Fig. 2.1
Three-dimensional cross section of the coronal third of a mandibular second molar root (a) illustrating the difference between pixel (b) and voxel (c). The word pixel stands for picture element. Every digital image is made up of pixels. They are the smallest unit of information arranged in a two-dimensional grid that makes up a picture. Voxel stands for volumetric element, and it is the three-dimensional equivalent of a pixel and the tiniest distinguishable element of a 3D object
Because micro-CT is mostly used in nonliving objects, the scanners were designed to take advantage of the fact that the items being studied do not move and are not harmed by X-rays. Basically, micro-CT technology employs four optimizations in comparison to conventional CT [80]:
(a)
It uses high-energy X-rays which are more effective at penetrating dense materials.
(b)
X-ray focal spots are smaller providing increased resolution at a cost in X-ray output.
(c)
X-ray detectors are finer and more densely packed which increases resolution at a cost in detection efficiency.
(d)
It uses longer exposure times increasing the signal-to-noise ratio to compensate for the loss in signal from the diminished output and efficiency of the source and detectors.
Application of micro-CT technology to endodontic research was recognized only 13 years after its development and described in a paper entitled Microcomputed Tomography: An Advanced System for Detailed Endodontic Research [3]. In this article, Nielsen et al. [3] evaluated the reliability of micro-CT in the reconstruction of the external and internal anatomy of four maxillary first molars, assessing the morphological changes in the root canal after instrumentation and obturation, using an isotropic resolution of 127 μm. Authors concluded that micro-CT had “potential as an advanced system for research, but also provides the foundation as an exciting interactive educational tool.” In this study, three-dimensional images of the internal and external structures of the teeth were also presented in a format previously unattainable [3].
With further developments of the micro-CT scanners, improvements in the speed of data collection, resolution, and image quality yielded greater accuracy compared with the first studies using computational methods, with voxel sizes decreasing to less than 40 μm [4, 117]. Dowker et al. [4] demonstrated the feasibility of this technology using a resolution of 38.7 μm to evaluate the morphological characteristics of the root canal before and after different steps of root canal treatment. Authors concluded that micro-CT technology would offer the possibility of learning tooth morphology by interactive study of surface-rendered images and slices, contributing to the development of virtual reality techniques for endodontic teaching. Later, the reliability of micro-CT as a methodological tool was also demonstrated in the quantitative assessment of the root canal preparation [62, 116–119], obturation [120], and retreatment [121], using innovative image software that allowed the alignment of pre- and post-image volumes.
Therefore, micro-CT has gained increasing significance in the detailed study of canal anatomy in endodontics because it offered a nondestructive reproducible technique that could be applied quantitatively as well as qualitatively for two- and three-dimensional accurate assessment of the root canal system [116]. Conversely, given that scanning and reconstruction procedures take considerable time, the technique is not suitable for clinical use, the equipment is expensive, and the complexity of the technical procedures requires a high learning curve and an in-depth knowledge of dedicated software. The technical procedures related to the micro-CT methodology with the aim to evaluate aspects related to the morphological analysis of the root canal anatomy are a complicated subject, and a thorough discussion is beyond the scope of this text. However, an understanding of basic principles is desirable to ensure a better comprehension of its potential as a tool for endodontic teaching and researching.
A typical micro-CT scanner consists of a microfocus X-ray source, a motorized high-precision sample rotation stage, a detection array, a system control mechanism, and computing software resources for reconstruction, visualization, and analysis of the root canal anatomy [122]. The source sends X-ray radiation through the tooth attached to the sample stage (Fig. 2.2a), and a detector array – coupled to a digital charge-couple device camera – records attenuated intensities of the X-ray beam, while the object rotates on its own axis (Fig. 2.2b); i.e., micro-CT involves gathering projection data of the tooth from multiple directions. If many projections are recorded from different viewing angles of the same tooth, each projection image will contain different information about its internal structure. At this stage, the only preparation that is absolutely necessary for scanning is to ensure that the previously cleaned tooth fits inside the field of view and does not move during the scan [80]. The entire operation of the scanner, including X-ray exposure, type of filter, flat-field correction, resolution, rotation step, rotation angle, number of frames, data collection, etc., is controlled by a software – the system control mechanism – which allows setting up these parameters in order to improve the further 3D reconstruction of the tooth.
