In vivo biofunctionalization of titanium patient-specific implants with nano hydroxyapatite and other nano calcium phosphate coatings: A systematic review

Accepted Manuscript In vivo biofunctionalization of titanium patient-specific implants with nano hydroxyapatite and other nano calcium phosphate coatings: A systematic review Alexander Bral, Maurice Y. Mommaerts PII:

S1010-5182(15)00418-7

DOI:

10.1016/j.jcms.2015.12.004

Reference:

YJCMS 2257

To appear in:

Journal of Cranio-Maxillo-Facial Surgery

Received Date: 31 August 2015 Accepted Date: 11 December 2015

Please cite this article as: Bral A, Mommaerts MY, In vivo biofunctionalization of titanium patient-specific implants with nano hydroxyapatite and other nano calcium phosphate coatings: A systematic review, Journal of Cranio-Maxillofacial Surgery (2016), doi: 10.1016/j.jcms.2015.12.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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In vivo biofunctionalization of titanium patient-specific implants with nano

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hydroxyapatite and other nano calcium phosphate coatings: A systematic review

Alexander Bral*

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Maurice Y. Mommaerts *

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* European Face Centre, University Hospital Brussels, Belgium.

Corresponding Author: Maurice Y. Mommaerts European Face Centre

Laarbeeklaan 101 B-1090 Brussels Tel. +32 02 477 60 12

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Universitair Ziekenhuis Brussel

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Email: [email protected]

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ABSTRACT AND KEYWORDS

Objective: To delineate the best procedures for increasing osseointegration in cranio-maxillo-facial

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surgery using nano-sized calcium phosphate coatings on titanium patient specific implants.

Materials and methods: A multi-database single-reviewer systematic literature review was conducted. Results: Twenty-eight papers consisting of twenty-five animal studies and three human studies met the

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selection criteria. The results of existing literature suggest that titanium implants coated with nano

calcium phosphate and hydroxyapatite improves osseointegration and implant fixation. However, not

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all coating techniques enhance biofunctionalization. Factors including implant microroughness, coating thickness, calcium phosphate solubility, and nanotopography contribute significantly to biofunctionalization. Nonetheless, additional data derived from clinical studies are needed to support

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this statement, as well as the possible influence of routine autoclaving procedures.

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Keywords: Implant, Hydroxyapatite, Calcium Phosphate, Titanium, Nanoparticles

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Summary

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INTRODUCTION Calcium phosphate (CaP) coatings on titanium implants have been shown to improve biofunctionalization, because they facilitate

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osseointegration and functional longevity (Le Guehennec et al., 2007). Furthermore, failure to achieve osseointegration results from

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insufficient bone formation on the implant surface, which can lead to incomplete fixation of the implant (Mendonca et al., 2008). Hence, the philosophy behind the use of nano CaP and hydroxyapatite (HA) coatings is that the chance of biological integration is higher when the structure mimics human bone more closely (Alberts et al., 2002).

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The nanoscale ranges from 0.1 nm to 100 nm. However, if the dimensions of the particles range from 100 nm to 1 µm, they are called submicron particles (Ehrenfest et al., 2004). Important inorganic components of bone are nanoscale CaP particles within the 20- to 40nm size range. Further, nanoparticles smaller than 100 nm have the highest reported efficacy regarding cellular integration, and it has

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been suggested that these particles induce responses different from submicron structures, which could imply that nano HA and

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possibly other CaP coatings could create biocompatible surfaces that unite with bone tissue (Webster et al., 2004, Basu et al., 2009). HA is a calcium orthophosphate that is composed of calcium, phosphorus, and hydroxide and has a chemical formula of Ca10(PO4)6(OH)2. Furthermore, HA has a CaP ratio of 1.67, and is the least soluble and most stable calcium orthophosphate. The

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various forms of CaP differ in solubility and stability, which are both characteristics that alter biocompatibility. As well, the coating

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technique is another important factor that can alter the solubility and the stability of the coating (Sergey 2007). The investigation and characterization of nanostructures on implant surfaces is challenging. At present, no quantitative technique is

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available to accurately assess the nanotopography on a micro-texturized surface due to an interference between both components. Consequently, only field emission scanning electron microscopy (FE-SEM) enables the accurate examination of micro-texturized

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surfaces (Ehrenfest et al., 2004). The majority of the publications included in the current review involved the use of scanning electron microscopy (SEM) to investigate the coating on implant surfaces. However, atomic force microscopy (AFM) and optical interferometry (OI) were also used to examine the coating roughness.

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Various techniques exist to create nano CaP coatings, such as the dip coating process (Guo et al., 2004), the sol-gel method (BenNissan et al,. 2006), the electrochemical method, the electrophoretic deposition process, the biomimetic deposition process, the

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hydrothermal treatment method, and ion beam-assisted deposition (IBAD). In addition, each technique has different advantages and

al., 2011).

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disadvantages in terms of processing and outcome (Li et al., 2003, Narayanan et al., 2008, Chae et al., 2008, Hu et al., 2010, Lobo et

The effectiveness of nano-CaP coatings can be compared in a hierarchical order on the basis of in vitro and in vivo studies and clinical studies. In vitro research of surface coatings primarily focuses on evaluating biocompatibility and assessing cytotoxicity, whereas in vivo studies principally involve histomorphometrical analysis and removal torque (RTQ) testing (Coelho et al., 2009b). The

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histomorphometrical measurements are capable of showing biocompatibility, osseoconductivity, and the general tissue response of

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implants, and the biomechanical tests measure the force or torque that is required to induce failure in the bond between the bone and implant surface (Recker, 1983). The objective of this paper is to provide a structural review of the techniques that can produce a CaP coating that yields good in vivo results, and to compare these results to micro CaP–coated and uncoated titanium implants.

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Furthermore, this paper includes a systematic review of CaP coatings on titanium implants using histomorphometrical analysis and

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RTQ testing.

MATERIAL AND METHODS

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To compare coatings with nano CaP particles with uncoated titanium implants, studies involving animal models as well as human subjects were included; however, studies that investigated implants with submicron coatings were excluded. Coatings were compared

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based on the use of histomorphometrical analysis to obtain the percentage of bone-to-implant contact (BIC) and the use of RTQ values

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to test mechanical stability and implant fixation.

