Radiological anatomy of head and neck

INTRODUCTION
The radiographic recognition of disease requires some knowledge of the
radiographic appearance of normal structures. A good diagnosis mandates appreciation of a
wide range of variation in the appearance of normal structures. Similarly most patients
demonstrate many of the normal radiographic landmarks, but it is a rare patient who shows
them all. Hence the absence of one or several landmarks in any individual should not be
necessarily considered abnormal.
The radiographic appearance of various structures which can be visualized on the intraoral
periapical radiograph can be classified as under:
1. Teeth
2. Supporting structures
3. Maxilla
4. Mandible.
5. Others, restorative materials.
All these structures appear either radiopaque or radiolucent.
However, there are many structures which may not be visible on the intraoral periapical radiographs,
these may be studied and observed on:
1. Panoramic radiographs
2. Cephalometric radiographs
3. Skull projections.
Normal anatomical landmarks seen on the intraoral periapical radiographs may also be classified as:
1. Radiopaque
2. Radiolucent.

1
 Radiological anatomy of head and neck

RADIOPAQUE STRUCTURES OF MAXILLA

1. Enamel
2. Dentin
3. Cementum
4. Lamina dura
5. Alveolar crest
6. Cancellous bone
7. Nasal septum
8. Anterior nasal spine
9. Floor of the nasal cavity
10. Inferior nasal conchae
11. Nasolabial fold
12. Floor of the maxillary sinus
13. Septa in maxillary sinus
14. Inverted Y- in maxillary sinus
15. Zygomatic process of the maxilla
16. Zygoma (malar bone)
17. Pterygoid plates
18. Hamular process
19. Maxillary tuberosity

2
 Radiological anatomy of head and neck

RADIOPAQUE STRUCTURES OF MANDIBLE

1. Enamel
2. Dentin
3. Cementum
4. Lamina dura
5. Alveolar crest
6. Cancellous bone
7. Genial tubercles
8. Mental ridge
9. Mylohyoid ridge
10. External oblique ridge
11. Inferior border of the mandible
12. Coronoid process
13. Internal oblique ridge

3
 Radiological anatomy of head and neck

RADIOLUCENT STRUCTURES OF MAXILLA

1. Pulp
2. Periodontal ligament space
3. Nutrient canals
4. Intermaxillary suture
5. Nasal fossa (nasal cavity)
6. Incisive foramen
7. Superior foramina of nasopalatine canal
8. Incisive fossa (lateral or canine fossa)
9. Nasolacrimal canal
10. Maxillary sinus
11. Nose
12. Nasolabial fold

4
 Radiological anatomy of head and neck

RADIOLUCENT STRUCTURES OF MANDIBLE

1. Pulp
2. Periodontal ligament space
3. Nutrient canals
4. Lingual foramen
5. Symphysis
6. Mental fossa
7. Mental foramen
8. Mandibular canal
9. Submandibular fossa
Tooth
The tooth structure that can be viewed on the radiograph are:
1. Enamel: This is the densest structure found in the human body. It is seen as the outer most radiopaque
layer of the crown of a tooth on the radiograph.
2. Dentin: is found beneath the enamel layer of a tooth and surrounds the pulp cavity. It appears radiopaque
and comprises most of the tooth structure. Dentin is less radiopaque than enamel.
3. Cementum: is not usually apparent on the radiograph because the cemental layer is very thin and the
contrast between the cementum and dentin is very low. Diffuse radiolucent areas with ill-defined borders
may be apparent radiographically on the mesial and distal aspects of the teeth in the cervical region between
the edge of the enamel cap and the the crest of the alveolar ridge, (cementoenamel junction), this is called
cervical burn out, which may be mistaken for cervical or root caries.
4. Pulp cavity: This consists of the pulp chamber and the root canals. It contains the blood vessels, nerves
and lymphatics and appears relatively radiolucent on the radiograph. The size of the pulp chamber is
generally large in children than in adults because it decreases with age owing to the formation of secondary
dentin. Great variation exists between individuals in size of the pulp chambers and extent of the pulp horn.
The root canal may be apparent, Extending to the apex of the root.
In some teeth the canal may appear constricted in the region of the apex and thus not discernible in the last
few millimeter or so of its length. In the above mentioned cases the canal may exit on the same side of the
tooth, just short of the radiographic apex. At the end of the developing tooth root, pulp canal diverges and
the walls of the root rapidly taper to a knife edge. In the recess formed in the root walls and extending a short
distance beyond is a small rounded, radiolucent area in the trabecular bone, surrounded by a thin layer of
hyperostotic bone. This is the dental papilla surrounded by its bony crypt. The papilla forms the dentin and
primordium of the pulp.

5
 Radiological anatomy of head and neck

In mature teeth the shape of the pulp chamber may change. With aging occurs a gradual deposition of
dentin. This process begins apically, precedes coronally, and may lead to pulp obliteration. Trauma may
also stimulate dentin production leading to reduction of the size of the pulp chambers and canals.

6
 Radiological anatomy of head and neck

SUPPORTING DENTOALVEOLAR STRUCTURES

LAMINA DURA
A radiograph of sound teeth in a normal dental arch demonstrates that thE tooth sockets are bounded
by a thin radiopaque layer of dense bone.Its name, lamina dura (“hard layer”), is derived from its
radiographic appearance. This layer is continuous with the shadow of the cortical bone at the alveolar
crest. It is only slightly thicker and with the same radiodensity as the trabeculae of cancellous bone in
the area. Its radiographic appearance is caused by the fact that the x-ray beam passes tangentially
through many times the thickness of the thin bony wall, which results in its observed attenuation (the
eggshell effect). Developmentally, the lamina dura is an extension of the lining of the bony crypt that
surrounds each tooth during development.

The appearance of the lamina dura on radiographs may vary, depending on the direction of the x-ray
beam relative to the cortical bone thickness. In addition, small variations and disruptions in the
continuity of the lamina dura may result from superimpositions of cancellous bone and small nutrient
canals passing from the marrow spaces to the periodontal ligament (PDL). The thickness and density
of the lamina dura on the radiograph vary with the amount of occlusal stress to which the tooth is
subjected. The lamina dura is thicker and more radiopaque around the roots of teeth in heavy occlusion
and thinner and less dense around teeth not subjected to occlusal function.
RADIOGRAPHIC PROJECTION OF THE LAMINA DURA
The radiographic appearance of the lamina dura is determined by the angulation of the x-ray
beam relative to the tooth root. When the x-ray beam is directed through a relatively long
expanse of the structure, the lamina dura appears radiopaque and well defined. When the beam
is directed more obliquely, the lamina dura appears more diffuse and may not be discernible.
In fact, even if the supporting bone in a healthy arch is intact, identification of a lamina dura
completely surrounding every root on each film is frequently difficult, although it is usually
evident to some extent about the roots on each image.
ALVEOLAR CREST
The gingival margin of the alveolar process that extends between the teeth is apparent on
radiographs as a radiopaque line—the alveolar crest. The level of this bony crest is considered

7
 Radiological anatomy of head and neck

normal when it is 0.5 to 2 mm apical to the cementoenamel junction of the adjacent teeth. The
alveolar crest may recede apically with age and show marked resorption with periodontal
disease. Radiographs can demonstrate only the position of the crest;
determining the significance of its level is primarily a clinical decision.

The length of the normal alveolar crest in a particular region depends on the distance between
the teeth in question. In the anterior region, the crest is reduced to only a point of bone between
the close-set incisors. Posteriorly it is flat, aligned parallel with and slightly below a line
connecting the cementoenamel junctions of the adjacent teeth. The crest of the bone is
continuous with the lamina dura and forms a sharp angle with it. Rounding of these sharp
junctions is indicative of periodontal disease. The image of the crest varies from a dense layer
of cortical bone to a smooth surface without cortical bone. In the latter case, the trabeculae at
the surface are of normal size and density. In the posterior regions, this range of radiodensity
of the crest is presumed to be normal if the bone is at a proper level in relation to the teeth.
However, the absence of an image of cortex between the incisors is considered by many to be
an indication of incipient disease, even if the level of the bone is not abnormal.
PERIODONTAL LIGAMENT SPACE
Because the PDL is composed primarily of collagen, it appears as a radiolucent space between
the tooth root and the lamina dura. This space begins at the alveolar crest, extends around the
portions of the tooth roots within the alveolus and returns to the alveolar crest on the opposite
side of the tooth.

8
 Radiological anatomy of head and neck

The PDL width varies between individuals, from tooth to tooth in the same individual and even
from location to location around one tooth. It is usually thinner in the middle of the root and
slightly wider near the alveolar crest and root apex, suggesting that the fulcrum of physiologic
movement is in the region where the PDL is thinnest. The thickness of the ligament relates to
the degree of function, because the PDL is thinnest around the roots of
embedded teeth and teeth that have lost their antagonists. The reverse is not true, however,
because an appreciably wider space is not regularly observed in persons with especially heavy
occlusion or bruxism.

CANCELLOUS BONE
The cancellous bone (also called trabecular bone or spongiosa) lies between the cortical plates
in both jaws. It is composed of thin radiopaque plates and rods (trabeculae) surrounding many
small radiolucent pockets of marrow. On twodimensional radiographs, the radiographic pattern
of the trabeculae comes from two anatomic sources. The first is the cancellous bone itself. The
second is the endosteal surface of the outer cortical bone where the cancellous bone fuses with
the cortical bone. At this surface, trabecular plates are relatively thick and make a significant
contribution to the radiographic image. There is wide variation in the trabecular pattern among
individuals and between different anatomic sites in the same patient. It is important to recognize
the limits of this variation so that it is not confused with disease. To evaluate the trabecular
pattern in a specific area, the practitioner should examine the trabecular distribution, size, and
density and compare them throughout both jaws and especially with the corresponding region

9
 Radiological anatomy of head and neck

on the opposite side. This comparison allows the clinician to assess whether a particularly
suspect region is anatomic or pathologic in nature. The trabeculae in the anterior maxilla are
typically thin and numerous, forming a fine, granular, dense pattern, and the marrow spaces
are consequently small and relatively numerous. In the posterior maxilla, the trabecular pattern
is usually quite similar to the pattern in the anterior maxilla, although the marrow spaces may
be slightly larger.

In the anterior mandible, the trabeculae are thicker than in the maxilla, resulting in a coarser
pattern with trabecular plates that are oriented more horizontally. The trabecular plates are also
fewer than in the maxilla, and the marrow spaces are correspondingly larger. In the posterior
mandible, the peri radicular trabeculae and marrow spaces may be similar to
those in the anterior mandible but are usually larger. The trabecular plates are also oriented
mainly horizontally in this region. Below the apices of the mandibular molars, the number of
trabeculae dwindles still more. In some cases, the area from just below the molar roots to the
inferior border of the mandible may appear to be almost devoid of trabeculae. The distribution
and size of the trabeculae throughout both jaws show a relationship to the thickness (and
strength) of the adjacent cortical plates. It may be speculated that where the cortical plates are
thick (e.g., in the posterior region of the mandibular body), internal bracing by the trabeculae
is not required, so there are relatively few except where required to support the alveoli. By
contrast, in the maxilla and anterior region of the mandible, where the cortical plates are
relatively thin and less rigid, trabeculae are more numerous and lend internal bolstering to the
jaw. Occasionally the trabecular spaces in this region are very irregular, with some so large
that they mimic pathologic lesions. This finding may be diagnostically challenging.

