HA coating stimulates osteoblastic cells in producing higher level of ALP and collagen, whereas in vivo this surface modification resulted in a higher removal torque and a larger bone-implant contact area. This behavior could be ascribed to the morphology and the chemical composition of the implants with rough and bioactive surfaces.

Vital staining of bone in stable, retrieved femoral surface replacement prostheses: a microscopic study of undecalcified ground sections.

We used vital staining with tetracycline to detect viability of bone at the bone-cement interface in 11 stable ICLH femoral surface replacement prostheses that were retrieved at revision surgery for acetabular loosening. The resected femoral heads were processed for undecalcified ground sections with the prostheses in situ. All sections showed direct bone-to-cement contacts. Bone in direct contact with or close to the cement sometimes showed an abnormal staining, indicating that the bone was not fully mineralized. Areas with fluorescence were observed within all femoral heads but never in direct bone-to-cement contact. From this study, we conclude that the mechanical stability of these cemented femoral surface replacement prostheses depends mainly on the original bone present at the time of primary operation.

The electrochemical oxide growth behaviour on titanium in acid and alkaline electrolytes.

Titanium implants have a thin oxide surface layer. The properties of this oxide layer may explain the good biocompatibility of titanium implants. Anodic oxidation results in a thickening of the oxide film, with possible improved biocompatability of anodized implants. The aim of the present study was twofold: (1) firstly, to characterize the growth behaviour of galvanostatically prepared anodic oxide films on commercially pure (c.p.) titanium and (2) secondly, to establish a better understanding of the electroche0mical growth behaviour of anodic oxide on commercially pure titanium (ASTM grade 1) after changes of the electrochemical parameters in acetic acid, phosphoric acid, calcium hydroxide, and sodium hydroxide under galvanostatic anodizing mode. The oxide thickness was measured by Ar sputter etching in Auger Electron spectroscopy (AES) and the colours were estimated by an L*a*b* system (lightness, hue and saturation) using a spectrophotometer. In the first part of our study, it was demonstrated that the interference colours were useful to identify the thickness of titanium oxide. It was also found that the anodic forming voltages with slope (dV/dt) in acid electrolytes were higher than in alkaline electrolytes. Each of the used electrolytes demonstrates an intrinsically specific growth constant (nm/V) in the range of 1.4--2.78 nm/V. In the second part of our study we found, as a general trend, that an increase of electrolyte concentration and electrolyte temperature respectively decreases the anodic forming voltage, the anodic forming rate (nm/s) and the current efficiency (nm.cm(2)/C), while an increase of the current density and the surface area ratio of the anode to cathode increase the anodic forming voltage, the anodic forming rate and the current efficiency. The effects of electrolyte concentration, electrolyte temperature, and agitation speed were explained on the basis of the model of the electrical double layer.

Oxidized implants and their influence on the bone response.

Surface oxide properties are regarded to be of great importance in establishing successful osseointegration of titanium implants. Despite a large number of theoretical questions on the precise role of oxide properties of titanium implants, current knowledge obtained from in vivo studies is lacking. The present study is designed to address two aspects. The first is to verify whether oxide properties of titanium implants indeed influence the in vivo bone tissue responses. The second, is to investigate what oxide properties underline such bone tissue responses. For these purposes, screw-shaped/turned implants have been prepared by electrochemical oxidation methods, resulting in a wide range of oxide properties in terms of: (i) oxide thickness ranging from 200 to 1000 nm, (ii) the surface morphology of barrier and porous oxide film structures, (iii) micro pore configuration - pore sizes<8 microm by length, about 1.27 microm2 to 2.1 microm2 by area and porosity of about 12.7-24.4%, (iv) the crystal structures of amorphous, anatase and mixtures of anatase and rutile type, (v) the chemical compositions of TiO2 and finally, (vi) surface roughness of 0.96-1.03 microm (Sa). These implant oxide properties were divided into test implant samples of Group II, III, IV and V. Control samples (Group I) were turned commercially pure titanium implants. Quantitative bone tissue responses were evaluated biomechanically by resonance frequency analysis (RFA) and removal torque (RT) test. Quantitative histomorphometric analyses and qualitative enzyme histochemical detection of alkaline (ALP) and acidic phosphatase (ACP) activities were investigated on cut and ground sections after six weeks of implant insertion in rabbit tibia. In essence, from the biomechanical and quantitative histomorphometric measurements we concluded that oxide properties of titanium implants, i.e. the oxide thickness, the microporous structure, and the crystallinity significantly influence the bone tissue response. At this stage, however, it is not clear whether oxide properties influence the bone tissue response separately or synergistically.

