4.1 Introduction

Digital technology is one of the most rapid and extensive evolution in dentistry. Remarkable developments of endodontic technology have been achieved in the last decades. The ultimate result in the digital transformation of endodontics has definitely improved the daily clinical practice of practitioner.

Endodontics is the only dental discipline where we cannot see what we are doing. It is based more on our clinical skills and tactile sensation. We must, therefore, rely on different technological methods to assure the predictability and prognosis of endodontic preparation and obturation.

4.2 Digital Radiography

Radiography has always been a fundamental tool in endodontic practice [1, 2]. It is an essential component of all phases of root canal treatment (RCT) procedures from diagnosis to follow-up period [3–5]. Periapical radiographs provide useful diagnostic information including position of the tooth, size of pulp chamber, anatomy of roots, location and size of periradicular lesions, and the proximity of adjacent anatomical structures [6]. In addition, they are very useful during RCT procedures to determine the actual working length, monitor the progress of canal preparation, confirm the correct placement of master cones before obturation, and evaluate the quality of root canal filling. The conventional radiography that depended on the usage of X-ray films has been replaced by digital radiography.

The conventional X-ray films depend on chemicals for development and fixation. They have several disadvantages including the need for a light safe environment for storage, a relatively high radiation dose, more time for development and extra time to be digitized using a scanner with a transparency adaptor. In addition, they provide static images with no availability of post-image treatments except for modifying brightness. Digital radiography systems have become widely acceptable with continuous improvements and additions. When optimal exposure parameters and suitable processing of signals are used, optimal image quality of the digital radiograph is produced [7]. The diagnostic quality of digital intraoral X-ray was early reported to be comparable to the conventional X-ray films [8]. Moreover, digital X-ray systems depend on computer technology in the capture, process, display, treatment, and storage of digital images. Contrast enhancement of the digital radiograph is very useful for the diagnosis of many endodontic cases (Fig. 4.1).

4.3 Optical Coherence Tomography (OCT)

Optical coherence tomography (OCT) is a noninvasive and nonhazardous method of imaging, it depends on the analyzing the scattered reflections of light close to the infrared region, to determine the microstructural details of the oral biological tissue. OCT is comparable to ultrasound as the general principle of using reflections to create the images is the same for both but the methods for detecting these reflections are different. Dental OCT has the potential to detect and diagnose early stages of demineralization, remineralization, recurrent caries, restorative failures, root canal anatomy/calcification, periodontal disease, and precancerous lesions in real time.

In endodontics, OCT has been used to determine enamel cracks, coronal cracks, and vertical root fractures, along with the fracture’s location along the root. The main advantage of using OCT in endodontics is that it does not require a dry root canal and in fact gives a microscopic detailed image through the surrounding root canal circumferential from dentin to cementum. This further helps in preventing root canal over preparation and possible perforation of canal walls. In addition, OCT imaging can also reveal transportation of the canals and accessory canals, if any.

There are different types of OCT such as endoscopic OCT, polarization-sensitive OCT, Doppler OCT, and high-resolution OCT. We believe that endoscopic OCT has the potential to be used in endodontics if suitable tips are developed [9]. However, all the studies with OCT imaging in dentistry have been in vitro, and no clinical devices are currently available for this purpose. Figure 4.2 shows the application of optical coherence tomography in the detection of enamel cracks [10].

4.4 Cone Beam Computed Tomography (CBCT)

The true innovation in radiographic imaging in recent years has been the advent of CBCT. This technology allows imaging and observation of the tooth and its surrounding structures in the coronal, sagittal, and axial planes, and has many advantages which have already been discussed in the previous chapter. This section will discuss its applications in the field of endodontics.

New generations of CBCT machines are currently able to provide high-resolution images using smaller submillimeter voxel sizes, more dynamic multiplane imaging navigation, and data correction applying imaging filters. Currently, the CBCT is considered as an effective tool for diagnosis and treatment planning with great facilities to manipulate brightness and contrast and change slice thicknesses [11].

