Section V. ANATOMIC RADIOGRAPHIC LANDMARKS
A number of anatomic landmarks are visible in dental radiographs. Knowledge of the location and normal appearances of these landmarks is important in identification and orientation of radiographs. This knowledge is valuable to the dentist in determining whether the area is normal or abnormal. The landmarks that appear as dark areas on the film are radiolucent. The areas that appear as light areas on the film are radiopaque. Anatomic characteristics and the relationship between individual teeth are anatomic landmarks with which all dental specialists should be familiar.
3-25. RADIOLUCENT LANDMARKS ON MAXILLARY RADIOGRAPHS
- Maxillary Sinus. The maxillary sinus (see figure 3-21) is a very prominent radiolucent structure. It sometimes appears as overlapping lobes or a single radiolucent area with a radiopaque border. The maxillary sinus is partially seen in all periapical radiographs of the bicuspid-molar area. It occupies a large part of the body of the maxilla, varying greatly in dimension, but normally extending into the alveolar process adjacent to the apices of the posterior teeth.
- Incisive Foramen. The incisive foramen (see figure 3-22) is seen as a dark area located between and extending above the central incisors. In radiographs exposed from the region of the cuspid or lateral incisor, the incisive foramen may appear as a radiolucency at the apex of one of the incisors.
Figure 3-21. Maxillary Sinus.
Figure 3-22. Incisive foramen.
- Median Palatal Suture. The median suture of the palate (see figure 3-23) may appear as a radiolucent line extending posteriorly from the alveolar border in the sagittal plane of the maxilla, on an anterior periapical film, or occlusal film.
- Nasal Fossae. In a radiograph of the maxillary central incisors, the images of the paired fossae appear as somewhat elliptical radiolucent areas of various sizes separated by a radiopaque band representing the nasal septum (see figure 3-24).
Figure 3-23. Median palatal suture.
Figure 3-24. Nasal fossae.
3-26. RADIOPAQUE LANDMARKS ON MAXILLARY RADIOGRAPHS
- Maxillary Tuberosity. The maxillary tuberosity (see figure 3-25) is the convex distal inferior border of the maxilla, curving upward from the alveolar process and distal of the third molar. An extension of the maxillary sinus is occasionally seen within the maxillary tuberosity.
- Coronoid Process of the Mandible. The coronoid process of the mandible (see figure 3-26) sometimes appears on maxillary molar films as a triangular opaque area located in the region of or distal to the maxillary tuberosity.
Figure 3-25. Maxillary tuberosity.
Figure 3-26. Coronoid process of the mandible.
- Zygomatic Process (Malar Bone). The zygomatic arch (see figure 3-27) commonly appears as a well-defined radiopaque area that may be superimposed over the molar roots. Additional radiographs are sometimes made at adjusted angulation to provide a better view of the molar root area.
Figure 3-27. Zygomatic process (malar bone).
- Nasal Septum. The nasal septum is usually seen as a white ridge extending above and between the central incisors.
3-27. RADIOLUCENT LANDMARKS ON MANDIBULAR RADIOGRAPHS
- Mandibular Foramen. The mandibular foramen is seen on extraoral mandibular films as a dark area near the middle of the mandibular ramus.
- Mandibular Canal. The mandibular canal (see figure 3-28) appears as a dark band with radiopaque borders running downward and forward from the mandibular foramen in the ramus to the region of the bicuspid teeth in the body of the mandible. It may be seen below the roots of the posterior teeth.
Figure 3-28. Mandibular canal.
- Mental Foramen. The mental foramen (see figure 3-29) is seen as a dark area below and between the bicuspids. Since it is not contiguous with either bicuspid, its relationship to these teeth appears different on radiographs made at different angulations.
3-28. RADIOPAQUE LANDMARKS ON MANDIBULAR RADIOGRAPHS
- Border of the Mandible. The border of the mandible is seen as a heavy white line (see figure 3-30). A similar line does not appear on maxillary radiographs.
- External Oblique Ridge. The external oblique ridge is a white line of variable density extending into the molar region as a continuation of the anterior border of the ramus of the mandible (see figure 3-31).
Figure 3-30. Border of the mandible.
Figure 3-31. External oblique ridge.
- Genial Tubercles. Genial tubercles are seen as round white areas, having dark centers, located below and between the central incisors (see figure 3-32).
Figure 3-32. Genial tubercles.
- Mental Process (Mental VRidge). The mental ridge may appear as a dense white ridge of varying density extending from the anterior midline to the bicuspid region, usually located below the anterior teeth, but occasionally superimposed over the apices.
- Mylohyoid Ridge (Internal Oblique Ridge). The mylohyoid ridge appears as a white line of varying width and indensity, extending from close to the lower border of the symphysis of the mandible, upward and distally, to end beyond the third molar. It reaches its greatest prominence in the molar region. It is generally not a prominent feature.