Synchrotron μCT imaging of bone, titanium implants and bone substitutes - a systematic review of the literature.

Journal of Cranio-Maxillo-Facial Surgery xxx (2013) 1e5

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Synchrotron mCT imaging of bone, titanium implants and bone substitutes e A systematic review of the literature Camilla Albeck Neldam*, Else Marie Pinholt Department of Oral and Maxillofacial Surgery (Head: Prof. Dr. Else Marie Pinholt), Institute of Odontology, Faculty of Health Sciences, University of Copenhagen, Nørre Alle 20, Copenhagen N, Denmark

a r t i c l e i n f o

a b s t r a c t

Article history: Paper received 17 May 2013 Accepted 4 November 2013

Today X-ray micro computer tomography (mCT) imaging is used to investigate bone microarchitecture. mCT imaging is obtained by polychromatic X-ray beams, resulting in images with beam hardening artifacts, resolution levels at 10 mm, geometrical blurring, and lack of contrasts. When mCT is coupled to synchrotron sources (SRmCT) a spatial resolution up to one tenth of a mm may be achieved. A review of the literature concerning SRmCT was performed to investigate its usability and its strength in visualizing fine bone structures, vessels, and microarchitecture of bone. Although mainly limited to in vitro examinations, SRmCT is considered as a gold standard to image trabecular bone microarchitecture since it is possible in a 3D manner to visualize fine structural elements within mineralized tissue such as osteon boundaries, rods and plates structures, cement lines, and differences in mineralization. Ó 2013 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.

Keywords: Synchrotron Bone microarchitecture Imaging Dental implants

1. Introduction Osseointegration of dental implants has been evaluated by classic 2D histomorphometry for many years. The advantage of this method has been the ease of access to observe and evaluate boneto-implant contact, the ratio of hard and soft tissue in proximity to the implant, vessels, and different cells in a light microscope. The major disadvantage is that the preparation for microscopy is a destructive process with grinding of the sample to a preferred thickness of 10e30 mm (Donath, 1993). This omits a lot of information as only a few samples can be evaluated compared to the evaluation of the entire bone sample in 3D. Hence, there is an uncertainty whether the 2D histological section analyzed represents the actual osseous integration of an implant (Sarve et al., 2011). In conventional radiography the X-ray beam passes through bone and implant, and is recorded as a 2D image. The information obtained in the radiograph depends on the absorption density of the object perpendicular to the direction of the X-ray beam (White and Pharoah, 2006). Since the microarchitecture and degree of mineralization of hard tissues are not possible to evaluate by histomorphometry and conventional radiography, additional 3D

* Corresponding author. Department of Oral and Maxillofacial Surgery, Institute of Odontology, Faculty of Health Sciences, University of Copenhagen, Nørre Allé 20, 2200 København N, Denmark. Tel.: þ45 35326611. E-mail address: [email protected] (C.A. Neldam).

evaluations are necessary. Four main sources of 3D imaging modalities are available; Magnetic Resonance Imaging (MRI) which is mainly used for comparing 3D data sets of soft tissues (Reinbacher et al., 2012), conventional third generation CT-scanners are wellestablished tools for hard tissue imaging (Sauerbier et al., 2013), cone-beam computer tomography (CBCT) which is a suitable tool for bone mass evaluation (Hohlweg-Majert et al., 2011), and X-ray micro computed tomography (mCT). Conventional third generation CT-scanners are well-established tools for hard tissue imaging (Sauerbier et al., 2013). mCT imaging is obtained by polychromatic X-ray beams, resulting in images with beam hardening artifacts, resolution levels at 10 mm, geometrical blurring, and lack of contrast (Feldkamp et al., 1989; Ruegsegger et al., 1996; Wiedemann, 2002; Ritman, 2004; Ruhli et al., 2007). When mCT is combined with synchrotron sources (SRmCT) a spatial resolution up to one tenth of mm may be achieved (www.esrf.eu, ESRF, 2013). Although mainly limited to in vitro examinations, it is considered as a gold standard to image trabecular bone microarchitecture in 3D (Peyrin et al., 2010). The evaluation of bone microarchitecture has traditionally been performed by measuring 2D histomorphometric parameters from bone slices obtained from iliac crest bone biopsies (Parfitt et al., 1987) and by algorithms turning these parameters into 3D volumetric estimations (Gundersen and Jensen, 1987). Synchrotron-based microtomography is an established technique available at various synchrotron light sources worldwide. Synchrotron radiation (SR) has a monochromatic beam, high photon flux, coherence, collimation, and sufficiently high spatial

