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&"~ he radiographic recognition of disease--requires a sound knowledge of the radi-ographic appearance of normal structures. Intelligentdiagnosis mandates an appreciation of the wide rangeof variation in the appearance of normal anatomicstructures. Similarly, most patients demonstrate manyof the normal radiographic landmarks, but it is a rarepatient who shows them all. Accordingly, the absence ofone or even several such landmarks in any individualshould not necessarily be considered abnormal.

Teeth

distal aspects of teeth in the cervical regions betweenthe edge of the enamel cap and the crest of the alveo-lar ridge (Fig. 9-2). This phenomenon, called cervicalburnout, is caused by the normal configuration of theaffected teeth, which results in decreased x-ray absorp-tion in the areas in question. Furthermore, the per-ception of these radiolucent areas results from thecontrast with the adjacent, relatively opaque enameland alveolar bone. Such radiolucencies should be antic-ipated in almost all teeth and not be confused withroot surface caries, which frequently have a similar

appearance.The pulp of normal teeth is composed of soft tissue

and consequently appears radiolucent. The chambersand root canals containing the pulp extend from theinterior of the crown to the apices of the roots.Although the shape of most pulp chambers is fairlyuniform within tooth groups, great variations existamong individuals in the size of the pulp chambers andthe extent of pulp horns. The practitioner must antici-pate such variations in the proportions and distributionof the pulp and verify them radiographically when plan-ning restorative procedures.

In normal, fully formed teeth the root canal may beapparent, extending to the apex of the root; an apicalforamen is usually recognizable (Fig. 9-3). In othernormal teeth the canal may appear constricted in theregion of the apex and not discernible in the last mil-limeter or so of its length (Fig. 9-4). In this case thecanal may occasionally exit on the side of the tooth, justshort of the radiographic apex. Lateral canals mayoccur as branches of an otherwise normal root canal.They may extend to the apex and end in a normal, dis-cernible foramen or may exit the side of the root.In either case, two or more terminal foramina might

Teeth are composed prImarIly 01 aenun, Wlill anenamel cap over the coronal portion and a thin layerof cementum over the root surface (Fig. 9-1). Theenamel cap characteristically appears more radiopaquethan the other tissues because it is the most densenaturally occurring substance in the body. Being 90%mineral, it causes the greatest attenuation of x-rayphotons. The dentin is about 75% mineralized, andbecause of its lower mineral content its radiographicappearance is roughly comparable to that of bone.Dentin is smooth and homogeneous on radiographsbecause of its uniform morphology. The enamelo-dentinal junction, between enamel and dentin, appearsas a distinct interface that separates these two struc-tures. The thin layer of cementum on the root surfacehas a mineral content (50%) comparable to that ofdentin. Cementum is not usually apparent radiograph-icallybecause the contrast between it and dentin is solow and the cementum layer is so thin.

Diffuse radiolucent areas with ill-defined bordersmay be apparent radiographically on the mesial or

100

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CHAPTER 9 NORMAL RADIOGRAPHIC ANATOMY 167

~

FIG. 9-1 Teeth are composed of pulp (arrow on thesecond molar), enamel (arrow on the first molar), dentin(arrow on the second premolar), and cementum (usually notvisible radiographically).

FIG. 9-3(arrows).

Root canals open at the apices of adult incisors

FIG. 9-2 Cervical burnout caused by overexposure of thelateral portion of teeth between the enamel and alveolarcrest (arrows).

FIG. 9-4 Although the root canal is not radiographicallyvisible in the apical 2 mm of a tooth, anatomically it is

present (arrow).

cause endodontic treatment to fail if they are notidentified.

At the end of a developing; tooth root the pulp canaldiverges and the walls of the toot rapidly taper to a knifeedge (Fig. 9-5). In the reces.\formed by the root wallsand extending a short distance beyond is a small,rounded, radiolucent area in the trabecular bone, sur-rounded by a thin layer of hyperostotic bone. This isthe dental papilla bounded by its bony crypt. Thepapilla forms the dentin and the primordium of thepulp. When the tooth reaches maturity, the pulpal wallsin the apical region begin to constrict and finally comeinto close apposition. Awareness of this sequence andits radiographic pattern is often useful in evaluating the

stage of maturation of the developing tooth; it alsohelps avoid misidentifying the apical radiolucency as aperiapical lesion.

In a mature tooth, the shape of the pulp chamberand canal may change. With aging occurs a gradualdeposition of secondary dentin. This process beginsapically, proceeds coronally, and may lead to pulp oblit-eration. Trauma to the tooth (e.g., from caries, a blow,


168 PART IV IMAGING PRINCIPLES AND TECHNIQUES

restorations, attrition, or erosion) also may stimulatedentin production, leading toa reduction in size of thepulp chamber and canals. Such cases usually includeevidence of the source of the pathologic stimulus. Inthe case of a blow to the teeth, however, only thepatient's recollection may suggest the true reason forthe reduced pulp chamber size.

thin radiopaque layer of dense bone (Fig. 9-6). Itsname, lamina dura ("hard layer"), is derived from itsradiographic appearance. This layer is continuous withthe shadow of the cortical bone at the alveolar crest. Itis only slightly thicker and no more highly mineralizedthan the trabeculae of cancellous bone in the area. Itsradiographic appearance is caused by the fact that thex-ray beam passes tangentially through many times thethickness of the thin bony wall, which results in itsobserved attenuation. Developmentally the laminadura is an extension of the lining of the bony crypt thatsurrounds each tooth during development.

The appearance of the lamina dura on radiographsmay vary. When the x-ray beam is directed through arelatively long expanse of the structure, the laminadura appears radiopaque and well defined. When thebeam is directed more obliquely, however, the laminadura appears more diffuse and may not be discernible.In fact, even if the supporting bone in a healthy archis intact, identification of a lamina dura completelysurrounding every root on each film is frequentlydifficult, although it usually is evident to some extentabout the roots on each film (Fig. 9-7). In addition,small variations and disruptions in the continuity ofthe lamina dura may represent superimpositions oftrabecular pattern and small nutrient canals passingfrom the mandibular bone to the periodontalligament.