The benefits of a CBCT imaging should outweigh any potential risks. Imaging with CBCT should only be considered in cases where conventional imaging does not provide sufficient information to allow proper diagnosis and management of the problem. The ALARA principle that is, “as low as reasonably achievable” should be always maintained to avoid unnecessary radiation exposure of the patient. CBCT systems can be further classified into limited and full CBCT. The limited CBCT, known also as dental or regional, has a field of view (FOV) ranging in diameter between 40 and 100 mm, whereas the full CBCT, also known as ortho or facial CBCT has a FOV that ranges between 100 and 200 mm.

The American Association of Endodontists (AAE) has stated that limited CBCT systems are considered better for endodontic applications [10]. CBCT machines can be further classified based on the scan position. The majority of CBCT machines are seated position. Few of them are supine or upright position machines.

CBCT is very valuable in diagnosis of endodontic and non-endodontic origin pathosis, canal morphology, external and internal resorption, invasive cervical resorption, root fractures, and presurgical endodontics planning. However, compared to intraoral film, CBCT has high levels of scatter and noise, higher contrast resolution but inferior spatial resolution. The spatial resolution is even higher than that with medical-grade CT scan. The cost of CBCT is also much more [12, 13].

For all these reasons, CBCT should not be considered as a preliminary diagnostic tool, that is, the usage of CBCT is not indicated for every patient. There is no sufficient evidence that CBCT is needed for routine dental and should be restricted to cases where benefits outweigh the potential risks. CBCT imaging can be used in preoperative phase as it provides better visualization of canal anatomy, canal morphology, periodontal ligament, bone abnormalities, and internal and external root resorption. It is recommended to detect apical periodontitis occult, evaluate developmental anomalies, and provide more information in cases of cysts, fractures, cortical bone invasion, adjacent soft tissue invasion, traumatic dental injuries, and all difficult cases where special attention and more information are required for diagnosis [14–16].

In a systemic review conducted by Aminoshariae et al., [17] CBCT has almost double odds to locate a lesion compared to the traditional radiograph for the same lesion. This is quite important for clinical cases where diagnosis or decision making is challenging. Rosen et al. [18] conducted a systematic search to evaluate the diagnostic efficacy of CBCT in endodontics using an efficacy model. It was found that the expected ultimate benefit of CBCT to the endodontic patient is not clear and mainly limited to its diagnostic accuracy efficacies. Therefore, one should be cautious and follow rational approach when considering CBCT for endodontic patients.

In another meta-analysis study to determine the diagnostic accuracy of CBCT for tooth fracture, Long et al. [19] found that the pooled prevalence of tooth fractures was 91% for cases of clinically suspected and radiographically undetected tooth fractures using periapical radiographs. The CBCT appeared to have a high diagnostic accuracy for tooth fractures and was highly recommended to be used in clinical settings. The authors were very confident with the results of positive test, but they recommended to be careful when interpreting the negative test results, especially for endodontically treated teeth. However, this meta-analysis has some limitations including following small sample sizes in some researches, the lack of applying reference standard test for all patients in some researches, and the lack of data for horizontal and oblique tooth fractures for some subgroups.

In summary, CBCT might become the first choice to manage and assess endodontic cases, especially if lower radiation doses and better resolution become available. There is still a need for clinical trials to provide evidence of increased efficacy possible for endodontic applications of CBCT. Furthermore, adequate training to use CBCT software and interpret CBCT images is needed to all CBCT practitioners. Examples of benefits of CBCT imaging in endodontics can be seen in Fig. 4.3.

4.5 Ultrasound (US) Imaging

US combined with color power Doppler (real-time imaging) is another noninvasive imaging technology that does not utilize ionizing radiation. Real-time ultrasound imaging, also called real-time echotomography or echography, has been the widely used diagnostic technique in many fields of medicine. The imaging system in echographic examination is based on the reflection of US waves called “echos” and its application to endodontics has shown success.

US was found to be a reliable diagnostic technique in the differential diagnosis of periapical lesions (granulomas versus cysts). Drawbacks include its use only in the anterior region where there is little or no overlying cortical bone, since sound waves are blocked by bone. In addition, the interpretation of US images is usually limited to radiologists who have extensive training.

