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J Am Dent Assoc, Vol 137, No 11, 1555-1561.
© 2006 American Dental Association
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RESEARCH

Three-dimensional imaging using microcomputed tomography for studying tooth macromorphology



Gianluca Plotino, DDS, Nicola M. Grande, DDS, Raffaella Pecci, MS, Rossella Bedini, MS, Cornelis H. Pameijer, DMD, DSc, PhD and Francesco Somma, MD, DDS


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Background. The authors conducted a study to demonstrate potential applications of microcomputed tomography (microCT) in the analysis of tooth morphology.

Methods. The authors selected for microCT analysis five maxillary first molars with a second canal in the mesiobuccal (MB) root, five mandibular first molars with a mesial root possessing a considerable curvature and five single-canal premolars with complicated apical anatomy. The hardware device used in this study was a desktop X-ray microfocus CT scanner (SkyScan 1072, SkyScan bvba, Aartselaar, Belgium).

Results. The authors obtained a three-dimensional image from each of the 15 teeth. In three cases, the MB canals coalesced into one canal, while in the other two molars the canals were separate. Four of the five mandibular molars exhibited a single canal in the mesial root, which had a broad, flat appearance in a mesiodistal dimension. In the premolar teeth, the canals were independent; however, the apical delta and ramifications of the root canals were obvious, yet intricate.

Conclusions. MicroCT offers a reproducible technique for 3-D noninvasive assessment of root canal systems.

Clinical Implications. While this technique is not suitable for clinical use, it can be applied to improve preclinical training and analysis of fundamental procedures in endodontic and restorative treatment.

Key Words: Microcomputed tomography; three-dimensional imaging; root canal anatomy

In 1925, Hess1 reported on the wide variation and complexity of root canal systems. Several studies2–5 examined the macro-morphology of root canals in permanent teeth using different methods of analysis. In the study of the morphological characteristics of root canal systems, conventional ex vivo methods have been informative; however, they cause irreversible changes to the samples. Some examples of these changes are the preparation of consecutive ground sections on extracted teeth,6–9 rendering the surrounding hard tissues transparent through decalcification after permeation of dyes,10–14 and the removal of all surrounding tissue from casts of the root canals with Wood’s metal, celluloid or resin.15–18 Radiographic techniques also have been used to obtain a two-dimensional image.19–23 Some of the techniques are complicated and time-consuming, and many difficulties can be encountered during their execution, introducing artifacts and distortion of the internal anatomy of the tooth. Furthermore, these techniques do not allow for the observation of the external and internal anatomy of teeth in three dimensions at the same time.

Three-dimensional methods for the morphological study of teeth are replacing the more limited two-dimensional techniques. Historically, several techniques have been described for visualization of the 3-D anatomy of root canals in human teeth. This usually has been done by reconstructing the image derived from tracings of the contours from serial cross-sections of the specimens.9,24–29 However, in the process of making the sections, the specimens are destroyed, and an accurate image cannot be obtained owing to the thickness of the sections.

Computed tomographic (CT) images can be formed from planar slices through objects. These can be physical sections, optical sections or CT reconstructions.30 The development of X-ray computed transaxial microtomography, or microCT, has gained increasing significance in the study of hard tissues.31–35 Significant improvements in both software and hardware reduced section thickness from conventional CT ranges (approximately1.5 millimeters)36 to those for microCT systems: 81 micrometers,30 34 µm37 and 12.5 µm.38 The miniaturized CT technique, with a resolution of 100 µm, has proven to be useful as a nondestructive technique for 3-D reconstruction of teeth ex vivo.39–42 It is anticipated that a section thickness of 5 µm may be attainable for ex vivo investigations in the near future.39

The feasibility of clinical CT studies of human teeth was suggested initially by Tachibana and Matsumoto43 in 1990. MicroCT has been used to observe the structure of bone,44–47 to measure enamel thickness in teeth48 and to measure surface areas and volumes of teeth.37,39,40,42,49,50 Root canal instrumentation techniques have been studied using microCT.30,36,38,51–56 Additionally, it has been used for research in restorative dentistry.57,58

To date, microCT is not available for use in a daily clinical setting; however, attempts are being made to develop a system to make 3-D imaging of teeth possible in vivo.59 Animal in vivo studies have shown microCT imaging to be a rapid, reproducible and noninvasive method that produces results comparable with those of histological sections60 and that 3-D analysis of microCT images has a high correlation with 2-D cross-sections of periradicular lesions.61 In addition, microCT allows assessment of microstructural features as well as subregional analysis of developing lesions.61

MicroCT has potential application in preclinical training of students with regard to tooth morphology and endodontic procedures. The advantage of using this approach is that it can show internal and external dental anatomy and the results of the treatment exercise before endodontic procedures are attempted in the clinic.

