Clinical Applications of Apex Locator Technology

Dr. Wyatt Simons


Technology has affected most aspects of our lives. Homes are smart, cars can drive themselves, and cell phones are more powerful than any computer available when we first landed a man on the moon 50 years ago. Inventor Ray Kurzweil said, “Technology goes beyond mere tool making; it is a process of creating ever more powerful technology using the tools from the previous round of innovation.” Clinicians who enjoy providing endodontic treatment today have been beneficiaries of this seemingly exponential increase in technology. For example, the recent advance of adding the third dimension to our imaging in CBCT has revolutionized our ability to see and treat diseased root canal systems.1 It was not long ago that a clinician only had a straight and an off-angled radiograph to estimate the 3-D anatomy of unique root canal systems. Today, clinicians manipulate high-resolution 3-D imaging of root canal systems before and throughout treatment. This analysis of individual root canal anatomy and surrounding periodontal tissues has had a profound impact on our ability to accurately diagnose and treat endodontic disease.2-4

Two technologic advances that are currently available to help clinicians providing endodontic treatment include the use of digital radiography and apex locator technology. These fairly modern technologies offer dynamic information to clinicians as they navigate through treatment. This adjunctive feedback gives the clinician knowledge of the position of endodontic devices relative to periradicular attachments during treatment. This is beneficial to all clinicians regardless of working length and obturation level preferences.

Many clinicians establish preoperative estimations of canal lengths and use tactile sensation when navigating root canal systems. To refine these working length estimations, digital radiographs and apex locator technologies are employed during root canal system exploration.5 This article spotlights clinical cases that illustrate how clinicians can use apex locator technology to guide exploration, instrumentation, and obturation of root canal systems.

Figure 1a. A mid-root radiolucency was seen on the 2-D, preoperative digital radiograph. Figure 1b. A diseased lateral portal of exit was seen feeding this radiolucency on the 3-D CBCT rendering. This helped in the diagnosis of a lesion of endodontic origin.
Figure 1c. A working digital radiograph that was acquired when the apex locator cautioned that the file was in contact with periradicular tissue several millimeters short of the main working length. This feedback helped limit over-instrumentation. Figure 1d. A postoperative digital radiograph revealing obturation of the mid-root lateral canal.

Apex Locator Verification of Root Canal Anatomy
Apex locator technology is an invaluable tool in the assessment and treatment of individual root canal systems. It provides valuable information to the clinician related to the position of instruments relative to the periradicular tissues when exploring root canal systems. This feedback increases the safety and efficacy of our treatment as we navigate and determine accurate working lengths. For instance, it helps to control over-instrumentation of accessory anatomy. Case 1 shows such a case in which engagement of a diseased lateral canal was confirmed with apex locator technology and over-instrumentation of the known lateral canal was limited. The unique, mid-root radiolucency was first seen on the preoperative digital radiograph in Figure 1a. The 2-D digital radiograph was not definitive in its assessment of the source of the radiolucent lesion; however, the diagnosis of a lesion of endodontic origin was supported by CBCT evaluation. Figure 1b is the 3-D CBCT representation of the diseased lateral portal of exit feeding the endodontic infection. The lateral canal was noted to be in the center of the lesion, which is the typical way the periradicular attachment is affected by diseased root canal systems.6,7 Figure 1c is a digital radiograph taken when the apex locator read that the sharply curved tip of a stiff #15 file engaged the periodontal ligament. In this case, apex locator technology helped to prevent over-instrumentation when the lateral canal was engaged several millimeters short of the main working length. Figure 1d is the postoperative radiograph that reveals obturation of the lateral portal of exit from the root canal system feeding the lesion.

Apex Locator Verification of the Anatomic Apex
Three-dimensional imaging has helped overcome the difficulty in assessing the difference between the 2-D radiographic apex and the true anatomic apex of a root canal system.1,3 This difference between the radiographic terminus and the true anatomic terminus of root canal systems is a common occurrence.6 Even when this difference is known and studied with 3-D imaging, apex locator technology can be a valuable tool in further measuring working lengths. It has been shown that apex locator technology is more accurate in determining working lengths than radiography, but it is generally still recommended that the prudent clinician utilize both radiography and apex locator technology to obtain accurate working lengths.8

Figure 2a. A sagittal CBCT scan through the diseased mandibular second molar, revealing apical root resorption. Figure 2b. A frontal CBCT slice through the distal root helped to visualize the terminus of the main canal compared to the terminus of the root.
Figure 2c. A working digital radiograph was acquired to visualize where the apex locator electronically measured contact with peri
radicular tissues.
Figure 2d. The post-op digital radiograph displays obturation that is short of the end of the distal root but likely in close proximity to the anatomic terminus of the canal.

Case 2 highlights this challenge of determining an accurate working length. Figure 2a is a sagittal CBCT slice through a mandibular second molar with chronic endodontic infection resulting in apical root resorption. The frontal CBCT slice through the distal root in Figure 2b aided in further visualization of the diseased root canal anatomy. The clinical application of CBCT technology for the diagnosis and treatment of root resorption is quite beneficial.9 Although mindful pre-op study of the challenging endodontic anatomy and infection was helpful, refinement of the true working length was enhanced during treatment with use of apex locator technology. Figure 2c is a digital radiograph acquired when the apex locator read that the endodontic file was in contact with periodontal tissues. This digital radiograph highlights the 2-D difference that often occurs between the radiographic terminus and the true portal of exit of the root canal system. Figure 2d is the post-op radiograph. It reveals obturation that is short of the radiographic terminus of the root yet likely in close approximation to the true anatomic terminus of the diseased root canal system.

