Non-destructive evaluation of teeth restored with different composite resins using synchrotron based micro-imaging

Abstract

BACKGROUND:

Application of high resolution synchrotron micro-imaging in microdefects studies of restored dental samples.

OBJECTIVE:

The purpose of this study was to identify and compare the defects in restorations done by two different resin systems on teeth samples using synchrotron based micro-imaging techniques namely Phase Contrast Imaging (PCI) and micro-computed tomography (MCT). With this aim acquired image quality was also compared with routinely used RVG (Radiovisiograph).

METHODS:

Crowns of human teeth samples were fractured mechanically involving only enamel and dentin, without exposure of pulp chamber and were divided into two groups depending on the restorative composite materials used. Group A samples were restored using a submicron Hybrid composite material and Group B samples were restored using a Nano-Hybrid restorative composite material. Synchrotron based PCI and MCT was performed with the aim of visualization of tooth structure, composite resin and their interface.

RESULTS:

The quantitative and qualitative comparison of phase contrast and absorption contrast images along with MCT on the restored teeth samples shows comparatively large number of voids in Group A samples.

CONCLUSIONS:

Quality assessment of dental restorations using synchrotron based micro-imaging suggests Nano-Hybrid resin restorations (Group B) are better than Group A.

Keywords

Phase contrast imaging (PCI)micro computed-tomography (MCT)composite resin dental restoration edge enhancement

1 Introduction

Over the past few decades intense research towards the improvement in conventional X-ray imaging techniques has resulted in the development of phase contrast imaging (PCI) [1 –6]. In addition to imaging bulk features it has demonstrated the potential to reveal the minute density difference details of both radio-opaque and radiolucent structures, which are otherwise not possible when conventional techniques are used. The enhancement in image quality in PCI technique is based on the phase effects which is sensitive to minute density differences. Any discontinuity in the sample such as presence of void, density variation etc. is visualized with high clarity due to the inherent edge enhancement [7 –9] in PCI. The choice of the samples varies from composites, polymers, biological tissues to livespecimens.

Phase contrast can be understood well by considering the change in refractive index of the material being subjected to hard X-rays. The refractive index of X-rays passing through the matter is written as n = 1 - δ + iβ where δ is the refractive component and β is absorptive component, both of them are wavelength dependent. The decay in the absorptive component of the refractive index with energy is much faster than the refractive component in the hard X-ray region. However, the contrasts due to refractive components are observable only when the source satisfies the condition of high coherence [10]. To achieve this, synchrotron radiation based beamlines and related instruments are being utilized, which demonstrate the application of PCI in medical and dental research [11 –13]. Synchrotron based source scores higher compared to lab based X-ray sources because the former one has high degree of both spatial and chromatic coherence.

Among the various PCI techniques such as interferometer based, propagation based imaging [14] and diffraction enhanced imaging, propagation based phase contrast has gained much attention because of its simplicity in implementation.

Propagation based PCI technique has shown strong potential in imaging material science samples such as composites, polymers, rocks as well as biological samples including animal tissues, tumors [15, 16]. In the present work, the authors have investigated two different types of resin restored human teeth samples to obtain information on teeth-resin interface and voids incorporated in the resin in the due course of artificial restoration by using resin composites of hybrid and nano-hybrid types. These composites are clinically used and are well accepted as teeth restorative materials [17]. The development of such resins has opened up new perspectives in dental field such as in case of traumatic dental injuries. However their application requires expertise as it influences the quality of the restored tooth. The resin is required to bond efficiently to the tooth structure through the mechanism of micromechanical interlocking between the resin adhesive and tooth surface.

Improper handling of the composite resins may lead to improper bonding and entrapment of air in the resin. These voids or porosities increase the risk of restorative failure by weakening the resin-teeth bond and also by reducing the resistance of resin restoration against fracture. Voids can lead to cracks, detachment of resin from the teeth and weakening of the restored resin part [18 –20]. The longevity of resin composite restorations can be assured by preventing or at least minimizing these voids. Thus it is necessary to characterize and visualize the resin-teeth interface, voids and imperfections to evaluate the quality of restorations. The process followed thus will help in standardizing the technique for the best restoration with minimum imperfections.

