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Normal Radiographic Anatomical Landmarks

Tooth Anatomy
Radiographic Appearance ENAMEL : Appears more radio-opaque than other tissues. It is 90% mineral causes greater attenuation of X-ray photons. DENTIN: Appears less radiopaque than enamel.It is 75% mineral content. Radiopacity similar to bone. DEJ: Appears as a distinct interface separating these two structures. CEMENTUM: Appears as a very thin layer on the root surface.It is usually not so apparent radiographically. 50%mineral content.

PULP: It is composed of soft tissues so it appears radiolucent. Pulp chambers and root canals extend from the interiors of the chamber till the root apices. It is seen radiographically also as apical foramen. In some cases, it may exit on the side of the canal. Lateral canals may end at the apex or may exit at the side of the root.

The pulp canals of a developing tooth root diverge and walls of the root taper to a knife edge. A radiolucent area is seen surrounding it in the trabecular bone. It is the dental papilla with its bony crypt. Its radiographic evaluation helps in determining the stage of maturation of the developing tooth.

Cervical burnout causes; the different parts of the tooth & supporting bone tissue penetrated by the same x-ray beam; In the crown- dense enamel cap & dentine. In the tooth neck- only the dentine. In the root- dentine & buccal & lingual plates of the alveolar bone.


Cervical burn-out can be distinguished by the following features; Its located at the neck of the tooth demarcated above by the enamel cap or restoration & below by the alveolar bone level. It's triangular in shape, gradually become less apparent towards the centre of the tooth. All the teeth on the radiograph are affected (diffuse radiolucent areas), especially in the premolars.

Supporting Structures

Periodontal ligament space Lamina dura Alveolar crest Trabecular bone


Periodontal ligament space
It is composed of collagen so appears as a radiolucent space between the root and lamina dura. It is thinner in the middle of the root and slightly wider near the alveolar crest and the apex ,suggesting that the fulcrum of the physiologic movements is in the region where PDL is thinnest.

Lamina dura

It is a thin radiopaque layer of dense bone surrounding the tooth socket. Its radiographic appearance is due to attenuation of the X-ray beam as it passes tangentially through the thickness of the bone. It is thicker than the surrounding trabecular bone and thickness increases with increase in amount of occlusal stress.

Alveolar crest

It is the radiopaque gingival margin of the alveolar process which surrounds the teeth. It is considered normal if it is 1.5mm or less from the CEJ. It shows apical recession with the age or periodontal disease.

Trabecular bone

Also called the cancellous bone ,Lies between the cortical plates in both the jaws. It is composed of thin radiopaque plates and rods (trabeculae)surrounding many small radiolucent pockets of marrow. *In the maxilla, the trabeculae tend to be finer, and more widely spaced. There is no predominant alignment pattern. *In the mandible, the trabeculae tend to be relatively thick and close together, and are often aligned horizontally.


ANATOMIC LANDMARKS OF MAXILLA Intermaxillary suture. Anterior nasal spine. Nasal fossa and Nasal septum. Incisive foramen. Superior foramina of nasopalatine canal. Lateral fossa. Nose. Nasolacrimal canal. Maxillary sinus. Zygoma & zygomatic process of maxilla. Nasolabial fold. Pterygoid plates.

Maxillary anterior region

Nasal septum Nasal fossa Nasal spine Insicive foramen Nose Median palatine suture

Intermaxillary Suture

Intermaxillary suture also called median suture. It appears as a thin radiolucent line in the midline between the two portions of premaxilla. It extends from the alveolar crest between the central incisors superiorly through the anterior nasal spine and continues posteriorly between the maxillary palatine process to the posterior aspect of the hard palate.


Palatal view
Median palatine suture

Anterior Nasal Spine

Mostly seen on PA of maxillary central incisors. Located in midline1.5-2cm above the alveolar crest. It is radiopaque and usually V-shaped.

Nasal Fossa & Nasal Septum

The nasal cavity shows the hazy shadow of the inferior nasal conchae extending from the right and left lateral walls
Floor of nasal fossa(black arrow)
Nasal septum(black arrow) nasal mucosa (white arrow)
Nasal fossa

a-Nasal septum b-Nasal fossa c-Anterior nasal spine

d-Incisive foramen e-Median palatine suture

Incisive Foramen

Also called NASOPALATINE or ANTERIOR PALATINE FORAMEN. It is the oral terminus of the nasopalatine canal. It transmits the nasopalatine vessels and nerves. Lies in the midline of palate behind the central incisors at the junction of the median palatine and incisive sutures. Radiographic image variability is due to: 1.Different angles of the X-ray beam. 2.Variability in its anatomic size. It is frequently the potential site of cyst formation ( incisive canal cyst .The presence of a cyst is presumed if the width of the foramen exceeds 1 cm.