Recent studies have shown US imaging use in monitoring the healing of periapical lesions following endodontic treatment, thereby stating that that ultrasound can detect healing earlier than radiography [20–22]. However, they are still not widely used as the differential diagnosis of granuloma and cyst is not considered important in treatment planning. Figure 4.4 describes the application of ultrasound in endodontics.

4.6 Magnetic Resonance Imaging (MRI)

MRI is also a noninvasive imaging technology which uses radio waves instead of ionizing radiation, and so does not have health hazards and is safe to use. The concept behind its use is a strong magnetic field that leads to excitation of the hydrogen atoms within tissues.

MRI may be used for the investigation of pulpal and periapical conditions, along with their extent and the anatomic implications. However, it has several drawbacks. These include poor resolution compared with conventional radiographs, longer scanning times compared to CT, increased costs, and limited access only in dedicated radiology units. Different hard tissues such as enamel and dentine cannot be differentiated from each other or from metallic objects as they all appear radiolucent. MRI imaging cannot be used in patients with a pacemaker due to the presence of a strong magnetic field.

A recent modification in MRI imaging, SWIFT-MRI (Sweep Imaging with Fourier Transform), shows promising use in endodontics as it offers simultaneous three-dimensional hard- and soft-tissue imaging of teeth (Fig. 4.5) [24].

Other advancements in endodontic imaging such as Tuned aperture computed tomography (TACT), Micro-CT, and Spiral computed tomography (SCT) are not discussed as they are not still widely used in practice. Micro-CT is not used for in vivo imaging due to the high radiation dose required. TACT (an alternative CT technique) is not yet commercially available for dental applications.

4.7 Electrical/Digital Pulp Testers

The determination of the status of dental pulp tissue is essential for the correct diagnosis in dental clinic. Currently, there is no single reliable technique that can diagnose all pulp conditions. However, carful analyzing of the chief complaint, dental history, clinical examination, radiographs, and other investigations usually lead to the diagnosis of the underlying diseases.

Histological examination of sections of pulp tissue specimen is considered the most accurate way of evaluating the pulp status as it allows to assess the presence and extent of inflammation or the presence of tissue necrosis. However, it is impractical and not feasible in dental practice, and thus clinicians have to use other investigations including pulp test devices to assess the dental pulp status during diagnosis. For long time, all pulp tests suffered from shortcoming related to accuracy, reliability, and reproducibility. The application of the suitable pulp test is important as not all pulp testing are appropriate for all clinical situations.

It is quite important to differentiate between vitality test and sensibility test. The pulp vitality test includes an assessment of the pulp’s blood supply. The pulp sensibility tests asses the pulp sensory response, that is, the ability of the pulp to respond to a stimuli. The positive response of the pulp to a stimulus indicates the presence of innervation, and clinicians assume that the pulp has a viable blood circulation. Thus, the pulp is either healthy or inflamed. The negative pulp response to a stimulus may suggest the necrosis of pulp tissues. However, one should be careful for the limitation of the sensibility tests and the possibility of false, positive or negative, responses.

Electric pulp testing (EPT) is one of the sensibility tests. EPT technology is based on the production of impulses of negative polarity that is able to reduce the voltages required to stimulate nerve response in the pulp and periodontium tissue [25]. The electrical stimuli can cause an ionic change across the neural membrane, and this induces an action potential with a rapid hopping action at the nodes of Ranvier in myelinated nerves [26]. There were two modes EPTs: bipolar and monopolar. Both of them can be subdivided into wire or wireless devices [27, 28]. The most common types are wireless, battery-operated EPTs.

Bipolar devices were common till the mid-1950s. They involved using two electrodes, one is placed on the tooth buccal surface and the other on the palatal/lingual surface. The electrical current passes from one electrode to the other through the crown. In monopolar EPT, only one electrode is applied to the tooth surface. The circuit should be completed by placing the metal clip on the patient’s lip. Touching the probe handle by the patient’s hand can also complete the circuit [29–31]. To test the pulp status, the current intensity is increased gradually. In cases of vital pulp tissue, the patient starts feeling a “tingling” sensation once the voltage reaches the level of pain threshold [32]. The threshold is reached when sufficient number of nerve terminals are activated [28, 33]. Pain threshold level varies between teeth as well as patients. It is affected by patient’s age, tooth surface conduction, pain perception, and other factors [34].

