Mechanism Of Osseointegration Research Articles

Histodynamics of calcium phosphate coating on the osseointegration of medical-grade polycaprolactone β-tricalcium phosphate scaffolds

Bone formation on implant surfaces occurs via distance and contact osteogenesis, with osseointegration influenced by the implant’s surface topography and coating. However, the traditional mechanisms of osseointegration around metal implant surfaces may not fully encompass the ultimate outcomes of using medical-grade polycaprolactone β-tricalcium phosphate calcium phosphate coated (mPCL-TCP-CaP) scaffolds for the reconstruction of large bone defects. Using histology, immunohistochemical (IHC) and scanning electron microscopy (SEM) analyses our studies on large bone defects using mPCL-TCP-CaP scaffolds show osteogenic cells forming a fibrous connective matrix around these scaffolds. Despite extensive research, the in vivo mechanisms of osseointegration of CaP-coated mPCL-TCP-CaP scaffolds remain unclear. This study investigates the structural details and spatial organization of the mPCL-TCP-CaP scaffold’s interface, providing insights into the histodynamic processes involved in their osseointegration with CaP coatings.

Evaluation of the Effectiveness of Bone Grafting in Alveolar Ridge Augmentation Using the Two-Stage Splitting Technique.

Stimulation of neoosteogenesis is the main mechanism of osseointegration during installation of dental implants, bone tissue recession, and alveolar process augmentation in adentia. In experiments on miniature pigs, we used the technology of two-stage splitting of the ridge of the alveolar process of the mandible in combination with a xenograft that was placed between the fragments of the split bone plate. The morphology of the reparative process and the distribution of osteogenic differentiation markers in the compact and trabecular bone of the alveolar crest were studied. Signs of reparative osteogenesis were observed in the bone regenerate that had a lamellar structure, formed osteons, and foci of woven tissue. It was found that the xenograft was replaced by newly formed trabecular bone tissue. These sites were characterized by increased expression of osteocalcin and CD44. Augmentation technology through two-stage splitting provides trophic relationship of osteoprogenitor cells and is an effective method of osteogenesis stimulation in the alveolar process.

Review of Local Cellular and Molecular Processes of Bone Tissue Regeneration Induced by Calcium Phosphate Materials

One of the leading causes of hospitalization, disability and mortality of 50% of women and 20% of men over the age of 50 are bone fractures and their complications caused by diseases of the musculoskeletal system. In this regard, an active search for a solution to the problem associated with the limitations of the use of auto-, allo-, and xenografts in the clinic to replace bone defects initiated the development of a regenerative approach based on the gradual replacement of artificial material with growing bone tissue. Promising in this regard are materials based on calcium phosphates, which act as an active source of chemical elements (calcium, phosphorus, etc.), which can optimize the process of bone defect fusion and ensure the replacement of the implant with new bone tissue. The review summarizes literature data on local biological activity, target cells, and molecular effects of calcium phosphates. It has been shown that calcium phosphate materials are biocompatible, capable of adsorbing regulatory proteins and cells, influencing their genetic and secretory apparatus and triggering the process of MSC differentiation in the osteogenic direction. At the same time, the successful implementation of local mechanisms of osseointegration at the “bone/implant” interface reduces the risk of periprosthetic infection (PJI) and rejection of artificial devices. Further study and use of calcium phosphate materials will make it possible to make a significant breakthrough in solving modern problems of bone tissue regeneration associated with an accurate (digital) bioengineering approach based on additive technologies and artificial intelligence.

MiR-155-5p can be involved in acquisition of osseointegration on titanium surface.