Six search engines were used, including PubMed, Web of Science, Directory of Open Access Journals, SAGE journals, the Wiley Online Library, and the Cochrane Library. A search of PubMed (http://www.ncbi.nlm.nih.gov/pubmed/) using the MeSH terms “nano hydroxyapatite” OR “nano calcium phosphate,” yielded 974 articles. A Web of Science (https://webofknowledge.com/) search with TOPIC: (nano hydroxyapatite titanium), OR TOPIC: (nano hydroxyapatite coating), OR TOPIC: (nano calcium phosphate coating),

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OR TOPIC: (nano calcium phosphate titanium) yielded 1431 articles. In the Directory of Open Access Journals, a search using the

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MeSH terms “nano hydroxyapatite” OR “nano calcium phosphate” generated 19 articles, whereas a search of SAGE premier 2011 (http://online.sagepub.com/) using the search terms “nano hydroxyapatite” OR “nano calcium phosphate” returned 93 articles. A search of the Wiley Online Library (http://onlinelibrary.wiley.com/) using the MeSH terms “nano hydroxyapatite titanium,” OR “nano

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hydroxyapatite coating,” OR “nano calcium phosphate coating,” OR “nano calcium phosphate titanium” in Full Text provided a total

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of 4389 articles. Finally, the Cochrane Library (http://www.cochranelibrary.com/) was searched using the MeSH terms “nano calcium phosphate” OR “nano hydroxyapatite,” which yielded 18 articles.

After the completion of the database searches, the resulting abstracts were screened using the following inclusion criteria: animal or

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human studies containing data on BIC or RTQ testing for nano-coated cpTi (commercially pure titanium) or Ti6Al4V (titanium alloy) implants. If the abstract met the inclusion criteria, the full article was checked for compliance with the inclusion criteria. Additional

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articles identified in the reference lists of the articles meeting the inclusion criteria were likewise searched. Only articles written in

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English, German, French, or Dutch were included, and the article publication dates were restricted to before September 1, 2014. After verifying that the articles met the inclusion criteria, PubMed yielded 12 articles, Web of Science database returned 9 articles, SAGE premier produced 1 article, and the Wiley Online Library yielded 11 articles. No articles from Open Access Journals or the Cochrane Database met the required inclusion criteria. After removal of duplicate articles, 18 articles remained. Another 6 articles

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were identified by manually searching the reference lists of the 18 articles that met the study inclusion criteria, which yielded a total of

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RESULTS

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24 articles (Figure 1).

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NanoTite™ Method

The NanoTite™ coating technique is a colloidal sol-gel process. The procedure starts with the dipping of the samples in an alcohol-

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based solution containing CaP nanoparticles. After withdrawal of the substrate, the sample is dried at 100°C. The procedure is able to generate a discrete crystalline deposition (DCD) composed of nano-structured CaP particles that cover 50% of the surface with CaP

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nanocrystals, with the remaining surface covered by a TiO2 layer. The CaP particles have a nominal size of 20–100 nm and a

In vivo human experiments

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crystallinity of over 95% (Mendes et al., 2007, Gubbi et Towse., 2007).

A study compared titanium implants implanted in the posterior maxilla for an average of 8 weeks. (Orsini et al., 2007) Average BIC values of nano HA coated implants was significantly higher than the BIC values of the control groups (Table 1). The results suggested

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that the coating of implants could shorten implant osseointegration time, which could be clinically advantageous for minimizing

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micromotions and decreasing the healing period. In another experiment involving human subjects, DAE implants were compared in the posterior maxillary bone with NanoTite™

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implants (Goene et al., 2007). The implants were harvested at 4 and 8 weeks after healing. Histomorphometrical analysis showed enhanced BIC at 4 and 8 weeks for NanoTite™ compared to OSSEOTITE®, which supported increased early osseointegration for

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NanoTite™ compared to DAE implants.

Another group investigated the histomorphometrical healing properties of dual acid-etched mini-implant surfaces and implants coated with nHA particles (Telleman et al., 2010). The study design entailed the fixation of iliac crest bone grafts onto maxillary bone with

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coated or uncoated DAE implants. Harvesting and analysis occurred after 3 months. Histomorphometrical measurements revealed higher BIC and bone area values for coated implants compared to uncoated DAE implants in the maxillary bone. The authors

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concluded that implants coated with nano HA particles improved the osseointegration in the maxillary bone only in comparison to

remodeling of bone in the graft.

In vivo animal experiments

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DAE treated titanium implants. NanoTite™ did not improve healing properties at the graft area, which might be due to reduced

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The interfacial bonding strength of NanoTite™ coated cpTi and Ti6Al4V implants were compared with uncoated cpTi and Ti6Al4V

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implants (Mendes et al., 2007). The mean RTQ indicated that uncoated cpTi and Ti6Al4V implants had significantly lower RTQ values than coated implants (Table 2). As well, the values of these 2 coatings was significantly higher for the Ti6Al4V coated implants. The authors concluded that nHA deposits are able to promote bone bonding on cpTi and Ti6Al4V surfaces. They

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hypothesized that the increased nanosurface complexity induced the bone bonding process, and not so the CaP chemistry.

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The same group tested bone growth following the implantation of “ingrowth chambers” in the same animal model (Mendes et al. 2009). Miniature bone ingrowth chambers were made of commercially pure titanium or titanium alloy that were dual acid etched (DAE) and coated by the NanoTite™ method, or only acid etched by a DAE method. Nine days after implantation, a statistically

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significant difference was detected between NanoTite™ coated implants, which had higher BIC values, compared to implants that were only acid-etched. No statistically significant difference was found between DCD CpTi and DCD titanium alloy Ti6Al4V implant

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osseointegration.

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chambers. The authors concluded that deposition of discrete CaP nanocrystals on a complex microtopography significantly enhanced

In a separate study, dual acid-etched implants and implants coated by DCD nanoparticles were compared following insertion in fresh extraction sockets of beagle dogs. Harvesting was performed after 2, 4, and 8 weeks (Vignoletti et al., 2009). Higher numerical BIC percentages were apparent at the early healing phases (2 and 4 weeks); however, no statistically significant differences were detected. Further, because each group was composed of only 3 dogs, the sample size might have been too low to show any significant

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difference. Another study compared the BIC values of grit-blasted and acid-etched implants with grit-blasted, acid-etched, and

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nanoscale HA surface-modified implants in canine premolar sockets (Al-Hamdan et al., 2011). Implantation was in perfectly sized implant beds, and in a non-submerged position. The authors observed increased BIC values for both implant groups during the implantation time between 2 and 8 weeks. As well, the authors confirmed that both implant surfaces were able to induce

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coatings resulted in an increased bone response at 2, 4, and 8 weeks.

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osseointegration and to stimulate crestal bone formation. However, the authors were not able to determine whether nanoscale CaP

Osseointegration was also evaluated in a canine mandibular model by histomorphometrical analysis of NanoTite™ implants versus DAE implants (de Barros et al., 2012). Insertion was performed in a no-gap model, as well as in a 1-mm, 1.5-mm, and a 2-mm gap

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model. After 8 weeks of healing, BIC values were not significantly higher for NanoTite™ coated implants, although the microroughened implants exhibited higher numerical values. The authors could not show any benefit of the DCD CaP coating.