The basic constituents of dental restorative composites are its polymeric matrix, which generally utilizes methacrylate based polymers and filler particles. The role of filler particles is to improve the mechanical properties of the resin and thus materials like glass, quartz, or ceramic oxide (example alumina or silica) are preferred choices. To make a strong bond between these filler particles and polymer matrix, suitable coupling agents are employed.

The first part of the present work aims at investigating the ability of PCI to qualitatively visualize the presence of voids and imperfections at the resin-tooth interface [21]. For this purpose six human teeth as mentioned in the next section were mechanically fractured and then artificially restored with hybrid and nano-hybrid composite resins, were subjected to synchrotron based phase contrast imaging. A comparison with the absorption radiographs was also done using quantitative evaluation of image contrast at specific locations of interest.

In the second part of this study, specimens of interest from the set of six samples were subjected to X-ray MCT for quantitative study of internal details of restored region in three dimensional perspective and to obtain knowledge about the imperfections in the sample. MCT is a high resolution, non-destructive 3D imaging technique to investigate internal structures of objects. It is used in various areas of science including biology, bone investigation, material research and dental research. X-ray MCT has been used for tooth macromorphological studies [22] and root canal assessment [23, 24]. MCT reports on biominerals [25] and biocompatible materials [26] are also available. MCT with synchrotron radiation has been widely used in endodontology [27, 28], investigation of voids, cracks and to ensure the bonding in the dental restorations [29]. There are reported studies of restorative composite resin fractures visualized using MCT in the literature [30].

2 Materials and method

2.1 Sample preparation

[Extracted primary anterior teeth (over retained), premolars (for orthodontic purposes) and permanent mandibular incisors (for periodontal reasons)] Extracted human teeth for various therapeutic reasons were obtained and were mounted on acrylic base. Crowns of the teeth were fractured mechanically involving only enamel and dentin, without the exposure of pulp chamber and divided into two groups (Group A and B) depending on the type of restorative composite materials used (Group A samples were restored with submicron Hybrid composite material and Group B samples were restored with Nano-Hybrid restorative composite material). The fractured teeth were cleaned with non-fluoridated polishing paste. Enamel from the fracture margin was beveled to increase the surface area. The prepared tooth surfaces were etched with 37% phosphoric acid gel for 20 seconds, which was followed by rinsing. After removal of excess water from the samples, teeth in Group A were coated with GLUMA^® 2Bond (Heraeus Kulzer, Hanau, Germany), gently air dried and photo-polymerized. In Group B Adper^TM Single bond 2 adhesive (3M ESPE AG, Seefeld, Germany) was applied, air dried gently and photo-polymerized. Teeth in Group A were restored with CHARISMA^® (Heraeus Kulzer, Hanau, Germany) and in Group B were restored with Filtek^TM Z250 XT (3M ESPE AG, Seefeld, Germany) using incremental technique as per manufacturer’s instructions. The margins of restoration were given proper finish using diamond abrasives and polished with a series of polishing disks (SHOFU, SHANK CA, PN 0306, Shofu Dental Corporation, USA).

Table 1 provides the detailed sample information.

Description of composite materials:

CHARISMA^®: It is a submicron Hybrid composite material.

Resin system: Bis-GMA (Bisphenol A –glycidyl methacrylate) and TEGDMA (Tri ethylene glycol dimethacrylate).

Filler system: Barium microglass with maximum particle size less than 2μm and mean particle size around 0.7μm. Pyrogenic SiO₂ with particle size between 0.01–0.07μm. This provides for the high packing density of 78% filler content by weight (approx. 61% by volume).

Filtek^TM Z250 XT: It is a Nano-Hybrid universal restorative composite material.

Resin system: Main constituents include Bis-GMA, TEGDMA, UDMA (urethane dimethacrylate), Bis-EMA (Bisphenol A polyethylene glycol diether dimethacrylate). Some of the TEGDMA is replaced with PEGDMA to moderate shrinkage.