Dental implants made of titanium are commonly used. Although titanium implants succeed by osseointegration with bone, the detailed molecular mechanism of osseointegration is unclear. To clarify the involvement of microRNA (miRNA) in the acquisition of osseointegration on titanium, here we compared the miRNA expression profiles of mouse osteoblast-like cells (MC3T3-E1) cultured on titanium-, gold-, and stainless steel-coating glass dishes by microarray analysis. Three kinds of metals, namely titanium, gold, and stainless steel, were coated on the surface of the glass dishes by sputtering with similar roughness and shape of their surface. After MC3T3-E1 cells were cultured on the dishes without coating or coating with titanium, gold, or stainless steel for 6h, total RNA was extracted, and miRNA expression was analyzed by microarray. To confirm the expression of the selected miRNA during osteogenic differentiation of MC3T3-E1 cells, real-time PCR analysis was performed. Furthermore, the effects of selected miRNA were examined by ectopic overexpression in MC3T3-E1 cells. The microarray analysis revealed that the expressions of miR-155-5p and miR-7023-3p were significantly increased in MC3T3-E1 cells cultured on titanium-coating glass dishes, compared to non-coating, gold-, and stainless steel-coating glass dishes. Interestingly, miR-155-5p was upregulated during osteogenic differentiation of MC3T3-E1 cells. Furthermore, overexpression of miR-155-5p enhanced the expression of Runx2 and Col1a1. In this study, miR-155-5p may be involved in the acquisition of osseointegration on titanium implant via upregulating osteogenic differentiation-related genes.

Non-Destructive Removal of Dental Implant by Using the Cryogenic Method.

Background and Objectives: The gold standard for a successful prosthetic approach is the osseointegration of an implant. However, this integration can be a problem in cases where the implant needs to be removed. Removing the implant with minimal damage to the surrounding tissues is important. Osteocytes cannot survive below −2 °C, but epithelial cells, fibroblasts, and other surrounding tissue cells can. Remodeling can be triggered by cryotherapy at temperatures that specifically affect osteocyte necrosis. In this study, we aimed to develop a method for reversing the osseointegration mechanism and for protecting the surrounding tissues by bone remodeling induced by CO2 cryotherapy. Materials and Methods: In this study, eight 2.8 mm diameter, one-piece mini implants were used in New Zealand rabbit tibias. Two control and six implants were tested in this study. After 2 months of osseointegration, a reverse torque force method was used to remove all osseointegrated implants at 5, 10, 20, and 30 Ncm. The osseointegration of the implants was proven by periotest measurements. Changes in bone tissue were examined in histological sections stained with toluidine blue after rabbit sacrifice. The number of lacunae with osteocyte, empty lacunae, and lacunae greater than 5 µm and the osteon number in a 10,000 µm2 area were calculated. Cryotherapy was applied to the test implants for 1 min, 2 min, and 5 min. Three implants were subjected to cryotherapy at −40 °C, and the other implants were subjected to cryotherapy at −80 °C. Results: Empty lacunae, filled osteocytes, lacunae >5 µm, and the osteon count around the implant applied at −40 °C were not significantly different from the control implants. The application of −40 °C for 1 min was found to cause minimal damage to the bone cells. The implants, which were applied for 1 min and 2 min, were successfully explanted on the 2nd day with the 5 Ncm reverse torque method. Test implants, which were applied cold for 5 min, were explanted on day 1. Tissue damage was detected in all test groups at −80 °C. Conclusions: The method of removing implants with cryotherapy was found to be successful in −40 °C freeze–thaw cycles applied three times for 1 min. To prove implant removal with cryotherapy, more implant trials should be conducted.

