Trabecular bone response to surface roughened and calcium phosphate (Ca-P) coated titanium implants

Modified Titanium Surface with Nano Amorphous Calcium Phosphate@Chitosan Oligolactate as Ion Loading Platform with Multifunctional Properties for Potential Biomedical Application

Titanium (Ti) is widely used in medical and dental implants. Calcium phosphate (CPs) coatings enhance Ti implants' osteoinductive properties, and additives further improve these coatings. Recently, a nano amorphous calcium phosphate (nACP) coating decorated with chitosan oligolactate (ChOL) and selenium (Se) showed immunomodulatory effects. This study investigates the surface morphology, composition, bioactivity, mechanical properties, and Se-release mechanism of the nACP@ChOL-Se hybrid coating on Ti substrates. Amorphous calcium phosphate (ACP) was synthesized, and the nACP@ChOL-Se hybrid coating was deposited on Ti substrates using in situ anaphoretic deposition. Physico-chemical characterization was used to analyze the surface of the coating (scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy). The distribution of Se within the coating was examined with energy-dispersive X-ray spectroscopy (EDS). Bioactivity was evaluated in simulated body fluid (SBF), and adhesion was tested using a scratch test method. In vitro testing determined the release mechanism of Se. SEM images illustrated the surface morphology, while AFM provided a detailed analysis of surface roughness. XRD analysis revealed structural and phase composition, and EDS confirmed Se distribution within the coating. The coating exhibited bioactivity in SBF and showed good adhesion according to the scratch test. In vitro testing uncovered the release mechanism of Se from the coating. This study successfully characterized the surface morphology, composition, bioactivity, and Se-release mechanism of the nACP@ChOL-Se hybrid coating on Ti substrates, offering insights for developing immunomodulatory coatings for medical and dental applications.

There Are over 60 Ways to Produce Biocompatible Calcium Orthophosphate (CaPO4) Deposits on Various Substrates

A The present overview describes various production techniques for biocompatible calcium orthophosphate (abbreviated as CaPO4) deposits (coatings, films and layers) on the surfaces of various types of substrates to impart the biocompatible properties for artificial bone grafts. Since, after being implanted, the grafts always interact with the surrounding biological tissues at the interfaces, their surface properties are considered critical to clinical success. Due to the limited number of materials that can be tolerated in vivo, a new specialty of surface engineering has been developed to desirably modify any unacceptable material surface characteristics while maintaining the useful bulk performance. In 1975, the development of this approach led to the emergence of a special class of artificial bone grafts, in which various mechanically stable (and thus suitable for load-bearing applications) implantable biomaterials and artificial devices were coated with CaPO4. Since then, more than 7500 papers have been published on this subject and more than 500 new publications are added annually. In this review, a comprehensive analysis of the available literature has been performed with the main goal of finding as many deposition techniques as possible and more than 60 methods (double that if all known modifications are counted) for producing CaPO4 deposits on various substrates have been systematically described. Thus, besides the introduction, general knowledge and terminology, this review consists of two unequal parts. The first (bigger) part is a comprehensive summary of the known CaPO4 deposition techniques both currently used and discontinued/underdeveloped ones with brief descriptions of their major physical and chemical principles coupled with the key process parameters (when possible) to inform readers of their existence and remind them of the unused ones. The second (smaller) part includes fleeting essays on the most important properties and current biomedical applications of the CaPO4 deposits with an indication of possible future developments.

A systematic review on the effect of inorganic surface coatings in large animal models and meta-analysis on tricalcium phosphate and hydroxyapatite on periimplant bone formation

The aim of the present systematic review was to analyse studies using inorganic implant coatings and, in a meta‐analysis, the effect of specifically tricalcium phosphate (TCP) and hydroxyapatite (HA) implant surface coatings on bone formation according to the PRISMA criteria. Inclusion criteria were the comparison to rough surfaced titanium implants in large animal studies at different time points of healing. Forty studies met the inclusion criteria for the systematic review. Fifteen of these analyzed the bone‐to‐implant contact (BIC) around the most investigated inorganic titanium implant coatings, namely TCP and HA, and were included in the meta‐analysis. The results of the TCP group show after 14 days a BIC being 3.48% points lower compared with the reference surface. This difference in BIC decreases to 0.85% points after 21–28 days. After 42–84 days, the difference in BIC of 13.79% points is in favor of the TCP‐coatings. However, the results are not statistically significant, in part due to the fact that the variability between the studies increased over time. The results of the HA group show a significant difference in mean BIC of 6.94% points after 14 days in favor of the reference surface. After 21–28 days and 42–84 days the difference in BIC is slightly in favor of the test group with 1.53% points and 1.57% points, respectively, lacking significance. In large animals, there does not seem to be much effect of TCP‐coated or HA‐coated implants over uncoated rough titanium implants in the short term.

The Oxidative Response of Human Monocytes to Surface Modified Commercially Pure Titanium

Cellular responses to implanted biomaterials are key to understanding osseointegration. The aim of this investigation was to determine the in vitro priming and activation of the respiratory burst activity of monocytes in response to surface-modified titanium. Human peripheral blood monocytes of healthy blood donors were separated, then incubated with surface-modified grade 2 commercially pure titanium (CPT) disks with a range of known surface energies and surface roughness for 30- or 60-min. Secondary stimulation by phorbol 12-myrisate 13-acetate (PMA) following the priming phase, and luminol-enhanced-chemiluminescence (LCL) was used to monitor oxygen-dependent activity. Comparison among groups was made by incubation time using one-way ANOVA. One sample from each group for each phase of the experiment was viewed under scanning electron microscopy (SEM) and qualitative comparisons made. The results indicate that titanium is capable of priming peripheral blood monocytes following 60-min incubation. In contrast, 30 min incubation time lead to reduced LCL on secondary stimulation as compared to cells alone. At both time intervals, the disk with the lowest surface energy produced significantly less LCL compared to other samples. SEM examination revealed differences in surface morphology at different time points but not between differently surface-modified disks. These results are consistent with the hypothesis that the titanium surface characteristics influenced the monocyte activity, which may be important in regulating the healing response to these materials.