We conducted a study to demonstrate the applicability of microCT in the analysis of the anatomy of teeth through the creation of a 3-D image, which represented a virtual reproduction.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Specimen selection and preparation We selected 15 permanent teeth for the microCT analysis from a pool of extracted teeth. After extraction, the teeth had been cleaned in 5 percent sodium hypochlorite solution for 24 hours, washed under running water, blotted dry and stored in a saline solution.

We selected five maxillary first molars, five mandibular first molars and five premolars. The criteria for selection were the following:

– Each tooth had to have fully formed apexes, no restorations with intact crowns and no defects or caries.
– The maxillary first molars had to have a second canal in the mesiobuccal root.
– The mandibular first molars had to show evidence of a mesial root that had a significant angle of curvature (± 90 degrees).
– The premolars had to have a single canal with an intricate apical anatomy (numerous secondary canals).

We selected the specimen holder of the microCT according to the specimen size and necessary magnification range; throughout our study, we used a specimen holder with a diameter of 15 mm. We fabricated a custom attachment from vinyl polysiloxane for each tooth to exactly fit the specimen and the specimen holder of the microCT machine. This attachment allowed a precise repositioning of the specimen in the scanning system along the z-axis (error < 1 voxel) with minimal rotational error (< 1 degree). The analysis of each sample consisted of two stages requiring approximately four hours in all: two hours for the scanning and two hours for the reconstruction procedure.

Scanning of the sample The hardware device we used in this study was a desktop X-ray microfocus CT scanner (SkyScan 1072, SkyScan bvba, Aartselaar, Belgium). We completed the scanning procedure using 10 watts, 100 kilovolts, 98 microamperes, a 1.0-mm aluminum filter and x15 magnification, resulting in a pixel size of 19.1 µm x 19.1 µm. During acquisition, we saved hundreds of 2-D projections through 180 degrees of rotation in digital format on a computer disk. To gain a 3-D perspective, we then transformed the data stored as projections into new two-dimensional images (axial cross-sections) with a pixel size of 19.1 µm x 19.1 µm and a slice thickness of 13.0 µm. The 3-D image is achieved by juxtaposition of 2-D images of adjacent slices.

A computer software analysis system recorded the data to realize a 2-D image of absorption coefficients. The use of a charge-coupled device detector allows the production of images with micrometer-sized resolution. We then stored these data for later use. After completion of the scanning procedure, we replaced the samples in the saline solution.

3-D reconstruction The reconstructed axial cross-sections have a 1,024 x 1,024-pixel (floating point) format. A typical cycle of data collection for reconstruction contains shadow image acquisitions from 200 to 400 views with object rotation of more than 180 degrees. For the reconstruction of complete 3-D objects, a serial reconstruction of axial cross-sections can be used. It consists of one acquisition cycle followed by an "off-line" reconstruction of the complete 3-D object in a 1,024 x 1,024 resolution for a maximum of 1,024 layers. Typically, these are cone-beam reconstructions. After the serial reconstruction, axial cross-sections of the object—as well as a construction of a 3-D object’s realistic view with possibilities to "rotate" and "cut" the object model—can be displayed on the screen. From the reconstruction results, it is possible to reconstruct 3-D objects with the use of an external program (3D-Creator, SkyScan).


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSIONS
 REFERENCES
 
We rendered a 3-D reconstruction of each tooth in the three categories. The 3-D models showed, in great detail, the anatomy of root canals from different angles.

The maxillary first molars had three roots with four canals. In three of five cases, the secondary mesiobuccal root canal joined the mesiobuccal root canal, while in the other two cases they were completely separate. Figure 1Go is an example of the 3-D imaging, showing the maxillary first molars that were scanned from both a buccolingual and a mesiodistal view (Figures 1A and 1BGo). This is an example in which the secondary canal origin, 2 to 3 mm below the level of the pulpal floor inside the orifice of the mesiobuccal root canal, is in a location that presents a clinical challenge in terms of finding it and of negotiating to the foramen, which in this case was independent (Figure 1CGo). Note also the particular loop (see arrow) of the mesiobuccal root canal at the apical one-third, which, when shown in a horizontal plane, reveals the presence of three canals (Figure 1DGo). Furthermore, the apical ramifications of the palatal and distobuccal roots have been faithfully reconstructed.


Figure 1
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  		Figure 1. An image from a first maxillary molar obtained by microcomputed tomographic imaging. A. A buccolingual view. B. A mesiodistal view. The secondary mesiobuccal root canal (MB II) can be seen originating from the mesiobuccal root canal (MB I), 2 to 3 millimeters below the level of the pulp floor. This anatomic feature presents considerable challenges in endodontic treatment, not only in finding the MB II canal but in negotiating it to the apex, which was independent. The MB I canal was further complicated by a loop (see arrow) at the apical end (C). When viewed in a horizontal plane (D), the presence of three canals in the MB can be seen clearly.

