MJDF Dental Radiology and Imaging 2 — Questions and Answers

Question 1: Which type of radiograph provides the best view of the periapical region and surrounding alveolar bone?

Bitewing radiograph
Periapical radiograph (Correct answer)
Panoramic (OPG) radiograph
Occlusal radiograph

Correct answer: Periapical radiograph

Periapical radiographs are specifically designed to show the entire tooth from crown to root apex, including the surrounding periapical bone. They are the gold standard for diagnosing periapical pathology.

Periapical radiographs are intraoral radiographs designed to capture the full length of one or more teeth, extending from the crown through the root tip (apex) and including the surrounding alveolar bone. They are taken using either the paralleling technique (preferred) or the bisecting angle technique. The paralleling technique positions the film/sensor parallel to the long axis of the tooth with the central X-ray beam directed perpendicular to both the film and the tooth. This minimizes geometric distortion and provides the most accurate representation of tooth length and periapical anatomy. The film holder maintains proper positioning. The bisecting angle technique directs the X-ray beam perpendicular to an imaginary line that bisects the angle formed between the film and the tooth's long axis. While less accurate in anatomical representation (tends to shorten or lengthen teeth), it may be used when anatomical constraints prevent ideal film placement. Clinical applications of periapical radiographs include: diagnosis of periapical pathology (periapical abscesses, granulomas, cysts); assessment of root morphology before endodontic treatment; evaluation of post-operative endodontic outcomes; detection of root fractures; assessment of alveolar bone levels in periodontal disease; and pre-extraction assessment of roots. For MJDF candidates, understanding the indications, technique, and interpretation of periapical radiographs is fundamental.

Question 2: A bitewing radiograph is MOST useful for detecting which of the following?

Periapical abscesses
Interproximal caries and alveolar crest bone levels (Correct answer)
Root resorption
Sinus pathology

Correct answer: Interproximal caries and alveolar crest bone levels

Bitewing radiographs are specifically designed to show the crowns of upper and lower teeth simultaneously, making them ideal for detecting interproximal caries and assessing the alveolar crest height.

Bitewing radiographs (also called interproximal radiographs) are taken with the patient biting on a tab or wing attached to the film/sensor holder, which results in an image showing the crowns of both upper and lower posterior teeth (or anterior teeth in anterior bitewings) on the same image. The alveolar crest is visible as it is in the same horizontal plane. Primary uses of bitewing radiographs include: detection of interproximal caries (cavities between teeth) that are not visible on clinical examination; assessment of the alveolar crest level (important for diagnosing bone loss in periodontitis — normal crest is 1.5-2mm below the cement-enamel junction); evaluation of secondary caries under existing restorations; and assessment of the depth and extent of restorations. Bitewings do NOT show the periapical region (the root apex), making them unsuitable for diagnosing periapical pathology. For a complete dental radiographic survey (full mouth series), both periapical radiographs (for root and periapical assessment) and bitewing radiographs (for caries and crest assessment) are typically used together. The frequency of bitewing radiographs for routine caries detection should be based on the patient's caries risk status, per UK/European guidelines and FGDP(UK) Selection Criteria for Dental Radiography. High-risk patients may need annual bitewings; low-risk adult patients may only need them every 2-3 years. MJDF candidates must understand the appropriate use and justification of all radiograph types.

Question 3: The radiation protection principle 'ALARP' stands for:

All Lateral Anterior Radiation Protocol
As Low As Reasonably Practicable (Correct answer)
Absorbed Linear Attenuation Radiation Principle
Alignment of Lead Apron and Rectangular Positioning

Correct answer: As Low As Reasonably Practicable

ALARP — As Low As Reasonably Practicable — is the fundamental radiation protection principle requiring that radiation dose be kept as low as reasonably achievable while still obtaining a diagnostically useful image.

ALARP (As Low As Reasonably Practicable) is a core principle of radiation protection in dentistry, derived from the broader principle known in medicine and physics as ALARA (As Low As Reasonably Achievable). In dental radiography, this means using the minimum radiation dose necessary to obtain a diagnostically adequate image. Practical implementation of ALARP in dental practice includes: selecting the correct film/sensor speed (E or F speed film, or digital sensors, are preferred over D speed as they require less radiation); using rectangular collimation (which limits the X-ray beam to the approximate size of the film, dramatically reducing patient dose compared to round collimation); applying appropriate kVp and mAs settings; using lead aprons and thyroid collars where indicated; using proper film holding devices and paralleling technique (reducing retakes due to poor positioning); and critically evaluating the indication for every radiograph to ensure diagnostic benefit outweighs radiation risk. The Ionising Radiations Regulations 2017 (IRR17) and the Ionising Radiation (Medical Exposure) Regulations 2017 (IR(ME)R 2017) in the UK provide the legal framework for radiation protection in dental practice. Operators, practitioners, and employers all have defined responsibilities. Referral criteria/selection criteria guidelines (such as those from FGDP(UK)) help clinicians justify radiographic examinations. MJDF Part 1 candidates are expected to understand both the scientific principles and the regulatory framework of dental radiography.

Question 4: On a periapical radiograph, which structure appears as a radiolucent crescent-shaped area around the apex of a non-vital tooth?

