Modern Dental Assisting, 14th Edition

Foundations of Radiography, Radiographic Equipment, and Radiation Safety

Key Terminology

• ALARA concept: Concept of radiation protection that states all exposures should be kept "as low as reasonably achievable".
• ampere: A unit of electric current.
• anode (AN-ode): Positive electrode in the x-ray tube.
• atom: Basic unit of matter.
• bremsstrahlung radiation: "Braking radiation"; the sudden deceleration of electrons as they interact with highly positively charged nuclei.
• cathode (KATH-ode): Negative electrode in the x-ray tube.
• central ray: X-rays at the center of the beam.
• contrast: Differences in degrees of blackness on an image.
• control panel: Portion of the x-ray unit that contains the master switch, the indicator light, the selector buttons, and the exposure button.
• density: Overall darkness or blackness of an image.
• dental radiography (ray-dee-OG-ruh-fee): Process of recording images of the teeth and adjacent structures by exposure to x-radiation.
• digital imaging: Filmless method of capturing an image and displaying it by using an image receptor, an electronic signal, and a computer to process and store the image.
• distortion: Change in the size of an image caused by incorrect angulation.
• dose (of radiation): Amount of energy absorbed by tissues.
• dosimeter: Device used to detect and measure an accumulated dosage of radiation.
• electron: Negatively charged particle in the atom.
• energy: Ability to do work.
• extension arm: Flexible arm that is attached to the x-ray tubehead.
• genetic (jNE-tik) effects: Effects of radiation that are passed on to future generations through genetic cells.
• image: Film-based or digitally produced recording of anatomic structures.
• image receptor: Recording medium for an image, normally film, phosphor storage plate, or a digital sensor.
• intensity: Total energy of the x-ray beam.
• ion (EYE-on): Electrically charged particle.
• ionization (eye-uh-ni-ZAY-shun): Process by which electrons are removed from atoms, causing the harmful effects of radiation in humans.
• ionizing (EYE-uh-nye-zing) radiation: Radiation that produces ionization, resulting in harmful effects.
• kilovoltage (KIL-uh-voel-tuj) peak (kVp): Highest voltage of x-ray tube used during an exposure.
• latent (LAY-tent) period: Time between exposure to ionizing radiation and appearance of image.
• lead apron: Device used to protect the reproductive and blood-forming tissues from scatter radiation.
• magnification: Proportional enlargement of an image.
• master switch, indicator light, selector buttons, exposure button: Components of control panel.
• matter: Anything that occupies space and has form or shape.
• milliampere (mil-ee-AM-peer) (mA): One one-thousandth ($\frac{1}{1000}$) of an ampere; a unit of measurement used to describe the intensity of an electrical current.
• penumbra (puh-NUM-bruh): Blurred or indistinct area that surrounds an image.
• personal radiation monitoring badge: Device that measures exposure of personnel to ionizing radiation by measuring the intensity of visible light emitted from a crystal in the detector when heated; the intensity of light emitted depends on the radiation exposure.
• photon (FOE-ton): Minute (tiny) bundle of pure energy that has no weight or mass.
• primary beam / primary radiation: Most penetrating beam produced at the target of the anode.
• quality (of x-ray beam): Mean energy or penetrating ability of the x-ray beam.
• quantity (of x-ray beam): Number of x-rays produced in the dental unit; the quantity of x-rays produced is controlled by milliamperage.
• radiation: Forms of waves of energy emission through space or material.
• radiograph (RAY-dee-oe-graf): Image produced on photosensitive film by exposing the film to radiation and then processing it.
• radiology (ray-dee-OL-uh-jee): Branch of medicine that uses imaging technology to diagnose and treat disease.
• scatter radiation: Form of secondary radiation that occurs when an x-ray beam has been deflected from its path by interaction with matter.
• secondary radiation: X-radiation that is created when the primary beam interacts with matter.
• sensor: Solid-state image receptor that contains a silicon chip with an electric circuit.
• sharpness: Measure of how well an image reproduces the fine details or outline of an object.
• somatic (soe-MAT-ik) effects: Effects of radiation that cause illness and are responsible for poor health (such as cancer, leukemia, and cataracts) but are not passed on to offspring.
• thyroid collar: Flexible lead shield that is placed securely around the neck.
• tubehead: Part of the x-ray unit that contains the x-ray tube, the high-voltage and low-voltage transformers, and insulating oil.
• tungsten target: Focal spot in the anode.
• x-radiation: High-energy ionizing electromagnetic radiation.