Nanohydroxyapatite-Blasted Bioactive Surface Drives Shear-Stressed Endothelial Cell Growth and Angiogenesis

Nanosized crystalline hydroxyapatite coating (HAnano®) accelerates the osteointegration of dental implants which is hypothesized to drive angiogenesis. In order to test this hypothesis, we have subjected shear-stressed human umbilical vein endothelial cells (HUVECs) to a HAnano®-enriched medium, as well as to surface presenting dual acid etching (DAE) as a control. To note, the titanium implants were coated with 10 nm in diameter HA particles using the Promimic HAnano method. Our data reveals that HAnano® modulates higher expression of genes related with endothelial cell performance and viability, such as VEGF, eNOS, and AKT, and further angiogenesis in vitro by promoting endothelial cell migration. Additionally, the data shows a significant extracellular matrix (ECM) remodeling, and this finding seems developing a dual role in promoting the expression of VEGF and control endothelial cell growth during angiogenesis. Altogether, these data prompted us to further validate this phenomenon by exploring genes related with the control of cell cycle and in fact our data shows that HAnano® promotes higher expression of CDK4 gene, while p21 and p15 genes (suppressor genes) were significantly lower. In conjunction, our data shows for the first time that HAnano®-coated surfaces drive angiogenesis by stimulating a proliferative and migration phenotype of endothelial cells, and this finding opens novel comprehension about osseointegration mechanism considering nanosized hydroxyapatite coating dental implants.

Influence of cold atmospheric plasma on dental implant materials \u2014 an in vitro analysis

Background and objectivesAlterations in the microenvironment of implant surfaces could influence the cellular crosstalk and adhesion patterns of dental implant materials. Cold plasma has been described to have an influence on cells, tissues, and biomaterials. Hence, the mechanisms of osseointegration may be altered by non-thermal plasma treatment depending on different chemical compositions and surface coatings of the biomaterial. The aim of the present study is to investigate the influence of cold atmospheric plasma (CAP) treatment on implant surfaces and its biological and physicochemical side effects.Materials and methodsDental implant discs from titanium and zirconia with different surface modifications were treated with CAP at various durations. Cell behavior and adhesion patterns of human gingival fibroblast (HGF-1) and osteoblast-like cells (MG-63) were examined using scanning electron microscopy and fluorescence microscopy. Surface chemical characterization was analyzed using energy-dispersive X-ray spectroscopy (EDS). Quantitative analysis of cell adhesion, proliferation, and extracellular matrix formation was conducted including real-time PCR.ResultsCAP did not affect the elemental composition of different dental implant materials. Additionally, markers for cell proliferation, extracellular matrix formation, and cell adhesion were differently regulated depending on the application time of CAP treatment in MG-63 cells and gingival fibroblasts.ConclusionsCAP application is beneficial for dental implant materials to allow for faster proliferation and adhesion of cells from the surrounding tissue on both titanium and zirconia implant surfaces with different surface properties.Clinical relevanceThe healing capacity provided through CAP treatment could enhance osseointegration of dental implants and has the potential to serve as an effective treatment option in periimplantitis therapy.

Chondroitin-4-sulfate transferase-1 depletion inhibits formation of a proteoglycan-rich layer and alters immunotolerance of bone marrow mesenchymal stem cells on titanium oxide surfaces

Successful osseointegration is essential for dental implants. However, the complete molecular mechanism of osseointegration remains to be elucidated. In this study, we focused on the proteoglycan (PG)-rich layer between titanium oxides (TiOx) and bone, and chondroitin-4-sulfate transferase-1 (C4ST-1), which forms the sugar chain in PGs. Human bone marrow mesenchymal stem cells (hBMSCs) depleted of C4ST-1 were cultured on titanium (Ti) plates, and the interface between hBMSCs and TiOx was analyzed using transmission electron microscopy. Immunotolerance, proliferation, initial adhesion, and calcification of the cells were analyzed in vitro. At 14 days of cultivation, a PG-rich layer was observed between hBMSCs and TiOx. However, the PG-rich layer was reduced in C4ST-1-depleted hBMSCs on TiOx. Real-time RT-PCR showed that conditioned media increased the levels of expression of M1-macrophage markers in human macrophages. However, depletion of C4ST-1 did not affect calcification, cell proliferation, or initial cell adhesion on Ti plates. These results suggested that C4ST-1 in hBMSCs affects their immunotolerance and alters the formation of PG-rich layer formation on TiOx.

