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Computed tomographic imaging in endodontics: a short

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C o p y r i g h t b y N o t f o r Q u i n t e s s e n c e Not for Publication n 27 ENDO (Lond Engl) 2010;4(1):27–40 REVIEW Lalit Boruah, MDS Department of Endodontics, Kothiwal Dental College and Research Centre, Morada- bad, India Atool Bhuyan, MDS Professor of Endodontics Department of Endodontics, Regional Dental College, Guwahati, India Shashi Tyagi, MDS Professor of Endodontics Department of Endodontics, Kothiwal Dental College and Research Centre, Morada- bad, India Correspondence to: Lalit Boruah Department of Endodontics Kothiwal Dental College and Research Centre Kanth Road Moradabad – 244001 India Tel: 0591 2452994/5 0975 881 8222 Email: [email protected] Lalit Boruah, Atool Bhuyan, Shashi Tyagi Computed tomographic imaging in endodontics: a short literature review Key words coherence tomography, computed tomography, cone-beam computed tomography, micro- computed tomography, optical tuned-aperture computed tomography, spiral computed tomography Introduction n Within the last 20 years, diagnostic digital imag- ing modalities in dentistry, including periapical, bitewing, panoramic and cephalometric imaging, have been replacing conventional (film-based) radiography. Drawbacks of two-dimensional (2-D) imaging include: inherent magnification, distortion and overlap of anatomy. As early as the 1920s, manufacturers attempted to overcome the inherent problems of 2-D imaging by devising movement of the receptor and source in opposite directions to produce tomographic ‘slices’ of oral and max- illofacial anatomy. This process is termed ‘linear’ or ‘multidirectional tomography’, and it led to the introduction of CT (computed tomography), including conventional and spiral micro-CT, CBCT (cone-beam computed tomography), OCT (optical coherence tomography) and TACT (tuned-aperture computed tomography). Recently, these modalities have been used in diagnosis of endodontic lesion, identification of root canal systems and postopera- tive evaluation 1,2 . Computed tomography n Computed tomography uses a fan-shaped beam and a multiple exposure around an object to reveal its internal architecture. In this way the clinician can view morphologic features as well as pathology from different three-dimensional perspectives 3 . This paper reviews the literature concerning computed tomography and other modalities such as spiral computed tomography, micro-computed tomography, cone-beam computed tomography, tuned-aperture computed tomography and optical coherence tomography in endodontics. Among the plethora of imaging modalities currently available, these recent imaging systems tend to draw attention from the clinicians. But still there is a lack of evidence-based data on the radiation dose and patient selection criteria for these imaging modalities, which calls for a set of guidelines to be introduced for their use in clinical practice in the future.
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ENDO (Lond Engl) 2010;4(1):27–40

REVIEW

Lalit Boruah, MDSDepartment of Endodontics, Kothiwal Dental College and Research Centre, Morada-bad, India

Atool Bhuyan, MDS Professor of EndodonticsDepartment of Endodontics,Regional Dental College,Guwahati, India

Shashi Tyagi, MDS Professor of EndodonticsDepartment of Endodontics, Kothiwal Dental College and Research Centre, Morada-bad, India

Correspondence to:Lalit BoruahDepartment of Endodontics Kothiwal Dental College and Research Centre Kanth RoadMoradabad – 244001IndiaTel: 0591 2452994/50975 881 8222Email: [email protected]

Lalit Boruah, Atool Bhuyan, Shashi Tyagi

Computed tomographic imaging in endodontics: a short literature review

Key words coherence tomography, computed tomography, cone-beam computed tomography, micro-computed tomography, optical tuned-aperture computed tomography, spiral computed tomography

Introduction n

Within the last 20 years, diagnostic digital imag-ing modalities in dentistry, including periapical, bite wing, panoramic and cephalometric imaging, have been replacing conventional (film-based) radiography. Drawbacks of two-dimensional (2-D) imaging include: inherent magnification, distortion and overlap of anatomy. As early as the 1920s, manufacturers attempted to overcome the inherent problems of 2-D imaging by devising movement of the receptor and source in opposite directions to produce tomographic ‘slices’ of oral and max-illofacial anatomy. This process is termed ‘linear’ or ‘multidirectional tomography’, and it led to the introduction of CT (computed tomography),

including conventional and spiral micro-CT, CBCT (cone-beam computed tomography), OCT (optical coherence tomography) and TACT (tuned-aperture computed tomography). Recently, these modalities have been used in diagnosis of endodontic lesion, identification of root canal systems and postopera-tive evaluation1,2.

