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 Table of Contents  
REVIEW ARTICLE
Year : 2023  |  Volume : 15  |  Issue : 1  |  Page : 80-86

Micro-computed tomography in endodontics


Department of Conservative Dentistry and Endodontics, Dr. Ziauddin Ahmad Dental College, Aligarh, Uttar Pradesh, India

Date of Submission26-Jul-2022
Date of Decision10-Oct-2022
Date of Acceptance11-Oct-2022
Date of Web Publication29-Dec-2022

Correspondence Address:
A Lavanya
Dr. Ziauddin Ahmad Dental College, No F2, Zakaria Apartment, New Sir Syed Nagar, Aligarh - 202 002, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jorr.jorr_37_22

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  Abstract 


In recent years, biomedical and dental researchers have started using micro-computed tomography (MCT) for research purposes. Due to a wide range of technological developments in various sources of X-ray and X-ray imaging techniques, the use of MCT in experimental studies has been improved. MCT systems allow researchers to analyze microstructures, differences in density, and morphological changes. This review article emphasizes on the recent advancements of MCT applied in endodontics. MCT applications in the analysis of root canal morphology, evaluation of biomechanical preparation, irrigation and intracanal medicament extrusion, restoration of root canal, and retreatment have been summarized.

Keywords: Endodontics, irrigation, micro-computed tomography, retreatment, root canal morphology


How to cite this article:
Lavanya A, Ali S, Tewari RK. Micro-computed tomography in endodontics. J Oral Res Rev 2023;15:80-6

How to cite this URL:
Lavanya A, Ali S, Tewari RK. Micro-computed tomography in endodontics. J Oral Res Rev [serial online] 2023 [cited 2023 Jan 31];15:80-6. Available from: https://www.jorr.org/text.asp?2023/15/1/80/365918




  Introduction Top


The X-rays were developed in 1895 by Wilhelm Roentgen, has revolutionized diagnostic medicine by enabling noninvasive visualization of internal structures. Computer-assisted tomography was created by Allan Cormack and Godfrey Hounsfield in the late 1970s. The computed tomography (CT) scanner was designed by Elliott and Dover built the 1st micro computed tomography (MCT) equipment with high resolution, and they used 12 μm resolution to image a snail's shell.

Early 1980s, custom-built MCT or CT systems were not commonly accessible. Compact systems are now widely accessible, and many academic and research investigations are quickly adopting them as necessary components.[1] Micro-CT can directly investigate a wide range of specimens, including materials such as ceramics, polymers, biomaterial scaffolds, and mineralized tissues such as teeth and bone. The pixel sizes of the cross sections of this new technology, which are measured in micrometers, are referred to as “micro” pixels. This also indicates that the machine is designed to model smaller items and is smaller in size than the human version. Thin-layer radiographs (tomography) and image synthesis in the computer are combined in the radiographic technique known as MCT.

The root canal space has also been analyzed and morphometrically described using MCT methods in dentistry, allowing for the evaluation of fundamental two-dimensional (2D) geometric metrics such as area, perimeter, roundness, and major and minor diameters. MCT devices' resolution of 1–200 m aids in the accurate and reliable measuring of tooth volumes and enamel thickness.[2] Because they can give a thorough quantitative and qualitative description of the external and interior anatomy of the teeth, they are currently being used for ex vivo dental anatomy research. Dentin thicknesses, canal diameters, and curvatures can also be quantified using MCT with mathematical modeling. The MCT method seldom ever requires sample preparation and allows for the imaging of teeth in their natural form without the requirement for sectioning, which may lead to artifacts or the loss of root material.[3] The root canal orientation within a tooth can be examined by imaging them separately or with the tooth superimposed. It is also possible to tilt and rotate the image while enlarging certain regions of interest. All of these options can be beneficial to clinicians since they can gain a better knowledge of dental anatomy. This technique has the potential to be not just a great tool to educate but also to have far-reaching clinical applications. This review article highlights various applications of MCT in endodontic THERAPY and its recent developments.


  Micro-Computed Tomography Scanning and Reconstruction Top


Volumetric pixels (Voxels) in MCT systems with micro-focused spot X-ray sources have significantly better spatial resolution and have volumes that are between 5 and 50 m, or around 1,000,000 times smaller than those in CT. By rotating projections across various viewing directions, the high-resolution detectors may produce 3D reconstructions of the materials. The photos show spatial distribution maps of linear attenuation coefficients that are based on the energy of the X-ray source and the atomic makeup of the material sample.

