3. Foramina of scarpa and stensen
The incisive foramen just behind the
upper central incisors, is formed by the
union of halves of the maxilla. Lateral
canals within this fossa, on each side of
the midline transmit the nasopalatine
nerves and terminal branch of
descending palatine artery and called
foramina of stensen.
In some individuals, additional canals
within the fossa are found in the
midline. These are called foramina of
scarpa.
4. Step ladder pattern of trabeculae
In the posterior mandible, the trabecular plates are arranged horizontally
which is called step ladder pattern.
5. Laminar rain/lightening:
Sometimes the extraction socket may become permanently
filled with fibres rather than new bone. This is called
fibroplasia phenomenon. In this situation,
radiographically the vertical remnants of lamina dura appear
as ragged often zig-zag structure. It is also called laminar
lightening.
7. Name for the opening of nasopalatine
canal in the nose?
In the nasal cavity, the canal continues as foramina of stensen which
are usually two in number.
8. INTRODUCTION
The radiographic recognition of disease requires
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.
9. The radiographic appearance of various anatomical
structures which can be visualized on the intraoral periapical radiograph
can be classified as under:
1.Teeth
2. Supporting structures
3. Structures seen in the maxilla
4. Structures seen in the mandible.
10. RADIOPAQUE:
COMMON
•Enamel
•Dentin
•Cementum
•Lamina dura
•Alveolar crest
•Cancellous bone
MAXILLA
•Nasal septum
•Anterior nasal spine
•Floor of nasal cavity
•Inferior nasal concha
•Nasolabial fold
•Floor of maxillary sinus
•Zygomatic process
•Zygoma
•Pterygoid plates
•Hamular process
•Maxillary tuberosity
•Coronoid process
MANDIBLE
•Genial tubercles
•Mental ridge
•Mylohyoid ridge
•External oblique ridge
•Inferior border of mandible
12. TEETH:
ENAMEL:The enamel characteristically appears more radiopaque than any other
structure. Because it is 90% mineral, it causes the greatest attenuation of x-ray photons. Its
radiographic appearance is uniformly opaque and without evidence of the fine structure.
DENTIN: is about 75% mineralized, and because of its lower mineral content, its
radiographic appearance is roughly comparable to that of bone. Dentin is smooth and
homogeneous on radiographs because of its uniform morphologic features. The junction
between enamel and dentin appears as a distinct interface that separates these two structures.
CEMENTUM: The thin layer of cementum on the root surface has a mineral content
(50%) comparable to that of dentin. Cementum is not usually apparent radiographically because
the contrast between it and dentin is so low and the cementum layer is so thin.
13. PULP: The pulp of normal teeth is composed of soft tissue and consequently
appears radiolucent.
The chambers and root canals containing the pulp extend from the interior of the
crown to the apices of the roots. Although the shape of most pulp chambers is
fairly uniform within tooth groups, great variations exist among individuals in the
size of the pulp chambers and the extent of pulp horns.
14. In normal, fully formed teeth the root canal may
be apparent, extending from the pulp chamber
to the apex of the root. An apical foramen is
usually recognizable.
In other normal teeth the canal may appear
constricted in the region of the apex and not
discernible in the last millimeter or so of its
length.
In this case the canal may occasionally exit on
the side of the tooth, just short of the
radiographic apex. Lateral canals may occur as
branches of an otherwise normal root canal.
15. At the end of a developing tooth root the pulp
canal diverges and the walls of the root rapidly
taper to a knife edge.
In the recess formed by 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
called dental papilla bounded by its bony crypt.
Its radiographic pattern is often useful in
evaluating the stage of maturation of the developing
tooth; it also helps avoid misidentifying the apical
radiolucency as a periapical lesion.
16. SUPPORTING STRUCTURES
LAMINA DURA:
It is the radiographic appearance of alveolar process.
This layer is continuous with the shadow of the cortical
bone at the alveolar crest. It is only slightly thicker and no
more highly mineralized than 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 egg-shell effect).
Developmentally the lamina dura is an extension of the
lining of the bony crypt that surrounds each tooth during
development.
17. The appearance of the lamina dura on radiographs may
vary.
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, however, 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.
