Endodontic Radiography : A Seminar

INTRODUCTION

Acc. To ADA, Oral & Maxillofacial Radiology can be defined as: 

“The speciality of dentistry and discipline of radiology concerned with the production and interpretation of images and data produced by all modalities of radiant energy that are used for the diagnosis and management of diseases, disorders and conditions of oral and maxillofacial region.”




Radiographs are essential they are a second set of "eyes" for the dentist.This is particularly true in endodontics, in which so many diagnostic and treatment decisions are based on radiographic findings. Because most structures of concern are not visible to the naked eye there is considerable dependence on radiographs which are an obvious necessity and a blessing. So, Endodontic radiographs traditionally form the backbone of the diagnosis, treatment procedures and follow-up of endodontic cases.

Radiographs perform essential functions in three areas. However, they have limitations that require special approaches. A single radiograph is a two-dimensional shadow of a three-dimensional object. For maximum information, the third dimension must be visualized and interpreted. The three general areas of application are diagnosis,treatment, and recall; each requires its own special approach.

New approaches to radiography have been and are being developed. These are unique; some will improve existing techniques in addition to decreasing the radiation dose to patients. The advent of digital imaging has revolutionized radiology. The term ‘Digital radiography’ refers to the method of capturing a radio graphical image by using a sensor, breaking it into electronic pieces and presenting and storing the image by using a computer.

This new technology includes digital radiography, digital subtraction radiology, and tomography.These systems are of considerable interest, offering the advantages of reduced radiation to thepatient, increased speed of obtaining the image,ability to be transmitted, computer storage and enhancement, and a system that does not require a darkroom or x-ray processor.Ease of use and cost are factors that currently preclude routine use of these systems in the general dental office.

HISTORY

In late 1895, a German physicist, W.C. Roentgen was working with a cathode ray tube in his laboratory, when he accidentally discovered x rays. Roentgen found that the X-ray would pass through the tissue of humans leaving the bones and metals visible. One of Roentgen’s first experiments late in 1895 was a film of his wife Bertha's hand with a ring on her finger.

14 days later the publication of Roentgen, Dr. Otto Walkhoff in Braunschweig made the first picture of the teeth.
William James Morton Junior published the first dental skiagraphs in USA the first article in the Dental Cosmos of April 24, 1896. In July 1896, Dr. C.E. Kells became the first man in the world to hold a dental clinic (held in Asheville, N.C.) using an X-ray machine .

•         HIGHLIGHTS OF HISTORY OF DENTAL RADIOGRAPHY

YEAR	EVENT	PIONEER/ MANUFACTURER
1895	Discovery of X-rays	W.C Roentgen
1896	First dental radiograph	O. Walkhoff
1896	First dental radiograph in united states( skull)	W. J Marton
1896	First dental radiograph in united states ( live patient)	C E Kells
1901	First paper on dangers of X-radiations	W H Rollins
1904	Introduction of bisecting technique	WA Price
1913	First dental text	HR Raper
1913	First pre wrapped dental film	Eastman Kodak Company
1913	First X-ray tube	W. D Coolidge
1920	First machine made film packets	Eastman Kodak Company
1923	First dental X-ray machine	Victor X-ray Corp, Chocago
1925	Introduction of bitewing technique	HR Raper
1933	Concept of rotational panaromics proposed
1947	Introduction of long cone paralleling technique	F G Fitzgerald
1948	Introduction of panaromic radiography
1955	Introduction of D speed film
1957	First variable kilovoltage dental X- ray machine	General electric
1978	Introduction of dental xeroradiography
1981	Introduction of E- Speed film
1987	Introduction of intraoral digital radiography
2000	Introduction of F speed film

VARIOUS RADIOGRAPHIC TECHNIQUES:-

Parallel Periapical Projection

Ideally, the part of the patient being radiographed is placed in the same plane as the film. The paralleling technique is used to position the film in the mouth parallel to the long axis of the tooth, and film-holding beam-aiming devices have been developed to facilitate film placement. The film tends to be held away from the tooth, except in the lower molar region.