Palatal view

Incisive foramen

Superior Foramina of the Nasopalatine canal

The nasopalatine canal originates at two foramina in floor of the nasal cavity. Radiographically, it can be recognized as two radiolucent areas above the apices of the central incisors in floor of the nasal cavity near its anterior border and both sides of the septum. They appear in projections of the maxillary incisors, when an exaggerated vertical angle is used.
Lateral wall of nasopalatine canal
Nasal fossa

Lateral Fossa

Also called as INCISIVE FOSSA. Appears as depression in the maxilla near the apex of the lateral incisor . Appears diffusely radiolucent in the PA.

Nasolacrimal Canal

It is formed by the nasal and maxillary bones. It runs from the medial aspect of the anteroinferior border of the orbit inferiorly, to drain under the inferior concha into the nasal cavity. On PA : It appears in the region above the apex of the canine, especially when steep vertical angulation is used . On maxillary occlusal projection: It appears as ovoid radiolucencies in the region of the molars.

The Nose

The soft tissue of the nose is frequently seen in the projections of the maxillary central and lateral incisors ,superimposed over the roots of these teeth. Image appears uniformly opaque with a sharp border.
The soft tissue outline of the nose


An oblique line demarcating a region that appears to be covered by a slight radio opacity frequently traverses PA radiographs of the premolar region . *The radiopaque area is the thick cheek tissue superimposed on the teeth and the alveolar process. *The image of the fold becomes more evident with age, due to creasing of the skin along the line and deepening of permanent folds. *The nasolabial fold is useful in identifying the side of the maxilla represented by a film of the area if it is edentulous and few other anatomic features are demonstrated.
The nasolabial fold
Nasolabial Fold

Red arrows: Soft tissues of nose. Green arrows: Lip line.

Floor of nasal fossa Maxillary sinus Lateral fossa Nose
Maxillary canine

The Maxillary Sinus

It is an air containing cavity lined by mucous membrane.Appears as the three sided pyramid :Base -formed by mesial wall adjacent to nasal cavity.Apex –extending laterally into the zygomatic process of maxilla. • A roof or upper border, bounded by the orbit.• A medial wall, bounded by the nasal cavity.• A posterior wall, related to the pterygopalatine fossa.• A lateral wall, related to the zygoma and cheek.• An anterior wall, related to the cheek.• A floor, related to the apices of the upper posterior teeth.

On the PA, maxillary sinus appears as a thin ,delicate radiopaque line. It extends from the distal aspect of the canine to the posterior wall of the maxilla above the tuberosity. There is often as much as 2-3mm of maxillary bone between the root ends and sinus floor.

floor of the nasal cavity

neurovascular channels
floor of the sinus


In response to the loss of function (associated with loss of posterior teeth) the sinus may expand further into the alveolar bone , occasionally extending to the alveolar ridge. Thin radiolucent lines of the uniform width are found within the image of the maxillary sinus.These are shadows of the neuro -vascular canals that accommodate the posterior superior vessels and nerves.
The neuro -vascular canals
Septum



Red arrows: Floor of nasal fossa and blue arrows anterior border of maxillary sinus forming the inverted (upside down ) Y.

 Zygomatic Process And Zygomatic Bone

The zygomatic process of the maxilla is an extension of the lateral maxillary surface that arises in the region of the apices of the first and the second molars and serves as the articulation for the zygomatic bone. Appears as a U-shaped radiopaque line with rounded ends projected in the apical region of the first and second molars.

Pterygoid Plates

The medial and lateral pterygoid plates lie immediately posterior to the maxillary tuberosity . They cast a single radiopaque shadow without any evidence of trabeculation. Extending inferiorly from the medial pterygoid plate, the hamular process may be seen.
Pterygoid plates
The hamular process

Black arrows : hamular process

Purple arrows : pterygoid plates

Maxillary sinus

Zygoma
Ptrygoid plate
Hamular process
Coronoid process
Maxillary tuberosity
Maxillary molar region

Anatomic Landmarks of Mandible

Symphysis Genial tubercles Lingual foramen Mental ridge Mental fossa Mental foramen Mandibular canal Nutrient canals Mylohyoid ridge Submandibular gland fossa External oblique ridge Inferior border of mandible Coronoid process