Computed tomography n

Computed tomography uses a fan-shaped beam and a multiple exposure around an object to reveal its internal architecture. In this way the clinician can view morphologic features as well as pathology from different three-dimensional perspectives3.

This paper reviews the literature concerning computed tomography and other modalities such as spiral computed tomography, micro-computed tomography, cone-beam computed tomography, tuned-aperture computed tomography and optical coherence tomography in endodontics. Among the plethora of imaging modalities currently available, these recent imaging systems tend to draw attention from the clinicians. But still there is a lack of evidence-based data on the radiation dose and patient selection criteria for these imaging modalities, which calls for a set of guidelines to be introduced for their use in clinical practice in the future.

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CT in endodontic applications was first reported by Tachibana and Matsumoto in 19904. They reported that CT had only limited usefulness in endodontics owing to inadequate image detail and high cost. However, one distinct advantage of CT is that it allows for 3-D reconstruction of root canal systems (RCSs)5. Three-dimensional information, along with tactile feedback during instrumentation, gives the clinician a more thorough understanding of the true morphology of RCSs.

Some CT software programs add colour-enhance-ment features to highlight pathologic lesions from normal anatomic structures. CT images have the ability to show slices of a given tissue, with each slice thickness and location chosen by the operator; therefore CT would enable the operator to look at multiple slices of tooth roots and their RCSs3. CT has been suggested as the preferential imaging modal-ity in difficult situations demanding localisation and description of RCSs because of its ability to render 3-D information6.

Robinson et al6 evaluated mandibular first premo-lars on 120 routine dental CT images for variations in root/RCS morphology. They identified two RCSs in 16 mandibular first premolars. Panoramic evaluation of the same teeth demonstrated that five of these teeth appeared uniformly radio-opaque at all root levels, which might suggest the presence of only one RCS. They reported that CT images identified a greater number of morphologic variations than did a pano-ramic radiograph. Their suggestion was that anatomic information and unusual RCS configuration should always be presented whenever a report on dental CT is performed. A high correlation was established between the shape of the root canal and the corre-sponding root and different instrumentations7,8.

Spiral computed tomography has proved to be useful in accurate diagnosis of a case of dens invagi-natus and its successful management9. Spiral CT has been found to be very useful in detection of radix entomolaris cases (Figs 1–3).

Peripheral quantitative computed tomography (pQCT) for qualitative and quantitative analysis of root canal anatomy and for assessing the extent of canal enlargement during root canal instrumentation shows promise10.

Computed tomography (CT) has been used to compare the volume of root canals before and after

instrumentation with different rotary nickel-titanium (NiTi) systems11. However, if radio-opaque materials are present, there can be scattering and creation of artefacts, which can significantly hamper visualisa-tion3. CT used to evaluate root canals prepared by nickel titanium and stainless steel hand endodontic instruments showed that the imaging system used in this study provided a repeatable non-invasive method of evaluating certain aspects of endodontic instrumentation12.

Spiral CT used for volumetric analysis of root fill-ing concluded that the greatest percentage of obtu-rated volume was obtained with System B (93.3%) and Thermafil® (93.7%) as compared to Obtura II (84.8%) and lateral compaction (80.4%)13.

Another study that compared high-resolution CT with conventional radiography in regard to detection of endodontic lesions and their relation to impor-tant anatomic structures such as mandibular canal concluded that use of CT provides additional 3-D information14.

Three-dimensional images from spiral computed tomography (CT) aided in evaluating the close rela-tionship between maxillary sinus disease and adja-cent periodontal defects and their treatment15. The possibility of using low-dose, low-cost CT to obtain anatomic information to plan periradicular surgery via the vestibular approach was explored success-fully16.

CT may play an important role in optimising palatal root-end surgery through vestibular access with regard to precision and preventing complica-tions and with relatively low biological and eco-nomic cost. It may also contribute to the affirma-tion of the new surgical procedure. Ebihara et al incorporated 3-D reconstruction in the diagnosis and monitoring of a case of Garee’s osteomyelitis managed by root canal treatment of a mandibular second molar17.

Traditional radiographs could only determine the mesiodistal extent of the pathology and not the buc-colingual extent18. Trope et al used CT scans for the first time in 1989 in the differentiation of radicular cysts and granulomas. A cyst could be differentiated from periapical granulomas by CT scans because of a marked difference in density between the content of the cyst cavity and granulomatous tissue19. Another recent study attempted to investigate the course of

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the inferior alveolar canal within the alveolar process using panoramic radiography and CT, with ground truth determined by cadaveric dissection. CT was found to be accurate20.