Filler system: Surface-modified zirconia/silica with a median particle size of approximately 3μm or less and non-agglomerated/non-aggregated 20 nanometer surface-modified silica particles. The filler loading is 82% by weight (68% by volume).

2.2 Experimental set-up

In the conventional method, the dental radiographs were taken using digital radiovisiography (RVG). The spatial resolution in this instrument (Suni plus) is given in terms of line pair per millimeter. The instrument images the features with lowest radiation exposure (Optimal Exposure). The images are obtained as a balance between highest resolution and lowest radiation exposure.

The experimental work (PCI and MCT) was carried out at Imaging Beamline (BL-4) at Indus-2 synchrotron radiation source operating at 2.5GeV energy and current 300 mA [31]. This beamline provides broad white band of electromagnetic radiation with high intensities and using a double crystal monochromator of Si(111) type, suitable energy in the range of 8–35 keV can be selected.

The experimental set up for propagation based phase contrast imaging at Imaging Beamline consists of motorized precision translation - rotation stage and an imaging detector. The sample holder has a centrally fitted chuk for holding the samples. The imaging detector is a high resolution CCD camera with an active area of 4 k× 2.5 k pixels; each pixel is of 4.5 micron, with Gadox scintillator at its input face coupled to the CCD via fibre-optic.

In this experimental study sample-to-detector distance (SDD) is varied from 5 mm to 450 mm to optimize phase contrast. The absorption radiographs of the samples were obtained at a distance of 5 mm and phase contrast images were obtained with detector placed at 450 mm. Energy and exposure time for all the samples are given in table for contrast (Table 2). The energy values for Sample no. 2 and Sample no. 5 were 28 keV and 32 keV respectively to get good visibility in the images for these thicker teeth samples. The energy value for remaining samples was 25 keV.

All acquired images were analyzed using ImageJ [32]. In order to measure quantitatively the image quality and visibility of the object details the parameter calculated here was image contrast. Intensity profile curves were plotted at the teeth-resin (edge of restoration) and the resin-void edges for absorption and phase contrast radiographs for all the six samples. The value of contrast [33] in absorption and phase contrast radiographs for all the samples was calculated by using: $C = \frac{I_{max} - I_{min}}{I_{max} + I_{min}}$ where, I _max and I _min are the maximum and minimum intensities in the intensity profile plot.

For tomography experiment the detector was placed at 450 mm away from the sample stage. The sample was rotated in steps of (0.2°) and was exposed to beam energy E = 28 keV and exposure time was 5 sec for all the samples. Dark field and flat field corrections were performed to limit CCD and beam related artifacts during reconstruction. Two dimensional tomographic slice images and volume rendered images were produced with suitable software [34].

3 Results and discussions

3.1 Comparative study of absorption, phase contrast and RVG

The absorption based clinical X-ray image (RVG- Radiovisiograph) of restored teeth (Fig. 1a) clearly depict that absorption imaging may show basic information like tooth-resin interface, but is unable to reveal any detailed information about the presence of voids in resin restorations. The synchrotron phase contrast imaging using the propagation based imaging (PBI) set-up is seen to bring quality improvement in the images. Figures 1 and 2 shows comparison of absorption and phase contrast images for Sample no. 1 in Group A and Sample no. 4 in Group B respectively. The region of interest in all the images are shown by blue rectangles and the enlarged view of these regions have enhanced visibility for both tooth-resin interface and voids. Profiles were plotted along the yellow line shown in the enlarged view of images in Figs. 1 and 2 using ImageJ. The phase contrast images of the tooth-resin boundary and resin part clearly demonstrates the presence of several voids as compared to that obtained from conventional absorption images.

The air inclusions have comparatively lower refractive index than the surrounding composite resin and therefore passing X-rays are refracted at the boundaries of these voids resulting in generation of phase variation in the transmitted beam. Due to Fresnel diffraction, contrast in the recorded refraction images is enhanced which is visible at the resin tooth interfaces as well as void boundaries in the sample and confirmed in the image profile plots along the boundaries of air voids and composite resin matrix. The density variations between the hydroxyapatite content of teeth and the hybrid resin (barium micro-glass and pyrogenic SiO₂ fillers in Bis-GMA and TEDGMA)/nanohybrid resin (zirconia/silica fillers in Bis-GMA, TEGDMA, UDMA) cause the refraction of X-rays at the tooth-resin interface thus increasing the visibility in the phase contrast images.

