Overseas Registration Exam (ORE) Radiology, Radiography and Diagnostic Imaging Syllabus

What is a controlled area in dental radiography, and how large is it?

An area requiring special procedures to restrict significant exposure. For dental units it extends to $1.5\,\mathrm{m}$ from the X-ray tube and patient in all directions, plus the primary beam until adequately attenuated. The operator must stand outside it (or behind a barrier) during exposure.

What is the recommended minimum operator distance and position when no protective barrier is used?

At least $1.5\,\mathrm{m}$ from the tube and patient, and standing at $90^{\circ}$ to $135^{\circ}$ to the primary beam direction (in the 'safe zone' to avoid the main beam and reduce scatter).

What is a Diagnostic Reference Level (DRL) and an example for a dental intraoral exposure?

A DRL is a dose level for a standard procedure that, if consistently exceeded, prompts investigation of technique. A typical national DRL for an adult intraoral (periapical) radiograph is around $1.2\text{–}1.5\,\mathrm{mGy}$ patient entrance dose (or about $0.8\,\mathrm{mGy}$ in some current standards).

What is the role of the Radiation Protection Adviser (RPA) versus the Radiation Protection Supervisor (RPS)?

The RPA is an external expert (e.g. medical physicist) who advises the practice on compliance with IRR17. The RPS is a member of the practice staff who supervises day-to-day compliance with local rules.

What is the Medical Physics Expert (MPE) responsible for under IR(ME)R?

The MPE advises on patient dosimetry, optimisation of exposures, equipment quality assurance and dose measurement, contributing to keeping patient doses as low as reasonably practicable.

List key quality assurance (QA) checks required for a dental radiography service.

Image quality monitoring and rejection (reject) analysis, equipment/tube checks, regular routine testing of equipment, processing/digital sensor checks, film/sensor and viewing conditions checks, staff training records, and audit of clinical image quality against standards.

What is the recommended quality rating scale for dental film/image quality, with target percentages?

Three grades: Grade 1 (Excellent/Acceptable — no errors), Grade 2 (Diagnostically acceptable — some errors but not impairing diagnosis), Grade 3 (Unacceptable). Targets: Grade 1 not less than $70\%$ (digital) and Grade 3 not more than $10\%$ (digital) / $\leq 5\%$ in some standards.

What are the main intraoral radiographic projections and their primary uses?

Periapical (whole tooth plus apex and surrounding bone), Bitewing (crowns of upper and lower posterior teeth and interproximal/alveolar crest), and Occlusal (larger area of an arch, e.g. for unerupted teeth, salivary calculi, palatal/lingual position assessment).

Compare the paralleling and bisecting-angle techniques for periapical radiography.

Paralleling: film/sensor parallel to tooth long axis, beam at right angles, using a holder/long cone — geometrically accurate, minimal distortion (preferred). Bisecting-angle: beam aimed perpendicular to the imaginary bisector of the angle between tooth and film — more prone to dimensional distortion/foreshortening.

State the bisecting-angle principle (rule of isometry).

The central X-ray beam is directed perpendicular to the line that bisects the angle formed between the long axis of the tooth and the plane of the film. This makes two triangles congruent so the image length equals the true tooth length.

What causes foreshortening versus elongation in the bisecting-angle technique?

Foreshortening (image too short) results from excessive vertical beam angulation. Elongation (image too long) results from insufficient vertical beam angulation. Correct angulation aims at the bisector.

Why is a long focus-to-skin distance (long cone/spacer) preferred in intraoral radiography?

A longer source-to-object distance produces a more parallel beam, reducing magnification and geometric unsharpness (penumbra) and improving image sharpness. The minimum focus-to-skin distance is $200\,\mathrm{mm}$ for units above $60\,\mathrm{kV}$.

What is the purpose of a bitewing radiograph and its typical beam angulation?

To detect interproximal (approximal) caries and assess alveolar crest bone levels. The horizontal beam is directed through the contact points with a slight downward vertical angulation of about $+5^{\circ}$ to $+8^{\circ}$.

What is a panoramic radiograph (OPT/DPT/OPG) and what imaging principle does it use?

A panoramic radiograph produces a single image of both dental arches and surrounding structures using tomography: the tube and receptor rotate around the patient in opposite directions, keeping a curved 'focal trough' (image layer) sharp while blurring structures outside it.

What is the focal trough (image layer) in panoramic radiography, and why does it matter?

It is the curved zone of sharp focus shaped to the average dental arch. Structures positioned outside it appear blurred, magnified or distorted, so accurate patient positioning is essential to keep the dentition within the trough.

List common indications for a panoramic radiograph.

Assessment of third molars/unerupted teeth, gross pathology (cysts, tumours), trauma/fractures of mandible, TMJ assessment, orthodontic assessment, generalised severe periodontitis, and patients unable to tolerate intraoral films.

What is a cephalometric (lateral ceph) radiograph used for?