Nair and Nair21 and Cotton et al22 reviewed the use of CT scans in the diagnosis of periapical lesions. A major concern with the use of CT scanning is its high radiation dosage. In a study23, guidelines by Cristoph et al24 were used. With these, effective radi-ation dosage reduced to 0.56 0.06 mGy, which is equivalent to a standard panoramic radiograph. The results of the study indicate that CT scanning and ultrasound with power Doppler flowmetry can pro-vide an additional or alternative, but more accurate, diagnosis of periapical lesion with validity equivalent to histopathological diagnosis.

Micro-computed tomography n(micro-CT)

Micro-CT has been evaluated in endodontic imag-ing. Comparision of the effects of biomechanical preparation on canal volume on reconstructed root canals in vitro using micro-CT has been shown to assist with characterisation of morphological changes associated with these techniques16,25.

Micro-CT evaluation of morphological changes in the apical third of root canals using three instru-mentation techniques concluded that stainless steel hand preparation was less conservative of apical dentine, and also there is less canal transportation with rotary nickel-titanium (ProFile®, ProTaper® and FlexMaster®) files26.

Fig 1 Intraoral periapical radiograph of tooth 36.

Fig 3a and b Spiral CT images of tooth 36 showing an extra distal root (radix entomolaris).

Fig 2 Digital radiograph of tooth 36.

a b

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Gu et al investigated the anatomic features of the isthmus in the mesial root of mandibular first molars using micro-computed tomography scans in a Chinese population. Each tooth was scanned and reconstructed, and then the prevalence and type of isthmus were recorded in three different age groups. It was observed that the percentage of isthmuses decreased with increasing age27.

Investigation of the apical anatomy of C-shaped canal systems in mandibular second molars by micro-computed tomography (micro-CT) and stereomicro-scopy concluded that apical anatomy of C-shaped root canal systems in mandibular second molars is extremely complex with many anatomical varia-tions28.

Micro-computed tomography is a new and objective means of quantitative evaluation of root canal instrumentation29. A study using non-destruc-tive high-resolution scanning tomography to assess changes in the canals’ paths after preparation con-cluded that the variations in canal geometry before preparation had more influence on the changes dur-ing preparation than the techniques themselves30.

The availability of 3-D information and a relatively high resolution and significantly lower dose makes it the imaging modality of choice in challenging situ-ations demanding localisation and characterisation of root canals. Potential applications in endodontics include diagnosis and evaluation of most aspects of endodontic treatment, such as determination of the configuration and length of root canals and the pres-ence of accessory canals31.

In vitro evaluation of the relative performance of FlexMaster® nickel-titanium instruments in shap-ing maxillary molar root canals, employing micro-computed tomography (micro-CT) at a resolution of 36 micrometres, was done to find out prepara-tion errors32.The behaviour of the instrument under bending or torsional loads was analysed on the basis of 3-D images produced by micro-CT scanned images33.

Cutting behaviour of nickel-titanium rotary instruments with and without irrigation was evalu-ated in a bovine bone model. Irrigation increased the cutting efficiency of the instruments significantly, except for Liberator. The cutting behaviour of NiTi rotary instruments depends on experimental set-up, instrument design and cutting condition34.

Micro-CT data were used to compare the effects of four preparation techniques on canal volume and surface area using three-dimensionally reconstructed root canals in extracted human maxillary molars. Within the limitations of the micro-CT system, there were few differences between the four canal instru-mentation techniques used35.

Measurement of the remaining filling volume of different obturation materials from root-filled teeth, extracted using two removal techniques, were as follows: teeth were scanned with a micro-computed tomography scan and then root fillings were removed by using ProTaper® retreatment files or hand K-files. Teeth were scanned again, and volume measure-ments were carried out with micro-computed tom-ography software. The study showed that all tested

Fig 4 i-CAT® CBCT system (Imaging Sciences Interna-tional, Hatfield, USA).

Fig 5 3-D Accuitomo CBCT system (J. Morita USA, Inc., Irvine, USA).

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filling materials were not completely removed during retreatment by using hand or rotary files36.

Comparision of the volumetric expansion of gutta-percha in the presence of eugenol or physi-ologic saline over time was studied on the basis of images scanned by micro-CT to determine their total volume and surface area. Sealers that incorporate eugenol could be attributed to gutta-percha volu-metric expansion over time, thereby creating a better seal of the obturation material37.

