Morphological measurements of two separate mesiobuccal canals in maxillary first molars using micro-computed tomography

Objectives

To obtain radicular measurements of two separate mesiobuccal (MB) root canals in maxillary first molars using micro-computed tomography (μCT) with customized software.

Materials and methods

Human maxillary first molar MB roots (N = 36) with two separate canals (MB1, MB2) and apical foramina were scanned by μCT and analyzed with Kappa2 software to reconstruct three-dimensional (3D) surface models of roots and canals. These models were sectioned at 0.1 mm intervals perpendicular to the central axis of each canal. Canal widths, 3D curvatures, and surrounding dentine thicknesses were measured concurrently on each section. Dentine thicknesses were analyzed statistically for differences between each direction and the different levels of both canals.

Results

Dentine walls around MB1 were thicker than MB2 (p < 0.05). Thinnest dentine was most often located at disto-inside direction in both canals. Canal widths were significantly smaller in MB2 than MB1 (p < 0.01). Apical constrictions were smaller (p < 0.05) and further (p < 0.05) from the apex in MB2 than MB1. Canal curvatures were greatest in the apical third of both canals (p < 0.001), and they were greater in MB2 than MB1 (p < 0.05).

Conclusions

MB2 canals had shorter lengths, smaller widths, and more severe curvatures and were surrounded by thinner dentine walls. In MB2, apical constrictions were between 1 and 2 mm from the apex, compared to about 1 mm for MB1.

Clinical relevance

These detailed measurements and in-depth 3D analyses of maxillary first molar MB roots with two separate canals and apical foramina provide morphologic references for root canal therapy.

     

Root canal morphology of the mesiobuccal root of maxillary first molars: a micro-computed tomographic analysis

Aim  To investigate ex vivo , the root canal morphology of the MB root of maxillary first molar teeth by means of micro-computed tomography.
Methodology  Thirty extracted intact human maxillary first molar teeth were selected for micro-tomographic analysis (SkyScan 1072, Aartselaar, Belgium) with a slice thickness of 38.0 μm. The following data regarding the MB root were analysed and recorded: number and type of root canals, prevalence of isthmuses, prevalence of intercanal connections, presence of accessory canals, presence of loops and number of apical foramina.
Results  The MB2 canal was present in 80% of specimens and was independent in 42% of these cases. When present, the MB2 canal merged with the MB1 canal in 58% of cases. Communications between the two canals were found in all specimens, with isthmuses in 71% of the cases. These communications and isthmuses were respectively in 42% and 54% of the cases in the coronal third, in 59% and 79% of the cases in the middle third and in 24% and 50% of the cases in the apical third. A single apical foramen was found in 37% of specimens, two apical foramina were present in 23% of the cases, with three or more separate apical foramina occurring in 40% of the specimens.
Conclusions  The MB root canal anatomy was complex: a high incidence of MB2 root canals, isthmuses, accessory canals, apical delta and loops was found.     

Morphometric study of the apical anatomy of C-shaped root canal systems in mandibular second molars

AIM: To investigate the apical anatomy of C-shaped canal systems in mandibular second molars by micro-computerized tomography (microCT) and stereomicroscopy. METHODOLOGY: Forty-four permanent mandibular second molars with a C-shaped root canal systems from a native Chinese population were scanned at 100 microm intervals by microCT at a resolution of 30 x 30 microm. The apical 5 mm of each tooth was reconstructed three-dimensionally for visualization and classification of the canal configuration using Vertucci's criteria. The main and auxiliary (accessory) foramina were examined under a stereomicroscope. RESULTS: Type IV and VIII canal configurations were most often found in the apical 5 mm of these canal systems. The prevalence of accessory canals, lateral canals, inter-canal communications and apical delta were 41%, 25%, 27% and 11%, respectively. Approximately 80% of C-shaped canals had 1-3 apical foramina; the prevalence of accessory foramina was about 48%. The mean distance between the main foramen and the anatomic root apex was 0.84 mm, and that between the accessory foramen and the apex was 1.61 mm. The mean (shortest and longest) diameters of major and accessory foramina were 0.19 - 0.32 mm and 0.07 - 0.10 mm, with a mean form factor of 0.73 and 0.82, respectively. CONCLUSION: The apical anatomy of C-shaped root canal systems in mandibular second molars is extremely complex with many anatomical variations.     

