Dental Radiology and Diagnostic Imaging
Core concepts
Understand image formation, radiation physics, and principles of radiation protection (ALARA, collimation, lead apron, thyroid shield). Know intraoral techniques (paralleling, bisecting angle) and common errors (elongation, foreshortening, cone cutting, overlapping). Interpret periapical, bitewing, and panoramic images, plus CBCT indications. Recognize radiographic features of caries, periodontal bone loss, periapical lesions, cysts, and tumors.
Traps
Bisecting angle technique errors: too steep = foreshortening; too flat = elongation. Paralleling technique reduces distortion but may be uncomfortable. Panoramic images have magnification and are not for fine detail. CBCT is indicated for complex anatomy, implant planning, and impacted teeth, not routine caries diagnosis. Radiation dose: CBCT > panoramic > intraoral. Beware questions asking which technique best shows bone level (bitewings/periapicals).
Worked example
Rule of thumb: "Steep angle shortens the image (foreshortening); flat angle lengthens it (elongation)." If a stem shows a tooth that looks short and squat, the cause is excessive vertical angulation. For assessing interproximal caries, bitewing radiographs are the standard; for root canal anatomy and implant planning, CBCT is preferred.