The thickness and density of the lamina dura on theradiograph vary with the amount of occlusal stress towhich the tooth is subjected. The lamina dura is widerand more dense around the roots of teeth in heavyocclusion, and thinner and less dense around teeth notsubjected to occlusal function.

FIG. 9-5 A developing root shown by a divergent apexaround the dental papilla (arrow), which is enclosed by an

opaque bony crypt.

A BFIG. 9.6 The lamina dura (arrows) appears as a thin opaque layer of bone around teeth,A, and around a recent extraction socket, B.

LAMINA DURA

A radiograph of sound teeth in a normal dental archdemonstrates that the tooth sockets are bounded by a


169NORMAL RADIOGRAPHIC ANATOMYCHAPTER 9

..dura around the apex of a tooth strongly suggests a vitalpulp. Because of the variable appearance of the laminadura, however, the absence of its image around an apexon a radiograph may be normal. Rarely, in the absenceof disease the lamina dura may be absent from a molarroot extending into the maxillary sinus. The clinicianis therefore advised to consider other signs and s~p-toms, as well as the integrity of the lamina dura, whenestablishing a diagnosis and treatment.

The image of a double lamina dura is not uncom-mon if the mesial or distal surfaces of roots present twoelevations in the path of the x-ray beam. A commonexample of this is seen on the buccal and lingual emi-nences on the mesial surface of mandibular first molarroots (Fig. 9-8). .

The appearance of the lamina dura is a valuablediagnostic feature. The presence of an intact lamina

FIG. 9-7 The lamina dura is poorly visualized on the distalsurface of this premolar (arrows) but is clearly seen on the

mesial surface.

ALVEOLAR CREST

The gingival margin of the alveolar process that extendsbetween the teeth is apparent on radiographs as aradiopaque line, the alveolar crest (Fig. 9-9). The levelof this bony crest is considered normal when it is notmore than 1.5mm from the cementoenamel junctionof the adjacent teeth. The alveolar crest may recede api-cally with age and show marked resorption with peri-odontal disease. Radiographs can demonstrate only theposition of the crest; determining the significance of itslevel is primarily a clinical problem (see Chapter 17).

The length of the normal alveolar crest in a particu-lar region depends on the distance between the teethin question. In the anterior region the crest is reducedto only a point of bone between the close-set incisors.Posteriorly it is flat, aligned parallel with and slightlybelow a line connecting the cementoenamel junctionsof the adjacent teeth. The crest of the bone is continu-ous with the lamina dura and forms a sharp angle withit. Rounding of these sharp junctions is indicative ofperiodontal disease.

The image of the crest varies from a dense layer ofcortical bone to a smooth surface without cortical bone.

FIG. 9-8 A double periodontal ligament space ana laminadura (arrows) may be seen when there is a convexity of theproximal surface of the root.

I-lu. Y-Y I ne alveolar crests (arrows) are seen as corticalborders of the alveolar bone.



FIG. 9-10 The periodontal ligament space (arrows) isseen as a narrow radiolucency between the tooth root andlamina dura.

FIG. 9-11 The periodontal ligament space appears wideon the mesial surface of this canine (arrows) and thin on thedistal surface.

In the latter case the t:rabeculae at the surface are ofnormal size and density. In the posterior regions thisrange of radiodensity of the crest is presumed to benormal if the bone is at a proper level in relation to theteeth. The absence of an image of cortex between theincisors, however, is considered by many to be an indi-cation of incipient disease, even if the level of the boneis not abnormal.

The shape of the tooth creates the appearance of adouble PDL space. When the x-ray beam is directed ~othat two convexities of a root surface appear on a film,the double PDL space is seen (see Fig. 9-8).

PERIODONTAL LIGAMENT SPACE

Because the periodontal ligament (PDL) is composedprimarily of collagen, it appears as a radiolucent spacebetween the tooth root and the lamina dura. This spacebegins at the alveolar crest, extends around the por-tions of the tooth roots within the alveolus, and returnsto the alveolar crest on the opposite side of the tooth(Fig. 9-10).

The PDL varies in width from patient to patient,from tooth to tooth in the individual, and even fromlocation to location around one tooth (Fig. 9-11).Usually it is thinner in the middle of the root andslightly wider near the alveolar crest and root apex, sug-gesting that the fulcrum of physiologic movement is inthe region where the PDL is thinnest. The thickness ofthe ligame~ relates to the degree of function becausethe PDL is thinnest around the roots of embeddedteeth and those that have lost their antagonists. Thereverse is not necessarily true, however, because anappreciably wider space is not regularly observed inpersons with especially heavy occlusion or bruxism.

CANCEllOUS BONE

The cancellous bone (also called trabecular bone or spon-giosa) lies between the cortical plates in both jaws. It iscomposed of thin radiopaque plates and rods (trabec-ulae) surrounding many small radiolucent pockets ofmarrow. The radiographic pattern of the trabeculaeshows considerable intrapatient and interpatient vari-ability, which is normal and not a manifestation ofdisease. To evaluate the trabecular pattern in a specificarea, the practitioner should examine the trabeculardistribution, size, and density and compare themthroughout both jaws. This frequently demonstratesthat a particularly suspect region is characteri~tic for theindividual. "

The trabeculae in the anterior maxilla are typicallythin and numerous, forming a fine, granular, densepattern (Fig. 9-12), and the marrow spaces are conse-quently small and relatively numerous. In the posteriormaxilla the trabecular pattern is usually quite similar tothat" in the anterior maxilla, although the marrowspaces may be slightly larger.

In the anterior mandible the trabeculae are some-what thicker than in the maxilla, resulting in a coarserpattern (Fig. 9-13), with trabecular plates that are ori-ented more horizontally. The trabecular plates are also


171CHAPTER 9 NORMAL RADIOGRAPHIC ANATOMY

FIG. 9-14 The trabecular pattern in the posteriormandible is quite variable, generally showing large marrowspaces and sparse trabeculation, especially inferiorly (arrows).