Systematic Review and Meta-Analysis of the Effectiveness of Calcium-Phosphate Coating on the Osseointegration of Titanium Implants

Ca-P coatings on Ti implants have demonstrated good osseointegration capability due to their similarity to bone mineral matter. Three databases (PubMed, Embase, and Web of Science) were searched electronically in February 2021 for preclinical studies in unmodified experimental animals, with at least four weeks of follow-up, measuring bone-to-implant contact (BIC). Although 107 studies were found in the initial search, only eight experimental preclinical studies were included. Adverse events were selected by two independent investigators. The risk of bias assessment of the selected studies was evaluated using the Cochrane Collaboration Tool. Finally, a meta-analysis of the results found no statistical significance between implants coated with Ca-P and implants with etched conventional surfaces (difference of means, random effects: 5.40; 99% CI: -5.85, 16.65). With the limitations of the present review, Ca-P-coated Ti surfaces have similar osseointegration performance to conventional etched surfaces. Future well-designed studies with large samples are required to confirm our findings.

Zn-HA/Bi-HA biphasic coatings on Titanium: Fabrication, characterization, antibacterial and biological activity

Hydroxyapatite (HA) coatings have been of important as biocompatible coatings for dental and bone tissue engineering application. However, the poor antibacterial performance and weak biological activity of HA coatings limited their clinical applications. As a strategy to improve the antibacterial performance and biological activity of HA, Zinc and bismuth ions were incorporated into HA lattice by substituting Ca²⁺ ions, respectively, and thus zinc substituted hydroxyapatite/bismuth substituted hydroxyapatite (Zn-HA/Bi-HA) biphasic coatings on titanium plates with various ratios were fabricated via sol-gel and dip-coating processes. The purity of the Zn-HA and Bi-HA phase was confirmed by X-ray diffraction (XRD) test. The biphasic coatings showed slower dissolution rate than pure HA coating. Furthermore, the Zn-HA/Bi-HA coatings reveal good biomineralization activity in simulated body fluid (SBF) by forming regular spherical apatite agglomerates. Moreover, the biphasic Zn-HA/Bi-HA coatings exhibited that improved antimicrobial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as compared to pure HA coatings. The CCK-8 assays demonstrate Zn-HA/Bi-HA coatings showed no toxicity to MG63 cells, and the Zn-HA/Bi-HA2 (Zn-HA:Bi-HA=64:1) coating is more effective to enhance the proliferation of MG63 cells compared to other coatings. This finding suggests Zn-HA/Bi-HA biphasic coatings are promising candidates for biomedical applications.

Effects of Aloe Vera Gel Extract in Doped Hydroxyapatite-Coated Titanium Implants on in Vivo and in Vitro Biological Properties

Hydroxyapatite-coated titanium alloys have been a popular choice as bone implants for load-bearing applications for the compositional similarity of hydroxyapatite to natural bone. The limited osteoinductive properties exhibited by the hydroxyapatite (HA) coatings have led to the incorporation of growth factor or dopants for improved osseointegration. This study aims to investigate the effects of a naturally occurring aloe vera gel extract, acemannan, in doped hydroxyapatite coatings on the in vitro osteoblast cell viability and in vivo new bone formation in a rat distal femur model. Silver oxide and silica-doped hydroxyapatite coatings were developed by the induction plasma spray coating method on Ti alloys to introduce antibacterial properties along with induction of angiogenic properties, respectively. The doped coating was further consecutively dip coated with acemannan to analyze its effects on the in vivo early stage osseointegration and chitosan to control the burst release of the acemannan from the calcium phosphate matrix. The results show controlled release of acemannan from the chitosan coatings, with enhanced osteoblast cell viability by the incorporation of acemannan in vitro. Improved osseointegration with a seamless implant interface and improved new bone formation was noted by the acemannan and chitosan coating in vivo, 5 weeks after implantation. Our results demonstrate the efficacy of a combination of natural medicine and naturally occurring polymer in a doped hydroxyapatite-coated titanium implant on the bone tissue regeneration for load-bearing orthopedic applications.

Characterization and Bone Response of Carbonate-Containing Apatite-Coated Titanium Implants Using an Aqueous Spray Coating

We performed thin carbonate-containing apatite (CA) coating on titanium (Ti) by an aqueous spray coating (ASC) method that consisted of a Ca-CO₃-PO₄ complex. Two different CA coatings were produced by two different spray amounts and were heat-treated after spraying. We evaluated three-dimensional structures, adhesiveness to Ti, and durability of the CA film. In addition, we performed immersion experiments in simulated body fluid (SBF), and bone responses were evaluated after implantation into a femoral bone defect in rats. The bonding ability of ASC-coated implant into the bone was examined by push-in tests. Unique network structures with small particles were identified on CA coatings. Although heat treatment produced no significant difference in surface morphology, scratch tests revealed that heat treatment improved the adhesion of CA coatings to Ti. Crystal formation progressed on CA-coated specimens, and the sample placement direction influenced crystal formation and growth in SBF immersion. Animal implantation experiments revealed significantly greater bone-to-implant contact ratio and bone mass in both cortical and bone marrow, respectively, four weeks after implantation. Push-in tests suggested that the bonding of the CA coating to Ti is clinically acceptable. Therefore, we conclude that CA coating to Ti by the ASC method would be possible for clinical applications, including dentistry.