18. The image of a double lamina dura is
common if the mesial or distal surfaces of
roots present two elevations in the path of
the x-ray beam.
A common example of this is seen on the
buccal and lingual eminences on the
mesial surface of mandibular first molar
roots.
19. 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 normal when it is not more than 1.5 mm from
the cementoenamel junction of the adjacent teeth.
The alveolar crest may recede apically with age and show marked resorption with
periodontal disease.
20. 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.
21. PERIODONTAL LIGAMENT SPACE
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.
The PDL varies in width from patient to patient, from tooth to tooth in the individual, and even
from location to location around one tooth.
Usually it is thinner in the middle of the root and slightly wider near the alveolar crest and
root apex.
The thickness of the ligament relates to the degree of function because the PDL is thinnest
around the roots of embedded teeth and those that have lost their antagonists.
22.
23. 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. The radiographic pattern of the trabeculae comes from two
anatomic sources. 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.
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
to the corresponding region on the opposite side. This frequently demonstrates that a particularly
suspect region is characteristic for the individual.
24. 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 that in the
anterior maxilla, although the marrow
spaces may be slightly larger.
25. In the anterior mandible the trabeculae are somewhat 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.
26. In the posterior mandible the periradicular
trabeculae and marrow spaces may be comparable
to those in the anterior mandible but are usually
somewhat larger. The trabecular plates are oriented
mainly horizontally in this region also.
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.
27. 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.
28. An abnormality is more likely when the comparison indicates a change in the trabecular
pattern.
If prior films are not available, it is frequently useful to repeat the radiographic
examination at a reduced exposure because this often demonstrates the presence of an
expected but sparse trabecular pattern that was overexposed and burned out in the initial
projection.
29. NORMAL ANATOMICAL
STRUCTURES SEEN IN MAXILLA
Intermaxillary Suture:
The intermaxillary suture (also called the median suture) appears
on intraoral periapical radiographs 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.
30. It terminates at the alveolar crest in a small rounded or V -
shaped enlargement. 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.
31. ANTERIOR NASAL SPINE:
The anterior nasal spine is most frequently demonstrated on periapical radiographs of
the maxillary central incisors. Located in the midline, it lies some 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 it is usually V shaped.
32. NASAL APERTURE:
Because the air-filled nasal aperture (and cavity) lies just above the oral cavity, its
radiolucent image may be apparent on intraoral radiographs of the maxillary teeth, especially
in central incisor projections.
On periapical radiographs of the incisors the inferior border of the fossa aperture
appears as a radiopaque line extending bilaterally away from the base of the anterior nasal
spine.
33. Above this line is the radiolucent space of the inferior portion of the
cavity.
If the radiograph was made with the x-ray beam directed in the sagittal
plane, 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 somewhat
curved.
34. The nasal cavity contains the opaque
shadows of the inferior conchae
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.
The floor of the nasal aperture and a
small segment of the nasal cavity are
occasionally projected high onto a
maxillary canine radiograph.
35. Also, in the posterior maxillary region,
the floor of the nasal cavity may be seen
in the region of the maxillary sinus.
36. INCISIVE FORAMEN:
The incisive foramen (also called the nasopalatine or anterior palatine foramen) in the maxilla is
the oral terminus of the nasopalatine canal. This canal originates in the anterior floor of the nasal
fossa.
The incisive foramen lies in the midline of the palate behind the central incisors at approximately
the junction of the median palatine and incisive sutures. Its radiographic image is usually projected
between the roots and in the region of the middle and apical thirds of the central incisors.
37. The foramen varies markedly in its radiographic shape, size, and sharpness.
It may appear smoothly symmetric, with numerous forms, or very irregular, with
a well-demarcated or ill-defined border.
The position of the foramen 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:
(1) the differing angles at which the x-ray beam is directed for the maxillary
central incisors and
(2) some variability in its anatomic size.
38. 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.
Also, if the radiolucency of the normal foramen is projected over the apex of one central
incisor, it may suggest a pathologic periapical condition. The absence of disease is
indicated by a lack of clinical symptoms and an intact lamina dura around the central incisor
in question.
39. The lateral walls of the nasopalatine canal are not usually
seen on periapical views but on occasion can be
visualized on a projection of the central incisors as a pair
of radiopaque lines running vertically from the superior
foramina of the nasopalatine canal to the incisive foramen.