1010-5182/$ e see front matter Ó 2013 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jcms.2013.11.015

Please cite this article in press as: Neldam CA, Pinholt EM, Synchrotron mCT imaging of bone, titanium implants and bone substitutes e A systematic review of the literature, Journal of Cranio-Maxillo-Facial Surgery (2013), http://dx.doi.org/10.1016/j.jcms.2013.11.015

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C.A. Neldam, E.M. Pinholt / Journal of Cranio-Maxillo-Facial Surgery xxx (2013) 1e5

resolution to evaluate the implant-to-bone contact (Kim et al., 2001a, 2001b). Utilizing volume images obtained with SR, the different material phases i.e. bone, titanium implant, cavities, and ceramic particles within a specimen may be distinguished by different absorption densities (Rack et al., 2006, 2011; Stiller et al., 2009). SRmCT uses the absorption of X-rays in order to detect density differences inside solid matter (Bernhardt et al., 2004). The information obtained is reconstructed by mathematical algorithms using the different absorption coefficients obtained by multiple tomography at different exposing angles of the samples resulting in a 3D image (Bernhardt et al., 2004). Due to its high resolution, SRmCT has been used to visualize the vascular canals in cortical bone in humans (Bousson et al., 2004) and in rats (Matsumoto et al., 2011a). The medical application of SRmCT is increasing, since SRmCT has been used to visualize the microarchitecture of osteoporotic bone and fractures (Ito, 2005; Kazakia et al., 2008; Cooper et al., 2011a), bone microcracks (Voide et al., 2009; Larrue et al., 2011), and bone changes after orthodontic treatment of teeth (Dalstra et al., 2006). SRmCT makes it possible to see fine structural elements within mineralized tissue such as osteon boundaries, rods and plate structures, cement lines, differences in mineralization of trabeculae (Nuzzo et al., 2002; Chappard et al., 2006), and of individual bone lamellae (Peyrin et al., 2010; Cooper et al., 2011b; Larrue et al., 2011). The aim of this study was to compare and analyze the literature on high resolution scans on bone microarchitecture and dental implants visualized by SRmCT and to discuss its usability in contrast to conventional mCT and histology. Hypothesis: The null hypothesis of this study is that there is no difference between SRmCT and mCT and that the studies are comparable so a meta-analysis can be performed. 2. Material and methods

Table 1 Inclusion and exclusion criteria. Inclusion criteria

Exclusion criteria

Studies published after January 2000 Published in English

Studies published before January 2000 Published in other languages than English Lack of parameters of bone structure

Grafting material in connection with bone High resolution synchrotron scans Human bone Animal bone Bone structure Dental implants in bone

Medical induced bone disease Lack of parameters of bone Orthodontic treatment Osteoporotic bone Osteoporosis

Table 2 Results of the MeSH search, results represent number of articles. Search

MeSH word

MeSH word

#1 #2 #3 #4 #5

Synchrotron Synchrotron Synchrotron Synchrotron Synchrotron

#6 #7 #8 #9 #10

Synchrotron Synchrotron Synchrotron Synchrotron Synchrotron

#11 #12 #13 Total

Synchrotron Synchrotron Synchrotron

Maxillofacial surgery Tricalcium phosphate MicroCT/mCT Dental implant Alveolar ridge augmentation Osseointegration Porosity Bone density HAeTCPb Electron microscope tomography Jaw Bone transplantation Histology

Results

Full text analysis

Included

0 1 40 2 0

0 1 5 1 0

0 1 2 1 0

7 23 25 0 1

7 6 16 0 0

7 3 3 0 0

4 2 13 118

3 2 0 41

0 0 0 17

A Medline search (PubMed) was conducted, and studies published in English from 2000 to 2012 were included in the review. The inclusion and exclusion criteria are listed in Table 1. The MeSH words used for the literature search as well as the search results are listed in Table 2. From the identified studies, the following variables were extracted: author, journal, year of publication, type of synchrotron mCT, which type of animal, human yes/no, body part, resolution, histology, mCT, and graft material.

bone evaluated by SRmCT and mCT, respectively (Nuzzo et al., 2002; Nogueira et al., 2010; Cooper et al., 2011b; Larrue et al., 2011). The studies comprise evaluation of different types of bone (Nuzzo et al., 2002; Cooper et al., 2011b; Larrue et al., 2011), while the fourth study (Nogueira et al., 2010) analyzed femoral bone tibia-, fibula-, humerus-, cuboid-, and calcaneus bone (Table 3).