Clinical Uses of Dental Images

• Dental Caries Detection: Detects dental caries on any surface of tooth structure, especially interproximal surfaces and beneath existing restorations that cannot be visually seen.
• Periodontal Assessment: Identifies periodontal disease involving bone loss in its early stages.
• Pathology Identification: Locates pathological abnormalities in surrounding hard and soft tissues.
• Growth Evaluation: Evaluates the growth and development of teeth.
• Intra-Procedural Status: Provides clinical status during a dental procedure, such as root canal therapy.
• Legal Record: Serves as a legal document of a patient's condition at a specific point in time.

Principles of X-Radiation Production and Physics

• Matter and Energy: Matter is defined as anything that occupies space and has form or shape. Energy is the ability to do work.
• Atomic Structure: The atom is the basic unit of matter, consisting of two main parts: a central nucleus and orbiting electrons (negatively charged particles).
• Ionization Process: Ionization occurs when electrons are removed from atoms, resulting in an electrically charged particle called an ion. Ionization is the mechanism responsible for the harmful biologic effects of radiation in humans.
• Main Components of a Dental X-Ray Unit:
  • Tubehead: Contains the x-ray tube, high-voltage and low-voltage transformers, and insulating oil. X-rays are produced inside the tubehead at the tungsten target (focal spot) located on the positive electrode (anode).
  • Extension Arm: A flexible arm attached to the tubehead that houses electrical wires and allows for precise positioning of the tubehead.
  • Control Panel: Houses the master switch, indicator light, selector buttons, and exposure button.
• Position Indicator Device (PID): Attached to the tubehead to direct and aim the central ray of the x-ray beam toward the image receptor.
• X-Ray Production Sequence: Initiated by engaging the exposure button, causing electrons to accelerate across the cathode-anode gap and strike the tungsten target, generating bremsstrahlung radiation ("braking radiation") and primary radiation.
• X-Ray Beam Characteristics:
  • Kilovoltage Peak (kVp): Controls the highest voltage, mean energy, penetrating ability (quality), and image contrast.
  • Milliamperage (mA): Controls the quantity of x-rays produced ($1\,\text{mA} = \frac{1}{1000}\,\text{A}$) and regulates overall image density.
  • Intensity: Represents the total energy of the x-ray beam per unit area per unit time.
• Geometric Image Characteristics:
  • Sharpness: Accuracy with which fine details or outlines of an object are reproduced.
  • Magnification: Proportional enlargement of an image.
  • Distortion: Change in true size or shape caused by incorrect angulation.
  • Penumbra: Unsharp, blurred, or indistinct area surrounding an image edge.
• Interaction of X-Rays with Matter: Four distinct effects can occur when x-rays interact with matter, including scatter radiation and secondary radiation.

Radiation Safety and Biologic Effects

• Biologic Effects:
  • Somatic Effects: Produce illness and poor health conditions (such as cancer, leukemia, and cataracts) in the exposed individual; these effects are not passed on to offspring.
  • Genetic Effects: Radiation-induced genetic cell mutations passed on to future generations.
• Latent Period: The time interval between initial exposure to ionizing radiation and the clinical appearance of biologic tissue damage.
• Critical Organs: Specific tissues highly sensitive to radiation exposure that must be protected during dental exposures.
• Radiation Dosimetry and Measurement: Measured using devices such as a personal radiation monitoring badge or a dosimeter. Badges determine exposure by measuring the intensity of visible light emitted from a crystal in the detector when heated.
• Patient and Operator Protection:
  • ALARA Concept: Mandates keeping all exposures "as low as reasonably achievable".
  • Protective Devices: Lead apron protects reproductive and blood-forming tissues from scatter radiation; flexible thyroid collar shields the neck and thyroid gland.