40. SUPERIOR FORAMINA OF THE NASOPALATINE CANAL:
The nasopalatine canal originates at two foramina in the floor of the nasal cavity.
The openings are on each side of the nasal septum, close to the anteroinferior border of
the nasal cavity, and each canal passes downward somewhat anteriorly and medially to
unite with the canal from the other side in a common opening, the incisive (nasopalatine)
foramen.
The superior foramina of the canal occasionally appear in projections of the maxillary
incisors, especially when an exaggerated vertical angle is used. They are usually round or
oval, although they may take a variety of outlines, depending on the angle of projection.
41. LATERAL FOSSA:
The lateral fossa (also called incisive fossa ) is a gentle depression in
the maxilla near the apex of the lateral incisor. On periapical projections
of this region it may appear diffusely radiolucent.
The image will not be misinterpreted as a pathologic condition, however,
if the radiograph is examined for an intact lamina dura around the root of
the lateral incisor. This finding, coupled with absence of clinical
symptoms, suggests normalcy of the bone.
42. 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.
43. 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.
Occasionally it can be visualized on periapical radiographs in the
region above the apex of the canine, especially when steep vertical
angulation is used.
44. MAXILLARY SINUS
The maxillary sinus, like the other paranasal sinuses, is an air containing cavity lined with
mucous membrane. It develops by the invagination of mucous membrane from the nasal
cavity.
The 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.
45. The borders of the maxillary sinus appear on periapical radiographs as a thin, delicate,
tenuous radiopaque line. In the absence of disease it appears continuous, but on close
examination it can be seen to have small interruptions in its smoothness or density.
46. 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.
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 dental
radiographs at approximately the same level around the age of puberty.
In older individuals the sinus may extend farther into the alveolar process, and
in the posterior region of the maxilla its floor may appear considerably below
the level of the floor of the nasal cavity.
47. 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 often superimposed and may be seen crossing
one another, forming an inverted Y of Ennis in the area.
The outline of the nasal fossa is usually heavier and more diffuse than
that of the thin, delicate cortical bone denoting the sinus.
48. The degree of extension of the maxillary sinus into the alveolar process is extremely
variable. In some projections the floor of the sinus will be well above the apices of the
posterior 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
due to pneumatization of bone.
49. 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. The thin layer of bone covering the root is seen as a fusion of the lamina dura
and the floor of the sinus.
When the rounded sinus floor dips between the buccal and palatal molar roots and is
medial to the premolar roots, the projection of the apices is superior to the floor.
This appearance conveys the impression that the roots project into the sinus cavity,
which is an illusion.
As the positive vertical angle of the projection is increased, the roots medial to the
sinus appear to project farther into the sinus cavity. In contrast, the roots that are
lateral to the sinus appear to move either out of the sinus or farther away from it as the
angle is increased.
50. This proximity of sinus and teeth is in part a consequence of the gradual developmental
expansion of the maxillary sinus, which thins the sinus walls and opens the canals that
traverse the anterolateral and posterolateral walls and carry the superior alveolar nerves.
The nerves are then 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 that portion of the nerve proximal to the insult. Subjective
symptoms in the area of the maxillary posterior teeth may require careful analysis to
differentiate tooth pain from sinus pain.
51. Frequently, thin radiolucent lines of uniform width are found within the 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.
52. 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 are projected a few millimeters away from the floor
and wall of the antrum or they may extend across the sinus.
They are usually oriented vertically, vary in number, thickness, and length. Septa deserve
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.
53. 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; and although they may be quite well defined, at certain points on their
surface they blend with the trabecular pattern of adjacent bone.
54. 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 the opaque veil is the thick cheek tissue superimposed on the
teeth and the alveolar process.
55. MAXILLARY TUBEROSITY
It is a rounded prominence of bone that extends posterior to the third molar
region. Blood vessels and nerves enter the maxilla in this region and
supply posterior teeth. Appears as a radiopaque bulge distal to third molar
region.
56. PTERYGOID PLATES:
The medial and lateral pterygoid plates lie immediately posterior to the tuberosity of the maxilla.