3. Results

Two studies were included reporting the degradation of porous bone substitute tricalcium phosphate (TCP) foam with poly(DLlactic acid) (PDLLA), and the microgap between a dental implant and the abutment, respectively (Ehrenfried et al., 2010; Rack et al., 2010) (Table 4).

The combination of synchrotron mCT and used MeSH words resulted in 118 articles. Some of the articles appeared multiple times during the different combination of MeSH words and are subsequently only accounted for once. Following screening of titles and abstracts by defining the chosen inclusion and exclusion criteria, 41 potentially relevant publications were found and full text analysis was performed by one author (CAN). Out of the 41 articles 17 articles were included in the study. The studies were divided into human studies (Table 3), studies reporting only graft or dental implant (Table 4), and animal studies (Table 5) for analyzing purposes.

3.2. Graft and dental implant studies

3.3. Animal studies 11 animal studies were included comprising six different animal species and various types of bone (Table 5). Bernhardt et al. (Bernhardt et al., 2004, 2005, 2012) described the use of high photon flux energies to evaluate titanium dental implants and compared it to histology and mCT.

3.1. Human studies

4. Discussion

Four human studies (Nuzzo et al., 2002; Nogueira et al., 2010; Cooper et al., 2011b; Larrue et al., 2011) described bone microarchitecture in cortical and trabecular bone of the extremities, osteons, microcracks and lacunae in bone, trabecular bone volume fraction and mineral content comparisons in cortical and trabecular

In a literature search comprising SRmCT, histology, and mCT only a few publications are available (Nuzzo et al., 2002; Gauthier et al., 2003; Jung et al., 2003; Weiss et al., 2003; Bernhardt et al., 2004, 2005, 2012; Tzaphlidou et al., 2006; Ehrenfried et al., 2010; Morelhao et al., 2010; Nogueira et al., 2010; Rack et al., 2010;



3

Table 3 Included human studies. Author

Year

Body part

SRmCT

Resolution SRmCT

mCT

Microscopy

Graft

Cooper, D.M.L. (Cooper et al., 2011b)

2011

Femoral heads

1

2011

Femoral heads

5

2010

12

2002

ELETTRA SYRMEP beam line, Italy ESRF, France

Nuzzo, S. (Nuzzo et al., 2002)

Tibia, fibula, femur, humerus, cuboid, and calcaneus Femur

þ Epifluorescence

Noguiera, L.P. (Nogueira et al., 2010)

26.4 KeV 1.4 mm 23 KeV 1.4 mm 20 KeV 14 mm 20 KeV 10.13 mm

Larrue, A. (Larrue et al., 2011)

Advanced Photon Source SR Chicago, USA ESRF ID19 France

4

þ Skyscan 1072

Sample size

Table 4 Included studies with only graft or dental implant, NS: non specified. Author

Year

Subject

SRmCT

Resolution SRmCT

mCT

Microscopy

Sample size

Ehrenfried, C.M. (Ehrenfried et al., 2010)

2010

TCP foam and PDLLA

ESRF ID 19, France

NS

Rack, A. (Rack et al., 2010)

2009

Titanium dental implant

BAMline, BESSY, Germany

30 KeV 5.05 mm 50 KeV 9 mm

1

Table 5 Included animal studies, NS: non specified, SEM: Scanning electron microscopy. Author

Year

Animal

Body part

SRmCT

Resolution SRmCT

mCT

Microscopy

Graft

Sample size

Bernhardt, R. (Bernhardt et al., 2004) Bernhardt, R. (Bernhardt et al., 2005) Bernhardt, R. (Bernhardt et al., 2012) Fu, Q. (Fu et al., 2011)