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Additionally, a separate study examined bone healing to dual acid-etched implants with and without a nano CaP coating (Abrahamson et al., 2013). The BIC was significantly higher for the uncoated implants compared to nano CaP–coated implants at 2 and 4 weeks

bone healing properties.

nHA promimic method

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after implantation. Hence, the authors theorized that the additional coating of dual acid-etched implants does not improve the early

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Method

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The nHA promimic method is a technique that involves an aqueous solution composed of calcium, phosphor, and a surfactant. The solution is placed in an ammonia atmosphere to induce the formation of nano-sized crystals, after which the treated liquid is diluted

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with a hydrophobic organic solvent to obtain a solvent of nano-sized crystals in water. An oxide coated substrate is then immersed in the nanocrystal solvent. After removal from the solvent, the organic solvent and surfactant are removed from the surface coating

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(Kjellin et Andersson. 2005). This technique has the capacity to produce a nano HA particle coating with dimensions ranging in width from 10 to 15 nm and in length from 100 to 200 nm (Jimbo et al., 2011b, Jimbo et al., 2012). In vivo animal experiments

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A comparison of the osseointegration of electropolished titanium implants and electropolished titanium implants modified using the nHA promimic method was conducted in an animal model (Meirelles et al., 2008b). Implants were fixed and stabilized by 2

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corticomedullary screws. The results of the experiment indicated that nHA implants had significantly higher BIC values after 4 weeks

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compared to the uncoated implants. Surface roughness parameters revealed similar summit densities, whereas AFM showed increased average height deviation at the nanomolar level for the nHA coated implants. However, the difference measured by AFM might have been due to increased surface porosity (percentage) and the number of pores in nHA-coated implants. Implant surface modification was also conducted to remove microstructures and prevent their interaction. Based on the information obtained, the authors concluded that differences in osseointegration are only explained by differences in nanotopography and surface chemical composition.

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Another study employed a similar rabbit model as well as electropolished titanium implants and nHA coated titanium implants, but

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involved implantation sites that were increased by a 0.35-mm radius to induce a gap healing model (Meirelles et al., 2008a). Electropolished implants showed higher values, but the differences were not statistically significant. These data did not support the observations of the previous study. The authors hypothesized that the 0.35-mm gap design might have disrupted osseointegration, and

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that a more precise surgical fit was needed.

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In another experiment, the enhancement of osseointegration was evaluated using nHA coatings compared to a nano-titanium–covered surface (Meirelles et al., 2008d). The nano-titanium implants were coated with the MetAlvive method, which is a dip-coating technique that produces a coating layer composed of titanium particles that are 30 nm in diameter. The results indicated that nano-

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titanium–coated implants had a higher feature density and percentage of implant coverage (45%) compared to nHA, which covered only 23% of the implant surface. In addition, AFM images revealed that the nano-titanium particles had a higher average diameter

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compared to the nHA particles. The histomorphometrical analysis showed BIC values of 17% for nHA and 21% for nano-titanium– coated implants measured on the lateral wall, but the difference was not significant. At the apical region, BIC values were 19% for

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nano-titanium–coated implants compared to 7% for nHA, which indicated a significant increase in osseointegration. However, the results in the nano-titanium implants might have been influenced by increased developed surface ratio (Sdr) values at the apical region. Similar differences were not detected at the lateral wall, and the values for bone area measurements were similar for both coatings (48%). Hence, these results did not support the enhancement of bone formation by bioactive HA. The authors concluded that the bone healing events in the study were dependent only on the nano feature size and distribution after a 4-week healing period.

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The results of a different study suggested that implants chemically modified with nHA would show enhanced osseointegration

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compared to uncoated implants with similar microtopography (Meirelles et al., 2008c). The authors evaluated osseointegration in the proximal rabbit tibia after 4 weeks. OI microscopy revealed similar average height deviations for blasted implants (1.42 µm) and nHA-coated implants (1.36 µm). At 4 weeks, a significantly higher BIC was observed for the nHA-coated implants compared to

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blasted implants. In addition, RTQ testing revealed similar values for nHA compared to titanium dioxide.

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A separate study involving a rabbit model evaluated bone apposition onto coated and uncoated heat treated pure titanium implants (Jimbo et al., 2011b). After 2 weeks of healing, the mean percentage of newly formed bone for the nHA coated implants was significantly higher. However, after 2 weeks of healing, the BIC values from uncoated implants seemed to reach a plateau. Therefore,

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the mean BIC value after 4 weeks of healing was in the uncoated implants, which was significantly lower than the BIC observed for nHa-coated implants. No significant differences in average height deviation or surface roughness were observed on the OI images.

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Early osseointegration in the rabbit tibia was likewise investigated using nHA-coated implants and sand-blasted, acid-etched, and

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heat-treated Ti6Al4V implants (Jimbo et al., 2012). The animals were euthanized after 3 weeks. No significant differences in BIC values were observed for the nHA-coated implants compared to the uncoated implants. However, nano-indentation testing revealed a significant difference between the uncoated and nHA implants. Consequently, the authors concluded that bone quality around the nHA coated implants is better.

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Another study compared implants in rabbit femurs at 12 weeks that were sand blasted and acid etched followed by either heat

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treatment or coating with nHA particles using the nanoHA promimic method (Bryingtong et al., 2013). Interferometer characterization revealed significant differences in the arithmetic average height deviation from a mean plane with a smoother surface for the nHAcoated implants (0.93 µm) relative to the controls (1.026 µm). All implants were stable at the time of implant retrieval. However, the

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heat treated implants exhibited improved BIC values compared to nHA-coated implants. Furthermore, the data indicated that after a

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healing period of 12 weeks, noncoated surfaces with increased microroughness had improved osseointegration compared to nHA coated surfaces. Hence, the authors concluded that nanocrystals deposited onto blasted and acid-etched titanium implants did not enhance the osseointegration after 12 weeks compared to the control implants. This could suggest that the microtopography is more

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important after longer healing periods, whereas the nHA coating has an higher impact on the early bone-healing period.

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Sol-gel method

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The methods used in these experiments were very similar to those used with NanoTite™. In the first experiment presented, the coating comprised nanoparticles between 25 and 35 nm, whereas the second experiment involved particles that were approximately 25 nm in size (Varis et al., 2013, Aksakal et al., 2014).