The image of these two plates is extremely variable, and on many intraoral radiographs of the
third molar area they do not appear at all.
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.
57. HAMULAR PROCESS
The hamulus is a small, hooklike projection of bone extending from the
medial pterygoid plate of the sphenoid bone. The hamulus is located
posterior to the maxillary tuberosity region.
Radiographically, it appears as a radiopaque hooklike projection posterior
to tuberosity and varies in length, shape and density.
58. ZYGOMATIC PROCESS OF MAXILLA:
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 serves as the articulation
for the zygomatic bone.
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.
59. 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.
When the sinus is recessed deep within the process, the
image of the air space within the process is dark, and
typically, the walls of the process are rather thin and well
defined.
When the sinus exhibits relatively little penetration of the
maxillary process, the image of the walls of the zygomatic
process tends to be somewhat thicker, and the appearance of
the sinus in this region is somewhat smaller and more
opaque.
60. It can be identified as a uniform gray or white radiopacity over the apices of the molars.
The prominence of the molar apices superimposed on the shadow of the zygomatic bone,
and the amount of detail supplied by the radiograph, depends in part on the degree of
aeration (pneumatization) of the zygomatic bone that has occurred, on the bony structure,
and on the orientation of the x-ray beam.
61. ZYGOMA
The zygoma or cheek bone articulates with the zygomatic process of
maxilla. It is composed of dense cortical bone.
On a maxillary periapical image, the zygoma appears as a diffuse
radiopaque band extending posteriorly from the zygomatic process of
maxilla.
62. 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
somewhat anteriorly, superimposed on the region of the third
molar.
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.
63. NORMAL ANATOMICAL
STRUCTURES OF 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.
If this radiolucency is found in older individuals, it is abnormal and may suggest a fracture or
a cleft.
64. 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 often are
divided into a right and left prominence and a superior and inferior
prominence.
They serve to attach the genioglossus muscles (at the superior tubercles)
and the geniohyoid muscles (at the inferior tubercles) to the mandible.
Their appearance on periapical radiographs of the mandibular
incisor region is variable: often they appear as a radiopaque mass (up to 3
to 4 mm in diameter) in the midline below the incisor roots. They also may
not be apparent at all.
65. LINGUAL FORAMEN:
There is usually a foramen on the lingual surface of the midline of the
mandible in the region of the genial tubercles, the lingual foramen.
Often there are two or even more such foramina. 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.
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.
66. 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 towards 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.
67. 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 may,
likewise, be mistaken for periapical disease involving the incisors.
68. MENTAL FORAMEN:
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 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.
69. 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.
70. When the mental foramen is projected over one of the premolar apices, it may mimic periapical
disease.
In such cases, evidence of the inferior dental canal extending to the suspect radiolucency or a
detectable lamina dura in the area would suggest the true nature of the dark shadow.
71. MANDIBULAR CANAL:
The radiographic image of the mandibular 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.
Usually, 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.
72. 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 film of the area is
not likely to separate the images of the apices and canal.
73. 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% of all patients. At times a nutrient canal
will be oriented perpendicular to the cortex and appear as a small
round radiolucency simulating a pathologic radiolucency.
74. MYLOHYOID RIDGE:
The mylohyoid ridge is a slightly irregular crest of bone on the lingual surface of the
mandibular body.
Extending from the area of the third molars to the lower border of the mandible in the region
of the chin, it serves as an attachment for the mylohyoid muscle.
Its radiographic 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.
75. Sometimes this image is 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. The contrary is also observed, however, where the ridge is relatively
dense with sharply demarcated borders.
It will be more evident on periapical radiographs when the beam is positioned with
excessive negative angulation
76. 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.
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).
77. 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; it is relatively prominent in its
upper part and juts considerably on the outer surface of the mandible in the region of the third
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.
78. INFERIOR BORDER OF THE MANDIBLE:
Occasionally the inferior mandibular border will be seen on periapical
projections as a characteristically dense, broad radiopaque band of bone.
79. REFERENCES
Textbook of Oral radiology- White and Pharoah.
Essentials of Oral and maxillofacial radiology- Freny R karjodkar.
Dental radiology principles and techniques: Joan and Howerton.
Internet source.
