Bone responses to zirconia implants with a thin carbonate-containing hydroxyapatite coating using a molecular precursor method

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.

Influence of the Surface Chemical Composition Differences between Zirconia and Titanium with the Similar Surface Structure and Roughness on Bone Formation

The osseointegration of zirconia (ZrO2) implants is still controversial. In this study, we aimed to make clear the influence of surface chemical composition, Ti or ZrO2, to osseointegration. First, a roughened Ti surface was prepared with a combination of large-grit sandblasting and acid treatment. Then, we applied molecular precursor solution containing Zr complex onto roughened Ti surface and can deposit thin ZrO2 film onto roughened Ti surface. We can change surface chemical composition from Ti to ZrO2 without changing the surface structure and roughness of roughened Ti. The tetragonal Zr was uniformly present on the ZrO2-coated Ti surface, and the surface of the ZrO2-coated Ti showed a higher apparent zeta potential than Ti. Ti and ZrO2-coated Ti rectangular plate implant was placed into the femur bone defect. After 2 and 4 weeks of implantation, histomorphometric observation revealed that the bone-to-implant contact ratio and the bone mass values for ZrO2-coated Ti implants inserted into the femur bone defects of the rats at 2 weeks were significantly higher than those for Ti implants (p < 0.05). It revealed that ZrO2 with a similar surface structure and roughness as that of roughened Ti promoted osteogenesis equivalent to or better than that of Ti in the early bone formation stage.

Surface modification of zirconia dental implants by laser texturing

The aim of this work was to perform an integrative literature review on the influence of laser irradiation on zirconia implants to enhance surface topographic aspects and the biological response for osseointegration. An electronic search was carried out on the PubMed database using the following search terms: "zirconia" AND "laser" AND "surface modification" OR "surface treatment" AND "dental implants" OR "bone" OR "osteoblast" OR "osseointegration." Of the identified articles, 12 studies were selected in this review. Results reported that the laser irradiation was capable of promoting changes on the zirconia surfaces regarding topographic aspects, roughness, and wettability. An increase in roughness was recorded at micro- and nano-scale and it resulted in an enhanced wettability and biological response. Also, adhesion, spreading, proliferation, and differentiation of osteogenic cells were also enhanced after laser irradiation mainly by using a femtosecond laser at 10nJ and 80 MHz. After 3 months of osseointegration, in vivo studies in dogs revealed a similar average percentage of bone-to-implant contact (BIC) on zirconia surfaces (around 47.9 ± 16%) when compared to standard titanium surfaces (61.73 ±16.27%), denoting that there is no significant difference between such different materials. The laser  approach revealed several parameters that can be used for zirconia surface modification such as irradiation intensity, time, and frequency. Laser irradiation parameters can be optimized and well-controlled to reach desirable surface morphologic aspects and biological response concerning the osseointegration process.

Mechanical properties of zirconia ceramics biomimetically coated with calcium deficient hydroxyapatite

Mechanical properties and stability of porous tetragonal yttria-stabilised zirconia (Y-TZ) ceramics, biomimetically coated with calcium deficient hydroxyapatite (CaDHA) to obtain a bioactive material, were investigated. The 5.7 mol% yttria-stabilised tetragonal zirconia was obtained by sol-gel process and sintered at different temperatures to obtain a homogeneous and porous structure whose strength would match that of human bone. Sufficient strength was achieved by sintering at 1400 °C. The CaDHA coating was obtained at room temperature by a simplified preparation method consisting of immersion of the Y-TZ ceramics into a calcifying solution, after a short surface pretreatment in HCl. Although HAP or β-TCP are more frequently used, CaDHA was chosen due to its structural similarity to the bone mineral and ability to support bone ingrowth to a greater extent than biphasic calcium phosphates. To verify the applicability CaDHA coatings, we tested their adherence to Y-TZ ceramics for the first time to the best of our knowledge. Vickers hardness (3.8 ± 0.2 GPa) reflected the hardness of underlying ceramic. The tensile strength (269 ± 52 MPa) and Weibull modulus (5) of the obtained biomaterials matched or exceeded those of bone. There was no statistical difference in the tensile strength between the coated (269 ± 52 MPa) and the uncoated (239 ± 46 MPa) ceramics. The Y-TZ-CaDHA coating system presented adequate structural integrity under scratch test with critical load for coating cracking of 18 ± 2 N. These results indicate the potential of the prepared bioceramic to be used as bone implants.