For (Group A) teeth restored with hybrid resin, it was observed in Sample no. 1, that large size air voids were clearly visible in the absorption images (Fig. 1b and c) obtained at SDD = 5 mm, but the smaller voids were poorly resolved. The phase contrast images (Fig. 1d, e) of this sample at SDD = 450 mm along with the phase contrast images after using enhance contrast and bandpass filtering (Fig. 1h, i) shows a large number of very small size voids. The diameter for smallest void from phase contrast radiograph was 54.6 micron. (Fig. 1f) and (Fig. 1g) shows profile plots for tooth-resin and void-resin interface. Contrast measured from (Fig. 1f) plot was 6.5% for absorption image and 11.7% for PCI. Similarly for (Fig. 1g) contrast measured for absorption and PCI images were 3.4% and 6.2% respectively. In this sample the contrast gain in PCI was just twice for the two interfaces.

Contrast was also measured for the full length of the interface for Sample no. 1 and Sample no. 4. The average value of contrast from the profile plots at different places along the tooth-resin interface for Sample no. 1 was 4.5 for absorption and 7.72 for phase contrast image. Similarly the profile plots for full length of tooth resin interface of Sample no. 4 gives the average contrast values 7.6 for absorption and 10.54 for phase contrast imaging.

RVG of Sample no. 4 (Fig. 2a) shows tooth-resin interface with less distinction. In the phase contrast radiograph for Sample no. 4 (permanent mandibular incisor) from Group B no voids were observed. Figure 2d–e represents tooth-resin interface by phase contrast imaging with a higher contrast than absorption image (Fig. 2c). The contrast value obtained from Fig. 2f is given in Table 2. A more improved view of region of interest is shown in processed phase contrast images (Fig. 2g and h).

3.2 Contrast optimization in phase contrast imaging

At the curved tooth-resin interface in Sample no. 1 (upper left corner) a void was observed near to the curvature. Presence of such voids near the curved interface increases the chance of restorative failures. Images were recorded at energy E = 25 keV and exposure time = 2 sec at several detector positions with the closest position being 5 mm (absorption image) and the farthest position at 450 mm (phase contrast image) from the sample (Fig. 3a–d).Image obtained at SDD = 5 mm, the interface was visible with poor contrast and no voids were visible near this interface. A void could be noticed at SDD = 123 mm. On further moving the detector to 250 mm and 450 mm away from the sample, the void periphery was observed more sharper due to increase in contrast (Table 3) because of edge enhancement [35].

Figure 3e and f are the profile plots obtained for the images, the curved tooth-resin interface and void-resin interface shows sharp intensity variations for image at a distance of 450 mm. Figure 3g–j shows the enlarged view of the images after image processing using ImageJ. The void diameter obtained was 252.9 micron.

3.3 Comparative discussion of imaging results of different teeth

For Sample no. 5 (maxillary premolar) and Sample no. 6 (primary maxillary canine) in Group B similar results were seen. The absence of voids at tooth-resin interface and within resin restored region for this Group B sample indicates that in this sample, there are lesser chances of crack initiation. The phase contrast imaging also shows air voids in Sample no. 2 and Sample no. 3 of Group A, with higher contrast (Table 4). In Sample no. 3 the biggest void at the tooth-resin interface might affect the micro bonding between tooth and resin. The qualitative comparison of the Group A and Group B phase contrast radiographs shows air voids in all the samples of Group A. If the readers have interest to observe the imaging results for Sample no. 2, 3, 5, 6 along with qualitative comparison between phase contrast and absorption images of Group A and Group B for region of interest, the supplementary data and images are also available upon the request to the contacting author.

