Endodontic root perforation is a serious dental complication that occurs in 3-10% of root canal treatments as perforations to the periodontal ligament at any location can have a negative effect on long term prognosis of the tooth1. It is an unnatural communication created between the root canal system and the periodontium. Early detection and immediate treatment of such incidence can significantly improve the prognosis2.
Based on location, perforations can be coronal, mid-root or in apical third of the root. Of these, the mid-root perforations are the hardest to locate, visualize and seal3. They may occur iatrogenically during canal exploration using high speed rotary instruments and improper post space preparation, or pathologically due to root resorption and root caries.
The etiologies, location, as well as the size of the perforation and the delay time before perforation repair are significant factors in prognosis and treatment planning or selecting the proper therapy5.
Detection of root perforations can be improved clinically with the use of diagnostic aids such as magnification or apex locators. The conventional radiographic techniques have numerous shortcomings rendering it impractical, such as superimposition of anatomic structures on the image of the root, and the inability to determine defects on the buccal or lingual surface of the tooth.
Studies by Suzuki, Sunada et al have shown a constant value of electrical resistance recorded between a file in the root canal and an electrode on the oral mucosa, thus forming basis for the principle of apex locators to determine the root canal length. This value is constant at all points of communication with the periodontium and not only the apical foramen, making it an excellent diagnostic tool to determine complex perforations of the root or root fractures.
The first generation of EALs were largely resistance based and were found to be inaccurate as pain was often felt due to high electric currents. Second generation EALs rely on impedance measurements to measure the location within a canal. These devices often have difficulty taking accurate measurements in wet canals, and require insulative sheaths over the probe to protect from conductive fluids. Third generation devices are largely frequency ”’ based and use multiple frequencies to determine the distance from the end of the canal. These units are able to process the complex algorithmic calculations required with their built-in microprocessors to give accurate readings11.
Early reports on the ability of electronic apex locators to detect perforations were carried out using the resistance type instruments. Only one study tested the accuracy of frequency dependent electronic apex locators to detect root perforation12. The Formatron D10 (Parkell electronic division, Farmingdale, New York, USA) which operates on a different electric principle uses a ratio algorithm between two electrical currents and is designed to make accurate readings regardless of fluid electrolytes being present within the canal13.
The aim of the study was to appraise the veracity of electronic apex locator Formatron D10 in detecting mid root perforation compared to the radiovisiography (RVG).
Materials and methods:
A total of forty extracted single and multiple rooted permanent intact human teeth were stored in distilled water containing 10% formalin. The teeth were examined visually to detect fractures or cracks or any signs of root resorption. Standard access cavities were prepared using diamond fissure bur in a high-speed contra angle hand piece with water coolant; canals were instrumented with K files upto size 40, 1mm short of anatomical apex with 2.5% sodium hypochlorite as an irrigating solution. Patency of the apical foramen was maintained with size 20 k file to avoid blockage by dentinal debris, which could interfere with the electrical conductance.
The roots were artificially perforated at the middle third of the root until the tip of the instrument was seen approximately 1mm beyond the external root surface. The patency was maintained with a size 20 k file. In maxillary multirooted teeth, the palatal root was perforated and in the mandibular teeth the distal root was perforated. The remaining roots of multi-rooted teeth were left intact to mimic clinical conditions during radiographic evaluation. The roots including the perforations, were then implanted in box containing freshly mixed bed of alginate and water, with crowns exposed (Kaufman et al)14.
The boxes were covered throughout the experiment to maintain the humidity of the alginate. The perforations were detected by the electronic apex locator (Parkell Foramatron D10, United States) (Figure 1) under dry conditions according to manufacturer”’s instruction with a size 25 K file (Figure 2). The lip clip of the electronic apex locators was attached to the alginate in one angle of the model. Detection of the perforation by the electronic apex locators was obtained when the indicator reached the sign APEX on the monitor (Figure1). The K file was then stabilized with composite resin to the crown (Figure 2).
For radiographic evaluation, measurements were recorded in two groups according to the position of the tooth in the model: Group A included measurements taken when the perforations were facing the long axis of the box (0 degrees; 30 degrees); Group B included measurements taken when the perforations were facing the short axis of the box (90 degrees; 120 degrees). Radiographs in Group A mimicked the clinical condition of perforations located at the buccal or lingual aspects of the root, whereas radiographs in Group B resembled clinical cases in which the perforations were located at the interproximal aspects.