Gingival fibroblasts behavior on bioactive zirconia and titanium dental implant surfaces produced by a functionally graded technique

Adding a biological apatite layer to the implant surface enhances bone healing around the implant.

Molecular precursor method for thin carbonate-containing apatite coating on dental implants

The molecular precursor method is an easy and simple method for coating thin carbonate-containing apatite (CA) films onto titanium surfaces. A molecular precursor solution containing ethanol, calcium-EDTA complex, and phosphate salt was dropped onto a titanium surface and then heated at 600°C for 2 h. An adherent thin CA coating was achieved. Animal implantation experiments showed that CA-coated implants had significantly higher bone-to-implant values than non-coated implants (p<0.05). The molecular precursor method was also used to coat three-dimensional titanium webs (TWs). Thin CA films could be coated inside the center area, as well as the surface of the TW, with excellent bone formation inside the CA-coated TW. Furthermore, the molecular precursor method was used to coat partially stabilized zirconia with CA. Better bone response was observed for CA-coated zirconia. From this, it is concluded that the molecular precursor method is useful for producing thin CA coatings on implant materials.

Leaching mechanism of bioapatite in carbonate-saturated water

Bioapatite, the main inorganic component of bone, is similar to hydroxyapatite (HAp, Ca₅[PO₄]₃(OH)) having some [CO₃]²⁻ content which plays an important role in leaching/precipitation processes in many biological lesions.

Surrounding Tissue Response to Surface-Treated Zirconia Implants

Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP), which are partially stabilized zirconia, have been used for fabricating dental implants. This study investigated the soft tissue attachment, the collagen fiber orientation to zirconia at different surface conditions, and the bone response using implantation experiments in animals. The zirconia implant surfaces were treated with ultraviolet irradiation (UV), a combination of large-grit sandblasting and hydrofluoric acid etching (blastedHF), and a combination of blastedHF and UV (blastedHF+UV). The surface treated with blastedHF and blastedHF+UV appeared rough and hydrophilic. The surface treated with blastedHF+UV appeared to be superhydrophilic. Subsequently, tapered cylindrical zirconia implants were placed in the alveolar sockets of the maxillary molars of rats. The bone-to-implant contact ratio of blastedHF and blastedHF+UV implants was significantly higher than that of the non-treated controls and UV-treated implants. The four different surface-treated zirconia implants demonstrated tight soft tissue attachments. Perpendicularly oriented collagen fibers towards zirconia implants were more prominent in blastedHF and blastedHF+UV implants compared to the controls and UV-treated implants. The area of the soft tissue attachment was the greatest with the perpendicularly oriented collagen fibers of blastedHF+UV-treated implants. In conclusion, blastedHF+UV treatment could be beneficial for ensuring greater soft-tissue attachment for zirconia implants.

Bioactive-hybrid-zirconia implant surface for enhancing osseointegration: an in vivo study

Background

Zirconia is characterized by a hard, dense, and chemically inert surface which requires additional surface treatments in order to enhance osseointegration. The proposed hypothesis of the study was that combination of a nano-porous surface infiltrated with a bioactive material may enhance osseointegration of zirconia implants.

