The significance of radiographs in endodontic therapy
The success of any endodontic therapy depends on adequate chemical and mechanical debridement of the infected root canal. This requires basic knowledge of the canal anatomy and the ability to identify any aberration in it. Studies have shown that micro-organisms in the root canal system reside in the main canal, the canal’s ramification, the accessory or lateral root canal, and even the dentinal tubules. Therefore, optimal debridement can only be achieved if the clinician is able to identify the presence of additional canals prior to or during treatment (Table 1).
Currently, the only method available to assess the root, the root canal anatomy and its periradicular area preoperatively is through dental radiographs. Whether radiographs are performed intra-orally (periapical) or extra-orally (dental panoramic tomogram or cone beam computed tomography, CBCT), fractures, resorptive defects or procedural errors can also be identified this way. Thorough examination of radiographs is important, as it can provide an indication of the complexity of the treatment, including anticipated difficulties (Table 2).
The use of CBCT has been widely explored and its advantages are well documented.[1,2] While its benefits for diagnosis in endodontic treatment cannot be disputed, the American Association of Endodontists and the American Academy of Oral and Maxillofacial Radiology jointly published a statement in 2011 in which they stated that limited volume should be preferred over large volume and that this imaging technique should not be used routinely for endodontic diagnosis or for screening purposes. Furthermore, the clinician must justify that the use of CBCT will be of benefit to the patient and that its use outweighs the potential risks.
Intra-oral radiographs, such as conventional and digital periapical radiographs, are still routinely used as one of the important investigative tools during endodontic examination and the diagnosis stage. Even though it has a few limitations, an appropriately taken and processed periapical radiograph can still provide enough information and evidence to aid in diagnosis. An acceptable periapical radiograph must have adequate contrast and no or minimal processing error and include at least 3 mm of the surrounding periapical area to allow accurate assessment of the tooth of interest and its surrounding area. Additional periapical radiographs at different angulations (10–30 degrees horizontally or vertically) could be taken to determine the location of a periradicular lesion or any resorptive defect present on the root and its surface (internal or external).[4–6] An earlier study has shown that accuracy in detecting the presence of twin canals increased using a periapical radiograph with a horizontal shift. Another concluded that the detection of periapical lesions was more accurate with an angulated radiograph. However, the degree of angulation should not be excessive, as it would result in overlapping of the image or changes in the image size, thus reducing the diagnostic quality of such a radiograph.
Periapical radiographs taken at different angulations may be necessary in order to determine the number of root and root canals of a tooth, especially in premolars and molars. Several studies have shown that radiographs taken at a horizontal angle of 30 degrees improves the ability to determine the canal type in premolar teeth.[9,6,4] Periapical radiographs can be taken either by using the paralleling or bisecting angle technique.
Dental radiographs are needed for the assessment of the crown, pulp chamber, root(s) and periradicular area of a particular tooth (Table 3). Clinicians should make it a routine to assess the entire radiograph thoroughly (i.e. the adjacent teeth and its surrounding tissue) before focusing on the tooth of interest. It is essential to ensure that the radiograph is mounted correctly prior to assessment. This is to prevent misdiagnosis or misinterpretation of the radiograph. Use of magnification, such as a magnifying glass, could aid in detailed assessment of the radiograph. Restoration status and the presence of a carious lesion or periapical pathology on any tooth should be identified, documented and included in the treatment plan. When assessing the radiograph of the tooth of interest, the clinician should start from the crown then move towards the root and its periradicular area. Any findings must be included in the documentation and considered when deciding on the treatment option.
The periapical radiograph must have minimal distortion and magnification, as any elongation or foreshortening would result in incorrect measurement of the root canal length. Careful assessment of the root is essential to identify any root aberration that may be present (Fig. 1). It is quite common to find a Chinese patient with a C-shaped canal or other Mongoloid trait with an aberrant root or root canal anatomy. Thus, thorough assessment of the radiograph is necessary to ascertain the presence of additional roots or root canals and thereby establish treatment difficulty.