 
The mandibular first molars had a mesial and distal root. Figure 2Go is a 3-D image of a mandibular molar viewed from buccal (Figure 2AGo), lingual (Figure 2BGo), mesial (Figure 2CGo) and distal (Figure 2DGo) aspects. The mesial root is characterized by a single canal, which had a broad, flat appearance (Figures 2C and 2DGo) and curved toward the distal aspect with an angle of curvature approximating 90 degrees (Figures 2A and 2BGo).


Figure 2
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  		Figure 2. A representative example of a microcomputed tomographic image of a mandibular first molar. A. The buccal view. B. The lingual view. C. The mesial view. D. The distal view. The mesial canal has one broad, flat root (2C and 3D) with a curvature of ± 90 degrees to the long axis of the root (2A and 2D).

 
Four of the five mandibular molars that we scanned had a single canal in the mesial root, which was flat in a mesiodistal direction. It may be hypothesized that the majority of mandibular first molars with rather extreme curved mesial roots, as specifically selected for this study, may have a single flattened mesial canal instead of two separate canals, as normally is seen in the majority of mandibular first molars. Figure 3Go is a separate rendering of the root canal system of the mandibular molar shown in Figure 2Go, done without the superimposition of the hard root structures. The rendering shows a buccolingual (Figure 3AGo), a mesial (Figure 3BGo), a distal (Figure 3CGo) and an apical view (Figure 3DGo). The pulp space of Figure 3BGo has a small loop in the middle one-third of the ribbon-shaped mesial canal, which broadens to a flattened portion toward the coronal aspect of the root (Figures 3B and 3CGo). When viewed from the apex (Figure 3DGo), the bifurcation of mesial and distal canals can be evaluated in detail, and the angles at which the root canals extend toward the apex become apparent. Note the delta-shaped appearance of both the mesial and distal apical portion of the mesial and distal canals.


Figure 3
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  		Figure 3. In these figures, the superimposition of hard root structure was omitted, resulting in isolation of the pulp space. A. A buccolingual view. B. A mesial view. C. A distal view. D. Tilting the image yielded an apical view that allowed for an examination of the furcation.

 
In the premolars, we rendered the images of the canals without superimposition of the hard tooth structure, thus allowing for a detailed analysis of the root canal anatomy—in particular, the apical "delta." Figure 4Go shows four examples of apical root canal ramification of the last millimeter of the root. The extremely complex apical anatomy, as shown in Figures 4A and 4BGo, represents a considerable challenge when cleaning, shaping and three-dimensionally obturating the root canal system are required for endodontic treatment. Figure 4CGo illustrates that the presence of an apical delta are not an uncommon occurrence, even in a single, straight root canal. The presence of an apical bifurcation and four separate apical foramina with multiple communications (Figure 4DGo) further complicates all phases of endodontic treatment.


Figure 4
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  		Figure 4. The apical anatomy of a premolar. A-C. The apical delta and ramifications present a considerable challenge in endodontic treatment. D. As can be seen, the presence of an apical bifurcation and numerous separate apical foramina with multiple communications in an otherwise single-rooted tooth complicates all phases of endodontic treatment.

 
What these samples have in common is the presence of even the smallest details, all reproduced from the original anatomy, thus demonstrating the ability of the microCT technique to reproduce three-dimensionally the internal and external anatomical features of teeth.


   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSIONS
 REFERENCES
 
Berutti,26 Blaskovic-Subat and colleagues,27 Hirano and colleagues,25 Lyroudia and colleagues28,29 and Mikrogeorgis and colleagues24 made serial cross-sections of teeth and traced the contours, the pulp cavities and the canals of each section. They then entered the data into a computer to produce a 3-D image. However, owing to inherent limitations of the technique, such as the width of the slices (0.5–0.7 mm), detailed observation was not possible.

In a study in which investigators used histologic slides to reconstruct a 3-D image, models of dentin and the root canal systems were produced.28 These models, however, are relatively crude owing to the low resolution of the acquired data.

An alternative method, CT, was introduced. Gambill and colleagues36 produced CT images of teeth to compare three endodontic instrumentation techniques. They constructed the images from 1-mm slices; however, reproducibility was not consistent along the length of the root canals. Using microCT with a pixel size of 127 µm, Nielsen and colleagues40 demonstrated that it was possible to reproduce tooth anatomy accurately using a noninvasive technique. Shibuya and colleagues62 reported that the measurements obtained by this method indeed were accurate. Rhodes and colleagues30 compared the internal root canal space and the external surface area using reconstructed microCT images and video-digitized images. They found that there was a highly significant correlation between the microCT and video-digitized images. Balto and colleagues60 and von Stechow and colleagues61 demonstrated in vivo that microCT imaging yields results that have a high correlation with data obtained from histology.