Fig. 2.2
Inside view of the chamber of a SkyScan 1174 v2 (Bruker-microCT, Kontich, Belgium) micro-CT device. Common elements of micro-CT: (a) X-ray source, an object attached to the sample stage to be imaged through which the X-rays pass, and a detector(s) that measures the extent to which the X-ray signal has been attenuated by the object. The source sends X-ray radiation through the tooth, and a detector array records attenuated intensities of the X-ray beam, while the object rotates on its own axis (b)
After recording the X-ray images, the projection data of the tooth from multiple directions (Fig. 2.3a) is then used as input for a reconstruction algorithm. This algorithm computes a three-dimensional image of the internal anatomy of the tooth, based on the two-dimensional projection images (Fig. 2.3b) [123]. The resulting volumetric images are then subjected to image segmentation using dedicated software. Image segmentation is a manual or automatic procedure that can remove the unwanted structures from the image based on the object density. The goal of segmentation is to simplify the representation of an image into something that is more meaningful and easier to analyze. More precisely, image segmentation is the process of assigning a label to every pixel in an image as such that pixels with the same label share certain visual characteristics [124]. Concerning the tooth, the different radiographic densities of the enamel, dentin, and root canal facilitate the segmentation procedures (Fig. 2.3c). The result of image segmentation is a set of segments that collectively cover the entire image. When applied to a stack of images, as in the study of the internal anatomy of the teeth, the resulting contours after image segmentation can be used to create 3D models with the help of interpolation algorithms, which can be visualized (Fig. 2.3d) or analyzed using different software.
Fig. 2.3
The projection data of the tooth from multiple directions (a) is used as input for a reconstruction algorithm which computes a 3D image of the internal anatomy of the tooth, based on the 2D projection images (b). The different radiographic densities of the tooth tissues (c) facilitate its segmentation which can be used to create 3D models (d)
Evaluation of Root Canal Anatomy Using Micro-CT
The first attempt to use micro-CT as a quantitative tool for the analysis of the root canal anatomy was done by Bjørndal et al. [125]. Authors correlated the shape of the root canals to the corresponding roots of five maxillary molars scanned at a resolution of 33 μm. However, the real potential for the analysis of several quantitative parameters using micro-CT was reported in the following year [116]. Peters et al. [116] evaluated the potential and accuracy of micro-CT for detailing the root canal geometry of 12 maxillary molars regarding volume, surface area, diameter, and structured model index. Then, micro-CT was used by different groups to evaluate geometrical changes in root canals after preparation with different instruments and techniques [62, 119, 126–129], as well as, for educational purposes [64, 130, 131]. Though, it took over 18 years for the micro-CT scanners gain accessibility [3] and the first in-depth studies evaluating the root canal anatomy started to be published. The main results of the studies published in indexed journals in English language are summarized in Tables 2.1, 2.2, 2.3, and 2.4.
Table 2.1
Micro-CT studies on the root and root canal morphology of incisors and canines
|
Authors
|
Aim
|
Scanner specifications
|
Main conclusions
|
|---|---|---|---|
|
Almeida et al. 2013 (Brazil) [132]
|
To investigate the root canal anatomy of mandibular incisors (n = 340)
|
SkyScan 1174 v2 (50 kV, 80 μA, voxel size: 19.6 μm)
|
Vertucci’s type III configuration represented 92 % of the samples. Oval-shaped canals in the apical third were not uncommon and were more prevalent in the type III anatomy. The incidence of 2 or more root canals at the apical third was 3.2 %
|
|
Leoni et al. 2014 (Brazil) [133]
|
To investigate the root canal anatomy of mandibular central (n = 100) and lateral (n = 100) incisors
|
SkyScan 1174 v2 (50 kV, 80 μA, voxel size: 22.9 μm)
|
Vertucci’s types I and III were the most prevalent canal configurations; however, 8 new types were described. Accessory canals were observed only at the apical third; however, most of the incisors had no accessory canals. No difference was observed in the comparison of the morphometric parameter analyzed between central and lateral incisors. The area of the root canal in both teeth increased gradually in the coronal direction. The average roundness represented a flat- or oval-shaped configuration of the canal in the apical third of both groups of teeth
|
|
Gu 2011 (China) [134]
|