The Effects of Syndecan on Osteoblastic Cell Adhesion Onto Nano-Zirconia Surface.

PurposeZirconia is one of the most promising implant materials due to its favorable physical, mechanical and biological properties. However, until now, we know little about the mechanism of osseointegration on zirconia. The purpose of this study is to evaluate the effect of Syndecan (Sdc) on osteoblastic cell (MC3T3-E1) adhesion and proliferation onto zirconia materials.Materials and MethodsThe mirror-polished disks 15 mm in diameter and 1.5 mm in thick of commercial pure titanium (CpTi), 3mol% yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) and nano-zirconia (NanoZr) are used in this study. MC3T3-E1 cells were seeded onto specimen surfaces and subjected to RNA interference (RNAi) for Syndecan-1, Syndecan-2, Syndecan-3, and Syndecan-4. At 48h post-transfection, the cell morphology, actin cytoskeleton, and focal adhesion were observed using scanning electron microscopy or laser scanning confocal fluorescence microscopy. At 24h and 48h post-transfection, cell counting kit-8 (CCK-8) assay was used to investigate cell proliferation.ResultsThe cell morphology of MC3T3-E1 cells on CpTi, 3Y-TZP, and NanoZr changed into abnormal shape after gene silencing of Syndecan. Among the Syndecan family, Sdc-2 is responsible for NanoZr-specific morphology regulation, via maintenance of cytoskeletal conformation without affecting cellular attachment. According to CCK-8 assay, Sdc-2 affects the osteoblastic cell proliferation onto NanoZr.ConclusionWithin the limitation of this study, we suggest that Syndecan affects osteoblastic cell adhesion on CpTi, 3Y-TZP, and NanoZr. Sdc-2 might be an important heparin-sensitive cell membrane regulator in osteoblastic cell adhesion, specifically on NanoZr, through the organization of actin cytoskeleton and affects osteoblastic cell proliferation.

Reduced Proteoglycan-Rich Layer and Altered Immunotolerance Capacity of C4ST-1-Depleted Bone Marrow Mesenchymal Stem Cells on Titanium Dioxide

Successful osseointegration of a bone and implant directly must be achieved for treatment of a dental implant. However, the mechanism of osseointegration at the molecular level has yet to be fully elucidated. In this study, we focused on the proteoglycans (PGs)-rich layer between titanium dioxide (TiO2) and bone and chondroitin-4-sulfate transferase-1 (C4ST-1) that forms the sugar chain in PGs. Human bone marrow mesenchymal stem cells (hBMSCs) depleted of C4ST-1 were cultured on TiO2, and the interface between hBMSCs and TiO2 was analyzed by transmission electron microscopy. Further, the immunotolerance capacity, cell proliferation, initial attachment, and calcification were analyzed in vitro. At 14 days cultivation, a PGs-rich layer was observed between hBMSCs and TiO2. However, the PGs-rich layer was reduced in C4ST-1-depleted hBMSCs on TiO2. Further, real-time RT-PCR showed that conditioned media increased gene expression levels of M1-macrophage markers in human macrophages. However, C4ST-1 did not affect calcification, cell proliferation, and initial cell attachment on TiO2. These results suggested that C4ST-1 in hBMSCs affected the width of the PGs-rich layer on TiO2 and their immunotolerance capacity.

Cellular response (osteoblasts and fibroblasts) depending on the type of surface of dental implants.

Background. There are many strategies for modifying the surface of implants to create optimal conditions for the development of bone tissue. At the same time, the question of correlation of the effect of surface roughness or surface chemical composition on cell activity or osteogenesis processes remains open. Objective. The study of cellular mechanisms of osseointegration using cell cultures that occur after implantation of implants with a different type of alloy and the nature of their surface. Methods. To analyze the adhesion and cell proliferaiton, the resazurin reduction method was used, scanning electron microscopy was used to determine the distribution of cells on the sample surface and the type of cell interaction with surface. Results. Cell adhesion is observed in all studied groups, and the degree of cell adhesion is directly related to the presence of hydroxyapatite on the surface. A growing trend in the proliferation of osteoblasts is noted, while fibroblast proliferation slows down from the 3rd to the 7th day. At the same time, slow cell proliferation occurs on the surface of the implants without modification, and the percentage the reduction of resazurin does not exceed 23.5%. It should be noted that there is no difference between the types of alloys, which proves the predominance of the influence of surface topography on the proliferative activity of osteoblasts. Scanning electron microscopy on the 7th day revealed the presence of osteoblasts and fibroblasts in all studied samples. However, in the absence of hydroxyapatite, the cells are unevenly located on the surface of the sample, they are large in size and have long processes that do not have a clear orientation, and on the surface with hydroxyapatite coating there is a higher cell growth density, which predominantly has 2 processes and oriented in the same direction. Conclusion. The use of hydroxyapatite coating significantly increases the ability of cells to adhere to the surface of the implant. The presence of calcium and phosphorus mainly stimulates the proliferation of osteoblastic dipheron cells and almost does not affect the ability of fibroblasts to proliferate.

Osseointegration of dental implants with various surface types

Despite numerous modifications to the surface of the implants, the use of calcium-phosphate components is the most used technique because of the similarity in composition to the extracellular bone matrix. It is the presence of calcium and phosphorus ions, as well as the optimal sizes of surface structures that can increase the absorption of proteins and the adhesion of osteoblastic differential cells on the implant surface. However, many questions remain regarding the effect of the size of surface modifications, the possibility of using micro- and nanoscale modifications, and the effectiveness of various types of coatings in the long-term post-implantation osteogenesis. In addition, the influence of the mechanical parameters of the implant itself in combination with various types of surface modification has not been sufficiently studied.Objective — to study using tissue electron microscopy of tissue mechanisms of osseointegration in an experiment on laboratory animals.Material and methods. In order to study the processes occurring after implantation, we used 5 types of dental implants. In the experiment, Chinchilla rabbits were used at the age of 4–5 months with an initial weight of 3–3.5 kg in an amount of 60 individuals. To study the processes of osseointegration in the early stages (5 days), the implant was separated from the bone and its preparation was carried out for scanning electron microscopy.Results. Analyzing the data of scanning electron microscopy in a month, bone tissue is formed, which is represented by lamellar and coarse-fibered bone and also connective tissue, which has a lower electron density and is well visualized in combination with calcified tissues. It should be noted that there is a significant difference (p≤0.05) between alloys without a hydroxyapatite coating and KTZ-125-HA and β (Ti-Zr) -NA. The presence of a significantly larger amount of connective tissue around implants with an unchanged surface indicates a significant effect of hydroxyapatite on the development of bone tissue.Conclusions. In the early stages after the implantation of metal structures with bioinert alloys, adhesion of the organic matrix occurs on their surface. Bone formation processes occur on the surface of the implant. The biomechanical parameters of alloys play a key role in the process of bone remodeling around implants.

Viability and collagen secretion by fibroblasts on titanium surfaces with different acid-etching protocols

BackgroundFrom the consolidation of surface treatments of dental implants and knowledge on the cellular mechanisms of osseointegration, studies have highlighted the importance of a connective tissue seal against the implant to prevent contamination from the oral environment and consequent biofilm formation.ObjectiveThis in vitro study aimed to evaluate whether different titanium surface treatments using acid solutions promoted an increase in collagen secretion, proliferation, and viability of fibroblasts.Material and methodsCommercially pure grade-4 titanium disks (6 × 2 mm) were treated with different acid solutions (hydrochloric, nitric, and sulfuric) for 20 and 60 min, respectively, obtaining mean surface roughness of 0.1 to 0.15 μm and 0.5 to 0.7 μm. Human fibroblasts were seeded onto different surfaces and assessed after 24 h, 48 h, and 72 h for cell proliferation and viability using Trypan blue staining and MTT, respectively, as well as the secretion of type I collagen on to such surfaces using ELISA. Machined titanium surfaces were used as controls. Data were statistically analyzed using one-way ANOVA and Fisher's LSD test for multiple comparisons, adopting a significance level of 5%.ResultsNo significant difference was observed in cell proliferation for the different surfaces analyzed. Cell viability was significantly lower on the machined surface, after 48 h, when compared to the groups treated with acid for 20 or 60 min, which did not differ from each other. The expression of type I collagen was lowest on the acid-treated surfaces.ConclusionThe results showed that the acid treatment proposed did not promote fibroblast proliferation and viability nor favor type I collagen synthesis.

On osseointegration in relation to implant surfaces.

The understanding of mechanisms of osseointegration as well as applied knowledge about oral implant surfaces are of paramount importance for successful clinical results. The aim of the present article is to present an overview of osseointegration mechanisms and an introduction to surface innovations with relevance for osseointegration that will be published in the same supplement of Clinical Implant Dentistry and Related Research. The present article is a narrative review of some osseointegration and implant surface-related details. Osseointegration has a changed definition since it is realized today that oral implants are but foreign bodies and that this fact explains osseointegration as a protection mechanism of the tissues. Given adequate stability, bone tissue is formed around titanium implants to shield them from the tissues. Oral implant surfaces may be characterized by microroughness and nanoroughness, by surface chemical composition and by physical and mechanical parameters. An isotropic, moderately rough implant surface such as seen on the TiUnite device has displayed improved clinical results compared to previously used minimally rough or rough surfaces. However, there is a lack of clinical evidence supporting any particular type of nanoroughness pattern that, at best, is documented with results from animal studies. It is possible, but as yet unproven, that clinical results may be supported by a certain chemical composition of the implant surface. The same can be said with respect to hydrophilicity of implant surfaces; positive animal data may suggest some promise, but there is a lack of clinical evidence that hydrophilic implants result in improved clinical outcome of more hydrophobic surfaces. With respect to mechanical properties, it seems obvious that those must be encompassing the loading of oral implants, but we need more research on the mechanically ideal implant surface from a clinical aspect.

Research on implants and osseointegration.

Osseointegration was originally defined as a direct structural and functional connection between ordered living bone and the surface of a load-carrying implant. It is now said that an implant is regarded as osseointegrated when there is no progressive relative movement between the implant and the bone with which it is in direct contact. Although the term osseointegration was initially used with reference to titanium metallic implants, the concept is currently applied to all biomaterials that have the ability to osseointegrate. Biomaterials are closely related to the mechanism of osseointegration; these materials are designed to be implanted or incorporated into the living system with the aims to substitute for, or regenerate, tissues and tissue functions. Objective evaluation of the properties of the different biomaterials and of the factors that influence bone repair in general, and at the bone tissue-implant interface, is essential to the clinical success of an implant. The Biomaterials Laboratory of the Oral Pathology Department of the School of Dentistry at the University of Buenos Aires is devoted to the study and research of the properties and biological effects of biomaterials for dental implants and bone substitutes. This paper summarizes the research work resulting from over 25years' experience in this field. It includes studies conducted at our laboratory on the local and systemic factors affecting the peri-implant bone healing process, using experimental models developed by our research team. The results of our research on corrosion, focusing on dental implants, as well as our experience in the evaluation of failed dental implants and bone biopsies obtained following maxillary sinus floor augmentation with bone substitutes, are also reported. Research on biomaterials and their interaction with the biological system is a continuing challenge in biomedicine, which aims to achieve optimal biocompatibility and thus contribute to patient health.

Bioactive TiNbSn alloy prepared by anodization in sulfuric acid electrolytes

The bioactivity of anodized near-β TiNbSn alloy with low Young's modulus prepared in sulfuric acid electrolytes was examined to explore the osseointegration mechanism with a focus on the role of anodic oxide. Hydroxyapatite (HA) precipitated on the surface of anodic oxide following immersion in Hank's solution, and precipitation accelerated with increase in the sulfuric acid concentration of the electrolyte. HA is formed on the surface of as-anodized oxide without subsequent annealing or hot water (HW) treatment. This outcome differs from that of a previous study using anodized TiNbSn alloy prepared in acetic acid electrolytes requiring for subsequent HW treatment. It was found that the oxide anodized in sulfuric acid electrolyte contains a large amount of internal pores and is highly crystallized thick TiO2, whereas the same prepared in the acetic acid electrolyte is low crystalline thin TiO2 containing a small amount of pores. The present anodized TiNbSn alloy is preferred for maintaining the low Young's modulus of the alloy and eliminating the subsequent treatment to increase the Young's modulus. A model to rationalize the bioactivity of the present anodic oxide is proposed based on the series of studies. It is concluded that the sulfuric acid electrolyte is favorable for both HA formation and low Young's modulus, and the bioactivity is attributed to the anodic TiO2 that facilitates incorporation of bone ingredients.

Effect of hyaluronic acid on the osseointegration of dental implants

The mechanism of osseointegration is related to many factors, including the quality of the bone, the biocompatibility and surface characteristics of the implant material, the surgical technique, and functional loading. The purpose of this study was to investigate the effects of hyaluronic acid gel on the osseointegration of implants placed in defined areas of the mandible in rabbits. Hyaluronic acid is known to have an osteoinductive effect during regeneration of bony defects, and we thought that it might also have a favourable effect on osseointegration, a specialised mechanism to heal bone. Ten New Zealand rabbits aged 10 weeks and weighing 2.5–3.0kg were used, and sites for implants that were far enough from the apices of the teeth in the mandibular molar area were chosen. Two cavities were prepared in each rabbit, one (anterior) for the control implant, and one (posterior) for the implant with hyaluronic acid gel (Medical Instinct GmbH, Bovenden). New bone and the osteoid matrix content around the dental implants were evaluated histologically and histomorphometrically two months after the operation, and no significant difference was found between the two groups.

Neuronal PAS domain 2 (Npas2) facilitated osseointegration of titanium implant with rough surface through a neuroskeletal mechanism

Titanium (Ti) biomaterials have been applied to a wide range of implantable medical devices. When placed in bone marrow, Ti-biomaterials integrate to the surrounding bone tissue by mechanisms that are not fully understood. We have previously identified an unexpected upregulation of circadian clock molecule neuronal PAS domain 2 (Npas2) in successfully integrated implant with a rough surface. This study aimed to elucidate the molecular mechanism of osseointegration through determining the role of Npas2. Human bone marrow stromal cells (BMSC) that were cultured on a Ti disc with SLA surface exhibited increased NPAS2 expression compared to BMSC cultured on a machined surface. A mouse model was developed in which miniature Ti implants were surgically placed into femur bone marrow. The implant push-out test and bone-to-implant contact measurements demonstrated the establishment of osseointegration in 3 weeks. By contrast, in Npas2 functional knockout (KO) mice, the implant push-out value measured for SLA surface Ti implant was significantly decreased. Npas2 KO mice demonstrated normal femur bone structure surrounding the Ti implant; however, the recovered implants revealed abnormal remnant mineralized tissue, which lacked dense collagen architecture typically found on recovered implants from wild type mice. To explore the mechanisms leading to the induced Npas2 expression, an unbiased chemical genetics analysis was conducted using mouse BMSC carrying an Npas2-reporter gene for high throughput screening of Library of Pharmacologically Active Compounds. Npas2 modulating compounds were found clustered in regulatory networks of the α2-adrenergic receptor and its downstream cAMP/CREB signaling pathway. Mouse primary BMSC exposed to SLA Ti disc significantly increased the expression of α2-adrenergic receptors, but the expression of β2-adrenergic receptor was unaffected. Our data provides the first evidence that peripheral clock gene component Npas2 plays a role in facilitating the enhanced osseointegration through neuroskeletal regulatory pathways induced by BMSC in contact with rough surface Ti implant.

Densitometric evaluation of bone-prosthetic counterface in hip and knee arthroplasty with modern implants.

Recent acquisitions of the complex mechanisms of osseointegration between implants and host bone have gained attention, accordingly to the methods of evaluation of these interactions. DEXA analysis is considered an useful tool to assess such phenomena, in order to analyse in a quantitative manner the local metabolic activity of the bone, and to evaluate over the time the integration between host bone and prosthetic components. The purpose of the present study is to report about a preliminary experience in the analysis of osseointegration processes of patients undergoing a primary Total Hip Arthroplasty (THA) or a revision Total Knee Arthroplasty (rTKA). Thirty patients undergoing THA and nineteen undergoing rTKA were included in this study. In fifteen cases of THA a standard cementless stem was used; in the other fifteen a short cementless stem was chosen. In all cases a cementless cup was implanted. In all patients undergoing rTKA, all implants had pressfit femoral and tibial diaphyseal stems; only the femoral component and the tibial plateau were cemented. DEXA evaluation was performed preoperatively, and at 3, 6, 12, and 24 months postoperatively for rTKA, and at 6 and 12 months for THA. DEXA in THA showed a significant decrease at the femoral ROIs 1 and 7, and an increase in ROI 4. In rTKA a reduction of femoral BMD in R1, R7, and R4 was found, with maximum values of -13.6% in R1 and -11.89% in R7 at 24 months and a value of -2.55% in R4 at 12 months. On the tibial side, an increase in BMD R4 (with values of 2.18% still at 24 months), and a reduction in R7 (progressively lesser over the time) and in R1 (progressively higher) were found. After a joint replacement a full adhesion of the prosthetic surface to the host bone should be achieved through a local biological process named osseointegration. In some cases this process may not fully realize, so the secondary stability of the implant may fail. DXA is a valuable tool to follow over time the bone remodelling at the bone-prosthesis counterface in THA and in rTKA, in order to early detect any alterations of such phenomenon.

A Novel In Vitro Technique for Assessing Dental Implant Osseointegration.

By definition, osseointegration means close contact between bone and implant. Bone response is related to implant surface properties. Various surfaces have been studied and applied to improve the biological properties of the implant and thereby favor the mechanism of osseointegration. This strategy aims to promote osseointegration by means of a faster and stronger bone formation, improving stability during the healing process, and thus allowing for earlier loading of the implant. Dental implant osseointegration has so far been studied in various animal models. The development of a method based on tissue engineering for assessing the osseointegration process in vitro could prove a valid biomimetic alternative to sacrificing animals. In this study, flat cylindrical dental implants with moderately rough surfaces and machined implants were set in bovine bone blocks. Then, adipose-derived stem cells (ADSCs) were three dimensionally cultured onto these blocks in osteo-endothelial medium for up to 30 days to mimic the osseointegration process in vitro. Scanning electron microscopy (SEM) and gene expression were used to examine stem cell commitment. Mechanical pull-out tests were also performed. SEM analysis identified cells with an osteoblast morphology adhering to the surface of the implants after their removal. Gene expression analysis showed that ADSCs seeded onto the bone blocks were able to express osteoblast and endothelial markers. The implants with the moderately rough surface generated higher pull-out strengths when compared with the machined implants. Nevertheless, the pull-out test values were higher for implants placed in bone blocks with ADSCs than for those set in scaffolds without stem cells. Our results demonstrate the validity of the method adopted and its potential for use in the in vitro assessment of the biological behavior of dental implant surfaces.