Micro-CT imaging of filled root canals showed it to be a highly accurate and non-destructive method of evaluation of root canal fillings and their constitu-ents. Qualitative and quantitative correlation between histological and micro-CT examination of root canal fillings was high27,38,39. A micro-CT study compared the volume of hard tissue change following endodon-tic procedure and post space preparation. It concluded that access cavity and post space preparation results in the largest loss of hard tissue, which is larger for cast post than fibre post preparation40.

The broad-based use of high-quality free soft-ware and the resulting exchange of experience might help to improve the quality of endodontic research with micro-computed tomography41.

Cone-beam computed ntomography (CBCT)

Volumetric CT or CBCT, a relatively new diagnos-tic imaging modality, has been used in endodontic imaging recently. This modality uses a cone beam instead of a fan-shaped beam, acquiring images of entire volume. The radiation beam, is 3-D in shape and similar in photon energy to that used in conven-tional and digital radiography. The receptor captures 2-D images and is solid-state (digital) or an image intensifier. Solid-state receptors absorb photons that are converted to an electric charge, which is meas-ured by the computer. Image intensifiers capture photons and convert them to electrons that con-tact a fluorescent screen that emits light captured by a charge-coupled device camera. As the source and receptor orbit once around the object, many exposures are made, ranging in duration from 8.9 to 40 seconds. The software ‘reconstructs’ the sum of the exposures via algorithms specified by the man-

ufacturer into as many as 512 axial-slice images. These images are in the Digital Imaging and Com-munications in Medicine (DICOM) data format. DICOM is a standard for handling, storing, printing and transmitting information in medical imaging. During a single rotation of the source and receptor, the receptor captures the entire volume of anatomy within the field of view40,41.

CBCT can be seen as a highly useful and indis-pensable part of the dental imaging armamentar-ium1,42. It appears to be an effective and safe way to overcome some of the problems associated with conventional radiography43.

Perhaps the greatest improvement in the spe-cialty, relative to treatment planning endodontic failures, is the advent of cone-beam computed tomography (CBCT) imaging. The traditional pro-jection radiograph is a two-dimensional shadow of a Z Plane object. Three-dimensional imaging over-comes this major limitation by allowing us to visu-alise the third dimension, while at the same time eliminating superimpositions. CBCT, also called dig-ital volume tomography, is a new technique that produces 3-D digital imaging at reduced cost with less radiation for the patient in comparison with tra-ditional CT scans1. It also delivers faster and easier image acquisition42.

Ludlow and colleagues reported that the effec-tive dose equivalent measured after an exposure using indirect digital panoramic imaging was 6–7 microSieverts. The effective dose equivalent is the amount of radiation received after taking into account the tissue’s sensitivity to radiation. The effective dose equivalent measured using CBCT is between 30 and 400 μSv, depending on the manu-facturer and technical factors involved. This com-pares with an effective dose equivalent of 2100 μSv from a conventional medical CT scan of the maxilla and mandible43.

An outstanding review by Cotton et al reported on the many possible endodontic applications of CBCT22. It offers relatively high resolution and iso-tropic images for effective evaluation of root canal morphology44. In a comparative study, Huybrechts et al reported that CBCT can detect voids in root fill-ings that were larger than 300 μm. For smaller void detection, all digital intraoral techniques performed better than CBCT imaging45.

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CBCT has been used successfully in endodon-tics for different purposes including study of root canal anatomy; external and internal macro-mor-phology in 3-D reconstruction of the teeth; evalu-ation of root canal preparation, obturation, retreat-ment and coronal micro-leakage; detection of bone lesion; and experimental endodontology46.

The value of cone-beam tomography in clinical endodontics for identification of complex root canal anatomy is increasing47.

Simons et al reported that the CBCT might pro-vide more accurate diagnostic information than biopsy and histology when evaluating large periapi-cal lesions24.

Rigolone et al used CBCT technology to measure the mean distance of the palatal root of the max-illary molar from the external vestibular cortex of the maxilla. They concluded that CBCT might have an important role in the decision to perform peri-radicular surgery on the palatal root of the maxillary molar through a vestibular-vs-palatal approach16. The anatomical structures, such as root canals and side canals, and communications between different root canals, as well as denticles, could be detected precisely with FD-VCT (flat-panel-detector volume-computed tomography). The length of curved root canals was also determined accurately. The spatial resolution of the system is around 140 μm. None of the side canals, shown with FD-VCT, was detect-able on conventional X-rays48. It is possible to calcu-late root-curvature radius in both apical and coronal directions with the help of CBCT-aided methods. That is easy to perform, reproducible, and more reli-able and predictable than endodontic planning49.