FIG. 9-12 The trabecular pattern in the anterior maxillais characterized by fine trabecular plates and multiple smalltrabecular spaces (arrow).

number of trabeculae dwindles still more. In some casesthe area from just below the molar roots to the inferiorborder of the mandible may appear to be almost devoidof trabeculae. The distribution and size of the trabecu-lae throughout both jaws show a relationship to thethickness (and strength) of the adjacent cortical plates.It may be speculated that where the cortical plates arethick (e.g., in the posterior region of the mandibularbody), internal bracing by the trabeculae is notrequired, so there are relatively few except whererequired to support the alveoli. By contrast, in themaxilla and anterior region of the mandible, where thecortical plates are relatively thin and less rigid, trabec-ulae are more numerous and lend internal bolsteringto the jaw. Occasionally the trabecular spaces in thisregion are very irregular, with some so large that theymimic pathologic lesions.

If trabeculae are apparently absent, suggesting thepresence of disease, it is often revealing to examine pre-vious radiographs of the region in question. This helpsdetermine whether the current appearance representsa change from a prior condition. An abnormality ismore likely when the comparison indicates a change inthe trabecular pattern. If prior films are not available,it is frequently useful to repeat the radiographic exam-ination at a reduced exposure because this oftendemonstrates the presence of an expec~ed but sparsetrabecular pattern that was overexposed and burnedout in the initial projection. Finally, if prior films arenot available and reduced exposure does not allay theexaminer's apprehension, it may be appropriate toexpose another radiograph at a later time to monitorfor ominous changes. Again, considerable variation

FIG. 9-13 The trabecular pattern in the anterior mandibleis characterized by coarser trabecular plates and largermarrow spaces (arrow) than in the anterior maxilla.

fewer than in the maxilla, and the marrow spaces arecorrespondingly larger. In the posterior mandible theperiradicular trabeculae and marrow spaces may becomparable to those in the anterior mandible but areusually somewhat larger (Fig. 9-14). The trabecularplates are oriented mainly horizontally in this regionalso. Below the apices of the mandibular molars the



Anterior Nasal SpineThe anterior nasal spine is most frequently demon-strated on periapical radiographs of the maxillarycentral incisors (Fig. 9-17). Located in the midline, itlies some 1.5 to 2 cm above the alveolar crest, usually ator just below the junction of the inferior end of thenasal septum and the inferior outline of the nasal fossa.It is radiopaque because of its bony composition and is

usually V-shaped.

may exist in trabecular pattern among patients, soexamining all regions of the jaws is important in evalu-ating a trabecular pattern for any individual. Thisenables the dentist to determine the general nature ofthe particular pattern ~nd whether any areas deviateappreciably from that norm.

The buccal and lingual cortical plates of themandible and maxilla do not cast a discernible imageon periapical radiographs.

MAXILLA

Intermaxillary SutureThe intermaxillary suture (also called the mediansuture) appears on intraoral periapical radiographs as athin radioluc~nt line in the midline between the twoportions of the premaxilla (Fig. 9-15). It extends fromthe alveolar crest between the central incisors superi-orly through the anterior nasal spine and continuesposteriorly between the maxillary palatine processes tothe posterior aspect of the hard palate. It is n6t unusualfor this narrow radiolucent suture to terminate at thealveolar crest in a small rounded or V-shaped enlarge-ment (Fig. 9-16). The syture is limited by two parallelradiopaque borders of thin cortical bone on each sideof the maxilla. The radiolucent region is usually ofuniform width. The adjacent cortical margins may beeither smooth or slightly irregular. The appearance ofthe intermaxillary suture depends on both anatomicvariability and the angulation of the x-ray beam throughthe suture.

FIG. 9-16 The intermaxillary suture may terminate in aV-shaped widening (arrow) at the alveolar crest.

FIG. 9-17 The anterior nasal spine is seen as an opaque

V-shaped projection from the floor of the nasal fossa in themidline (arrow).

FIG. 9-15 The intermaxillary suture (arrows) appears as acurving radiolucency in the midline of the maxilla.



.

in front of or behind the other unless the conclusion isbased on an awareness of the anatomic features andrelationships.) It may falsely convey the impression of aseptum in the sinus or a limiting superior sinus wall(Fig. 9-22).

Nasal Fossa Because the air-filled nasal fossa (cavity) lies just abovethe oral cavity, its radiolucent image may be apparenton intraoral radiographs of the maxillary teeth, espe-cially in central in.cisor projections. On periapical radi-ographs of the incisors the inferior border of the fossaappears as a radiopaque line extending bilaterally awayfrom the base of the anterior nasal spine (Fig. 9-18).Above this line is the radiolucent space of the inferiorportion of the fossa. If the radiograph was made withthe x-ray beam directed in the sagittal plane, the rela-tively radiopaque nasal septum is seen arising in themidline from the anterior nasal spine (Fig. 9-19). Thesh,,!-dow of the septum may appear wider than antici-pated and not sharply defined because the image is asuperimposition of septal cartilage and vomer bone.Also the septum frequently deviates slightly from themidline, and its plate of bone (the vomer) is somewhatcurved.

The nasal cavity contains the hazy shadows of theinferior conchae extending from the right and leftlateral walls for varying distances toward the septum.These conchae fill varying amounts of the lateral por-tions of the fossa (Fig:9-20). The floor of the nasal fossaand a small segment of the nasal cavity not uncom-monly are projected high onto a maxillary canine radi-ograph (Fig. 9-21). Also, in the posterior maxillaryregion, the floor of the nasal cavity and a portion of thefossa above it may be seen in the region of the maxil-lary sinus. (It is not possible from a single radiographto determine which of two superimposed structures is

FIG. 9-19 The nasal septum (black arrow) arises directlyabove the anterior nasal spine and is covered on each sideby nasal mucosa (white arrow).

FIG. 9-18 The anterior floor of the nasal fossa (arrows)appears as opaque lines extending laterally from the ante-

rior nasal spine.

FIG. 9-20 The mucosal covering of the inferior concha(arrow) is occasionally visualized in the nasal fossa.



FIG. 9-21 The floor of the nasal fossa (arrows) may oftenbe seen extending above the maxillary lateral incisor andcanine.

(. incisive sutures. Its radiographic image is usually pro-

jected between the roots and in the region of the middleand apical thirds of the central incisors (Fig. 9-23). Theforamen 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 theforamen is also variable and may be recognized at theapices of the central incisor roots, near the alveolarcrest, anywhere in between, or extending over the entiredistance. The great variability of its radiographic imageis primarily the result of (1) the differing angles at whichthe x-ray beam is directed for the maxillary central inci-sors and (2) some variability in its anatomic size.