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In vivo animal experiments

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One study compared bioresorbable screws, uncoated Ti6Al4V screws, and Ti6Al4V screws coated with nano HA or micro HA (Aksakal et al., 2014). The bioresorbable screws were composed of lactic acid and trimethylene carbonate. The screws were implanted

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in the tibial bone of sheep, and harvested after 8 weeks by axial pull-out testing. The highest fixation strength was achieved using nanoscale HA-coated screws, which was higher than microscale-coated implants and the uncoated implants. The authors concluded

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that nHA coated screws provide good and stable retention during the bone healing process without inducing any adverse effects. Another experiment compared intramedullary nails that were uncoated or coated with nHA or microscale HA (mHA).(Varis et al., 2013). The titanium implants were placed endomedullary in a rabbit model for 45 days. The affiliated analyses revealed that the nHA

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and mHA group had a statistically higher tensile strength than implants in the control group. As well, the results of axial pull-out tests

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demonstrated statistically significant increases in tensile resistance in the mHA and nHA groups compared to the control group.

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Biomimetically deposited calcium phosphate and electrochemically deposited hydroxyapatite coating Biomimetically deposited calcium phosphate coating (BCaP) and electrochemical deposited hydroxyapatite (EDHA) coatings were investigated and compared by a single experimental group, which explains the grouping of these 2 different coatings. Method

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The biomimetically deposited CaP coating is produced in 2 steps. The implants are first soaked in a supersaturated calcium and

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phosphate solution at a high salt concentration. Inhibitors of crystal growth are then added to aid heterogeneous nucleation. Implants are soaked for 24 hours and afterward soaked in another solution of supersaturated CaP solution with another composition of salts. This technique yields a sharp crystal flake approximately 6 to 8 µm long and 100 nm thick composed of octacalcium phosphate, which

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covers the entire surface of the implant (Figure 2B).

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The electrochemical deposition of hydroxyapatite uses the implant as a working electrode, and a platinum plate as the counter electrode. The electrolyte solution contains calcium nitrate (Ca(NO3)2) and ammonium phosphate (NH4H2PO4) with a CaP ratio of 1.67. A direct current induces the deposition of CaP nanocrystals onto the implant surface, and the process is completed within 2

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In vivo animal experiments

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2C) (Guo-Li et al., 2009, Guo-Li et al., 2010)

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hours. The coating homogenously covers the entire surface with oriented and dense rod-like crystals 70–80 nm in diameter (Figure

The interfacial biomechanical properties of biomimetically deposited CaP and electrochemically deposited nano HA coatings were compared with roughened implants (Figure 2A) (Guo-Li et al., 2009). IThe mean RTQ of the EDHA coated implants exhibited significantly greater values at all healing periods compared with the roughened and biomimetically deposited calcium phosphate coatings. The biomimetic deposition did not increase implant fixation compared to roughened implants. The authors concluded that

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EDHA coatings improve fixation between implant and bone compared to the roughened surface; however, biomimetic CaP coatings

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have little effect on fixation. To assess osseous healing of biomimetically and electrochemically deposited nHA coatings, the same research group examined

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intracortical implants in the tibial bone of rabbits (Guo-Li et al., 2010). The animals were divided into 2 groups, the first of which was sacrificed at 6 weeks and the second at 12 weeks. Histomorphometrical measurements for electrochemically deposited nano HA

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coatings showed significantly greater values at both healing periods compared to the BDCaP implants. No significant differences were found between BDCaP and roughened implants. At 6 weeks, EDHA implants showed significantly higher BIC values compared to roughened implants, but no changes were noted after a 12-week healing period. The results of the study indicated that the thinner

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EDHA coating is more favorable for bone integration, which could ensure long-term stable bony fixation of a porous implant. A separate study tested electrochemically deposited nano HA-coated implants in ovariectomized rats to assess osseointegration

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(Zhipeng et a., 2012). The animals were sacrificed after 12 weeks, and RTQ testing and histomorphometrical analysis were conducted.

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Mean surface roughness of the roughened titanium implants (control group) and of the HA-coated implants (experimental group) were 1.185 and 1.167, respectively; however, no significant difference in mean surface roughness was found between the groups. The histomorphometrical results revealed significantly greater BIC and bone area percentages for nano HA–coated implants compared to roughened implants by large corundum grit blasting. The authors also found significantly greater RTQ values for the nano HA–coated

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implants. Hence, the authors demonstrated that a thin nano HA coating is able to increase bone bonding strength and to improve

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osteogenesis around implants.

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Ion beam–assisted deposition

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In vivo animal experiments

The performance of a nano-thick ion beam–assisted deposition (IBAD) coating was evaluated after 3 and 5 weeks in a canine model. Four different groups of alumina-blasted/acid-etched Ti6Al4V implants were compared, as well as uncoated implants (control group),

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and implants coated by either 1 of 2 IBAD setups or plasma sprayed HA (PSHA) (Coelho et al., 2009c). The difference between the 2 IBAD coating techniques was the duration of coating procedure, which yielded a thickness of 30–50 nm for IBAD II and a submicron

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coating of 300–500 nm for IBAD I. As well, in vivo testing showed significantly higher torque-to-interface fracture values for PSHA and IBAD II. Higher BIC values were also found for the PSHA, IBAD I , and IBAD II coatings compared to the control group.

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Therefore, the nanocoating yielded inferior results for bone anchorage compared to the micron and submicron coatings. The same group compared BIC percentages and bone anchorage of the proximal tibia in dogs using a rotational torque test (Coelho et al., 2009a). The implant surfaces consisted of alumina-blasted and acid-etched Ti6Al4V implants, as well as the same implants modified with an IBAD coating. The control group had higher RTQ values at 2 weeks and 4 weeks compared to the nano group. The

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resulting BIC values were similar at 2 weeks and 4 weeks for control and nano-coated implants. The results of the study indicated that

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there were no significant differences between the implant surfaces.

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Other techniques

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In the proximal tibial metaphysis and femur of rabbits, the BIC percentage and bone anchorage for CaP-coated implants and porous oxide surface coated implants were compared (Fontana et al., 2011). The coating procedure comprised of dip coating the implant in a solution of water, surfactant, and nano CaP particles. Afterward, the implants were dried and heat treated. The coating was comprised

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of nano CaP particles with a nominal size of 10 nm and a thickness of 200 nm, and both implant surfaces had a surface roughness of 1.3 µm. After healing periods of 2, 4, and 9 weeks, no significant differences were found in BIC or RTQ values. Furthermore, the

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authors did not detect an improvement in interfacial strength or bone apposition with nano CaP coated implants, and even noted decreases during the 2- to 9-week healing period. In a separate study, grit-blasted/acid-etched surface Ti-implants were compared with

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hydrothermally treated implants in the femoral condyles of rats (mJin-Woo et al., 2009). The CaP coating consisted of a 100 nm thick CaP layer, with the surface containing micron, submicron, and nano features. After 6 weeks, the harvested implants demonstrated significantly greater osseointegration with the CaP-coated implants compared to grit-blasted/acid-etched implants.