The sample can be thoroughly examined in three-dimensions utilizing MCT and mathematical modeling. To reconstruct whole 3D objects, cross-sections taken in axial directions can be serially reconstructed. It has a single acquisition cycle, then 1024-by-1024-pixel reconstruction (offline) of the full 3D object. Typically, cone-beam reconstructions are used. In the (X) Coronal, (Y) Sagittal, and (Z) Facial orientations, 0.125–1 mm slice intervals are used to observe the reconstructed 3D pictures. After the serial reconstruction, the object's axial cross sections and a creation of a 3D object's realistic perspective with the ability to “cut” and “rotate” the object model may be seen on the screen.[4]


  Training and Education Top


In the realm of endodontics, educational practice is critical. Given that it can produce accurate, helpful images of tooth anatomy, MCT is an exciting technique for endodontic experiments. It has the potential to be an effective research tool since it may also assist researchers and clinicians who wish to learn more about dental anatomy in obtaining better preclinical training in the core endodontic therapy approaches. The use of MCT for teaching preclinical students about tooth morphology and endodontic operations has the potential to be beneficial. The 3D graphics assist students in visualizing and comprehending the results of root canal preparation and obturation. It was thought to be useful for inexperienced students to evaluate endodontic therapy.[5]


  Advantages of Micro-Computed Tomography Top


The sample can be examined more than once because to the imaging technique's nondestructive nature.

It supports multiplanar reconstructions and has a high spatial resolution (5 m).

As a result, it allows for excellent differentiation of extremely small variations in attenuation coefficient (1%), providing increased resolution compared to cone-beam computed tomography (CBCT).

As opposed to histological examination, which similarly impacts the internal structural organization of the specimen, it does not require time-consuming specimen preparation.

It helps with 3D relationship analysis among various structures, and the data can be preserved for comparison or qualitative evaluation in the future.


  Clinical Significance Top


The complex internal tooth anatomy can be easily assessed with the 3D reconstruction ability of MCT.

It is helpful to examine the thickness and distance between anatomical components, which helps in presurgical assessment, as well as the mesiodistal extent of pathology, such as tumor margins.

It aids in the accurate identification of maxillofacial, dentoalveolar, and root fractures.

With superior image quality and resolution than CBCT, it aids in the diagnosis of root fractures, apical periodontitis, and alterations within the morphology of the root canal.


  Root Canal Morphology Analysis Top


For many years, it was believed that the clearing method was the best tool for examining the changes in the morphology of the root canal system. The tooth was demineralized by the injection of fluid substances such as molten metal, gelatin, or ink, which made the tooth transparent. The disadvantages of this technique are injected material does not flow laterally into delicate anatomical tissues, and this approach causes irreversible alterations in the tooth structure and produces artifacts. A number of methodological issues with the clearing procedure have been resolved by the development of the MCT imaging technology, which has made it possible to report on a number of new unclassified anatomical variations and root canal complexity in human dentition.[6] Therefore, it is necessary to investigate whether to incorporate these distinctive anatomical configurations into a future root canal classification scheme.

The root canal shapes can be analyzed qualitatively and quantitatively using MCT. Differentiating between the external and internal morphology of a tooth is made easier by the ability to recognize the dental hard tissues as transparent and the pulp chamber and root canal system as opaque in 3D morphologic features of the root canal system. It was possible to measure the pulp chamber's overall areas, the volume ratio at the level of the pulp horn, the pulpal floor, and the root canal orifice diameters on the buccal and lingual sides. Some researchers discovered that triangulation methods could be used to appreciate the surface morphology and volumes of each root canal, while model-independent approaches could be used to evaluate canal diameters and configuration.[7]

Dentists, on the other hand, frequently confront anatomically abnormal cases in clinical practice. The C-shaped canal is the most intricate anatomical variation of the root canal. It can pose several biomechanical and obturation difficulties and is seen in mandibular second molars most frequently. One cannot assume that the C-shaped canal will remain the same for the entire length of the canal, not even when examined under the dental operating microscope. The MCT delivered high-resolution serial cross-sections of the root canal system over its entire length. The C-shaped canal was seen in these images to vary in shape significantly at different levels. The C-shaped canal system's 3D reconstruction is aided by the surface rendering method. It can be visualized at different angles and showed that the C-shaped canals were not found in the root's center, but rather toward the fused root's deep groove surface. This understanding led to the measurement of the depth of the groove and thickness of the root, the ratio of the groove depth to the buccal-lingual thickness of the root. It also aids in determining the location and appearance of canal orifices, cross-sectional form, canal bifurcation level, and level of fusion across the whole length of the root.[8],[9]

