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).

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).

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.

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

FIGURE 2-5 The Rinn XCP film positioner.

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.

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.

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.

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.

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).

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.

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

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

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

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).

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.

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.

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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