4.3
Working Length Determination
Bhavin Bhuva and Shanon Patel
Objectives
At the end of this case, the reader should understand the importance of accurate working length determination during root canal treatment. Accurate working length determination is critical to ensure the root canal system has been chemo‐mechanically prepared and filled to full length, to minimise iatrogenic complications such as under‐/over‐preparation. The reader should be aware of the methods available to determine working length, as well as the advantages and disadvantages of each technique.
Introduction
A 43‐year‐old female patient presented complaining of sensitivity and acute pain on the right side of the mouth.
Chief Complaint
Spontaneous radiating intense pain on the right‐hand side; the pain was poorly localised and would last for several hours.
Medical History
Unremarkable.
Dental History
The patient gave a history of acute pain that had been relapsing and remitting in nature for the previous two days. Prior to the acute pain, there had been sensitivity to hot and cold foods and liquids that had progressively worsened.
Clinical Examination
The patient had a moderately restored dentition. The lower right first and second molar teeth (LR6 and LR7) were restored with ceramic onlay restorations. The LR6 was tender to percussion, whilst no other teeth in the upper or lower right quadrants elicited a similar response. There were no probing depths greater than 3 mm associated with either the LR6 or LR7.
The LR6 gave a pronounced and prolonged response to both thermal and electric sensibility testing. The LR5, LR7 and LR6 all responded normally to both thermal and electric testing.
A pre‐operative radiograph of the lower right molar region was taken and did not reveal any periapical changes associated with either the LR6 or LR7 (Figure 4.3.1). There were moderately deep restorations evident in both teeth.
Diagnosis and Treatment Planning
A diagnosis of symptomatic irreversible pulpitis was reached for the LR6.
The treatment options for the LR6 were:
- No treatment.
- Root canal treatment of LR6 followed by cuspal coverage restoration.
- Extraction.
Following discussion of the treatment options, the patient elected to have root canal treatment and definitive cuspal coverage restoration.
Treatment
Prior to carrying out root canal treatment, it is important to have at least one periapical radiograph taken with a beam‐aiming device. Two radiographs taken with different horizontal (parallax) angulation may be useful to assess the anatomy of teeth with multiple roots (Figure 4.3.2). A good‐quality pre‐operative radiograph facilitates treatment planning in advance of the endodontic procedure, and provides important information to the clinician, for example the working length(s) of the canal(s) may be estimated (Table 4.3.1).
What is the working length of a root canal?
The working length of a root canal is the distance from a designated coronal reference point (for example, incisal edge) on the tooth crown to the end point of root canal preparation (Figure 4.3.3).
Table 4.3.1 Essential information provided by pre‐operative radiograph.
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What are the drawbacks of conventional radiography?
With two‐dimensional (2D) radiographs, estimated working length(s) may be measured directly from the radiograph. With digitally acquired images, a measurement facility is provided with the accompanying software, which can be used to estimate the root canal length(s).
Conventional radiographic techniques produce a compressed 2D image that can only provide limited clinical information with respect to three‐dimensional (3D) anatomy. For example, a radiograph will not demonstrate root curvatures in the bucco‐lingual plane. Even with the use of a beam‐aiming device, periapical radiography has poor geometrical accuracy and is susceptible to image distortion. Therefore, the length(s) derived from these images will always be subject to a degree of error. All periapical radiographic images are magnified by up to 5%.
Problems with positioning of the film or digital sensor may also occur, reducing the quality of the image further. For example, when taking radiographs of the upper posterior teeth, the film may bend, leading to image distortion. A further problem may be encountered with lower molar teeth as the patient may have difficulty tolerating the image receptor when it is placed into the lingual sulcus. This may lead to an image which does not capture the root apices and surrounding periapical tissues.
Bisecting angle radiographs should, if possible, be avoided as they are susceptible to even greater distortion and inaccuracy. These images are also very difficult to reproduce. Superimposition of various anatomical structures and image distortion may result in limited diagnostic yield from conventional radiography. For example, superimposition of the root apices of the upper molar root teeth with the floor of the maxillary sinus or zygomatic arch may commonly occur during periapical radiography in this region.
What additional information does a pre‐treatment cone beam computed tomography scan give?
Small field‐of‐view cone beam computed tomography (CBCT) has been shown to be highly reliable for determining the pre‐operative working length, as it provides geometrically accurate images and overcomes the issue of superimposition of anatomical structures. This technique may be employed to assess both periapical status and root canal anatomy/length when 2D imaging does not provide the necessary information. CBCT may be utilised in cases of complex root canal anatomy.
The pulp chamber was accessed, and the root canal orifices were located and coronally flared. Following this, the length of each of the root canals was determined and root canal treatment was completed. One year review demonstrated healthy periapical tissues (Figure 4.3.1).
What are the important apical anatomical landmarks?
The apical region of the root canal has been studied in great detail and descriptions of the anatomy of this area are well documented. Changes in the apical anatomy occur throughout life as the effects of destructive resorption and reparative cementum deposition occur.
The main anatomical landmarks of the apical region of the tooth are as follows (Figure 4.3.4):
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