Figure 3. The apex-locating obturation device shown here is produced with different sizes of gutta-percha molded to a removal carrier. The carrier extends the entire length of the gutta-percha, permitting apex locator functionality prior to removal of the carrier during obturation. Figure 4. This off-angled, post-op digital radiograph reveals the outcome of the apex locator-guided obturation process in a complex maxillary molar.

Apex Locator Control of Rotary Instrumentation
In addition to the benefits of using apex locator technology during exploration of root canal anatomy and in establishing working lengths, apex locator technology has great efficacy in regulating rotary instrumentation.10 The benefit of limiting rotary functionality when a file is electronically measured to be in close proximity to periradicular tissues is self-evident. The use of apex locator technology with our rotary systems is becoming more widespread. There are simple ways to connect basic apex locator attachments to rotary files, and there are rotary systems available that have apex locator technology embedded within them.

Apex Locator Use in Obturation
A new frontier in maximizing the benefits of apex locator technology is in its use in obturation. An obturation device that uses apex locator technology to guide the placement and delivery of gutta-percha is shown in Figure 3. This device comprises varying sizes of gutta-percha plugs molded to a removable carrier that extends the entire length of the device. This design enables apex locator functionality during obturation.11,12 It was developed to focus on bringing apex locator technology to clinicians to help overcome the challenge of acquiring a precise apical fill. Current development has been focused on its use in facilitating an apex locator-guided automated fill of the entire root canal system in one step. Figure 4 is a post-op digital radiograph revealing the outcome of using this apex locator-guided obturation device in a complex maxillary molar.

Figure 5a. A digital radiograph of the apex-locating obturation device positioned in a 32-mm canine. Figure 5b. A digital radiograph taken after the automated obturation process was completed. The device was removed, and the obturation level was extended to the desired level for post placement.
Figure 6a. A digital radiograph of the apex-locating obturation device positioned in the distal canal of a mandibular molar. In this case, the end of the device was pre-bent to facilitate its placement around the apical turn. Figure 6b. The post-obturation digital radiograph revealed the ability of the device to produce conditions favorable to molding of the entire canal in one automated step.

Case 3 reveals the position of this device in a 32-mm maxillary canine. Figure 5a is a digital radiograph taken when the apex locator electronically confirmed that the apical plug of gutta-percha was in its desired position relative to the periodontal ligament. After confirming the fit with the apex locator, the automated obturation process was activated. This process warmed and molded the apical gutta-percha and was followed by the removal of the carrier and 3-D obturation of the remaining canal to the desired level. Figure 5b shows the level of obturation that was established for post placement.

Case 4 highlights how apex locator technology enhances the precision of placement of the obturation device. Figure 6a is a digital radiograph of the position of the device in the distal canal of a mandibular molar. In this case, the end of the device was pre-bent to facilitate placement around the apical turn. The tactile awareness of the fit of the device around the apical turn was confirmed with apex locator technology. The device was then employed to produce conditions favorable to molding and was removed as part of the obturation of the entire canal. Figure 6b shows the outcome of the one-step, automated obturation process.

The passionate, international endodontic educator Dr. John West likens the benefit of apex locator technology to that of obtaining local knowledge when we travel to new places. Endodontic clinicians are fortunate to benefit from the local knowledge that apex locator technology provides us regarding individual root canal anatomy as we travel through the unique complexities that each root canal system offers. This knowledge increases the precision of our craft as it provides us with valuable information as we are performing root canal treatment. This article focuses on clinical examples of how apex locator technology affords the clinician more information while exploring, engaging, and obturating root canal systems. This adjunctive local knowledge aids the compulsory requirements that are essential for clinicians to have when performing root canal treatment. One of the legendary pioneers of the endodontic profession, Dr. Herbert Shilder, advised to never take root canal treatment lightly. He cautioned that even the most skilled clinician could get into trouble if tenacious attention to detail was not honored.

Endodontic clinicians today have overwhelmingly more tools than the pioneers of our profession. These visionaries used an open flame to warm gutta-percha to establish their objectives for success; however, it was their commitment to excellence that guided their outcomes. Passion and commitment to provide the highest level of care possible for our patients drives our outcomes more than technology.

Future advances in endodontics will certainly build on prior advances. These advances will strive to enable clinicians to reproducibly reach their objectives for successful outcomes with more ease. As sophisticated and fun as clinical endodontics is now, it will undoubtedly become more enjoyable and better as technology evolves. Future technologic breakthroughs will likely bridge the benefits of CBCT technology in producing high-resolution 3-D renderings with technologies that are similar to apex locator technology in giving the clinician live feedback regarding where they are as they journey through the intricacies of individual root canal systems. Enjoy the ride!


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Dr. Simons is a Diplomate of the American Board of Endodontics. He received his DDS degree from the University of the Pacific, Arthur A. Dugoni School of Dentistry, and he completed his postdoctoral specialty training in Endodontics at Boston University. Dr. Simons is committed to the advancement of the profession of endodontics, and he is passionately devoted to inspiring clinicians to reach their potential. He founded Signature Specialists in San Clemente, Calif, in 2004, where he practices and provides live-patient demonstrations. He has lectured nationally with presentations focused on live-patient treatment. He has published many articles in national and international journals. Dr. Simons is the inventor of the CORK system of obturation, which is in development. Dr. Simons can be reached via email at

Disclosure: Dr. Simons holds 4 patents on the use of apex locator technology in obturation.

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