Symphysis

The region of mandibular symphysis in infants demonstrate a radiolucent line through the midline of the jaw between the images of the forming deciduous central incisors. The suture usually fuses by the end of 1st year of life and is no longer radiographically apparent. If this radiolucency is found in older individuals, it is abnormal and may suggest a fracture or a cleft.
Symphysis
Bilateral supernumerary primary incisors
Symphysis Fracture


These are tiny bumps of bone that serve as attachment for the genioglossus and geniohyoid muscles. Present on lingual side. On PA, appears as ring shaped radiopacity below the apices of mandibular incisors. On mandibular occlusal radiographs as one or more small projections.
 Genial Tubercles

Mandibular incisor region

Mental fossa
Lingual foramen
Genial tubercle
Mental ridge


Lingual Foramen
It is a hole or tiny opening located on the internal surface of the mandible and surrounded by the genial tubercles. Lingual nutrient vessels pass through it. Radiographically, appears as a radiolucent dot inferior to the apices of the mandibular incisors.
Lingual foramen. b. genial tubercles.

Mental Ridge

It is a linear prominence of cortical bone located on the external surface extending from the premolar region to the midline and slopes upward. Radiographically, appears as two radiopaque lines sweeping bilaterally(from the premolar region) forward and upward toward the midline (to the incisor region).

Mental Fossa

The mental fossa is a radiolucent depression on the labial surface of the mandible overlying the roots of the incisors between the alveolar ridge and mental ridge.
The resultant radiolucency may be mistaken for pathology.

Mental Foramen

It is usually the anterior limit of the inferior dental canal that is apparent on radiographs. Located on the external surface of the mandible as an opening in the region of the mandibular premolars. Mental nerves and blood vessels exit through it. Radiographically, it appears as a small ovoid, round, oblong, slitlike radiolucent area or very irregular and partially or completely corticated. When the mental foramen is projected over one of the premolar apices, it may mimic periapical disease.

Nutrient Canals

Nutrient canals are tube like passage-ways through bone that contains nerves and blood vessels that supply the teeth. Radiographically seen as vertical radiolucent lines. They are visible in about 5% of all patients and are more prominent in anterior mandible where bone is thin, older persons, and individuals with high blood pressure or advanced periodontitis. They also indicate a thin ridge, useful in implant assessment.

Mandibular premolar region

a – Mylohyoid ridge b - Mandibular canal c – Submandibular gland fossa d – Mental foramen


Mandibular Canal
Tube like passage arises at the mandibular foramen on the lingual side of the ramus and passes downward and forward, moving from the lingual side in the third molar region to the buccal side in the premolar region. It contains the inferior alveolar nerves and vessels. Radiographically: Appears as a radiolucent band outlined by two radiopaque lines of cortical plate.

Mylohyoid Ridge

Linear prominence of bone located on the internal surface of mandible. Extends from the molar region downward and forward towards the lower border of mandibular symphysis. On PA, appears as radiopaque band extending downward from molars. It serves as an attachment for the mylohyoid muscle.

Submandibular Gland Fossa

Depressed area of bone located on the internal surface of mandible. Submandibular salivary gland lies in this fossa. It appears as a radiolucent area in the molar region below the mylohyoid ridge.
b - Mylohyoid ridge. d -Submandibular gland fossa.

Mandibular molar region

a – External oblique ridgeb – Mylohyoid ridge c – Mandibular canald- Submandibular gland fossa

External Oblique Ridge

Linear prominence of bone located on external surface of mandible extending downwards and is a continuation of anterior border of ramus. It appears as a radiopaque line extending downwards and forwards from ant. border of mandible & ends in 3rd molar region. It is a line of attachment of the buccinator muscle.

The external oblique ridge (red arrows) and the mylohyoid ridge (blue arrows) usually run parallel to each other , with the external oblique ridge always being higher on the film .

Internal Oblique Ridge

Linear prominence of bone located on internal surface of the mandible. It appears as a radio opaque Line, descending downwards and forward from coronoid process, in a horizontal position, stop at the third molar area or become continuous with the mylohyoid line. Its placed below the external oblique ridge.


 Inferior Border Of The Mandible
Occasionally, seen as a dense broad radiopaque band of bone.

Coronoid Process

It is a marked prominence of bone on the ant. ramus of the mandible. Not seen on a mandibular PA but appears on a maxillary molars PA. It is seen as a triangular radiopacity superimposed over or inferior to maxillary tuberosity.