Early animal study on dogs showed that EPT may interfere with a pacemaker resulting in risk of precipitating cardiac arrhythmia [35]. Based on this study, a recommendation not to use EPT in patient with pacemaker was established. However, more recent in vitro and human studies have shown that with the new generations of pacemakers that have better shielding, there is no interference from EPT or any other electrical dental devices on pacemakers [36, 37].

EPTs have the limitation of being unreliable in many cases. For example, they may produce false results in healthy immature teeth [26]. This is because it may take up to 5 years after tooth eruption for the myelinated fibers to reach the pulp-dentine border at the plexus of Rashkow. Patients undergoing orthodontic treatment may also show false EPT results because of disturbance of sensory elements due to the orthodontic treatment [38]. Similarly, recently traumatized teeth may show false results for the same reason [39]. Pulp canal calcification is another situation of false EPT reading. In such a case, the sensory response threshold is increased. This might be due to complete blockage of sensory response. Patients of hyperthyroidism may require higher intensity of electrical current compared to normal patients to elicit an EPT response [26]. Loss of pulp sensibility to EPT may also be observed in case of pulp hyperemia [40]. On the opposite, the breakdown products from necrotic pulp tissues may cause EPT stimulation leading to false positive responses [41]. False positive response in necrotic teeth was also reported to be caused by current passing through periodontal or gingival tissues [42].

4.7.1 Clinical Considerations

The EPT device is technique-sensitive with multiple limitations [43]. To avoid false reading, an EPT requires an appropriate application method, adequate stimulus, and careful interpretation [44]. The correct method includes first the good isolation of the tooth and the tight placement of the probe tip on the tooth surface. The occlusal two-thirds of the labial surface is recommended as it allows more consistent results [45]. However, it was reported that placing the electrode at the incisal edge of anterior teeth triggers a response with the least amount of electrical current [46]. For permanent molars, the highest concentration of neural elements is observed in the pulp horns, and the lower is in the cervical region of the pulp [47]. Thus, the optimum site for EPT electrode placement was reported to be at the tip of the mesiobuccal cusp [25].

It is highly recommended to use a conducting medium between the probe tip and the tooth surface to improve the electrical conductivity [48]. It is also important to confirm that the target tooth does not contact with the adjacent teeth, as this may cause inaccurate response as observed when two adjacent teeth have proximal metallic restorations. The same can be said for patients wearing orthodontic bands [42, 49].

4.8 Apex Locators

The procedures of RCT (i.e., cleaning, shaping, and root filling) should be confined within the root canal system. Working length (WL) determination is an essential step in the RCT. WL is usually defined as “the distance between a coronal reference point and the apical limit of preparation” [50]. Many dental schools consider the dentinocemental junction (DCJ) as ideal point to end the preparation (Fig. 4.6) [51]. However, the DCJ is a histological point that cannot be located clinically. However, the apical constriction (AC) is almost at the level of the DCJ and are usually located at about 1 mm far from the root apex [50]. For many clinicians, the AC is considered the end of the root canal, and any instrumentation or filling beyond this point is considered as over-instrumentation/overfilling. Other clinicians consider the anatomical apex as the end of root canal and over-instrumentation/overfilling starts only beyond this level.

Traditionally, the WL has been determined by taking PA radiographs when a file is inserted to a previous estimated length of the canal. However, the development of new electronic devices known as electronic apex locators has proven to determine WL more accurate, precise, and predictable [52, 53]. Apex locator is defined as an electronic endodontic device used to determine the length of the root canal space by determining the position of the AC. The AC has found to have an electric resistance of 6.5 kilo ohms (kΩ), and this specific characteristic was behind the development of apex locators.