3.4 Micro-tomography study and comparative discussion of different teeth

To further explore the restored teeth samples and to assess the quality of restoration efficiently, synchrotron based MCT experiment was also conducted on permanent mandibular incisor tooth (Sample no. 1), primary maxillary canine (Sample no. 3) from Group A and Sample no. 4, Sample no. 6 from Group B, which were of similar types. The volume rendered images of restored teeth samples shows tooth-resin interface voids that are formed due to entrapment of air during the restoration process. The volume rendered tomographic images of Sample no. 1 (Fig. 4b) has a better visualization of air voids as bubbles within the composite resin. These large number of voids observed with tomography were not detectable using 2D. In Sample no. 1 (Fig. 4b) and Sample no. 3 (Fig. 4d) voids were observed at the tooth-resin interface also. Micro crack formation and propagation of these cracks may affect the strength of restoration. Volume rendered image of Sample4 (Fig. 4f) shows voids which were not seen with the phase contrast radiography. The qualitative observation of the MCT image in Sample no. 6 reveals vertical fracture of the tooth along with the restoration. This might have occurred after the restoration procedure was completed and the reason cannot be predicted.

From the 2D tomographic slices noise was removed with despeckle and median filtering. The gray-scale images were then binarized using thresholding to segment the voids. In the segmented images voids were assigned black colour. Median filtering was again used to remove noise left after threshold operation. These 2D images corresponding to sample cross-section were used to find Feret’s diameter (indicates an object’s theoretical diameter if it had a circular shape) for different sizes of voids marked with arrows (Fig. 5). The biggest void for Fig. 5a and b which are Group A samples is shown with circles in red. There were cracks visible in all the tomographic slices which are shown in blue ellipses. The gaps at the restorative interface for Sample no. 1 (Fig. 5a) and Sample no. 4 (Fig. 5b) are shown with green rectangles.

The quantitative analysis of MCT data shows that restored teeth samples in Group A have more voids with bigger size. The maximum and minimum void sizes for Sample no. 1 (permanent mandibular incisor) were 552.04μm and 10.6μm. For Sample no. 3 (primary maxillary canine) the values were 472.99μm and 6.36μm. The void size varied between 6.36μm to 552.06μm in Group A. In Group B, Sample no. 4, maximum and minimum void sizes were 240.5 and 5.3μm, in Sample no. 6 the values were 289.71and 8.2μm. Table 5 shows the mean and standard deviation values for void diameter and void count for the samples in the two groups.

Figure 6a shows the variation of Feret’s diameter of voids in the restored region with the distance of the tomographic slices from the top region of tooth, for the investigated Sample no. 1 and Sample no. 3. Voids of different sizes were observed in a larger portion of the restored region in Group A samples. Fig. 6b obtained for a fewer number of tomographic slices for Group B samples shows comparatively lesser voids in Sample no. 4 and Sample no. 6.

4 Conclusions

The assessment of quality of restoration in dental samples with synchrotron based micro-imaging has shown formation of large number of voids of different sizes in Group A samples which could influence the longevity of restorations. It is seen that synchrotron phase contrast imaging provides improved visibility of imperfections in the restored regions and tooth-resin interface as compared to absorption contrast imaging as well as RVG. It is also seen that phase contrast visibility need to be optimized using suitable setting of experimental parameters. Comparison of voids shows Group B restorations with Nano-Hybrid resin are better than Group A. The application of synchrotron based micro-tomography has revealed three dimensional comparison of void distribution and their quantitative comparison. Synchrotron micro-imaging with high spatial resolution and non- destructive feature is well suited for studying dental restorations. Future studies will focus on optimization of mechanical strength of restoration using in-situ synchrotron micro-tomography.

Conflict of interest

There are no conflicts of interest.

Footnotes

Acknowledgments

The author AF would acknowledge Board of Research in Nuclear Sciences project, BARC, Mumbai (No. 2009/34/52/BRNS) for funding and UGC-MANF for subsequent fellowship.

References

Davis

T.J.

, Gao

, Gureyev

T.E.

, Stevenson

A.W.

and Wilkins

S.W.

, Phase-contrast imaging of weakly absorbing materials using hard X-rays, Nature 373 (1995), 595–598.

