Pocket Atlas of Dental Radiology (eBook)

Intraoral Dental Radiographs

Apical and Periodontal Projections

For all dentists who elect to use a panoramic radiograph for basic data collection during the initial examination of a patient, individual intraoral dental radiographs are relegated to a supplementary role to answer special, specific questions that demand exceptional radiograph quality. A complete 18-film intraoral radiographic survey in patients of all ages should—today—only be performed if the practice does not have panoramic radiographic equipment. There exists considerable risk for both the patient and the dentist if the radiographic examination is incomplete, i.e., if pathologic conditions go undetected. This is especially true concerning incomplete initial examinations performed using individual intraoral radiographs (of all types).

From the standpoint of direction of the central ray, intraoral dental radiographs can be differentiated into the following types of special films:

1. a. Apical projection with the central ray directed through the region of the tooth apex, for optimum depiction of apical or periapical lesions.
2. b. Periodontal projection with the central ray directed through the upper third of the tooth root for radiographic examination of periodontal lesions.
3. c. Coronal projection (bitewings) with the central ray directed at the height of the tooth crown; this is particularly indicated for caries detection.
4. d. Occlusal projection with axial (mandible) or half-axial (maxilla) central ray projection for depicting the jaws in the third dimension.

The lowest level of distortion and the highest level of image clarity will always be found in the region of the central ray projection. The clinical indication actually sets the priority for selection of the individual types of intraoral radiographs, and the radiographic quality of other structures is of secondary importance. The image receptor should be as perpendicular as possible to the central ray and as parallel as possible to the tooth long axis in order to guarantee optimum radiographic interpretability.

Fig. 58 Intraoral radiographic survey in the mixed dentition. This figure shows a 10-film series using 2 × 3 cm films in the mixed dentition stage, taken using a film holder for the right-angle technique. Depending upon the age and size of the child, a radiographic survey may also be possible using only six films (for anterior regions and posterior segments), or with use of 3 × 4 cm film format. With digital radiography, a mixed dentition survey will be similar, but using similar sizes of phosphor-coated imaging plates or a digital sensor. The use of an image receptor holder (IRH) and a targeting device is highly recommended.

Fig. 59 Intraoral radiographic survey for adolescents or adults. This figure depicts the “classic” 14-film series using 3 × 4 cm film in a young adult patient, performed using the right-angle technique in an IRH holder as the targeting device. If, in a patient of this age, the third molar is not captured on the molar radiograph, a different projection angle must be attempted. The radiographic survey depicted here can also be performed digitally using imaging plates or sensors of similar sizes. If it is necessary to use a small sensor, the posterior teeth must be radiographed in vertical format, and this will require an extra 1–2 exposures per quadrant. It is recommended that an image receptor holder be used as the targeting device.

Fig. 60 Periodontal survey. In comparison to a normal, apically targeted radiographic survey, individual intraoral projections or even entire surveys for periodontitis patients should be targeted more toward the alveolar ridge margin, so that the central ray directly impacts the primary area of interest, the alveolar bone crest. This guarantees a sharp and undistorted view of osseous periodontal lesions. Such periodontal (marginal) projections, taken to supplement a panoramic radiograph, need not necessarily display the root apex; therefore, during placement and adjustment of the selected IRH, one need concentrate only on the alveolar ridge. The periodontal survey shown here, with a total of 14 films, can be viewed as a variation of a normal radiographic survey in completely dentulous adults. The use of bite-wing radiographs in the posterior areas can reduce radiation exposure significantly (see pp. 54–57).

Fig. 61 a Vertical central ray projection angle adjustment for the intraoral bisecting angle technique. In all instances where it is not possible for anatomic reasons to place the image receptor parallel to the tooth long axis, the plane of the IRH (2) assumes a vertical angle of varying degree to the tooth long axis (1). It is therefore not easy to target the central ray onto the tooth so that the tooth is depicted in its true length. A tooth will only be depicted in its correct length if the central ray (4) can be projected through the apex perpendicular to the bisected angle (3). Otherwise the tooth will be depicted as too short (5) or too long (6). In any case, the root will appear more or less widened depending upon the relationship of the distance of the apex from the image receptor.

Fig. 61 b Intraoral right-angle technique. Proper targeting of the tooth of interest will be considerably simplified through use of a device that both holds the image receptor (IR) and permits precise targeting of the central ray (4) and which defines definitively that the central ray will be at a right angle (3) to the plane of the selected IR (2). Using the naked eye to position the IR parallel to the tooth long axis (1 ) will guarantee correct depiction of the tooth in proper size and spatial relationships. If the intraoral anatomic relationships make it impossible to position the image receptor over the apex and parallel to the entire tooth, the position of the receptor holding device can be slightly altered more toward the bisecting angle technique.

Fig. 62a Indication-based use of the intraoral radiographic technique. For proper depiction of a mandibular molar, the central ray (4) is directed perpendicular to the tooth long axis (1) and the plane of the IR (2). Given these circumstances, the tooth will be depicted in its true size, and without distortion. On the other hand, if the tooth is targeted steeply cranially (from below; 5), it will appear much shorter in the final image. But if the intent is to evaluate the location of the root apex vis-à-vis the mandibular canal, it will be necessary to combine the steeper projection (5) with a modified receptor position (2a). The important concept is that the projection of the central ray will be dictated in each individual case by the clinical indication for taking the radiograph. This must be clearly conveyed to the person taking the radiographs.

Fig. 62b Horizontal angle adjustment for intraoral radiographs. In general, teeth are radiographed orthoradially in the horizontal angle (i.e., perpendicular to the chord of a section of the dental arch). The figure illustrates the “orthoradial” shadow of a vertical bar with a square cross-section on the image receptor (7). If the same metal bar is targeted laterally (i.e., eccentrically; 8), it is depicted on the image receptor as both distorted and in some areas blurred.

Fig. 63a Orthoradial projections for individual teeth or groups of teeth. The illustration shows the proper direction of the central ray and the proper positioning of the IR in the horizontal angle for the ideal orthoradial projection. The IR should be positioned at a right angle to the central ray and must therefore be positioned where there is adequate space, i.e., as near as possible to the middle of the palatal vault and not necessarily near to the teeth. This is also true for the mandible, where the IR should be placed toward the tongue and in such a position that no pain is elicited at the floor of the mouth.

Fig. 63b Excentric positioning for intraoral radiographs. For special diagnostic questions such as depiction of complicated root canal relationships and localization of impacted teeth or root fragments, one may employ excentric central ray targeting, which is described as mesial-excentric (9) or distal-excentric (10) projections depending upon their deviation from a normal projection. Such radiographs are usually taken as supplements to standard orthoradial projections. The position of the IR will therefore not be identical to that used to take the original radiograph. The most important consideration is the proper targeting of the central ray.

Fig. 64a Skull photograph, labial view of anterior region. Visible are the cementum surfaces of the tooth necks, the median suture, nasal crest of the maxilla, the anterior nasal spine, and the incisive foramen dorsal to the piriform aperture.

Fig. 64b Periapical radiograph of the maxillary anterior region. The lateral incisors are usually not completely depicted. The tip of the nose overlaps the tooth roots. The cervical areas exhibit the typical burn-out effect (see also Fig. 106a, b).

Fig. 64c Proper position for taking a radiograph of the maxillary anterior region. The occlusal plane of the maxillary teeth is horizontal, with the mouth slightly open. The central ray is focused laterally symmetrically. The position of the IR device as described by Pasler...