In endodontics, it is difficult at times for clinicians to evaluate the extent of inferior cortical border ero-sion of the maxillary sinus, or of associated mucosal thickening extending to the periapical region of the roots of maxillary teeth, using 2-D periapical imaging, owing to superimposition of structures. At spatial resolutions of 300 μm (0.3 mm) and less, images produced with CBCT show the position of the apexes of roots of maxillary teeth extending to the nasal cavity and maxillary sinus, as well as corti-cal border erosion of these structures resulting from apical rarefying osteitis43.

A large number of studies with different diag-nostic methods, including CBCT, have evaluated the type and incidence of periapical lesions, root fractures, root canal anatomy and the nature of the alveolar bone topography around teeth19,50–53. Sci-entific consensus has been reached about the fact that apical periodontitis (AP) is identified accurately by histologic analyses. Few studies have compared the difference in AP image interpretation by using

Fig 6a CBCT image of maxillary molar (3-D Accuitomo. i-dixel. One Data Viewer – J. Morita USA).

Fig 6b CBCT image of maxillary molar – X axis revolutions (3-D Accuitomo. i-dixel. One Data Viewer – J. Morita USA).

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CBCT conventional periapical radiography or digital radiography. CBCT has provided promising results with more accurate detection of apical periodon-titis14,22,54. Estrela et al compared periapical radi-ography and CBCT scanning for the preoperative diagnosis of apical periodontitis and concluded that a tomographic scan more accurately identified the apical periodontitis55.

The findings of an investigation demonstrated that CBCT images present high accuracy for the detection of apical periodontitis (AP). CBCT images tend to offer higher scores than periapical and pan-oramic radiographs, suggesting that diagnosis of graduation of AP with conventional images is fre-quently underestimated. AP was correctly identified in 54.5% of the cases with periapical radiograph and 27.8% with panoramic radiograph. Accuracy of peri-apical radiograph was significantly higher than that of panoramic radiograph. AP was correctly identified with conventional methods when a severe condition was present55, 56. Influence of root canal obturation on apical periodontitis at different levels detected by periapical radiography and CBCT showed that AP was detected more frequently by CBCT57. CBCT cor-rectly identified periapical lesions in 100% of cases, as compared to 24.8% with intraoral conventional radiography, of artificial periapical bone defects in dry human jaws58. Simon et al, in 2006, used Gray values obtained by cone-beam CT scans to differen-tially diagnose 17 large periapical lesions and dem-onstrated that cone-beam computed tomography can determine the difference in density between the cystic cavity content and the granulomatous tissue, favouring the choice of a non-invasive diagnosis59.

Unfavourable outcomes occurred more fre-quently after one-visit therapy than two-visit ther-apy when determined by CBCT scans60.

Velvart et al correlated the information gathered from standard dental radiography and resolution CBCT scans to the findings obtained during surgery regarding the presence of endodontic lesions in 50 patients. All 78 lesions diagnosed during surgery were also visible with CBCT scans. In contrast, only 61 (78.2%) lesions were identified by conventional radiographs14.

Another study demonstrated the application of cone-beam computed tomography in the diagno-sis of iatrogenic root perforation61. CBCT seems to

be useful in the evaluation of inflammatory root resorption and its diagnosis performance was bet-ter (100%) compared with periapical radiography (68.8%)62.

The diagnosis and three-dimensional imaging assessment of the resorption is important in order to determine the treatment complexity and expected outcome based on the location and extension of the root defect with the potential use of the NewTom 3G (CBCT system) for root resorption63.

Computed tomography, magnetic resonance imaging and cone-beam computed tomography are among the most commonly used systems for dental and maxillofacial surgery. CBCT, in particular, has potential in the diagnosis and treatment of dento-alveolar traumatic injuries64.

CBCT scans are desirable to assess posterior teeth prior to periapical surgery, as the thickness of the cortical and cancellous bone can be determined accurately, as can the inclination of roots in relation to the surrounding jaw. The relationship of anatomi-cal structures such as the maxillary sinus and inferior dental nerve to the root apices may also be clearly visualised50,65.