To investigate the anatomical features of radicular grooves (RG) in maxillary lateral incisors (n = 11)
|
Siemens Inveon (n.r., voxel size: 15 μm)
|
RG were classified into type I (n = 3), short RG at the coronal third; type II (n = 5), long and shallow RG extended beyond the coronal third of the root (in one specimen, a cross-sectional teardrop-like canal was observed); and type III (n = 3), long and deep RG associated with a complex root canal system (C shaped, invagination, and additional root/canal). RG were located at mesial (n = 3), distal (n = 6), and in both (n = 1) aspects of the root
|
|
Versiani et al. 2011 (Brazil) [68]
|
To investigate the root canal anatomy of mandibular canines (n = 14) with two roots and two distinct canals
|
SkyScan 1174 v2 (50 kVp, 80 μA, voxel size: 16.7 μm)
|
Bifurcation was located in both apical (44 %) and middle (58 %) thirds of the root. From a buccal view, no curvature toward the lingual or buccal direction occurred in either roots. From a proximal view, no straight lingual root occurred. In both views, S-shaped roots were found in 21 % of the specimens. Location of the apical foramen tended to the mesiobuccal aspect of both roots. Lateral and furcation canals were observed mostly in the cervical third. SMI ranged from 1.87 to 3.86. Mean volume and area of the canals were 11.52 ± 3.44 mm3 and 71.16 ± 11.83 mm2, respectively
|
|
Versiani et al. 2013 (Brazil) [63]
|
To investigate the root canal anatomy of single-rooted mandibular canines (n = 100)
|
SkyScan 1174 v2 (50 kVp, 80 μA, voxel size: 19.6 μm)
|
31 % of the samples had no accessory canals. The location of the apical foramen varied considerably and its major diameter ranged from 0.16 to 0.72 mm. The mean distance from the root apex to the major apical foramen was 0.27 ± 0.25 mm. Mean major and minor diameters of the canal 1 mm short of the foramen were 0.43 and 0.31 mm, respectively. The mean area, perimeter, form factor, roundness, major and minor diameters, volume, surface area, and SMI were 0.85 ± 0.31 mm2, 3.69 ± 0.88 mm, 0.70 ± 0.09, 0.59 ± 0.11, 1.36 ± 0.36 mm and 0.72 ± 0.14 mm, 13.33 ± 4.98 mm3, 63.5 ± 16.4 mm2, and 3.35 ± 0.64, respectively
|
Table 2.2
Micro-CT studies on the root and root canal morphology of premolars
|
Authors
|
Aim
|
Scanner specifications
|
Main conclusions
|
|---|---|---|---|
|
Cleghorn et al. 2008 (Canada) [135]
|
To investigate unusual variations in the root and canal morphology of mandibular first (n = 1) and second (n = 1) premolars
|
Feinfocus 160 (n.r., voxel size: 30 μm)
|
Mandibular first premolar exhibited three distinct, separate roots. Corresponding canals divided in the middle to apical third of the root. A prominent furcation canal was present. The mandibular second premolar exhibited a single root, a single apical foramen, and a prominent vertical root groove on buccal surface. Canal system had a C-shaped morphology through the majority of the mid-canal system, which terminated in a single apical foramen
|
|
Fan et al. 2008 (China) [136]
|
To investigate the root and canal morphology of C-shaped mandibular first premolars with (n = 86) and without (n = 54) radicular groove (RG) by accessing the morphology of canal orifices
|
Scanco μCT-80 (n.r., voxel size: 37 μm)
|
Two canals and bifurcations were dominant at the middle and apical third. It was not possible to define the canal configurations in the middle and apical canal third by just assessing the morphology of coronal canal. Detection and instrumentation of a second canal of a bifurcation located further apically may be a difficult task
|
|
Fan et al. 2012 (China) [137]
|
To investigate the root and canal morphology of C-shaped mandibular first premolars with (n = 146) and without (n = 181) radicular groove (RG)
|
Scanco μCT-20 and μCT-80 (n.r., voxel size: 38 and 30 μm)
|
No C-shaped canals were found in teeth without RG. C-shaped canals were identified in 66.2 % of premolars with RG. C-shaped mandibular first premolars had a groove on the external root surface. The morphology of C-shaped canals was classified as continuous, semilunar, continuous combined with semilunar, and interrupted by non-C-shaped canal. Seventy furcation canals were observed and 57 were located in C-shaped premolars
|
|
Gu et al. 2013 (China) [138]
|
To investigate the wall thickness and groove configuration in C-shaped mandibular first premolars (n = 148) with radicular groove (RG)
|
Siemens Inveon (n.r., voxel size: 15 μm)
|
C-shaped canals was observed in 29 teeth (19.6 %) and 107 cross sections. 102 sections exhibited a mesial groove. The root length ranged from 9.7 to 14.9 mm. The wall thickness decreased at increasing distances from the CEJ. Buccal and lingual walls were thicker than the distal and mesial walls. Overall, the minimum thickness occurred at the lingual aspect of the mesial (67.3 %) and distal (69.2 %) root walls