For clinicians, curved canals pose a substantial problem since they add on the potential of iatrogenic mistakes such as ledge formation, perforation, and transportation. By creating a fictitious central axis for each canal, the curvature of the canals may be calculated using specialized mathematical modeling software. Calculate the tangent vector's rate of rotation at a specific location on the central axis; this value is then reversed to get the canal curvature.[10] Recent MCT investigations have evaluated 3D canal curvature by intersecting points of the minor and major axes of the canal cross in each slice using Kappa software (Custom made software designed by JK Lee, V works program, Germany) specifically designed.[11] Park et al. examined different canal forms and curvatures of mesiobuccal (MB) roots in the maxillary first molar using the same software and MCT. These investigations gave a thorough and precise description of the root canal curvatures present in maxillary first molars. The P (palatal) canals have the least root canal curvatures, whereas the MB canals have the most prominent root canal curvatures. The apical third of the curvatures increases, especially in the MB (mesiobuccal) and DB (distobuccal) canals, and the curvatures in the apical third rise with the presence of accessory canals. According to previous research that employed radiography, the precise measurements of canal curvature in mandibular molars made using MCT showed that the curvatures were larger in the MB canal than in the mesiolingual. They were most prominent in the apical and coronal regions, and straight in the mid root area of the mandibular molar's mesial root. The knowledge gained from this study will help us deliver endodontic therapy, and the techniques it developed will advance continuing endodontic research.[11],[12]

Clinically, it is difficult to access the middle mesial root canals because of where their orifices are located. If untreated, these canals could harbor germs, jeopardize the effectiveness of the therapy, and cause persistent apical periodontitis. Previous studies showed that the use of MCT technology ensured a good visibility of additional canals that were consistently smaller than the major canals at each level. This was in contrast to standard sectioning or casting techniques. The second canal was more frequently found using MCT and CBCT than with the other diagnostic techniques. Furthermore, the creation of more accurate and comprehensive 3D models of the root canal region was made possible by the ability of MCT devices to acquire imaging projections with a wider degree rotation of the specimen (360°) than the CBCT unit (200°). 7.7% of mandibular molars were discovered to have three canals along any position of the mesial root, which is higher than the previously reported percentage (2.3%) by de Pablo et al.[13] In order to boost the success rate of nonsurgical endodontic procedures, these results together with a 3D image of the mesial root canal aid in the identification of additional canals and their root canal preparation.[14]

The apical delta is considered a delicate system of root canals allowing blood vessels and nerves to transverse through pulp tissue. The root canal in this area divides into three or more ramifications, with the main canal being indispensable. The most common sites for apical deltas are, mandibular lateral incisors, mandibular second premolars and maxillary second premolars. Tooth clearance is the most often utilized approach for assessing apical deltas. The disadvantages of this technique are that they are destructive to specimen and precise quantitative data collection cannot be achieved. Due to lack of resolution, both intraoral periapical radiography and CBCT was unable to adequately identify this critical zone. With the high resolution of MCT, apical delta branches (ADBs) diameter was measured, which varies between apical deltas. The median diameter was found to be 132.3 μm, and only 24% ADBs had a diameter of more than 180 μm. It is also feasible to observe the prevalence of apical deltas, their number and morphology, and their vertical extension inside the root canal system with the use of MCT.[15]

If left untreated, an isthmus, which is described as a small, ribbon-shaped passage between two root canals that contain pulp tissue, necrotic debris, tissue fragments, or organic substrates, will enable the growth of microbes and result in the failure of endodontic treatment.[16] As a result, the management and location of the isthmus is a crucial components that may enhance the prognosis of root canal therapy in long term. It is impossible to see band-shaped isthmuses on standard 2D radiographs because they are located in the buccolingual direction. In particular, for roots with diverse anatomical configurations, the efficacy of CBCT to identify root canal morphology has been characterized as ambiguous.[6] Owing to the advantage of high resolution, currently, MCT studies are focused in analyzing this anatomic variation and reported that the prevalence of isthmus is high in the mandibular first molars mesial root, in the apical portion.