Using the FD-VCT, vertical root fractures or crack lines could be detected clearly in different views, depic-tion modes and cross-sections at a spatial resolution of

Fig 6c CBCT image of maxillary molar – Z axis revolutions (3-D Accuitomo. i-dixel. One Data Viewer – J. Morita USA) (images courtesy of Prof V. Kumar).

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140 μm. The evaluation of the fracture lines and teeth could be performed in three-dimensional views66. VCT was used to visualise vertical root fractures in extracted teeth. Vertical root fractures were successfully detected at a spatial resolution of 140 μm66.

CBCT was better than conventional radiography for the diagnosis of root fractures, thereby constitut-ing an excellent alternative for diagnosis67.

Comparison of the accuracy of CBCT scans and periapical radiographs in detecting vertical root frac-tures (VRFs) and to assess the influence of root canal filling (RCF) on fracture visibility showed an overall higher accuracy for CBCT (0.86) scans than for PRs (0.66) for detecting VRFs68.

Stavropoulos and Wenzel verified intraoral digital and conventional film radiography in mechanically cre-ated periapical defects in pig jaws. The results showed that the NewTom 3G has a higher sensitivity69.

Regarding CBCT images, the presence of intra-canal metallic post might lead to equivocated interpretation as a result of artefact formations56. Lofthag-Hansen et al reported that when metallic objects are present in either the tooth of interest or the adjacent one, artefacts can pose difficulties in the analysis of images. In these cases periapical radio-graphs are helpful to complement the diagnosis70.

A positive factor in the choice of CBCT is the production of high-resolution images. CBCT images provide the clinician with submillimetre spatial resolu-tion images of high quality with relatively short scan-ning times (10–70 s) and a radiation dose equivalent to that needed for 4–15 panoramic radiographs. However, image quality might vary according to the CBCT source56.

A great advantage of using CBCT in endodontics is its usefulness in aiding identification of periapical lesions, and a differential diagnosis with a non-inva-sive technique with high accuracy concluded that the prevalence of AP was significantly higher with CBCT in comparison with periapical and panoramic radio-graphs. In an advanced stage, CBCT was demon-strated to be an accurate diagnostic method for iden-tifying AP56. Simonton et al used CBCT to evaluate age- and gender-related differences in the position of the inferior alveolar nerve, and it was concluded that the overall width of mandibular bone decreased in both genders from the third to the sixth decade of life (P < .01)71. Rigolone et al suggested that although

the irradiation doses and costs are negligible, the cost–benefit ratio could swing in favour of this tech-nology16.

In conclusion, evaluation of CBCT images always resulted in a greater number of RCSs identified than evaluation with PSP or CCD images in vitro56. Examples of currently available CBCT units include: 3D Accuitomo FPD XYZ Slice View Tomograph® (J. Morita USA, Inc., Irvine, USA), 3D X-ray CT Scan-ner Alphard series (Asahi Roentgen Industrial Co., Kyoto, Japan) and Quolis Alphard-3030-Cone-Beam (Belmont Equipment, Somerset, USA). In addi-tion, some digital panoramic radiographic systems include CBCT technology43.

Optical coherence tomography n(OCT)

OCT is a new diagnostic imaging technology that was first introduced in 199172. Modern imaging techniques are clinically applied during root canal treatment, as important information about inner canal anatomy and dentine thickness is still limited to in vitro observations.

One difficulty in treating oval or curved canals like lower incisors is the chance of strip perforations because of the short distance between the inner canal wall and the periodontal ligament. In these zones, clinicians often face the challenge of cleaning and enlarging the root canal space sufficiently, while not perforating the mesial or distal walls. OCT com-bines the principles of an ultrasound with the imag-ing performance of a microscope, although ultra-sound produces images from back-scattered sound echoes. OCT uses infrared light waves that reflect off the internal microstructure within the biological tissues. Using the principle of low-coherence inter-ferometry, it achieves depth resolution of the order of 10 μm and in a plane resolution similar to the optical microscope. By scanning the probe along the imaged specimen while acquiring image lines, a two-dimensional or three-dimensional image is built up. The OCT light source has a wavelength of 1300 nm. Visible light that has a shorter wavelength is prone to a higher level of scattering and absorption and produces shallower imaging depth36. The frequency and bandwidths of infrared light are significantly

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higher than medical ultrasound signals, resulting in increased image resolution53,73. In endoscopic OCT imaging, near-infrared lighting is delivered to the imaging site (usually blood vessels) through a thin fibre. The imaging tip contains a lens prism assembly to focus the beam and direct it towards the vessel wall. The fibre can be retracted inside the catheter sheath to perform a so-called ‘pullback’, allowing the user to make a stack of cross-sections, scanning the investigated vessels lengthwise. Modern OCT systems reach a 6 mm imaging depth, with 8-μm resolution at 50 to 80 frames per second74.