上颌第一磨牙根管系统的研究

目的 观察上颌第一磨牙的根管系统。方法 制备50个上颌第一磨牙透明牙标本,显露根管系统的空间构型,在体视显微镜下观察并记录根管系统的形态,结合应用加以统计。结果 ①上颌第一磨牙近中颊根单根管率为66%,其中Ⅰ型占38%,双根管率为34%,远中颊根Ⅰ型占74%,腭根Ⅰ型占94%。②根管侧支、根尖分歧、根尖分叉多见于近颊根,在近颊根的发生率为40%, 远颊根的发生率为24%,腭根的发生率为6%,发生部位多见于根尖1/3。结论 上颌第一磨牙近颊根的根管系统最为复杂,根管变异较远颊根多,腭根变异最少。     

Anatomic determination of the mesiobuccal root resection level in maxillary molars

Surgical endodontics involving root resection/apical fill are often performed when retreatment by orthograde endodontic procedures are not possible. Because of the potential presence of accessory canals within the root, a preferred minimal root resection level should be investigated for the removal of the majority of these canals. One hundred fifty-three extracted, uninstrumented, mesiobuccal roots from first and second maxillary molars were examined for the presence of accessory canals, canal isthmus, and canal wall thickness. Three hundred ninety accessory canals were identified, with 80% of these canals located within 3.64 mm of the apex of the tooth. Canal isthmus was often not evident until 3.12 mm of the root was resected, with canal wall thickness only approximating 1 mm thick. The observations here suggest a minimal resection level to 3.6 mm for accessory canal incidence, canal isthmus detection, and canal wall thickness and provide a better understanding of maxillary mesiobuccal (MB) root anatomy for retrograde root resection/apical filling.     

Root and root canal variations of the human maxillary and mandibular third molars in a Chinese population: A micro–computed tomographic study

ObjectivesTo investigate the anatomical variations of the root and root canal configuration of the human third molars.DesignsA total of 130 maxillary and 130 mandibular third molars were collected from a native Chinese population. All teeth were scanned by micro–computed tomography. After 3D reconstruction, the root and canal morphology of each tooth was examined both qualitatively and quantitatively.ResultsFor maxillary molars, a single fused root (67 cases, 51.5%) and a single root canal system (64 cases, 49.2%) was most common root/canal form; the typical three-rooted molars were detected only in 33 cases (25.4%), and the secondary MB canals were detected only in 9 molars (6.9%). For mandibular molars, 62 teeth were single-rooted (47.7%) and 42 had a single root canal system (32.3%); 20 singled-rooted and 60 double-rooted molars exhibited independent mesial and distal root canal systems (61.5%), and the type 1-1 canal was the most common configuration for mesial (57 cases) and distal (81 cases) root canal systems. C-shaped canals were detected in 11 maxillary and 36 mandibular single-rooted molars. The mean root surface area, root and crown volume of mandibular third molars were significantly higher than the maxillary third molars (P < 0.01).ConclusionThe root canal system of the third molars may exhibit several anatomic variations. Whereas in most of cases, the degree of the canal differentiation was at a low level, and the canal form was not complicate.     

Root and canal morphology of Burmese maxillary molars

AIM: To investigate the root and canal morphology of Burmese maxillary molars using a canal staining and tooth clearing technique. METHODOLOGY: Maxillary molars (239) were collected from indigenous Burmese patients and designated; first (90), second (77), third (72) molars. Following pulp tissue removal and canal system staining with Indian ink, the teeth were decalcified with 10% nitric acid, dehydrated and cleared with methyl salicylate. The following features were evaluated: (i) number of roots and morphology; (ii) number of canals per root: (iii) root canal configuration (Vertucci's classification); (iv) number of apical foramina per root; (v) number and location of lateral canals; and (vi) the presence of intercanal communications. RESULTS: All first and second molars had three separate roots, whilst third molars had one of five different root forms, of which three separate (25%) or fused (31%) roots were most prevalent. The majority of palatal (100%) and disto-buccal (96%) roots possessed one canal (type I). The prevalence of mesio-buccal roots with two canals decreased from first to third molars (68%, 49%, 39%, respectively); type II (two orifices, one apical foramen) and IV (two orifices, two apical foramina) configurations were the most common. Single/fused rooted third molars had a range of number and type of canals. Most roots in all molars had one apical foramen, those with four apical foramina were confined to third molars. Intercanal communications were most prevalent in mesio-buccal roots and two/three fused rooted third molars. Lateral canals were most prevalent in the apical third of the roots of all molars. CONCLUSIONS: The mesio-buccal roots of Burmese maxillary molars possessed a variety of canal system types. Over 50% of the first and second molars had a second mesio-buccal canal, of which over 20% had intercanal communications. The palatal and disto-buccal canals mainly had type I canals. Lateral canals were equally prevalent in all tooth types but were most common in the apical third.     