|
|
Gu et al. 2013 (China) [139]
|
To investigate the relation between the root canal and the groove in C-shaped mandibular first premolars (n = 148) with radicular groove (RG)
|
Siemens Inveon (80 kVp, 500 μA, voxel size: 15 μm)
|
Mean root length was 12.98 ± 1.36 mm. Shallow and deep RGs were found on 37.5 % and 18.5 % of the specimens, respectively. 155 RGs were observed in 140 premolars. If one RG was present (n = 125), the location was mostly on the mesiolingual side of the root; if two RGs were present (n = 15), another groove was located on the distobuccal side. C-shaped canals were found in 29 specimens (19.6 %) and 107 cross sections. The complexity of canal systems in mandibular premolars may be determined by the severity of the RGs
|
|
Li et al. 2013 (China) [140]
|
To investigate the furcation grooves in the buccal root of bifurcated maxillary first premolars (n = 42)
|
Scanco μCT-80 (n.r., voxel size: 36 μm)
|
The prevalence of furcation grooves was 85.7 %. Most of them (69.4 %) were located in the coronal and middle thirds of the buccal roots. The mean groove length was 3.94 mm. The wall thickness of the buccal roots was buccopalatally asymmetric
|
|
Li et al. 2012 (China) [141]
|
To evaluate the anatomical aspects of the lingual canal in mandibular first premolars with Vertucci’s type V canal configuration (n = 26)
|
Siemens Inveon (80 kVp, 500 μA, voxel size: 14.97 μm)
|
The lingual canal orifice was located at the middle-apical third with severe angle. 69 % of lingual canals began at the middle third and the remainder at the apical third. The greatest angles “a” [curvature at the beginning of the lingual canal] and “b” [lingual canal curvature] were 65.24° and 43.39°, respectively
|
|
Liu et al. 2013 (China) [142]
|
To investigate the canal morphology of mandibular first premolars (n = 115)
|
Siemens Inveon (80 kVp, 500 μA, voxel size: 14.97 μm)
|
The shape of the canal orifice was classified as oval (84.3 %), flattened ribbon shaped (7.0 %), eight shaped (7.0 %), and triangular (1.7 %). Root canal configuration was identified as types I (65.2 %), V (22.6 %), III (2.6 %), and VII (0.9 %). Ten specimens did not fit Vertucci’s classification. Accessory canals were present in 35.7 % of the teeth and most of them (92.7 %) located in the apical third. The presence of one (50.4 %), two (28.7 %), three (14.8 %), or four (6.1 %) apical foramens was observed mostly laterally (77.4 %). Apical delta and intercanal communications were present in 6.1 % and 3.5 % of the samples, respectively. Mesial invagination of the root was observed in 27.8 % of teeth
|
|
Marca et al. 2013 (Brazil) [143]
|
To evaluate the applicability of micro-CT and iCat CBCT system to study the anatomy of three-rooted maxillary premolars (n = 16)
|
SkyScan 1072 (50 kVp, voxel size: 34 × 34 × 42 μm)
|
Mesiobuccal (MB) canal area was greater than distobuccal (DB) canal. Micro-CT images revealed more details than CBCT including the presence of 3 and 2 canals in the middle third of the MB and DB root of one specimen, lateral canals, canal trifurcation in the apical third, and differences in cross-sectional canal shapes in different levels of the root
|
|
Ordinola-Zapata et al. 2013 (Brazil) [144]
|
To describe the morphometric aspects of the external and internal anatomy of mandibular premolars with Vertucci’s type IX canal configuration (n = 16)
|
SkyScan 1174 v2 (50 kVp, 80 μA, voxel size: 18 μm)
|
Type IX configuration was found in 15.2 % of mandibular premolars with radicular grooves. Most of them had a triangle-shaped pulp chamber in which the distance between the MB and L canals was the largest. Complexities of the root canal systems such as the presence of furcation canals, fusion of canals, oval-shaped canals at the apical level, small orifices at the pulp chamber level, and apical delta were observed
|
Table 2.3
Micro-CT studies on the root and root canal morphology of mandibular molars
|
Authors
|
Aim
|
Scanner specifications
|
Main conclusions
|
|---|---|---|---|
|
Cheung et al. 2007 (China) [145]
|
To investigate the apical canal morphology of C-shaped mandibular second molars (n = 44)
|
Scanco μCT-20 (n.r., voxel size: 30 μm)
|
Most of the samples had 2 (i.e., type II, IV, V, or VI) or 3 (i.e., type VIII) root canals. 1/5 of specimens showed 4 or more canals. Prevalence of accessory and lateral canals ranged from 11 to 41 %. A total of 115 main and 41 accessory foramina were observed. The diameters of the main and accessory foramina ranged from 0.19 to 0.32 mm and from 0.07 to 0.10 mm, with a mean form factor of 0.73 and 0.82, respectively
|
|
Fan et al. 2009 (China) [146]
|
To investigate effective ways to negotiate the root canal system of C-shaped mandibular second molars (n = 44)
|
Scanco μCT-20 (n.r., voxel size: n.r.)