Film placed parallel to the long axis of the teeth and exposed by cathode rays at a right angle to the surface of the film yields accurate images, with no foreshortening or elongation.

The reliability of the paralleling technique increases with practice. It is possible to obtain reproducible undistorted views, and by using localizing rings coning off can be avoided.

Taking paralleling radiographs with film holders may cause the patient discomfort, and is cumbersome with a rubber dam in place. Compromises involve the use of cotton wool rolls tongue spatulas and forceps .

Advantages

Geometrically accurate images are produced with little magnification. 

The shadow of the zygomatic buttress appears above the apices of the molars.

The periodontal bone levels are well represented.

The periapical tissues are accurately shown with minimal foreshortening or elongation.

The crowns of the teeth are well shown enabling the detection of proximal caries.

The horizontal & vertical angulations of the X-ray tube head are automatically determined by the positioning devices if placed correctly.

The X-ray beam is aimed accurately at the center of the image receptor.

Reproducible radiographs are possible.

The relative position of the image receptor, teeth & X-ray beam are always maintained, irrespective of the position of the patient’s head. This is useful for patient with disabilities.

Disadvantages

·        Positioning of the image receptor can be very uncomfortable.

·        Anatomy of mouth sometimes makes it impossible.

·        The apices of teeth can sometimes appear very near the edge of the image.

·        Positioning the holders in lower third molar regions can be very difficult.

Bisecting Angle Projection

When taking these projections one edge of the film is placed level with the occlusal or incisal surface of the tooth. The film axis may be parallel to the tooth in the lower molar region but in the anterior regions a considerable angle may be produced between the axis of the tooth and the film.

                 The main beam is directed at right angles to the plane bisecting the angle between the tooth and film. The dose of radiation used in these projections is very similar to that in parallel periapical radiographs.

The bisecting angle technique requires no additional equipment, is quick and easy to use with the rubber dam in place and is relatively comfortable for all patients, even those with small months. It does; however, tend to produce distorted and partial images, particularly if varying the angles or if the cone is incorrectly sited in relation to the film.

Advantages

·        Positioning of the image receptor is relatively comfortable.

·        Positioning is relatively simple & quick.

·        If all angulations are assessed correctly, the image of the tooth will be same length as the tooth itself and should be adequate (but not ideal) for most diagnostic purposes.

Disadvantages

·        Buccal roots of the maxillary premolars & molars are foreshortened.

·        Incorrect horizontal angulation will result in overlapping of the crowns & roots.

TYPES OF RADIOGRAPHS

Dental radiographic film is supplied in various sizes and degree of sensitivity, each designed for a specific purpose.

•         Intraoral Radiographs

▫         Intraoral Periapical (IOPA)

▫         Occlusal Radiographs

▫         Bitewing Radiographs

•         Extraoral Radiographs

▫         Panoramic Radiographs

▫         Lateral Cephalograms

                                                                       

Intraoral film.:Periapical, bite-wing, and occlusal are three types of intraoral film used to reveal different dental structures.

Periapical film is used primarily for radiographic examination of teeth and adjacent tissues to include the periapical region. Film packs come in three sizes: 0 for small children (22×35mm); 1which is relatively narrow and used for views of anterior teeth (24×40 mm); and 2, the standard film size used for adults(31×41 mm).

Bite-wing film is used to obtain a radiograph of the coronal two-thirds of opposing maxillary and mandibular teeth and their adjacent tissues on a single film. The film packets are provided with tabs that extend from the center of the film. When a radiograph is being made, the patient is instructed to bite down on the tab. The tab holds the film firmly in position with the lower half lying lingual to the mandibular teeth and the upper half held lingual to the maxillary teeth. They are useful for detecting interproximal caries and evaluating the height of alveolar bone. Size 2 film is normally used in the adults; the smaller size 1 is preferred in children. In small children size 0 may be used.

