ABOMR cheat sheet

Absorbed dose is measured in gray (Gy); 1 Gy = 1 joule/kg; 1 Gy = 100 rad.

Equivalent dose uses sievert (Sv) and applies a radiation weighting factor (wR = 1 for x-rays); 1 Sv = 100 rem.

Effective dose sums tissue-weighted equivalent doses; a panoramic radiograph is roughly 0.01–0.03 mSv, a CBCT scan roughly 0.03–1 mSv depending on field of view.

Half-value layer (HVL) is the absorber thickness that reduces beam intensity by half; filtration increases HVL and removes low-energy photons.

Photoelectric effect dominates at low kVp and high atomic number (bone, metal), producing high subject contrast; Compton scatter dominates at higher energies and degrades contrast.

Linear attenuation coefficient μ decreases as photon energy increases; attenuation follows I = I0·e^(−μx).

Law of Bergonié and Tribondeau: tissues are most radiosensitive when rapidly dividing, poorly differentiated, and young.

Stochastic effects (carcinogenesis, heritable) are probabilistic with no threshold; deterministic effects (erythema, cataract) have thresholds and increase in severity with dose.

Inverse square law: intensity is inversely proportional to the square of the distance from a point source.

Intraoral bitewing/PA exposure settings typically 60–70 kVp and 7–8 mA with rectangular collimation to reduce dose.

Panoramic imaging uses a rotating x-ray tube and receptor moving about a stationary rotation center, producing a focal trough; patient positioning errors cause ghost images and distortion.

The focal trough (image layer) is the curved zone of sharpness; structures outside it appear blurred or magnified.

CBCT uses a cone-shaped beam and flat-panel detector, acquiring a single 180–360° rotation; voxel size determines spatial resolution (commonly 0.075–0.4 mm).

Digital receptors: indirect systems use a scintillator (phosphor) converting x-rays to light; direct systems convert x-rays to charge directly.

mA controls quantity of x-rays (tube current); kVp controls quality/penetrating power and therefore contrast.

Lateral cephalometric radiographs use a fixed source-to-mid-sagittal distance (typically 5 ft/60 in) with ear rods and a collimated slit beam.

Bitewing technique requires the receptor parallel to the occlusal plane with the central ray perpendicular to the receptor.

ALARA principle: keep exposures as low as reasonably achievable using time, distance, and shielding.

Occupational dose limit is 50 mSv/year effective dose (ICRP); public limit is 1 mSv/year.

Lead apron and thyroid collar reduce dose to radiosensitive organs; rectangular collimation reduces absorbed dose substantially versus round collimation.

QA for intraoral units includes kVp accuracy, exposure reproducibility, half-value layer, and collimation checks; film/digital receptor processing must be monitored for artifacts.

Digital image processing includes window/level (contrast/brightness), edge enhancement, and gray-scale inversion; these alter display, not the acquired data.

Noise in digital images arises from quantum mottle (low photon count) and electronic/readout noise; increasing exposure reduces quantum mottle.

Personnel dosimetry uses film badges or optically stimulated luminescence (OSL) badges, read monthly and reported as deep dose.

CBCT QA includes voxel size verification, geometric accuracy, contrast resolution, and uniformity testing with phantoms.

Mandibular canal contains the inferior alveolar nerve, artery, and vein; it runs from the mandibular foramen to the mental foramen.

Maxillary sinus floor is related to the roots of maxillary posterior teeth; pneumatization can extend between roots.

Nutrient canals appear as radiolucent lines within the mandible and can mimic fractures.

Developmental anomalies include dens invaginatus (dens in dente), dens evaginatus, taurodontism, and enamel pearls.

Nasopalatine (incisive) canal appears as a midline radiolucency between maxillary central incisors, often heart-shaped.

Stafne defect is a well-defined radiolucency near the mandibular angle below the canal, representing a lingual bone depression.

Supernumerary teeth most commonly occur in the anterior maxilla (mesiodens); hyperdontia and hypodontia are developmental anomalies.

The temporomandibular joint comprises the condyle, glenoid fossa, articular eminence, and articular disc; the disc is biconcave.