OCT potential in dentistry was not overlooked. OCT images of hard and soft tissues in the oral cavity were compared with the histologic images using an animal model showing an excellent match75. A study to directly position the tip of the endoscope fibre in the root canal via a navigation system concluded that the application of the endoscopic navigation system could increase the success rate for root canal treat-ments with recalcitrant lesions76.

In another study, Otis et al discussed the clear depiction of periodontal tissues contour, sulcular depth, connective tissue attachment and marginal adaptation of restorative material to dentine, concluding that OCT is a powerful method for generating high-resolution cross-sectional images of oral structure77. Amaechi et al and Baumgartner et al described the recognition of car-ies with OCT78,79. OCT could provide the dentist with an unprecedented level of image resolution to assist in the evaluation of periodontal disease, dental restora-tions and detection of caries. Commercial development of a chair-side OCT dental system is already underway (www.lantislaser.com)74. Excellent correlation between the histologic images and the OCT output is observed from results of a study74. OCT images provided the insight into dentinal substrate about 0.65 mm deep and can generate images of the boundaries of pulp and its relation to dentine.

OCT can be used in the future to prevent iatro-genic exposure of pulp, complementing other exist-ing methods, and will permit a more predictive prog-nosis of treatments80. New computed tomography methods prove to be more accurate in the evaluation of the bone lesions than conventional radiography8. Similarly, canal mor-phology44, root fracture46, tooth anatomy31 and the interface between the root canal and filling materials

were successfully shown with different computed tomographic techniques. These methods use ionis-ing radiation, which could be harmful at higher doses when used in vivo.

Furthermore, two major disadvantages are limit-ing the successful application of these methods for intracranial imaging. First, the resolution is usually not suitable for microscopic-level imaging; digital dental radiography systems have a pixel size approaching 100 μm. Second, the probe sizes are usually much bigger than a root canal. These methods are also time-consuming and often require the interpretation of thousands of images. In contrast, OCT combines a very narrow optical fibre measuring 0.5 mm in diameter with high-resolution capacities, enabling imaging of the object measuring a few micrometres, and does not involve ionising radiation. The imaging wire can be deployed independently or integrated straightforwardly into existing therapeutic or imag-ing catheters. Furthermore, it can easily fit into a pre-pared root canal and is flexible, allowing penetration through curvatures. The optical probe rotates inside the image vessel so that adjacent lines in each rota-tion compose a frame showing a cross-section of the tissue architecture in the wall; thus scanning is quick and takes 15 s for a 15-mm-long root74.

Tuned-aperture computed ntomography (TACT)

TACT is a flexible 3-D imaging method that converts any number of 3-D projections produced from any number of arbitrary or unknown projection source positions and angles into a true 3-D image. The image produced is similar to viewing the original object with unlimited visual access through a win-dow or aperture whose size is determined by the original projection. It is a software-driven imaging innovation for intra- and extraoral procedures, which can produce 3-D concepts of the teeth or structures within the recorded region. Such 3-D displays could be useful for caries/demineralisation detection. The displays are useful in the determination of root frac-tures, especially vertical fractures. Such sophisticated techniques will also allow better perception of signifi-cant periodontal lesions. Three-dimensional technol-ogy enables reconstructions, with suitable enhance-

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Table 1 Comparative analysis of currently available CBCT systems (as mentioned by man-ufacturers – Imaging Sciences International, Hatfield, USA)86.