Digital Imaging, Dental Film, and Radiographic Processing

Key Terminology

• automatic processor: Machine that automates all film-processing steps.
• beam alignment device: Assists in the positioning of the position indicator device.
• bitewing image: View that shows the crowns of both arches on one film.
• calcium tungstate: Common type of phosphor.
• cassette: Contains extraoral films during exposure.
• cephalometric film: Shows the bony and soft tissue areas of the facial profile.
• charge-coupled device (CCD): Solid-state image sensor used in intraoral digital imaging.
• digital image: Electronic signals captured by sensors and displayed on computer monitors.
• digitize: Scanning of traditional film-based radiographs into a digital image.
• duplicating film: Film designed for use in film duplicating machines.
• emulsion (ee-MUL-shun): Coating on the x-ray film that contains energy-sensitive crystals.
• extraoral film: Film designed for use in cassettes.
• film speed: Amount of radiation required to produce a radiograph and the exposure time.
• intensifying screen: Part inside an extraoral cassette that converts x-ray energy into visible light, which in turn exposes screen film.
• intraoral film: Film designed for placement in the patient's mouth.
• label side: Colored side of the film that faces the tongue.
• latent image: Invisible image on the x-ray film after exposure but before processing.
• occlusal: Radiographic view that shows large areas of the maxilla or mandible.
• panoramic: Used in cassettes to provide a wide view of both the upper and lower jaws.
• periapical (ree-AP-i-kul): Radiographic view that shows the crown, tip, and surrounding structures.
• phosphor storage plate (PSP): Reusable film-sized storage plate that converts film-based imaging to a digital format.
• positioning instruments: Intraoral devices used to position and hold the film, sensor, or PSP.
• processing: Series of steps that change exposed film into a radiograph; steps include developing, rinsing, fixing, washing, and drying.
• radiograph (RAY-dee-oe-graf): Image produced on photosensitive film by exposing the film to radiation and then processing it.
• tube side: Solid white side of the film packet that faces the x-ray tube.

Digital Radiography Transition & Statistics

• Transition Timeline: The transition from traditional film to digital radiography has taken place over the last $30\,\text{years}$.
• Adoption Statistics: Currently, $66\%$ of dentists use digital x-ray procedures, whereas $34\%$ still use traditional film.
• Fundamental Nature: Digital images are not radiographs, but electronic signals captured by sensors and displayed almost instantaneously on computer monitors.

Advantages and Disadvantages of Digital Imaging

• Advantages:
  • Immediate Viewing of Images: Eliminates processing delays associated with film. Charge-coupled devices (CCDs) allow immediate viewing. (Note: Phosphor storage plates require scanning in a dedicated processing device prior to computer display).
  • Less Radiation: Sensors are more sensitive to x-rays than film; exposure times are $70\%$ to $80\%$ less than conventional film, significantly reducing patient absorbed dose.
  • No Chemicals: Eliminates the darkroom, hazardous chemical solutions, odors, and processing solution maintenance.
  • No Processing Errors: Prevents darkroom errors such as light leaks, stuck films, chemical contamination, or mechanical film damage.
  • Ability to Enhance Images: Dentists can modify contrast (lighter/darker), enlarge sections, apply color enhancements, and use images for chairside patient education.
  • Rapid Communication: Images can be emailed to consulting practitioners in minutes while the patient remains in the dental chair.
  • No More Lost Films: Secure digital software backups prevent the permanent loss of patient records.
  • Remote Consultation Capability: Teledentistry allows electronic transfer of records for insurance processing and expert consultations.
• Disadvantages:
  • Equipment Cost: High initial financial investment for hardware, digital sensors, and software.
  • Converting Previous Records: Scanning historical paper/film records into digital files is labor-intensive and costly; recommended to be completed gradually during patient recall appointments.
  • Software Learning Curve: Time required for dental staff to master manufacturer software programs.
  • Thickness and Rigidity of Sensors: Rigid CCD sensors can cause patient discomfort during placement. PSPs are thinner but lack instantaneous viewing capabilities.