Since endodontic therapy involves the treatment of the root canal, which is not visible to the naked eye, radiographs aid in determining whether treatment was carried out satisfactorily and adequately.
Dental radiographs are important in endodontic therapy to determine tooth morphology, ascertain the cause of the dental problem and provide an early assessment of the tooth of interest. Based on a radiograph, the restorability of a tooth and the complexity of the treatment can be assessed.
It also helps clinicians decide whether he or she has the skills to perform the treatment or should refer the patient to a specialist. The presence of a pulp stone in the pulp chamber or another obstruction within the tooth or root canal (e.g. a post, a pin, a separated instrument or root filling material) can be determined prior to treatment (Fig. 2). This is important, as it will give the clinician some indication of the prognosis and any difficulties that might occur during treatment. All of these factors must be discussed with the patient prior to treatment, so that he or she can decide whether to proceed with the endodontic therapy.
While the use of a periapical radiograph alone may be sufficient in most cases, supplementary radiographs may be needed if the clinician finds that the tooth may have additional roots or to ascertain the root curvature. Taking another periapical radiograph at a different horizontal angulation (10–30 degrees) may therefore be necessary. Again, care must be taken to minimise the extent of superimposition on adjacent teeth. The SLOB rule (same lingual, opposite buccal) can be used to determine the location of an additional root or root canal.
The size of the root canal can also be assessed from the radiograph. This information will provide some indication of the complexity of the treatment and the choice of the obturation material and technique. A tooth with an open apex may require placement of a calcific barrier, such as mineral trioxide aggregate, apically prior to obturation.
The status and quality of the existing coronal restoration must be assessed radiographically and clinically. All defective restorations must be removed and replaced with either permanent or temporary restorations. Any carious lesion must be noted, and the depth of the lesion must be determined clinically. This is important in order to ensure that the tooth is deemed restorable prior to treatment. The clinician must decide on how to restore the tooth after completion of endodontic therapy prior to initiation of treatment.
Posts, separated instruments or root filling material within the root canal may complicate the endodontic treatment (Fig. 3). The size and type of post will determine the feasibility of removing such a post. A separated instrument in the apical third of the root and below the curved root may be more difficult to remove than a more coronally located fragment.
Operative assessment (treatment phase)
Working length is confirmed and quality of obturation is assessed during treatment to ensure the treatment is carried out satisfactorily. A periapical radiograph may also be taken to ascertain the correct angulation of the bur or endodontic file when negotiating a blocked or calcified canal, during post space preparation and even during access preparation through a calcified pulp chamber (Fig. 4). This is essential for preventing procedural errors, such as perforation of the pulpal floor or canal wall.
During obturation, it is important that the root canal be obturated to the predetermined working length and have no voids. This can be confirmed by taking a periapical radiograph during treatment. Obturation that is shorter or longer than the working length may affect the treatment outcome.
After therapy has been completed, a periapical radiograph should be taken to ensure that the treatment was carried out adequately. This will function as a baseline when reviewing the patient six to 12 months later. From this immediate post-operative radiograph, the quality of the final coronal restoration can be ascertained and the size of the periapical lesion, if present, can be assessed. At the recall appointment, a new periapical radiograph of the endodontically treated tooth is taken to monitor the healing of the periapical lesion and to confirm the success of treatment. The presence of a new periapical lesion or the enlargement of an existing one should be noted, and necessary measures should be taken to identify the cause of treatment failure.
Using intra-oral radiographs is the only method in endodontic therapy that allows the clinician to make an assessment of the root and its supporting tissue. In order to gain the full benefit of this radiograph, clinicians have to ensure that it is appropriately exposed, shows no processing errors and has no or minimal image distortion. It also has to be correctly mounted, labelled and dated. Clinicians must be able to select which radiograph is necessary to aid in their endodontic diagnosis based on the patient’s history and clinical examination.
Editorial note: A complete list of references is available from the publisher.