4.8.1 Development of Electronic Apex Locators

Electronic apex locators have been in practice for more than 40 years. The apical constriction of the root has a specific resistance to electric current. This resistance can be measured using a pair of electrodes. The electrodes in apex locator are the endodontic file and the lip clip. These devices are able to detect the point where file becomes in contact with the periodontal tissue [54, 55]. The first generations of apex locators were unreliable and suffered from a lot of errors. The presence of fluids in the root canal led to errors. However, the new generations are more accurate, more reliable, and become basic devices used in endodontic treatment.

The first electronic method to determine WL was developed by Sunada (1962), who constructed a simple device that can be used clinically to determine the root canal length [54]. The device depended on the constancy of the electrical resistance between the mucosa and periodontium which is about 6.5 kΩ. This value was found to be constant at any part of periodontium regardless of the patient’s age, tooth type, and root shape. A great evolution was achieved in 1970 by Inoue who reported the use of Sono Explorer. Later, based on Inoue researches, an oscillator loop was used to calibrate and measure frequency at periodontal pockets depth of each tooth. The third generation of apex locators was launched in the late 1980s when a multiple channel impedance ratio-based device was used by Kobayashi to measure the impedance of two different frequencies simultaneously [54].

The ability of apex locators to determine the moment when a file becomes in contact with periodontal tissue extends their benefits. They are very useful to detect perforations in roots or pulp chambers, horizontal fractures, internal and external resorptions. They are also helpful in RCT of immature teeth that have incomplete root formation. Some apex locators can be used to detect the sensibility of the teeth. Others are combined with electronic handpiece (e.g., Root Zx II) and are able to determine WL precisely as the stand-alone units [56].

4.8.2 How Do Apex Locators Work?

The principle of apex locator is based on the electrical resistance of different tissues. The electrical resistance value between the periodontal ligament and the oral mucosa was found to be constant (6.5 kΩ) [57]. Apex locators produce a direct electrical current of a known voltage that passes through the endodontic file and being recaptured back by a metal hook. When the tip of the file reaches the periodontal ligament (R = 6.5 kΩ), the circuit is complete and the apex locator beeps and displays a “0” value on its screen. Some devices may show other signals like flashing light or pointer on screen display, digital readout or a Buzzer sound.

4.8.3 Generations of Apex Locators

The first generation of apex locators, the “Resistance-Based Apex Locator” was designed to measure the resistance of the electrical current considering that the resistance of periodontal ligament equals that of oral mucous membrane. The device should be used in a dry canal and K-file can be used with it. However, many shortcomings were reported for these devices. Accuracy is reduced in a wet canal, that is, the presence of remaining pulp tissue, excessive hemorrhage, or inflammatory exudate in the root canal system. False reading may also be encountered in case of obstructed canals, carious teeth, and presence of defective restorations, metallic restorations, and case of perforations [54, 58]. The devices used a direct electrical current that may cause the feeling of electric shock sensation by the patient. Furthermore, compared with WL determined by radiographs, these devices were found to be unreliable as many of the readings were significantly longer or shorter than the real WL [55]. Some examples of apex locators from the first generation: The Root Canal Meter (Onuki Medical Co., Japan), (Fig. 4.7a), Meter S II (Onuki Medical Co., Japan), the Dentometer (Dahin Electro medicine, Denmark), and the Endo Radar (Electronica Liarre, Italy).

The second generation was known as impedance-type apex locators because the devices here depended on the principle of impedance. Impedance principle suggests the presence of electrical impedance across the canal wall of the tooth. This impedance increases gradually and reaches its greater value at the apical part before being dropped dramatically at the cemento-dentinal junction. The devices in this generation used alternating electrical current which allowed the design of an electronic system. However, similar problems of incorrect readings were observed. To obtain accurate reading, the root canal should be free of electroconductive materials [59]. Other disadvantage of the devices were that they required calibration before using, complicated calculations after using, and no digital readout was present. In addition, there was a need to use special coated probes with these devices instead of endodontic instrument. The coated probes have the problem to be difficult place in narrow canals, and they lose their benefit after autoclaving [53, 58]. Sono-Explorer M-III (Hayashi Dental Supply, Japan) and Analytic/Endo (Orange, USA) (Fig. 4.7b) are some examples of devices from this generation.