Occlusal film is a highly sensitive double-emulsion film supplied in packets similar to periapical film but in a size convenient for obtaining a view of the entire upper or lower arch or portions thereof. It is three times larger than size 2 film (57×76 mm). These films are used to obtain right angle views to the usual periapical view. Some packets contain two films. The first film is developed at normal time to give a detailed image of hard structures. The second film is developed in one half the normal time to reveal soft tissue images.

Extraoral film is used for radiographs of the jaws, facial bones, the temporomandibular joints, and other relatively large areas. This film has no embossed dot to identify right and left.

Intensifying screens are used with extraoral film to intensify the effects of the exposing rays and lessen the exposure time. A cassette is constructed of rigid metal, plastic, or cardboard. It often contains intensifying screens that magnify the x-ray beam, thus reducing exposure time. The film must be transferred to the cassette from its paper covering in the protection of the dark room.

Panoramic film, a type of extraoral film, is used in panoramic radiography. This film shows the entire dentition and surrounding bone structure.

ROLE OF RADIOGRAPHS IN ENDODONTICS

•         Presence of Caries that may involve or threaten to involve the Pulp

•         Number, course, shape and length of root canals

•         Calcification or obliteration of pulp cavity

•         Internal and External Resorption

•         Thickening of Periodontal Ligament

•         Nature and extend of Periapical and Alveolar Bone Destruction

•         Diagnose abnormalities like Dilaceration and Taurodontism

•         Diagnose fracture of root

•         To estimate and confirm the length of root canals before instrumentation (working length determination)

•         To confirm the position and adaptation of master cone

•         Evaluation of outcome of root canal therapy (post operative radiograph)

NORMAL RADIOGRAPHIC LANDMARKS

HOW TO OBTAIN A GOOD RADIOGRAPH

1.     Proper placement of film in the patient’s mouth

2.     Correct Angulation of the cone in relation to the film and oral structures

3.     Correct exposure time

4.     Proper developing technique

FILM HOLDERS

Film holders are beam-aiming devices, designed to hold the film at right angles to the X-ray beam to reduce distortion and produce a more exact image. Using these devices means that patients do not need to support the film with their fingers and the possibility of 'cone cutting' is reduced. Their use improves the diagnostic quality and allows the angle of radiographs to be similarly reproduced during recall assessment.

       The Rinn EndoRay allows parallel radiographs to be taken in the presence of endodontic hand instruments. It is in two parts, the body (or film holder), and the handle .The film holder is placed over the tooth and the patient asked to bite lightly on it. The handle is then attached to the body to aid the operator in centering the film in the beam. More recent versions include a centering ring.²²

The film holder is a modification of the commercially available Unibite Universal Dental X-Ray Film Holder (Indento flex, Switzerland). A square hole is cut on the bite-block of the film holder to accommodate the reamer or file .

IOPA RADIOGRAPHS IN ENDODONTIC THERAPY

•         Diagnostic Radiographs

•         Working Radiographs

•         Post operative Radiographs

•         Follow up Radiographs

DIAGNOSTIC RADIOGRAPHS

•         Ideally, these radiographs should be taken using paralleling angle technique

•         They should be of high quality without any foreshortening or elongination

•         They help for proper diagnosis of the case

•         These radiographs helps in determining the prognosis by comparison with post operative and follow up radiographs

WORKING RADIOGRAPHS

•         These radiographs are used for determining the position of instruments – files etc during the procedure.

•         These radiographs are to be taken without removing the rubber dam as it can cause contamination of the operating field.

•         A better alternative is the use of a hemostat as a film holding device.

POSTOPERATIVE RADIOGRAPHS

•         They are used to evaluate the endodontic treatment

•         They are taken after removing the rubber dam

•         Ideally paralleling angle technique should be used

•         They can be compared with the diagnostic radiograph 

FOLLOW-UP RADIOGRAPHS

•         These radiographs are taken to evaluate the  prognosis of the endodontically treated tooth

•         After obturation, the tooth may have to undergo procedures like core build up, crown fabrication etc

•         The follow up radiograph gives the health of the periodontium and the tooth by evaluating the presence of root resorption, other treatment failures etc

CONE IMAGE SHIFT TECHNIQUE

Clarke’s Rule (S.L.O.B Rule)

•         The object that moves in the SAME direction as the cone is located toward the LINGUAL

•         The object that moves in the OPPOSITE direction as the cone is located toward the BUCCAL

Advantages

•         Helps in separation of overlapping canals.