10
 Radiological anatomy of head and neck

TRABECULAR SPARSENESS: ANATOMIC VARIATION VERSUS DISEASE

Sparseness or apparent absence of trabeculae may suggest the presence of disease in an
otherwise asymptomatic patient. Considerable variation may exist in trabecular patterns among
patients, so it is important to examine other regions of the jaws, preferably on the contralateral
side, to assess the general trabecular pattern for that individual. Assess whether the area of
trabecular sparseness deviates appreciably from that norm. Compare with previous radiographs
of the region in question to determine whether the current appearance represents a change from
a prior condition. An abnormality is more likely when the comparison indicates a change in the
trabecular pattern. If prior films are unavailable, it is frequently useful to repeat the
radiographic examination at a reduced exposure because this may demonstrate the presence of
a sparse trabecular pattern that was overexposed and “burned out” in the initial projection. In
an asymptomatic patient, it may be appropriate to expose another radiograph at a later time to

monitor for interval changes.

CORTICAL BONE
Buccal and lingual cortical plates of the mandible and maxilla do not cast a discernible image
on periapical, bitewing and panoramic radiographs. They are well depicted on CBCT images,
best visualized on the axial, coronal, or cross-sectional images. Cortical bone has higher
mineral content than the adjacent cancellous bone, and appears more radiopaque. The endosteal
surface of the cortex is smooth and merges with the trabeculae of the cancellous bone. The
thickness of the cortical bone varies with anatomic location. In particular, buccal bone adjacent
to teeth is often thin and barely discerned on radiographs. CBCT images reveal the proximity
of the root surface to the cortical plates of the alveolar bone and detect anatomic variations,
such as fenestrations or dehiscence defects.

11
 Radiological anatomy of head and neck

MAXILLA AND MIDFACIAL BONES

The maxilla and palatine bones form the upper jaw. The maxilla comprises a pyramidal-shaped
body and four processes—alveolar, palatine, zygomatic, and frontal.
INTERMAXILLARY SUTURE
The alveolar and palatine processes articulate in the midline to form the intermaxillary suture
between the central incisors. On intraoral periapical radiographs this suture appears as a thin
radiolucent line in the midline between the two portions of the premaxilla. It extends from the
alveolar crest between the central incisors superiorly through the anterior nasal spine and
continues posteriorly between the maxillary palatine processes to the posterior aspect of the
hard palate. It is not unusual for this narrow radiolucent suture to terminate at the alveolar crest
in a small rounded or Vshaped enlargement.

On CBCT images, the intermaxillary suture is best evaluated on coronal and axial sections.
The suture is limited by two parallel radiopaque borders of thin cortical bone on each side of
the maxilla. The radiolucent region is usually of uniform width. The adjacent cortical margins
may be either smooth or slightly irregular. The appearance of the intermaxillary suture depends
on both anatomic variability and, in the case of periapical radiography, on the angulation of the
x-ray beam through the suture. Evaluation of the intermaxillary suture is important in planning
for orthodontic expansion of the palate.
ANTERIOR NASAL SPINE
The anterior nasal spine is frequently demonstrated on periapical radiographs of the maxillary
central incisors. Located in the midline, it lies approximately 1.5 to 2 cm above the alveolar
crest, usually at or just below the junction of the inferior end of the nasal septum and the inferior
outline of the nasal aperture. It is radiopaque because of its bony composition and is usually
V-shaped. On CBCT images, the anterior nasal spine is best observed on axial and sagittal

12
 Radiological anatomy of head and neck

sections as a triangular projection from the anterior surface of the maxilla at the level of the
nasal floor.

NASAL APERTURE AND NASAL CAVITY

Because the air-filled nasal aperture and cavity lie just above the oral cavity, its radiolucent
image may be apparent on intraoral radiographs of the maxillary teeth, especially in central
incisor projections. On maxillary incisor periapical views, the inferior border of the fossa
aperture appears as a radiopaque line extending bilaterally away from the base of the anterior
nasal spine. Above this line is the radiolucent space of the inferior portion of the nasal cavity.
The relatively radiopaque nasal septum is seen arising in the midline from the anterior nasal
spine. The shadow of the septum may appear wider than anticipated and not sharply defined
because the image is a superimposition of septal cartilage and vomer bone. Also, the septum
frequently deviates slightly from the midline, and its plate of bone (the vomer) is curved.

13
 Radiological anatomy of head and neck

NASAL CONCHAE AND NASAL TURBINATES

The lateral walls contain thin bony projections called conchae. The conchae plus their mucosal
covering are called turbinates. There are three nasal turbinates—superior, middle, and
inferior—which define spaces termed superior, middle, and inferior meati .
Pneumatization of the concha is termed concha bullosa and is a common variant with a reported
frequency of 14% to 53%. On periapical radiographs of the maxillary incisor and canine
regions, the inferior nasal conchae is often visualized, extending from the right and left lateral
walls for varying distances toward the septum. These conchae fill varying amounts of the lateral
portions of the cavity.

NASAL FLOOR AND HARD PALATE

The palatine processes are thick horizontal bony projections that form the anterior three-fourths
of the hard palate and the floor of the nasal cavity. On periapical radiographs, the floor of the
nasal aperture and a small segment of the nasal cavity are occasionally projected high onto a
maxillary canine radiograph. In the posterior maxillary region, the floor of the nasal cavity may
be seen in the region of the maxillary sinus. It may falsely convey the impression of a septum
in the sinus or a limiting superior sinus wall.

14
 Radiological anatomy of head and neck

NASOPALATINE CANAL AND INCISIVE FORAMEN

The nasopalatine canal originates in the anterior floor of the nasal cavity and exits on the
anterior maxilla as the incisive foramen, located in the midline on the anterior aspect of the
palatine process immediately palatal to the maxillary central incisors. Within this foramen are
two lateral canals—the incisive canals or foramina of Stensen—that transmit the terminal
branch of the descending palatine artery and the nasopalatine nerve. Occasionally there may
be two additional midline canals—the foramina of Scarpa, which transmit the nasopalatine
nerves. On intraoral and panoramic radiographs, the incisive foramen is usually projected
between the roots and in the region of the middle and apical thirds of the central incisors. It
appears as an ovoid radiolucency, often with diffuse borders. Occasionally the lateral walls of
the nasopalatine canal are seen as a pair of radiopaque lines running vertically from the floor
of the nasal aperture to the incisive foramen. When an exaggerated vertical angle is used, as in
anterior maxillary occlusal projections, the openings of the foramina of Stensen at the nasal
floor may be seen.

15
 Radiological anatomy of head and neck

There is wide variation in the appearance of the incisive foramen on periapical radiographs.
The foramen varies markedly in its radiographic shape, size, and sharpness. It may appear
smoothly symmetric or very irregular, and its borders may be well demarcated or ill defined.
The position of the foramen's image is also variable and may be recognized at the apices of the
central incisor roots, near the alveolar crest, anywhere in between, or extending over the entire
distance. The great variability of its radiographic image is primarily the result of the differing
angles at which the x-ray beam is directed for the maxillary central incisors and some
variability in its anatomic size. Often, a large incisive foramen may mimic disease.
NASOPALATINE CANAL—ANATOMIC VARIATION VERSUS DISEASE
• The nasopalatine canal is a potential site of cyst formation. A nasopalatine canal cyst is
radiographically discernible because it frequently causes enlargement of the foramen and canal.
Often the appearance of a large incisive foramen may mimic a cyst. The presence of a cyst is
presumed if the width of the foramen exceeds 1 cm or if enlargement can be demonstrated on
successive radiographs.
• On a periapical radiograph, the radiolucency of the normal incisive foramen may be projected
over the apex of one central incisor to mimic a periapical radiolucency. The presence of an
intact lamina dura around the central incisor in question and a lack of clinical symptoms will
indicate absence of periapical disease.
LATERAL FOSSA
The lateral fossa (also called the incisive fossa) is a gentle depression in the maxilla near the
apex of the lateral incisor. It may appear diffusely radiolucent on periapical projections of this
region, superimposed over the root of the lateral incisor. An intact lamina dura around the root

16
 Radiological anatomy of head and neck

of the lateral incisor coupled with absence of clinical symptoms will indicate absence of
periapical disease.

NOSE
The soft tissue of the tip of the nose is frequently seen in projections of the maxillary central
and lateral incisors, superimposed over the roots of these teeth. The image of the nose has a
uniform, slightly opaque appearance with a sharp border. Occasionally the radiolucent nares
can be identified, especially when a steep vertical angle is used.

NASOLACRIMAL CANAL
The nasal and maxillary bones form the nasolacrimal canal. It runs from the medial aspect of
the anteroinferior border of the orbit inferiorly to drain under the inferior concha into the nasal
cavity. The anatomy of the nasolacrimal canal is distinct on CBCT and best evaluated in the
axial and coronal planes. Occasionally it can be visualized on periapical radiographs in the
region above the apex of the canine, especially when a steep vertical angulation is used. The

17
 Radiological anatomy of head and neck

nasolacrimal canals are usually seen on maxillary occlusal projections in the region of the
molars.

PARANASAL SINUSES
The paranasal sinuses consist of four pairs of air-filled cavities—the maxillary, frontal, and
sphenoid sinuses and ethmoid air cells—and drain into, the nasal cavity via ostia. The sinuses
are lined by mucous membrane. Only the maxillary sinuses are visualized on periapical
radiographs. CBCT scans encompass the sinuses to different extents depending on the FOV
and the region being imaged. Limited- and medium-FOV CBCT imaging of the posterior
maxillary arch will image some portion of the maxillary sinuses, and often the ethmoid air
cells. Full-FOV CBCT scans will encompass all paranasal sinuses. The intricate anatomy of
the sinus boundaries and its drainage routes into the nasal cavity are the basis of radiologic
sinus evaluation.
MAXILLARY SINUS
The maxillary sinus develops by the invagination of mucous membrane from the nasal cavity.
The largest of the paranasal sinuses, it normally occupies virtually the entire body of the
maxilla. Its function is unknown. The maxillary sinus may be considered as a three-sided
pyramid, with its base the medial wall adjacent to the nasal cavity and its apex extending
laterally into the zygomatic process of the maxilla. Its three sides are (1) the superior wall
forming the floor of the orbit, (2) the anterior wall extending above the premolars, and (3) the
posterior wall bulging above the molar teeth and maxillary tuberosity. The sinus communicates
with the nasal cavity by the ostium, approximately 3 to 6 mm in diameter and positioned under
the posterior aspect of the middle concha of the ethmoid bone. Periapical radiographs show the
inferior portion of the maxillary sinus. The maxillary sinus floor is a thin layer of cortical bone
and appears as a thin radiopaque line. In adults, the sinuses are usually seen to extend from the
distal aspect of the canine to the posterior wall of the maxilla above the tuberosity. In the
absence of disease, it appears continuous, but on close examination it can be seen to have small

18
 Radiological anatomy of head and neck

interruptions in its continuity or radiodensity. When viewed on periapical radiographs, these

discontinuities are probably illusions caused by superimposition of small marrow spaces.

The maxillary sinuses show considerable variation in size. They enlarge during childhood,
achieving mature size by age 15 to 18 years. They may change during adult life in response to
environmental factors. The right and left sinuses usually appear similar in shape and size,
although marked asymmetry is occasionally present. The floors of the maxillary sinus and nasal
cavity are seen on periapical radiographs at approximately the same level around the age of
puberty. In older individuals, the sinus may extend farther into the alveolar process; in the
posterior region of the maxilla, its floor may appear considerably below the level of the floor
of the nasal cavity. Anteriorly, each sinus is restricted by the canine fossa and is usually seen
to sweep superiorly, crossing the level of the floor of the nasal cavity in the premolar or canine
region. Consequently, on periapical radiographs of the canine, the floors of the sinus and nasal
cavity are superimposed and seen crossing one another, forming an inverted “Y” in the area.

