2: Problem-Solving Techniques in Making Radiographic Images

Chapter 2

Problem-Solving Techniques in Making Radiographic Images

Problem-Solving List

Problem-solving challenges and dilemmas relative to making diagnostic radiographic images addressed in this chapter are:

The Ideal Dental Radiographic Image
Handling of Film and Digital Sensors
Controlling Variables

    Exposure
    Film/sensor position
    Radiation beam angulation
Problem Solving in Evaluation of Image Quality

    Correct and accurate images
Effects of Incorrect Angulation on Images of the Teeth

    Foreshortening
    Elongation
    Anterior-posterior angulation
A Quality Dental Image Revealing Normal Structures
Advances in Radiology: Digital and Cone-Beam Computed Tomography
Clinical Directives

“The most commonly used clinical tool to assist in making a diagnosis is without doubt the x-ray. It has been an invaluable boon to mankind, giving him a sixth sense to penetrate into the otherwise unknown. It leads us out of the dark as no other diagnostic can. Without x-rays one can hardly practice dentistry in an adequate manner or render the patient a satisfactory oral health service.”< ?xml:namespace prefix = "mbp" />7

L.I. Grossman, 1946

Before a meaningful discussion of the diagnostic interpretation of radiographs can begin, the technical quality of the image must first be assessed. A poorly made radiographic image will not contribute as much to the process of diagnosis as a well made one, but this self-evident concept is missed by many clinicians. The process of diagnosis may be entirely subverted by erroneous conclusions drawn from inadequate radiographs and could lead to inappropriate treatment. Tension arises when the clinician has made an inadequate image and a decision must be made. Is the information to be gained by remaking the image worth the added exposure of the patient to radiation? This ethical dilemma is usually resolved by remaking the image if the first fails to provide necessary information. Fortunately, modern dentistry has both low-exposure radiographic film and low-exposure digital radiography, so additional exposures have far less long-term risk than in the past. Nevertheless, it is incumbent on the clinician to review the cause of the radiographic error and correct it prior to additional exposures. It is the purpose of this chapter to review principles and practical techniques for obtaining diagnostically useful dental radiographic images, primarily for diagnosis in endodontics.

The Ideal Dental Radiographic Image

What is an ideal radiographic image? There are several aspects to be considered in answer to this question. First, the image should be neither too light nor so dark that it fails to show desired detail. It should have clarity of detail and be free of marks and blemishes. The image should represent the teeth without overlapping of proximal surfaces or roots. It should also represent the teeth as dimensionally accurate as possible, which occurs when the film is able to be placed in a position that is exactly parallel to the long axis of the tooth and the x-ray beam exposes the film at right angles. Clinically, this ideal is difficult to achieve in some areas because of the anatomy of the location into which the intraoral film or digital sensor is to be placed.

Handling of Film and Digital Sensors

Improper handling of film and poor darkroom technique can ruin otherwise excellent images. Dark spots, general foggy darkening, or a completely black film can indicate exposure to radiation or light, either by leaving unexposed film unprotected in the area where films are exposed or by natural light leaking into the darkroom during processing. It can also result from storage in areas where the temperature may exceed 80°F. Blemishes can be due to chemicals on the hands while handling undeveloped film and scratching of the emulsion before complete drying. Problems such as too much or too little contrast may indicate that the kVp is too high or too low. Discoloration such as brown staining of finished radiographs may indicate a problem with the fixer, either insufficient time for fixing or an exhausted fixer solution. If any of these problems arise with persistence, it is wise to review the recommendations of the manufacturer for both the x-ray machine and film to be sure the exposures and film are well matched. Secondly, it is worthwhile to review film handling and darkroom technique with all auxiliary personnel.

Digital sensors are less affected than film by environmental factors. There are no problems with exposure to light or radiation of the sensors not in use. The most frequent problems arise from infection control, frequent use and wear of connections, mechanical degradation, mishandling, the sensor itself wearing out, and patient concerns.5

Controlling Variables

Good image making with appropriate equipment consists in the control of three variables: exposure, film or digital sensor position, and beam angulation. A good radiographic image for endodontic diagnostic and treatment purposes is obtained when the center of the x-ray beam passes through the apex and projects the tooth on the receptor film or sensor at a right angle (Fig. 2-1).

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FIGURE 2-1 Art diagram.

Exposure

Always follow the recommended exposure settings provided by the manufacturer of the radiographic equipment. For conventional film, the film type and speed must also be considered. Underexposure results in the loss of details such as the periodontal ligament space and lamina dura around the apex (Fig. 2-2, A). There is also a loss of contrast which makes it difficult to detect pathosis that lacks clear borders, such as caries. Increasing the exposure to recommended guidelines will result in a clinically useful film (see Fig. 2-2, B).

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FIGURE 2-2 A, Radiograph that is underexposed. B, An ideal, clinically useful exposure.

Overexposure tends to make normal structures appear pathologic. Radiolucency is observed in areas such as the cervical regions of teeth just above crestal bone, often referred to as cervical burnout, which resembles caries. There can also be loss of detail owing to excessive contrast in the film (Fig. 2-3).

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FIGURE 2-3 Radiograph that is overexposed.

Film/Sensor Position

If a film packet or digital sensor is not completely behind the tooth to be studied, the tooth or portion of interest will not be on the image. In endodontics, the area of interest is almost always the apex (Fig. 2-4). Commercially available intraoral film positioners such as the Rinn XCP (Dentsply Rinn, Elgin, IL, USA) are designed to place the film or sensor in the ideal position to capture the entire tooth (Fig. 2-5). When the patient bites on the film holder, the film is positioned to the maximum depth, and the apices will inevitably be present on the image (Fig. 2-6). The use of positioners can eliminate many problems in preoperative and postoperative image making.

