Teeth and jaws in x-ray images

In the dental formula used for abbreviation, temporary teeth (20) are designated by Roman numerals, permanent teeth (32) by Arabic numerals. The right or left halves of the upper and lower jaws are designated by the sign of the angle, open respectively to the left, right, up or down.

The main mass of the tooth is dentin. In the area of the crown, dentin is covered by enamel, and the root is covered by cement. On the radiograph, enamel is represented by an intense linear shadow bordering the dentin of the crown; it is better visible on the contact surfaces of the tooth. Dentin and cement are not distinguished on the radiograph.

Between the root of the tooth and the cortical plate of the alveolus of the jaw there is a narrow slit-like space - the periodontal gap (width 0.15-0.25 mm), which is occupied by the periodontium (dental ligament). It consists of dense connective tissue (bundles of fibrous fibers, layers of loose connective tissue, blood and lymphatic vessels, nerves), fixed to the cement and cortical plate of the socket. The periodontium provides fixation of the tooth and participates in its blood supply.

On radiographs, baby teeth differ from permanent teeth: the crown and roots of baby teeth are smaller, the root canals and cavities of the tooth are wider. The roots of the molars depart from each other at a greater angle.

The cavity of the tooth is determined on radiographs as a rarefaction area with clear contours against the background of the tooth crown, and the root canals are determined as linear rarefaction areas with smooth and clear closing contours.

In the alveolar process, the teeth are separated from each other by an interdental septum covered with gum. The tops of the interdental septa in children are located at the level of the enamel-cement border, in adults - at a distance of 1.5-2 mm from it. Constructed from spongy bone, the septa are bordered on the periphery by a clearly defined closing cortical plate, which is a continuation of the cortical plate of the socket. The tops of the interdental septa are pointed in the area of the anterior teeth and have the shape of a truncated pyramid in the area of the premolars and molars. After tooth extraction, the interdental septa atrophy, the alveolar edge flattens.

Upper jaw

The maxilla is a paired bone consisting of a body and four processes (frontal, zygomatic, palatine and alveolar). The body of the maxilla has four surfaces (anterior, nasal, orbital and infratemporal).

The anterior surface is located between the lower edge of the orbit and the alveolar process. At 0.5-1 cm below the edge of the orbit, the inferior orbital canal opens, in which the maxillary nerve (the second branch of the trigeminal nerve) and the corresponding artery and vein pass. Below the opening on the anterior wall there is a depression (canine or dog fossa), where the sinus is usually opened during surgery.

The infraorbital canal with the maxillary nerve and vessels passes through the upper (orbital) surface, which forms the roof of the sinus. The upper wall of the sinus is very thin and is easily destroyed by inflammatory and tumor diseases of the upper jaw with involvement of the orbit in the process.

The nasal surface of the inner wall of the sinus forms the outer wall of the nasal cavity. In the anterior part of it passes the nasolacrimal canal, opening into the inferior nasal passage. The outlet of the sinus, located above its bottom, opens into the middle nasal passage. This explains the fact that the outflow from the sinus occurs better in the lying position.

The infratemporal surface of the posterolateral wall faces the pterygopalatine fossa, the site of administration of anesthetic drugs during “tuberal” anesthesia.

In the body of the jaw there is an air-filled maxillary sinus, which is shaped like a pyramid.

The maxillary sinuses appear in the 5th month of intrauterine development as small pits on the nasal surface of the body of the upper jaw. Already in seven-month fetuses, the bone walls of the sinus are visible on the X-ray of the skull.

In children aged 2.5-3 years, the sinuses are occupied by tooth rudiments and are defined as triangular clearings in the upper and outer sections. There are tooth rudiments at the bottom of the sinus; in children up to 8-9 years old, they are located at the level of the bottom of the nasal cavity. In children and adolescents, the roots of the molars are sometimes in direct contact with the mucous membrane of the maxillary sinus.