The degree of extension of the maxillary sinus into the alveolar process is extremely variable.
In some periapical projections, the floor of the sinus is well above the apices of the posterior

19
 Radiological anatomy of head and neck

teeth; in others, it may extend well beyond the apices toward the alveolar ridge. In response to
a loss of function (associated with the loss of posterior teeth), the sinus may expand farther into
the alveolar bone, occasionally extending to the alveolar ridge. The roots of the molars usually
lie in close apposition to the maxillary sinus. Root apices may project anatomically into the
floor of the sinus, causing small elevations or prominences along the maxillary sinus floor.
Periapical images may convey the impression that the roots project into the sinus cavity, which
is an illusion. The intimate relationship between the tooth roots and the maxillary sinus is
evaluated better with CBCT, and this is the modality of choice when critical evaluation of the
maxillary sinus floor is clinically indicated. The thin layer of bone covering the root is seen as
a fusion of the lamina dura and the floor of the sinus. Rarely, defects may be present in the
bony covering of the root apices in the sinus floor, and the apical lamina dura may be indistinct.
Due to this close relationship, manifestations of odontogenic disease and maxillary sinus
disease is often diagnostically challenging.

RELATIONSHIP BETWEEN TEETH AND THE MAXILLARY SINUS

The close relationship between the maxillary sinus and teeth leads to the possibility that clinical
symptoms originating in the sinus may be perceived in the teeth and vice versa.
• Canals that carry the superior alveolar nerves traverse the anterolateral and posterolateral
walls of the sinus. The nerves are in intimate contact with the membrane lining the sinus. As a
result, an acute inflammation of the sinus is frequently accompanied by pain in the maxillary
teeth innervated by the portion of the nerve proximal to the area of sinus inflammation. Careful
clinical evaluation of the maxillary posterior teeth to rule out dental disease is important to
differentiate true odontogenic pain from sinus-related pain.

20
 Radiological anatomy of head and neck

• Occasionally periapical and periodontal inflammation from the maxillary molar teeth may
extend to cause inflammation of the maxillary sinus mucosa, referred to as odontogenic
maxillary sinusitis. Unlike chronic rhinosinusitis, odontogenic maxillary sinusitis is usually
unilateral. Approximately 10% of maxillary sinusitis is due to odontogenic causes. Frequently,
thin radiolucent lines of uniform width are found within the periapical image of the maxillary
sinus.These are the shadows of neurovascular canals or grooves in the lateral sinus walls that
accommodate the posterior superior alveolar vessels, their branches, and the accompanying
superior alveolar nerves. Although they may be found coursing in any direction (including
vertically), they are usually seen running a curved posteroanterior course that is convex toward
the alveolar process.

Often one or several radiopaque lines traverse the image of the maxillary sinus. These opaque
lines are called septa. They are thin folds of cortical bone that project a few millimeters away
from the floor and wall of the antrum, or they may extend across the sinus. They are usually
oriented vertically and vary in number, thickness, and length. Although septa appear to separate
the sinuses into distinct compartments, this is seldom the case.
Rather, the septa typically extend only a few millimeters into the central volume of the sinus.
Septa warrant attention because they sometimes mimic periapical disease, and the chambers
they create in the alveolar recess may complicate the search for a root fragment displaced into
the sinus. In these clinical situations, CBCT is the modality of choice in performing this
anatomic evaluation.

21
 Radiological anatomy of head and neck

The floor of the maxillary sinus occasionally shows small radiopaque projections, which are
nodules of bone. These must be differentiated from root tips, which they resemble in shape. In
contrast to a root fragment, which is quite homogeneous in appearance, the bony nodules often
show trabeculation; although they may be quite well defined, at certain points on their surface
they blend with the trabecular pattern of adjacent bone. A root fragment may also be recognized
by the presence of a root canal.

On periapical radiographs, it is common to see the floor of the nasal fossa in periapical views
of the posterior teeth superimposed on the maxillary sinus. The floor of the nasal fossa is
usually oriented more or less horizontally, depending on film placement, and is superimposed
high on maxillary views. The image, a solid opaque line, frequently appears thicker than the
adjacent sinus walls and septa.

ETHMOID, SPHENOID, AND FRONTAL SINUSES

The ethmoid, sphenoid, and frontal sinuses are not in the imaging field for periapical
radiography. However, these sinuses are well visualized on CBCT scans and on panoramic and
cephalometric radiographs. When the paranasal sinuses are imaged on CBCT scans, the
anatomic boundaries and drainage patterns of the sinus must be systematically examined.

22
 Radiological anatomy of head and neck

The ethmoidal sinuses are divided into the anterior and posterior ethmoidal air cells, and the
number of air cells per side ranges from 3 to 18. Frequently extramural air cells—air cells
outside of the ethmoid bone—can be visualized. These include agger nasi air cells, causing
pneumatization of the lacrimal bone, and Haller cells, which cause pneumatization of the
orbital floor. Occasionally Haller cells are seen on panoramic images. The sphenoid sinuses
are midline structures in the body of the sphenoid bone and start to develop at approximately
4 months in utero. The sinuses vary considerably in size, and the right and left sphenoid sinuses
are often asymmetric and separated by a bony septum. Often multiple septa are present, giving
the sinus a “locular” appearance. The sphenoid sinuses may extend inferiorly, resulting in
pneumatization of the pterygoid bones. The sphenoid sinuses are not visualized on periapical
images but are well demonstrated on CBCT scans and on lateral cephalometric radiographs.
The frontal sinuses are the last paranasal sinuses to develop, usually starting at approximately
6 to 7 years of age. Hypoplasia of the frontal sinus is a common normal variant, and aplasia of
the frontal sinuses is noted in approximately 4% of the population. The frontal sinuses are well
demonstrated on CBCT scans and on cephalometric radiographs.
ZYGOMATIC PROCESS AND ZYGOMA
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 second molars and articulates with the maxillary
process of the zygoma. On periapical radiographs, the zygomatic process appears as a U-shaped
radiopaque line with its open end directed superiorly. The enclosed rounded end is projected
in the apical region of the first and second molars. The size, width, and definition of the
zygomatic process are quite variable, and its image may be large, depending on the angle at
which the beam was projected. The maxillary antrum may expand laterally into the zygomatic
process of the maxilla (and into the zygomatic bone after the maxillozygomatic suture has
fused), resulting in a relatively increased radiolucent region within the U-shaped image of the
process.

23
 Radiological anatomy of head and neck

When the sinus is recessed deep within the process, as in, the image of the air space within the
process is dark. Typically the walls of the process are thin and well defined (in contrast
to the very dark radiolucent air space). When the sinus exhibits relatively little penetration of
the maxillary process, as in (usually in younger individuals or individuals who have maintained
their posterior teeth and vigorous masticatory function), the image of the walls of the zygomatic
process of the maxilla tends to be thicker, and the appearance of the sinus in this region is
smaller and more opaque. The inferior border of the zygoma extends posteriorly from the
inferior border of the zygomatic process of the maxilla to the zygomatic process of the temporal
bone. It can be identified as a uniform radiopacity over the apices of
the molars. The zygomatic process of the temporal bone and the body of the zygoma compose
the zygomatic arch. The prominence of the molar apices superimposed on the shadow of the
zygoma and the amount of periapical detail supplied by the radiograph depend primarily on the
extent of aeration (pneumatization) of the zygoma by the maxillary sinus and on the orientation
of the x-ray beam.

The zygomatic processes of the maxilla articulate posteriorly with the maxillary process of the
zygoma. These two processes form the anterior segment of the zygomatic arch. The
zygomaticomaxillary suture is visualized as a thin, radiolucent, jagged line in this portion of
the arch. Disruptions of the integrity or symmetry of the arch may be associated with
craniofacial developmental abnormalities or facial trauma.
NASOLABIAL FOLD
An oblique line demarcating a region that appears to be covered by a veil of slight radiopacity
frequently traverses periapical radiographs of the premolar region. The line of contrast is sharp,
and the area of increased radiopacity is posterior to the line. The line is the nasolabial fold, and

24
 Radiological anatomy of head and neck

the opaque veil is the thick cheek tissue superimposed on the teeth and the alveolar process.
The image of the fold becomes more evident with age, as the
repeated creasing of the skin along the line (where the elevator of the lip, zygomatic head, and
orbicularis all insert into the skin) and the degeneration of the elastic fibers finally lead to the
formation and deepening of permanent folds. This radiographic feature frequently proves
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.

PTERYGOID PLATES
The medial and lateral pterygoid plates lie immediately posterior to the maxilla. These
structures are best visualized on coronal and axial CT sections and must be carefully evaluated
when assessing a patient with facial trauma. Involvement of the pterygoid plates is an essential
feature of Le Fort fractures. The images on these two plates are extremely variable, and they
do not appear at all on many intraoral radiographs of the third molar area. When they are
apparent, they almost always cast a single radiopaque homogeneous shadow without any
evidence of trabeculation. Extending inferiorly from the medial pterygoid plate is the hamular
process, which on close inspection can show trabeculae.

25
 Radiological anatomy of head and neck

MANDIBLE
SYMPHYSIS
Radiographs of the region of the mandibular symphysis in infants demonstrate a radiolucent
line through the midline of the jaw between the images of the forming deciduous central
incisors. This suture usually fuses by the end of the first year of life, after which it is no longer
radiographically apparent. It is not frequently encountered on dental radiographs because few
young patients have cause to be examined radiographically. If this radiolucency is found in
older individuals, it is abnormal and may suggest a fracture or a cleft.
GENIAL TUBERCLES
The genial tubercles (also called the mental spine) are located on the lingual surface of the
mandible slightly above the inferior border and in the midline. They are bony protuberances,
more or less spine-shaped, that are often divided into a right and left prominence and a superior
and inferior prominence. They attach the genioglossus muscles (at the superior tubercles) and
the geniohyoid muscles (at the inferior tubercles) to the mandible. They
are well visualized on mandibular occlusal radiographs as one or more small projections. Their
appearance on periapical radiographs of the mandibular incisor region is variable; often they
appear as a radiopaque mass (3 to 4 mm in diameter) in the midline below the incisor roots.
They may also not be apparent at all.

LINGUAL FORAMEN
Midline lingual foramina are present in 96% to 100% of individuals, located in the region of
the genial tubercles. The superior foramen contains a neurovascular bundle from the lingual
arteries and nerve, whereas the inferior foramen is supplied from the sublingual or submental
arteries and from the mylohyoid nerve. On periapical radiographs, the lingual foramen
is typically visualized as a single round radiolucent canal with a well-defined opaque border
lying in the midline below the level of the apices of the incisors.

26
 Radiological anatomy of head and neck

MENTAL RIDGE
On periapical radiographs of the mandibular central incisors, the mental ridge (protuberance)
may occasionally be seen as two radiopaque lines sweeping bilaterally forward and upward
toward the midline. They are of variable width and density and may be found to extend from
low in the premolar area on each side up to the midline, where they lie just inferior to or are
superimposed on the mandibular incisor tooth roots. The image of the mental ridge is most
prominent when the beam is directed parallel with the surface of the mental tubercle (as in
using the bisecting-angle technique).
MENTAL FOSSA
The mental fossa is a depression on the labial aspect of the mandible extending laterally from
the midline and above the mental ridge. Because of the resulting thinness of jawbone in this
area, the image of this depression may be similar to that of the submandibular fossa and
likewise may be mistaken for periapical disease involving the incisors.