Osseointegration of standard and mini dental implants: a histomorphometric comparison

Background

Mini dental implants (MDIs) are becoming increasingly popular for rehabilitation of edentulous patients because of their several advantages. However, there is a lack of evidence on the osseointegration potential of the MDIs. The objective of the study was to histomorphometrically evaluate and compare bone apposition on the surface of MDIs and standard implants in a rabbit model.

Methods

Nine New Zealand white rabbits were used for the study to meet statistical criteria for adequate power. Total 18 3M^™ESPE^™ MDIs and 18 standard implants (Ankylos^® Friadent, Dentsply) were inserted randomly into the tibia of rabbits (four implants per rabbit); animals were sacrificed after a 6-week healing period. The specimens were retrieved en bloc and preserved in 10% formaldehyde solution. Specimens were prepared for embedding in a light cure acrylic resin (Technovit 9100). The most central sagittal histological sections (30–40 μm thick) were obtained using a Leica SP 1600 saw microtome. After staining, the Leica DM2000 microscope was used, the images were captured using Olympus DP72 camera and associated software. Bone implant contact (BIC) was measured using Infinity Analyze software.

Results

All implants were osseointegrated. Histologic measures show mineralized bone matrix in intimate contact with the implant surface in both groups. The median BIC was 58.5 % (IQR 8.0) in the MDI group and 57.0 % (IQR 5.5) in the control group (P > 0.05; Mann-Whitney test). There were no statistical differences in osseointegration at 6 weeks between MDIs and standard implants in rabbit tibias.

Conclusions

Based on these results, it is concluded that osseointegration of MDIs is similar to that of standard implants.

Synthesis, Characterization, and Biological Evaluation of Nanostructured Hydroxyapatite with Different Dimensions

Nanosized hydroxyapatite (HA) is a promising candidate for a substitute for apatite in bone in biomedical applications. Furthermore, due to its excellent bone bioactivity, nanosized strontium-substituted HA (SrHA) has aroused intensive interest. However, the size effects of these nanoparticles on cellular bioactivity should be considered. In this study, nanosized HA and SrHA with different dimensions and crystallization were synthesized by hydrothermal methods. The phase, crystallization and chemical composition were analyzed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR), respectively. The morphology was observed under field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The degradation behaviors of the samples were monitored by determining the ions release profile with inductively coupled plasma mass spectrometry (ICP-MS). The releasing behavior of Ca2+ and Sr2+ showed that the degradation rate was proportional to the specific surface area and inversely proportional to crystallization. The in vitro experiment evaluated by MG63 cells showed that SrHA nanorods with a length greater than 100 nm had the best biological performance both in cell proliferation and differentiation (* p < 0.05 compared with HA-1 and SrHA-1; * p < 0.01 compared with HA-2). In addition, HA nanoparticles with a lower aspect ratio had better bioactivity than higher ones (* p < 0.05). This study demonstrated that nanosized HA and SrHA with subtle differences (including dimensions, crystallization, specific surface area, and degradation rate) could affect the cellular growth and thus might have an impact on bone growth in vivo. This work provides a view of the role of nano-HAs as ideal biocompatible materials in future clinical applications.

Calcium orthophosphate deposits: Preparation, properties and biomedical applications

Since various interactions among cells, surrounding tissues and implanted biomaterials always occur at their interfaces, the surface properties of potential implants appear to be of paramount importance for the clinical success. In view of the fact that a limited amount of materials appear to be tolerated by living organisms, a special discipline called surface engineering was developed to initiate the desirable changes to the exterior properties of various materials but still maintaining their useful bulk performances. In 1975, this approach resulted in the introduction of a special class of artificial bone grafts, composed of various mechanically stable (consequently, suitable for load bearing applications) implantable biomaterials and/or bio-devices covered by calcium orthophosphates (CaPO4) to both improve biocompatibility and provide an adequate bonding to the adjacent bones. Over 5000 publications on this topic were published since then. Therefore, a thorough analysis of the available literature has been performed and about 50 (this number is doubled, if all possible modifications are counted) deposition techniques of CaPO4 have been revealed, systematized and described. These CaPO4 deposits (coatings, films and layers) used to improve the surface properties of various types of artificial implants are the topic of this review.

Effect of calcium phosphate coating and rhBMP-2 on bone regeneration in rabbit calvaria using poly(propylene fumarate) scaffolds

Various calcium phosphate based coatings have been evaluated for better bony integration of metallic implants and are currently being investigated to improve the surface bioactivity of polymeric scaffolds. The aim of this study was to evaluate the role of calcium phosphate coating and simultaneous delivery of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the in vivo bone regeneration capacity of biodegradable, porous poly(propylene fumarate) (PPF) scaffolds. PPF scaffolds were coated with three different calcium phosphate formulations: magnesium-substituted β-tricalcium phosphate (β-TCMP), carbonated hydroxyapatite (synthetic bone mineral, SBM) and biphasic calcium phosphate (BCP). In vivo bone regeneration was evaluated by implantation of scaffolds in a critical-sized rabbit calvarial defect loaded with different doses of rhBMP-2. Our data demonstrated that scaffolds with each of the calcium phosphate coatings were capable of sustaining rhBMP-2 release and retained an open porous structure. After 6weeks of implantation, micro-computed tomography revealed that the rhBMP-2 dose had a significant effect on bone formation within the scaffolds and that the SBM-coated scaffolds regenerated significantly greater bone than BCP-coated scaffolds. Mechanical testing of the defects also indicated restoration of strength in the SBM and β-TCMP with rhBMP-2 delivery. Histology results demonstrated bone growth immediately adjacent to the scaffold surface, indicating good osteointegration and osteoconductivity for coated scaffolds. The results obtained in this study suggest that the coated scaffold platform demonstrated a synergistic effect between calcium phosphate coatings and rhBMP-2 delivery and may provide a promising platform for the functional restoration of large bone defects.