Two canals in mesiobuccal roots of maxillary molars

The purpose of this study was to examine extracted root canal treated maxillary molars cleared for: (i) the presence of a mesiopalatal (MP) canal in both first and second molars, (ii) the extension of MP canal from the pulp to the apical area, and (iii) the incidence of two foramina in the MB root. Seventy-two extracted maxillary molars (42 first and 30 second molars) were root canal treated by graduate students. The mesiobuccal (MB) roots of these samples were rendered transparent using a clearing technique. The results demonstrated that 52.3% of first and 40% of second molars had two canals obturated in the MB root. After clearing the same roots, the presence of MP canals rose to 80.9% and 66.6%, respectively. The MP canals were root canal treated as far as the foramen in 35.2% of first and 35% of second molars. However, after making them transparent, 91.1% and 90% showed the presence of this canal to the anatomical apex. The MB roots of the root canal treated first molars showed the presence of two foramina in 47% of cases but in 88.2% after clearing. The second molars showed 50% and 70%, respectively. The differences between root canal treated teeth before and after clearing were significantly different in almost all comparisons in both first and second molars. The only exception was when the presence of two foramina was compared before and after the clearing process in second molars (McNemar test P < 0.05).     

Dentin Thickness at Danger Zone and Canal Morphology of Maxillary Molars

ObjectivesDentin thickness in concave areas of the root creates risk for complications such as strip perforation during endodontic treatment. The study aims to examine dentin thickness of the danger (DZ) and safety zone (SZ), canal configuration, and the presence of isthmus in the mesiobuccal root of maxillary molars.Material and MethodsCone-beam Computed Tomography (CBCT) images of 1251 teeth belonging to 642 patients were retrospectively reviewed. The dentin thicknesses at DZ and SZ in maxillary molars with one (MB) or two mesiobuccal canals (MB1, MB2) were measured at the 3 mm apical to the furcation level. Vertucci''s canal configurations and the isthmus rate were recorded. The Chi-square test andThe Student’s t-test were performed.ResultsMB2 rate was higher in maxillary first molars (61.68%) than second molars (39.36%). Isthmus rates were 27.3% and 44.11% in first and second molars. DZ thickness was thinner than the dentin thickness in the SZ in both first and second molars with one or two mesial canals (p< 0.05). In teeth with single canal, the mean DZ thickness was 0.88mm. In teeth with two canals, the mean DZ thicknesses were 0.83mm and 0.80mm for MB1 and MB2 canals, respectively.ConclusionMB2 rate was higher in the first molar (61.68%), and the isthmus rate was higher in the second molar (44.11%). DZ and SZ were thinner in MB2 than in MB1 at the maxillary molars with two mesial canals. The results indicated that more conservative preparation must be applied to the MB2 canal in the maxillary molars.     

Root canal morphology of the mesiobuccal root in maxillary first molars of a Jordanian population

This in vitro study investigated the presence of second (MB2) root canals and the number of apical foramina found in mesiobuccal roots of the permanent maxillary first molars; in addition, the study evaluated the effectiveness of magnification to detect MB2 canals. One hundred extracted maxillary first molars were collected from Jordanian patients. The number of roots (as well as their morphology) was investigated. The number of canal orifices in mesiobuccal root was assessed, with and without magnification, and findings were compared. The number of apical foramina and the distance between mesiobuccal and second canal orifices were investigated under magnification. Of the 97 specimens that were subject to additional investigation, all teeth had three separated roots, except for three specimens that had either mesiobuccal or distobuccal roots fused with the palatal root. The number of MB2 canals that were detected increased from 55 (56.7%) to 61 (62.9%) teeth when magnification was used. Within the limits of this in vitro study, it was concluded that the Jordanian population had a high percentage of MB2 canals in the mesial buccal roots. Moreover, the use of clinically used magnifying devices increased the number of MB2 canals detected.     