MENTAL FORAMEN

27
 Radiological anatomy of head and neck

The mental foramen is usually the anterior limit of the inferior dental canal that is apparent on
periapical radiographs. Its image is quite variable, and it may be identified on periapical
radiographs only about half the time because the opening of the mental canal is directed
superiorly and posteriorly. As a result, the usual view of the premolars is not projected through
the long axis of the canal opening. This circumstance is responsible for the variable appearance
of the mental foramen. Although the wall of the foramen consists of cortical bone, the density
of the image of the foramen varies, as does the shape and definition of its border. It may be
round, oblong, slit-like, or very irregular and partially or completely corticated. The foramen
is seen about halfway between the lower border of the mandible and the crest of the alveolar
process, usually in the region of the apex of the second premolar. Also, because it lies on the
surface of the mandible, the position of its image in relation to the tooth roots is influenced by
projection angulation. It may be projected anywhere from just mesial of the permanent first
molar roots to as far anterior as mesial of the first premolar root.

The location and size of the mental foramen is better evaluated on CT sections. When
visualization of the mental foramen is critical to the treatment plan, as in implant placement,
CBCT is the modality of choice. An important anatomic variation to detect when placing
implants in the premolar region is the anterior loop, where the inferior alveolar canal extends
anterior to the mental foramen before it loops posteriorly to exit through the mental foramen.
The incidence of an accessory mental foramen is about 7%.
When the mental foramen is projected over one of the premolar apices, it may mimic periapical
disease. In such cases evidence of the inferior alveolar canal extending to the suspect
radiolucency or a detectable lamina dura in the area would suggest the true nature of the dark
shadow. However, the relative thinness of the lamina dura superimposed with the radiolucent
foramen may result in considerable “burnout” of the lamina dura image, which complicates its

28
 Radiological anatomy of head and neck

recognition. Nevertheless, a second radiograph from another angle is likely to show the lamina
dura clearly as well as some shift in position of the radiolucent foramen relative to the apex.

INFERIOR ALVEOLAR CANAL

The radiographic image of the inferior alveolar canal is a dark linear shadow with thin
radiopaque superior and inferior borders cast by the lamella of bone that bounds the canal.
Sometimes the borders are seen only partially or not at all. The width of the canal shows some
interpatient variability but is usually constant anterior to the third molar region. The
canal's course may be apparent between the mandibular and mental foramina. Only rarely is
the image of its anterior continuation toward the midline discernible on the radiograph.

The relationship of the inferior alveolar canal to the roots of the lower teeth
may vary from one in which there is close contact with all molars and the second premolar to
one in which the canal has no intimate relationship to any of the posterior teeth. In the usual
picture, however, the canal is in contact with the apex of the third molar, and the distance
between it and the other roots increases as it progresses anteriorly. When the apices of the
molars are projected over the canal, the lamina dura may be overexposed, conveying the
impression of a missing lamina or a thickened PDL space that is more radiolucent than
apparently normal for the patient. To ensure the soundness of such a tooth, other clinical testing
procedures must be used (e.g., vitality testing). Because the canal is usually located just inferior
to the apices of the posterior teeth, altering the vertical angle for a second periapical radiograph
of the area is not likely to separate the images of the apices and

29
 Radiological anatomy of head and neck

canal.

The course of the inferior alveolar canal is well demonstrated on CT scans. In cross-sectional
and coronal slices, the inferior alveolar canal is typically seen as an oval or round radiolucency
with corticated borders. Sometimes the cortication may be thin or imperceptible. The
relationship of the canal to the tooth roots should be assessed. This relationship varies greatly
among patients, especially in the molar region, with the inferior alveolar canal occupying a
position from close to the root apices to adjacent to the inferior border of the mandible. Other
variations include bifid inferior alveolar canal with a reported frequency of about 15%; these
can be seen on panoramic and cone beam images. Patients with bifid canals are at greater risk
of inadequate anesthesia or surgical complications, for example, from implant placement.
NUTRIENT CANALS
Nutrient canals carry a neurovascular bundle and appear as radiolucent lines of fairly uniform
width. They are most often seen on mandibular periapical radiographs running vertically from
the inferior dental canal directly to the apex of a tooth or into the interdental space between the
mandibular incisors. They are visible in about 5% to 40% of all patients and are more frequent
in black patients, male patients, older patients, and patients with high blood pressure, diabetes
mellitus, or advanced periodontal disease. They may be accentuated in a thin ridge. Because
they are anatomic spaces with walls of cortical bone, their images occasionally have
hyperostotic borders. Sometimes a nutrient canal is oriented perpendicular to the cortex and
appears as a small round radiolucency simulating a pathologic radiolucency.

30
 Radiological anatomy of head and neck

MYLOHYOID RIDGE
The mylohyoid ridge (also called the internal oblique ridge) is a slightly irregular crest of bone
on the lingual surface of the mandibular body. Its anterior margin lies about 10 mm inferior to
the alveolar ridge lingual to the second premolar and extends posteriorly to the area of the third
molar about 5 mm below the alveolar crest. This ridge serves as an attachment for the
mylohyoid muscle. On a periapical radiograph, its image runs diagonally downward and
forward from the area of the third molars to the premolar region at approximately the level of
the apices of the posterior teeth. This image is sometimes superimposed on the images of the
molar roots. The margins of the image are not usually well defined but appear quite diffuse and
of variable width. Occasionally, the ridge is relatively dense with sharply demarcated borders.
It is more evident on periapical
radiographs when the beam is positioned with excessive negative angulation. Generally, as the
ridge becomes less defined, its anterior and posterior limits blend gradually with the
surrounding bone.

SUBMANDIBULAR GLAND FOSSA

On the lingual surface of the mandibular body, immediately below the mylohyoid ridge in the
molar area, there is frequently a depression in the bone. This concavity accommodates the
submandibular gland and often appears as a radiolucent area with the sparse trabecular pattern
characteristic of the region. This trabecular pattern is even less defined on periapical and
panoramic radiographs of the area because it is superimposed on the relatively reduced mass

31
 Radiological anatomy of head and neck

of the concavity. The radiographic image of the fossa is sharply limited superiorly by the
mylohyoid ridge and inferiorly by the lower border of the mandible but is poorly defined
anteriorly (in the premolar region) and posteriorly (at about the ascending ramus). Although
the image may appear strikingly radiolucent, accentuated as it is by the dense mylohyoid ridge
and inferior border of the mandible, awareness of its possible presence should preclude its
being confused with a bony lesion by inexperienced clinicians.

EXTERNAL OBLIQUE RIDGE

The external oblique ridge is a continuation of the anterior border of the mandibular ramus. It
follows an anteroinferior course lateral to the alveolar process and is relatively prominent in its
upper part; it juts considerably on the outer surface of the mandible in the region of the third
molar. This bony elevation gradually flattens and usually disappears at about where the
alveolar process and mandible join below the first molar. The ridge is a line of attachment of
the buccinator muscle. Characteristically it is projected onto posterior periapical radiographs
superior to the mylohyoid ridge, with which it runs an almost parallel course. It appears as a
radiopaque line of varying width, density, and length, blending at its anterior end with the
shadow of the alveolar bone.

INFERIOR BORDER OF THE MANDIBLE

Occasionally the inferior mandibular border is seen on periapical projections as a
characteristically dense, broad, radiopaque band of bone.

32
 Radiological anatomy of head and neck

CORONOID PROCESS
The image of the coronoid process of the mandible is frequently apparent on periapical
radiographs of the maxillary molar region as a triangular radiopacity, with its apex directed
superiorly and anteriorly, superimposed on the region of the third molar. In some cases it may
appear as far forward as the second molar and be projected above, over, or below these
molars, depending on the position of the jaw and the projection of the x-ray beam. Usually the
shadow of the coronoid process is homogeneous, although internal trabeculation can be seen
in some cases. Its appearance on maxillary molar radiographs results from the downward and
forward movement of the mandible when the mouth is open. Consequently, if the opacity
reduces the diagnostic value of the image, the radiograph must be remade, and the second view
should be acquired with the mouth minimally open. (This contingency must be considered
whenever this area is radiographically examined.) Occasionally, especially when its shadow is
dense and homogeneous, the coronoid process is mistaken for a root fragment. The true nature
of the shadow can be easily demonstrated by obtaining two radiographs with the mouth in
different positions and noting the change in position of the suspect shadow.

TEMPOROMANDIBULAR JOINT
The temporomandibular joint (TMJ) region is imaged on panoramic, cephalometric, and CBCT
imaging. The TMJ is the articulation between the glenoid fossa of the temporal bone and the
condyle of the mandible. The glenoid fossa is a concave depression located in the squamous
portion of the temporal bone. It is bordered anteriorly by the articular eminence and posteriorly

33
 Radiological anatomy of head and neck

by the squamotympanic and petrotympanic fissures. The articular eminence is usually

described as a posterior slope, adjacent to the fossa, and the crest, which is the inferiormost tip
of the eminence. The condyle is typically ellipsoid and is longer in the
mediolateral dimension than in the anteroposterior dimension. The condyle is angulated with
the medial pole being positioned posterior to the lateral pole, typically forming an angle of 15
to 30 degrees with the sagittal plane. When viewing sections through the TMJ, it is useful to
make custom reconstructions through the axial long axis of the condylar head. The resulting
oblique sections are referred to as “corrected” sagittal and frontal sections.

34
 Radiological anatomy of head and neck

RESTORATIVE MATERIALS
Restorative materials vary in their radiographic appearance, depending principally on their
atomic number and also influenced by their thickness and density. A variety of restorative
materials may be recognized on projection radiographs and CT scans.
• Silver amalgam is completely radiopaque

• Gold is equally opaque to x-rays, whether cast as a crown or an inlay or condensed as gold
foil.

• Stainless steel pins and stainless steel crowns appear highly radiopaque.

• A calcium hydroxide base is placed in a deep cavity to protect the pulp. Such base material is
typically composed to be radiopaque so that the development of recurrent caries (radiolucent)
can be identified.

35
 Radiological anatomy of head and neck

• Gutta-percha, a rubber-like substance used to fill pulp Canals during endodontic therapy, is
also radiopaque, but Lower in radiodensity than amalgam.

• Silver points, previously used to obliterate pulp canals during endodontic therapy, are highly
radiopaque.

• Composite restorations are typically partially radiopaque, as are porcelain restorations, which
are usually fused to a metallic coping.

36
 Radiological anatomy of head and neck

• Orthodontic appliances around teeth are relatively radiopaque, although less than stainless
steel crowns.

CEPHALOMETRIC AND SKULL IMAGING

In extraoral radiographic examinations, both the x-ray source and the image receptor (film or
digital sensor) are placed outside the patient's mouth. This chapter describes the most common
projections for extraoral radiographic examinations in which the source and sensor remain
static. These include the lateral cephalometric projection of the sagittal or median plane; the
submentovertex (SMV) projection of the transverse or horizontal plane; and
the Waters, posteroanterior (PA), cephalometric, and reverse Towne projections of the
coronal or frontal plane.

37
 Radiological anatomy of head and neck

CEPHALOMETRIC PROJECTIONS
Cephalometric projections are standardized projections that allow for reproducible imaging of
the craniofacial region. All cephalometric radiographs, including the lateral view, are made
with a cephalostat, which helps to maintain a constant relationship between the skull, the
receptor, and the x-ray beam. A cephalometric projection is made with a long source-to object
distance of 5 ft; this large distance minimizes image magnification. The object-to-receptor
distance is typically 10 to 15 cm and should be maintained constant for sequential radiographs
of the same patient. These projections may be made using film or digital receptors. Skeletal,
dental, and soft tissue anatomic landmarks delineate the lines, planes, angles, and distances
used to generate measurements and to classify patients’ craniofacial morphology. At the
beginning of treatment, these measurements are often compared with an established standard
or norm; during treatment, the measurements are usually compared with measurements from
previous cephalometric radiographs of the same patient to monitor growth and development as
well as treatment-induced changes.
LATERAL CEPHALOMETRIC PROJECTION (LATERAL SKULLPROJECTION)
Of the extraoral radiographs described in this chapter, the lateral cephalometric projection is

the one most commonly used in dentistry.

