AGD Fellowship Review Course: Dental Imaging

Comprehensive review flashcards covering radiation physics, bitewing criteria, panoramic exposure and positioning errors, extraoral projections, CBCT, MRI, Hounsfield units, ADA prescription guidelines, and the differential diagnosis of jaw cysts, tumors, hamartomas, and soft tissue calcifications.

What are the four geometric rules for accurate radiographic image formation?

1. The distance between the focal spot and the film should be as long as possible; 2. The film should be as close to the object as possible; 3. The long axis of the object should be parallel to the film; 4. The central ray should be perpendicular to the film.

How are radiographic density and contrast defined?

Density is the degree of blackness of an image. Contrast is the difference in densities or shades of gray.

What three primary factors affect radiographic density, and how do they alter it?

1. Milliampere Seconds ($mAs$): increasing $mAs$ increases the number of X-rays reaching the sensor, creating a denser image; 2. Kilovoltage ($kVp$): increasing $kVp$ increases X-ray penetrating power so more X-rays reach the film, producing a denser image; 3. Source-to-film distance: increasing the distance reduces the X-rays reaching the film, decreasing image density.

According to the Inverse Square Law, what happens to film density when the source-to-film distance is doubled?

Doubling the distance results in a film with $\frac{1}{4}$ of the original density ($\text{Intensity } I = \frac{1}{D^2}$).

What is the relationship between kilovoltage ($kVp$) and radiographic contrast?

They share an inverse relationship. Increasing $kVp$ increases the penetration of X-rays, causing more blackening and resulting in lower contrast.

What characterizes long scale contrast, and what clinical conditions is it best for visualizing?

It is associated with higher $kVp$ and greater tissue penetration, yielding smaller differences between densities (many shades of gray). It is best for evaluating osseous changes in periodontal disease, periapical disease, and apical root resorption.

What characterizes short scale contrast, and what is its primary diagnostic application?

It is associated with lower $kVp$ and less tissue penetration, yielding greater differences in density (high contrast with black-and-white transitions and minimal gray). It is best for detecting dental caries and secondary caries on bitewing images.

What is the requirement for interproximal contacts on an acceptable bitewing radiograph (BWXR)?

Interproximal contacts should not be overlapped from the distal surface of the canine to the mesial surface of the third molar, to the extent that interpretation is possible.

What are the bitewing criteria regarding crown centering, bone crest visibility, occlusal plane, and cusp tips?

Crowns of maxillary and mandibular teeth should be centered top-to-bottom; the crest of alveolar bone must be visible without superimposition of adjacent crowns; the occlusal plane should be as horizontal as possible; and cusp tips should be nearly superimposed without excessive separation of buccal and lingual cusps.

What are the Buccal Object Rule and the SLOB rule?

The Buccal Object Rule states that the image of the most buccal object moves relative to the lingual object in the same direction the beam is directed. The SLOB rule stands for 'Same Lingual, Opposite Buccal,' meaning the lingual object moves in the same direction that the tubehead is moved.

What clinical conditions are assessed using tube shift techniques (SLOB / Buccal Object Rule)?

Assessing external resorption versus internal resorption and localizing superimposed hard tissue structures such as sialoliths relative to the root canal system or roots.

What are the most likely causes of an excessively dark radiograph?

Long exposure time, high $kVp$, short source-to-film distance, high $mAs$, and an inaccurate timer.

What are the most likely causes of an excessively light radiograph?

Energy level too low (low $mAs$), film packet positioned backwards, $kVp$ too low, and low-contrast film.

What radiographic error occurs when a patient is positioned too far forward in the panoramic focal trough?

Maxillary and mandibular anterior teeth appear out of focus, blurred, and excessively narrow, and the cervical spine is superimposed over the ramus.

What radiographic error occurs when a patient is positioned too far backward in the panoramic focal trough?

Maxillary and mandibular anterior teeth appear out of focus, blurred, and excessively wide, accompanied by ghosting of the mandible and spine.

What patient positioning error produces this panoramic appearance, where lower incisors are blurred, the hyoid bone is superimposed, and condyles are cut off at the top of the image?

Chin down (patient's head is tilted downward, chin is back, and forehead is too far forward).

What positioning error causes the upper incisors to be out of focus and the hard palate to be superimposed over the apices of the maxillary teeth as shown here?

Chin up (patient's head is tilted upward).

What positioning error creates the radiolucent shadow below the palate that obscures the maxillary root apices in this radiograph?