Systemically administered human growth hormone improves initial implant stability: an experimental study in the rabbit.

PURPOSE: This study was an investigation to determine whether human growth hormone (hGH) continuously administered to rabbits may improve implant integration in bone. MATERIALS AND METHODS: Thirty-two commercially pure titanium (c.p. Ti) implants were inserted in the tibiae of 16 rabbits. Human growth hormone (0.3 U/kg/d) or sodium chloride (NaCl) was administered by subcutaneous pumps. Insulin-like growth factor-1 (IGF-1) levels in blood were measured. Two biomechanical tests were performed: (1) every second week resonance frequency analysis (RFA) was used to investigate implant stability or stiffness at the interface and, after 8 weeks of follow-up, (2) removal torque (a measure of implant integration and stability) was registered. Further evaluation was performed by dual energy x-ray analysis (DEXA), to evaluate bone mineral density, and histomorphometric analysis of tissue-to-implant integration on undecalcified cut and ground sections. RESULTS: A difference in implant stability was detected with the RFA technique after 2 weeks and 8 weeks in favor of the hGH-treated rabbits. No significant differences were detected with removal torque, DEXA, and histomorphometric measurements. The blood test demonstrated antibody development in the rabbits treated with hGH after 4 weeks. CONCLUSION: Growth hormone has an initial beneficial effect on implant integration; however, owing to rapid antibody formation, this study did not demonstrate whether this effect remains in the long term.

Application of oxygen ion implantation to titanium surfaces: effects on surface characteristics, corrosion resistance, and bone response.

BACKGROUND: The surface oxide layer of titanium plays a decisive role in determining biocompatibility. However, there are some reports demonstrating that the natural oxide film may not be sufficiently protective in the aggressive biologic environment. PURPOSE: The goal of this study was to examine the effectiveness of a thick oxide layer on corrosion resistance in vitro and the bone formation around titanium implants in vivo. MATERIALS AND METHODS: A plasma source ion implantation (PSII) method was used to increase the thickness of the surface oxide layer. Several instruments were employed to confirm the surface properties before and after the surface modification. Potentiodynamic polarization measurements in a phosphate-buffered saline (PBS) solution were carried out to investigate corrosion resistance in vitro. Bone formation around this surface-modified specimen was examined in a rabbit model and assessed in histomorphometry. RESULTS: Improved corrosion resistance was demonstrated by the potentiodynamic polarization measurements. Light microscopic histomorphometry showed that all implants were in contact with bone and had some proportion of bone within the threads at 4 weeks; however, there were no significant differences compared with as-machined controls. CONCLUSIONS: The results indicate that in spite of improved corrosion resistance in vitro, a thick oxide layer fabricated with the PSII method does not influence early bone formation around titanium implants in vivo.

A microradiographic investigation of cancellous bone healing after irradiation and hyperbaric oxygenation: a rabbit study.