INDICATIONS
• Evaluate the anteroposterior (AP) relationships between the maxilla, mandible, and cranial
base.
• Assess skeletal and soft-tissue relationships.
• Monitor progress of treatment and treatment outcomes.
• Proceed with orthognathic surgical treatment planning.

38
 Radiological anatomy of head and neck

POSTEROANTERIOR CEPHALOMETRIC PROJECTION

The second most common skull radiograph used in dentistry is the PA cephalometric
projection. The PA cephalogram is mainly used for the evaluation of facial asymmetries and
assessment of orthognathic surgery outcomes involving the patient's midline or mandibular-
maxillary relationship.
INDICATIONS
• Evaluate craniofacial asymmetry.
• Assess jaw skeletal relationships.
• Monitor progress of treatment and treatment outcomes.
• Proceed with orthognathic surgical treatment planning.

39
 Radiological anatomy of head and neck

CRANIOFACIAL AND SKULL PROJECTIONS

SUBMENTOVERTEX (BASE) PROJECTION
INDICATIONS
SMV radiographs display the base of the skull, the zygomatic arches, and the sphenoid sinuses.
These radiographs can demonstrate osseous changes from skull base tumors, fractures of the
zygomatic arches, and the integrity and aeration of the sphenoid sinuses. These imaging
indications are largely achieved by computed tomography.

40
 Radiological anatomy of head and neck

WATERS PROJECTION
INDICATIONS
The Waters projection, also referred to as the occipitomental projection, displays the paranasal
sinuses, predominantly the maxillary sinus and to a lesser extent the frontal sinus and ethmoid
air cells. It also demonstrates the midfacial bones and orbits. A Waters projection was used to
evaluate maxillary sinusitis and midfacial fractures. Today these diagnostic objectives are
accomplished by computed tomography. The American College of Radiology Appropriateness
Criteria considers that this projection is usually not appropriate for the evaluation of trauma,
orbits, and sinonasal disease.

41
 Radiological anatomy of head and neck

REVERSE TOWNE PROJECTION (OPEN MOUTH)

INDICATIONS
The reverse Towne projection was frequently used to evaluate patients with suspected fractures
of the condyle and condylar neck. Today these diagnostic objectives are best achieved by
computed tomography.

42
 Radiological anatomy of head and neck

PANORAMIC IMAGING
Panoramic radiography (also called pantomography) is a body section imaging technique that
results in a wide, curved image layer depicting the maxillary and mandibular dental arches and
their supporting structures. This is achieved by using a single rotation of the x-ray source and
image receptor around the patient's head. Panoramic images are most useful clinically for
diagnostic challenges requiring broad coverage of the jaws. Common clinical applications
include evaluation of trauma including jaw fractures, location of third molars, extensive dental
or osseous disease, known or suspected large lesions, tooth development and eruption
(especially in the mixed dentition), impacted or unerupted teeth and root remnants (in
edentulous patients), temporomandibular joint (TMJ) pain, and developmental anomalies.
Panoramic imaging is often used in initial patient evaluation that can provide the required
insight or assist in determining the need for other projections. Panoramic images are also useful
for patients who do not tolerate intraoral procedures well.

PANORAMIC IMAGING
INDICATIONS
• Overall evaluation of dentition
• Examine for intraosseous pathology, such as cysts, tumors, or infections
• Gross evaluation of temporomandibular joints
• Evaluation of position of impacted teeth
• Evaluation of eruption of permanent dentition
• Dentomaxillofacial trauma
• Developmental disturbances of maxillofacial skeleton
ADVANTAGES COMPARED WITH A FULL-MOUTH EXAMINATION
• Broad coverage of facial bones and teeth

43
 Radiological anatomy of head and neck

• Low radiation dose

• Ease of panoramic radiographic technique
• Can be used in patients with trismus or in patients who cannot tolerate intraoral radiography
• Quick and convenient radiographic technique
• Useful visual aid in patient education and case presentation
DISADVANTAGES
• Lower-resolution images that do not provide the fine details provided by intraoral radiographs
• Magnification across image is unequal, making linear measurements unreliable
• Image is superimposition of real, double, and ghost images and requires careful visualization
to decipher anatomic and pathologic details
• Requires accurate patient positioning to avoid positioning errors and artifacts
• Difficult to image both jaws when patient has severe maxillomandibular discrepancy
Real, Double, and Ghost Images
Because of the rotational nature of the x-ray source and receptor, the x-ray beam intercepts
some anatomic structures twice during the single exposure cycle. Depending on their location,
objects may cast three different types of images:
• Real images: Objects that lie between the center of rotation and the receptor form a real
image. Within this zone, objects that lie within the focal trough cast relatively sharp images,
whereas images of objects located outside the focal trough are blurred show the positions of
the x-ray source during imaging of the left and right sides of the mandibular ramus,
respectively. the left ramus lies between the center of rotation and the receptor
and casts a real image. Because it is within the focal trough, its image is sharp. Also
demonstrated in is the formation of the real images of the hyoid bone and cervical
spine. However, because these structures are away from the center of the focal trough and
closer to the x-ray source, their images are blurred and magnified shows in blue the anatomic
region that makes real images.
• Double images: Objects that lie posterior to the center of rotation and that are intercepted
twice by the x-ray beam form double images. This region includes the hyoid bone, epiglottis,
and cervical spine, all of which cast images on both the right and left side of the image.
• Ghost images: Some objects are located between the x-ray source and the center of rotation.
These objects cast ghost images. On the panoramic image, ghost images appear on the opposite
side of its true anatomic location and at a higher level because of the upward inclination of the
x-ray beam. As the object is located outside of the focal plane and close to the x-ray source,

44
 Radiological anatomy of head and neck

the ghost image is blurred and significantly magnified. Several anatomic structures cast ghost
images. For example, the right mandibular ramus lies between the xray
source and the center of rotation and its ghost image is superimposed over the left side of the
image. Similarly, the ghost image of the left ramus is superimposed over the right side of the
image. The hyoid bone and cervical spine also form ghost images when the anterior
regions of the jaws are imaged. In addition, metallic accessories, such as earrings, necklaces,
and hairpins, form ghost images, which appear as blurred radiopaque images that can obscure
anatomic details, mask pathologic changes, or mimic pathologic changes. The ghost images of
the hard palate and mandibular body and angle are clearly visualized in a panoramic
image.Some anatomic zones form both real double and ghost images. These zones are the
regions of overlap.

The bones of the mandible, midface, cervical spine, and skull base as they appear on a
panoramic image. The image is composed of left and right lateral views of the facial bones
posterior to the canines and a coronal view anterior to the premolars.

45
 Radiological anatomy of head and neck

MIDFACIAL REGION
The midface is a complex mixture of bones, air cavities, and soft tissues, all of which appear
on panoramic images. Individual bones that may appear on the panoramic image of the midface
include temporal, zygoma, mandible, frontal, maxilla, sphenoid, ethmoid, vomer, nasal, nasal
conchae, and palate; thus it is a misnomer to refer to the midfacial region on the panoramic
image as “the maxilla.” Maintaining the discipline and focus of a systematic examination of all
aspects of the midfacial images is difficult and critical in the overall examination of the
panoramic image.

46
 Radiological anatomy of head and neck

This region can be compartmentalized into major sites for examination, as follows:
• Cortical boundary of the maxilla, including the posterior border and the alveolar ridge
• Pterygomaxillary fissure
• Maxillary sinuses
• Zygomatic complex, including inferior and lateral orbital rims, zygomatic process of maxilla,
and anterior portion of zygomatic arch
• Nasal cavity and conchae
• TMJs (also viewed in the mandible, but visualizing important structures multiple times is
always a good idea in image interpretation)
• Maxillary dentition and supporting alveolus
MANDIBLE
Assessment of the mandible can be compartmentalized into the major anatomic areas of this
curved bone, as follows:
• Condylar process and TMJ
• Coronoid process
• Ramus
• Body and angle
• Anterior sextant
• Mandibular dentition and supporting alveolus
Shadows of other structures that can be superimposed over the mandibular ramal area include
the following:
• Oropharyngeal and nasopharyngeal airway shadows, the former specifically when the patient
is unable to expel the air and place the tongue in the palate during the exposure
• Posterior wall of the nasopharynx
• Cervical vertebrae, especially in patients with pronounced anterior lordosis, typically seen in
severely osteoporotic individuals
• Earlobe
• Nasal cartilage
• Soft palate and uvula
• Dorsum of the tongue
• Ghost shadows of the opposite side of the mandible
• Real and ghost shadows of metallic jewelry or other ear,
nose, tongue decorations.
SOFT TISSUES
47
 Radiological anatomy of head and neck

Numerous opaque soft tissue structures may be identified on panoramic radiographs, including
the tongue arching across the image under the hard palate (approximately extending from the
right to the left mandibular angle), lip markings (in the middle of the image), the soft palate
extending posteriorly from the hard palate over each ramus, the posterior wall of the oral and
nasal pharynx, the nasal septum, the earlobes, the nose, and the nasolabial folds. Radiolucent
airway shadows superimpose on normal anatomic structures and may be delineated by the
borders of adjacent soft tissues. They include the nasal fossa, nasopharynx, oral cavity, and
oropharynx. The epiglottis and thyroid cartilage are often seen in panoramic images.

48
 Radiological anatomy of head and neck

CONE BEAM COMPUTED TOMOGRAPHY

Cone beam computed tomographic (CBCT) imaging was originally developed for angiography in the
early 1980s with the first dental and maxillofacial units introduced commercially in the late 1990s and
early 2000s. Unlike other extraoral dental imaging procedures, such as panoramic and cephalometric
radiography, CBCT acquires data volumetrically providing three-dimensional (3D) radiographic
imaging for the assessment of the dental and maxillofacial complex facilitating dental diagnosis. With
expanding availability of third party application software capable of importing data in Digital Imaging
and Communications in Medicine (DICOM) file format, the role of maxillofacial CBCT has now
expanded to image guidance of operative and surgical procedures and, more recently, additive
manufacturing of biomodels and surgical guides. There are three main processes in CBCT
imaging: (1) image production, (2) visualization, and (3) interpretation. This chapter addresses
the technical issues of image production including image data-set acquisition and “for
presentation reconstruction”.

STRENGTHS AND LIMITATIONS

CBCT imaging has numerous features that make it suitable for many dental applications, but
it also has a number of limitations.

49
 Radiological anatomy of head and neck

SIZE AND COST

CBCT equipment has a greatly reduced size and physical footprint compared with conventional
CT equipment, and it is approximately one-fourth to onefifth the cost. Both of these features
make it available for the dental office.
FAST ACQUISITION
With more recent advances in solid-state detector achievable frame rates, computer processing
speed, and units incorporating reduced trajectory arcs, most CBCT scanning is performed in
less than 30 seconds.
SUBMILLIMETER RESOLUTION
All CBCT units currently use megapixel solid-state devices for x-ray detection, which provide
submillimeter voxel resolution in all orthogonal planes. Some CBCT units are capable of high-
resolution imaging (nominal 0.076- to 0.125- mm voxel resolution) and may be required for
tasks requiring discernment of fine detail structures and disease processes, such as the
periodontal space, root canal morphology, and root resorption or fracture.

