Radiation Health and Safety (RHS)
Production and dose
X-rays are produced when electrons from a heated tungsten filament (thermionic emission) accelerate toward a tungsten target. mA controls the number of x-rays produced (quantity and density); kVp controls their energy, meaning penetration and contrast scale; exposure time interacts with both. Raising kVp darkens the image across a wider range of tissue thicknesses and lowers patient dose for a given density compared with raising mA.
Protection. ALARA governs every decision: fastest available receptor speed, rectangular collimation when possible, 2.75-inch round collimation otherwise, filtration of at least 2.5 mm aluminum equivalent on units operating at 70 kVp or above, lead apron with thyroid collar, and a 16-inch position-indicating device. The operator stands at least 6 feet from the tubehead and out of the primary beam, ideally behind a barrier. No one holds a receptor in a patient's mouth.
Technique and errors. Paralleling gives the most accurate image; bisecting uses the angle rule so the receptor and tooth appear equal in length. Insufficient vertical angulation elongates the image, excessive angulation foreshortens it, incorrect horizontal angulation overlaps contacts, a cone cut means the PID was misdirected, and a herringbone pattern means the film was placed backwards. Overexposure looks dark, underexposure light, and fog follows light leaks or a failing safelight.
Processing and interpretation. Manual processing depends on time and temperature: developer, rinse, fixer, wash, dry. A sudden temperature change causes reticulation. Digital sensors and phosphor plates skip the chemistry but not the technique. Mount films with the embossed dot facing the viewer so the image reads as though you were facing the patient; maxillary sinus, zygomatic process, and mandibular canal are common landmarks.
Rule of thumb
Before blaming the machine, check technique: elongation means the angulation was too shallow, foreshortening means it was too steep, overlap means horizontal angulation was off.