PURPOSE: To analyze the effect of irradiation on cancellous bone healing at different times after irradiation and to study if hyperbaric oxygen therapy (HBO) would affect the bone healing capacity, when delivered directly after irradiation. METHODS AND MATERIALS: Rabbits were given a single dose of 15 Gy (60)Co radiation to one hind leg, the other hind leg serving as control. A standardized defect through the femoral metaphysis of the rabbits was created by a trephine drill biopsy at different times after irradiation. New bone formation in the defect was evaluated by a new biopsy through the previous defect after a healing time of 8 weeks. The mineral contents of the biopsies were analyzed by microradiography and microdensitometry. RESULTS: There was a large variation in the bone-forming capacity expressed as bone mineral content between the animals. No statistically significant differences could be detected regarding the effect of irradiation, HBO, or delayed surgery. Qualitative histology revealed more pronounced inflammation, fibrosis, and bone resorption in the irradiated bone. CONCLUSIONS: No definite conclusions can be drawn from the results of this study, however it might be hypothesized that cancellous bone recovers faster than cortical bone from radiation trauma.

Generalized potential of adult neural stem cells.

The differentiation potential of stem cells in tissues of the adult has been thought to be limited to cell lineages present in the organ from which they were derived, but there is evidence that some stem cells may have a broader differentiation repertoire. We show here that neural stem cells from the adult mouse brain can contribute to the formation of chimeric chick and mouse embryos and give rise to cells of all germ layers. This demonstrates that an adult neural stem cell has a very broad developmental capacity and may potentially be used to generate a variety of cell types for transplantation in different diseases.

A new approach to demonstrate cellular activity in bone formation adjacent to implants.

Bone tissue repeatedly formed in titanium 6-aluminum 4-vanadium rabbit bone harvest implants was collected in vivo at various times between 12 days and 5 weeks. Qualitative and quantitative examinations on undecalcified thin sections were performed in the light microscope. The amount of bone tissue was calculated on routinely stained sections. Alkaline (ALP) and acid phosphatase (ACP) enzyme activities were investigated. We also performed immunohistological detection of bone matrix proteins. Increasing bone density as well as an increasing mineralization of the tissue was observed in the biopsies with increasing time. The ALP and ACP activities were similar at short times (12 days and 2 weeks). With increasing time the ALP activity was stronger than that of ACP. The results from the immunohistochemical detection of osteonectin, osteopontin, bone sialoprotein, and collagen I and II demonstrated changes in the tissue differentiation with time. The tissue formation in the canal became more mature with time of ingrowth, as observed with the various techniques used in this study. Owing to these methodical developments, undecalcified ground sections may be used for detailed analysis of various phases of tissue formation in close proximity to implants.

In vitro effects of clarithromycin on human polymorphonuclear leukocyte functions.

BACKGROUND: It has been shown that antibacterial agents affect polymorphonuclear leukocytes (PMNs), which are active in the body's first line of defense, in different ways. However, few studies have investigated the effects of tablet dosage forms as opposed to pure powder forms. There is a need to demonstrate the clinical relevance of previous results with commercially available products. METHODS: We examined the effects of clarithromycin solutions, prepared separately from either pure powder or commercially available tablets (250 mg), on human PMNs. The in vitro effects of each solution, adjusted to therapeutic concentration (1 mg/l), on PMN adherence, chemotaxis, phagocytosis, candidacidal capacity and superoxide production were studied. RESULTS: Solutions prepared from pure clarithromycin powder did not affect the adherence, phagocytosis or superoxide production of PMNs, but did inhibit (p<0.05) chemotaxis and candidacidal capacity. By contrast, a decrease (p<0.05) in all functions except phagocytosis was observed with solutions prepared from the tablet dosage form of clarithromycin. CONCLUSION: The results of this study suggest that the tablet dosage form of clarithromycin may have a more pronounced inhibitory effect on human PMN functions than solutions prepared from the pure powder form.

Tissue regeneration adjacent to titanium implants placed with simultaneous transposition of the inferior dental nerve: a study in dogs.