Traditional Dental Film and Processing Procedures

• Intraoral Film Composition: Emulsion layer containing energy-sensitive crystals that store radiation energy as an invisible latent image until chemical processing.
• Film Packet Anatomy: Has a solid white tube side facing the x-ray tube and a colored label side facing the tongue.
• Extraoral Film: Uses rigid cassettes equipped with intensifying screens (e.g., containing calcium tungstate phosphor) that convert x-rays to visible light to expose screen film. Examples include panoramic and cephalometric films.
• Five Steps of Manual Processing: Developing, rinsing, fixing, washing, and drying.
• Automatic Processing Protocol:
  1. Insert exposed film packets into alternate slots slowly to prevent jamming and overlap.
  2. In the darkroom/daylight loader, remove lead foil and place it into a designated disposable container.
  3. Drop exposed films onto a clean paper towel.
  4. Wrap contaminated paper towels and gloves away, placing them into a second cup to prevent cross-contamination.
  5. Handle films strictly by the edges/corners to avoid fingerprints and scratches.
  6. Allow $4\text{ to }6\,\text{min}$ for the full automated processing cycle to complete.
  7. If drying manually, hang films at room temperature in a dust-free environment or use a film dryer; confirm complete drying prior to mounting.

Legal Issues, Quality Assurance, and Infection Prevention

Key Terminology

• artifact: Blemish or unintended radiographic image that is not present in the actual structure.
• confidentiality: Keeping personal information private about the patient.
• disclosure: Process of informing the patient, for example, the procedure for taking x-rays.
• image receptor: Recording medium for an image—a digital sensor, a phosphor storage plate (PSP), or conventional dental x-ray film.
• informed consent: Permission granted by a patient after being informed about the risks, benefits, and alternatives of a procedure.
• liability: Accountability or legal responsibility.
• malpractice: Professional negligence.
• negligence: Failure to provide a proper or reasonable level of care.
• phosphor storage plates (PSPs): Reusable film-sized flexible plates coated with phosphor as the image receptor.
• positioning devices: Intraoral devices used to position and hold the film, sensor, or PSP.
• quality assurance (QA): Plan to ensure that the dental office produces consistent, high-quality images with a minimum of exposure to patients and personnel.
• quality control tests: Specific tests used to ensure quality in dental x-ray equipment, supplies, and film processing.

Legal Considerations and Patient Management

• Federal and State Regulations: Regulates dental x-ray equipment installations, maintenance, and operator licensure requirements for dental assistants.
• Legal Liability: The dentist is legally responsible (respondeat superior) for all actions performed by dental staff. All radiographs must be prescribed by the dentist.
• Risk Management Protocol:
  • Disclosure & Informed Consent: Full disclosure of procedure details, benefits, risks, and alternative options must be explained to the patient prior to obtaining informed consent.
  • Patient Record Documentation: Every exposure must be documented, including the number of images, type of view, date exposed, and clinical rationale.
  • Patient Refusal: If a patient refuses prescribed radiographs, the dentist cannot provide care without diagnostic images, as treating without proper imaging constitutes negligence.

Quality Assurance (QA) and Infection Control

• Quality Control Tests: Regular monitoring of x-ray machines, darkrooms (light tightness), image receptors, cassettes, and processing solutions to prevent artifacts and unintended radiation exposure.
• Infection Prevention Standards: Centers for Disease Control and Prevention (CDC) guidelines require standard infection control practices across all clinical operations:
  • Surface barrier protection and disinfection of radiographic operatory equipment.
  • Strict cross-contamination protocols during sensor/plate handling, darkroom film unwrapping, daylight loader operations, and PSP scanning procedures.