DISCUSSION

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It is known that microcoatings improve early fixation, increase BIC, and aid in the distribution of forces on the implant surface (Stellino et al., 2002). Clinical studies have established high implant survival rates; however, controversy exists regarding the clinical benefit of PSHA-coated implants (McGlumphy et al., 2003). This is partly due to the coating adhesion strength, which is poor and may

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separate after long implantation periods. The loosened fragments subsequently dissolve in the surrounding tissue fluids and contribute

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to the breakdown of bone around the implant. Furthermore, there is a risk that coating mechanical properties diminish and result in fractures in the coating surface (Lacefield et al., 1998, Yang et al., 2005). For nanocoatings, the problem of a secondary interface can be avoided with total dissolution, which has been verified in multiple studies (Guo-Li et al. 2009, Guo-Li et al., 2010). Furthermore, the dissolution of nanocoatings occurs gradually due to contact with tissue fluids and osteoclastic breakdown. An added benefit is that

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the nHA promimic and NanoTite™ coatings do not fully cover the surface. The NanoTite™ coatings are composed of small islands that prevent the occurrence of fractures, which is a great advantage compared to coatings with a microthickness, because coating

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detachment is a major problem with micro-thick CaP coatings.

It has already been determined that nHA particles enhance osteoblast proliferation, adhesion, and calcium deposition (Guo et al., 2007). Additionally, previous studies have established that nano CaP coatings improve osseointegration in vivo. However, whether this can be attributed to the chemical alteration or the nanotopography, or whether they act synergistically to improve biofunctionality, is not known. Two studies investigated the importance of both factors. One study compared the nHA promimic method with nano-

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titanium. One group investigated chemically different coatings, but there were also dissimilarities in surface coverage and particle

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size. (Mereilles et al., 2008c) Considering the smaller surface coverage of the nHA coating compared to nano-titanium coating, these findings could be biased. However, these data support the theory that the nano feature size and distribution improves tissue response. The other study showed that CaP coatings improve osteogenic gene expression and enhance distinct biochemical responses in vivo,

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but there was a difference in chemical alteration as well as nanotopography (Jimbo et al., 2011a). It can be concluded that the

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nanotopography improves biofunctionality; however, it has not been established whether chemical alteration has a significant effect in vivo.

Roughened implants improve biofunctionality and ensure higher bone anchorage as opposed to smooth implants. As well, roughened

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implants have shown a higher success rate compared to smooth implants (Cochran, 1999). The optimal roughness parameters have been investigated in numerous studies, and they can be defined as an Sa of approximately 1.5 µm with an Sdr of 50%. The ideal

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nanotopography has not yet been established in vivo, although it has been studied thoroughly in vitro, and has been shown to improve

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adhesion (Curtis and Wilkinson, 1997) The implant coatings used in prior research have different nanotopography and particle size, which is a likely explanation for the apparent dissimilarities in the reported results. Thus, future research should be performed in vivo to identify the ideal nanotopography and particle size.

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Seven studies were identified that utilized the nHA promimic technique, all of which compared titanium implants with or without

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nano HA modification. No clinical studies were identified. One study demonstrated that the nHA coating could improve osseointegration on smooth implants (Meirelles et al., 2008b). However, the improved biofunctionality did not correlate with a gap model, which would suggest that the nHA coating is not capable of enhancing osseointegration in the absence of a tight fit (Meirelles

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et al., 2008a). Another study with similar microroughness reported no significant differences in BIC values; however, at 4 weeks, the

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BIC values were numerically higher than corresponding values in the control group (Jimbo et al., 2012). Additionally, the study demonstrated improved bone strength quality with a nano-indenter. A different study reported improved RTQ, whereas another showed similar results as well as improved BIC values (Meirelles et al., 2008c, Jimbo et al., 2011b). Moreover, these studies

microroughened surface.

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demonstrated improved osseointegration and higher fixation strength for nHA-coated implants on a smooth surface and on a

One study comparing uncoated implants with a higher microroughness during a 12-week healing span showed lower BIC values for

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the nano HA promimic–coated implants compared to sand-blasted and acid-etched implants (Bryingtong et al., 2013). The results

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indicate that microroughness has a higher impact on short-term periods compared to nanotopography, which has already been shown to be of great importance. The early enhancement of osseointegration is hypothesized to be due to dissolution of nano HA particles from the surface coating. Hence, the nano HA particles accounted for improved bone formation and supported the differentiation and proliferation of osteoblast cells (Guo-Li et al., 2010). The microroughness has an important effect early and following longer healing periods, when dissolution of nHA particles no longer occurs. These findings suggest that the nHA promimic coating technique is

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capable of improving osseointegration by altering the surface nanotopography and chemical composition. Therefore, this coating

reported, which indicates the need for testing in long-term clinical studies.

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assists in improving the micro-roughened implant fixation and shortens the required healing period. No long-term survival rates were

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Six animal and 3 human studies involving NanoTite™ implants were included. Two animal studies reported an increase in

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osseointegration and bone anchorage over a short-term healing period of 9 days (Mendes et al., 2007, Mendes et al., 2009). As well, numerically higher BIC values were noted in 1 animal study; however, it should be noted that the relatively small sample size might have negatively influenced the significance of this difference (Vignoletti et al., 2009). Two studies reported no improved osseointegration after a long-term healing period, 1 of which did not establish any enhancement of BIC at early implantation.

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Furthermore, 1 study reported poor results for nHA-coated dual acid-etched implants, which exhibited significantly lower histomorphometrical results for the test implants. All 3 human studies demonstrated increased BIC values after 4 to 8 weeks of

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implantation (Goene et al., 2007, Orsini et al., 2007, Telleman et al., 2010). These findings suggest improved osseointegration and

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bone anchorage for NanoTite™ implants compared to DAE implants. Furthermotr, 2 clinical studies published by the same group evaluated immediate loading implants coated with the NanoTite™ coating, and both studies demonstrated high survival rates within a 1-year follow-up period. Moreover, they established that NanoTite™ implants are viable if the implants have an adequate primary stability (Ostman et al., 2010, Ostman et al., 2013). Nonetheless, further research involving a longer implantation time is warranted to substantiate these findings.

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Two animal studies involving different sol-gel coating techniques showed promising results, which is in accordance with the sol-gel method used for NanoTite™ implants but has yet to be confirmed in long-term clinical studies (Varis et al., 2013, Aksakal et al., 2014). However, the histomorphometrical measurements of nHA IBAD coatings revealed inferior osseointegration results when

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compared to PSHA coated and submicron IBAD coated implants (Coelho et al., 2009c, Coelho et al., 2009a). We can conclude that

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the results of this type of nanocoating are inferior to those of submicron IBAD and PSHA coatings, and that the nHA IBAD coating does not improve osseointegration or fixation over short-term healing periods.