Machine name

Machine name

Next generation i-CAT@

Classic i-CAT

NewTom 30047

NewTom VG ILUMA ULTRA CBCT

Kodak 9000 3D

Manufacturer Imaging Sciences International

Imaging Sciences International

Dent-X / AFP Imaging

Dent-X / AFP Imaging

IMTEC / Kodak Dental Systems

IMTEC / Kodak Dental Systems

Gray scale 14 bit 14 bit 12 bit 14 bit 14 bit 14 bit

Footprint 1.2 m x 1.16 m

H 1.83 m x W 1.12 m x D 1.27 m

H 1.5m x W 1.9m x D 2.5m

H 2.28m xW 1.14m x D 1.49m

H 1.06m x W 1.42m x D 2.15m

L 2.3m x W 1.15m x D 1.75m

Image detec-tor

Amorphous silicon flat panel

Amorphous silicon flat panel 20 cm x 5 cm

l.l. + CCD camera

Amorphous silicon flat panel

Amorphous silicon flat panel

CMOS sensor with optical fibre

Rotation per scan

single single single 360° rotation

single 360° rotation

single 360° rotation

single 360° rotation

Patient posi-tioning

seated seated supine sitting/ standing/ wheelchair

seated standing

Pre-installed software

i-CAT visionTM 3DVR

Xron Cat Vision & 3 DVR

NNT Dolphin imaging & NNT

ILUMA Vision 3D

Kodak imaging software

Scan time 8.5 s standard scan

20 s standard

36 s 18 s 20–40 s 130 – 13.9 s

Scan diameter

8.23 cm diameter field of view

16 cm 20–15–10 cm 16 cm 17–19 cm 5 cm

Scanheight

4–17 cm height field of view

13 / 22 cm 20 cm 14 cm 10–19 cm 3.8 cm

Scan thickness

0–1.25 mm – 0.4 mm

0.12–0.4 mm 0.1 –0.5 mm

0.2–0.5 mm (0.3 type)

0.09 mm 0.076 mm

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Machine name

CB Mercu- Ray

Gendex GXCB-500TM

3D Accui-tomo

Prexion 3D

Planmeca Promex 3D

Galileos Picasso Trio SC

Picasso Master Standard

Hitachi Medical Systems

Gendex J. Morita USA

Prexion Inc. Planmeca Sirona Dental Systems

EWOO Tech-nologies

EWOO Technologies

12 bit 14 bit 12 bit 16 bit 12 bit 12 bit 12 bit 14 bit

H 2.25m x W 1.96m x D 1.9m

1.2m x 1.6m

H 2.08m x W 1.62m x D 1.2m

H 2m x W 1.49m x D 0.99m

H 1.53m x W 1.07m x D 1.25m

H 2.00m x W 1.60m x D 1.60m

H 2.2m x W 1.8m x D 1.1m

H 1.9m x W 1.3m x D 1.5m

Image inten-sifier CCD

Amorphous silicon flat panel

CMOS flat panel

Csl flat panel CMOS flat panel

Proprietary Seimens technique

Csl coated CMOS flat panel

Amorphous silicon flat panel

single single single single 360°

single 200° single shots

single 360° rotation

single 360° rotation

seated seated seated seated seated / standing

standing / sitting

standing seated

CB Works i-CAT visionTM 3DVR

i-Dixel Tera Recon Xtrillion

Romexis/ N-Liten

SIDEXIS / GALAXIS

Easy Dent Ezimplant

Easy Dent Ezimplant IC

10 s 8.9 s stand-ard scan

18 s or less 360° scan, 9 s

19 cm –37 cm

2.5–18.7 s 14 s 15 s / 24 s 24 s

25 cm 8–14 cm field of view

6/4 cm 8 cm 8 cm 15 cm 12 cm 20 cm

15–30 cm 4–8cm height field of view

6 / 4 cm 8 cm 8 cm 15 cm 7 cm 19 cm

0.1–0.5 mm 0.125 mm –0.4 mm

0.09 mm 0.1 mm & up

variable starting at 16 mm

isotropic voxel size: 0, 3/ 0, 15 mm

0.1 mm –1.0 mm

0.1 mm –1.0 mm

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ment and refining of the digital image, from up to seven images of the region of interest at different angles. At the moment, the development of TACT in dentistry is centred on using a panoramic system as the radiation source81,82,83.

TACT is a relatively new 3-D imaging modality with the significant advantages that the doses are relatively low; no expensive equipment is required; image acquisition is relatively simple; artefacts associated with CT, such as starburst patterns seen with metallic restorations, do not exist; and resolution is as good as conventional 2-D radio-graphs. It was noted that root canals were easier to detect on TACT images than on conventional radiographs84.

Conclusion n

Several advanced radiography techniques for the precise detection of lesions and root canal systems have been in use in endodontics, namely CT, CBCT, TACT and micro-CT for in vitro studies and OCT (experimental). The use of these novel imaging tech-niques is gaining a lot of attention in the field of endodontics85, but the need of the hour is to develop a cost-effective, chair-side, three-dimensional imag-ing system for routine use with standard radiation dose protocols and clinical guidelines.

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