Methods

Custom-made zirconia implants (3.7 mm × 8 mm) were designed, milled, and sintered according to manufacturer recommendations. All implants received selective infiltration etching (SIE) technique to produce a nano-porous surface. Surface porosities were either filled with nano-hydroxy apatite particle- or platelet-rich plasma while uncoated surface served as a control (n = 12, α = 0.05). New surface properties were characterized with mercury porosimetry, XRD analysis, SEM, and EDX analysis. Implants were inserted in femur head of rabbits, and histomorphometric analysis was conducted after healing time to evaluate bone–implant contact percentage (BIC%).

Results

Selective infiltration etching produced a nano-porous surface with interconnected surface porosities. Mercury porosimetry revealed a significant reduction in total porosity percent after application of the two coating materials. XRD patterns detected hexagonal crystal structure of HA superimposed on the tetragonal crystal phase of zirconia. Histomorphometric analysis indicated a significantly higher (F = 14.6, P < 0.001) BIC% around HA–bioactive–hybrid surface (79.8 ± 3%) and PRP-coated surface (71 ± 6 %) compared to the control (49 ± 8%).

Conclusions

Bioactive–hybrid–zirconia implant surface enhanced osseointegration of zirconia implants.

A new 3D printed titanium metal trabecular bone reconstruction system for early osteonecrosis of the femoral head

Presently, biomechanical support therapy for the femoral head has become an important approach in the treatment of early osteonecrosis of the femoral head (ONFH). Previous studies have reported that the titanium metal trabecular bone reconstruction systems (TMTBRS) achieved satisfactory clinical results for the treatment of early femoral head necrosis. Electron beam melting technology (EBMT) is an important branch of 3D printing technology, which enables the construction of an interface that is required for support of bone in-growth. However, the effect of TMTBRS created using EBMT for clinical applications for early ONFH is still unknown. At present, there are no reports on this topic worldwide. The purpose of this study was to assess the safety of a new 3D printed TMTBRS implant and to evaluate its clinical efficacy in early ONFH.Thirty patients who underwent surgery for ONFH were selected. The stages of ONFH were classified according to the Association Research Circulation Osseus (ARCO) classification. They were followed-up and radiological examination was performed at 6, 12, and 24 months post-surgery to assess TMTBRS stability and bone growth in the bone trabecular holder portion surface. To evaluate hip function, postoperative Harris and Visual Analogue Scale (VAS) scores were used.The postoperative Harris score increased significantly and VAS score decreased significantly at the 12-month follow-up compared to the 24-month follow-up, wherein the Harris score declined slightly and the VAS score was slightly elevated with the aggravation of ONFH. With the passage of time, postoperative improvement rates were 100% for IIA, 70% for IIB, and 0% for IIC. Hip-preserving rates were 100% for IIA, 100% for IIB, and 50% for IIC.The effect of TMTBRS treatment for early ONFH in ARCO IIA and ARCO IIB is satisfactory. However, it is not recommended for a relatively large area of necrosis such as in ARCO IIC.

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 zirconia dental implants in animal investigations: A systematic review and meta-analysis

OBJECTIVE

To determine the osseointegration rate of zirconium dioxide (ZrO₂) dental implants in preclinical investigations.

DATA

Data on the osseointegration rate was extracted considering the bone to implant contact (BIC), removal torque analysis (RTQ) and push-in tests. Meta analyses were conducted using multilevel multivariable mixed-effects linear regression models. The Šidák method was used in case of multiple testing.

SOURCES

An electronic screening of the literature (MEDLINE/Pubmed, Cochrane Library and Embase) and a supplementary manual search were performed. Animal investigations with a minimum sample size of 3 units evaluating implants made of zirconia (ZrO₂) or its composites (ZrO₂>50vol.%) were included.

STUDY SELECTION

The search provided 4577 articles, and finally 54 investigations were included and analyzed. Fifty-two studies included implants made from zirconia, 4 zirconia composite implants and 37 titanium implants. In total, 3435 implants were installed in 954 animals.

CONCLUSIONS

No significant influence of the evaluated bulk materials on the outcomes of interest could be detected. When comparing different animal models, significant differences for the evaluated variables could be found. These results might be of interest for the design of further animal investigations.

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.