|
8 teeth had a continuous C-shaped orifice (type I), 16 had a type II configuration, 14 a type III configuration, and 6 a type IV configuration. The total number of the orifices was 83 including 8 continuous C-shaped, 14 mesiobuccal-distal, 14 flat, 41 oval, and 6 round orifices
|
|
Fan et al. 2010 (China) [147]
|
To investigate the morphology of the isthmuses in the mesial root of mandibular first (n = 70) and second (n = 56) molars
|
Scanco μCT-80 (n.r., voxel size: 37 μm)
|
107 molars (85 %) had isthmuses in the apical 5 mm of mesial roots. The total number of isthmuses was 120, in which 94 samples had only 1 isthmus, and 13 samples had 2. Mandibular first molars had more isthmuses with separate and mixed morphological types, while second molars had more isthmuses with sheet connections
|
|
Fan et al. 2004 (China) [148]
|
To investigate the canal morphology of C-shaped mandibular second molars (n = 54)
|
Scanco μCT-20 (n.r., voxel size: n.r.)
|
C-shaped canals varied in shape at different levels. None of the orifices was found at the level of the CEJ. 1/4 of the orifices were found 1 mm below CEJ, while 98.1 % were located within 3 mm below the CEJ. Canal bifurcation was observed in the apical 4 mm of 17 teeth, with most of them occurring within 2 mm from the apex
|
|
Fan et al. 2004 (China) [149]
|
To investigate the predictability of the radiography in detecting C-shaped canals in mandibular second molars (n = 54)
|
Scanco μCT-20 (n.r., voxel size: n.r.)
|
C1 (uninterrupted “C”) and C2 (shape resembled a semicolon) configurations always have narrow isthmuses closed to the groove. C1 and C2 configurations were prevalent in types I (mesial and distal canals merge into one before exiting) and III (separated canals) teeth, suggesting that the debridement of these canals would be more demanding than type II (canals continue on their own pathway to the apex). C-shaped canal system in mandibular molars might be predicted according to the radiographic appearance
|
|
Fan et al. 2007 (China) [150]
|
To investigate the predictability of the radiography in detecting C-shaped canals in mandibular second molars (n = 30), using a contrast medium
|
Scanco μCT-20 (n.r., voxel size: n.r.)
|
The contrast medium helped to discern the C-shaped canal anatomy in mandibular second molars. The development of a device for contrast medium introduction into anatomically complex root canal systems might lead to a useful clinical diagnostic tool
|
|
Fan et al. 2008 (China) [151]
|
To investigate the predictability of the digital subtraction radiography (DSR) in detecting C-shaped canals in mandibular second molars (n = 30), using a contrast medium
|
Scanco μCT-20 (n.r., voxel size: n.r.)