Biomimetic approaches in bone tissue engineering: Integrating biological and physicomechanical strategies

The development of responsive biomaterials capable of demonstrating modulated function in response to dynamic physiological and mechanical changes in vivo remains an important challenge in bone tissue engineering. To achieve long-term repair and good clinical outcomes, biologically responsive approaches that focus on repair and reconstitution of tissue structure and function through drug release, receptor recognition, environmental responsiveness and tuned biodegradability are required. Traditional orthopedic materials lack biomimicry, and mismatches in tissue morphology, or chemical and mechanical properties ultimately accelerate device failure. Multiple stimuli have been proposed as principal contributors or mediators of cell activity and bone tissue formation, including physical (substrate topography, stiffness, shear stress and electrical forces) and biochemical factors (growth factors, genes or proteins). However, optimal solutions to bone regeneration remain elusive. This review will focus on biological and physicomechanical considerations currently being explored in bone tissue engineering.

Enhanced osteogenicity of bioactive composites with biomimetic treatment

Purpose. This study aimed to explore if initiation of biomimetic apatite nucleation can be used to enhance osteoblast response to biodegradable tissue regeneration composite membranes. Materials and Methods. Bioactive thermoplastic composites consisting of poly(ε-caprolactone/DL-lactide) and bioactive glass (BAG) were prepared at different stages of biomimetic calcium phosphate deposition by immersion in simulated body fluid (SBF). The modulation of the BAG dissolution and the osteogenic response of rat mesenchymal stem cells (MSCs) were analyzed. Results. SBF treatment resulted in a gradual calcium phosphate deposition on the composites and decreased BAG reactivity in the subsequent cell cultures. Untreated composites and composites covered by thick calcium phosphate layer (14 days in SBF) expedited MSC mineralization in comparison to neat polymers without BAG, whereas other osteogenic markers—alkaline phosphatase activity, bone sialoprotein, and osteocalcin expression—were initially decreased. In contrast, surfaces with only small calcium phosphate aggregates (five days in SBF) had similar early response than neat polymers but still demonstrated enhanced mineralization. Conclusion. A short biomimetic treatment enhances osteoblast response to bioactive composite membranes.

In vivo evaluation of resorbable bone graft substitutes in beagles: histological properties

Calcium phosphate cement (CPC) is a promising material for use in minimally invasive surgery for bone defect repairs due to its bone-like apatitic final setting product, biocompatibility, bioactivity, self-setting characteristics, low setting temperature, adequate stiffness, and easy shaping into complicated geometrics. However, even though CPC is stable in vivo, the resorption rate of this bone cement is very slow and its long setting time poses difficulties for clinical use. Calcium sulfate dehydrate (CSD) has been used as a filler material and/or as a replacement for cancellous bone grafts due to its biocompatibility. However, it is resorbed too quickly to be optimal for bone regeneration. This study examines the invivo response of a hydroxyapatite (HA), [apatitic phase (AP)]/calcium sulfate (CSD) composite using different ratios in the mandibular premolar sockets of beagles. The HA (AP)/CSD composite materials were prepared in the ratios of 30/70, 50/50, and 70/30 and then implanted into the mandibular premolar sockets for terms of 5 and 10 weeks. The control socket was left empty. The study shows better new bone morphology and more new bone area in the histological and the histomorphometric study of the HA (AP)/CSD in the 50/50 ratio.

Calcium orthophosphate coatings, films and layers

In surgical disciplines, where bones have to be repaired, augmented or improved, bone substitutes are essential. Therefore, an interest has dramatically increased in application of synthetic bone grafts. As various interactions among cells, surrounding tissues and implanted biomaterials always occur at the interfaces, the surface properties of the implants are of the paramount importance in determining both the biological response to implants and the material response to the physiological conditions. Hence, a surface engineering is aimed to modify both the biomaterials, themselves, and biological responses through introducing desirable changes to the surface properties of the implants but still maintaining their bulk mechanical properties. To fulfill these requirements, a special class of artificial bone grafts has been introduced in 1976. It is composed of various mechanically stable (therefore, suitable for load bearing applications) biomaterials and/or bio-devices with calcium orthophosphate coatings, films and layers on their surfaces to both improve interactions with the surrounding tissues and provide an adequate bonding to bones. Many production techniques of calcium orthophosphate coatings, films and layers have been already invented and new promising techniques are continuously investigated. These specialized coatings, films and layers used to improve the surface properties of various types of artificial implants are the topic of this review.

Structural influence from calcium phosphate coatings and its possible effect on enhanced bone integration

OBJECTIVE

The aim of this review was to summarize our present knowledge about calcium phosphate (CaP) coatings on implants with respect to their topographical appearance at micrometer as well as nanometer level and also the reported influence on bone healing.

MATERIAL AND METHODS

The PubMed database was used with the key words - surface roughness, CaP coating, implant, bone integration, clinical studies, experimental studies - used in different combinations. Only in vivo studies were taken into consideration.

CONCLUSIONS

A significantly improved healing capacity associated with CaP-coated implants is often reported, but individual importance of the several modes of surface changes introduced, deliberately or not, is usually very difficult to interpret. Several studies claim this difference to be due to altered chemistry, but in many the result may equally well be dependent on the surface topography. The few studies that have been published indicate that nanometer structures have an impact on early bone healing. However, the optimal size and distribution of nanometer-sized particles or pores applied on implant surfaces is still unknown, as are the evaluation effects of micrometer roughness. Improved surface characterization is needed if we are to reveal effects dependent on isolated nanometer alterations.