Both studies involving BDCaP coatings failed to show an improvement in porous titanium implants with regard to osseointegration

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and bone anchorage. (Guo-Li et al., 2009, Guo-Li et al., 2010). Moreover, the authors reported that the EDHA coating is a better coating in the short-term healing period. Consequently, these findings demonstrate the superiority of the EDHA coating compared to

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the BDCaP coating for short-term healing periods. The findings can be attributed to the composition of the BDCaP coating, which is

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composed of octacalciumphosphate, which renders it more prone to dissolve in vivo compared to the HA in the EDHA coating (Kamakura et al., 2002). This difference in solubility is presumed to be partially responsible for the resulting variable bone formation. The dissolution of CaP is essential for ideal bone growth and strong anchorage during early implantation (Barrere et al., 2003). In fact, it has been suggested that the ideal outcome is for dissolution to occur gradually and completely. This would imply that the dissolution rate of the coating is similar to the formation of new bone, and that total resorption does not occur before completion of

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new bone formation. In addition, the total resorption ensures that no possible fractures can occur after long-term healing periods at the

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interfacial bonding (Barrere et al., 2003). The dissolution rate of the BDCaP coating was higher than the corresponding rate for the EDHA coating, and total dissolution occurred before 2 weeks. Furthermore, improved osseointegration could also be attributed to the surface chemistry or nanotopography of the HA coating compared to the CaP coating. It has already been established that nHA

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particles improve osteoblast proliferation, adhesion, and calcium deposition (Lacefield 1998, Wennerberg 1998). In fact, 1 of the

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studies demonstrated that bone failure appeared in the bone trabeculae for the EDHA-coated implants, whereas bone failure occurred at the interface between the implant and bone in the BDCaP-coated implants (Guo-Li et al., 2009). Based on all of these findings, we can conclude that BDCaP-coated implants produce inferior bone anchorage and integration compared to the EDHA-coated implants. These results are in accordance with the findings of a different study that evaluated titanium implants dip coated with nHA, and

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reported no difference in implant fixation or osseointegration within a short healing period. Likewise, the lack of biofunctionality can be attributed to the faster dissolution of the CaP produced by this coating technique (Fontana et al., 2011).

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The limitations of the current study are that the majority of the prior studies that were included investigated implants over a short

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healing period (i.e., between 2 and 12 weeks), and involved relatively small sample sizes, which might have introduced a bias. As well, because the 24 studies that were included consisted of different animal models and different implant designs, the data cannot be compared. We can only report the coatings that improved biofunctionality, and the evidence on which our findings are based. It should be noted that the results of numerous studies were not significant, which could be due to the small sample sizes. It is likewise important to note that the animal studies were based on study models for dental or orthopedic implants. Furthermore, although the

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human and clinical studies involved the maxillary and mandibular alveolar bone, it is not definite that the findings correlate with

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CONCLUSION

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patient-specific implants for maxillo-facial defects.

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Many prior studies have demonstrated that nano-CaP coatings improve biocompatibility and implant fixation; however, not all nanoCaP coatings yield the same results. It has been established that the IBAD technique, dip-coating, and BDCaP coatings revealed no enhancement on roughened implants. However, the nHA promimic coating has exhibited good results in vivo and in human studies involving early and intermediate healing periods. As well, the NanoTite™ coating demonstrated good results in vivo, as well as in

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clinical studies within a 1-year follow-up period. Two different sol-gel methods and a hydrothermal treatment have shown favorable results in early healing periods. These coatings do not appear to exhibit the problems encountered with conventional mHA coatings,

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and seem to improve the biofunctionality of the implant. The effect of these added coatings is the ability to minimize the problems of

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slow osseointegration and implantation failure. The different techniques produce coatings with varying thickness, nanotopography, particle size, and solubility, which all influence the reaction of bone. At present, the best coating surface is not known. Based on the current data, the NanoTite™ and nHA promimic coatings yield the most promising results. However, future research should involve a randomized controlled clinical trial to investigate the coating that yields the best results.

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The authors have no financial interest regarding the content of this article.

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Conflict of interest

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Kamakura S, Sasano Y, Shimizu T, Hatori K, Suzuki O, Kagayam M, Motegi K: Implanted octacalcium phosphate is more resorbable

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histomorphometric evaluation of implants with nanometer-scale calcium phosphate added to the dual acid-etched surface in the human

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posterior maxilla. J Periodontol 78:209-218, 2007.

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properties of dual acid-etched mini-implants with a nanometer-sized deposition of CaP: a histological and histomorphometric human study. Clin Implant Dent Relat Res 12:153-160, 2010

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2004.

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Figure 1. PRISMA diagram: selection procedure of the articles included in the review.

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Figure 2. (A) Roughened group; (B) BDCaP-coated surface; (C) EDHA coated surface (Guo-Li

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et al., 2009).

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Table 1.: Human study data

Article

position

Orsini et

Posterior

al., 2007

maxilla

Implantation of

Implant

Surface modification

Ti6Al4V Dual acid etched

Nanoparticles

SC

Anatomical

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Number

G

si

period

implants (m

8 wk

16

0

8 wk

16

0

4 wk

3

0

4 wk

3

0

8 wk

5

0

8 wk

5

0

12 wk

15

0

Posterior

al., 2007

maxilla

Dual etched and DCD

20-100nm in

coating

size

Ti6Al4V Dual acid etched

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Goene et

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CaP particles

CaP particles 20-100nm in

coating

size

EP

Dual etched and DCD

Posterior

Ti6Al4V Dual acid etched

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maxilla

Telleman

Posterior

et al.,

maxilla

CaP particles Dual etched and DCD

20-100nm in

coating

size

Ti6Al4V Dual acid etched

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2010 CaP particles 20-100nm in

coating

size

12 wk

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Dual etched and DCD

15

0

Implantation period, duration between implantation and harvesting of implant; Number of

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implants, number of implants in that group that were implanted; Gap size, difference in diameter

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between implant and implantation bed; BIC, bone implant contact of implant after harvesting; P value, P value between bone–implant contact values of implant group and implant group of the row below.