|
It was observed that some factors, such as the X-ray-projecting angulation and the degree to which the contrast medium is distributed within the canal system, could change the shape and size of canal images, affecting the classification of the canal anatomy. This discrepancy could be the result of incomplete cleaning in the apical canal merging area, which would prevent contrast media from entering this area
|
|
Gao et al. 2006 (China) [152]
|
To investigate the morphology and canal wall thickness at different levels of C-shaped mandibular second molars (n = 98)
|
Scanco μCT-20 (n.r., voxel size: 11 × 11 × 500 μm/30 × 30 × 100 μm)
|
C-shaped canals were assigned as follows: in type I (n = 32), canals merged into one major canal before exiting at the apical foramen. In type II (n = 38), separated mesial and distal canals were located at the mesial part and distal part of the root, respectively. Symmetry of the mesial canal and distal canal was present along the root. In type III (n = 28), separate mesial and distal canals were evident. The distal canal may have a large isthmus across the furcation area, which commonly made the mesial and distal canals asymmetrical. Differences in the minimum canal wall thickness were observed in the apical and middle portion, but not in the coronal portion
|
|
Gu et al. 2009 (China) [153]
|
To investigate the isthmuses in mesial roots of mandibular first molars (n = 36)
|
GE Explore Locus SP (n.r., voxel size: 15 μm)
|
The morphology of the isthmuses includes the presence of fin, web, or ribbon connecting the individual canals. In the apical third, 32 teeth had isthmus somewhere along its length. Seven out of 32 roots had a continuous isthmus from coronal to apical end, while 25 roots showed a pattern of sections with and without isthmus. The prevalence of an isthmus was higher at the apical 4- to 6-mm level in the 20- to 39-year-old age group (up to 81 %)
|
|
Gu et al. 2010 (China) [154]
|
To investigate the root canal configuration in three- (n = 20) and two-rooted (n = 25) mandibular first molars
|
GE Explore Locus SP (n.r., voxel size: 21 μm)
|
Pulp floors with two mesial and two distal orifices were frequent (n = 16). The third root usually curved severely in the proximal view. The lingual edge of the orifice might form a dentinal shelf, which blocks the view of the canal. Grooves could be observed between adjacent orifices. In 65 % of the 3-rooted teeth, mesial root contained a type 2-2 root canal configuration. Type 1-1 canal occurred more frequently in the DL and DB roots. In mesial and distal roots of three-rooted molars, the incidences of lateral canals were 65 % and 40 %, respectively. Furcation canals were not observed
|
|
Gu et al. 2010 (China) [155]
|
To investigate the root canal curvature in three- (n = 20) and two-rooted (n = 25) mandibular first molars
|
GE Explore Locus SP (n.r., voxel size: 21 μm)
|
In the 3-rooted molars, the mean degrees of curvature in the MB and ML canals were 24.34° and 22.39°, respectively (Schneider method). Secondary curvature was rare in the mesial root. The frequency of S-shaped canals was 60 % of the DB canals. The mean angle of the second curvature was approximately twice that of the primary one. In proximal view, the DL canal exhibited the greatest degree of curvature (32.06°). Using Pruett method, the mean angle and radius of the DL canals were 59.04° and 6.17 mm in proximal view and 26.17° and 20.99 mm in central view, respectively. The curvature in the DL canals had a more severe angle and smaller radius in the proximal view
|
|
Gu et al. 2011 (China) [156]
|
To investigate the root canal morphology in three- (n = 20) and two-rooted (n = 25) mandibular first molars
|
GE Explore Locus SP (n.r., voxel size: 21 μm)
|
The length of DL roots was shorter than the DB and mesial roots. The buccal and lingual canal walls were thicker than the distal and mesial for MB, ML, and DB canals. The distal wall of the MB/ML canal and the mesial wall of the DB and DL canals were the thinnest zones. It was suggested that the initial apical file for a DL canal should be 2 sizes smaller than that for a DB canal; DB, DL, and MB/ML canals should be instrumented to a mean size of #55, #40, and #45, respectively. The MB, ML, and DB canals were mostly oval, while the DL canals were relatively rounder
|
|
Harris et al. 2013 (USA) [157]
|
To investigate the canal morphology of the mandibular first molars (n = 22)
|
n.r. (n.r., voxel size: 11.41 × 12.21 × 17.53 μm)
|
Mean distance from the mesial to distal orifices at the pulpal floor was 4.35 mm. In the apical third of the distal root, the mean thickness of dentin on the furcation side ranged from 0.25 to 1.47 mm. Types V and I were the most common configurations of the canal in the mesial and distal roots, respectively. Isthmuses were found along the length of all of the mesial roots (100 %) and within 9.1 % of the distal roots. In the mesial and distal roots, an average of 3.73 and 3.36 portals of exit was observed in the apical 0.5 mm of the roots
|
|
Mannocci et al. 2005 (U.K.) [158]
|
To investigate the isthmus at the apical third of the mesial root of mandibular first molars (n = 20)
|
GE Testing Lab (100 kVp, voxel size: 12.5 × 12.5 × 25.0 μm)
|
17 roots had isthmuses in one or more sections of the apical third. Only 4 out of 17 roots with isthmuses had a continuous isthmus from coronal to the apical end. The other 3 roots showed sections with and without isthmuses. The percentage of sections showing isthmuses ranged from 17.25 to 50.25 % in the apical 5 mm of the root canals. The morphology of the isthmuses varied between teeth and within the same tooth
|
|
Min et al. 2006 (China) [159]
|
To investigate the morphology of the pulp chamber floor of C-shaped mandibular second molars (n = 44)
|
Scanco μCT-20 (n.r. voxel size: n.r.)