2004

Dog

Mandible

HASYLAB at DESY, Germany

Titanium implant

NS

Goat

Femoral condyle

16

Mini pig

Maxilla

þ SEM þ

Titanium implant

2012

HASYLAB, beam line BW5, Germany BESSY II, Germany

þ Microfocus

þ

2005

Titanium implant

6

2011

Rabbit

Tibia

þ

2002

Rabbit

Femur

þ SEM

Jung, H. (Jung et al., 2003)

2002

Rabbit

Tibia

Matsumoto, T. (Matsumoto et al., 2011b) Morelhao, R. (Morelhao et al., 2010) Tzaphzidou, M. (Tzaphlidou et al., 2006) Weiss, P. (Weiss et al., 2003) Yue, S. (Yue et al., 2010)

2011

Mouse

Knee and tibia

þ Skyscan

Borate bioactive glass CaSO4 CaP, BCP, and ionic hydraulic bone cement Titanium dental implant

12

Gauthier, O. (Gauthier et al., 2003)

60 KeV 6.4 mm 60 KeV 10 mm 50 KeV 3e58 mm 27 KeV 4.4 mm NS KeV 1.4 mm

2009

Rat

Calvaria

b-TCP

3

2006

Rat

3

2003

Rabbit

Femoral neck and tibia Femur

HA/b-TCP, CPC, CaP

12

2009

Mouse

Tibia

Bioactive glass from scaffolds

1

Lawrence Berkeley Nat. Lab. Beam line 8.3.2, USA ESRF ID 22, France

5C1 beam line Pohang Light Source, Korea Hutch 3. Japan SR Research Institute (JASRI), Japan NSLS Brookhaven National laboratory, USA ELETTRA, Italy ESRF ID 22, France ESRF ID 19, France

Yue et al., 2010; Cooper et al., 2011b; Fu et al., 2011; Larrue et al., 2011; Matsumoto et al., 2011b). Since no available data made possible a meta-analysis a descriptive analysis is presented. Only eight of the included studies concern SRmCT and related this evaluation method to light microscopy and mCT, hence a direct comparison is not possible and a description of the studies’ use of these different evaluation tools are analyzed and discussed in relation to the other included studies. Only one human study compares SRmCT with histology (Larrue et al., 2011), one compare SRmCT with mCT (Nuzzo et al., 2002), while four of the included animal studies compare SRmCT to light microscopy (Gauthier et al., 2003; Bernhardt et al., 2005, 2012; Fu et al., 2011), and one study compared it to mCT (Jung et al., 2003). Bernhardt et al. are the only authors who discuss and compare SRmCT, mCT, and histology (Bernhardt et al., 2004). Many of the studies included use different synchrotron light sources, resolutions, and photon

16 KeV NS mm 25 KeV 11.7 mm NS KeV 30 mm 20 KeV 28 mm 20 KeV 1e1.4 mm 20 KeV 1.4 mm

10

1 13

energy (KeV) for different purposes, hence results are difficult to compare. Our aim was to compare and discuss the usability of SRmCT in relation to microscopy and mCT. Bone microarchitecture is evaluated in some of the studies (Weiss et al., 2003; Cooper et al., 2011b; Fu et al., 2011; Larrue et al., 2011; Matsumoto et al., 2011b). Fu et al. (2011) described visualization of the rod- and plate-like structures in trabecular bone, the osteocyte lacunae depicted like cavities in cortical bone, and a 3D evaluation of the vascular tissue in cortical bone without using perfused contrast agents (Fu et al., 2011). 2D histological sections compared with 3D SRmCT scans were well correlated concerning vascular tissue infiltrations, integration of trabecular bone and graft, and micro pores in the graft, but SRmCT provided a clearer and more distinct picture of the bone-like graft (Fu et al., 2011). A distinct determination of the graft comprising borate glass was