Antibacterial and biological characteristics of silver containing and strontium doped plasma sprayed hydroxyapatite coatings

Infection in primary total joint prostheses is estimated to occur in up to 3% of all surgery. As a measure to improve the antimicrobial properties of implant materials silver (Ag) was incorporated into plasma sprayed hydroxyapatite (HA) coatings. To offset potential cytotoxic effects of Ag in the coatings strontium (Sr) was also added as a binary dopant. HA powder was doped with 2.0 wt.% Ag(2)O, 1.0 wt.% SrO and was then heat treated at 800 °C. Titanium substrates were coated using a 30 kW plasma spray system equipped with a supersonic nozzle. X-ray diffraction confirmed the phase purity and high crystallinity of the coatings. Samples were evaluated for mechanical stability by adhesive bond strength testing. The results show that the addition of dopants did not affect the overall bond strength of the coatings. The antibacterial efficacies of the coatings were tested against Pseudomonas aeruginosa. Samples that contained the Ag(2)O dopant were found to be highly effective against bacterial colonization. In vitro cell-material interactions using human fetal osteoblast cells were characterized by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay for cell viability, field emission scanning electron microscopy for cell morphology and confocal imaging for the important differentiation marker alkaline phosphatase (ALP). Our results showed evidence of cytotoxic effects of the Ag-HA coatings, characterized by poor cellular morphology and cell death and nearly complete loss of functional ALP activity. The addition of SrO to the Ag-HA coatings was able to effectively offset these negative effects and improve performance compared with pure HA-coated samples.

Dental implant systems

Among various dental materials and their successful applications, a dental implant is a good example of the integrated system of science and technology involved in multiple disciplines including surface chemistry and physics, biomechanics, from macro-scale to nano-scale manufacturing technologies and surface engineering. As many other dental materials and devices, there are crucial requirements taken upon on dental implants systems, since surface of dental implants is directly in contact with vital hard/soft tissue and is subjected to chemical as well as mechanical bio-environments. Such requirements should, at least, include biological compatibility, mechanical compatibility, and morphological compatibility to surrounding vital tissues. In this review, based on carefully selected about 500 published articles, these requirements plus MRI compatibility are firstly reviewed, followed by surface texturing methods in details. Normally dental implants are placed to lost tooth/teeth location(s) in adult patients whose skeleton and bony growth have already completed. However, there are some controversial issues for placing dental implants in growing patients. This point has been, in most of dental articles, overlooked. This review, therefore, throws a deliberate sight on this point. Concluding this review, we are proposing a novel implant system that integrates materials science and up-dated surface technology to improve dental implant systems exhibiting bio- and mechano-functionalities.

Effects of implant surface coatings and composition on bone integration: a systematic review

OBJECTIVE

The aim of the present review was to evaluate the bone integration efficacy of recently developed and marketed oral implants as well as experimental surface alterations.

MATERIALS AND METHODS

A PubMed search was performed for animal studies, human reports and studies presenting bone-to-implant contact percentage or data regarding mechanical testing.

RESULTS

For recently developed and marketed oral implants, 29 publications and for experimental surface alterations 51 publications fulfilled the inclusion criteria for this review.

CONCLUSIONS

As demonstrated in the available literature dealing with recently developed and marketed oral implants, surface-roughening procedures also affect the surface chemical composition of oral implants. There is sufficient proof that surface roughening induces a safe and predictable implant-to-bone response, but it is not clear whether this effect is due to the surface roughness or to the related change in the surface composition. The review of the experimental surface alterations revealed that thin calcium phosphate (CaP) coating technology can solve the problems associated with thick CaP coatings, while they still improve implant bone integration compared with non-coated titanium implants. Nevertheless, there is a lack of human studies in which the success rate of thin CaP-coated oral implants is compared with just roughened oral implants. No unequivocal evidence is available that suggests a positive effect on the implant bone integration of peptide sequences or growth factors coated on titanium oral implants. In contrast, the available literature suggests that bone morphogenetic protein-2 coatings might even impede the magnitude of implant-to-bone response.

Fabrication and evaluation of Zn containing fluoridated hydroxyapatite layer with Zn release ability

A biphasic layer with a Zn-containing beta-tricalcium phosphate (ZnTCP) phase and a fluoridated hydroxyapatite (FHA) phase on titanium alloy substrate was prepared by the sol-gel technique. Scanning electron microscopy and energy-dispersive X-ray analysis results showed the ZnTCP/FHA layer to have a heterogeneous surface with microscaled gibbous structures originating from ZnTCP particle agglomeration. This layer had a slow and sustained Zn release behavior. The scratch test result of the ZnTCP/FHA layer was 489+/-4mN, indicating good interface bonding between the layer and substrate. The ZnTCP/FHA layer supported cell growth, and showed a statistically significant increase in cell viability in comparison with another biphasic layer (TCP/FHA) without Zn. This work demonstrates that the present biphasic ZnTCP/FHA layer has the potential to play a significant role in enhancing bone growth when used as the outermost part of bioactive coatings on metallic implants.

Characterization andin vitro evaluation of biphasic calcium pyrophosphate–tricalciumphosphate radio frequency magnetron sputter coatings

The objective of this study was to characterize the physicochemical, dissolution, and osteogenic properties of radio frequency magnetron sputtered dicalcium pyrophosphate/tricalciumphosphate (Pyro/TCP) and hydroxylapatite (HA) coatings. Therefore Pyro/TCP and HA coatings were deposited on grit-blasted titanium discs. The results showed that the deposited coatings were amorphous and changed into a crystalline structure after IR heat-treatment of 550 degrees C for HA and 650 degrees C for Pyro/TCP. Heat-treated HA coatings appeared to be stable during immersion in simulated body fluid (SBF), that is no changes in the XRD pattern were observed. Also, no dissolution of the coating was observed by scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) revealed that the Ca/P ratio of the HA coatings remained constant during SBF immersion. On the other hand, the heat-treated Pyro/TCP coatings showed a surface reaction of calcium pyrophosphate into a beta-tricalcium phosphate phase during SBF immersion. This was confirmed by EDS analysis. Rat bone marrow-derived osteoblast-like cells cultured on the heat-treated substrates showed that cell proliferation and differentiation occurred on both types of bioceramic coatings. No significant differences for proliferation and early differentiation were observed between cells cultured on heat-treated Pyro/TCP and HA at individual time points. However, osteocalcin expression, a late marker for osteoblast-like cell differentiation, was significantly increased after 12 days of culture on HA-coatings. These results were confirmed by SEM observations and suggest increased osteogenic properties for HA-coatings over Pyro/TCP-coatings. Additional research is necessary to obtain conclusive evidence on the in vivo osteogenic capacity of Pyro/TCP coatings.