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FIGURE 2-4 Radiograph that fails to capture the root apices. Use on an increased angulation cannot compensate for this error.

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FIGURE 2-5 The Rinn XCP film positioner.

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FIGURE 2-6 The Rinn XCP in place for exposure of a mandibular molar. Note how the bite block device holds the film at full depth. The upper edge of the film is even with the occlusal plane.

The major challenge during root canal treatment is to make accurate images while the dental dam is in place.6 The hemostat can function similarly to the film positioner. The film packet is clamped along the edge and positioned in the mouth so that the instrument rests on the incisors or premolar. This positions the film to the maximum depth. The patient can maintain the film in position extraorally (Fig. 2-7). Digital sensors come with holders of similar design, and once the film/sensor is in place, the hemostat/holder also provides a measure of safety. A film packet or sensor held by a finger might easily become loose in the mouth.

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FIGURE 2-7 A, Hemostat holding the film or sensor. B, If the dental dam were in place, the hemostat could function like the film holder.

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CLINICAL PROBLEM

Problem

Even with a hemostat/holder, the patient is unable to keep the film deep enough to capture the apices of a mandibular molar on a preoperative image.

Solution

The film is placed in position with the hemostat/holder, and the patient is instructed to bite together. This will force the film/sensor downward to the proper depth, and at the same time the musculature of the floor of the mouth will relax (Fig. 2-8). There is also less of a tendency to lose this position if the patient should swallow before the film/sensor is exposed. This approach will be effective even with the rubber dam in place.

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FIGURE 2-8 A, It is difficult for some patients to hold the film sufficiently deep in the floor of the mouth. B, The hemostat will aid in maintaining the proper position by resting on the incisors. It also helps to have the patient close the mouth.

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CLINICAL PROBLEM

Problem

The patient has a narrow mandibular arch which makes placement of the film packet/sensor difficult for imaging the anterior teeth.

Solution

A conventional film packet can be bent at the edges to allow placement in the narrow space (Fig. 2-9, A and B). Pediatric-sized radiographic films can also serve but are shorter in length and may not capture the apices. The only option with digital radiography is to obtain a sensor of narrow width, which is available with some systems. If the mandibular arch is very narrow, as is sometimes the case with mandibular exostoses (tori), the film packet can be bent in half and clamped in the hemostat. Using a sensor in the presence of an exostosis can be most challenging and requires careful placement of the sensor. It is equally important to position the film/sensor as parallel as possible to the long axis of the tooth. The mandibular molars are the easiest teeth to make images of, since placement of the film/sensor is almost always automatically parallel to the tooth (Fig. 2-10). In the mandibular anterior region, the floor of the mouth and the attachment of the tongue to the genial tubercles are impediments to placement of the film/sensor to the proper depth. Images of the anterior teeth often appear very short. So long as the film/sensor is parallel to the tooth, it can be placed farther back into the mouth to allow the base of the tongue to be depressed (Fig. 2-11). It is not necessary to have the film/sensor immediately adjacent to or in contact with the tooth. By placing the film/sensor farther back into the mouth, the base of the tongue may be depressed. Placing a plastic cushion along the lower border of the film/sensor where it contacts the soft tissues is more comfortable for the patient (Fig. 2-12).

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FIGURE 2-9 A, Standard sized film packet can be adapted to variable anatomic situations by bending the sides or corners. This will leave a line on the resultant image. Do not place the bend where it will interfere with the desired image of the tooth. B, A standard sized film adapted to a narrow arch.

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FIGURE 2-10 The anatomy of the lingual space is usually ideal for placement of the film or sensor parallel to the tooth.

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FIGURE 2-11 For mandibular anterior teeth, film placement should be as parallel as possible. Contact or proximity to the teeth is not important.

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FIGURE 2-12 Edge-Ease cushions make placement of films in the sublingual spaces more comfortable.

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CLINICAL PROBLEM

Problem

The patient has a muscular tongue and has a difficult time maintaining the film in position behind the anterior teeth, even though the tongue can be depressed.

Solution

Position the film/sensor using the hemostat/holder. Instruct the patient to maintain the handle of the hemostat/holder in contact with an incisor to the side as the hemostat exits the mouth. This will usually work with or without the dental dam in place but may require anesthesia (Fig. 2-13).

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FIGURE 2-13 For muscular tongues, instruct the patient to force the hemostat down to rest on the incisor. Most patients can tolerate this without anesthesia. A film positioner functions in exactly the same way.

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Maxillary teeth are always a greater challenge in imaging because of the limited depth of the palatal vault and the anatomic lack of parallelism between the long axes of the teeth and the surface of the palate. To counter this, it is not necessary to have the film in contact with the tooth. For maxillary imaging, having the film or sensor in contact with the crowns (Fig. 2-14, A) is actually counterproductive. In this position, the film/sensor is never parallel to the long axis of the tooth and will lead to elongated teeth on the image. In ideal palatal placement, the apical edge of the film/sensor is usually in the midline of the vault, and the incisal edge is far from the crown of the tooth (see Fig. 2-14, B). This is the exact position obtained with a film positioner. When the dental dam is in place, the same positioning can be obtained using the hemostat/holder. The dental dam and clamp actually help to keep the occlusal edge of the film/sensor away from the tooth.

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FIGURE 2-14 A, If the film or sensor is in contact with the crown, the resultant image may be elongated. B, Ideal film placement should be as paralle/>

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Jan 2, 2015 | Posted by in Endodontics | Comments Off on 2: Problem-Solving Techniques in Making Radiographic Images
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