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Table 2. Animal study data

Implantation

Anatomical

Aksakal et al., 2014

Position

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Animal

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Article

Sheep

Sheep

Femur

Femur

Implant Surface Modification

Nanoparticles

Ti6Al4V No modification

45d

Sol gel method nHA

CaP particles

coated

25-35nm

Sol gel method mHA

CaP particles

Ti6Al4V coated

Period

20-30µm

45d

45d

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Sol gel method nHA

CaP particles

coated

25-35 nm

Beagle dogs

sockets

Premolar Beagle dogs

sockets

de Barros

sockets

EP

Beagle dogs

Ti6Al4V etched

Dual etched and DCD

CaP particles

coating

20-100 nm

2w

2w

Grit blasted and acid

Ti6Al4V etched

4w

Dual etched and DCD

CaP particles

coating

20-100 nm

4w

Grit blasted and acid

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Premolar

Grit blasted and acid

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al.,2011

Premolar

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Hamdan et

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Al-

45d

Ti6Al4V etched test:

8w

dual etched and DCD

CaP particles

coating

20-100 nm

8w

Premolar

Mongrel dogs

sockets

AC C

et al., 2012

Ti6Al4V Dual acid etched

8w

Dual etched and DCD

CaP particles

coating

20-100 nm

8w

Premolar

Mongrel dogs

sockets

Ti6Al4V Dual acid etched Dual etched and DCD

8w CaP particles 8w

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coating

20-100 nm

Premolar sockets

Ti6Al4V Dual acid etched Dual etched and DCD

CaP particles

coating

20-100 nm

Premolar

Bryingtong Swedish lopeared rabbits

Femur

EP

al., 2009c

Beagle dogs

Tibia

AC C

Coelho et

Dual etched and DCD

CaP particles

coating

20-100 nm

8w

8w

8w

Sand blasted, acid etched,

Ti6Al4V and heat treatment

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et al., 2013

Ti6Al4V Dual acid etched

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sockets

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Mongrel dogs

8w

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Mongrel dogs

12w nHA particles: 10-

Sand blasted, acid etched,

15 nm wide

and nHA promimic

and 100-200

method

nm long

12w

Alumina blastting/acid Ti6Al4V etched

3w

Alumina blastting/acid etched and ion beam–

HA 30-50

assisted deposition I

nm thick

3w

Alumina blasting/acid Beagle dogs

Tibia

Ti6Al4V etched

5w

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Alumina blasting/acid HA 30-50

assisted deposition I

nm thick

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etched and ion beam–

5w

Alumina blasting/acid etched and ion beam– Tibia

Ti6Al4V assisted deposition I

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Beagle dogs

HA 300-500 nm thick

3w

Alumina blasting/acid

HA 30-50

assisted deposition I

nm thick

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etched and ion beam–

3w

Alumina blasting/acid etched and ion beam–

Tibia

Ti6Al4V assisted deposition I

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EP

TE D

Beagle dogs

Beagle dogs

Beagle dogs

Tibia

Tibia

HA 300-500 nm thick

5w

Aluminum blasting/acid etched and ion beam

HA 30-50

assisted deposition I

nm thick

5w

Commercialy available plasma sprayed Ti6Al4V hydroxyapatite coating

3w

Alumina blastting/acid etched and Ion beam

HA 30-50

assisted deposition I

nm thick

Ti6Al4V Commercialy available

3w 5w

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Plasma sprayed hydroxyapatite coating Aluminum blasting/acid