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observed in SRmCT, in contrast to the image on the 2D section (Jia et al., 2010; Fu et al., 2011). Hence by using SRmCT it is possible to visualize the vascular tissue, scaffold, and bone, due to the high spatial resolution, high photon flux, and signal-to-noise ratio of the SRmCT. Yue et al. (2010) found it possible to visualize vessels and soft tissue inside pores of a scaffold using a 1.4 mm resolution. However, using SRmCT compared to mCT it is necessary to infuse contrast agents in order to visualize the vessels in bone with the consequence of injecting too little or too much and with subsequent development of artifacts or lack of visualization (Guldberg et al., 2008). Thus, when visualizing vessels in mCT the bone sample needs to be demineralized before mCT scanning to facilitate segmentation of the vascular structures, which prevents visualization of the vascularization in the new bone (Fu et al., 2011). Larrue et al. (2011) compared SRmCT to epifluorescence microscopy and found the appearance of microcracks more complex than suggested by 2D observations. Microcrack evaluation requires a high resolution at the micrometer scale to visualize such small porosities. In the epifluorescence 2D microscopy and at the SRmCT scans the same simple microcracks were possible to visualize, while the more complex ones were only visualized in 3D. When Cooper et al. (2011b) used 3D in a resolution of 1.4 mm it was not possible to visualize lamellae within the osteons in cortical bone. They argued that an image of a higher resolution would reveal additional features within cortical bone, but an improved resolution often come with a trade off in terms of field of view. Bernhardt et al. (Bernhardt et al., 2004, 2005, 2012) did not find a significant difference between histology and SRmCT. They conclude that using 3e4 histological sections per implant does not result in a significant difference between bone-to-implant contact (BIC) and bone volume. Jung et al. (2003) wanted to evaluate BIC by using SRmCT. They compared it to mCT and concluded that SRmCT scans showed clearer boundaries and greater details of the tissues surrounding a dental implant compared to mCT with resolutions of 10 mm (Jung et al., 2003). Different mineralization levels of bone due to different absorption coefficients is easier to evaluate by different histologic staining methods compared to images of SRmCT where bone with different levels of mineralization is visualized by slight change in gray colors in the reconstructed image due to almost equal numbers of absorption coefficients (Fu et al., 2011). Newly formed bone inside bone substitutes is imaged as an interconnected bony network with scattered empty spaces representing restoration of the initially formed trabecular bone (Gauthier et al., 2003; Fu et al., 2011). Osteoconduction and osteointegration of the different bone substitutes can be evaluated and provide 3D images representing the microarchitecture in proximity to the bone substitute (Weiss et al., 2003; Fu et al., 2011). Newly formed bone was well mineralized tissue in close proximity to the bone substitutes and a degradation of the substitutes was observed (Gauthier et al., 2003; Weiss et al., 2003; Morelhao et al., 2010; Fu et al., 2011). Gauthier et al. (2003) compared the SRmCT with scanning electron microscopy (SEM), which confirmed newly formed bone in close contact with the biphasic calcium phosphate and in the intergranular spaces. The SRmCT images showed in 3D an interconnected bone network (Gauthier et al., 2003). Bone substitutes with micro pores of size 5d10 mm, and of size 300d565 mm, showed vascularization and ingrowth of newly formed bone, respectively inside the bone substitutes (Gauthier et al., 2003; Weiss et al., 2003; Fu et al., 2011). Weiss et al. (2003) described osteocyte lacunae, many interconnected tubes that appeared to be vascular canals of bone, and large marrow spaces between bone trabeculae in proximity to different bone substitutes. They evaluated a macroporous biphasic calcium phosphate where