A standardised lateral skull projection used mainly in orthodontics and orthognathic planning to assess skeletal relationships (e.g. SNA, SNB, ANB angles) and soft-tissue profile, taken at a fixed source-to-patient distance for reproducibility.

What is Cone Beam Computed Tomography (CBCT) and its main dental advantage?

CBCT uses a cone-shaped beam and a single rotation to acquire a volumetric (3D) dataset, reconstructed into multiplanar views. Its advantage is high-resolution 3D imaging of hard tissues at a lower dose than medical CT, useful for implants, impactions, endodontics and pathology assessment.

How do effective doses compare: intraoral, panoramic, CBCT, and medical CT?

Approximate effective doses: intraoral $\approx 1\text{–}8\,\mathrm{\mu Sv}$, panoramic $\approx 3\text{–}24\,\mathrm{\mu Sv}$, dental CBCT $\approx 10\text{–}1000\,\mathrm{\mu Sv}$ (field-dependent), medical head CT $\approx 1000\text{–}2000\,\mathrm{\mu Sv}$. CBCT is much higher than intraoral/panoramic and must be specifically justified.

Compare direct digital sensors (CCD/CMOS) with photostimulable phosphor (PSP) plates.

CCD/CMOS: solid-state, cabled (usually), instant image, rigid, smaller active area, often thicker. PSP plates: flexible, film-like, store a latent image read by a laser scanner (delayed display), thin and comfortable, but require separate processing and can be scratched.

What is the latent image and how is it produced/read in PSP plates?

In PSP, X-rays excite electrons into 'traps' in the phosphor, storing a latent image. A scanning laser releases this energy as light (photostimulated luminescence), which is detected and digitised; the plate is then erased with bright light for reuse.

Define spatial resolution and contrast resolution in digital imaging.

Spatial resolution is the ability to distinguish small adjacent structures, measured in line pairs per millimetre ($\mathrm{lp/mm}$). Contrast resolution is the ability to distinguish small differences in tissue density (grey levels). Digital systems excel at contrast resolution; film/PSP often have high spatial resolution.

What is the chief radiation-dose advantage of digital imaging over conventional film?

Digital sensors are more sensitive, requiring less radiation for an acceptable image — typically a dose reduction of around $50\%\text{–}80\%$ compared with conventional film, in addition to instant viewing and post-processing capability.

Define image density and image contrast on a radiograph.

Density is the overall degree of blackening (darkness) of the image, governed mainly by exposure ($mAs$). Contrast is the difference in density between adjacent areas, governed mainly by kV — low kV gives high contrast (more black-and-white), high kV gives low contrast (more greys).

What are the radiographic appearances of normal enamel, dentine, pulp and cortical bone?

Enamel is the most radiopaque (densest). Dentine is slightly less radiopaque than enamel. The pulp chamber and root canal are radiolucent. Cortical bone (e.g. lamina dura, inferior border) is radiopaque; cancellous bone shows a trabecular pattern.

Identify the lamina dura, periodontal ligament space and on a periapical radiograph.

The lamina dura is the radiopaque cortical bone lining the tooth socket. The periodontal ligament (PDL) space is a thin radiolucent line between the root and lamina dura. Loss/widening of these is a sign of periapical pathology.

Name key radiopaque anatomical landmarks seen on maxillary periapical/panoramic films.

Zygomatic process/buttress, maxillary tuberosity, anterior nasal spine, hard palate/nasal floor, and the radiopaque borders around the maxillary sinus and nasal fossa.

Name key radiolucent anatomical landmarks in the maxilla and mandible.

Maxilla: maxillary (antral) sinus, nasal fossa, incisive (nasopalatine) foramen, intermaxillary suture. Mandible: mandibular canal, mental foramen, lingual foramen, submandibular fossa, and the radiolucent marrow spaces of cancellous bone.

Describe the radiographic classification of caries by depth (zones).

Caries is classified as: confined to enamel (outer/inner enamel), reaching the enamel-dentine junction, into outer/middle/inner third of dentine, and into/through the pulp. Radiographically caries appears as a radiolucency because demineralisation reduces X-ray absorption.

What is the typical radiographic appearance and shape of approximal (interproximal) caries on a bitewing?

A radiolucent notch or triangular ('V'-shaped') defect below the contact point, with its base toward the enamel surface and apex pointing toward the dentine/EDJ; it widens again as a second triangle on reaching dentine.

How do you distinguish horizontal from vertical (angular) periodontal bone loss radiographically, and what crestal change indicates active disease?

Horizontal bone loss: the crest stays roughly parallel to a line joining adjacent CEJs (even reduction). Vertical/angular bone loss: an oblique defect along one tooth surface (uneven). Loss of the normally sharp, corticated (radiopaque) alveolar crest, with crestal radiolucency, indicates active periodontal disease; bone level normally sits about $1\text{–}2\,\mathrm{mm}$ apical to the CEJ.