Transposition of the inferior alveolar nerve was performed in an experimental dog model. Four adult greyhounds were used in the study. Surgical transposition of the nerve was made bilaterally, and 3 implants were placed on each side while the nerve was lateralized. On one side, the nerve was repositioned in contact with the implants, while on the contralateral side a resorbable membrane was positioned between the implant surface and the neurovascular bundle. Histologic section after 4 months of healing showed an intimate contact between implants and nerve tissue in all cases without an interpositional membrane, in contrast to cases with membranes. Histomorphometric measurements of the distance between the implants and the nerve tissue showed that the membrane side had a considerably larger distance between the implant and the nerve, although not with concomitant bone formation.

Get to know your stem cells.

Our view of the central nervous system has changed dramatically over the past few years. It is now well established that new neurons are generated continuously in adult mammals, including humans. These neurons derive from self-renewing multipotent neural stem cells. The identify of these stem cells has recently been unveiled.

Expression of the adenovirus receptor and its interaction with the fiber knob.

The coxsackievirus group B (CVB) and adenovirus (Ad) receptor (HCVADR, formerly HCAR) is a cell surface protein with two immunoglobulin-like regions (IG1 and IG2) that serves as a receptor for two structurally unrelated viruses. We have established the tissue distribution of the receptor in the rodent by immunohistochemistry and show that the receptor is broadly expressed during embryonic development in the central and peripheral nervous systems and in several types of epithelial cells. The tissue distribution is more restricted in the adult but remains high mainly in epithelial cells. Using site-directed mutagenesis, based on computer modeling of the IG1 region, Ad5 binding could be inhibited but CVB attachment was unaffected. A double amino acid substitution in a three-stranded anti-parallel beta sheet that may form a face of the receptor completely inhibited Ad5 binding. Therefore, we conclude that the molecular interactions critical for Ad5 binding to HCVADR do not overlap with those of CVB3. In fact a specific antibody interfering with only CVB binding recognizes the IG2 domain in the receptor, suggesting that the CVB interacts with this region or an overlap between the IG1 and the IG2 regions.

Bone response to implant-supported frameworks with differing degrees of misfit preload: in vivo study in rabbits.

PURPOSE: To study the bone response around implants placed in tibia of rabbits that supported misfitting superstructures secured with different degrees of preload. MATERIALS AND METHODS: Twelve rabbits were provided with two terminal 10-mm and one intermediate 7-mm-long implant in each tibia. After an integration time of about 9 weeks, nine of the animals received one control framework each (n = 9), designed with good fit to all three implants. In the other tibia of these animals, and in both tibias in the remaining three rabbits, test frameworks (n = 15) were connected with a vertical misfit of about 1 mm to the intermediate implant. The intermediate set screws were tightened with a torque ranging from 15 Ncm to 26 Ncm in the different test frameworks. The fascia and skin was then sutured back over the implants. After a loading period of 2 to 3 weeks, the animals were sacrificed, and histomorphometric measurements were made and correlated to the different levels of preload of the central implant. RESULTS: The mean bone-to-metal contact for the three best consecutive threads of the central implant was 40% for both test and control sites (p > .05). Compared to the other regions of the implant thread, less bone-to-metal contact was found at the tip of the test implant threads in the low preload group (p < .05). However, the same relation was not observed in the high preload group. A significant correlation was observed between increasing degree of preload in the central screw joint and increasing bone-to-metal contact, most obviously noticed at the tip of the implant thread (p < .01). CONCLUSIONS: Misfit stress levels of clinical magnitudes do not seem to jeopardize osseointegration per se. On the contrary, clinical levels of preload stress seem to significantly promote bone remodeling at the tip of the implant thread.

Neural stem cells in the adult human brain.

New neurons are continuously generated in certain regions of the adult brain. Studies in rodents have shown that new neurons are generated from self-renewing multipotent neural stem cells. Here we demonstrate that both the lateral ventricle wall and the hippocampus of the adult human brain harbor self-renewing cells capable of generating neurons, astrocytes, and oligodendrocytes in vitro, i.e., bona fide neural stem cells.