|
90.91 % of the pulp chamber floors were within 3 mm below the CEJ. The location of grooves was usually 4 mm below the CEJ. Eight teeth had a continuous C-shaped orifice and type I canal configuration. Types II and III were observed in 16 and 14 teeth, respectively. Six teeth with a C-shaped canal system showed non-C-shaped chamber floors. In type II teeth, the canal configuration was similar to those present in conventional mandibular molars with separated roots. In type III teeth, there was a large MB-D orifice and a small ML orifice
|
|
Villas-Boas et al. 2011 (Brazil) [160]
|
To evaluate the morphology of the canal and the presence of isthmus at the apical third of the mesial root of mandibular first and second molars (n = 60)
|
SkyScan 1076 (n.r., voxel size: 18 μm)
|
The median mesiodistal diameter (in mm) at the 1-, 2-, 3-, and 4-mm levels were 0.22, 0.23, 0.27, and 0.27 in the MB canal and 0.3, 0.3, 0.36, and 0.35 in the ML canal, respectively; while the buccolingual diameters were 0.37, 0.55, 0.54, and 0.54 in the MB canal and 0.35, 0.41, 0.49, and 0.6 in the ML canal, respectively. The presence of isthmuses was more prevalent at the 3- to 4-mm level. 27 teeth presented complete or incomplete isthmuses at the 1-mm apical level. The volume of the apical third ranged from 0.02 to 2.4 mm3
|
Table 2.4
Micro-CT studies on the root and root canal morphology of maxillary molars
|
Authors
|
Aim
|
Scanner specifications
|
Main conclusions
|
|---|---|---|---|
|
Bjørndal et al. 1999 (Denmark) [125]
|
To analyze the correlation between the shapes of the outer surface of the root and the canal in maxillary molars (n = 5)
|
THX1430 GKV (n.r., voxel size: 33 μm)
|
There was a strong correlation between the shape of the canals and the root components. Authors suggested that 3D volumes generated by micro-CT technology would constitute a platform for preclinical training in fundamental endodontic procedures
|
|
Domark et al. 2013 (USA) [161]
|
To evaluate the reliability of radiography, CBCT, and micro-CT in determining the number of canals in the MB root of maxillary first (n = 13) and second (n = 14) molars
|
Scanco VivaCT 40 (70 kVp, 114 μA, voxel size: 20 μm)
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Using human cadavers, it was verified that the number of canals determined with micro-CT was different compared to digital radiography, but similar from those acquired using CBCT system (Kodak 9000). In all maxillary first molars, MB roots had 2 canals, of which 69 % (9 out of 13) exited as 2 or more foramina. Fifty-seven percent (8 out of 14) of maxillary second molar MB root had 2 canals exiting as 2 or more foramina
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Gu et al. 2011 (South Korea) [162]
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To evaluate the use of minimum-intensity projection technique as an adjunct to evaluate the morphology of the MB root of maxillary first molars (n = 110)
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SkyScan 1172 (n.r., voxel size: 31.8 μm)
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24 roots had a single canal. Multiple canals were observed in 76.2 % of the MB roots. 15 MB roots had a completely independent second canal, while 9 had 3 canals. 53 roots had 2 canals that joined into 1 or had 1 canal that divided into 2. Eleven roots showed 6 new configuration types. 82.2 % of roots had multiple apical foramina. Intercanal communications were found in all roots having multiple canals. The incidences of intercanal communication in the coronal, middle, and apical thirds were 40.6 %, 49.5 %, and 44.6 %, respectively
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Hosoya et al. 2012 (Japan) [163]
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To evaluate the reliability of different methods in detecting a second canal in the MB root of maxillary first molars (n = 86)
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Hitachi MCT100-MFZ (65 kVp, 100 μA, voxel size: n.r.)