RELATIVELY LOW PATIENT RADIATION DOSE

Published reports indicate that there is a wide range in patient effective dose (International
Commission on Radiation Protection [ICRP] 2007) for maxillofacial CBCT depending on the
type and model of CBCT equipment and parameters used in clinical practice, such as FOV,
exposure (kVp and mA), and acquisition (e.g., rotational arc, number of basis images) settings.
Reported adult effective doses for any protocol ranged from 46 to 1073 μSv for extended FOVs,
9 to 548 μSv for large FOVs, 4 to 421 μSv for medium FOVs, and 5 to 297 μSv for small
FOVs. These values are approximately equivalent to 1 to 42 digital panoramic radiographs
(approximately 20 μSv) or 3 to 123 days’ equivalent per capita natural background radiation
(approximately 3100 μSv in the United States). Patient radiation dose can be reduced by
collimating the beam, elevating the chin, and using protective eyewear and thyroid and cervical
spine shielding. CBCT imaging provides a range of potentially
substantial dose reductions compared with conventional head MDCT imaging (range, 430 to
1160 μSv).
INTERACTIVE ANALYSIS
CBCT data reconstruction and viewing is performed natively by use of a personal computer.
In addition, some manufacturers provide software with extended functionality for specific
applications, such as implant placement or orthodontic analysis. Finally, the availability of

50
 Radiological anatomy of head and neck

cursor-driven measurement algorithms provides the practitioner with an interactive capability

for real-time dimensional assessment, annotation, and measurements.
LIMITATIONS
CBCT images have limitations compared with conventional CT images.
IMAGE NOISE
The cone beam projection acquisition geometry irradiates a larger tissue volume yielding more
scatter radiation from Compton interactions. Much of this scattered radiation is produced
omnidirectionally and recorded by detector pixels. Consequently, the number of photons
detected at each pixel does not reflect the true attenuation of an object along a specific path of
the xray beam. This difference, referred to as noise, contributes to image
degradation. The amount of scattered radiation is generally proportional to the total mass of
tissue contained within the primary x-ray beam; this increases with increasing object thickness
and field size. The contribution of this scattered radiation to production of the CBCT image
may be greater than the primary beam. In clinical applications, the scatter-to-primary ratios are
about 0.01 for single-ray CT imaging and 0.05 to 0.15 for fan-beam and spiral CT imaging and
may be 0.4 to 2 in CBCT imaging. For these reasons, it is always
desirable to use the smallest FOV possible when making a CBCT image. Additional sources
of image noise in CBCT are statistical variations in the homogeneity of the incident x-ray beam
(quantum mottle) and added noise of the detector system (electronic). The inhomogeneity of
x-ray photons depends on the number of the primary and scattered x-rays absorbed, the primary
and scattered x-ray spectra incident on the detector, and the number of basis projections.
Electronic noise is due to the inherent degradations of the detector
system related to the x-ray absorption efficiency of energy at the detector. In addition, because
of the increased divergence of the x-ray beam over the area detector, there is a pronounced heel
effect. This effect produces a large variation or nonuniformity of the incident x-ray beam on
the patient and resultant nonuniformity in absorption with greater signal-to-noise ratio (noise)
on the cathode side of the image relative to the anode side.
POOR SOFT TISSUE CONTRAST
Contrast resolution is the ability of an image to reveal subtle differences in image radiodensity.
Variations in image intensity are a result of differential attenuation of x-rays by tissues that
differ in density, atomic number, or thickness. Two principal factors limit the contrast
resolution of CBCT. First, scattered radiation is a significant factor in reducing the contrast of
the CBCT image. Scattered x-ray photons reduce subject contrast by adding background
signals that are not representative of the anatomy, reducing image quality.
51
 Radiological anatomy of head and neck

CBCT units have noticeably less soft tissue contrast than MDCT units, and are inadequate for
critical evaluation of soft tissue pathology. Second, there are numerous inherent FPD-based
artifacts that affect linearity or response to x-radiation. Saturation (nonlinear pixel effects above
a certain exposure), dark current (charge that accumulates over time with or without
exposure), and bad pixels (pixels that do not react to exposure) contribute to nonlinearity. In
addition, the sensitivity of different regions of the panel to radiation (pixel-to-pixel gain
variation) may not be uniform over the entire region.
OTHER IMAGING MODALITIES
The imaging modalities described in this chapter employ equipment and techniques that are
beyond the routine needs of most general dental practitioners. Of these modalities,
multidetector computed tomographic (MDCT) and magnetic resonance (MR) imaging are
often prescribed by specialist dentists for diagnosis and treatment planning of maxillofacial
diseases. Nuclear medicine, ultrasonography, and positron emission tomographic (PET)
imaging are used for more specialized purposes, and have applications in dentistry. Thus,
dentists should have a basic understanding of their operating principles and clinical
applications.

52
 Radiological anatomy of head and neck

MULTIDETECTOR COMPUTED TOMOGRAPHY

Multidetector CT (MDCT), also referred to as multislice CT (MSCT), was introduced in the
late 1990s and has now become the most widely used CT scanner design across the world. In
MDCT, multiple rows of detectors are incorporated into the array in the z-axis (craniocaudal
axis, patient's head to foot), allowing capture of multiple image slices during each gantry
revolution. MDCT technology has considerably reduced scan times, limiting motion artifact
from breathing, peristalsis, or heart contractions; this is important for patients who cannot hold
their breath for long periods and for pediatric and trauma patients. Current detector,
configurations have improved spatial resolution to submillimeter dimensions. Volumetric
acquisition with isotropic imaging allows reformatting in planes different from the axial
acquisition, without compromising image quality. Contemporary MDCT scanners have 64 to
128 rows of detectors, with some vendors manufacturing scanners with 320 and 640 detector
rows.
INDICATIONS FOR MAXILLOFACIAL MULTIDETECTOR
COMPUTED TOMOGRAPHY
• Infections, including osteomyelitis and space infections
• Midfacial and mandibular trauma
• Developmental anomalies of the craniofacial skeleton
• Benign intraosseous cysts and neoplasms of the jaws
• Benign and malignant neoplasms that originate in, or extend into, the orofacial soft tissues
• Soft-tissue cysts

53
 Radiological anatomy of head and neck

MAGNETIC RESONANCE IMAGING

Magnetic resonance imaging (MRI) is an imaging technique with a revolutionary impact in
diagnostic imaging, both in terms of the spectrum of tissue contrast and lack of risks associated
with ionizing radiation. In 1973, Paul Lauterbur described the potential of making images based
on the principles of nuclear magnetic resonance (NMR). Subsequently, Sir Peter Mansfield
developed use of the magnetic field and the mathematical analysis
of the signals for image reconstruction. In the 1980s, MRI was developed and refined for
practical clinical application. Lauterbur and Mansfield were awarded the Nobel Prize in
Physiology or Medicine in 2003. To make an MR image, the patient is first placed inside a
large magnet. This magnetic field causes the nuclei of many atoms in the body, particularly
hydrogen, to align with the magnetic field. The scanner directs a radiofrequency (RF) pulse
into the patient, causing some hydrogen nuclei to absorb energy (resonate). When the RF pulse
is turned off, the hydrogen nuclei release the stored energy, which is detected as a signal in the
scanner. This signal is used to construct the MR image—in essence, a map of the distribution
of hydrogen plus local tissue properties that influence the strength of the
magnetic resonance signal. MR imaging is noninvasive and uses nonionizing radiation. It
makes images with excellent soft-tissue resolution in any imaging plane. Practical limitations
of MR imaging include high cost and long scan times. Additionally, metallic objects in the
imaging field, such as dental restorations and orthodontic appliances, may produce image
artifacts. Ferromagnetic objects, such as foreign bodies or surgical devices, may move into the
strong magnetic field, injuring the patient.
ADVANTAGES AND LIMITATIONS OF MAGNETIC RESONANCE IMAGING
MR imaging has several advantages over other diagnostic imaging procedures.
• Superior contrast resolution of soft tissues. X-ray attenuation coefficients of soft tissues may
vary by no more than 1%, limiting radiographic contrast. However, T1 and T2 relaxation times
may vary by up to 40%.
• No ionizing radiation associated risks.
• Direct multiplanar imaging in all three planes is possible without reorienting the patient.
Disadvantages of MR imaging include:
• Relatively long imaging times limit its use in patients who may not be able to hold still for
extended periods of time.
• Patients with claustrophobia may not be able to tolerate the confined imaging space within
the MRI scanner.

54
 Radiological anatomy of head and neck

• The presence of ferromagnetic substances within the patient's body poses potential hazards—
the strong magnetic fields can move these objects, cause excessive heating, or induce strong
electrical currents, which may harm the patient. MRI is contraindicated in patients with
implanted electronic medical devices such as cardiac pacemakers, some cerebral aneurysm
clips, and in patients with embedded ferrous foreign bodies, such as shrapnel or bullets.
• Metals used in dental restorations do not move but often significantly distort the image in
their vicinity. Titanium implants cause only minor local image degradation.
Removable dental appliances must be removed prior to MRI scanning.
Special considerations in imaging patients undergoing orthodontic treatment:
• Steel orthodontic archwires are subject to substantially high forces and may need to be
removed. Archwires made of cobalt chromium, nickel titanium, and titanium molybdenum
exhibit minimal forces.
• Stainless steel brackets, bands, and fixed retainers should be checked to ensure secure
attachment, and may be left in place if secure, unless they interfere with the region of the image
being examined.
APPLICATIONS OF MAGNETIC RESONANCE IMAGING IN MAXILLOFACIAL
DIAGNOSIS
Because of its excellent soft-tissue contrast resolution, MR imaging is useful in evaluating soft
tissue conditions. Applications of MRI in dentistry include:
• Evaluate the position and integrity of the TMJ articular disk.
• Evaluate neoplasms of oral cavity and jaws to determine soft-tissue extent, lymph node
involvement, and perineural invasion.
• Evaluate salivary gland diseases, including cysts and neoplasms, infections, and obstructions.
• Evaluate vascular lesions in the orofacial region.

55
 Radiological anatomy of head and neck

ULTRASONOGRAPHY
This technique may be used for the initial assessment of the parotid and submandibular glands,
especially when an abnormality is located superficially. It may also be used to guide biopsies
and further imaging choices. HRUS is helpful at differentiating cysts from neoplasms, and
benign from malignant lesions. HRUS has become more specific at detecting Sjögren
syndrome, but it is still lacking in its ability to detect sialoliths. The major disadvantage of
HRUS lies in its inability to detect deep salivary gland lesions, whereas its major advantage is
its relative safety because it does not use ionizing radiation.

56
 Radiological anatomy of head and neck

SIALOGRAPHY
First performed in 1902, sialography is an imaging technique exclusively used for the parotid
and submandibular salivary glands. The technique involves infusion of the gland ductal system
with an iodinated contrast agent, and then imaging the gland with projection imaging,
fluoroscopy, MDCT, or cone beam computed tomography (CBCT). Sialography is the only
imaging technique that can assess both the morphology of the parotid and submandibular
glands in addition their function. The rate of clearance of the contrast agent from the gland,
especially when prolonged, is used as an indirect indicator of reduced secretory function. MRI
may be combined with sialography, but in these cases the patients’ own saliva is used as a
contrast agent and the imaging is done using heavily weighted T2 protocols. The primary
indication for sialography is chronic inflammatory conditions, especially when obstruction is
suspected. There are two contraindications for sialography. The first of these is acute infection
because injection of the contrast agent may disperse the infection into otherwise unaffected
regions within the gland and cause further pain for the patient. The second
contraindication is an immediately anticipated thyroid function test because the iodine in the
contrast agent may concentrate in the thyroid gland and interfere with the results of the test.
Recently, sialography has been coupled with CBCT, and this coupling has resulted in three-
dimensional images with submillimeter resolution and multiplanar capabilities that have
revolutionized the visualization of the parotid and submandibular glands.