nm thick

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assisted deposition I

5w

Alumina blasting/acid Beagle dogs

Tibia

Ti6Al4V etched

2w

Aluminum blasting/acid HA 30-50

assisted deposition I

nm thick

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etched and ion beam–

2w

Aluminum blasting/acid

Beagle dogs

Tibia

Ti6Al4V etched

4w

EP

TE D

Aluminum blasting/acid

Beagle dogs

Tibia

AC C

al., 2009a

HA 30-50

SC

Coelho et

etched and ion beam–

Beagle dogs

Tibia

etched and ion beam–

HA 30-50

assisted deposition I

nm thick

4w

Aluminum blasting/acid

Ti6Al4V etched

2w

Aluminum blasting/acid etched and ion beam–

HA 30-50

assisted deposition I

nm thick

2w

Aluminum blasting/acid Ti6Al4V etched Aluminum blasting/acid

4w HA 30-50

4w

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etched and ion beam–

nm thick

assisted deposition I New Zealand

al., 2011

white rabbits

Titanium porous oxide Tibia

Ti6Al4V surface

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Fontana et

2w

<200 nm

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thick, HA

Tibia

EP

New Zealand

Tibia

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white rabbits

nm in

surface

diameter

2w

Titanium porous oxide

Ti6Al4V surface

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white rabbits

Ca-P–coated implant

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New Zealand

particles 10

4w <200 nm thick, HA particles 10

Ca-P coated implant

nm in

surface

diameter

4w

Titanium Porous oxide Ti6Al4V surface

9w <200 nm thick, HA particles 10

Ca-P–coated implant

nm in

surface

diameter

9w

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New Zealand white rabbits

Titanium porous oxide Femur

Ti6Al4V surface

2w <200 nm

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thick, HA particles 10

diameter

Ti6Al4V surface

M AN U

Femur

Femur

AC C New Zealand white rabbits

2w

4w <200 nm thick, HA particles 10

Ca-P–coated implant

nm in

surface

diameter

4w

Titanium porous oxide

Ti6Al4V surface

EP

white rabbits

surface

Titanium porous oxide

TE D

New Zealand

nm in

SC

New Zealand white rabbits

Ca-P–coated implant

9w <200 nm thick, HA particles 10

Ca-P–coated implant

nm in

surface

diameter

9w

Titanium porous oxide Tibia

Ti6Al4V surface

2w

ACCEPTED MANUSCRIPT

<200 nm thick, HA

Guo-Li et

White rabbits

surface

diameter

M AN U

Ti6Al4V surface

TE D

Tibia

Tibia

AC C

white rabbits

10nm

2w

Titanium porous oxide

EP

New Zealand

Ca-P–coated implant

SC

New Zealand white rabbits

RI PT

particles

Tibia

4w <200 nm thick, HA particles 10

Ca-P–coated implant

nm in

surface

diameter

4w

Titanium porous oxide

Ti6Al4V surface

9w <200 nm thick, HA particles 10

Ca-P–coated implant

nm in

surface

diameter

Titanium Polished, sandblasted, and

9w 6w

ACCEPTED MANUSCRIPT

al., 2009

dual acid etched 100-nm thick crystal flake

biomimetical deposited

6-8 µm long

CaP

CaP

RI PT

Roughened and

6w

Polished, sandblasted, and Titanium dual acid etched

SC

Tibia

12w

100 nm thick

Roughened and

crystal flake

biomimetical deposited

6-8 µm long

CaP

CaP

M AN U

White rabbits

12w

Polished, sandblasted, and

Tibia

Titanium dual acid etched

EP

TE D

White rabbits

Tibia

AC C

White rabbits

White rabbits

Tibia

6w

Roughened and

Crystals with

electrochemically

diameter 70-

deposited HA

80 nm HA

6w

Polished, sandblasted, and Titanium dual acid etched

12w

Roughened and

Crystals with

electrochemically

diameter 70-

deposited HA

80 nm HA

Roughened and

100-nm thick

Titanium biomimetical deposited

crystal flake

12w

6w

ACCEPTED MANUSCRIPT

CaP

6-8 µm long CaP crystals with

electrochemically

diameter 70-

deposited HA

80 nm HA

RI PT

Roughened and

6w

100-nm thick

CaP

Roughened and

Crystals with

electrochemically

diameter 70-

deposited HA

80 nm HA

12w

12w

Polished, sandblasted, and

Femur

EP

White rabbits

AC C

al., 2010

6-8 µm long

Titanium CaP

TE D

Guo-Li et

biomimetical deposited

SC

Tibia

crystal flake

M AN U

White rabbits

Roughened and

White rabbits

Femur

Titanium dual acid etched

2w 100-nm thick

Roughened and

crystal flake

biomimetical deposited

6-8 µm long

CaP

CaP

2w

Polished, sandblasted, and Titanium dual acid etched

4w

Roughened and

100 nm thick

biomimetical deposited

crystal flake

CaP

6-8 µm long

4w

ACCEPTED MANUSCRIPT

CaP Polished, sandblasted, and White rabbits

Femur

Titanium dual acid etched

8w

RI PT

100-nm thick crystal flake

biomimetical deposited

6-8 µm long

CaP

CaP

SC

Roughened and

8w

Polished, sandblasted, and Femur

Titanium dual acid etched

M AN U

White rabbits

2w

Roughened and

Crystals with

electrochemically

diameter 70-

deposited HA

80 nm HA

2w

Femur

AC C

EP

White rabbits

TE D

Polished, sandblasted, and

White rabbits

White rabbits

Femur

Femur

Titanium dual acid etched

4w

Roughened and

Crystals with

electrochemically

diameter 70-

deposited HA

80 nm HA

4w

Polished, sandblasted, and Titanium dual acid etched

8w

Roughened and

Crystals with

electrochemically

diameter 70-

deposited HA

80 nm HA

Titanium Roughened and

8w

100-nm thick 2w

ACCEPTED MANUSCRIPT

Biomimetical deposited

crystal flake

CaP

6-8 µm long CaP Crystals with

electrochemically

diameter 70-

deposited HA

80 nm HA

SC

RI PT

Roughened and

EP

Jimbo et al., 2011b

Femur

crystal flake

biomimetical deposited

6-8 µm long

Titanium CaP

CaP

Roughened and

Crystals with

electrochemically

diameter 70-

deposited HA

80 nm HA

4w

4w

100-nm thick Control: roughened and

crystal flake

biomimetical deposited

6-8 µm long

Titanium CaP test

AC C

White rabbits

100-nm thick

Roughened and

M AN U

Femur

TE D

White rabbits

2w

CaP

Roughened and

Crystals with

electrochemically

diameter 70-

deposited HA

80 nm HA

8w

8w

Swedish lopeared rabbits

Femur

cpTi

No modification nHA promimic method

2w nHA

2w

ACCEPTED MANUSCRIPT

particles: 1015 nm wide and 100-200

RI PT

nm long

Swedish lopFemur

cpTi

No modification

M AN U

SC

eared rabbits

nHA promimic method

Swedish lop-

al., 2012

eared rabbits

Femur

EP AC C

Jin-Woo et

New Zealand

al., 2009

white rabbits

Femur

nHA

particles: 1015 nm wide and 100-200 nm long

Ti6Al4V Heat treatment

TE D

Jimbo et

4w

4w

3w nHA particles: 10-

Grit blasted, acid-etched

15 nm wide

surface and hydrothermal

and 100-200

treatment

nm long

3w

Heat treatment and nHA Ti6Al4V promimic method

6w

Grit blasted, acid-etched

CaP particles

surface and hydrothermal

with 100-nm

treatment

dimensions

6w

ACCEPTED MANUSCRIPT

Meirelles et al.,

New Zealand

2008b

rabbits

cpTi

Electropolished Electropolished and nHA

nHA

promimic method

particles

2008a

rabbits

Tibia

Meirelles et al.,

New Zealand

2008d

rabbits

EP

Meirelles New Zealand

2008c

rabbits

al., 2007

Tibia

AC C

et al.,

Mendes et

cpTi

TE D

Tibia

cpTi

Wistar rats

Femur

Electropolished

4w

4w

Electropolished and nHA

nHA

promimic method

particles

Grit blasting and titanium

24-nm nano-

coating

titanium

Grit blasting and nHA

30-nm nHA

promimic method

particles

M AN U

New Zealand

SC

Meirelles et al.,

4w

RI PT

Tibia

Ti6Al4V Titanium oxide blasting

4w

4w

4w

4w nHA

nHA promimic method

cpTi

Dual acid etched Dual etched and DCD

particles

4w

9d CaP particles 9d

ACCEPTED MANUSCRIPT

coating

20-100 nm

Mendes et

New Zealand

al., 2013

rabbits

Tibia

cpTi

Dual acid etched Dual etched and DCD

CaP particles

coating

20-100 nm

Titanium No modification

sol gel method nHA

New Zealand Tibia

Titanium sol gel method mHA

Vignoletti

EP

TE D

rabbits

9d

RI PT

Varis et

Femur

SC

Wistar rats

M AN U

al. 2009

9d

6w

nHA particles 25 nm

6w

mHA particles 25 µm

6w

nHA particles 25 sol gel method nHA

nm

6w

Premolar

Beagle dogs

sockets

AC C

et al., 2009

Ti6Al4V Dual acid etched

2w

Dual etched and DCD

CaP particles

coating

20-100 nm

2w

Premolar

Beagle dogs

sockets

Ti6Al4V Dual acid etched Dual etched and DCD

4w CaP particles 4w

ACCEPTED MANUSCRIPT

coating

20-100 nm

Premolar

al., 2012

rats

Tibia

Ovariectomized Tibia

Dual etched and DCD

CaP particles

coating

20-100 nm

Titanium Roughened

8w

12w

Rodlike

Roughened and nHA

crystals, size

coated

not shown

Titanium Roughened

12w

12w Rodlike

Roughened and nHA

crystals, size

coated

not shown

EP

TE D

rats

8w

RI PT

Ovariectomized

Ti6Al4V Dual acid etched

SC

Zhipeng et

sockets

M AN U

Beagle dogs

AC C

Implantation period, duration between implantation and harvesting of implant; Number of implants, number of implants in that group that were implanted; Gap size, difference in diameter between implant and implantation bed, given in millimeters; RTQ, removal torque values in newton centimeters and standard deviation if known; BIC, bone implant contact of implant after harvesting in percentage and standard deviation if known; P value, P value between bone– implant contact or removal torque values of implant group and implant group of row below.

12w

ACCEPTED MANUSCRIPT

*Some data are repeated due to the statistical comparison of the implant group with the implant

AC C

EP

TE D

M AN U

SC

RI PT

group of the row below.

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT