Normal Radiographic Anatomy - Teeth and Bones

Normal Radiographic Anatomy

• The entire chapter is important, with emphasis on the accompanying pictures.

Teeth

• Teeth are composed of enamel, dentin, cementum, and pulp.
• Enamel is the most radiopaque component.
• Dentin is smooth and homogeneous, unlike bone.
• Differentiation between enamel and dentin is possible at the dentin-enamel junction (DE junction).
• Cementum is not easily distinguishable due to its low mineral content.
• Pulp is radiolucent and can be traced from the pulp chamber to the apical foramen.
• A "cervical burnout" phenomenon occurs at the cemento-enamel junction.
• The apex of a developing tooth shows a divergent appearance.

Alveolar Crest

• The alveolar crest is the gingival extension of the alveolar process, situated between adjacent teeth.
• It typically lies up to 1.5 mm below the cemento-enamel junction (CEJ) of the teeth.
• The crest of the bone is continuous with the lamina dura.

Lamina Dura

• Lamina dura is a thin, radiopaque layer of dense bone.
• Its mineral content is similar to the trabeculae of cancellous bone.
• It thickens with increased occlusal force.
• In multi-rooted teeth, a double image of the lamina dura may be visible.

Periodontal Ligament Space

• The periodontal ligament space appears as a radiolucent line between the lamina dura and the root.
• It extends from the alveolar crest, around the roots, and back to the opposing alveolar crest.
• The width varies between patients and individual teeth.
• The space is thinner in the middle of the root.
• The thickness is related to the functional load on the tooth.

Cancellous Bone

• Located between the cortical plates.
• Composed of thin radiopaque plates (trabeculae) surrounding numerous radiolucent marrow spaces.
• Examine the distribution, size, and density of the trabeculae in both the jaws, comparing them.

Maxilla

• In the anterior maxilla, trabeculae are thin and numerous, forming a fine, dense, granular pattern.
• In the posterior maxilla, marrow spaces are slightly larger.

Mandible

• In the anterior mandible, trabeculae are thicker than in the maxilla.
• Trabecular plates are mainly oriented horizontally.
• In the posterior mandible, plates are oriented horizontally in the periradicular region.
• Fewer trabeculae are observed in the apical region of the mandible.
• A thicker cortical plate corresponds to fewer trabeculae.

Significance of Alveolar Bone

• Absence of trabeculae could suggest a disease condition.
• Verification should be done by reviewing prior radiographs or repeating the imaging procedure.

Maxillary Landmarks

• Intermaxillary suture (median palatal suture)
• Anterior nasal spine
• Nasal fossa
• Incisive foramen
• Maxillary sinus
• Zygomatic bone/process

Intermaxillary Suture

• Appears as a thin radiolucent line in the midline.
• Extends from the alveolar crest between the central incisors.
• It continues posteriorly to the hard palate.

Anterior Nasal Spine

• Located in the midline.
• Visually identifiable from maxillary central incisor radiographs.
• Located approximately 1.5-2 cm above the alveolar crest.
• Located just below the junction of the nasal septum and nasal fossa.

Nasal Fossa

• Visible from maxillary central incisor projections.
• It's a radiolucent area with radiopaque borders extending from the anterior nasal spine.
• Nasal conchae (hazy) may be seen on the lateral wall of the nose.
• The nasal fossa floor can be observed in maxillary canine projections.

Incisive Foramen

• Oral end of nasopalatine canal.
• Lies in the midline, behind the central incisors.
• Usually images are projected between the roots of the central incisors.
• Shape and size vary considerably.
• Image assessment is dependent of projection angles.
• Sometimes mistaken as pathology.
• The lateral walls of the nasopalatine canal might be visible.

Maxillary Sinus

• An air-filled cavity with mucosal lining.
• The border appears as a thin, delicate, radiopaque line (a thin cortical bone layer)
• In adults, it extends from the distal canine to the posterior maxillary wall above the tuberosity.
• Exhibits significant shape and size variations.
• Generally symmetric, although asymmetry can occur.

Zygomatic Process and Zygomatic Bone

• An extension of the lateral maxillary surface, visible from molar apices on periapical projections.
• Appears as a U-shaped radiopacity on periapical projections, with the open ends oriented superiorly.
• The enclosed rounded end is closely aligned to the molar apices.
• Size, width, and definition are variable.

Mandibular Landmarks

• Genial tubercle
• Mental foramen
• Mandibular canal
• Mylohyoid ridge
• Submandibular gland fossa
• External oblique ridge
• Coronoid process

Genial Tubercle

• Located on the lingual surface, slightly above the inferior border in the midline.
• A bony, spine-shaped protuberance.
• Used for muscular attachment.
• Appears as a single radiopaque mass on occlusal radiographs.

Mental Foramen

• Anterior boundary of the inferior alveolar canal.
• Difficult to visualize from its superior and posterior orientation.
• Mid-way between the lower border and the crest of the alveolar process (second bicuspid apical area).
• Potentially misidentified as periapical pathology.

Mandibular/Inferior Alveolar Canal

• Appears as a dark linear shadow with thin superior and inferior radiopaque borders.
• The position of the canal relative to the molar apices varies.
• Generally closely associated with the roots of the third molars.
• It gradually moves away from the roots of the molars as it extends anteriorly.

Mylohyoid Ridge

• An irregular crest of bone on the lingual surface of the mandible body.
• Extends from the third molar region to the chin.
• The image extends downward and forward in the molar apical region.
• Margins may not be well-defined.
• More prominent when a significant negative angle is present.

Submandibular Gland Fossa

• A depression in the bone on the lingual side, below the mylohyoid ridge in the molar area.
• Accommodates the submandibular gland.
• Appears as a radiolucent area with sparse trabeculae.
• Superiorly limited by the mylohyoid ridge and inferiorly by the inferior border of the mandible.

External Oblique Ridge

• Continuation of the ramus's anterior border.
• Runs antero-inferiorly, lateral to the alveolar process.
• Becomes flatter and fades below the first molar.
• The shadow is superior to the mylohyoid ridge.

Coronoid Process

• Observeable from periapical radiographs in the maxillary third molar region.
• Its appearance is due to the downward and forward movement of the mandible during opening.
• Its shadow is homogeneous.

Radiographic Evaluation Process

• Mandibular assessment first.
• Then maxillary examination.
• Zygomatic area evaluation follows.
• Soft tissue shadows are next.
• Pharyngeal air spaces are then looked at.
• Teeth assessment is last.

Explore the essential concepts of normal radiographic anatomy focusing on teeth and alveolar structures. Learn about the composition of teeth, the characteristics of enamel, dentin, cementum, and pulp, as well as important landmarks like the alveolar crest and lamina dura. This quiz emphasizes critical details and visual aids to enhance understanding.