Using Radiographs In Endodontics: Types And Applications

Abstract

Radiographs are important tools used in endodontics. They are the most accurate and least subjective diagnostic aids available to endodontists for diagnosis of diseases affecting the pulp. They are also important for treatment planning, monitoring and recall. Good radiographs serve as the “eye” of the dentist before, during and after the treatment.

Introduction

Endodontics is defined by the American Association of Endodontists as the branch of dentistry that is concerned with the morphology, physiology and pathology of the human dental pulp and periradicular tissues. It encompasses the basic clinical sciences including biology of the normal pulp, the aetiology, diagnosis, prevention and treatment of diseases and injuries of the pulp; and associated periradicular conditions. The pulp contains blood vessels, nerve fibres and connective tissues. It extends from the crown of the tooth to the tip of the root where it connects to the periapical structures. Pulp pathologies include: reversible pulpitis, irreversible pulpitis, hyperplastic pulpitis and pulp necrosis. These can be sequel to dental caries, tooth fracture or tooth wear and result in a need for treatment of the affected teeth. Depending on the severity, treatment options include removing the affected teeth and replacing them with prostheses or saving the affected teeth by endodontic treatment. In modern dentistry, more importance is placed on saving a tooth rather than extracting it and this has resulted in an upward trend in endodontic activities. Scope of endodontic include but not limited to: diagnosis and treatment of pain of pulpal and or periradicular origin, vital pulp therapy such as direct pulp capping and indirect pulp capping, pulpotomy, non surgical root canal therapy with or without periradicular pathology, surgical removal of tooth structures such as in apicectomy, hemisectioning, retreatment of previously treated teeth, pulp regeneration, bleaching of discoloured teeth, endodontic implant amongst others. Successful root canal therapy depends on ability to obtain accurate radiographs. Imaging is an important, indispensable tool in the diagnosis, treatment and follow-up in endodontics. It illumines the inner parts of teeth which are otherwise taken to be dark and hidden zones. It allows endodontists and dentists generally to visualize areas not accessible by other diagnostic means. In the history of radiography, Professor Wilhelm Konrad Roentgen in 1895 discovered cathode rays. The first dental radiograph was taken by Dr. Otto Walkoff in his own mouth in 1895. Dr. C. Edmund Kells used X-ray to determine tooth length during root canal therapy in 1899. Dr. Weston A. Price advocated the use of radiographs to check the adequacy of root canal filling in 1900. Since the use of radiology began, imaging in dentistry and particularly in relation to endodontics has undergone a lot of development. The aim of this article is to give enlightenment on the effectiveness of the widely used radiography system with regards to endodontic treatment. A clinician must be trained to identify normal anatomical landmarks and their variations as well as variations owing to pathology in a radiograph.

Uses/application of radiograph in endodontics:

1. Aid in diagnosis of hard tissue alterations of the teeth and periradicular structures.
2. Determine the number, location, shape, size, and direction of roots and root canals.
3. Estimate and confirm the length of canals before instrumentation (working length determination).
4. Aid in locating a pulp space markedly calcified and/or receded.
5. Determine the relative position of structures in the facial–lingual dimension.
6. Confirm the position and adaptation of master cone.
7. Evaluation of outcome of root canal therapy.

Types:

1. Conventional radiography
2. Digital radiographs
3. Digital subtraction
4. Ultrasound
5. Radio visiography
6. Computed tomography (CT)
7. Cone beam computed tomography (CBCT).

Conventional radiograph This involves the exposure of X-ray film to radiation; the film is chemically processed to produce a 2D image. Examples of intra oral conventional radiograph used in endodontics include: periapical radiograph, bitewing radiograph.

Periapical radiograph In most endodontic cases, periapical radiograph is commonly used as it provides a high definition image at a low radiation dose; it also provides useful information for the presence and location of periradicular lesions, root canal anatomy and the proximity of adjacent anatomical structures. An intraoral periapical radiograph can reveal the following findings: coronal radiolucency, tooth fillings, length of root, apical foramen, periapical radiolucencies, lateral radiolucencies, curved root, number of roots present, number of canals present, lamina dura (continuity, shape and density), periodontal ligament (shape and width), resorbed root, canal calcification. A properly placed film shows approximately three teeth and at least 3-4mm beyond the apex. However, a limitation of periapical radiograph is geometric distortion. Techniques for taking periapical radiographs include: bisecting angle technique, paralleling technique and modified paralleling technique.