The patient's tongue was not held closely against the roof of the mouth during exposure.

What causes the dense, pyramid-shaped opacity superimposed in the midline of this panoramic radiograph?

Patient slumping with a non-erect spinal column (casting a dense ghost image of the spine), or a lead apron positioned too high.

Why does patient movement during a panoramic radiograph typically blur only a specific portion of the image?

Because only a small vertical increment of the panoramic film or sensor is exposed at any given moment during the rotational cycle.

According to ADA/FDA guidelines, what is the bitewing recall interval for recall patients exhibiting clinical caries or increased caries risk?

For children with primary or transitional dentition: posterior bitewings at $6\text{–}12\text{ month}$ intervals. For adolescents and dentate adults: posterior bitewings at $6\text{–}18\text{ month}$ intervals.

According to ADA/FDA guidelines, what are the bitewing recall intervals for patients with no clinical caries and not at increased risk?

Child with primary dentition: $12\text{–}24\text{ month}$ intervals; Adolescent with permanent dentition: $18\text{–}36\text{ month}$ intervals; Adult with dentate dentition: $24\text{–}36\text{ month}$ intervals.

Which extraoral radiographic projection is shown, and what is its primary diagnostic indication?

Waters projection; primarily used for evaluating the maxillary sinuses.

Which extraoral projection is shown in this radiograph, and what is it indicated to assess?

Reverse Towne's projection; indicated for condylar fractures and medially displaced condyles.

What radiographic view is shown in this image, often referred to as the 'jug handle' view?

Submentovertex (SMV) projection; primarily used to visualize the zygomatic arches.

What are the indications for Posteroanterior (PA) skull and Lateral Skull projections?

Posteroanterior (PA) evaluates disease, trauma (midface fractures), and developmental abnormalities. Lateral Skull evaluates facial growth, retrognathia, and prognathia.

How do direct and indirect digital imaging differ in sensor hardware and operational workflow?

Direct digital imaging uses rigid CCD or CMOS sensors with a cord or direct transmission, offering instant viewing at higher equipment cost. Indirect digital imaging uses photostimulable phosphor (PSP) plates that have no cord, lower cost, and thinner dimensions, but require laser scanning in a darkroom environment.

What does DICOM stand for, and what is its function?

Digital Imaging and Communications in Medicine; it is the universal standard format that allows radiographic images to be shared and opened across different manufacturers' software.

How do CT and CBCT compare regarding the reliability of Hounsfield Units (HU)?

Hounsfield Units are calibrated and quantitatively accurate for medical CT scans. CBCT is not calibrated for Hounsfield Units; its gray levels roughly correlate to HU but are not reliable.

What are the standard Hounsfield Unit (HU) values for air, fat, water, and bone?

Air: $-1000\,HU$; Fat: $-50\text{ to }-100\,HU$; Water: $0\,HU$; Bone: $+1000\,HU$.

What are the primary imaging artifacts encountered when acquiring and viewing CBCT reconstructions?

Beam hardening, scatter (especially in the axial plane), aliasing, cone effect (peripheral distortion), and patient movement.

How do soft tissues and bone/air appear on an MRI image, and when do dentists most commonly order an MRI?

Soft tissues appear lighter/whiter (high signal intensity), while bone and air appear darker/black (low signal intensity). Dentists most commonly order an MRI when soft tissue pathology of the TMJ is suspected (e.g., severe internal derangement, disc displacement, or limited opening unresponsive to conservative therapy).

How do T1-weighted and T2-weighted MRI scans differ in appearance and clinical utility?

T1 is a 'fat image' where fat is bright and water is dark, highlighting soft tissue anatomy and TMJ architecture. T2 is a 'water image' where water is bright and fat is intermediate or dark, highlighting edema, fluid collections, and cerebrospinal fluid (CSF).

What are the major contraindications to Magnetic Resonance Imaging (MRI)?

Cardiac pacemakers, ferromagnetic metallic implants (such as cochlear implants), and intracranial ferromagnetic aneurysm clips.

What terminology is used to describe radiodensities across Plain Radiography, CT Imaging, and MR Imaging?

Plain Radiography: Radiopaque, Radiolucent, Mixed density. CT Imaging: Hyperdense, Hypodense, Mixed intensity/heterogeneous. MR Imaging: Low signal intensity, High signal intensity, Mixed intensity.

What three pericoronal radiolucent lesions are commonly associated with an impacted crown, and what distinguishes them?