Radicular cyst is the most common odontogenic cyst, arising from a nonvital tooth at the apex.

Dentigerous cyst surrounds the crown of an unerupted tooth and attaches at the CEJ; it is the most common developmental odontogenic cyst.

Odontogenic keratocyst (OKC) shows a scalloped border, minimal expansion, and high recurrence; it is associated with nevoid basal cell carcinoma syndrome.

Ameloblastoma is a locally aggressive odontogenic tumor, often multilocular (soap-bubble) in the posterior mandible.

Odontoma is the most common odontogenic tumor; compound type shows tooth-like denticles, complex type an irregular mass.

Non-odontogenic cysts include nasopalatine duct cyst and Stafne defect; nasolabial cyst is a soft-tissue cyst.

Adenomatoid odontogenic tumor typically presents as a well-defined radiolucency associated with an impacted canine.

Cementoblastoma is a radiopaque mass fused to a tooth root with a radiolucent rim.

Osteomyelitis shows ill-defined radiolucency with sequestra (radiopaque fragments) and involucrum; chronic form may show sclerosis.

Periapical inflammatory lesions begin as widened PDL space and progress to periapical radiolucency.

Fractures appear as radiolucent lines; mandibular fractures are common at the angle, condyle, and symphysis.

Le Fort I, II, and III fractures involve maxillary levels: I transverse, II pyramidal, III craniofacial disjunction.

Condylar fracture may show shortening of the ramus and deviation of the mandible toward the fractured side.

Paget disease shows cotton-wool radiopacities, bone expansion, and hypercementosis; it is a metabolic bone disorder.

Hyperparathyroidism causes subperiosteal bone resorption (classically radial side of middle phalanges) and brown tumors.

Osteoradionecrosis follows high-dose radiation and presents as non-healing exposed bone with ill-defined margins.

MRI is the modality of choice for the TMJ articular disc; the disc is hypointense on T1 and T2.

Anterior disc displacement with reduction shows the disc anterior to the condyle in closed mouth and reducing on opening.

Sialography uses contrast to outline the ductal system; sialadenitis shows ductal dilatation and sialectasis.

Ultrasound is useful for superficial salivary gland lesions and differentiating cystic from solid masses.

Sialoliths appear radiopaque on plain film or CT; CT is more sensitive than plain radiography.

Pleomorphic adenoma is the most common benign salivary gland tumor, typically well-defined and in the parotid.

Soft tissue calcifications include phleboliths (round, laminated), sialoliths, and carotid artery calcifications.

T2-weighted MRI shows high signal in fluid-filled structures such as cysts and inflamed glands.

CBCT provides high spatial resolution of bone at lower dose than MDCT but has poor soft-tissue contrast.

MDCT uses a fan beam with a rotating gantry and provides cross-sectional images with Hounsfield units for tissue density.

MRI uses strong magnetic fields and radiofrequency pulses; T1 shows fat bright, fluid dark; T2 shows fluid bright.

MRI is contraindicated with certain ferromagnetic implants and pacemakers; gadolinium contrast is used for enhancing lesions.

Ultrasound uses high-frequency sound waves; higher frequency gives better resolution but less penetration.

Nuclear medicine (e.g., bone scan with Tc-99m) shows physiologic uptake and is sensitive for metastasis and active bone disease but has low spatial resolution.

Hounsfield unit scale: water = 0, air ≈ −1000, bone > 400; used for density assessment on CT.

CBCT artifacts include beam hardening, scatter, and motion; metal produces streak artifacts.

Informed consent must be obtained before radiographic examination, including explanation of benefits and risks.

Radiographs should be ordered only when clinically justified; routine screening without indication is not supported.

Records must be maintained per jurisdictional requirements; images are part of the legal patient record.

Radiation protection follows the ALARA principle and the principle of justification and optimization.

Interpretation and reporting should be documented; dentists are responsible for reading films they order.

Confidentiality and privacy are governed by HIPAA (US) and comparable regulations; sharing images requires authorization.

Continuing education and quality assurance programs are required to maintain competence and equipment performance.

Delegation of radiographic exposure to auxiliaries requires appropriate training and supervision per local regulation.