Author : Dr. Subodh sontakke MDS, Assistant Professor Department of Oral Medicine and Radiology, Nair Hospital and Dental College, Mumbai

Introduction

Radiographic examination is an essential component in the management of endodontic problems. It is required in all the aspects of endodontic treatment from diagnosis and treatment planning to assessing outcome. Until recently, most of this core information was obtained only from conventional radiographs. The amount of information gained from traditional film and digitally captured periapical radiographs is limited by the fact that the three dimensional anatomy of the region is shown as a two dimensional image. Periapical radiographs reveal limited aspects of the three-dimensional anatomy as a result of superimposition. In addition, there may also be geometric distortion of the anatomical structures being imaged1 .The limitations of periapical radiograph were overcome by CT images, but at high radiation dose, high cost, availability, poor resolution, difficulty in interpretation & poor communication between the endodontist and radio-technician which have resulted in limited use of CT imaging in endodontics. Cone Beam Computed Tomography (CBCT) gives alternative imaging modality to CT for studying the morphology of roots and root canals and more at low radiation, high resolution and low cost 2,3.

Cone beam computed tomography utilizes an extraoral imaging scanner which was developed in the late 1990’s to produce three-dimensional scans of the maxillo-facial skeleton at a considerably lower radiation dose than conventional computed tomography (CT) 4. The conical beam computed tomography (CBCT) technique presents an innovation of tomographic imaging systems and subsequent volumetric image reconstruction for dentistry. The field view of limited CBCT ranges in diameter from 40-100 mm and the voxel size is generally smaller (0.1-0.2mm).  Thus limited CBCT systems offer higher resolution and are better suited for endodontic applications 5.

Following are some cases illustrating the role of CBCT in endodontics

Case 1

A patient came with a complaint of persistent, poorly located discomfort from his upper left posterior teeth. Tooth 25 was heavily restored, no cracked tooth was suspected in the region and the opposing dentition. The periapical radiograph showed radiolucency in the coronal portion approaching pulp beneath the radiopaque material with a slight widening of periodontal ligament space in the apical region with 25 (figure 1A).  The CBCT images of the same patient revealed a confirmed periapical lesion. The CBCT images showed the lesion was larger in extent than appreciated on periapical radiograph (figure 1B &C).

Case 2

A patient reported with a complaint of missing teeth in the lower anterior region. The periapical radiograph in this case showed congenitally missing 31 and 41. The root of 33 was bifid with 2 root canals.  Single root was seen with 32 (figure 2A). The CBCT was taken to evaluate the morphology of roots and root canals of 32 and 33. The CBCT axial images  revealed bifid roots of 32, 33 with 2 root canals and was classified as Weine’ Type IV canal. (figure 2B,C &D). An incidental findings was of two root canals in 42 which were fused in the apical portion terminating in one apical opening (vertucci’s Type II canal)

Case 3

A patient reported with a chief complaint of spontaneous toothache in his right posterior maxilla. From the clinical and radiographic findings, a diagnosis of symptomatic irreversible pulpitis was made and endodontic treatment was suggested to the patient. The periapical radiograph of 26 showed apical periodontitis and three roots with three root canals. During the access cavity opening multiple canals were suspected. To confirm this unusual morphology, a CBCT imaging was performed which revealed 6 canals in 26. The CBCT axial image revealed MB1 (mesiobuccal), MB2, MB3, DB1 (distobuccal), DB 2 and palatal canal (figure 3A).At various level of axial section we were able to trace the root canal to the apex.

Case 4

A patient was referred to oral medicine and radiology department with the complaint of pain in anterior region of maxilla. History of trauma was reported one day back. The panaromic image showed no pathology related to anterior maxillary region (figure 4A). CBCT was taken for further evaluation of the same region. CBCT images showed fracture line running horizontally at the middle third of root, which was missed in OPG. The coronal and sagittal views confirmed the horizontal fracture of the root (figure4B, C).

Case 5

A patient presented with discoloration of upper front tooth, with history of traumatic injury 10 years ago. Root canal treatment of the same was done 10 years back. The periapical radiograph in case of 21 showed resorption of the pulp (figure. 5 A). No evidence of perforation was seen on the periapical radiograph. The nature and bucco lingual extent of resorption cannot be determined on periapical radiograph alone. CBCT was acquired for the same patient.  The CBCT images revealed resorptive lacunae inside the pulp chamber of 21 (figure. 5 B& C). The sagittal section of CBCT depicted perforation of root on palatal side which was instrumental in treatment plan and predicting the prognosis of tooth (figure 5C).The prognosis of 21 was found to be poor and was extracted.