Familiarity with the incisive foramen is importantbecause it is a potential site of cyst formation. An inci-sive canal cyst is radiographically discernible: it fre-quently causes a readily perceived enlargement of theforamen and canal. The presence of a cyst is presumed ifthe width of the foramen exceeds 1 cm or if enlargementcan be demonstrated on successive radiographs. Also, ifthe radiolucency of the normal foramen is projectedover the apex of one central incisor, it may suggest apathologic periapical condition. The absence of pathosisis indicated by a lack of clinical symptoms and an intactlamina dura around the central incisor in question.

The lateral walls of the nasopalatine canal are notusually seen but on occasion can be visualized on a pro-jection of the central incisors as a pair of radiopaquelines running vertically from the superior foraminaof the nasopalatine canal to the incisive foramen(Fig. 9-24).

Superior Foramina of the Nasopalatine CanalThe nasopalatine canal originates at two foramina inthe floor of the nasal cavity. The openings are on eachside of the nasal septum, close to the anteroinferiorborder of the nasal cavity, and each branch passes down-ward somewhat anteriorly and medially to unite withthe canal from the other side in a common opening,the incisive (nasopalatine) foramen. The superiorforamina of the canal occasionally appear in pro-jections of the maxillary incisors, especially when anexaggerated vertical angle is used. When apparentradiographically, they can be recognized as two radi-olucent areas above the apices of the central incisors inthe floor of the nasal cavity near its anterior border andon both sides of the septum (Fig. 9-25). They are usuallyround or oval, although they make take a variety of out-lines depending on the angle of projection.

FiG. 9-22 The floor of the nasal fossa (arrows) extendsposteriorly, superimposed with the maxillary sinus.

Incisive ForamenThe incisive foramen (also called the nasopalatine oranterior palati~ foramen) in the maxilla is the oral termi-nus of the nasopalatine canal. It transmits the nasopala-tine vessels and nerves (which may participate in theinnervation of the maxillary central incisors) and lies inthe midline of the palate behind the central incisors atapproximately the junction of the median palatine and

Lateral FossaThe lateral fossa (also called incisive fossa) is a gentledepression in the maxilla near the apex of the lateral



A BFIG. 9-23 A, The incisive foramen appears as an ovoid radiolucency (arrows) betweenthe roots of the central incisors. 8, Note its borders, which are diffuse but within normallimits:

FIG. 9-24 The lateral walls of the nasopalatine canal(arrows) extend from the incisive foramen to the floor of thenasal fossa.

FIG. 9-25 The superior foramina of the nasopalatinecanal (arrows) appear just lateral to the nasal septum andposterior to the anterior nasal spine.



FIG. 9-26 The lateral fossa is a diffuse radiolucency(arrows) in the region of the apex of the lateral incisor. It isformed by a depression in the maxilla at this location.

FIG. 9-27 The soft tissue outline of the nose (arrows) issuperimposed on the anterior maxilla.

incisor (Fig. 9-26). On periapical projections of thisregion it may appear diffusely radiolucent. The imagewill not be misinterpreted as a pathologic condition,however, if the radiograph is examined for an intactlamina dura around the root of the lateral incisor. Thisfinding, coupled with absence of clinical symptoms,suggests normalcy of the bone.

NoseThe soft tissue of the tip of the nose is frequently seenin projections of the maxillary central and lateral inci-sors, superimposed over the roots of these teeth. Theimage of the nose has a uniform, slightly opaqueappearance with a sharp border (Fig. 9-27). Occasion-ally the radiolucent nares can be identified, especiallywhen a steep vertical angle is used.

Nasolacrimal CanalThe nasal and maxillary bones form the nasolacrimalcanal. It runs from the medial aspect of the anteroin-ferior border of the orbit inferiorly, to drain under theinferior concha into the nasal cavity. Occasionally it canbe visualized on periapical radiographs in the regionabove the a~x of the canine, especially when steep ver-tical angulauon is used (Fig. 9-28). The nasolacrimalcanals are routinely seen on maxillary occlusal pro-jections (see Chapter 8) in the region of the molars(Fig. 9-29).

FIG. 9-28 The nasolacrimal canal (arrow) is occasionallyseen near the apex of the canine when steep vertical angu-lation is used. Note the mesiodens (supernumerary tooth)superior to the central incisor.



FIG. 9-30 The inferior border of the maxillary sinus(arrows) appears as a thin radiopaque line near the apices ofthe maxillary premolars and molars.FIG. 9-29 The nasolacrimal canals are commonly seen

as ovoid radiolucencies (arrows) on maxillary occlusal

projections.

during adult life in response to environmental factors.The right and left sinuses usually appear similar inshape and size, although marked asymmetry is occa-sionally present. The floors of the maxillary sinus andnasal cavity are seen on dental radiographs at approxi-mately the same level around the age of puberty. Inolder individuals the sinus may extend farther intothe alveolar process, and in the posterior region of themaxilla its floor may appear considerably below thelevel of the floor of the nasal cavity. Anteriorly eachsinus is restricted by the canine fossa and is usually seento sweep superiorly, crossing the level of the floor of thenasal cavity in the premolar or canine region. Conse-quently, on periapical radiographs of the canine, thefloors of the sinus and nasal cavity are often superim-posed and may be seen crossing one another, formingan inverted Yin the area (Fig. 9-31).

The outline of the nasal fossa is usually heavier andmore diffuse than that of the thin, delicate corticalbone denoting the sinus. The degree of extensionof the maxillary sinus into the alveolar process isextremely variable. In some projections the floor of thesinus will be well above the apices of the posterior teeth;in others it may extend well beyond the apices towardthe alveolar ridge. In response to a loss of function(associated with the loss of posterior teeth) the sinusmay expand farther into the alveolar bone, occasionallyextending to the alveolar ridge (Fig. 9-32).

