3.23: Dental radiology

Akshay A. Shah, Harpreet Kaur Gandhoke

Abbreviations

CBCT – Cone beam computed tomography
IANC – Inferior alveolar nerve canal
IOPA – Intraoral periapical radiograph
MF – Mental foramen
MS – Maxillary sinus
OPG – Orthopantomograph

Introduction

Dental Radiology is a unique part of head and neck imaging and involves specific imaging techniques and interpretation.

Radiographic examinations are one of the primary diagnostic aids used in dentistry to identify disease and formulate an appropriate treatment plan. The radiographic diagnosis of disease requires the adequate knowledge of the radiographic appearance of normal structures. A good diagnosis requires appreciation of a wide range of variation in the appearance of normal structures. Most patients show most of the normal radiographic landmarks, but it is rare for a patient to show them all. Hence, the absence of one or several landmarks in any individual should not be necessarily termed abnormal.

Radiographic interpretation is the process of recognizing the apparent details on the radiograph, which aids in the identification of diseases, lesions and conditions that are not clinically identifiable.

‘Interpretation refers to an understanding of what is seen on the radiograph’, which leads to ‘diagnosis that is the recognition of disease by examination or analysis’.

A diagnosis is made by the dentist after a complete review of medical and dental history, clinical examination, radiographic evaluation and clinical or laboratory tests.

The commonly used imaging techniques are

1. Conventional and
2. Advanced
1. 1. Conventional
  1. a. Intraoral radiography – Intraoral periapical radiograph (IOPA), Bitewing Radiograph and Occlusal radiograph
  2. b. Extraoral Radiograph – Orthopantomograph (OPG)
2. 2. Advanced
  1. a. Cone Beam Computed Tomography (CBCT)

Panoramic radiograph (OPG)

Panoramic radiograph is a technique for producing a single tomographic image of the facial structures that includes both maxillary arch and mandibular arch and their supporting structures. It is a curvilinear variant of conventional tomography and based on the principal of the reciprocal movement of an X-ray source and an image receptor around a central point or plane called the image layer in which the object of interest is located.

Anatomical landmarks on a panoramic radiograph

Normal landmarks seen on the panoramic radiography may seem different from machine to another, but generally, they may subdivide into:

I. Real or actual shadows; of structures in or close to the focal trough
1. a. Hard tissue
  1. 1. Teeth
  2. 2. Mandible
  3. 3. Maxilla, including the antrum
  4. 4. Hard palate
  5. 5. Zygomatic arches
  6. 6. Styloid process
  7. 7. Hyoid bone
  8. 8. Nasal septum and conchae
  9. 9. Orbital rim
  10. 10. Base of skull

(An additional real shadow is often casted by the vertical plastic head supports).

b. Soft tissue
1. 1. Ear lobes
2. 2. Nasal cartilages
3. 3. Soft palate
4. 4. Dorsum of the tongue
5. 5. Lips and cheeks
6. 6. Nasolabial folds
c. Air shadows
1. 1. Mouth/oral opening
2. 2. Oropharynx

Outline of the anatomical landmarks seen in the maxillary region (Figs. 3.23.1–3.23.8)

Fig. 3.23.1 Normal anatomical landmarks of the maxilla and surrounding structures. 1. Mastoid process, 2. Styloid process, 3. External Auditory meatus, 4. Glenoid fossa, 5. Articular eminence, 6. Lateral pterygoid plate, 7. Pterygo-maxillary fissure, 8. Maxillary tuberosity, 9. Infraorbital foramen, 10. Orbit, 11. Incisive canal, 12. Incisive foramen, 13. Anterior nasal spine, 14. Nasal cavity and conchae, 15. Nasal septum, 16. Hard palate, 17. Maxillary sinus, 18. Floor of the maxillary sinus, 19. Zygomatic process of maxilla, 20. Zygomatic arch, 21. Zygoma, 22. Hamulus, 23. Dentition. *Source:* (From Nidaan Diagnostic Centre, Pune.)