The volume of the sinus increases as the teeth erupt, its formation ends by the end of the eruption of permanent teeth (by 13-15 years). After 50-60 years, the volume of the sinus (15-20 cm ³ ) begins to decrease. In adults, the sinus is located between the first premolar (sometimes the canine) and the second or third molar. Increased pneumatization of the sinus can be observed after tooth extraction. Sometimes the sinus extends into the septa between the premolars and molars, to the area of the maxillary tubercle.

The left and right sinuses can be of different sizes, and bony partitions are found in them.

On radiographs, the lower border of the sinus is presented as a thin linear shadow that is not interrupted anywhere. Depending on the pneumatization and the features of the sinus location (high or low), layers of spongy substance of different thickness are determined between the roots of the teeth and the compact plate of the sinus floor. Sometimes the roots of the teeth are located near the maxillary sinus or in it itself, which facilitates the spread of infection from the periapical tissues to the mucous membrane (odontogenic sinusitis). Above the lower border of the sinus, a thin linear shadow is visible - a reflection of the bottom of the nasal cavity.

The cortex of the base of the zygomatic process is visible on intraoral radiographs over the area of the first molar as an inverted loop. When the shadow of the body of the zygomatic bone overlaps the roots of the molars, it becomes difficult or impossible to assess the condition of the periapical tissues. Overlap can be avoided by changing the direction of the central beam of X-rays.

The lower parts of the maxillary tubercle are visible on intraoral radiographs of the upper molars. Behind it projects the hook of the pterygoid process, which has different lengths and widths. The relationship between the tubercle and the pterygoid processes of the sphenoid bone is clearly visible on orthopantomograms, which can also be used to assess the condition of the pterygopalatine fossa.

The apex of the coronoid process is seen behind the maxillary molars on some intraoral contact radiographs.

In the posterior sections of the hard palate, bite-wing images at the level of the first or second molars may show a rounded area of enlightenment with clear contours - a projection of the nasolacrimal canal, located at the junction of the maxillary sinus and the nasal cavity.

The structure of the bone tissue of the alveolar process is fine-meshed, predominantly with a vertical course of bone crossbars.

On intraoral radiographs, a clear stripe passes between the central incisors through the interdental septum - the intermaxillary (incisor) suture. At the level of the apices of the roots of the central incisors, sometimes projecting onto them, the incisor opening is revealed in the form of an oval or round, clearly defined focus of clearing of varying sizes. Along the midline of the hard palate at the level of the premolars, a smooth or tuberous bone formation of varying sizes is sometimes visible - torus palatinum.

Lower jaw

The lower jaw is an unpaired flat bone of horseshoe shape with a spongy structure, consisting of a body and two branches, departing at an angle of 102-150° (angle of the lower jaw). In the body of the jaw, a base and an alveolar part are distinguished, containing 8 dental alveoli on each side.

The variations in the structure of the jaw bones are most clearly revealed on direct panoramic radiographs and orthopantomograms. X-ray anatomical details are presented in the diagrams with orthopantomograms and panoramic radiographs of the upper and lower jaws. Along the lower edge of the jaw with the transition to the branch there is a cortical layer, thicker in the central sections (0.3-0.6 cm) and thinning towards the corners of the jaw.

The bone structure of the lower jaw is presented by a looped pattern with more clearly contoured horizontal (functional) beams. The structure of the bone structure is determined by the functional load: pressure on the teeth is transmitted through the periodontium and the cortical plate of the socket to the spongy bone. This is what causes the pronounced looping of the bone tissue in the alveolar processes precisely along the periphery of the tooth sockets. The size of the bone cells is not the same: smaller ones are in the anterior section, larger ones are in the premolar and molar zone.

In a newborn, the lower jaw consists of two halves, between which connective tissue is located along the midline. In the first months after birth, ossification and fusion of them into one bone occurs.

On extraoral radiographs, in the lateral projection, the hyoid bone is projected onto the angle or roots of the molars, and the air column of the pharynx, continuing downward almost vertically beyond the jaw, is projected onto the branch posterior to the molars.

Below the roots of the molars, a rarefaction of bone tissue with unclear contours is sometimes determined - a reflection of the submandibular fossa (location of the submandibular salivary gland).

