Medical Radiology - Lazar A.P. 2008

Radiation Examination of the Maxillofacial Region
X-ray Anatomy of the Oral Cavity and Teeth

A prerequisite for the correct interpretation of an X-ray image is not only familiarity with the imaging technique, but also a profound knowledge of the Morphology of the depicted Organs. The Study of the X-ray Anatomy of the dentomaxillary region requires a detailed understanding of the Water/140.html">Anatomical Structure of the Teeth and jaws.

The Oral Cavity is divided into two parts: the oral vestibule and the oral cavity proper. These are separated by the alveolar processes of the maxillae, the alveolar part of the Mandible, and the teeth and gingivae of both jaws. The teeth, fixed in the dental alveoli of the upper and lower jaws, form the upper and lower dental arcades, respectively (Fig. 302). Each dental arcade comprises teeth belonging to different groups: incisors, canines, premolars, and molars.

Throughout human life, two generations of teeth develop and succeed one another. The first generation consists of deciduous ( temporary) teeth, 20 in total—10 in each jaw: two medial incisors, two lateral incisors, two canines, and four molars. Premolars are absent in the deciduous dentition. Deciduous teeth erupt between the ages of 6 months and 2 years and function During the first 12 years of a child's life, gradually being replaced by permanent teeth. Tooth replacement begins at the age of 5.

The second generation consists of 32 permanent teeth, 16 in each jaw: two medial incisors, two lateral incisors, two canines, four premolars, and six molars.

Class="center">

Fig. 303. Tooth structure: 1 - pulp chamber (pulp); 2) gingival sulcus; 3 - desmodont; 4 - pulp; 5 - apical foramen; 6 - ROOT canal; 7 - cementum; 8 - periodontal ligament; 9 - dentin; 10 - crown (enamel).

A graphical record of the teeth present in the oral cavity is called a dental formula. A two-digit tooth-recording system proposed by the World Health Organization is widely used. It designates each tooth with two Arabic numerals: the first digit indicates the quadrant of the dental formula, and the second indicates THE POSITION OF the tooth According to the standard system. In this notation, the complete formula for permanent teeth is as follows:

The complete formula for deciduous teeth is as follows:

Each tooth consists of a crown, one or more roots, and a neck (Fig. 303). A distinction is made between the anatomical and clinical crowns. The anatomical crown is the part of the tooth covered by enamel. The clinical crown is the part that projects above the gingival margin into the oral cavity. The roots of the teeth are anchored in the alveoli of the alveolar processes of the jawbones. The neck of the tooth is the transitional zone between the crown and the root. Inside the crown, There is a pulp cavity that extends into the root canal and terminates at the root apex as the apical foramen. The pulp cavity and root canal are filled with dental pulp—a loose Connective Tissue containing numerous Blood Vessels and nerve endings. On radiographs, the pulp cavity (pulp chamber) appears as a radiolucent area in the center of the tooth. Its shape generally mirrors the overall contour of the crown. The root canal is a slit-like space in the center of the root; its radiographic visibility depends on its width. Occasionally, root canals branch out, forming blind-ending lateral canals that diverge from the main canal at various angles. Such branching may occur along the entire length of the canal or be restricted to the apical region. Less frequently, the canal bifurcates, resulting in two canals within a single root that may anastomose via short connecting branches.

A tooth is composed of hard Tissues: dentin, enamel, and cementum.

Dentin is a calcified tissue that forms the hard core of the tooth and determines its shape. It is located in the crown, neck, and root. In the crown, dentin is covered by enamel, whereas in the root, it is covered by cementum. Chemically, dentin consists of 70–72% inorganic substances, 20% organic matter, and 8–10% water. Depending on its Location, dentin is divided into two layers: the circumpulpal (inner) dentin, which, together with predentin, forms the walls of the pulp chamber; and the mantle (outer) dentin, located peripherally.

Enamel is the hardest tissue in The Human Body. It covers the crown of the tooth, reaching its maximum thickness at the cuspal tips (up to 2.5 mm), and performs a protective function. Enamel consists of 96–97% inorganic substances.

Cementum is a hard tissue covering the root dentin that also serves a protective function. Structurally, cementum resembles coarse-fibered Bone tissue, but unlike bone, it lacks blood vessels. It is composed of Collagen fibers, intercellular substance, and Inorganic Components, which account for 65–70% of its mass.

Because the tissues forming the crown and root differ in structure, degree of mineralization, and density, they absorb X-rays to varying degrees. Enamel, having the highest degree of mineralization and density but minimal thickness, is clearly outlined only at the edges of the crown as a narrow rim of dense shadow. The intensity and width of the enamel shadow are maximal in the mandibular molars and are more distinct in permanent teeth than in deciduous ones. Dentin has a slightly lower density than enamel; however, because the dentin layer in both the crown and root is quite thick, it forms the main component of the dental radiographic image. The difference in X-ray absorption between dentin and cementum is negligible due to their very similar densities; consequently, root dentin and cementum are practically indistinguishable on radiographs, although dentin tends to cast a slightly denser shadow. Teeth of different groups vary in crown shape and number of roots. Incisors, canines, and premolars typically have a single root, with the exception of the maxillary first premolar, which has two roots (palatal and buccal). Maxillary molars possess three roots: a robust, straight palatal root and two shorter, laterally flattened buccal roots (mesial and distal), with the mesiobuccal root occasionally containing two canals. Mandibular molars are two-rooted, featuring a mesial root with two canals (mesiobuccal and mesiolingual) and a distal root with a single canal.