The nondestructive approach in our study made it possible to achieve a 3-D analysis of the external and internal macromorphology of the root complex using a spatial resolution of 13 µm between tomographic slices. It appears that this method is a highly useful tool for studying the external and internal anatomy of teeth. Three-dimensional knowledge of root canal anatomy is of great importance, since it allows for transfer of information obtained from laboratory experiments to a clinical setting. One of the advantages of this method is that the dentist can observe the internal anatomy of teeth from different angles.

In a pilot study, it was possible, by rotating the sample 360 degrees, to qualitatively assess the effect of root canal instrumentation in molars. Furthermore, it was possible to tilt and rotate the image while areas of interest were magnified. All of these possibilities can be important for clinicians, because through proper use of light, color and texture, a better understanding of dental anatomy as a whole can be achieved. Root canals can be imaged separately or with the tooth superimposed, thus showing the orientation of root canals within a tooth. Not only can this technique be a useful educational tool, it also can have far-reaching implications for clinical dentistry. While we have not discussed this possibility in this article, it also is possible to obtain an animation, showing movement of each tooth around all of its axes. This proved to be a helpful method of visualizing tooth morphology.

Several published studies in the dental literature discuss areas that may benefit from microCT. For example, the morphogenesis of carious lesions and the development of subjacent tertiary dentinogenesis53 have been examined and interpreted on the basis of invasive 2-D data.63–65

The technique reported here is not suitable for clinical use, but cone-beam CT (CBCT) systems have been introduced for imaging hard tissues of the maxillofacial region.66 CBCT is capable of producing submillimeter resolution (ranging from 400 µm to as low as 125 µm) with images of high diagnostic quality. The scanning times (10–70 seconds) and radiation dosages reportedly are as much as 15 times lower than those of conventional CT scans.

Although the CBCT principle has been in use for almost two decades, only recently have affordable systems become commercially available. An increase in availability of this technology provides the clinician with an imaging modality that is capable of achieving a 3-D representation of the maxillofacial region with minimal distortion. These systems are promising and eminently more suitable than microCT scans, which are limited to ex vivo applications only and are not suitable for patient care. Nevertheless, microCT is a powerful tool for research and preclinical education in fundamental procedures of endodontic treatments, as well as for clinicians and researchers who desire to study dental anatomy in great detail.

MicroCT offers exciting potential; however, current imaging times—two hours for scanning a sample and two hours for the reconstruction—are long. The equipment is expensive, and the 3-D reconstruction requires a high degree of computer expertise.


   CONCLUSIONS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
REFERENCES
 
MicroCT offers a noninvasive reproducible technique for the 3-D assessment of root canal systems and can be applied quantitatively as well as qualitatively. Because CT is nondestructive, it is possible to analyze root canals before, during and after endodontic instrumentation. Internal and external anatomy can be demonstrated simultaneously or separately. A significant amount of information can be gleaned from the scans and slices can be recreated in any plane, while data can be presented in 2-D or 3-D images. Its use is not limited to root canal morphology. Applications to restorative dentistry and other areas are anticipated.

The microCT technology is an exciting tool for experimental endodontology and can produce detailed informative images of the anatomy of teeth. The technique is not suitable for clinical use, but it can become a powerful tool for research. It also can allow for better preclinical training in fundamental procedures of endodontic treatments, and it gives clinicians and researchers who desire to study dental anatomy in detail a new means of doing so.


   FOOTNOTES
 

Dr. Plotino is a professor of endodontics, Department of Endodontics, Catholic University of the Sacred Heart, Largo Francesco Vito 1, 00168 Rome, Italy, e-mail "gplotino{at}fastwebnet.it". Address reprint requests to Dr. Plotino.


Dr. Grande is a professor of endodontics, Department of Endodontics, Catholic University of the Sacred Heart, Rome.


Ms. Pecci is a researcher, Italian National Institute of Health, Technology and Health Department, Rome.


Ms. Bedini is the lead researcher, Italian National Institute of Health, Technology and Health Department, Rome.


Dr. Pameijer is a professor emeritus, University of Connecticut School of Dental Medicine, Farmington.


Dr. Somma is chair and a professor of endodontics, Department of Endodontics, Catholic University of the Sacred Heart, Rome.


The authors did not receive any grants or other assistance from SkyScan or any other company in carrying out this study.


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 RESULTS
 DISCUSSION
 CONCLUSIONS
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 Dentomaxillofac RadiolHome page
K Kamburoglu, S F Barenboim, T Ariturk, and I Kaffe
Quantitative measurements obtained by micro-computed tomography and confocal laser scanning microscopy
Dentomaxillofac. Radiol., October 1, 2008; 37(7): 385 - 391.
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