Dental Radiography and Imaging

ALARA stands for As Low As Reasonably Achievable and is the cornerstone of radiation safety in dentistry. It has three components: Time (minimize exposure duration and frequency; use digital sensors that require less exposure than film), Distance (increase the distance between the X-ray source and the patient's body; stand behind a barrier during exposure), and Shielding (use lead aprons and thyroid shields for every patient). Dental X-rays deliver extremely low radiation doses compared to medical imaging, but cumulative exposure over a lifetime matters. ALARA compliance involves selecting the lowest milliamperage (mA) and kilovoltage (kVp) settings that still produce diagnostic images, using fast film speeds or sensitive digital sensors, limiting retakes by proper positioning, and maintaining equipment calibration. Following ALARA protects patients, staff, and your license.

Intraoral radiographs are taken with the X-ray sensor or film positioned inside the mouth and are the most commonly used in general dentistry. Types include: periapical (PA) images showing the entire tooth crown and root for diagnosing cavities, bone loss, and endodontic treatment; bitewings showing the crowns and interproximal (between-tooth) areas for cavity detection; and occlusal images of the entire arch from above or below. Intraoral images provide high detail and are essential for treatment planning. Extraoral radiographs are taken with the sensor outside the mouth and include panoramic (showing all teeth and bone in one image for survey and implant planning), cephalometric (jaw and skull for orthodontics), and CBCT (three-dimensional cone beam imaging for complex cases). Panoramic images are fast and good for screening but have less detail; CBCT is gold standard for implants and complex surgical cases but carries higher radiation dose. Most general practices use periapical and bitewings for routine care and panoramic for new patients or implant planning.

Proper positioning is key to avoiding retakes. Start by seating the patient upright with the spine straight and occlusal plane parallel to the floor. For periapical images, place the bite block (indicator arm) to establish the vertical and horizontal angulation (usually 45 degrees vertical for anterior teeth, 30 degrees for posterior). The aiming ring ensures the X-ray beam passes through the tooth and exits the cheek at a predictable location. For bitewings, the horizontal angulation is critical to open the interproximal contacts so cavities are visible; angle the cone tip to bisect the angle between the buccal and lingual tooth surfaces. For panoramic imaging, the patient's chin rests on the chin cup with the occlusal plane parallel and the Frankfort plane (top of ear canal to below the eye) level with the floor. Small rotations or tilts cause distortion and repeats. Practice on a phantom skull or manikin before patients. Always check positioning on a preview image before making the final exposure.

Cone cut (part of the image is blank): aiming ring misalignment; ensure the indicator rod is parallel to the bite block. Foreshortening (tooth looks too short): vertical angle too steep; decrease the angle or use a longer source-to-image distance. Elongation (tooth looks too long): vertical angle too flat; increase the angle. Overlapping interproximal contacts: horizontal angle aimed too mesially or distally; adjust the horizontal angulation to open contacts. Blur or motion: patient movement during exposure or operator movement of the handheld unit; ask the patient to hold still and stabilize your hand with the other arm. Double image or ghost shadows on panoramic: patient rotation; ensure the patient is centered on the midline and the occlusal plane is level. Herringbone pattern: film or sensor inserted backwards; always check the sensor orientation. Fogged or dark images: exposure setting too high or processing error; verify mA and kVp on the equipment before each patient. Light images: exposure too low; increase mA or time or check for automatic exposure control (AEC) malfunction.

Digital radiography captures X-ray images on a sensor rather than film, allowing instant preview, adjustment, and storage on the EHR. Processing tools include: brightness and contrast adjustment (darker or lighter areas can be corrected without retaking), magnification for small details, window-and-level adjustment to highlight bone or tooth structure, and even colorization to help identify specific pathology. Software also allows annotation (marking areas of concern), measurement tools for implant planning, and comparison with previous images side-by-side to track changes over time. Filters such as edge enhancement highlight caries and bone margins. Digital images use 50–70% less radiation than traditional film because of the efficiency of the sensor. However, processing can mask poor technique or overexposure; always start with the best-quality raw image you can capture, then enhance as needed. Over-processing can introduce artifacts that mimic pathology.

Patient consent is required before taking radiographs; explain the frequency, reason, and low radiation dose. Risk-benefit: routine bitewings on all patients is no longer standard; take radiographs based on clinical indication (cavity risk, symptoms, treatment planning). Pregnant patients can receive radiographs if necessary (use a lead apron and thyroid shield), but avoid elective radiographs during the first trimester. Document radiographs in the patient's chart, including type, date, and number taken. Radiographs are legal property of the dentist or practice and must be retained as part of the patient's record (typically 7–10 years). If a patient requests a copy to take to another provider, provide a duplicate for a fee. Equipment must be regularly calibrated and inspected for safety; dosimeters should be worn by staff to monitor cumulative exposure. Staff must complete radiation safety training annually. Radiographs must be stored securely to comply with HIPAA.

CBCT (Cone Beam Computed Tomography) is three-dimensional imaging that produces a volumetric dataset of the head and neck, allowing cross-sectional slices in any plane and 3D reconstruction. Indications include implant planning (bone volume and proximity to sinuses/nerves), impacted teeth (canines, wisdom teeth, supernumeraries), complex oral pathology (cysts, tumors), orthognathic surgery planning, temporomandibular joint (TMJ) imaging, and airway evaluation. CBCT delivers 100–600 times more radiation than a single periapical radiograph, so it is used judiciously, not for routine screening. Advantages: precise bone anatomy, soft tissue visualization, virtual implant placement, and guided surgery tools. Disadvantages: high cost ($200–500 per scan), higher radiation, and need for specialized training in interpretation. Many practices outsource CBCT to imaging centers; some general practices and specialists own in-house units. CBCT images are typically reviewed by the dentist or specialist, though some practices employ a radiologist for formal interpretation.