57
 Radiological anatomy of head and neck

SIALENDOSCOPY
Since its first use in the 1990s, this examination that involves direct visualization of the parotid
and submandibular major ducts has transformed the diagnosis and management of obstructive
conditions of these glands. The minimally invasive technique can be equipped with sialolith
retrieval and stricture dilation tools that have enabled management of these common conditions
with reported success rates greater than 95%. Acute inflammation is the only known
contraindication for this relatively new technique because of the possible pain that may be
elicited.

58
 Radiological anatomy of head and neck

APPLIED ASPECTS
DENTAL CARIES
A thorough clinical examination that includes imaging is needed to diagnose carious lesions.
A clinical examination may be able to identify carious lesions on the occlusal and exposed
smooth surfaces of the teeth. However, it is nearly impossible to clinically identify caries
occurring on the proximal surfaces of teeth (i.e., interproximal caries), unless there has been
cavitation. When this occurs, it usually means that the carious lesion has become large enough
to be identified clinically. Unfortunately, when a caries lesion reaches this stage, the
affected tooth may require endodontic treatment or, if the tooth is determined to be
unrestorable, it may require extraction. The intraoral bitewing image is the preferred image to
detect interproximal caries in posterior teeth. As long as the operator can position the image
receptor (sensor or film) correctly, the proximal surfaces should be clearly visible. Since a
caries lesion causes a demineralization of the enamel and the dentin, more x-ray photons will
penetrate a demineralized region of the tooth, creating a radiolucent (dark) region on the
images. Caries are sometimes visible on a panoramic image, but in these cases the caries are
usually large enough to be clinically apparent. Since panoramic images have comparatively
poor resolution compared with intraoral receptors, they should not be relied on to detect caries.

Even when demineralization is detected on an image, this does not mean that it represents an
active carious lesion. This could simply represent an older, inactive (arrested) lesion that can
be described as a “scar” in the enamel. This is possible because the minerals from the saliva
are in the contact with the outermost surface of the tooth and can remineralize it but cannot
reach into deeper tissues. No single image can differentiate active caries from arrested
caries; to do so requires a second image, made at another time point, for comparison.

59
 Radiological anatomy of head and neck

DETECTION OF CARIOUS LESIONS

PROXIMAL SURFACES
TYPICAL APPEARANCE
As the enamel rods are oriented at 90 degrees to the surface of the enamel, the penetration of
acid and therefore demineralization occurs along the long axes of the enamel rods. Thus the
classic shape of an enamel caries lesion is a triangle with its broad base on the proximal surface
of the tooth and its tip pointing toward the dentinoenamel junction (DEJ). Other shapes may
also be seen; these can include a band, a rectangle, or simply a notch. When the leading edge
of a caries lesion reaches the DEJ, it spreads along the enamel-dentin interface and penetrates
the dentin, where a second triangle forms. Here, the broad base is located at the DEJ and its tip
is pointed toward the pulp chamber. One can expect the demineralization in the dentin to be
more aggressive because of the lower mineralized content, creating a
triangle with a wider base than in the enamel. The caries lesion then progresses through the
dentinal tubules toward the pulp chamber. Compared with enamel demineralization, once a
dentinal lesion has reached a certain size, it may lose its triangular shape, especially if
cavitation has occurred.

FALSE-POSITIVE INTERPRETATIONS
Every published study on this subject has shown that there is not 100% agreement on caries
diagnosis between different observers. This is especially true with enamel caries but can also

60
 Radiological anatomy of head and neck

sometimes occur with dentin caries. As mentioned earlier, the experience of the observer also
plays a pivotal role in the interpretation process. When a carious lesion is thought to be detected
on an image but the tooth structure is in fact intact, it is called a false-positive
finding. Although this can be caused by a variation in the morphology of the tooth, the most
common source of error is the misinterpretation of cervical burnout as dental caries.
Cervical burnout produces an artifact that mimics a carious lesion near the cementoenamel
junction (CEJ) area of the tooth. As the x-ray beam meets the convex proximal surface of the
tooth, those x-ray photons that pass almost tangentially through the tooth surface “see” less
tooth structure than those photons that pass deeper through the tooth. This area of convexity is
commonly located apical to the CEJ, near the normal height of the alveolar crest. The thinner
tooth structure here absorbs fewer x-rays; consequently the area appears relatively more
radiolucent on an image. Cervical burnout can also be seen in multirooted teeth when roots that
are more buccally positioned do not overlap perfectly with a lingual or palatal root in a
mesiodistal direction. The presence of a shallow furcation on either the mesial or distal surface
of the tooth can make the area appear more radiolucent. However, the presence of two
overlapping roots can be confirmed by identifying the periodontal ligament spaces of each root.

Staging and Cavitation

Multiple classification or scoring systems have been used over the years to categorize caries
size and depth. One of the most recent is the International Caries Classification and
Management System (ICCMS). This system separates caries progression into four stages:
sound (0), initial (RA), moderate (RB), and extensive (RC) enamel and subcategories therein.
In the initial stage (RA), demineralization is scored as appearing as a radiolucency within the
outer half of the enamel (RA1), the inner half of the enamel without or with involvement
of the DEJ (RA2) and the outer third of the dentin (RA3). The moderate stage (RB) is scored
as a radiolucency reaching the middle third of the dentin (RB4). Finally, when the radiolucency

61
 Radiological anatomy of head and neck

reaches the inner third of the dentin or the pulp, it is scored as RC5 and RC6, respectively. A
study has shown that on average 32% of carious lesions extending into the outer third of the
dentin also present with clinical cavitation. This value climbs to 72% for
lesions in the middle third of the dentin or deeper. The ability to identify or at least suspect
cavitation is important, because once this occurs, the bacteria in the lesion will maintain the
activity of the carious lesion unless it is managed surgically.

PERIODONTAL DISEASES
RADIOGRAPHIC ASSESSMENT OF PERIODONTAL CONDITIONS
Radiographs are especially helpful in the evaluation of the following features:
• Amount of bone present
• Condition of the alveolar crests
• Bone loss in the furcation areas
• Width of the periodontal ligament space
• Local irritating factors that increase the risk of periodontal disease
• Calculus
• Poorly contoured or overextended restorations
• Root length and morphology and crown-to-root ratio
• Open interproximal contacts, which may be sites for food impaction
• Anatomic considerations
• Position of the maxillary sinus in relation to a periodontal deformity
• Missing, supernumerary, impacted, and tipped teeth
• Pathologic considerations
• Caries
• Periapical lesions

62
 Radiological anatomy of head and neck

• Root resorption
In summary, a complete diagnosis of periodontal disease requires a thorough clinical
examination of the patient, combined with evidenceidentified on diagnostic images.
The dentist must also determine the optimal frequency of imaging examinations for patients
being managed for periodontal disease. The extent of continued disease activity, which can be
determined clinically, should dictate the frequency of subsequent imaging examinations.
IMAGING MODALITIES FOR THE ASSESSMENT OF PERIODONTAL DISEASE
INTRAORAL IMAGING
Intraoral images provide the highest spatial resolution of any imaging modality, which allows
the dentist to detect fine details of the periodontium. Image detail is essential since the
structures being assessed are often submillimeter in size, and many of the radiologic signs of
periodontal disease are subtle, including early loss of bone, and changes to the PDL space and
lamina dura. Intraoral imaging modalities used for the assessment of periodontal disease
include bitewing (interproximal) and periapical images. Bitewing images should be considered
the primary imaging choice for characterizing the periodontal diseases. These images most
accurately depict the distance between the cementoenamel junction (CEJ) and the crest of the
interradicular alveolar process because the incident x-ray beam is oriented at
almost right angles to the long axes of the teeth. Periapical images have the benefit of
demonstrating the full length of the tooth, which allows for the evaluation of the percentage of
root affected by bone loss. However, periapical images may provide a distorted view of the
relationship between the teeth and the location of the alveolar crest because of greater
variations in the obliquity of the primary x-ray beam. This occurs most commonly in the
maxilla because of anatomical limitations placed on receptor positioning by the height of the
palatal vault. In such circumstances, the level of the buccal alveolar crest may be projected near
or above the level of the palatal CEJ, making the bone height appear greater than it actually is.
The usefulness of intraoral images in the evaluation of the periodontal diseases can be
optimized by making images of high technical quality. The technique for obtaining bitewing
and periapical images is covered in greater detail in the chapters on projection geometry and
intraoral projections, but the features that are particularly important for imaging the relationship
between the teeth and the alveolar processes are emphasized here. The plane of the image
receptor should be placed parallel to the long axis of the tooth or tooth row, or as near to this
ideal position as the anatomical limitations of the mouth permit. The x-ray beam is directed
along an axis that is perpendicular to the long axis of the tooth and the plane of the image
receptor; this orientation minimizes distortion of the images of the teeth and periodontal tissues.
63
 Radiological anatomy of head and neck

In doing this, the teeth are depicted in their correct positions relative to the alveolar process
when there is (1) no overlapping of the interproximal contacts between the tooth crowns; (2)
no overlapping of the roots of adjacent teeth; and (3) the buccal and lingual cusps of molars
are superimposed over one another. In patients with moderate to severe clinical attachment loss
that has been identified on the clinical examination, standard (i.e., horizontal) bitewing images
may not depict the alveolar crest because of the extent of bone loss. In this instance, the dentist
must decide before the images are made, to reorient the receptor 90 degrees so that a vertical
bitewing image can be made. The vertical bitewing method uses the same American National
Standards Institute (ANSI) size 2 image receptors, but oriented in such a way that the long axis
of the receptor is in a vertical orientation. Although the image geometry is unchanged compared
with the standard horizontal method, the additional receptor area made available by reorienting
it allows the dentist to visualize the alveolar process when there has been significant clinical
attachment loss.

IMAGING FEATURES OF PERIODONTAL DISEASES

Because gingivitis is an inflammatory condition confined to the gingiva, there are no changes
to the underlying bone. Therefore the appearance of the bone in a diagnostic image is normal.
For all types of periodontal disease, the changes seen in diagnostic images reflect changes seen
with any inflammatory condition of bone. These changes can be divided into changes in the
morphology of the supporting bone, and changes to the trabecular density and pattern.
Changes in morphology become apparent by observing a loss of the interproximal crestal bone,
and the bone overlapping the buccal or lingual surfaces of the tooth roots. Alterations to the
trabecular pattern of the alveolar processes reflect either a reduction or an increase in bone
structure, or a combination of both. A reduction is seen as an increase in radiolucency

64
 Radiological anatomy of head and neck

(rarefaction) because of a decrease in either the number or density of existing trabeculae, or

both. An increase in bone is seen as an increase in radiopacity (sclerosis) as the result of an
increase in the thickness and/or density of trabecula, and/or their number. As with all
inflammatory lesions of bone, periodontal disease usually involves a combination of both bone
loss and bone formation. However, acute early lesions predominantly display bone loss,
whereas chronic lesions have a greater component of bone sclerosis. The following patterns of
bone loss may be seen in the diagnostic image as the result of periodontitis.
CHANGES IN MORPHOLOGY OF ALVEOLAR PROCESSES
EARLY BONE CHANGES
The early bone changes that occur in periodontitis appear as areas of localized erosion of the
interproximal alveolar crest. In the anterior regions of the jaws, there is blunting of the alveolar
crests and slight loss of alveolar crestal bone height. In the posterior regions of the jaws, there
may be loss of the normally acute angle between the lamina dura and alveolar crest. In early
stages of periodontal disease, this angle may lose its normal cortical surface
(margin) and appear “rounded off,” with an irregular and diffuse border. Even if only slight
changes are apparent, the onset of the disease process may not be recent, because there is a
delay before evidence of bone loss is visible in an image. As well, variations in the projection
angle of the incident x-ray beam can cause a slight change in the apparent height of the alveolar
crest. Small regions of bone loss on the buccal or lingual aspects of the teeth are also much
more difficult to detect.