Sol-gel-derived TiO(2)-SiO (2) implant coatings for direct tissue attachment. Part I: design, preparation and characterization

A series of sol-gel derived TiO(2)-SiO(2) mixed oxide coatings were prepared by carefully controlling the process parameters to obtain silica-releasing coatings consisting of nanoparticles. These features are of paramount importance for enhanced cell adhesion and activation. To achieve both these goals the Ti-alkoxide and Si-alkoxide were first separately hydrolysed and the titania-silica mixed sol was further reacted before the dipping process to obtain the desired particle sizes resulting to the biologically favourable topographical features. Silica release was observed from all the prepared coatings and it was dependent on SiO(2) amount added to the sols, i.e., the higher the added amount the higher the release. In addition, calcium phosphate was able to nucleate on the coatings. From the obtained SiO(2) dissolution data, together with the detailed XPS peak analysis, the mixed oxide coatings are concluded to be chemically heterogeneous, consisting of TiO(2) and SiO(2) species most likely linked together by Ti-O-Si bonds. TiO(2) is chemically stable making long-term implant coating possible and the desired nanoscale dimensions were well preserved although the composition was changed as a consequence of SiO(2) dissolution under in vitro conditions.

Early Trabecular Bone Healing Around Titanium Implants: A Histologic Study in Rabbits

BACKGROUND

A detailed insight into the early healing response of trabecular bone to unloaded titanium implants is lacking.

METHODS

Cylindrical implants were inserted in the tibial epiphysis of rabbits and left to heal for 1 to 42 days. Samples were processed into paraffin or methylmethacrylate sections and histomorphometrically analyzed.

RESULTS

A hematoma was observed after 1 and 3 days of implant placement. In addition, small fragments of bone trabeculae were detected around the implant as a result of the implant installment procedure. Soon, osteoclasts were observed resorbing these fragments, whereas osteoblasts incorporated them in strands of new bone, thereby making them difficult to distinguish from day 7 onward. At that time, osteoblasts were detected at the edges of the preexisting bone, actively depositing new bone, resulting in maximal osteoid deposition around the implant after 28 days (58%). After 7 days of healing, the presence of basic remodeling units in the surrounding bone was already maximal (P <0.05 versus t = 1 and 3 days). This remodeling activity, together with the new bone formation, provided a firm anchoring of the implant in the trabecular bone.

CONCLUSIONS

This study evaluated the early cellular events in trabecular bone surrounding titanium implants. The insertion of an implant into bone initiates a series of biologic processes, including the formation of a hematoma, shattered bone fragments adjacent to the implantation site, intensive bone remodeling, and the formation of new bone, eventually leading to the osseointegration of the implant.

Adsorption of bisphosphonate onto hydroxyapatite using a novel co-precipitation technique for bone growth enhancement

Premature bone resorption and remodeling by osteoclasts can limit the longevity of implant fixation and recovery time. Orally administered bisphosphonates (BPs) have been used to inhibit osteoclast action at the implant/bone interface. Ideally, these should be delivered at the interface with the osteoblast-active hydroxyapatite (HA) for maximum effect. This investigation introduces a novel BP loading technique to achieve improved BP release from a simulated body fluid-grown HA (SBF-HA) with the aim of improving implant fixation. A solution co-precipitation technique incorporates the BP (pamidronate) into a thin SBF-HA coating. Surface analysis, using X-ray photoelectron spectroscopy (XPS), of the resultant coating was employed to confirm the presence of the adsorbed BP on the surface of SBF-HA. XPS analysis was also used to determine the optimal adsorption process. Osteoclast cell culture experiments confirmed the biological effectiveness of BP adsorption and proved that the pamidronate was biologically active, causing both decreased osteoclast numbers and decreased resorption.

Mineralization at the interface of implants

Osseointegration of implants is crucial for the long-term success of oral implants. Mineralization of the bone's extracellular matrix as the ultimate step of a mature bone formation is closely related to implant osseointegration. Osteogenesis at oral implants is a complex process, driven by cellular and acellular phenomena. The biological process of the maintenance and emergence of minerals in the vicinity of oral implants is influenced to a great extent by biophysical parameters. Implant-related structural and functional factors, as well as patient-specific factors, govern the features of osteogenesis. To understand the influence of these factors in peri-implant bone mineralization, it is important to consider the basic biological processes. Biological and crystallographic investigations have to be applied to evaluate mineralization at implant surfaces at the different hierarchical levels of analysis. This review gives insight into the complex theme of mineral formation around implants. Special focus is given to new developments in implant design and loading protocols aimed at accelerating osseointegration of dental implants.