The external oblique line extends to the anterior margin of the branch, projecting onto the molars as a strip of sclerosis of varying shape and density. After the removal of the molars and atrophy of the alveolar part, it may turn out to be marginal.

The internal oblique line, which runs below the external oblique line (the attachment site of the mylohyoid muscle), is located on the inner surface and can be projected onto the roots of the molars.

The upper part of the branch ends in front with the coronoid process, behind with the condylar process, separated by the notch of the lower jaw.

On the inner surface in the middle of the branch there is an opening of the mandibular canal (a triangular or rounded area of rarefaction of bone tissue, rarely reaching 1 cm in diameter).

The position of the mandibular canal, which appears as a strip of rarefaction of bone tissue, is variable: it passes at the level of the apices of the roots of the molars, less often - directly above the lower edge of the jaw.

The mandibular canal is visible throughout its length on panoramic radiographs, its clearance is 0.4-0.6 cm. The canal begins with the mandibular foramen, located in the branch at different heights. The cortical plates of the canal, especially the upper one, are clearly visible. In children, the canal is located closer to the lower edge, in young people, as well as in case of tooth loss and atrophy of the alveolar part, it is displaced cranially. This fact should be taken into account when planning surgical interventions.

Intraoral radiographs do not allow the relationship between the roots of the teeth and the canal to be established. On orthopantomograms, a layer of spongy bone 0.4-0.6 cm thick is usually determined between the upper wall of the canal and the apices of the teeth.

At the level of the root apices of premolars in adults and canines in children, the canal ends with a mental foramen of a round or oval shape (diameter 5-7 mm), sometimes extending in front of it. When projecting the foramen onto the apex of the premolar, it becomes necessary to differentiate it from a pathological process (granuloma).

The mental spine in bitewing images of the frontal section of the lower jaw is determined as a protruding bone formation on the lingual surface of the jaw.

On the lingual surface of the lower jaw, corresponding to the roots of the canine and premolars, a smooth or tuberous bone formation of varying size is sometimes determined - torus mandibulars.

In the case of absence of the cortical plate of the lower jaw on the lingual side (developmental anomaly), a bone defect measuring 1 x 2 cm of a round, oval or ellipsoid shape with clear contours is determined on the X-ray in the lateral projection, which is localized between the angle of the jaw and the mandibular canal, without reaching the apices of the roots of the teeth.

Vessels passing through the bone are sometimes reflected as a band or area of rarefaction of the bone tissue of a round or oval shape, located between the roots. They are more visible after tooth loss. The posterior superior alveolar artery passes through the lateral wall of the maxillary sinus.

Sometimes a large palatine foramen is visible above or between the apices of the roots of the second and third molars as an ill-defined area of rarefaction.

Involutional changes in teeth consist of gradual abrasion of enamel and dentin, deposition of replacement dentin, sclerotic changes and petrification of the pulp. As a result of deposition of replacement dentin, radiographs show a decrease in the size of tooth cavities, the root canals are narrowed, poorly contoured, and are not visible in case of complete obliteration. Involutional changes in teeth, especially in the lower jaw, are noted during radiographic examination already at the age of 40-50 years in the form of focal osteoporosis. At the age of 50-60 years, radiographs reveal diffuse osteoporosis, atrophy and decrease in the height of the interalveolar septa, narrowing of the periodontal spaces. As a result of the decrease in the height of the alveolar margin, the necks of the teeth are exposed. Along with thinning of the bone beams and a decrease in their number per unit volume, thinning of the cortical layer occurs, which is especially well detected radiographically along the lower and posterior edge of the branch of the lower jaw. The structure of the body of the lower jaw acquires a large-mesh character; the horizontal course of the trabeculae in accordance with the force trajectories is not traced.

Involutional changes are more pronounced in people with complete loss of teeth, if they do not use removable dentures.

After tooth extraction, the alveoli gradually disappear, and the height of the alveolar ridge decreases. Sometimes, alveoli after tooth extraction are seen on radiographs as a rarefaction site for several years (more often after the extraction of lower molars and incisors).