1. Dentigerous Cyst: most common developmental odontogenic cyst, attached at the cemento-enamel junction (CEJ); 2. Hyperplastic Follicle: normal anatomical variant presenting with a radiolucent space $< 3\,mm$; 3. Ameloblastic Fibroma: occurs predominantly in children and teenagers in the posterior mandible.

How do Adenomatoid Odontogenic Tumor (AOT) and Calcifying Epithelial Odontogenic Tumor (CEOT) differ in typical location and radiographic calcification pattern?

AOT typically occurs in the anterior maxilla surrounding the crown and root, containing delicate 'snowflake' calcifications. CEOT (Pindborg tumor) typically occurs in the posterior mandible, exhibiting mixed density with 'driven-snow' or 'snowplow' radiopacities.

What multilocular radiographic appearances are classically associated with Ameloblastoma, Odontogenic Myxoma, and Odontogenic Keratocyst (OKC)?

Ameloblastoma exhibits a 'soap bubble' multilocular appearance with high potential for root resorption. Odontogenic Myxoma presents with a 'honeycomb' or 'tennis racket' pattern. OKC exhibits anteroposterior growth along the internal aspect of the jaw with minimal cortical bone expansion.

Where does Central Giant Cell Granuloma (CGCG) typically occur, and what diagnostic laboratory tests should be ordered upon its discovery?

CGCG typically occurs in the anterior mandible and frequently crosses the midline. Its discovery warrants screening for primary or secondary hyperparathyroidism by evaluating parathyroid hormone (PTH), serum calcium, phosphorous, and renal function (with cherubism considered in young patients).

What is the most common odontogenic hamartoma/tumor, and how do its two subtypes appear radiographically?

Odontoma. Compound odontoma presents as multiple small, recognizable 'toothlets' (typically anterior maxilla); Complex odontoma presents as a solitary, amorphous, conglomerate radiopaque mass (typically posterior jaws).

What are the clinical, demographic, and vitality hallmarks of Periapical Cemento-Osseous Dysplasia (PCOD)?

It is most common in African American females, localizes to the apices of mandibular anterior teeth, and the involved teeth invariably remain vital.

How do Fibrous Dysplasia and Paget's disease differ radiographically and biochemically?

Fibrous Dysplasia displays a 'ground glass' or 'orange peel' texture that blends imperceptibly into surrounding normal bone without a distinct border. Paget's disease is a systemic condition displaying a 'cotton wool' appearance involving entire bones and causing elevated serum alkaline phosphatase.

What are the most common overall malignancy of the jaws, the most common primary oral malignancy, and the most common primary bone malignancy?

Most common overall jaw malignancy: Metastatic disease (originating from breast, lung, or prostate); Most common primary oral malignancy: Squamous cell carcinoma (characterized by ragged, 'motheaten' borders); Most common primary bone malignancy: Osteosarcoma (characterized by a 'sunburst' periosteal reaction and Garrington Sign/symmetric PDL widening).

What radiographic findings characterize Multiple Myeloma and Langerhans Cell Histiocytosis (LCH)?

Multiple Myeloma displays multiple non-corticated, 'punched-out' radiolucent lesions in the skull and jaws of adults. LCH causes severe alveolar bone destruction resulting in 'floating-in-air' teeth in children.

What mandibular anatomical variation/pseudocyst is indicated by the white arrow in this panoramic section?

Stafne defect (lingual mandibular salivary gland depression), located below the inferior alveolar canal.

What is the most common non-odontogenic cyst of the jaws, and how does it appear radiographically?

Nasopalatine duct cyst (incisive canal cyst); it presents as a well-defined heart-shaped radiolucency in the midline of the anterior maxilla between the central incisors.

What features define a Traumatic Bone Cyst on a dental radiograph?

It is a pseudocyst (lacking an epithelial lining) that scallops superiorly between the roots of vital teeth without displacing them.

Which specific pathologies are suggested by 'onion skin' opacification, 'stepladder' trabeculation, 'tramline' calcification, and Wormian bones?

'Onion skin' opacification: osteomyelitis with proliferative periostitis (Garrè) or Ewing sarcoma; 'Stepladder' trabeculation: Sickle cell disease; 'Tramline' calcification: Sturge-Weber angiomatosis; Wormian sutural bones: cleidocranial dysplasia or osteogenesis imperfecta.

What conditions constitute the primary differential diagnosis when carotid artery calcifications are suspected on a panoramic radiograph?

Calcified thyroid (triticeous) cartilage, calcified cervical lymph nodes, and non-carotid phleboliths.