The third generation is also known as frequency-dependent apex locators. In this generation, the devices use multiple frequencies to determine how far the instrument is from the end of the canal. The device here depended on the fact that different sites of the root canal show different impedances between low and high frequencies (400 Hz to 8 kHz). The lowest value is at the coronal part. As the file progress deeper into the canal, difference in impedances increases and reaches the highest value at CDJ. The devices contain more microprocessors that can do the required algorithm calculation. Unlike the previous generations, the devices can operate more accurately in the presence of electrolyte such as saline or sodium hypochlorite. The main disadvantage of these devices is that they need to be calibrated for each canal [53, 58]. An example of this generation is Apit or Endex/Apit-Endex (Osada, Japan) (Fig. 4.7c).

In the fourth generation (Ratio Type Apex Locators), the devices depended on the fact that it is possible to find difference in the combination of values of resistance and capacitance that provide the same value of impedance. Thus, instead of measuring the impedance as performed in the previous generation, the locators of this generation measure the resistance and capacitance separately, compare them with a database, and determine the distance to the apical foramen of the root canal. The accuracy of the devices becomes better with less chance of errors. The main disadvantage of the fourth-generation devices is that they should work in a dry canal or partially dried canal which make them inapplicable in heavy exudate cases or in the presence of bleeding [55, 58]. Some of the devices under this generation are RootZX^® (Morita, France), Elements Diagnostic Unit (SybronEndo), AFA Apex Finder, ROOT ZX II (Fig. 4.7d), and PROPEX II (Henry Schein Dental).

A great improvement can be observed in the fifth generation where apex locators can work precisely in any condition of the root canal: dry, wet, bleeding, or filled with any type of irrigants [59]. The devices can be used without the need for previous calibration. They use multiple frequencies instead of dual frequencies. Some examples of electronic apex locators from this generation are currently available in the market: Raypex 5^®, VDW, Allemagne, Apex Pointer+^® (Micro-Mega, France), Propex II^® (Dentsply Maillefer, France), Novapex^® (VDW, Munich), and Endometr e-Magic Finder (S-Denti Co., Ltd) (Fig. 4.7e).

The sixth generation, also known as adaptive apex locators, continue using multifrequency system. They can operate with good accuracy in dry and wet conditions, even with the presence of blood or exudates [60]. It can continuously adapt to the humidity degree in the root canal [55]. Furthermore, the devices are able to produce different kinds of sound to indicate the progress of the file in the root canal. Raypex^® 6 Apex Locator (VDW) and ProPex Pixi (Dentsply, USA) are examples of this generation (Fig. 4.7f).

4.8.4 Clinical Tips to Avoid False Reading

4.9 Sonics and Ultrasonic

Ultrasonic in dentistry was first introduced by Richman [62] in 1957. Its main use in dentistry is for scaling and root planning of teeth and in root canal therapy [58]. The term endosonics (Ultrasonics in endodontics) was first coined by Martin and Cunningham [63, 64] and was defined as the ultrasonic and synergistic system of root canal instrumentation and disinfection.

In endodontics, ultrasonic devices can be used either in instrumentation or passive ultrasonic irrigation (PUI). However, due to their aggressive nature, and difficulty in controlling dentin removal, they are no longer used for instrumentation [65–67].

Advantages of using ultrasonic in endodontics include access preparation and refinement of root canals, removal of intra-canal obstructions such as broken instruments and posts, root-end cavity preparation and refinement, placement of retrograde filling materials, ultrasonic condensation of gutta-percha, passive irrigation (sonic or ultrasonic), and needle activation during sonic or ultrasonic irrigation (active irrigation).

Ultrasonic and, more recently, sonic irrigation is a technology that relies on vibrating the irrigating needle itself, thus enhancing the flushing and increased permeation of the root canal system by the irrigating solution.

4.9.1 Types of Sonic Devices

Rispi-Sonic file and EndoActivator	These devices facilitate penetration of the irrigant, and improve mechanical cleansing, compared to needle irrigation [68]
Vibringe	This uses traditional syringe–needle delivery, in addition to the sonic vibration, thus showing better results than traditional syringe irrigation in the apical part of the canal [69]

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