The roots of the molars usually lie in close apposi-tion to the maxillary sinus. Root apices may projectanatomically into the floor of the sinus, causing smallelevations or prominences. The thin layer of bone cov-ering the root is seen as a fusion of the lamina dura and

Maxillary SinusThe maxillary sinus, like the other paranasal sinuses, isan air-containing cavity lined with mucous membrane.It develops by the invagination of mucous membranefrom the nasal cavity. Being the largest of the paranasalsinuses, it normally occupies virtually the entire body ofthe maxilla. Its function is unknown.

The sinus may be considered as a three-sidedpyramid, with its base the medial wall adjacent to thenasal cavity and its ap~x extending laterally into thezygomatic process of the maxilla. Its three sides are (1)the superior wall forming the floor of the orbit, (2) theanterior wall extending above the premolars, and (3)the posterior wall bulging above the molar teeth andmaxillary tuberosity. The sinus communicates with thenasal cavity via the ostium some 3 to 6 mm in diameterpositioned under the posterior aspect of the middleturbinate.

The borders of the maxillary sinus appear onperiapical radiographs as a thin, delicate, tenuousradiopaque line (actually a thin layer of cortical bone)(Fig. 9-30). In the absence of disease it appears contin-uous, but on close examination it can be seen to havesmall interruptions in its smoothness or density. Thesediscontinuities are probably illusions caused by super-imposition of small marrow spaces. In adults the sinusesare usually seen to extend from the distal aspect of thecanine to the posterior wall of the maxilla above the

tuberosity.The maxillary sinuses show considerable variation in

size. They enlarge during childhood, achieving maturesize by the age of 15 to 18 years. They may change



.

FIG. 9-31 The anterior border of the maxillary sinus(white arrows) crosses the floor of the nasal fossa (black

arrow).

illusion. As the positive vertical angle of the projectionis increased, the roots medial to the sinus appear toproject farther into the sinus cavity. In contrast, theroots lateral to the sinus appear to move either out ofthe sinus or farther away from it as the angle isincreased.

The intimate relationship between sinus and teethleads to the possibility that clinical symptoms originat-ing in the sinus may be perceived in the teeth, and viceversa. This proximity of sinus and teeth is in part a con-sequence of the gradual developmental expansion ofthe maxillary sinus, which thins the sinus walls andopens the canals that traverse the anterolateral and pos-terolateral walls and carry the superior alveolar nerves.The nerves are then in intimate contact with the mem-brane lining the sinus. As a result, an acute inflamma-tion of the sinus is frequently accompanied by pain inthe maxillary teeth innervated by that portion of thenerve proximal to the insult. Subjective symptoms inthe area of the maxillary posterior teeth may requirecareful analysis to differentiate tooth pain from sinus

pain.Frequently, thin radiolucent lines of uniform width

are found within the image of the maxillary sinus (Fig.9-33). These are the shadows of -neurovascular canals orgrooves in the lateral sinus walls~that accommodate theposterior superior alveolar vessels, their branches, andthe accompanying superior alveolar nerves. Althoughthey may be found coursing in any direction (includingvertically), they are us~ly seen running a curved pos-teroanterior course that is convex toward the alveolarprocess. On occasion they may be found to branch, andrarely also to extend outside the image of the sinus andcontinue as an interradicular channel. Because such

the floor of the sinus. Rarely, defects may be present inthe bony covering of the root apices in the sinus floor,and a periapical radiograph will fail to show laminadura covering the apex.

When the rounded sinus floor dips between thebuccal and palatal molar roots and is medial to the pre-molar roots, the projection of the apices is superiorto the floor. This appearance conveys the impressionthat the roots project into the sinus cavity, which is an

AFIG. 9-32teeth.

BThe floor of the maxillary sinus (arrows) extends toward the crest of the alveolar ridge in response to missing



t;I

FIG. 9-35 This bony nodule (arrow) is a normal variant ofthe floor of the maxillary sinus.

FIG. 9-33 Neurovascular canals (arrows) in the lateral wallof the maxillary sinus.

this view the x-ray beam is rarely directed tangential tothem. Although septa appear to separate the sinusesinto distinct compartments, this is seldom the casebecause the septa are usually of limited extent. It hasbeen reported, however, that in 1% to 10% of exam-ined skulls, complete septa did in fact divide the sinusinto individual compartments, each compartment withseparate ostia for drainage. ~pta deserve attentionbecause they sometimes mimic periapical pathoses, andthe chambers they create in the alveolar recess maycomplicate the search for a root fragment displacedinto the sinus.

The floor of the maxillary sinus occasionally showssmall radiopaque projections, which are nodules ofbone (Fig. 9-35). These must be differentiated fromroot tips, which they resemble in shape. In contrast toa root fragment, which is quite homogeneous inappearance, the bony nodules often show trabecula-tion; and although they may be quite well defined, atcertain points on their surface they blend with the tra-becular pattern of adjacent bone. A root fragment mayalso be recognized by the presence of a root canal. It isnot uncommon to see the floor of the nasal fossa inperiapical views of the posterior teeth superimposed onthe maxillary sinus (see Fig. 9-22). The floor of thenasal fossa is usually oriented mOre or less horizontally,depending on film placement, and is superimposedhigh on maxillary views. The image, a solid opaque line,frequently appears somewhat thicker than the adjacentsinus walls and septa.

FIG. 9-34 A septum (arrow) in the maxillary sinus formedby a low ridge of bone on the sinus wall. (See also Fig. 9-

32/ B).

vascular markings are not seen in the walls of cysts, theymay serve to distinguish a normal sinus from a cyst.

Often one or several radiopaque lines traverse theimage of the maxillary sinus (Fig. 9-34). These septarepresent folds of cortical bone projecting a few mil-limeters away from the floor and wall of the antrum.They are usually oriented vertically, although horizon-tal bony ridges also occur, and it is not uncommon forthem to vary in number, thickness, and length. Septaare believed by some to have been formed through theuneven resorption of bone as the sinus was pneuma-tized, but others hold that they are remnants of incom-pletely fused cavities from which the sinus formed. Theyappear on many periapical intraoral radiographs,although seldom in extraoral projections because for

Zygomatic Process and Zygomatic BoneThe zygomatic process of the maxilla is an extensionof the lateral maxillary surface that arises in the regionof the apices of the first and second molars and serves



A B .FIG. 9-36 The zygomatic process of the maxilla (arrows) protrudes laterally from the maxillary wall. Its size may be quitevariable: small with thick borders (A) or large with thin borders (8).