Root canal anatomy of maxillary first and second permanent molars

AIM: The aim of this investigation was to study the root canal anatomy of maxillary first and second molar teeth from an Irish population sample using a clearing technique. METHODOLOGY: Eighty-three extracted permanent maxillary right first molars and 40 permanent right maxillary second molars were included in this investigation. The specimens were demineralized and then cleared using methyl salicylate. The following observations were made: number of roots, prevalence of fusion, types of root canals using Vertucci's classification, presence and position of lateral canals, presence and position of transverse anastomoses, number and position of apical foramina and the frequency of occurrence of apical deltas. RESULTS: Eleven per cent of maxillary first molars and 43% of maxillary second molars had fused roots. A total of 78% of mesiobuccal roots in maxillary first and 58% in maxillary second molars had two canals. Sixty-two per cent of maxillary first and 50% of maxillary second molars had two apical foramina. There was a significant inverse relationship between age and the occurrence of two canals and between age and the occurrence of transverse anastomoses in both tooth morphotypes (P < or = 0.05). CONCLUSIONS: It is concluded that a significant proportion of the first and second molar specimens studied had two canals in the mesiobuccal root (78% and 58%, respectively) and that the occurrence of two canals and transverse anastomoses decreased significantly with increasing age.     

Safety of large preparation with different instruments in the buccal canals of maxillary molars

This study aimed to evaluate the influence of large apical preparations with Reciproc (REC), Hyflex CM (HCM) and Twisted File Adaptive (TFA) systems using micro‐computed tomography (MCT). Ninety mesiobuccal (MB) and distobuccal (DB) root canals of maxillary molars (n = 45) were scanned using MCT before and after the shaping procedures. The root canals (n = 15) were prepared until REC 40.06, HCM 40.04 and TFA 35.04. The root canal transportation (RCT), centring ability (CA), change in volume of the root canal and at different levels (VC), remaining dentine thickness (RDT), removal of dentine wall (RDW) and working time (WT) were evaluated. Data were analysed using the Kruskal–Wallis and Dunn tests, and the one‐way ANOVA and Tukey tests with a level of significance set at 5%. No significant difference among the instruments was found regarding the RCT, CA, RDT, RDW and WT (P > 0.05), in larger apical preparations in curved MB and straight DB canals of maxillary molars.     

Anatomic Analysis of Palatal Roots of Maxillary Molars Using Micro–computed Tomography

IntroductionThe morphology of the palatal root of maxillary first and second molars was analyzed and compared using micro–computed tomographic scanning.MethodsForty-seven extracted maxillary molars were scanned with a micro–computed tomographic device to analyze the palatal radicular dentin dimensions, canal working width, root length, canal curvature, lateral canals, and apical constriction anatomy. Quantitative data were analyzed with mean and standard deviation for first and second molars, respectively. Comparison was made between first and second molars using an unpaired t test.ResultsThe palatal root of maxillary first molars was found to have statistically significantly thinner dentin than second molars on the palatal aspect of the root 8–11 mm from the apex, correlating to the coronal and middle thirds of the root. First molar palatal roots also had a statistically significantly wider canal mesiodistally than second molars at 13–15 mm from the apex, correlating approximately to the level of the cementoenamel junction and pulpal floor. Significant canal curvature was present. These findings suggest the need for conservative coronal flaring and instrumentation.ConclusionsThe absence of an apical constriction in 76.6% of the specimens highlights the importance of creating an apical seat through instrumentation to maintain obturation materials. A minimum master apical file size of 40 is recommended based on preoperative working widths in the apical 0.5–1.0 mm. A root-end resection of 3.5 mm would remove a greater majority of lateral canals.     