Case 6

A patient reported with complaint of swelling in left upper region. The OPG revealed homogenous radiolucency in periapical area in relation to 21,22 ,23,24,25 (figure 6A).The CBCT images showed the accurate size and extent of lesion ( extending up to palate, maxillary sinus and nasal  floor),expansion of the cortical plates and displacement of nasal floor (figure 6 B, C,D).  Perforation of plate was also noted.

Discussion

Earlier detection of periradicular radiolucent changes should result in earlier identification and management of endodontic disease; this in turn should result in a better outcome from endodontic treatment as teeth could be treated sooner. CBCT is a useful tool in identifying periapical lesions. Estrela C et al (2008) showed that apical periodontitis was detected more frequently when CBCT was used as compared with periapical radiograph6. The prevalence of apical periodontitis as reported Lofthag-Hansen S (2007) was found to be significantly higher when using CBCT, in comparison with periapical radiograph7,8.
CBCT can be used to determine root morphology; to measure the number of roots, canals, and accessory canals, whether they converge or diverge from each other and also to establish their working lengths and angulations. CBCT is very useful in the teeth with anatomic variation root and crown as shown in (figure 2C). Unidentified and untreated root canals may be identified using axial slices, which may not be readily identifiable with periapical radiographs9. Here the overlapping of root canals in periapical radiographs is overcome. Blattner TC10 et al(2010) reported that CBCT is useful in study of variation in the tooth morphology and identification of MB2 canal. The location of MB1 and MB2 can be determined accurately with CBCT (figure 3).Precaution can be taken knowing the position of root canal within root to prevent perforation10.
Root fractures are sometimes difficult to detect with conventional methods like periapical radiographs and OPG due to superimposition and distortion of image (figure 4A) .The fracture line is only evident on the radiographs like periapical radiographs or OPG when the X rays pass through the fracture line. It is recommended to take radiographs with different angulations to see fracture line. In CBCT this limitation is overcome irrespective of the orientation of fracture line it will be evident in three dimensional images.
CBCT is considered superior to periapical radiographs in the detection of fractures in vertical, buccolingual or mesiodistal directions, in the detection of horizontal root fractures (N. Cohenca, J. H. Simon,2007)11.CBCT may also prove useful in the diagnosis of dento-alveolar trauma, because the exact nature and severity of alveolar and luxation injuries can be accessed from just one scan11, 12. As illustrated (figure 4 B,C &D) the CBCT was more informative and reliable than periapical radiographs.

CBCT is able to detect lesions in cases of root resorption, whereas conventional 2D x-rays cannot detect them in early stage. The resorption of tooth, external or internal, cannot be differentiated on periapical radiographs or OPG as reported in figure 5A. The treatment plan differs with the type of resorption. CBCT is able to detect lesions and differentiate between external and internal resroption13. CBCT (figure 5B,C)not only detects the presence of resorption, but also its extent and presence of perforation, which can assist in making right treatment plan.

CBCT is a reliable tool for the pre-surgical assessment of the tooth, periodontal structure and proximity of the tooth to adjacent vital structures. The true size, location and extent of periapical lesion (figure 6B C,D) can be appreciated with reliability14. It also gives approximation of lesion with the apices of adjacent teeth to determine presurgical prophylactic root canal of adjacent teeth. CBCT may play an important role in planning for periapical microsurgery on the palatal roots of maxillary first molars as reported by Rigolone M et al (2003)15.

Conclusion: Conventional intraoral radiography provides clinicians with cost-effective, high-resolution imaging that continues to be the front-line method for dental imaging. However, CBCT is very useful in many specific situations in endodontia where the 3-D images facilitates the diagnosis that leads to a better treatment plan as compared to the conventional radiography.  CBCT is a valuable imaging modality, producing minimal radiation exposure to the patient and providing maximal information to the endodontist.