MCT is being used to know the location and extent of peri radicular lesions in recent years, in addition to evaluating cross-sections of teeth. Data acquisition in MCT are automated after the sample has been inserted into the apparatus and does not need any additional operator attention. On the other hand, histological processing of the same number of samples takes roughly 2 months and necessitates numerous hours of labor by laboratory staff. Because of the oblique rather than sagittal sections produced by the inaccurate sectioning orientation, the fraction of samples cannot be measured. Balto et al. found that results of MCT have correlated strongly with histology results through in vivo examinations of animals.[17]

The remaining thickness of dentin along the walls of the roots was measured using a quantitative analysis of MCT.[18] Due to the higher concavity exhibited on its distal surface, dentin thickness is restricted in the mandibular first molars mesial roots 2 mm below the furcation. Because they are more chances of strip perforation during root canal shaping and postspace preparation treatments, they are referred to as danger zones. Since 2D radiographs depicted increased thicknesses, they were not a valid approach for determining the remaining thickness of dental walls.[19] This knowledge of root canal complexities is important so that instrumentation could be directed away from this risk zone toward the lateral and mesial canal walls, which have significantly increased dentin thickness.


  Evaluation of Access Cavity and Root Canal Preparation Top


The primary aim of root canal treatment is to remove infectious organisms from the root canal by performing sufficient cleaning and shaping. To assist clinical judgments during endodontic procedures, knowledge of the dimensional variations of complicated root canals and adequate apical canal preparation with available instruments is required. The effectiveness of endodontic devices in cleaning the root canal system can be assessed using MCT. The area cleaned by the equipment can be evaluated, as well as the amount of pre and after instrumentation. Earlier analyses of the instrumentation process were carried out utilizing various techniques. Endodontic research studies use the most up-to-date approaches, such as morphometric analysis, scanning electron microscopy, and stereomicroscopy, to evaluate the shaping operation. Sections reduce the size of the specimen in all of these approaches. Instead, MCT obviates the need for sectioning by allowing the study of the entire root canal. Paque et al.[20] described a technique of slice-by-slice assessment of the area between the furcation wall and the apical stop. MCT scans of teeth performed pre- and postinstrumentation help in quantitative assessment of the remaining unprepared surface area and the associated morphological changes. The color mapping technique further aids in the spatial location of potentially infected dentin and its successful removal after instrumentation.[21],[22]

Using (Micro- CT) testing, Almeida et al. discovered that current biomechanical preparation methods and instruments leave 10%–50% of unprepared areas in root canals that are narrow or circular, and these percentages tend to increase in canals that are oval shaped or flattened. Because apical canal diameters vary greatly and are occasionally incompatible with the dimensions of currently available tools, unprepared walls are very common. Furthermore, constant or reciprocating rotation of instruments tends to carve spherical preparations while leaving recesses in irregular noncircular canals intact. This suggests the need for instrument modification, including the use of smaller instruments, the use of instruments that are adjustable or expandable, and the importance of activation and agitation during the irrigation process rather than the use of rotary or reciprocating instruments alone to optimize disinfection.[23]

When the root canal is enlarged, followed by excessive dentin removal, the tooth structure is weakened, and transportation of the canal is a crucial metric to assess. The center of gravity in each canal cross-section was connected with a hypothetical line (z-axis), passing along the root length; by correlating the data collected before treatment and after preparing the canal, it is possible to measure canal transportation caused by instrumentation using MCT. Then, comparison of the separation between the center of gravity at each level of the root canal, is made, and mean transportation may be computed. They also give a thorough representation of the 3D canal architecture and surrounding root structure, and canal widths, which can be used to guide instrumentation and enhance cleaning and shaping while reducing errors.[24] The smallest dimensions of canal widths were recorded as a measure of canal narrowness, which is significant in selecting the initial apical file size for preparing the apical third area. According to findings of MCT study by Lim and Stock, the dentine thickness should be kept between 200 and 300 μm after preparation to withstand forces of compaction during obturation and avoid perforations or vertical root fractures. The “risk zone” of insufficient dentin thickness of the sides of the root canal should be considered when selecting great taper NiTi tools. Strip perforations would be reduced, if not eliminated, if the dentin thickness which is remaining in the root is known, particularly in the mesial roots on their distal areas.

According to a 3D research employing high-resolution MCT imaging, certain areas with a radiopaque substance were noted in the canal space after rotational instrumentation. This confirmed that hard tissue debris is being generated inside the root canal in the form of microscopic dentin chips.[25] This nondestructive imaging technology has established itself as the standard technique for the evaluation of accumulated hard tissue debris (AHTD) into the abnormalities of the root canal system, permitting a longitudinal observation of the same specimen during numerous experimental procedures. A recent MCT investigation found that increasing the size of the apical preparation lowered the overall quantity of packed debris. Previous research analyzed the elimination of AHTD only at the root level and used qualitative score-based scanning electron microscopy to assess its efficacy. Current studies use MCT imaging to analyze the elimination of AHTD promoted by the final irrigation treatments. When this technique is combined with image analysis, quantifiable data on dentin morphology along the entire canal may be extracted automatically, reducing human bias.[26]

