Radiographic Interpretation of Pathologies & Structures

Radiographic Interpretation of Pathologies & Structures

Accurate radiographic interpretation requires the dental hygienist to differentiate normal anatomical landmarks from pathological conditions. Understanding how various structures interact with the x-ray beam allows the clinician to identify anomalies, evaluate dental caries progression, and detect periapical pathologies.

Normal Anatomical Landmarks

Anatomical landmarks are categorized based on their density. Radiopaque structures represent dense tissues that absorb x-rays, appearing light or white. Radiolucent structures represent soft tissues, spaces, or cavities that permit x-rays to pass through, appearing dark or black.

Maxillary Landmarks

• Incisive (Nasopalatine) Foramen: A small, oval or round radiolucent area located between the roots of the maxillary central incisors.
• Median Palatal Suture: A thin radiolucent line delineating the junction of the palatine processes of the maxilla, extending vertically between the central incisors.
• Maxillary Sinus: A large radiolucent cavity located superior to the apices of the maxillary premolars and molars. The thin, radiopaque line outlining the sinus is the sinus floor.
• Anterior Nasal Spine: A V-shaped radiopaque projection located at the intersection of the floor of the nasal cavity and the nasal septum.
• Nasal Septum: A vertical, radiopaque partition dividing the nasal cavity.
• Zygomatic Process of Maxilla: A U-shaped or J-shaped radiopaque line located superior to the maxillary first and second molar apices.
• Maxillary Tuberosity: A rounded, radiopaque prominence distal to the third molar region.
• Hamulus: A small, hook-like radiopaque projection distal to the maxillary tuberosity.

Mandibular Landmarks

• Mental Foramen: A small, round or oval radiolucent area located near the apices of the mandibular premolars. Because of its location, it is often mistaken for a periapical lesion. Pulp vitality testing must be used to differentiate it from pulpal pathology.
• Mandibular Canal: A radiolucent tube-like pathway bordered by two thin, parallel radiopaque lines (representing cortical bone), extending from the mandibular foramen to the mental foramen.
• Genial Tubercles: Small, ring-shaped radiopaque projections surrounding the lingual foramen, located on the lingual surface of the mandible near the midline.
• Lingual Foramen: A tiny, pinpoint radiolucent opening in the center of the genial tubercles.
• Mental Ridge: A thick, radiopaque band extending from the premolar region to the incisor region on the labial surface of the mandible.
• Mylohyoid (Internal Oblique) Ridge: A dense, radiopaque band extending downward and forward from the molar region on the internal surface of the mandible.
• External Oblique Ridge: A dense, radiopaque band extending downward and forward from the anterior border of the ramus along the external surface of the mandible.
• Submandibular Fossa: A radiolucent area in the molar region inferior to the mylohyoid ridge, representing a depression where the submandibular salivary gland resides.

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Radiographic Interpretation of Dental Caries

Dental caries appear radiolucent because the demineralization process decreases the density of the tooth structure. Radiographs are primarily used to detect interproximal caries, but they underestimate the actual depth of demineralization by up to 30%.

Interproximal Caries Classification

Interproximal caries are classified based on the depth of penetration through the enamel and dentin:

1. Incipient (Class I) Interproximal Caries: Extends less than halfway through the thickness of the enamel. It is typically triangular in shape, with the apex pointing toward the dentinoenamel junction (DEJ). It is reversible through remineralization.
2. Moderate (Class II) Interproximal Caries: Extends more than halfway through the enamel but does not involve the DEJ.
3. Advanced (Class III) Interproximal Caries: Extends to or through the DEJ and into the dentin, but does not extend more than half the distance through the dentin toward the pulp. It involves both enamel and dentin.
4. Severe (Class IV) Interproximal Caries: Extends through the dentin and more than half the distance toward the pulp chamber. It presents as a large, obvious radiolucency.

Occlusal Caries

• Incipient: Cannot be seen radiographically; must be detected clinically.
• Moderate: Appears as a thin, radiolucent line under the occlusal enamel.
• Severe: Appears as a large, cup-shaped radiolucency under the occlusal enamel, extending deep into the dentin.

Buccal, Lingual, and Root Caries

• Buccal and Lingual Caries: Appears as a well-defined, round radiolucency in the center of the crown. Clinical examination is necessary to determine if it is on the buccal or lingual surface.
• Root (Cemental) Caries: Involves only the cementum and dentin located below the CEJ. It appears as a saucer-shaped, ill-defined radiolucency just below the CEJ, and it is always accompanied by bone loss and gingival recession.
• Clinical Trap: Cervical Burnout is a normal radiographic phenomenon appearing as a radiolucent band at the necks of teeth due to the difference in tissue thickness. It must not be misdiagnosed as root caries. Root caries will have clinical cavitation and involve bone loss.

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Radiographic Interpretation of Root-Tip Pathologies

Pathological changes in the periapical region are key indicators of pulpal necrosis and inflammatory responses.

1. Periodontal Ligament (PDL) Space Widening: The PDL normally appears as a thin, continuous radiolucent line around the root. Widening of this space (especially at the apex) is the earliest radiographic sign of pulpal inflammation, trauma from occlusion, or early periapical infection.
2. Periapical Abscess: An acute or chronic inflammatory lesion at the apex of a non-vital tooth. It appears as a diffuse, poorly-defined radiolucency with irregular margins. The tooth is non-vital.
3. Periapical Granuloma: A localized mass of chronically inflamed granulation tissue at the apex of a non-vital tooth. It appears as a well-defined, round-to-oval radiolucency without a radiopaque border.
4. Periapical (Radicular) Cyst: A true cyst lined with epithelium, arising from the epithelial rests of Malassez in response to chronic pulpal inflammation. It appears as a well-defined radiolucency with a thin, radiopaque cortical border. It is indistinguishable from a granuloma based on radiographs alone; histopathological analysis is required for definitive diagnosis.
5. Root Resorption:
   • Internal Resorption: Occurs within the crown or root, involving the pulp chamber/canal. It appears as a round or symmetrical radiolucent expansion of the pulp canal. It is often caused by trauma or chronic inflammation.
   • External Resorption: Occurs on the outer surface of the root, appearing as a blunting, shortening, or irregular loss of the root apex. Commonly caused by orthodontic forces, trauma, cysts, tumors, or chronic periapical pathology.