Paralleling technique Paralleling technique is the technique of choice in endodontics because it produces most accurate periapical radiograph. Some studies have proven it to have more effective and superior diagnostic quality than other techniques. In this technique, an x-ray film is placed parallel to the long axis of the tooth to be exposed and the x-ray beam is directed perpendicular to the film. Film holders should be used to get best result. Advantages of this technique over bisecting technique are better accuracy of image, reduced dose of radiation, reproducibility. The limitation of this technique includes difficulty in using it in patients with shallow vault, gag reflex and when rubber dam is in place. Bisecting angle technique In this technique, the X-ray beam is directed perpendicular to an imaginary plane which bisects the angle formed by recording plane of X-ray film and the long axis of the tooth. The limitations of bisecting technique include cone cutting, image distortion, superimposition of anatomical structures. Modified paralleling technique Central beam is oriented perpendicular to radiographic film but not to teeth. It is beneficial in some special situations where paralleling technique is not feasible. Bitewing radiograph This reveals crowns of maxillary teeth, crowns of mandibular teeth and alveolar crest on the same film. They are indicated primarily to detect interproximal caries and recurrent caries under existing restoration.

Limitations of Conventional X-ray

1. Uses an analog film.
2. Produces two-dimensional (2D) image and compress three dimensional anatomy into two dimensional image and reduces the diagnostic value.
3. Geometric distortion: due to complexity of the maxillo-facial skeleton, radiographic images do not always accurately replicate the anatomy being assessed.
4. Superimposition of anatomic structures due to complex anatomy of the oral cavity, this causes difficulty interpreting the radiograph.
5. Does not accurately demonstrate the presence of every lesion.
6. Inability to manipulate images.
7. Higher radiation dosage required.
8. Inability to archive images.
9. Increased time between exposure and image interpretation.
10. Films are easily distorted through improper techniques.

Advances in endodontic imaging

Many limitations of the conventional radiographic techniques have been overcome by the newer methods. The newer digital systems rely on an electronic detection of an X-ray generated image which is then electronically processed and reproduced on a computer screen. Digital Radiograph

Digital radiograph system utilizes computer technology in the capture, display, enhancement, and storage of radiographic images. It uses x-ray sensitive plates to directly capture data and immediately transfers it to a computer system without the use of an intermediate cassette. This gives advantages of immediate image preview and availability, elimination of costly film processing steps, a wider dynamic range as well as the ability to apply special image processing techniques that enhance overall display quality of the image (22). There are two major technologies used in intraoral digital radiography: 1. Solid-state detectors a. Charge-coupled device (CCD) b. Complementary metal oxide semiconductor (CMOS) Both can be indirect detectors using a scintillating screen such as caesium iodide or gadolinium oxysulfide, or (less commonly) can use direct conversion of X-ray photons to electrons (e. g. , Cadmium-Telluride technology). 2. Storage phosphor detectors - Photostimulable phosphor (PSP). Digital Subtraction Radiograph (DSR)

The use of Digital Subtraction Radiograph has made a significant improvement in the detection of dental & maxillofacial lesions. It can be used in the evaluation of the progression, arrest, or regression of caries lesions. It also has the ability to detect root resorption as low as 0. 5mm and when underexposed radiographs are used, it can detect even soft tissue changes. In addition, it is used for evaluation of periradicular healing of endodontically treated teeth. So any lesion (including bony cysts or tumours) with potential of change over time can be studied in this technique. Radiographs are taken precisely in the same position and with the same beam geometry and exposure parameters, images can then be subtracted to show changes over time. This technique has been widely used for research purposes. It offers greater visualization of radiographic changes between a pair of radiographs by subtracting out the unchanged. It is used to compare standardized radiographs taken at different time. It involves subtracting all unchanged structures and these areas are displayed in neutral gray shade in the subtraction image while regions that have changed are displayed in darker or lighter shades of gray Advantages include: lower dose of radiation, computer manipulation, image analysis, no film processing. Ultrasound in endodontic

Ultrasound does not expose patients to any radiation. It uses sound waves with a frequency outside the range of human hearing (20 kHz) and can be used to view normal and pathological conditions involving the bones and soft tissues of the oral and maxillofacial regions. The application of echographic examination to the study of endodontic disease has been attempted with success. The alveolar bone appears as a total reflecting surface (white). If healthy, the root contours of the teeth are even whiter (hyperechoic). A fluid-filled cavity in the bone appears as a hypo-reflecting surface (dark). The degree of reflection depends on the clarity of the fluid (hypo echoic).