Wilkins

S.W.

, Gureyev

T.E.

, Gao

, Pogany

and Stevenson

A.W.

, Phase-contrast imaging using polychromatic hard x-rays, Nature (London) 384 (1996), 335–338.

Wilkins

S.W.

, Gao

, Gureyev

, Pogany

and Stevenson

A.W.

, X-ray phase-contrast radiography, Radiology 205 (1997), 907.

Gureyev

T.E.

, Mayo

S.C.

, Myers

D.E.

, Nesterets

, Paganin

D.M.

, Pogany

, Stevenson

A.W.

and Wilkins.

S.W.

, Refracting Röntgen’s rays: Propagation-based x-ray phase contrast for biomedical imaging, Journal of Applied Physics 105 (2009), 102005.

Mayo

S.C.

, Stevenson

A.W.

and Wilkins

S.W.

, In-Line Phase-Contrast X-rayImaging and Tomography for Materials Science, Materials 5 (2012), 937–965.

Bravin

, Coan

and Suortti

, X-ray phase-contrast imaging: From pre-clinical applications towards clinics, Phys Med Biol 58 (2013), R1–R35.

Hirano

and Yamasaki

, Estimation of contrast of refraction contrast imaging compared with absorption imaging-basic approach, Nuclear Instruments andMethods in Physics Research A 548 (2005), 187–193.

Pagot

, Fiedler

, Cloetens

and Bravin

, Quantitative comparison between two phase contrast techniques: Diffraction enhanced imaging and phase propagation imaging, Phys Med Biol 50 (2005), 709–724.

Yadav

P.S.

, Kashyap

Y.S.

, Roy

, Sarkar

P.S.

and Sinha

, Quantitative studies of pyro carbon-coated materials using synchrotron radiation, J Synchrotron Rad 15 (2008), 100–105.

10.

Margaritondo

, Hwu

and Tromba

, Šynchrotron light: Frombasics to coherence and coherence-related applications, in: Synchrotron Radiation: Fundamentals, , Methodologies and Applications, Mobilio and Vlaic , ed., SIF Bologna (2003), 25–53.

11.

Tafforeau

and Smith

T.M.

, Nondestructive imaging of hominoid dentalmicrostructure using phase contrast X-ray synchrotron microtomography, Journal ofHuman Evolution 54 (2008), 272–278.

12.

Zabler

, Riesemeier

, Fratzl

and Zaslansky

, Fresnel-propagated imaging for the study of human tooth dentin by partially coherent x-ray tomography, Opt Exp 14 (2006), 8584–8597.

13.

Baruchel

, Lodini

, Romanzetti

, Rustichelli

and Scrivani

, Phase-contrast imaging of thin biomaterials, Biomaterials 22 (2001), 1515–1520.

14.

Gureyev

T.E.

, Mayo

S.C.

, Myers

D.E.

, Nesterets

, Paganin

, Pogany

, Stevenson

A.W.

and Wilkins

S.W.

, Refracting Rontgen’s rays: Propagation-based X-ray Phase contrast for biomedical imaging, J Appl Phys 105 (1020), 102005:1–12.

15.

Snigirev

, Snigireva

, Kohn

, Kuznetsov

and Schelokov

, On the possibilities of x-ray phase contrast imaging by coherent high energy synchrotronradiation, Rev Sci Instrum 66 (1995), 5486–5492.

16.

Cloetens

, Barrnett

, Baruchel

, Guigay

J.P.

and Schlenjer

, Phase objects in synchrotron radiation hard x-ray imaging, J Phys D 29 (1996), 133–146.

17.

García

A.H.

, Martínez Lozano

M.A.

, Vila

J.C.

, Escribano

A. Barjau

and Galve

P.F.

, Composite resins: A review of the materials and clinical indications, Lecturers inDental Pathology and Therapeutics.

18.

Elbishari

, Silikas

and Satterthwaite

, Filler size of resin-composites, percentage of voids and fracture toughness: Is there a correlation, Dental MaterialsJournal 31 (2012), 523–527.