•         Working length of radiographs is better traced.

•         Helps in location of root resorptive process in relation to the tooth.

•         Helps in identification of anatomic landmarks and pathosis.

•         Also used to increase the visualisation of apical anatomy by moving anatomical landmarks.

Disadvantages

•         Results in blurring of the object that is directly proportional to cone angle.

•         Causes superimposition of structures in objects that have natural separation on parallel technique with cone shift.

BITE WING RADIOGRAPHS

Bitewing also known as interproximal radiographs includes the crowns

of the maxillary and mandibular teeth and the alveolar crest on the same film.

Types:

▫         Horizontal bitewing films

▫         Vertical bitewing films

•         Horizontal bitewing film:-

To obtain the desired characteristics of the bitewing examination described above, the beam Is carefully aligned between the teeth and parallel with the occlusal plane.

•         Vertical bitewing film:-

Are usually used when the patient has moderate to extensive alveolar bone loss. Orienting the length of the film vertically increases the likelihood that the residual alveolar crest in the maxilla and mandible will be recorded on the radiograph.

DIGITAL RADIOGRAPHY IN DENTISTRY

•         Digital radiography was introduced in Dentistry in 1987. 

•         The technology has been gaining in acceptance.

•         In 2005 more than 22% of dentists were using digital radiography.

•         The digital systems relies on an electronic detection of an X ray generated image that is electronically processed and reproduced on a computer screen

•         A conventional x-ray tube is the source of X-radiation in most digital systems.

•         Digital radiography requires 50-80% less radiation exposure in order to achieve an image compared to film systems.

Advantages

•         Reduced exposure to radiation

•         Increased speed of obtaining the image

•         Possibility for digital enhancement

•         Storage as digital data in computers

•         Ease of transmissibility

•         Elimination of manual processing steps

•         No lead foil waste generated.

DENTAL RADIOGRAPHY SAFETY

The goal of dental radiography is to obtain useful diagnostic information while keeping radiation exposure to the patient and dental staff to a minimum.

•         The operator of the dental unit must stand at least six feet from the useful beam or behind a protective barrier.

•         Stand at an angle of from 90 to 135 degrees from the central ray.

•         Do NOT stand in the path of the primary x-ray beam.

•         If a protective barrier is used, it must have a viewing window to allow the operator to see the patient.

INFECTION CONTROL IN DENTAL RADIOLOGY

Infection Control Procedures Before Exposure

•         Before bringing the patient into x-ray room clean and disinfect all surfaces you will touch including chair and counter

•         Cover this surfaces with plastic wrap

•         Gloves should be worn at all times

•         Operators must wash hands when change gloves between patients

  Operatory Breakdown After Taking Radiographs

•         Leave the operatory neat and clean

•         Dismantle the instruments and place them in the containers provided

•         Dispose of other contaminated items in the plastic bag

•         Wipe all contaminated surfaces with a disinfectant (do not spray)

•         Turn off x-ray unit and put tube head against the wall

•         Lead apron is cleaned and placed over the backside of the chair

•         Disinfect the gloves before go to the darkroom

Darkroom Infection Control Guidelines

•         Strip films from packets using gloves

•         Insert films in the processor with the gloves

•         Films should be handled as little as possible, preferably by the edges.

•         After all films are in the processors, remove the gloves and wash your hands

•         Handle processed film with clean hands

ADVANCE RADIOGRAPHIC TECHNIQUES FOR ENDODONTIC DIAGNOSIS

1. Tuned Aperture Computed Tomography    (TACT)

2. Magnetic Resonance Imaging (MRI)

3. Ultrasound

4. Computed Tomography

5. Cone Beam Computed Tomography

Tuned Aperture Computed Tomography (TACT)

•         Tuned aperture computed tomography works on the basis of tomosynthesis (Webber & Messura 1999).