Radio visiography

This system is based on digital image capture with a charged coupled device (CCD) capable of image enhancement using up to 256 shades of gray. Radio visiography (RVG) comprises of four basic components, an x -ray unit, an electronic timer, an intraoral sensor, a display processing unit (DPU), and a printer. In endodontics, radio visiography is used for diagnosing carious lesions, measuring root lengths, detecting periapical pathology and root fractures. RVG requires 23% of the radiation dose when compared to the conventional radiograph. Other advantages include ability to enlarge specific areas that may be of use during endodontic treatment. It can also be stored in the computer. However, the sensors are relatively small in size and the films are thicker than the conventional films.

Computed tomography (CT)

Computed tomography produces 3D images of an object by using a series of 2D image data, to mathematically reconstruct a cross-section of the object. It helps in identification of anatomical structures, pathologies involving the tooth and the tooth structures.

Cone beam computed tomography (CBCT)

Cone-beam computed tomography produces three-dimensional information of the teeth and their surrounding tissues and maxillofacial skeleton. This is usually achieved with a substantially lower radiation dose that is very effective, compared to conventional computed tomography (CT). Potential endodontic applications include diagnosis of endodontic pathology and canal morphology, assessment of pathology of the non-endodontic origin, evaluation of root fractures and trauma, analysis of external, internal root resorption, invasive cervical resorption, and pre-surgical planning. It can also be used for early detection of periapical diseases. While the advantages include better accuracy, higher resolution, reduced scan time and lower radiation dose. It also has drawbacks of limited availability, significant capital investment, and medico-legal considerations. The improvements in imaging technology have helped in obtaining a near perfect image for accurate diagnosis. Cone-beam computerized tomography should however not be seen as a replacement for conventional dental radiography, but rather as a diagnostic adjunct. Radiation safety

As multiple radiographs are often implicated in endodontic, the ability to take radiographs of high diagnostic value, at the first attempt, during various stages of treatment is paramount. Recognition of the harmful effects of radiation and the risks involved made the International Commission on Radiological Protection (ICRP) to establish guidelines for limiting the amount of radiation received by both dentists and the public. The three important principles include: A) Justification – no radiograph should be taken unless it is absolutely necessary and provides benefit to the patient. B) Optimisation – exposure dose should be kept as low as reasonably achievable (ALARA principle) to coincide with high image quality, taking economic and social factors into account. C) Limitation – the dose equivalent to individuals should not exceed the limits recommended by the ICRP. The dentist should also inform the patient the importance and benefits of radiographs in endodontics, which makes it a requirement in diagnosis and treatment. Although levels of radiation used in endodontic radiography is very much lesser than that which can cause harm to the patient. It is still best to keep ionizing radiation to a minimum, for the protection of both the patient and dental delivery team. The principles of ALARA (as low as reasonably achievable), which are essentially ways to reduce radiation exposure, should be followed as closely as possible to minimize the amount of radiation that both patient and treatment team receive. Other ways of reducing radiation dosage are: a) Use of high-speed films – E speed film is almost twice as fast (sensitive) as D-speed film, whereas F-speed film requires about 75% the exposure of E-speed film and only about 40% of D-speed. In practice, this means patients are exposed to radiation for only 0. 2 second for E-speed film and 0. 15 second for F-speed film without compromising image quality. b) Field size trimming, long cone and collimation – field size of radiation is constrained by collimation of the beam. Employing a rectangular collimation (which closely matched the film size 30mm x 40mm) can result in reducing 60% of x-ray dose. Use of long cone (at least 200mm) increases the distance between the radiation source and the skin, therefore deducting the size of the X-ray beam. This results in a smaller volume of tissue irradiated and a more accurate image. c) X-ray filtration – absorbs low-energy photons whose penetrating power is limited and contributing nothing to film image, but which will be absorbed by the patient. Its use results in reduced exposure with no loss of radiological information. d) Use of leaded aprons and collars – these protect the vital organs against scattered radiation.

Conclusion

Radiographs are essential to all phases of endodontic therapy. They contribute information important for the diagnosis and the various treatment phases. They also help evaluate the success or failure of treatment. It is imperative to master radiographic techniques to achieve maximum quality and management of patients. Advances in endodontic radiography and imaging have made it possible for better diagnosis, treatment and evaluation in endodontics. Expertise in interpretation is however, essential for recognizing deviations from the normal and for understanding the limitations associated with endodontic radiography.

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