Root Canal Morphology of Permanent Maxillary Teeth in the Han Nationality in Chinese Guanzhong Area: A New Modified Root Canal Staining Technique

IntroductionThe purpose of this study was to investigate the canal morphology of 504 maxillary permanent teeth of subjects of Han nationality in Chinese Guanzhong area.MethodsMaxillary permanent teeth were randomly collected in Guanzhong area. After regular preparation, the teeth were immersed into ink without preparing access cavities and then put into hyperbaric oxygen chamber (0.6 Mpa) for 2 hours to let the ink penetrate into root canal from apical foramen, apical deltas and foramen of lateral canals under stable positive pressure. After demineralization and clearing, the following observations were made: (1) number of root canals, (2) root canal configuration by using Vertucci's classification, (3) presence of lateral canals, and (4) frequency of apical deltas.ResultsAll the teeth were well-stained, and the fine details were well-revealed. Apical deltas (12.2%–83.3%) and lateral canals (13.7%–68.8%) could be frequently found in all types of maxillary teeth. Most of central incisors (95.8%), lateral incisors (91.4%), and canines (75.4%) displayed type I canal configuration, whereas most of first premolars (87.3%) and second premolars (72.3%) possessed 2 canals with type II, IV, or VI canal configuration. The majority of distobuccal roots and palatal roots of first molars (88.9%, 97.8%), second molars (92.0%, 94.0%), and third molars (87.5%, 91.6%) possessed type I canal configuration. The prevalence of mesiobuccal roots with type I configuration was 66.7% in maxillary first molars, 82% in second molars, and 62.5% in third molars.ConclusionsThe modified technique of canal staining can effectively reveal detailed root canal system. The canal configuration of maxillary teeth in subjects of Han nationality in Chinese Guanzhong area is consistent with previous reports in other races.     

Three-dimensional imaging using microcomputed tomography for studying tooth macromorphology

BACKGROUND: The authors conducted a study to demonstrate potential applications of microcomputed tomography (microCT) in the analysis of tooth morphology. METHODS: The authors selected for microCT analysis five maxillary first molars with a second canal in the mesiobuccal (MB) root, five mandibular first molars with a mesial root possessing a considerable curvature and five single-canal premolars with complicated apical anatomy. The hardware device used in this study was a desktop X-ray microfocus CT scanner (SkyScan 1072, SkyScan bvba, Aartselaar, Belgium). RESULTS: The authors obtained a three-dimensional image from each of the 15 teeth. In three cases, the MB canals coalesced into one canal, while in the other two molars the canals were separate. Four of the five mandibular molars exhibited a single canal in the mesial root, which had a broad, flat appearance in a mesiodistal dimension. In the premolar teeth, the canals were independent; however, the apical delta and ramifications of the root canals were obvious, yet intricate. CONCLUSIONS: MicroCT offers a reproducible technique for 3-D noninvasive assessment of root canal systems. CLINICAL IMPLICATIONS: While this technique is not suitable for clinical use, it can be applied to improve preclinical training and analysis of fundamental procedures in endodontic and restorative treatment.     

Deviations of Mesial Root Canals of Mandibular First Molar Teeth at the Apical Third: A Micro–computed Tomographic Study

Introduction

The present study aimed to quantitatively analyze apical foramen deviations of mesial root canals of mandibular first molar teeth by means of micro–computed tomographic (micro-CT) imaging.

Maxillary Molars With Morphologic Variations of the Palatal Root Canals: A Report of Four Cases

IntroductionThe purpose of this article was to show the importance of the knowledge of the anatomy of root canals. Unusual root and root canal morphologies associated with both buccal roots of upper molars have been recorded in several studies in the literature. However, scientific information focusing on variations of the palatal root is rare.MethodsIn this report, four cases are presented involving the root canal treatment of maxillary first and second molars with unusual morphologic configurations of the palatal root canals.ResultsDuring root canal treatment, type IV and V configurations as defined by Vertucci of the palatal canals of two first and two second maxillary molars were identified. After mechanical instrumentation, the canals were obturated. Radiologic and clinical re-evaluation showed no signs of inflammation.ConclusionsThis report describes and discusses the possibility of different root and canal variations of the maxillary molars from a clinical point of view. Anatomic variations can occur in any tooth, and palatal roots of maxillary first and second molars are no exception. Therefore, careful examination of radiographs and internal anatomy of teeth is essential.     