•         A series of 8–10 radiographic images are exposed at different projection geometries using a programmable imaging unit, with specialized software to reconstruct a three-dimensional data set which may be viewed slice by slice.

Advantages of TACT

•         The images produced have less superimposition of anatomical noise over the area of interest (Webber et al. 1996, Tyndall et al. 1997).

•         The overall radiation dose of TACT is no greater than 1–2 times that of a conventional periapical X-ray film as the total exposure dose is divided amongst the series of exposures taken with TACT (Nair et al. 1998, Nance et al. 2000).

•         Additional advantages claimed for this technique include the absence of artefacts resulting from radiation interaction with metallic restorations.

•         The resolution is reported to be comparable with 2-D radiographs (Nair & Nair 2007).

•         Webber & Messura (1999) compared TACT with conventional radiographic techniques in assessing patients who required minor oral surgery. And They concluded that TACT was ‘more diagnostically informative and had more impact on potential treatment options than conventional radiographs.

•         Recently, studies have concluded that TACT is suitable for detecting vertical root fractures (Nair et al. 2001, 2003)

Magnetic Resonance Imaging (MRI)

•         An MRI scan is a specialized imaging technique which does not use ionizing radiation.

•         It involves the behaviour of hydrogen atoms (consisting of one proton and one electron) within a magnetic field which is used to create the MR image.

•         The main dental applications of MRI to date have been the investigation of soft-tissue lesions in salivary glands, investigation of the temporomandibular joint and tumour staging.MRI has also been used for treatment planning dental implant placement.

•         Recently, Tutton & Goddard (2002) performed MRI on a series of patients with dental disease. The authors also claimed that the nature of periapical lesions could be determined as well as the presence, absence and/orthickening of the cortical bone.

Advantages of MRI

•         Goto et al. (2007) compared measurements taken from three-dimensional reconstructed MRI and CT images of a dry mandible and hemi-mandible. They concluded that the accuracy of MRI was similar to CT.

•         MRI scans are not affected by artefacts caused by metallic restorations (for example amalgam, metallic extracoronal restorations and implants) which can be a major problem with CT technology (Eggars et al. 2005).

•         Cotti & Campisi (2004) suggested that MRI may be useful to assess the nature of endodontic lesions and for planning periapical surgery.

•         Drawbacks Poor resolution compared with simple radiographs

•         Long scanning times,

•         Great hardware costs and limited access only in dedicated radiology units.

•         Different types of hard tissue  (for example enamel and dentine) cannot be differentiated from one another or from metallic objects;

It is for these reasons that MRI is of limited use for the management of endodontic disease.

Ultrasound

•         Ultrasound is based on the reflection (echoes) of US waves at the interface between tissues which have different acoustic properties (Gundappa et al. 2006).

•         Ultrasonic waves are created by the piezoelectric effect within a transducer (probe).

•         The greater the difference between tissues, the greater the difference in the reflected US energy and the higher the echo intensity.

•         Tissue interfaces which generate a high echo intensity are described as hyperechoic (e.g. bone and teeth), whereas anechoic (e.g. cysts) describes areas of tissues which do not reflect US energy.

•         Cotti et al. (2003) used US to assess if it was possible to differentially diagnose periapical lesions.

•         Ultrasound is blocked by bone and is therefore useful only for assessing the extent of periapical lesions where the there is little or no overlying cortical bone.

•         Whilst US may be used with relative ease in the anterior region of the mouth, the positioning the probe is more difficult against the buccal mucosa of posterior teeth.

•         In addition, the interpretation of US images is usually limited to radiologists who have had extensive training in the use and interpretation of US images.

Computed Tomography

•         Computed tomography is an imaging technique which produces three-dimensional images of an object by taking a series of two-dimensional sectional X-ray images.

•         Early generations of the CT scanner acquired ‘data’ in the axial plane by scanning the patient ‘slice by slice’ using a narrow collimated fan shaped X-ray beam passing through the patient to a single array of reciprocal detectors.