Wiseman et al. conducted the 1st MCT investigation on root canal irrigation to examine the performance of two irrigation devices, passive ultrasonic irrigation (PUI) activation and Endo-Activator (EV), in removing calcium hydroxide from human molar root canals. A recent MCT investigation found that the (EV system) in conjunction with (PUI) was the only method that could achieve irrigant solution penetration up to the Working length and in the accessory canals. A protocol combining these two techniques would be useful for better chemical irrigant dispersion throughout the canals and a continuous flow of new irrigants. Further investigation is required to determine how these final irrigation regimens' improved root canal system cleanliness affects the clinical success rate of endodontic treatment.[22],[27],[28]


  Estimating the Root Canal Sealing and Retreatment Top


The interface of dentin in the root canal should have a thin layer of sealer and a greater amount of gutta-percha in an adequate root canal sealing. The accessory and lateral root canals, as well as the debrided root canal, must all be taken into account while filling the root canal space. The existence of spaces between filling and leakage must be avoided as there is higher chance of fluid penetration and subsequent infection of the root canal system. Numerous techniques, including confocal laser scanning and stereomicroscopy, which require cutting the samples into sections before analysis, have been utilized to assess the quality of root canal sealing. Leakage tests were also used to analyze but the models proposed were considered unreliable and time-consuming.[29]

MCT is currently the most effective tool for studying microleakage in vitro and has the advantages of being quick, precise, and nondestructive. This method has also been used to evaluate the amount of sealing material reaching the isthmus regions and branching. These areas can be visualized with varying intensities of sealer, gutta-percha into different colors by processing pictures obtained with μCT on the computer. Calculations can be made to determine the volume of voids and gaps in the root canal. The investigations involve void and gap demarcation in the 2D slices, followed by image reconstruction in three dimensions. The capability of additional analysis is the key benefit of using MCT to assess root canal fillings. After studying obturation, the substance can be removed using a different retrieval system, and retreatment procedures can also be researched.[30]

Nonsurgical root canal retreatment, which entails removing the old root canal filling material, additional cleaning and shape, and refilling, is primarily intended to restore the health of periapical tissues. The majority of the earliest laboratory-based research employed destructive and 2D techniques to evaluate the quantity of filler material still present following retreatment. These approaches have drawbacks, making it impossible to properly determine the volume of filler material left following retreatment. The nondestructive MCT methodology, on the other hand, enables for an accurate volumetric evaluation of filler materials left after various retreatment regimens, incapacitating earlier methodologies' shortcomings. It uses visual image analysis to locate the specific area of interest, and the quantities can be computed using dedicated software. MCT was also utilized to assess the effectiveness of instrumentation like Pro-Taper files and hand K-files were used to remove root fillings. The use of additional aids during retreatments, such as the use of Ultrasonic tips or Laser irradiation, has been shown to improve the removal of filling remnants from the root canal space using MCT.[31]


  Conclusion Top


The evaluation of morphological characteristics has been successfully carried out using the nondestructive method known as MCT, which also enables the evaluation of successive steps in root canal therapy. High-resolution imaging makes it possible to examine endodontic morphology in more detail and learn new details about the intricate root canal system. This approach has the benefit of exhibiting both internal and external dental anatomy in addition to the outcomes of the mechanical preparation, demonstrating the incapacity of shaping instruments to function within the intricate anatomical structure of the root canal. Hence, it has the potential to be used in preclinical student teaching for tooth morphology and endodontic operations. It is a fast, reproducible, and noninvasive technology that yields results comparable to histological sections, according to the animal in vivo investigations, and 3D analysis of MCT pictures has a strong correlation with 2D cross-sections of periradicular lesions. MCT also enables for the evaluation of microstructural characteristics as well as the subregional investigation of emerging lesions. Although, due to its inherent limitations, it is not currently accessible for use on a daily clinical basis; nevertheless, efforts are being made to build a device that will allow in vivo 3D imaging of teeth. The influence of aging and deposition of cementum causing the deviation of the main apical foramen will be determined in future MCT studies.

Limitations

Radiation doses, long scanning times, and limited specimen size.[32]

Increased cost and need for technical knowledge.[33]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Abstract
Introduction
Micro-Computed T...
Training and Edu...
Advantages of Mi...
Clinical Signifi...
Root Canal Morph...
Evaluation of Ac...
Estimating the R...
Conclusion
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