Fig. 304. STRUCTURE OF THE maxillary region: 1 - tooth #24; 2 - palatal root of tooth #24; 3 - buccal root of tooth #24; 4 - palatal cusp of tooth #24; 5 - buccal cusp of tooth #24; 6 - periodontal space; 7 - lamina dura; 8 - pulp of tooth #25; 9 - crown of tooth #25; 10 - pulp chamber of tooth #26.

Between the tooth root and the wall of the dental alveolus, a thin radiolucent line—the periodontal space—is clearly delineated on radiographs (Fig. 304). Its content is connective tissue that forms the suspensory apparatus of the tooth (the periodontium), which anchors the root within the alveolus. The width of the periodontal space remains virtually uniform throughout, measuring 0.15–0.25 mm. In a healthy individual, its width is typically equal across all teeth. The roots of the teeth and the surrounding periodontal tissues reside within the dental alveoli of the alveolar processes of the jaws. A dental alveolus comprises the periosteum of the alveolar process and the bony alveolar wall. The sockets of multi-rooted teeth contain interradicular bony septa that arise from the Cytology/practical/108.html">Fundus of the socket and divide it into separate compartments for each root branch. On radiographs, the crests of the interdental septa appear as sharp cones in the region of incisors and canines, and as truncated pyramids in the premolar and molar regions. The contours of the septa are smooth. In the presence of diastemas or tremas, the interseptal bone height decreases slightly and assumes a rectangular shape, whereas in dental crowding, the septa become narrower.

The bone architecture of the jaws exhibits individual variations in every person; however, general patterns characterize the trabecular pattern of the Maxilla and mandible across different regions. The bone tissue of the alveolar processes appears on radiographs as characteristic spongy bone—a dense lattice of intersecting bony trabeculae with small radiolucent spaces between them. The maxilla is characterized by a uniform, fine-meshed trabecular pattern with a predominantly vertical orientation of the trabeculae. The Bone Structure of the alveolar part of the mandible differs significantly from that of the maxilla and is heterogeneous throughout. In the anterior (frontal) teeth region, compared to the posterior segments, the trabecular pattern of the alveolar processes is finer-meshed. The closer one gets to the crests of the processes, the finer the trabecular pattern becomes. In the premolar and molar regions, the pattern correspondingly coarsens. The mandible is dominated by a horizontal orientation of the bone trabeculae. The meshwork and clarity of the bone pattern are slightly more pronounced at the level of the tooth roots than in the interdental septa.

The margins of the alveolar processes and interdental septa terminate slightly below the cementoenamel junction on radiographs; consequently, the depth of the dental alveoli is somewhat less than the root length. The cortical layer of the alveolar margin and the lamina dura of the dental sockets appear as a continuous thin white line, which is well-defined in the interdental spaces and less distinct over the roots due to the superimposition of dental tissue shadows. In the maxilla, the intensity of the lamina dura is significantly lower than in the mandible. Normally, coronal to the alveolar crest, the neck of the tooth is encircled by the gingival margin.

For the topographical identification of the region depicted on a radiograph—which is particularly crucial for intraoral radiographs—one relies on key diagnostic features indicating whether the image belongs to a specific zone of the upper or lower jaw.

The Characteristic Features of the anterior maxilla include:

- the presence of broad, chisel-shaped crowns of the maxillary incisors;

- the presence of the intermaxillary suture as a narrow, serrated radiolucent line between the central incisors;

- PROJECTION OF THE Nasal cavity above the roots of the incisors in the form of two semi-ovals separated by the shadow of the nasal septum, which appears as a wide strip;

- presence of a clear circular opening of the incisive canal at the level of the apices of the central incisor roots (may be slightly shifted laterally).

The lateral Regions of the maxilla are characterized by:

- presence of three roots in the molars;

- presence of a significant radiolucent area (maxillary sinus), the size and shape of which vary considerably;

- presence of the shadow of the maxillary tuberosity posterior to the third molar.

The central part of the mandible is characterized by:

- narrow chisel-shaped crowns of the lower incisors;

- narrow, long roots of the lower incisors, flattened in the mesiodistal direction;

- sometimes a visible shadow of the mental spine.

The radiographic image of the lateral regions of the mandible is indicated by:

- presence of two roots in the molars;

- mental foramen, most frequently located beneath the second premolar and horizontally elongated by 1.5–2.5 cm;

- shadow of the mandibular canal;

- external and internal oblique lines visible at the level of the third molar.