Apical anatomy in mesial and mesiobuccal roots of permanent first molars

The purpose of this in vitro study was to investigate the canal configuration types, and the prevalence and location of anatomical variations in the mesiobuccal (MB) and mesial roots of permanent maxillary and mandibular first molars after instrumentation. The number and the type of canals were determined before instrumentation using conventional methods. All root canals from the 47 MB roots and 42 mesial roots were then instrumented to size #30 with ProFile .04 taper rotary instruments in a crown-down method and then filled with a single gutta-percha cone and sealer. Transverse 1 mm-thick cross-sections at 2, 3, 4, and 5 mm from the apex were obtained, stained and examined using a stereomicroscope. The canal configuration types and the prevalence and location of isthmi and accessory canals in roots with two canals were evaluated. The prevalence of two canals was 80.8% in the maxillary MB roots and 95.2% in the mandibular mesial roots. There were six types of canal configurations in the instrumented root apices. The prevalence of anatomical variations was highest at the apical 4 mm level, and was more frequent in mandibular first molars, and in roots with Weine type III canal. chi test showed that the prevalence of the anatomical variations was statistically higher in the maxillary MB roots with Weine type III canals than in those with Weine type II canals (p < 0.05). Different canal configurations were often found at different levels in the same root. The results indicate that anatomical variations persist following instrumentation of roots with two canals in first molars. These anatomical variations should be considered during surgical or nonsurgical endodontic procedures of the permanent first molars.     

Root and canal morphology of Thai maxillary molars

AIM: To investigate the root and canal morphology of 268 maxillary permanent molars collected from an indigenous Thai population. METHODOLOGY: The cleaned teeth were accessed, the pulp dissolved by sodium hypochlorite under ultrasonication, and the pulp system injected with Indian ink. The teeth were rendered clear by demineralization and immersion in methyl salicylate. The following observations were made: (i) number of roots and their morphology; (ii) number of root canals per root; (iii) root-canal configuration in each root using Vertucci's classification with additional modifications; and (iv) presence and location of lateral canals and intercanal communications. RESULTS: All the maxillary first and second molars had three separate roots. Only, half (51%) of the maxillary third molars had three separate roots; the other half had fused or conical roots. The majority of the distobuccal (98.1-100%) and palatal (100%) roots had type I canals. Over half of the mesiobuccal roots of first (65%) and second (55%) molars had two canals. The most common (44.2%) canal configuration in mesiobuccal roots of first molars was type IV (two canals, two foramina). A variety of canal types were found in the mesiobuccal roots of second molars. Maxillary third molars showed the greatest diversity of canal morphology. There was an increase in the prevalence of lateral canals towards the apical part of the roots and intercanal communications were present in 16% of each of first, second and third Thai maxillary molars. CONCLUSIONS: The mesiobuccal roots of Thai maxillary molars possessed a variety of canal system types. Over 50% of the first molars had a second mesiobuccal canal. The palatal and distobuccal canals mainly had type I canals. Only, a small proportion (7.3-13.3%) of the roots exhibited lateral canals which were the most common in the apical third     

Detection of the second mesiobuccal canal in mesiobuccal roots of maxillary molar teeth ex vivo

AIM: To assess the effectiveness of magnification and dentine removal (troughing) when locating the second mesiobuccal canal in mesiobuccal roots of maxillary molars. METHODOLOGY: A total of 208 extracted human maxillary molars were examined. After crown and pulp removal, the MB1 and 2 canals in the mesiobuccal root were located in three stages that were performed by two undergraduate dental students. Stage 1: canals were located with an endodontic explorer; stage 2: additional canals in the same teeth were located under magnification with a digital microscope (VH-8000, Keyence, Japan); stage 3: additional canals in the same teeth were located by removing dentine (troughing) from the pulp chamber floor within 3 mm from MB1 canal towards the palatal canal with an Enac ultrasonic tip (ST 21, Osada, Japan). In each group, the canals were prepared with Gates Glidden burs and K-files. The distal and palatal roots were then removed, and Indian ink was injected into the canal system within the mesio-buccal root. The root surfaces were washed with 6% NaOCl, and then rendered transparent to observe canal morphology. The root canal configurations were classified into five categories following the modified Weine's classification. RESULTS: More than one canal in the mesio-buccal root was observed in 48% of specimens. Detection rates of multiple canals were 7, 18 and 42% following stages 1, 2 and 3, respectively. There was a significant difference between the stages for detecting the MB2 canal (P < 0.05, Friedman test). CONCLUSIONS: Both magnification (stage 2) and dentine removal under magnification (stage 3) were effective in detecting the presence of the MB2 canal. However, MB2 canals could not be detected in 13% of the teeth because of canal calcification or branching located more apically.