Fig. 3.23.2 The OPG depicts the anatomical landmarks. Arrows depict the anatomical landmarks in maxillary region, which can be in corelation with pictorial diagram. Normal anatomical landmarks of the maxilla and surrounding structures: 1. Mastoid process ( *White arrow*), 2. Styloid process ( *black arrow*), 3. External Auditory meatus, 4. Glenoid fossa, 5. Articular eminence, 6. Lateral pterygoid plate, 7. Pterygo-maxillary fissure, 8. Maxillary tuberosity, 9. Infraorbital foramen, 10. Orbit, 11. Incisive canal, 12. Incisive foramen, 13. Anterior nasal spine, 14. Nasal cavity and conchae, 15. Nasal septum, 16. Hard palate, 17. Maxillary sinus, *Yellow arrow* – cervical vertebra, 18. Floor of the maxillary sinus, 19. Zygomatic process of maxilla, 20. Zygomatic arch, 21. Zygoma, 22. Hamulus, 23. Dentition. *Source:* (From Nidaan Diagnostic Centre, Pune.)

Fig. 3.23.3 Normal anatomical landmarks of the mandible and surrounding structures. 1. Mandibular condyle, 2. Coronoid notch, 3. Coronoid process, 4. Mandibular foramen, 5. Ramus, 6.Lingula, mandibular canal, 7. Mental foramen, 8. Mandibular or Inferior alveolar canal, 9. Mental ridge, 10. Mental fossa, 11. Lingual foramen, 12. Genial tubercles, 13. Inferior border of mandible, 14. Mylohyoid ridge, 15. Internal oblique ridge, 16. External oblique ridge, 17. Angle of mandible, 18. Dentition, 19. Hyoid bone. *Source:* (From Nidaan Diagnostic Centre, Pune.)

Fig. 3.23.4 The OPG depicts the anatomical landmarks. *Arrows* depict the anatomical landmarks in maxillary region, which is in corelation with the pictorial diagram. 1. Mandibular condyle, 2. Coronoid notch, 3. Coronoid process, 4. Mandibular foramen, 5. Ramus, 6. Lingula, mandibular canal, 7. Mental foramen, 8. Mandibular or Inferior alveolar canal, 9. Mental ridge, 10. Mental fossa, 11. Lingual foramen, 12. Genial tubercles, 13. Inferior border of mandible, 14. Mylohyoid ridge, 15. Internal oblique ridge, 16. External oblique ridge, 17. Angle of mandible, 18. Dentition, 19. Hyoid bone. *Source:* (From Nidaan Diagnostic Centre, Pune.)

Fig. 3.23.5 Air space images seen on panoramic films: 1. palatoglossal air space, 2. Nasopharyngeal air space, 3. Glossopharyngeal air space. *Source:* (From Nidaan Diagnostic Centre, Pune.)

Fig. 3.23.6 Air spaces are visible on the panoramic radiograph. The *arrows* depict the air spaces. 1. Palatoglossal air space, 2. Nasopharyngeal air space, 3. Glossopharyngeal air space. *Source:* (From Nidaan Diagnostic Centre, Pune.)

Fig. 3.23.7 Soft tissue images seen on panoramic films: 1. Tongue, 2. soft palate and uvula, 3. Lip line, 4. Ear. *Source:* (From Nidaan Diagnostic Centre, Pune.)

Fig. 3.23.8 Soft tissue images are visible on panoramic radiograph. *Arrows* depict it. 1. Tongue, 2. Soft palate and uvula, 3. Lip line, 4. Ear. *Source:* (From Nidaan Diagnostic Centre, Pune.)

Intraoral radiography

Intraoral dental radiographs fall into two main categories: bitewings and periapical radiographs. Bitewing radiographs are the best diagnostic tool available for the detection of interproximal caries and assessment of alveolar bone levels. Bitewings are used in the posterior regions of the mouth. Periapical radiographs record the entire tooth and supporting bone and are in use to evaluate the extent of caries and periodontal bone loss and aid in the diagnosis and treatment of root and bony pathology. Periapical radiographs and bitewings are in combination to form surveys of varying configurations, for a comprehensive view of the entire dentition. Intraoral radiographs can be captured using film or digital receptors. Digital receptors are available as wired and wireless rigid sensors (CCD—charge-coupled device; CMOS—complementary metal oxide semiconductor) and photostimulable phosphor plates.