FIG. 9-37 The inferior border of the zygomatic arch(arrows) extends posteriorly from the inferior portion of thezygomatic process of the maxilla.

zygomatic bone, and the amount of detail supplied bythe radiograph, depends in part on the degree of aera-tion (pneumatization) of the zygomatic bone that hasoccurred, on the bony strutture, and on the orienta-tion of the x-ray beam. .

as the articulation for the zygomatic bone. On periapi-cal radiographs the zygomatic process appears as a V-shaped radiopaque line with its open end directedsuperiorly. The enclosed rounded end is projected inthe apical region of the first and second molars (Fig. 9-36). The size, width, and definition of the zygomaticprocess are quite variable, and its image may be large,depending on the angle at which the beam was pro-jected. The maxillary antrum may expand laterally intothe zygomatic process of the maxilla (and even into thezygomatic bone after the maxillozygomatic suture hasfused), thereby resulting in a relatively increased radi-olucent region within the V-shaped image of theprocess.

When the sinus is recessed deep within the process(and perhaps into the zygomatic ~one), the image ofthe air space within the process is dark and typically thewalls of the process are rather thin and well defined (incontrast to the very dark radiolucent air space). Whenthe sinus exhibits relatively little penetration of themaxillary process (usually in younger individuals orthose who have maintained their posterior teeth andvigorous masticatory function), the image of the wallsof the zygomatic process tends to be somewhat thicker,and the appearance of the sinus in this region is some-what smaller and more opaque.

The inferior portion of the zygomatic bone may beseen extending posteriorly from the inferior border ofthe zygom~c process of the maxilla (thereby complet-ing the zygomatic arch between the zygomatic processesof the maxillary and temporal bones). It can be identi-fied as a uniform gray or white radiopacity over theapices of the molars (Fig. 9-37). The prominence ofthe molar apices superimposed on the shadow of the

Nasolabial FoldAn oblique line demarcating a region th(\t appears tobe covered by a veil of slight radiopacity frequently trav-erses periapical radiographs of the premolar region(Fig. 9-38). The line of contrast is sharp, and the areaof increased radiopacity is posterior to the line. The lineis the nasolabial fold, and the opaque veil is the thickcheek tissue superimposed on the teeth and the



fI

FIG. 9-39 Pterygoid plates (arrows) located posterior to

the maxillary tuberosity.

FIG. 9-38 The nasolabial fold (arrows) extends across the

canine-premolar region.

alveolar process. The image of the fold becomes moreevident with age, as the repeated creasing of the skinalong the line (where the elevator of the lip, zygomatichead, and orbicularis all insert into the skin) and thedegeneration of the elastic fibers finally lead to the for-mation and deepening of permanent folds. This radi-ographic feature frequently proves useful in identifyingthe side of the maxilla represented by a film of the areaif it is edentulous and few other anatomic features aredemonstrated.

FIG. 9-40 The hamular process (arrow) extends down-

ward from the medial pterygoid plate.

Pterygoid PlatesThe medial and lateral pterygoid plates lie immediatelyposterior to the tuberosity of the maxilla. The image ofthese two plates is extremely variable, and on 'manyintraoral radiographs of the third molar area they donot appear at all. When they are apparent, they almostalways cast a single radiopaque homogeneous shadow

'" without any evidence of trabeculation (Fig. 9-39).Extending inferiorly from the medial pterygoid platemay be seen the hamular process (Fig. 9-40), which onclose inspection can show trabeculae.

which it is no longer radiographically apparent. It is notfrequently encountered on dental radiographs becausefew young patients have cause to be examined radi-ographically. If this radiolucency is found in older indi-viduals, it is abnormal and may suggest a fracture or acleft.

Genial TuberclesThe genial tubercles (also called the mental spine) arelocated on the lingual surface of the mandible slightlyabove the inferior border and in the midline. They arebony protuberances, more or less spine-shaped, thatoften are divided into a right and left prominenceand a superior and inferior prominence. They serveto attach the genioglossus muscles (at the superior

MANDIBLE

Symphysi$;Radiographs of the region of the mandibular symphysisin infants demonstrate a radiolucent line through themidline of the jaw between the images of the formingdeciduous central incisors (Fig. 9-41). This sutureusually fuses by the end of the first year of life, after



FIG. 9-43 The genial tubercles (arrow) appear as aradiopaque mass, in this case without evidence of the lingualforamen.FIG. 9-41 Mandibular symphysis (arrows) in a newborn

infant. Note the bilateral sup~rnumerary primary incisorsadjacent to it.

FIG. 9-44 Lingual foramen (arrow), with a scleroticborder, in the symphyseal region of the mandible.FIG. 9-42 Genial tubercles (arrow) on the lingual surface

'of the mandible in this cross-sectional mandibular occlusalview.

When the genial tubercles are seen on periapical films,it is often possible to see the lingual foramen (Fig. 9-44). This foramen contains the termination of the inci-sive branch of the mandibular canal and is seen as aradiolucent dot surrounded by its cortical wall.

tubercles) and the geniohyoid muscles (at the inferiortubercles) to the mandible. They are well visualized onmandibular~cclusal radiographs as one or more smallprojections (Fig. 9-42). Their appearance on periapicalradiographs of the mandibular incisor region is vari-able: often they appear as a radiopaque mass (up to 3to 4mm in diameter) in the midline below the incisorroots (Fig. 9-43). They also may not be apparent at all.

Mental RidgeOn periapical radiographs of the mandibular centralincisors, the mental ridge (protuberance) may occa-sionally be seen as two radiopaque lines sweeping



FIG. 9-45 Mental ridge (arrows) on the anterior surface

of the mandible, seen as a radiopaque ridge.FIG. 9-46 The mental fossa is a radiolucent depression onthe anterior surface of the mandible (arrows) between the

alveolar ridge and mental ridge.

bilat~rally forward and upward toward the midline (Fig.9-45). They are of variable width and density and mayDe found to extend from low in the premolar area oneach side up to the midline, where they lie just inferiorto or are superimposed on the mandibular incisor toothroots. The image of the mental ridge is most prominentwhen the beam is directed parallel with the surface ofthe mental tubercle (as when using the bisecting-angle

technjque).