REFERENCES

1. Gro¨ ndahl H-G, Huumonen S Radiographic manifestations of periapical inflammatory lesions. Endodontic Topics 2004; 8:55–67.
2. A. G. Farman, C. M. Levato, and W. C. Scarfe, “A primer on cone beam computed tomography,” Inside Dentistry 2007;3: 90–92.
3. Scarfe C, Farman AG, Sulovic P. Clinical applications of cone beamcomputed tomography in dental practice. J Can Dent Assoc. 2006; 72: 75-80.
4. Mozzo P, Procacci C, Tacconi A, Martini PT, Andreis IA. A new volumetric CT machine for dental imaging based on the cone-beam technique: preliminary results. European Radiology 1998;8: 1558–64.
5. Taylor P. Cotton, Todd M. Geisler, David T. Holden, Scott A. Schwartz, William G. Schindler. Endodontic Applications of Cone Beam Volumetric Tomography. J Endod.2007; 33:1121-32.
6. Estrela C, Bueno MR, Leles CR, Azevedo B, Azevedo JR. Accuracy of cone beam computed tomography and panoramic radiography for the detection of apical periodontitis. J Endod 2008;34:273-9.
7. Lofthag-Hansen S, Huumonen S, Gro¨ ndahl K, Gro¨ ndahl H-G (2007) Limited cone-beam CT and intraoral radiography for the diagnosis of periapical pathology. Oral Surgery, Oral Medicine, Oral Pathology,Oral Radiology and Endodontology 2007; 103: 114–9.
8. Friedman S. Prognosis of initial endodontic therapy. Endodontic Topics 2002; 2:59–98.
9. Cotton TP, Geisler TM, Holden DT, Schwartz SA, Schindler WG. Endodontic applications of cone beam volumetric tomography. J Endod 2007;33: 1121-32.
10. Blattner TC, George N, Lee CC, Kumar V, Yelton CD. Efficacy of cone beam computed tomography as a modality to accurately identify the presence of second mesiobuccal canals in maxillary first and second molars: A pilot study. J Endod 2010; 36:867–70.
11. N. Cohenca, J. H. Simon, R. Roges, Y.Morag, and J.M.Malfaz, “Clinical indications for digital imaging in dento-alveolar trauma—part 1: traumatic injuries,”Dental Traumatology.2007; 23 : 95–104.
12. S. Patel and A. Dawood, “The use of cone beam computed tomography in the management of external cervical resorption lesions,” International Endodontic Journal 2007; 40: 730–737.
13. E. Kim, K.-D. Kim, B.-D. Roh, Y.-S. Cho, and S.-J. Lee “Computed tomography as a diagnostic aid for extracanal invasive resorption,” Journal of Endodontics 2003; 29: 463–465.
14. Use of Cone Beam-Computed Tomography in Endodontics. Joint Position Statement of the American Association of Endodontists and the American Academy of Oral and Maxillofacial Radiology 2010.
15. Rigolone M, Pasqualkini D, Bianchi L, Berutti E, Bianchi SD. Vestibular surgical access to the palatine root of the superior first molar: low-dose cone beam CT analysis of the pathway and its anatomic variations. J Endod 2003;29: 773-5.

LEGENDS

Figure 1
Fig 1A: IOPA shows widening of apical Periodontal ligament space
Fig 1B & 1C: Oblique section and coronal section showing apical lesion larger than evident in IOPA

Figure 2
Fig.2A  : IOPA shows bifid roots and two canals in 33 and one root canal in 32.
Fig 2B: Axial section at cervical level of teeth shows cross section of lower anterior teeth with single root canal.
Fig.2C: Axial section showing cross section at mid root level with 2 roots in 32,33 and 2 root canals in 32,33,42.
Fig 2D: axial section at root apices level showing single canal with 42 (vertucci’s Type II canal )and 2 canal with 32 and 33.

Figure 3
Fig 3A:Axial section at pulpal floor level showing multiple root canals (six) that are MB1,MB2,MB3,DB1,DB2 and palatal.
Fig 3B: Axial section at mid root level showing fusion of root canals resulting in four canals.
Fig 3C: Axial section at apices level showing fusion of canals resulting in three canals.


Figure 4
Fig 4A:- Cropped OPG shows no evidence of fracture or any other pathology.
Fig 4B &Fig 4C: Sagittal section & coronal section of the region showed fracture 21 in mid root level.


Figure 5
Fig 5A: IOPA shows radiolucency in the pulp region causing resorption of pulpal wall, without perforation on mesial or distal wall
Fig 5B: Coronal section shows internal resorption of 11.
Fig 5C: Sagittal section shows internal resorption with perforation on palatal surface of root.


Figure 6
Fig. 6A: OPG shows well defined radiolucency in anterior region.
Fig 6 B axial section at mid root level showing the extension of cyst, palatal perforation of cyst .Fig. 6C: axial section at apices level showing palatal perforation by cyst and buccal expansion. Fig. 6D: axial section above the level of apices shows displacement of nasal cavity and expansion of buccal cortical plate.