Intraoral radiographs are a key tool in diagnosis as it gives minute and fine details leading to diagnosis.

Normal tooth anatomy (Fig. 3.23.9)

The radiographic appearances of structures observed on the intraoral periapical radiograph are:

1. Teeth
2. Supporting structures
3. Maxilla
4. Mandible
5. Others, restorative materials

Fig. 3.23.9 *White arrow* – enamel, *Yellow arrow* – Dentin, *Orange arrow* – Pulp, *Brown arrow* – cementum *Black arrow* – PDL space, *Red arrow* – Lamina dura, *Yellow arrow* – dentin. *Source:* (From Nidaan Diagnostic Centre, Pune.)

Normal anatomical landmarks observed on the intraoral periapical radiographs may be classified as²:

1. Radiopaque
2. Radiolucent

Radiopaque

A. Maxilla B. Mandible
1. 1. Enamel 1. Enamel
2. 2. Dentin 2. Dentin
3. 3. Cementum 3. Cementum
4. 4. Lamina dura 4. Lamina dura
5. 5. Alveolar crest 5. Alveolar crest
6. 6. Cancellous bone 6. Cancellous bone
7. 7. Nasal septum 7. Genial tubercles
8. 8. Anterior nasal spine 8. Mental ridge
9. 9. Floor of the nasal cavity 9. Mylohyoid ridge
10. 10. Inferior nasal conchae 10. External oblique ridge
11. 11. Nasolabial fold 11. Inferior border of the mandible
12. 12. Floor of the maxillary sinus 12. Coronoid process
13. 13. Septa in maxillary sinus 13. Internal oblique ridge
14. 14. Inverted Y in maxillary sinus
15. 15. Zygomatic process of maxilla
16. 16. Zygoma (malar bone)
17. 17. Pterygoid plates
18. 18. Hamular process
19. 19. Maxillary tuberosity

Radiolucent

A. Maxilla B. Mandible
1. 1. Pulp 1. Pulp
2. 2. Periodontal ligament space 2. Periodontal ligament Space
3. 3. Nutrient canals 3. Nutrient canals
4. 4. Intermaxillary suture 4. Lingual foramen
5. 5. Nasal fossa 5. Symphysis
6. 6. Incisive foramen 6. Mental fossa
7. 7. Superior foramina of nasopalatine canal 7. Mental foramen
8. 8. Incisive fossa (lateral or cranial) 8. Mandibular canal
9. 9. Nasolacrimal canal 9. Mandibular fossa
10. 10. Maxillary sinus
11. 11. Nose

Normal anatomical landmarks seen on the intraoral periapical radiographs are classify as:

Supporting structures

1. Lamina Dura
2. Alveolar Crest
3. Periodontal Ligament Space
4. Cancellous Bone

Maxilla

1. Intermaxillary Suture
2. Anterior Nasal Spine
3. Nasal Aperture
4. Incisive Foramen
5. Superior Foramina of the Nasopalatine Canal
6. Lateral Fossa

Nose

8. Nasolacrimal Canal

Maxillary Sinus

1. Zygomatic Process and Zygoma
2. Nasolabial Fold
3. Pterygoid Plates

Mandible

1. Symphysis
2. Genial Tubercles
3. Lingual Foramen
4. Mental Ridge
5. Mental Fossa
6. Mental Foramen
7. Mandibular Canal
8. Nutrient Canals
9. Mylohyoid Ridge
10. Submandibular Gland Fossa
11. External Oblique Ridge
12. Inferior Border of the Mandible
13. Coronoid Process

Supporting structures

1. Lamina Dura

Lamina dura, meaning hard layer, refers to the thin layer of dense bone that encircles the tooth sockets of a healthy tooth in an arch. Radiographically, it appears as a thin radiopaque layer (Fig. 3.23.10).

Fig. 3.23.10 IOPA showing the lamina dura ( *arrows*) appearing as a thin opaque layer of bone around teeth. *Source:* (From Nidaan Diagnostic Centre, Pune.)