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A second canal in the MB root was observed in 60.5 % of the samples. Types I, II, III, and IV (Weine’s configuration) were observed in 39.5, 15.1, 27.9, and 17.5 % of the samples, respectively. Detection of the second canal was higher for micro-CT and dental CT than the other diagnostic tools
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Kim et al. 2013 (South Korea) [164]
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To investigate the canal configuration in the MB roots of maxillary first molars (n = 154)
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SkyScan 1172 (100 kVp, 100 μA, voxel size: 15.9 μm)
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73.4 % roots presented additional canals. 94 roots had two canals and 19 roots had three or more canals. The most prevalent configurations were Weine’s types III (32.8 %), II (23 %), and IV (15 %). Using Vertucci’s classification, the most common configurations were types II (23 %), IV (19.5 %), VI (13.3 %), III (10.6 %), V (9.7 %), VII (5.3 %), and VIII (0.9 %). Twenty (17.7 %) roots had 12 new configuration types
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Lee et al. 2006 (South Korea) [165]
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To evaluate the root canal curvature in maxillary first molars (n = 46)
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SkyScan 1072 (n.r., voxel size: 19.5 × 19.5 × 39.0 μm)
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Curvatures were most pronounced in the MB canals, moderate in the DB canals, and least in the P canals. Accessory canals within the apical third were present in almost half of the MB canals and nearly a quarter of the DB canals. The curvatures increased in the apical third when accessory canals are present, particularly in MB and DB canals
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Meder-Cowherd et al. 2011 (USA) [166]
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To evaluate the apical morphology of the palatal canal of maxillary first and second molars (n = 40)
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Siemens Micro-CAT II (n.r. voxel size: n.r.)
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65 % of the specimens had no constriction in the apical 1–3 mm, while the 35 % had a constriction. The morphology frequencies of apical constrictions were parallel (35 %), single (19 %), flaring (18 %), tapered (15 %), and delta (12 %)
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Park et al. 2009 (South Korea) [167]
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To investigate the canal configuration of the MB root of maxillary first molars (n = 46)
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SkyScan 1072 (n.r., voxel size: 19.5 × 19.5 × 39 μm)
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65.2 % of the roots had 2 canals, 28.3 % had 1 canal, and 6.5 % had 3 canals. The most common configuration was type III (2 distinct MB canals; 37 %) followed by types I (single canal; 28.3 %), II (2 MB canals that joined; 17.4 %), IV (1 MB canal that split into 2; 10.9 %), and V (3 canals; 6.5 %)
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Somma et al. 2009 (Italy) [168]
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To investigate the canal configuration of the MB root of maxillary first molars (n = 30)
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SkyScan 1072 (100 kVp, 98 μA, voxel size: 19.1 × 19.1 × 38 μm)
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80 % of the roots had 2 canals. An independent canal was observed in 42 % of roots. Communications between canals were found mainly in the coronal and middle thirds, while accessory canals and loops were mainly found in apical third. In 5 teeth (21 %), a second canal had its origin some distance down the orifice. Isthmus and intercanal connections were observed in different regions of the same root. A single apical foramen was found in 37 % of the samples, while 2 foramina were present in 23 % of the samples. Three separated apical foramina and apical delta were present in 20 % of the samples
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Verma and Love 2011 (New Zealand) [169]
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To investigate the canal configuration of the MB root of maxillary first molars (n = 20)
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SkyScan 1172 (80 kVp, 85 μA, voxel size: 11.6 μm)
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Multiple foramina and accessory canals were found in 17 roots. Types II and III (Weine’s classification) were the most prevalent configuration; however, 40 and 30 % of the roots had configurations that could not be classified by Weine’s or Vertucci’s classification systems, respectively. Intercanal communications were found in 55 % of the roots located in all areas of the roots. In 18 roots with multiple canals, two had completely independent MB canals. Two roots had three canals with separate orifices, while 14 roots had two canals that either joined into one canal, or one canal divided into two or multiple canals, or showed multiple intercanal communications
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Versiani et al. 2012 (Brazil) [67]
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To investigate the canal morphology of four-rooted maxillary second molars (n = 25)
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SkyScan 1174 v2 (50 kVp, 80 μA, voxel size: 22.6 μm)
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Most of the roots presented straight with 1 main canal, except the MB root, which presented 2 canals in 24 % of the sample. No furcation canals were observed. Accessory canals were located mostly in the apical third of the roots, and apical delta was observed in 12 % of the roots. 56 % of the sample presented an irregular quadrilateral-shaped orifice configuration. The mean distance from the pulp chamber floor to the furcation was 2.15 ± 0.57 mm. No difference was observed between roots by considering their length, the configuration of the root canal in the apical third, the SMI, the volume, and the surface area of the root canals
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Yamada et al. 2011 (Japan) [170]
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To investigate the canal anatomy of the MB root of maxillary first molars (n = 90)
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HMX225 ACTIS4 (100 kVp, 75 μA, voxel size: n.r.)
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Single root canals were observed in 44.5 % of the samples, incomplete separation of root canals in 22.3 %, and completely separated canals in 33.3 %. Accessory canals were observed in 76.6 % of the samples
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