Biological stability and osteoconductivity in rabbit tibia of pulsed laser deposited hydroxylapatite coatings

A comparative study of the biological stability and the osteoconductivity of hydroxylapatite (HA) coatings produced by pulsed laser deposition (PLD) and plasma spraying (PS) was conducted. Three different implant groups were used: grit-blasted titanium rods coated with HA-PLD (2-microm-thick), grit-blasted titanium rods coated with HA-PS (50-microm-thick), and uncoated. Implantation took place into the proximal tibia of 12 mature New Zealand White rabbits for 24 weeks. Samples were evaluated using descriptive histology and histomorphometry. While HA-PS implants showed considerable instability and reduction in thickness after 24 weeks, but no statistical difference to the titanium group, the HA-PLD group showed a significant higher amount of bone apposition (Scheffé test, p<0.05) than the other two groups, without signs of degradation or dissolution. Remarkably, after 6 months, the almost intact thin pulsed laser deposited coating could be observed by electron microscopy in extended areas.

Bone-implant contact at calcium phosphate-coated and porous titanium oxide (TiUnite)-modified oral implants

BACKGROUND

Calcium phosphate (CP)-coated implants are usually referred to as having osteoconductive properties, whereas titanium implants with a native oxide layer are considered less osteoconductive. Often smooth titanium oxides (TOs) are compared to relatively rough CP structures. The objective of this study was to evaluate osteoconduction by comparing bone-implant contact at a relatively smooth, highly crystalline CP coating with a structured, porous TO (TiUnite)-modified surface.

MATERIAL AND METHODS

Ten adult Hound Labrador mongrel dogs were used. Four titanium implants (Nobel Biocare) with CP-coated (2) or TO-modified (2) surfaces were installed 12 weeks following mandibular premolar and molar teeth extraction. The implants were alternated within and between jaw quadrants in consecutive animals. Mucosal flaps were advanced and sutured leaving the implants in a submerged position. The animals were injected with fluorescent bone labels at 3 and 4 weeks postsurgery, and pre-euthanasia to monitor progress of bone formation. The animals were euthanized at 8 weeks postsurgery and block biopsies were prepared for histologic and histometric analysis.

RESULTS

There were no remarkable differences in bone formation and apparent bone-implant contact comparing the TO-modified and CP-coated surfaces. However, the measured average bone-implant contact was 71% and 57% (P=0.027) for TO-modified and CP-coated implants, respectively.

CONCLUSIONS

We conclude that the TO surface exhibits osteoconductive properties exceeding that of the CP surface. One or several of the chemical and physical properties of the TO surface may result in the remarkable bone formation along its surface. This study indicated that crystallinity and/or chemistry may be important.

Biological fixation of endosseous implants

Primary implant stability is ensured by a mechanical fixation of implants. However, during implant healing a biological anchorage is necessary to achieve final osseointegration. Aim of this study was to investigate the histological aspects of biological fixation around titanium screws. Forty-eight titanium screws with different surfaces (smooth, plasma sprayed, sand blasted) were inserted in tibiae and femura of sheep and analyzed by light microscope and SEM 1 hour, 14 and 90 days after implantation. One hour after implantation the implant-bone gap was filled with a blood clot and host bone chips arising from burr surgical preparation or friction during implant insertion. Fourteen days after implantation new trabecular bone and enveloped bone chips were observed in the gap: no osteogenesis developed where implant threads were in contact with host bone. Ninety days after surgery all trabecular bone and most of the bone chips were substituted by a mature lamellar bone with few marrow spaces. Our results suggest that the trabecular bone and bone chips represent a three-dimensional network ensuring a biological implant fixation in all different implant surfaces 2 weeks after surgery. Host bone chips could favour the peri-implant osteogenesis. Inter-trabecular and implant-trabecular marrow spaces of both trabecular and lamellar bone may favour the peri-implant bone turnover.

Physical characterization of different-roughness titanium surfaces, with and without hydroxyapatite coating, and their effect on human osteoblast-like cells

The aim of this study was to characterize and compare various titanium (Ti) and hydroxyapatite (HA) coatings on Ti6Al4V, in view of their application on noncemented orthopedic implants. Two innovative vacuum plasma sprayed (VPS) coatings, the first of ultrahigh rough and dense Ti (PG60, Ra=74 microm) and the second of ultrahigh rough and dense Ti coated with HA (HPG60, Ra=52 microm), have been developed, and the response of osteoblast-like cells (MG-63) seeded on these new coatings was evaluated in comparison to: a low roughness and sandblasted (Ti/SA, Ra=4 microm) Ti6Al4V surface; Ti medium (TI01, Ra=18 microm), and high (TI60, Ra=40 microm) roughness VPS coatings; and the relative Ti plus HA duplex coatings (HT01, Ra=12 microm and HT60, Ra=36 microm respectively), also obtained by VPS. PG60 coating presented no open porosity, making it dense and potentially intrinsically stronger. Cell adhesion and proliferation on PG60 was similar to those of the smoothest one (Ti/SA) and adhesion on ultrahigh roughness was lower than the medium- and high-roughness coatings, whereas cell proliferation on PG60 was lower than TI60. The HA coating determined significant increases in cell proliferation at medium and high roughness levels when compared to the relative Ti coating, but not compared to the ultrahigh one; all HA-coated surfaces showed a decrease in alkaline phosphatase activity and collagen I production. Surface morphology and the HA coating strongly affected cell behavior. However, ultrahigh values of roughness are not correctly seen by cells, and the presence of HA has no improving effects.