This layer is in continuation with the shadow of the cortical bone at the alveolar crest.

2. Alveolar Crest

The alveolar crests are visible as radiopaque lines between the gingival margins of the alveolar processes of adjacent teeth (Fig. 3.23.11). The normal level of the crest is not more than 1.5 mm from the cemento-enamel junction of the adjacent teeth.

3. Periodontal Ligament Space

Fig. 3.23.11 Alveolar crest seen between the teeth ( *arrow*). *Source:* (From Nidaan Diagnostic Centre, Pune.)

PDL is composed primarily of collagen; hence, it appears as a radiolucent space between the tooth root and the lamina dura. This space is visible from the alveolar crest on one side extending around the tooth roots within the alveolus and then returning to the alveolar crest on the opposite side of the tooth (Fig. 3.23.12).

4. Cancellous bone

Fig. 3.23.12 PDL space ( *arrow*). *Source:* (From Nidaan Diagnostic Centre, Pune.)

The cancellous bone (also called Trabecular bone or Spongiosa) occupies the space between the cortical plates in both maxilla and mandible. It is composed of thin radiopaque plates and rods (trabeculae) encircling many small radiolucent marrow spaces. The radiographic pattern of the trabeculae is deriving from the cancellous bone and the endo-osteal surface of the outer cortical bone (Fig. 3.23.13).

Fig. 3.23.13 The trabecular pattern in the anterior mandible is characterized by coarser. *Source:* (From Nidaan Diagnostic Centre, Pune.)

Trabecular plates (arrow) and larger marrow spaces than in the anterior maxilla (Figs 3.23.14 and 3.23.15).

Fig. 3.23.15 The trabecular pattern in the posterior mandible is quite variable, often showing large marrow spaces and sparse trabeculation, especially inferiorly ( *arrows*). *Source:* (From Nidaan Diagnostic Centre, Pune.)

Maxilla

1. Intermaxillary suture:

The two halves of the premaxilla fuse along the midline forming the intermaxillary suture or the median suture which is visible on an intraoral periapical radiograph as a thin radiolucent line (Fig. 3.23.16). It is visible along the alveolar bone between the central incisors passing through the anterior nasal spine, posteriorly between the palatine processes ending into the posterior aspect of the hard palate.

Fig. 3.23.16 Maxillary mid-line showing the radiolucent line of intermaxillary suture ( *arrows*). *Source:* (From Nidaan Diagnostic Centre, Pune.)

It is common for this narrow radiolucent suture to end in the alveolar crest in a small rounded or V-shaped widening. The other name for intermaxillary suture is the midpalatine suture (Fig. 3.23.17).

2. Nasal Aperture

Fig. 3.23.17 A radiopaque, irregular or V-shaped projection seen emerging from the floor of the nasal aperture in the midline is the anterior nasal spine ( *arrow*). *Source:* (From Nidaan Diagnostic Centre, Pune.)

Intraoral radiographs of the maxillary teeth (especially the central incisors) show a radiolucent air-filled nasal aperture and nasal cavity that lie just above the oral cavity. A radiopaque line is visible on the inferior border of the fossa and aperture extending bilaterally distal to the base of the anterior nasal spine in periapical radiographs (Fig. 3.23.18). Above this line is the inferior portion of the nasal cavity seen as radiolucent space on the radiograph. A radiograph projecting in the sagittal plane shows the relatively radiopaque nasal septum placed superior to the anterior nasal spine (Figs. 3.23.19 and 3.23.20).

3. Incisive Foramen

Fig. 3.23.18 The radio opaque nasal aperture ( *arrows*) seen lateral to radiopaque anterior nasal spine. *Source:* (From Nidaan Diagnostic Centre, Pune.)

Fig. 3.23.19 The nasal septum ( *black arrow*) seen above the anterior nasal spine and covered with mucosa ( *white arrow*). White arrow depicts the inferior nasal concha and blue arrow depicts the nasal fossa. *Source:* (From Nidaan Diagnostic Centre, Pune.)