Intraoral Imaging Techniques and Anatomic Principles

Key Terminology

• angulation: Alignment of central ray of x-ray beam in horizontal and vertical planes.
• bisecting (bisection of the angle) technique: Intraoral technique of exposing dental images where the x-ray beam is directed perpendicular to an imaginary line which bisects the angle.
• bitewing: Type of image used for interproximal examination.
• central ray: X-ray at center of beam.
• contact area: Area of the mesial or distal surfaces of a tooth where it touches an adjacent tooth in the same arch.
• crestal bone: Coronal portion of alveolar bone found between teeth.
• diagnostic quality: Referring to images with the proper structures and necessary density, contrast, definition, and detail for diagnostic purposes.
• interproximal: Between two adjacent surfaces.
• intersecting: Cutting across or through.
• long axis of the tooth: Imaginary line dividing the tooth longitudinally (vertically) into two equal halves.
• occlusal: Technique used to examine large areas of the maxilla or mandible.
• parallel: Moving or lying in the same plane, always separated by the same distance.
• paralleling technique: Intraoral technique of exposing periapical and bitewing images where the x-ray beam is directed to the tooth and film which are parallel to the long axis of the tooth.
• perpendicular: Intersecting at or forming a right angle ($90^\circ$).
• positioning instrument: Intraoral device used to position and hold the film, sensor, or phosphor storage plate.
• right angle: Angle of $90^\circ$ formed by two lines perpendicular to each other.

Full-Mouth Survey (FMX)

• Comprehensive Dental Exam: The full-mouth survey (FMX) is the preferred radiographic procedure for a comprehensive dental examination.
• Composition: Contains both periapical views and bitewing views.
• Individualization: Exact number of views varies based on dentist preference, oral anatomy, number of present teeth, and selected exposure technique.

Intraoral Radiographic Projections and Techniques

• Periapical Radiographs:
  • Coverage: Displays the entire tooth crown, root tip, and surrounding bone structures up to $2\text{ to }3\,\text{mm}$ beyond the apex.
  • Clinical Utility: Diagnoses pathologic conditions of root and bone, monitors tooth formation/eruption, and is essential for endodontics and oral surgery.
  • Paralleling Technique: The primary choice technique. Five basic rules mandate placing the receptor parallel to the long axis of the tooth and directing the central ray perpendicular ($90^\circ$) to both, using extension-cone paralleling (XCP) instruments.
  • Bisecting Technique: Placement where the receptor touches the tooth, creating an angle. The central ray is directed perpendicular ($90^\circ$) to an imaginary line that bisects the angle formed between the long axis of the tooth and the image receptor. Incorrect PID angulation causes foreshortening, elongation, or overlapping.
• Bitewing Radiographs:
  • Coverage: Shows crowns of maxillary and mandibular teeth in occlusion, interproximal contact areas, crestal bone, and a small portion of the root.
  • Clinical Utility: Detects interproximal caries, early periodontal bone loss, recurrent decay beneath restorations, and restoration margins.
  • Angulation: Positioning instruments or bitewing tabs are utilized with a standard recommended vertical angulation of $+10^\circ$ to compensate for the slight tilt of the upper crowns.
• Occlusal Radiographs: Captures large anatomic areas of the maxilla or mandible on a single large image receptor.

Special Patient Modifications

• Physical/Developmental Needs: Requires custom adjustments in receptor placement and machine stability, including the use of portable imaging systems when indicated.
• Pediatric and Edentulous Patients: Modified image receptor size, reduced exposure settings, and specific positioning adjustments for primary dentition or edentulous arches.
• Endodontic Modifications: Special positioning devices to accommodate rubber dams and endodontic instruments.
• Gag Reflex Management: Implementation of rapid placement, proper breathing instructions, and clinical management strategies to alleviate gagging.