19.

Drummond

J.L.

, Degradation, fatigue and failure of resin dental composite Materials, J Dent Res 87 (2008), 710–719.

20.

Dehyle

, Schmidli

, Krastl

and Muller

, Evaluating tooth restorations: Micro- computed tomography in practical training for students in dentistry Developments in X-ray tomography, VII Proc of SPIE 7804 (2010), 7804171.

21.

Cloetens

, Pateyron-Salome

, Buffiere

J.Y.

, Peix

, Baruchel

, Peyrin

and Schlenker

, Observation of microstructure and damage in materials by phase sensitive radiography and tomography, J Appl Phys 81(1997), 5878–5886.

22.

Plotino

, Grande

N.M.

, Pecci

, Bedini

, Pameijer

C.H.

and Somma

, Three-dimensional imaging using microcomputed tomography for studying toothmacromorphology, JADA 137 (2006), 1555–1561.

23.

Grande

N.M.

, Plotino

, Gambarini

, Testarelli

, D’Ambrosio

, Pecci

and Bedini

, Present and future in the use of micro-CT scanner 3D analysis for the study of dental and root canal morphology, Ann Ist Super Sanità 48 (2012), 26–34.

24.

Paque

, Boessler

and Zehnder.

, Accumulated hard tissue debris levels in mesial roots of mandibular molars after sequential irrigation steps, International Endodontic Journal 44 (2011), 148–153.

25.

Prymak

, Tiemann

, Sotje

, Marxen

J.C.

, Klocke

, Kahl-Nieke

, Beckmann

, Donath

and Epple

, Application of synchrotron-radiation-based computer microtomography (SRμCT) to selected biominerals: Embryonic snails, statoliths of medusae, and human teeth, J Biol Inorg Chem 10 (2005), 688–695.

26.

Müller

, Thurner

, Beckmann

, Weitkamp

, Rau

, Bernhardt

, Karamuk

, Eckert

, Brandt

, Buchloh

, Wintermantel

, Scharnweber

and Worch

, Non-destructive three-dimensional evaluation of biocompatible materials by micro-tomography using synchrotron radiation, Proc SPIE 4503 (2002), 178–188.

27.

Rhodes

J.S.

, Ford

T.R.

, Lynch

J.A.

, Liepins

P.J.

and Curtis

R.V.

, Micro-computed tomography: A new tool for experimental endodontology, J Int Endod 32 (1999), 165–170.

28.

Beckmann

, Bonse

and Biermann

, New developments in attenuation and phase contrast micro tomography using synchrotron radiation with low and high photon energies in Developments in X-Ray Tomography II, SPIE 3772 (1999), 179–187.

29.

Rengo

, Spagnuolo

, Ametrano

, Juloski

, Rengo

and Ferrari

, Micro-computerized tomographic analysis of premolars restored with oval and circular posts, Clin Oral Invest 18 (2013), 571–578.

30.

Drummond

J.L.

, Carlo

F.D.

and Super

B.J.

, Three- dimensional tomography of composite fracture surfaces, J Biomed Mater Res Part B Appl Biomater 74 (2005), 669–675.

31.

Agrawal

A.K.

, Singh

, Kashyap

Y.S.

, Shukla

, Sarkar

P.S.

and Sinha

, Design, development and first experiments on the X-ray imaging beamline at Indus-2 synchrotron source at RRCAT, India, J Synchrotron Rad 22 (2015), 1531–9. doi: 10.1107/S1600577515016276

32.

ImageJ. http://rsb.info.nih.gov/ij

33.

Born

and Wolf

M.E.

, Principles of Optics, 7th ed., Cambridge University Press, Cambridge 1999.

34.

Limaye

, DRISHTI: a volume exploration and presentation tool in Developments in X-Ray Tomography VIII, Proc. SPIE 8506 (2012), p. 85060X. doi: 10.1117/12.935640.

35.

Gao

, Davis

T.J.

and Wilkins

S.W.

, X-ray phase-contrast imaging study of voids and fibres in a polymer matrix, Aust J Phys 48 (1995), 103–111.