Fig. 3.23.20 The floor of the nasal aperture ( *arrows*) is often visible posterior to the anterior nasal spine in the region of maxillary lateral incisor and canine. *Source:* (From Nidaan Diagnostic Centre, Pune.)

The nasopalatine canal terminates into the incisive foramen (also called the nasopalatine foramen or anterior palatine foramen) in the anterior floor of the nasal fossa in the maxilla. The contents of the foramen are the nasopalatine vessels and nerves (which may innervate the maxillary central incisors) and lie along the midline behind the central incisors approximately at the junction of median palatine suture and incisive sutures. The radiographic image is projecting in the middle and apical third regions of the roots of central incisors. Incisive foramen is of significance as cyst formation is common in this region. An incisive canal cyst is radiographically, recognized as it causes enlargement of the foramen and canal. Evaluation of these structures is important when an implant insertion is considered (Fig. 3.23.21).

4. Superior Foramina of the Nasopalatine Canal

Fig. 3.23.21 The ovoid radiolucency ( *arrows*) with diffuse borders between the roots of the maxillary central incisors is the incisive foramen. *Black arrow* depicts the lateral wall of nasopalatine canal. *Source:* (From Nidaan Diagnostic Centre, Pune.)

The two foramina in the floor of the nasal cavity give rise to superior foramina of nasopalatine canal. It opens bilaterally to the nasal septum, near the antero-inferior border of the nasal cavity. It is passing downward anteriorly and medially to join and form a common opening, the incisive (nasopalatine) foramen. The superior foramina of the canal are rarely visible in sharply angled projections of the maxillary incisors (Fig. 3.23.22).

5. Lateral Fossa

Fig. 3.23.22 IOPA radiographs showing the superior foramina of the nasopalatine canal ( *arrows*) just lateral to the nasal septum and posterior to the anterior nasal spine. *Source:* (From Nidaan Diagnostic Centre, Pune.)

The apex of the maxillary lateral incisors shows a depression in the cortical bone known as the lateral fossa (Fig. 3.23.23). It appears as a diffuse radiolucency visible on a periapical radiograph.

6. Nose

Fig. 3.23.23 The lateral fossa is visible as a diffuse radiolucency ( *arrows*). *Source:* (From Nidaan Diagnostic Centre, Pune.)

The soft cartilaginous tip of the nose is mostly visible as a uniform, slightly radiopaque region with a well-defined border in the radiographic projections of the maxillary central and lateral incisors, superimposed over the roots of these teeth (Fig. 3.23.24).

7. Nasolacrimal canal

Fig. 3.23.24 The radiograph showing a radiopaque tip of the nose (arrows) at the apical 1/3rd portion of the tooth whereas, the arrows at the cervical level indicates the lip line ( *White arrows*). *Source:* (From Nidaan Diagnostic Centre, Pune.)

The nasal and maxillary bones form the nasolacrimal canal and it courses from the medial side of antero-inferior border of the orbit to drain under into the nasal cavity. Occasionally, it can be visible on a sharply angled periapical radiograph of the canine (Figs 3.23.25 and 3.23.26).

8. Maxillary sinus

Fig. 3.23.25 The nasolacrimal canal ( *arrow*) is occasionally, visible near the apex of canine when steep vertical angulation is used. *Source:* (From Nidaan Diagnostic Centre, Pune.)

Fig. 3.23.26 The nasolacrimal canal viewed as an ovoid radiolucency bilaterally ( *arrows*) on maxillary occlusal radiograph. *Source:* (From Nidaan Diagnostic Centre, Pune.)

The maxillary sinus is the largest paranasal sinus occupying virtually the entire body of maxilla. It is an air-filled cavity lined with mucous membrane. It develops because of invagination of mucous membrane from the nasal cavity. The sinus may be consider as a three-sided pyramid, medial wall adjacent to the nasal cavity as base and its apex extending laterally into the zygomatic process of the maxilla. The sinus connects to the nasal cavity with an opening of about 3–6 mm passing through the middle concha of the ethmoidal bone. Periapical radiographs of the canine show the floors of the sinus and nasal cavity superimposed on one another, forming an inverted ‘Y’ in the area (Figs 3.23.27 and 3.23.28).