Determinations of all perforations were carried out with K file No 25 attached to the apex locators tested. The teeth were removed from alginate, the actual location of the file tip in relation to the perforation was determined with a stereomicroscope. Zero values were recorded when the tip was at the same level of the external root surface. Short and long values were recorded when the tip was detected beyond or short. All the measurements were performed by two examiners who were not informed of the perforation site.
The average distance measured from the tip of the file to the external outline of the root surface was short for all instruments and clinically acceptable.
On stereomicroscopic analysis of 40 samples the perforation was accurately determined in 36 (90%) teeth, whereas it was found short in 2 (5%) teeth within a range of (0.2 ”’ 0.5) and extended beyond in 2 (5%) teeth within a range of (0.2 – 0.4) in millimeters.
Sample At the perforation (0) / Short (-) / Beyond the perforation (+) in millimeters
4 + 0.2
29 + 0.4
Table 1: Stereomicroscopic evaluation of the determination of perforation
Groups Angulations in degrees Number of teeth Percentage of perforations detected
A 0 40 35%
30 40 38%
B 90 40 85%
120 40 88%
Table 2: Radiovisographic examination of the perforation.
Root perforations are procedural mishaps that can occur due to numerous reasons and complicate endodontic triumph. It results in consequences such as gingival growth of epithelium into the perforation area, inflammation, infection due to bacterial ingrowth, bone resorption and necrosis. Thus prompt diagnosis and immediate repair not only allow completion of endodontic therapy but also improve the chances of success. Prompt diagnosis however, is still a difficult issue3,15.
As analyzed in this study, Radiovisiography is highly unreliable and inaccurate in detecting bucco- lingual perforations. Even in an in-vitro set-up bucco-lingual view failed to show the presence of the perforations while it could be accurately visualized in the mesio- distal view. Such a view is impossible in a clinical situation6. The reliability of radiographs is compromised because they provide a two”’dimensional image of a three dimensional object, are technique sensitive and subject to observer interpretation. Additional difficulties exist in-vivo including superimposition of anatomical structure and biologic risk of radiation. Hence the need was felt for a rapid, easier and accurate means of detecting perforation, which is where electronic apex locators could be the answer12.
However, it is essential to radiograph the teeth after locating the perforation with an EAL to determine the location relative to the crestal bone. The prognosis and treatment are directly related to the proximity of the root perforation to the epithelial attachment and crestal bone3, 5
EALs generally operate upon on the difference in electric gradient between the biologic tissues. Thus all in-vitro models need to be created with similar electrical resistance as to the periodontium. Based on the competent in-vitro model used by Kaufman and Katz, in this study also, we have used alginate as the surrounding medium for the extracted teeth. The alginate is easy to use and has high elasticity, viscosity thus preventing material extrusion into smaller openings of apical foramen and perforations. Comparisons made between the measurements to determine tooth length by apex locator with actual tooth length and length determined by radiographs prove the validity of the model. 12, 14.
As we have shown in our study electronic apex locators detected the perforation in all samples. The 3rd generation electronic apex locators are exceptionally advantageous in this aspect since they will be accurate even in presence of blood, generally found at the perforation site7,17,18.
Various studies in the recent years have investigated the accuracy of EAL”’s in the determination of perforation19, 20 as well as establishing working length21, 22 and found that they can effectively and reproducibly detect root canal perforations.
Thus, in this study, electronic apex locators were accurate tools for locating mid root perforation within a clinically acceptable range. Radiographs were unreliable in identifying mid root perforations. Despite the fact that in vitro results cannot be directly extrapolated to the clinical situation, they can provide information that might be clinically beneficial. Further research is required to determine the sensitivity of these devices in various clinical situations. More in vivo studies should be conducted to confirm the in vitro results.
Electronic apex locators are eminently perceptive devices that can be used to accurately determine the location of perforation. The quantum jump in endodontics and the resulting complications had forced endodontists to be innovative and inventive. Innovative use of electronic apex locators can improve perforation detection and overall success.