Radiology & Radiation Protection Flashcards

What is the significance of 'lamina dura' in periapical radiographs?

Answer: A white line on the radiograph representing the dense cortical bone lining the tooth socket — loss of lamina dura indicates periapical pathology or periodontitis

The lamina dura (radiographic white line) represents the dense cortical bone (alveolar bone proper) lining the tooth socket. Its loss in the periapical region indicates periapical pathology; loss in the crestal region suggests periodontitis.

What is the purpose of the 'FGDP Selection Criteria for Dental Radiography'?

Answer: Evidence-based guidance for UK dentists on when radiographs are clinically justified — specific criteria for new patients, recall intervals, and specific clinical situations

The FGDP (Faculty of General Dental Practice, UK) Selection Criteria provide evidence-based guidance on clinical situations justifying radiographic exposures, including recall bitewing intervals, periapical indications, and specific clinical scenarios.

What is the dose-area product (DAP) and why is it recorded?

Answer: DAP measures the total radiation energy delivered (dose × area of beam) in mGy·cm² — recorded for quality assurance, dose optimisation, and IR(ME)R audit requirements

DAP (dose-area product) represents the absorbed dose multiplied by the area of the beam at the point of measurement, giving total radiation output. Recording DAP is required under IR(ME)R 2017 for audit and dose optimisation purposes.

What error on a periapical radiograph is caused by incorrect horizontal angulation?

Answer: Overlapping of adjacent tooth contacts — proximal surfaces of adjacent teeth appear superimposed rather than open

Incorrect horizontal angulation of the X-ray beam causes overlapping of adjacent proximal contacts, making it impossible to see interproximal surfaces clearly for caries detection. The beam must be directed through the contact points.

What radiation dose does a lateral cephalometric radiograph deliver compared to a periapical?

Answer: Cephalometric radiograph delivers approximately 2–5 µSv — similar to or slightly higher than a single periapical (1–8 µSv)

A lateral skull cephalometric radiograph delivers approximately 2–5 µSv effective dose, comparable to a small number of intraoral periapical radiographs. This relatively low dose supports its use in orthodontic treatment planning.

What is the difference between 'absorbed dose' (Gray) and 'effective dose' (Sievert) in radiation protection?

Answer: Absorbed dose measures energy deposited per unit mass (Gy); effective dose accounts for radiation type (weighting factor) and tissue sensitivity to allow comparison of biological risk across different exposures

Absorbed dose (Gray, Gy) = energy deposited per kg of tissue. Effective dose (Sievert, Sv) = absorbed dose × radiation weighting factor × tissue weighting factor — converting to a uniform risk basis enabling comparison across different types of exposure.