Mental FossaThe mental fossa is a depression on the labial aspect ofthe mandible extending laterally from the midline andabove the m~ntal ridge. Because of the resulting thin-ness of jawbone in this area, the image of this depres-sion may be similar to that of the submandibular fossa(see below) and may, likewise, be mistaken for periapi-cal disease involving the incisors (Fig. 9-46).

FIG. 9-47 The mental foramen (arrow) appears as an ovalradiolucency near the apex of the second premolar.

.Mental ForamenThe mental foramen is usually the anterior limit of theinferior dental canal that is apparent on radiographs(Fig. 9-47). Its image is quite variable, and it may beidentified only about half the time because the openingof the mental canal is directed superiorly and posteri-orly. As a result, the usual view of the premolars is notprojected tbJough the long axis of the canal opening.This circumstance is responsible for the variableappearance of the mental foramen. Although the wallof the foramen is of cortical bone, the density of theforamen's image varies, as does the shape and defini-tion of its border. It may be round, oblong, slitlike, or

very irregular and partially or completely corticated.The foramen is seen about halfway between the lowerborder of the mandible and the crest of the alveolarprocess, usually in the region of the apex of the secondpremolar. Also, because it lies on the surface of themandible, the position of its image in relation to thetooth roots is influenced by projection angulation. Itmaybe projected anywhere from just mesial of the per-manent first molar roots to as far anterior as mesial ofthe first premolar root. The image of two mental foram-ina, one above the other, has also been observed.



FIG. 9-48 The mental foramen (arrow) (over the apex ofthe second premolar) may simulate periapical disease. Con-tinuity of the lamina dura around the apex, however, indi-cates the absence of periapical abnormality.

FIG. 9-49 Mandibular canal. Arrows denoteradiopaque superior and inferior cortical borders.

its

When the mental foramen is projected over one ofthe premolar apices, it may mimic periapical disease(Fig. 9-48). In such cases, evidence of the inferiordental canal extending to the suspect radiolucency ora detectable lamina dura in the area would suggest thetr1:le nature of the dark shadow. It is well to point out,however, that the relative thinness of the lamina durasuperimposed with the radiolucent foramen may resultin considerable "burnout" of the lamina dura image,which will complicate its recognition. Nevertheless, asecond radiograph from another angle is likely to showthe lamina dura clearly, as well as some shift in positionof the radiolucent foramen relative to the apex.

FIG. 9-50 The mandibular canal superimposed over theapex of a molar causes the image of the periodontal liga-ment space to appear wider (arrow). The presence of anintact lamina dura, however, indicates that there is no peri-apical disease.

the lamina dura may be overexposed, conveying theimpression of a missing lamina or a thickened PDLspace that is more radiolucent than apparently normalfor the patient (Fig. 9-50). To ensure the soundness ofsuch a tooth, other clinical testing procedures must beemployed (e.g., vitality testing). Because the canal isusually located just inferior to the apices of the poste-rior teeth, altering the vertical angle for a second filmof the area is not likely to separate the images of theapices and canal.

Mandibular CanalThe radiographic image of the mandibular canal is adark linear shadow with thin radiopaque superior andinferior borders cast by the lamella of bone that boundsthe canal (Fig. 9-49). Sometimes the borders are seenonly partially or not at all. The width of the canal showssome interpatient variability but is usually rather con-stant anterior to the third molar region. The canal'scourse may be apparent between the mandibularforamen and the mental foramen. Only rarely is theimage of its anterior continuation toward the midlinediscernible on the radiograph.

The relationship of the mandibular dental canal tothe roots of the lower teeth may vary, from one in whichthere is close contact with all molars and the secondpremolar to one in which the canal has no intimate rela-tion to any of the posterior teeth. In the usual picture,however, the canal is in contact with the apex of thethird molar, and the distance between it and the otherroots increases as it progresses anteriorly. When theapices of the molars are projected over the canal,

Nutrient CanalsNutrient canals carry a neurovascular bundle andappear as radiolucent lines of fairly uniform width.They are most often seen on mandibular periapical



radiographs running vertically from the inferior dentalcanal directly to the apex of a tooth (Fig. 9-51) or intothe interdental space between the mandibular incisors(Fig. 9-52). They are visible in about 5% of all patientsand are more frequent in blacks, males, older per-sons, and individuafs with high blood pressure oradvanced periodontal disease. They also indicate a thinridge, useful in implant assessment. Because they areanatomic spaces with walls of cortical bone, theirimages occasionally have hyperostotic borders. At times

'a nutrient canal will be oriented perpendicular to thecortex and appear as a small round radiolucency simu-lating a pathologic radiolucency.

Mylohyoid RidgeThe mylohyoid ridge is a slightly irregular crest of boneon the lingual surface of the mandibular body. Extend-ing from the area of the third molars to the lowerborder of the mandible in the region of the chin, itserves as an attachment for the mylohyoid muscle. Itsradiographic image runs diagonally downward andforward from the area of the third molars to the pre-molar region, at approximately the level of the apicesof the posterior teeth (Fig. 9-53). Sometimes this imageis superimposed on the images of the molar roots. Themargins of the image are not usually well defined butappear quite diffuse and of variable width. The contraryis also observed, however, where the ridge is relativelydense with sharply demarcated borders (Fig. 9-54). Itwill be more evident on periapical radiographs whenthe beam is positioned with excessive negative angula-tion. In general, as the ridge becomes less defined, itsanterior and posterior limits blend gradually with thesurrounding bone.

FIG. 9-51 Nutrient canals (arrows), demonstrated byradiopaque cortical borders, descend from the mandibularfirst molar.

Submandibular Gland FossaOn the lingual surface of the mandibular body, imme-diately below the mylohyoid ridge in the molar area,there is frequently a depression in the bone. This con-cavity accommodates the submandibular gland andoften appears as a radiolucent area with the sparse tra-becular pattern characteristic of the region (Fig. 9-55).This trabecular pattern is even less defined on radi-ographs of the area because it is superimposed onthe relatively reduced mass of the concavity. The

c"""FIG. 9-52 Nutrient canals demonstrated by radiolucen-cies (arrows) in the anterior mandible of a patient with severeperiodontal disease.