A Stage I or II lesion does not always develop into a more severe lesion later; however, if there
is progression of the periodontal disease, bone changes can extend beyond the early changes to
the alveolar crest. Defects in the morphology of the alveolar process and crest may be described
as being horizontal or vertical (angular) in nature, as interdental craters and furcation defects,
and as a loss of the buccal or lingual cortical plate loss. The presence

65
 Radiological anatomy of head and neck

and severity of these bone defects may, of course, vary regionally within a patient, and certainly
among different patients.
HORIZONTAL BONE LOSS
Horizontal bone loss describes the appearance of a loss in height of the alveolar process where
the crest is still horizontal (i.e., parallel to an imaginary line joining the CEJs of adjacent teeth).
The bone crest is positioned more apically than the 0.5 mm to 2.0 mm from the CEJ that is
considered to be the range of normal. In horizontal bone loss, the crest of the buccal and lingual
cortical plates and the intervening interdental bone have been resorbed.

Early stage (I) bone loss may be defined as loss of up to 15% of the tooth root length, or a
probing depth of 4 mm or less. Stage II periodontitis is defined as bone loss between 15% and
33% of the root length, and probing depths of up to 5 mm. More severe Stages III and IV
periodontal disease are defined as bone loss extending to the middle-third of the tooth root and
beyond, with probing depths of 6 mm or more. The normal crest of the alveolar process can be
up to as much as 2 mm apical to the CEJ, and therefore assessment of the quantity of
bone loss must be considered from this point and not from the CEJ itself. When the CEJs of
adjacent teeth are at different horizontal levels, the alveolar crest may have an angled
appearance. Careful assessment of the imaginary line connecting the adjacent CEJs, as well as
the sharp angle made by the bone crest to the lamina dura, should not be confused with a true
vertical (angular) bone defect. Care must also be taken in using the CEJ as a reference point in
cases of tooth supraeruption and severe attrition. With supraeruption, the alveolar process will
not necessarily remodel so that a normal relationship is maintained to the CEJ. The situation is
similar in passive eruption, which may accompany severe attrition, although
in this case, bone loss is not due to periodontitis. Even so, there may still be loss of attachment,
which could be of clinical significance.

66
 Radiological anatomy of head and neck

VERTICAL BONE DEFECTS

A vertical (or angular, infrabony) defect describes the appearance of bone loss that is localized
at one or both root surfaces of a single tooth, although an individual may have multiple vertical
osseous defects. These defects are associated with Stages III and IV periodontitis, and develop
when bone loss progresses down the root of the tooth, resulting in a deepening of the
periodontal pocket. This manifests as a V- or triangular-shaped defect within the bone that
extends apically along the root of the affected tooth from the alveolar crest. Radiologically, the
outline of the remaining alveolar process typically displays an angulation that is oblique to an
imaginary line connecting the CEJ of the affected tooth to the adjacent tooth. In its early form,
a vertical defect appears as abnormal widening of the PDL space at the alveolar crest.

The vertical defect is described as three-walled (surrounded by three bony walls) when both
the buccal and lingual cortical plates remain intact. It is described as two-walled when one of
these plates has been resorbed, and as one-walled when both plates have been lost. Depending
on the amount of bone loss, vertical bitewing images may be required to show the entire extent
of the loss. The distinctions among these groups are important in designing the treatment plan.
The number of walls associated with a vertical defect is difficult or impossible to recognize on
intraoral images, because one or both of the cortical bony plates may remain superimposed
over the defect. Visualization of the depth of pockets may be aided by inserting a gutta-percha

67
 Radiological anatomy of head and neck

point before making the intraoral image. The point appears to follow the defect, because gutta-
percha is relatively inflexible and radiopaque. Clinical and surgical inspections are the best
means of determining the number of remaining bony walls. CBCT imaging can also help
characterize a defect more clearly, although this should not be routinely used for this purpose.

INTERDENTAL CRATERS
The interproximal crater is a two-walled, trough-like depression that develops in the crest of
the alveolar process between adjacent teeth. The buccal and lingual outer cortical walls of the
interproximal bone extend further coronally than the cancellous bone between them, which has
been resorbed. In an image, this appears as a band-like or irregular region of bone with less
density at the crest, immediately adjacent to the more dense normal bone apical to the base of
the crater. These defects are more common in the posterior segments of the jaws as a result of
the broader buccal-lingual dimension of the alveolar crest in these regions.

BUCCAL OR LINGUAL CORTICAL PLATE LOSS

The buccal or lingual cortical plate adjacent to the teeth may resorb. Loss of a cortical plate
may occur alone or with another type of bone loss, such as horizontal bone loss. This type of
bone loss is seen as an increase in the radiolucency of the tooth root near the alveolar crest.
The shape seen is usually semicircular, with the depth of the radiolucency directed apically in
relation to the tooth. Lack of bone loss at the interproximal region of the tooth may make this
kind of defect difficult to detect on conventional images.

68
 Radiological anatomy of head and neck

DENTAL ANOMALIES
Dental anomalies can develop in a variety of ways, and are broadly classified as being
congenital, developmental, or acquired. Congenital abnormalities are typically genetically
inherited, and developmental anomalies occur during the formation of a tooth or teeth. These
anomalies may include variations in the normal number, size, morphology, or eruptive pattern
of the teeth. Acquired abnormalities result from changes to teeth after normal formation. Teeth
that form abnormally short roots may represent congenital or developmental
anomalies, whereas the shortening of normal tooth roots by external resorption represents an
acquired change.
MALIGNANT NEOPLASMS
Diagnostic imaging has many important roles in the assessment and management of a patient
with a malignant neoplasm. First, imaging may aid in the establishment of an initial diagnosis
of a neoplasm. Second, imaging also aids in describing the extent of disease; specifically, local
and lymph node involvement, and more distant sites of spread. Appropriate radiologic
investigations assist the oncologist and surgeon to determine the anatomic spread of the
neoplasm so a plan can be developed for treatment or follow-up. Radiologic investigations may
also help to determine the presence of osseous involvement from a soft tissue neoplasm, assist
in determining the best site for biopsy, and stage the neoplasm for prognosis. Finally, a
thorough diagnostic imaging examination is part of the management of a patient who has
survived cancer, who often is rendered xerostomic, neutropenic, and susceptible to
dental caries, periodontal disease, and systemic infection. Various diagnostic imaging
modalities may be used to aid in the diagnosis. Intraoral images provide the best image
resolution, and may reveal subtle changes, such as periodontal ligament space widening that
computed tomography (CT) or magnetic resonance imaging (MRI) may be incapable of
demonstrating. Panoramic imaging can provide an overall assessment of the osseous structures
of the jaws, and can reveal relevant changes such as the destruction of the borders of the
69
 Radiological anatomy of head and neck

maxillary sinus. Either cone beam computed tomography (CBCT) or multidetector computed
tomography (MDCT) images can demonstrate the three-dimensional involvement of osseous
structures, while MDCT and MRI may show the extent of the soft tissue component of a
neoplasm and the involvement of adjacent tissues. MRI has been found to be
particularly useful for demonstrating perineural spread of disease and lymph node involvement.
Positron emission tomographic (PET) imaging, a technique capable of detecting abnormal
cellular metabolic activity associated with malignant neoplasms, has been used with MDCT
and MRI for localizing a neoplasm for surgery and radiation therapy.

TRAUMA
The initial assessment of a patient with craniofacial trauma is directed toward developing a
prioritized treatment plan based on the severity of the trauma and to determine the presence of
any life-threatening injuries. Diagnostic imaging is an important component guiding this
management. Depending on the extent of the injuries and the clinical context, the imaging
examination may encompass the brain, facial bones, dentoalveolar arches, and cervical spine.
In acute trauma settings, this is typically accomplished with multidetector computed
tomography (MDCT) and magnetic resonance imaging (MRI), depending on the clinical
presentation, and may be supplemented with conventional oral and maxillofacial images.
However, the choice of the imaging examination may be limited by the extent of the patient's
injuries and the availability of imaging modalities.

70
 Radiological anatomy of head and neck

TEMPOROMANDIBULAR JOINT ABNORMALITIES

Imaging of the TMJ may be necessary to supplement information obtained from the clinical
examination. Diagnostic imaging should be considered when an osseous abnormality or
infection is suspected, in patients with a history of trauma, significant dysfunction, alteration
in range of motion, sensory or motor abnormalities, or significant changes in occlusion. TMJ
imaging is not indicated for joint sounds if other signs or symptoms are absent, or for
asymptomatic children and adolescents before orthodontic treatment. The purposes of TMJ
imaging are to evaluate the integrity and relationships of the hard and soft tissues, confirm the
extent or stage of progression of disease, and evaluate the effects of treatment. There is often
poor correlation between the severity of findings on TMJ imaging and the severity of the
patient's signs and symptoms. For example, severe degenerative changes may be noted on an
imaging study, but the patient has only mild discomfort, or vice versa. The clinician must
correlate the imaging information with the patient's history and clinical findings to arrive at a
final diagnosis and to plan the management of the underlying disease process.

SALIVARY GLAND DISEASES

Imaging is often used to diagnose and to plan management and follow-up of patients with
salivary gland disorders. It provides crucial information regarding the nature of the disease
affecting the salivary glands, the extent and severity of glandular involvement, and the effect
on the surrounding structures. Many of the available imaging modalities have been used to
image the salivary glands including projection radiography, high-resolution ultrasonography
(HRUS), multidetector computed tomography (MDCT), magnetic resonance imaging (MRI),
nuclear medicine, sialography, and most recently sialendoscopy.

71
Radiological anatomy of head and neck

72
 Radiological anatomy of head and neck

CONCLUSION
Radiographic interpretation is an essential part of diagnostic process. The ability to
recognize what is revealed by a radiograph enables a dental professional to play a vital
role in the detection of diseases, lesions and condition of the jaw that cannot be
identified clinically. Hence as a dentist one should know to differentiate the normal
anatomy and pathological conditions inorder to prevent the misinterpretation

73
 Radiological anatomy of head and neck

REFERENCES
1. Mallya S, Lam E. White and Pharoah's Oral Radiology E-Book: Principles and
Interpretation: Second South Asia Edition E-Book. Elsevier India; 2019 May 15.
2. Karjodkar FR. Textbook of Dental and Maxillofacial Radiology by Karjodkar. Jaypee
Brothers Publishers; 2006.
3. Glendinning DE. Differential diagnosis of oral lesions: By Norman K. Wood and Paul
W. Goaz. St Louis: CV Mosby. 1975, price $24.50. British Journal of Oral Surgery.
1977 Nov 1;15(2):188-9.
4. Givol N, Buchner A, Taicher S, Kaffe I. Radiological features of osteogenic sarcoma
of the jaws. A comparative study of different radiographic modalities.
Dentomaxillofacial Radiology. 1998 Nov 1;27(6):313-20.
5. Stoppie N, Pattijn V, Van Cleynenbreugel T, Wevers M, Sloten JV, Ignace N. Structural
and radiological parameters for the characterization of jawbone. Clinical Oral Implants
Research. 2006 Apr;17(2):124-33.
6. Whaites E, Drage N. Essentials of dental radiography and radiology. Elsevier Health
Sciences; 2013 Jun 20.
7. Pasler FA, Visser H. Pocket atlas of dental radiology.

74