Condensing osteitis
Periapical granuloma (Correct answer)
Cementoma
Hypercementosis

Correct answer: Periapical granuloma

A periapical granuloma (and early periapical abscess) typically appears as a well-defined radiolucent area around the root apex, representing inflammatory tissue replacing normal bone in response to pulpal necrosis.

A periapical granuloma is the most common periapical lesion, resulting from pulpal necrosis and subsequent chronic periapical inflammation. Bacteria and their toxins from the necrotic pulp exit through the apical foramen, stimulating a chronic inflammatory response in the periapical bone, replacing it with granulomatous (inflammatory) tissue. Radiographic appearance: a well-defined or ill-defined radiolucent area at the root apex, typically less than 1cm in diameter, often with a narrow radiopaque border (lamina dura around the lesion may be maintained or lost). It appears dark because the inflammatory granulomatous tissue does not attenuate X-rays as well as bone. Differential diagnosis of periapical radiolucencies is important and includes: periapical granuloma (most common), periapical cyst (larger, often more well-defined and corticated, often >1cm), periapical abscess (may be associated with sinus tract, often less well-defined than granuloma), and keratocystic odontogenic tumour or other jaw cysts if not at the tooth apex. In contrast, condensing osteitis appears as a radiopaque area around the apex of a tooth with a chronic low-grade pulpitis — it represents a dense bone reaction to chronic low-level stimulation. Hypercementosis is excess cementum deposition on the root, appearing as root widening with maintained PDL space and lamina dura. Cementoma (periapical cemento-osseous dysplasia) progresses through radiolucent, mixed, and radiopaque stages. MJDF candidates must interpret these radiographic patterns accurately.

Question 5: Which of the following best describes the appearance of enamel on a radiograph?

Radiolucent — appears dark as enamel is less dense than dentine
Radiopaque — appears very bright/white as enamel has the highest mineral content of any body tissue (Correct answer)
Uniformly grey — same density as dentine but thicker
Radiolucent at the surface with a radiopaque core

Correct answer: Radiopaque — appears very bright/white as enamel has the highest mineral content of any body tissue

Enamel is the most highly mineralized tissue in the human body (96% inorganic mineral) and therefore appears as the most radiopaque (brightest/whitest) structure on a dental radiograph.

Dental radiographs display tissues based on their density and atomic number — denser, more mineralized tissues attenuate more X-rays and appear whiter/brighter (radiopaque), while less dense tissues allow more X-rays to pass through and appear darker (radiolucent). Enamel is 96% inorganic mineral (hydroxyapatite), making it the most radiopaque tissue in the body — it appears as the brightest white structure on a dental radiograph. Enamel is visible as the outer covering of the crown (it does not extend onto the root). Dentine is approximately 70% mineralized and appears less radiopaque than enamel but more radiopaque than pulp. On a radiograph, dentine forms the main bulk of the tooth and appears as a lighter grey than pulp but distinctly less bright than enamel. The pulp chamber and root canals contain soft tissue and appear radiolucent (dark). As patients age, secondary dentine deposition progressively narrows the pulp chamber and root canals, so they appear smaller on radiographs of older patients. Cementum has similar density to dentine and is not distinguishable from dentine on conventional dental radiographs. The periodontal ligament (PDL) space appears as a thin radiolucent line around the root, bounded by the radiopaque root cementum and the radiopaque lamina dura (compact cortical bone lining the tooth socket). Understanding radiographic anatomy is fundamental for MJDF Part 1 dental science questions.

Question 6: A panoramic radiograph (OPG) is MOST appropriate for:

Detecting early interproximal caries in posterior teeth
Overview assessment of all teeth, jaws, and TMJ in a single image (Correct answer)
Accurate measurement of individual tooth root lengths
Detecting hairline root fractures

Correct answer: Overview assessment of all teeth, jaws, and TMJ in a single image

The OPG (orthopantomogram) provides a broad overview of the entire dentition, alveolar bone, TMJs, sinuses, and mandibular condyles in a single extraoral image — ideal for screening and treatment planning.

The panoramic radiograph (OPG — orthopantomogram) is an extraoral tomographic technique that produces a single image showing a broad overview of the entire mouth and surrounding structures. The X-ray source and film/detector rotate around the patient's head in a programmed arc, with the focal trough capturing structures at the approximate curvature of the dental arches. Advantages of OPG: shows all teeth (including unerupted and impacted third molars), both jaws, TMJ condyles, maxillary sinuses, and the mandibular canal in a single image; low radiation dose; useful for patients with limited mouth opening; useful for children to assess developing dentition; good overview for treatment planning orthodontic, surgical, and implant cases. Limitations of OPG: inherently lower resolution than intraoral radiographs; geometric distortion and magnification vary across the image; patient movement causes blurring; structures outside the focal trough (thin curved zone) are blurred; not suitable for detecting early interproximal caries; cannot accurately measure root lengths for endodontic working length; cannot reliably detect hairline fractures. Indications per FGDP(UK) Selection Criteria include: assessment of third molars and other impacted teeth, orthodontic assessment, jaw fractures, periodontal overview, implant site assessment, and pathology screening. OPG should not replace periapical and bitewing radiographs for caries detection or periodontal assessment where more detailed views are needed. MJDF candidates must be able to select the appropriate radiograph type for specific clinical questions.

MJDF Dental Radiology and Imaging 2

Which type of radiograph provides the best view of the periapical region and surrounding alveolar bone?