FIG. 9-53 Mylohyoid ridge (arrows) running at the levelof the molar apices and above the mandibular canal.



FIG. 9-56 External oblique ridge (arrows), seen as aradiopaque line near the alveolar crest in the mandibularthird molar region.

FIG. 9-54 The mylohyoid ridge (arrows) may be dense,especially when a radiograph is exposed with excessive neg-ative angulation.

FIG. 9-57 The inferior border of the mandible (arrows) isseen as a dense, broad radiopaque band.

FIG. 9-55 Submandibular gland fossa (arrows), indicatedby a poorly defined radiolucency and sparse trabecular bonebelow the mandibular molars.

considerably on the outer surface of the mandiblein the region of the third molar (Fig. 9-56). This bonyelevation gradually flattens, and usually disappears, atabout where the alveolar process and mandible joinbelow the first molar. The ridge is a line of attachmentof the buccinator muscle. Characteristically, it is pro-jected onto posterior periapical radiographs superior tothe mylohyoid ridge, with which it runs an almost par-allel course. It appears as a radiopaque line of varyingwidth, density, and length, blending at its anterior endwith the shadow of the alveolar bone.

radiographic image of the fossa is sharply limited supe-riorly by the mylohyoid ridge and inferiorly by the lowerborder of the mandible, but is poorly defined anteriorly'(in the premolar region) and posteriorly (at about theascending ramus). Although the image may appearstrikingly radiolucent, accentuated as it is by the densemylohyoid ridge and inferior border of the mandible,awareness of its possible presence should preclude itsbeing confused with a bony lesion by the inexperiencedclinician. :~'

Interior Border of the MandibleOccasionally the inferior mandibular border will beseen on periapical projections (Fig. 9-57) as a charac-teristically dense, broad radiopaque band of bone.External Oblique Ridge

The external oblique ridge is a continuation of theanterior border of the mandibular ramus. It follows ananteroinferior course lateral to the alveolar process,being relatively prominent in its upper part and jutting

Coronoid ProcessThe image of the coronoid process of the mandible isfrequently apparent on periapical radiographs of the


CHAPTER 9 NORMAL RADIOGRAPHIC ANATOMY 187

~

FIG. 9-58 Coronoid process of the mandible (arrows)superimposed on the maxillary tuberosity. FIG. 9-59 Amalgam restorations appear completely

radiopaque (arrows).

maxillary molar region as a triangular radiopacity, withits apex directed superiorly and somewhat anteriorly,superimposed on the region of the third molar (Fig.9-58). In some cases it may appear as far forward as thesecond molar and be projected above, over, or belowthese molars, depending on the position of the jaw andthe projection of the x-ray beam. Usually the shadow ofthe coronoid process is homogeneous, although inter-nal trabeculation can be seen in some cases. Its appear-ance on maxillary molar radiographs results from thedownward and forward movement of the mandiblewhen the mouth is open. Consequently, if the opacityreduces the diagnostic value of a film and the film mustbe remade, the second view should be acquired with themouth minimally open. (This contingency must be con-sidered whenever this area is radiographically exam-ined.) On occasion, and especially when its shadow isdense and homogeneous, the coronoid process is mis-taken for a root fragment by the neophyte clinician.The true nature of the shadow can be easily demon-strated by obtaining two radiographs with the mouth indifferent positions and noting the change in position

-of the suspect shadow.

FIG. 9-60 A cast gold crown, appearing completely

radiopaque (arrow), serves as the terminal abutment of a

bridge.

steel pins also appear radiopaque (Fig. 9-61). Often acalcium hydroxide base is placed in a deep cavity toprotect the pulp. Although such base material may beradiolucent, most is radiopaque (Fig. 9-62). Anothermaterial of comparable radiopacity is gutta-percha, arubberlike substance used to fill tooth canals duringendodontic therapy (Fig. 9-63). Silver points were pre-viously used to obliterate canals during endodontictherapy (Fig. 9-64). Other restorative materials thatappear rather radiolucent on intraoral films include sil-icates, usually in combination with a b~e but nowseldom used (Fig. 9-65), composite, usually in anteriorteeth (Fig. 9-66), and porcelain, now usually fused to ametallic coping (Fig. 9-67). Composite restorativematerials may also be opaque (Fig. 9-68). In addition,stainless steel crowns (Fig. 9-69) and orthodonticappliances around teeth (Fig. 9-70) are relativelyradiopaque.

Restorative MaterialsRestorative materials vary in their radiographic appear-ance, depending primarily on their thickness, density,and atomic number. Of these, the atomic number ismost influential.

A variety of restorative materials may be recognizedon intraoral radiographs. The most common, silveramalgam, is completely radiopaque (Fig. 9-59). Gold isequally opaque to x rays, whether cast as a crown orinlay (Fig. 9-60) or condensed as gold foil. Stainless



FIG. 9-63 Gutta-percha (arrows) is a radiopaque rubber-like material used in endodontic therapy.

FIG. 9-61 Stainless steel pins (arrows) provide retentionfor amalgam restorations.

FIG. 9-62 Base material (arrow) is usually radiopaque butless opaque than the amalgam restoration.

FIG. 9-64 Silver points (arrow) were used to fill the rootcanals in this patient.



~

Porcelain appears radiolucent (arrow) over aFIG. 9-65 Radiolucent. silicate restorations (arrows) wereplaced over a base to protect the pulp in this patient.

FIG. 9-67metal coping.

FIG. 9-68 Composite restorations containing particles ofbarium glass are radiopaque and not likely to be confusedwith caries.

FIG. 9-66 Composite restorations may be radiolucentand may suggest caries but can be recognized by their well-demarcated border with dentin.



BIBLIOGRAPHY

Berkovitz BKB, Holland GR, Moxham BL: Oral Anatomy, His-tology & Embryology, ed 3, London, 2002, Mosby.

Kasle MJ: An Atlas of Dental Radiographic Anatomy, ed 4,Philadelphia, 1994, WB Saunders. .

FIG. 9-69radiopaque.

Stainless steel appear mostlycrowns

FIG. 9-70 Orthodontic appliances have a characteristic

radiopaque appearance.


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