the osteoconduction seemed homogenously at the ceramic surface, and where 10% of the biphasic calcium phosphate was resorbed between 3 and 8 weeks. They conclude that as porosity and interconnection of the pores in the bone substitute increases, bone ingrowth becomes greater and the bone substitute resorbs. These results are relevant when using different bone substitutes since the difference between a well-integrated grafting material and one situated passively in bone depends on the size of the pores and the content of material that can be resorbed (Ehrenfried et al., 2010). These different study designs clarify the diversity of the SRmCT evaluation method. Hence, the visualization of cortical bone microarchitecture confirms that SRmCT has a great potential to shed new information about bone microarchitecture not only in trabecular but also in cortical bone, and in bone substitutes, which underlines why SRmCT should be considered golden standard when it comes to describing and visualizing the microarchitecture of bone. Specific types of tissue cannot always be identified using SRmCT due to similar absorption coefficients, but it gives qualitative information on the density of tissue and a given material. Mature bone has a higher density than osteoid and soft tissue and is therefore depicted brighter than osteoid and soft tissue. The different tissue densities can be distinguished using a histogram. Yue et al. found that tissue growing on and in a scaffold had a lower density than the scaffold, indicating that it was soft tissue. They installed a bioactive glass scaffold (70 mol%SiO2, 30 mol% CaO) into the muscular fascia of the tibia of a mouse (Yue et al., 2010). The ingrowth of soft tissue was explained by micro movements between the scaffold and the tibia since the scaffold was not implanted into bone (Yue et al., 2010). However, it could also have been de novo osteoid formation of lower absorption coefficient. Microgap formation at the dental implanteabutment interface has also been studied (Gauthier et al., 2003; Broggini et al., 2006; Rack et al., 2010; Meleo et al., 2012). Implanteabutment misfit is known to raise mechanical and biological issues. A mechanical stress can rise on the connection structure and on peri-implant bone, which can lead to screw fracture. This can also have biological outcomes, since misfit at the implanteabutment interface creates a microgap which allows bacteria to penetrate and colonize, causing inflammatory processes (Broggini et al., 2006; Meleo et al., 2012). Rack et al. (2010) studied the microgap at the implante abutment interface of a conical shaped dental implant, using SRmCT, under different mechanical loads to precisely illustrate the gap. The gap ranged between 1 and 22 mm, a finding which is very relevant within oral implantology (Rack et al., 2010), and had never been investigated by SRmCT before, where the high resolution and contrast, due to the propagation makes it possible to investigate the microgap in internal conical implanteabutment joints (Rack et al., 2010). 5. Conclusion A review of the literature emphasizes the usability of SRmCT ranging from visualization of bone microarchitecture and vessels to development of newly formed bone within different bone substitutes. Using SRmCT makes it possible to evaluate bone microstructures in 3D at levels never obtained before, either by conventional mCT or by classical light microscopy. Within dental practice more detailed evaluations in higher resolutions than previously obtained are required within osseointegration of dental implants, comparison of osseointegration of different bone substitutes, bone microarchitecture at the bone-toimplant interface and the high resolution SRmCT evaluation may be the way.



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Bone augmentation with TiMesh. autologous bone versus autologous bone and bone substitutes. A systematic review.

Osteointegration of porous absorbable bone substitutes: A systematic review of the literature.

Bone grafts and bone substitutes for opening-wedge osteotomies of the knee: a systematic review.

Does PRP enhance bone integration with grafts, graft substitutes, or implants? A systematic review.

Comparative evaluation of the combined application of titanium implants and calcium phosphate bone substitutes in a rabbit model.

Bone substitutes for peri-implant defects of postextraction implants.

Rapid prototyped porous nickel-titanium scaffolds as bone substitutes.

Surface Functionalization of Orthopedic Titanium Implants with Bone Sialoprotein.

Short dental implants in reduced alveolar bone height: a review of the literature.

Bone graft substitutes for spine fusion: A brief review.

Dental follicle stem cells in bone regeneration on titanium implants.

Low elastic modulus titanium-nickel scaffolds for bone implants.

Implants in the zygomatic bone for maxillary prosthetic rehabilitation: a systematic review.

Permanent, skin penetrating, bone-anchored titanium implants. A clinical study of host-reaction in bone and soft tissue.

Longevity of dental implants in type IV bone: a systematic review.

Micro-CT analysis of the rodent jaw bone micro-architecture: A systematic review.

Crestal bone loss and periimplant inflammatory parameters around zirconia implants: A systematic review.

Effect of breastfeeding on bone mass from childhood to adulthood: a systematic review of the literature.

A comparative study of zirconium and titanium implants in rat: osseointegration and bone material quality.

Decontamination of autogenous bone grafts: systematic literature review and evidence-based proposal of a protocol.

Titanium-Nitride Coating of Orthopaedic Implants: A Review of the Literature.

Bone Morphogenetic Protein Coating on Titanium Implant Surface: a Systematic Review.

Direct metal laser sintering titanium dental implants: a review of the current literature.

Annual failure rates and marginal bone-level changes of immediate compared to conventional loading of dental implants. A systematic review of the literature and meta-analysis.