Calcium phosphate sol–gel-derived thin films on porous-surfaced implants for enhanced osteoconductivity. Part II: Short-term in vivo studies

Osseointegration rates of porous-surfaced Ti6Al4V implants with control (unmodified sintered coatings) were compared to porous-surfaced implants modified through the addition of either an Inorganic or Organic Route-formed-Ca-P film. Implants were placed in distal femoral rabbit condyle sites and, following a 9-day healing period, implant fixation strength was evaluated using a pull-out test. Three groups of ten rabbits each were evaluated. Inorganic Route Ca-P-coated implants were compared with control implants in Group I. Organic Route Ca-P-coated implants with control implants in Group II, and Inorganic- with Organic Route-Ca-P-coated implants in Group III. Maximum pull-out force and interface stiffness were compared while selected extracted implants were examined by SEM to characterise failure surfaces. Both types of Ca-P coatings significantly enhanced the early rate of bone ingrowth and fixation as evidenced by higher pull-out force and interface stiffness compared with controls. However, there was no significant difference between Ca-P-coated implants prepared using the two different methods. The enhanced osteoconductivity observed with the Organic Route-formed films despite the absence of any obvious new surface topographic features introduced with the films suggests that the increased rate of bone ingrowth was due primarily to altered surface chemistry rather than changes in topography, at least for these sintered porous-surfaced implants.

Characterization and protein-adsorption behavior of deposited organic thin film onto titanium by plasma polymerization with hexamethyldisiloxane

Plasma polymerized hexamethyldisiloxane (HMDSO) thin film was deposited onto titanium using a radio-frequency apparatus for the surface modification of titanium. A titanium disk was first polished using colloidal silica at pH=9.8. Plasma-polymerized HMDSO films were firmly attached to the titanium by heating the titanium to a temperature of approximately 250 degrees C. The thickness of the deposited film was 0.07-0.35mum after 10-60min of plasma polymerization. The contact angle with respect to double distilled water significantly increased after HMDSO coating. X-ray photoelectron spectroscopy revealed that the deposited thin film consisted of Si, C, and O atoms. No Ti peaks were observed on the deposited surface. The deposited HMDSO film was stable during 2-weeks immersion in phosphate buffer saline solution. Fourier transform reflection-absorption spectroscopy showed the formation of Si-H, Si-C, C-H, and Cz.dbnd6;O bonds in addition to Si-O-Si bonds. Quartz crystal microbalance-dissipation measurement demonstrated that the deposition of HMDSO thin films on titanium has a benefit for fibronectin adsorption at the early stage. In conclusion, plasma polymerization is a promising technique for the surface modification of titanium. HMDSO-coated titanium has potential application as a dental implant material.

Bone healing around titanium and titanium nitride-coated dental implants with three surfaces: an experimental study in rats

BACKGROUND

Titanium nitride (TiN) has been used in many fields as a coating of surgical instruments, with the purpose of creating materials more resistant to wear and corrosion and also reducing adhesion.

PURPOSE

The aim of this study was to evaluate the biocompatibility of TiN-coated dental implants.

MATERIALS AND METHODS

Forty-five rats were used in this study. One hundred eighty 2 mm x 2 mm implants (P.H.I. San Vittore Olona, Milano, Italy) were used. The implants were divided into the following three groups: Group 1 (n = 60): 30 machined and 30 machined coated with Group 2 (n = 60): 30 sandblasted and 30 sandblasted coated with Group 3 (n = 60): 30 titanium plasma sprayed, 30 titanium plasma sprayed and coated with TiN Four implants were placed in each rat, two implants coated with TiN on the right tibia and two uncoated implants on the left. The animals were killed after 5, 10, 20, 30, or 60 days. Another 18 implants were used for surface roughness analysis.

RESULTS

The present study showed that the healing around the TiN-coated implants was similar to that observed around the uncoated surfaces.

CONCLUSIONS

TiN coating demonstrated a good biocompatibility, did not have untoward effects on the periimplant bone formation, and did not change the surface roughness values.

Biomechanical and histomorphometric investigations on two morphologically differing titanium surfaces with and without fluorohydroxyapatite coating: an experimental study in sheep tibiae

The influence of fluorohydroxyapatite (FHA) coating and surface roughness of Ti6Al4V implants on bone response was investigated. Uncoated and FHA-coated screws with lower (LR and LR+FHA; Ra: 5.7+/-0.2 microm) and higher (HR and HR+FHA; Ra: 21.8+/-0.9 microm) surface roughness, were inserted into the diaphyses of 8 sheep tibiae. Twelve weeks after implantation, extraction torque and bone-to-implant contact were evaluated. The smoothest surfaces showed an improved extraction torque and significant differences were observed between LR and HR (-24.6%, p<0.0005), LR and HR+FHA (-30.7%, p<0.0005), LR+FHA and HR (-17.4%, p<0.005), and LR+FHA and HR+FHA (-24.0%, p<0.005). The bone-to-implant contact data paralleled the biomechanical data: the smoother the surface, the greater the bone-to-implant contact. Significant (p<0.0005) decreases in bone-to-implant contact were observed between LR+FHA and HR (-24.2%), and between LR+FHA and HR+FHA (-29.2%). The current findings suggest that LR surfaces significantly improve the osteointegration rate of implanted cortical screws independently of the FHA coating.

Effect of biphasic calcium phosphate on human macrophage functions in vitro

Bioceramics may initiate several and complex biological reactions in host tissues. The cell-biomaterial interaction can determine macrophage activation that may elicit and sustain inflammatory response at the implant site. The current study describes some of the in vitro phenomena regarding the effect of surface reactivity of biphasic calcium phosphate (BCP) granules on human macrophages locomotion and secretion. X-ray diffraction analysis indicated that the synthesized ceramic presented 80% hydroxyapatite and 20% tricalcium phosphate. When BCP was put in contact with human macrophage cells, we observed that cells and BCP granules attached to each other. Cells attached to BCP presented a higher intracellular free Ca(2+) concentration compared with nonattached neighbors and secreted calcium phosphate particles into the medium. Energy dispersive X-ray analysis showed that the secreted particles presented a calcium/phosphorus ratio of 1.64 +/- 0.05, similar to hydroxyapatite. We propose that the secreted particles create a transition zone that allows further macrophage adhesion.