•         The detectors measured the intensity of X-rays emerging from the patient.

•         Over the last three decades, there have been considerable advances in CT technology. Current CT scanners are called Multislice CT (MSCT) scanners

Advantages

•         Three-dimensional images.

•         Elimination of anatomical noise

•         High contrast resolution, allowing differentiation of tissues with less than 1% physical density difference to be distinguished compared with a 10% difference in physical difference which is required with conventional radiography (White & Pharaoh 2004).

•         Tachibana & Matsumoto (1990) were able  to gain additional information on the root canal anatomy and its relationship to vital structures such as the maxillary sinus.

•         Velvart et al. (2001) found that CT detected the presence of an apical lesion and the location of the inferior alveolar nerve in all cases, compared with 78% and 39% respectively with periapical radiographs.

•         Furthermore, additional essential information such as the buccolingual thickness of the cortical and cancellous bone, the position and inclination of the root within the mandible could only be assessed using CT.

Disadvantages

•         The uptake of CT in endodontics has been slow for several reasons,

▫         High effective dose (Ngan et al. 2003) and

▫         Relatively low resolution of this imaging technique.

▫         High costs of the scans, scatter because of metallic objects,

▫         Poor resolution compared with conventional radiographs & the fact that these machines are only found in dedicated radiography units (for example hospitals).

CT technology has now become superceded by cone beam computed tomography (CBCT) technology in the management of endodontic problems.

Cone Beam Computed Tomography (CBCT)

•         Cone beam computed tomography is a major breakthrough in dental imaging. For the first time, the clinician is able to use a patient-friendly imaging system to easily view areas on interest in any plane rather than being restricted to the limited views available up to now with conventional radiography

•         Cone beam computed tomography or digital volume tomography is an extra-oral imaging system which was developed in the late 1990s to produce 3-D scans of the maxillo-facial skeleton at a considerably lower radiation dose than CT.

•         Most CBCT scanners either scan the patient sitting or standing up. The X-ray beam is cone-shaped, & captures a cylindrical or spherical volume of data, described as the field of view.

•         CBCT differs from CT imaging in that the entire 3-D volume of data is acquired in the course of a single sweep of the scanner, using a simple, direct relationship between sensor and source which rotate synchronously around the patient’s head.

•         Depending on the CBCT scanner used, the X-ray source and the detector rotate between 180⁰ and 360⁰ around the patient’s head.

Use Of CBCT In The Management Of Endodontic Problems

•         Detection of apical periodontitis.

•         Pre-surgical assessment.

•         Assessment of dental trauma.

•         Assessment of root canal anatomy.

•         Its major advantage over CT scanners is the

•         Substantial reduction in radiation exposure, because of rapid scan times, pulsed X-ray beams and sophisticated image receptor sensors.

•         Simple to use and take up about the same space as panoramic radiographic machines,

•         The radiation dose may be further reduced by decreasing the size of the field of view, increasing the voxel size and/or reducing the number of projection images taken as the X-ray source rotates around the patient.

Limitations of CBCT

•         Do not have the resolution of conventional radiographs.

•         Scatter and beam hardening caused by high density neighbouring structures, such  as enamel, metal posts and restorations.

CONCLUSION

•         Radiograph is a very powerful tool for a dentist, especially an Endodontist with which he is able to examine the status of hard tissue which are beyond the field of his naked eyes.

•         Application of radiology gives new standards for the diagnosis, treatment and prognosis of a dental problem

REFERENCES:

•      John I. Ingle, Leif K. Bakland. Endodontics. 5^th Ed.

•     Stuart C. White, Michael J. Pharoah. Oral radiology Principles and interpretation. 5^th Ed.

•    Parks ET, Williamson GF. Digital Radiography: An Overview. J Contemp Dent Pract 2002 November;(3)4:023-039.

•   Patel S, Dawood A, Whaites E, Pitt Ford T. New dimensions in endodontic imaging: part 1. Conventional and alternative radiographic systems. International Endodontic Journal.2008.

•       Alexi Assmus. Early history of X-Rays.