Topic 1

Topic 1: History, Physics, & Infection Control

Speaker: Melissa Calhoun, RDH
Date: Calhoun, 2026

Chapter 1: Radiation History

History of Radiology

  • Wilhelm Conrad Roentgen

    • Discovered the X-ray in 1895.

Definition of Radiograph

  • A radiograph is a two-dimensional representation of a three-dimensional object.

  • Properties of X-ray:

    • An X-ray beam is an energy form capable of penetrating substances.

    • It records image shadows on an image receptor.

Uses of Dental Images

  1. Detect lesions.

  2. Evaluate growth and development.

  3. Confirm or classify suspected diseases.

  4. Illustrate changes due to caries, periodontal disease, or trauma.

  5. Localize lesions or foreign objects.

  6. Document the condition of a patient.

  7. Provide information during dental procedures.

  8. Aid in the development of a clinical treatment plan.

Timeline of Advancements in Radiology

  • 1895: W.C. Roentgen discovers the X-ray.

  • 1896: W.A. Price introduces the bisecting technique.

  • 1913: H.R. Raper proposes the bitewing technique.

  • 1920: O. Walkhoff produces the first dental radiograph.

  • 1925: W.J. Morton produces the first dental radiograph in the UK.

  • 1947: C.E. Kells conducts the first dental radiograph in the US.

  • 1955: Introduction of D-speed film.

  • 2001: Introduction of CBCT for dental use.

Chapter 2: Part 1: Radiation Physics

Atom Structure

  • An atom is the smallest component of an element.

  • Atoms combine to form molecules.

  • Each atom consists of:

    • A nucleus (positively charged central core).

    • Orbiting electrons.

Nucleus

  • Composed of:

    • Protons: Positively charged.

    • Neutrons: Neutral (no charge).

    • The nucleus contains nearly all the atom's mass.

Electrons

  • Electrons: Negatively charged particles.

    • Orbit around the nucleus in 3-dimensional structures (orbitals).

    • Shell designations: K, L, M, N, O, P, Q

    • The K shell has the strongest bond and the highest binding energy.

  • Removing an electron from its shell requires energy equal to or greater than the binding energy of that specific shell.

Radiation Concepts

  • Radiation: Emission and propagation of energy through space or a substance in the form of waves or particles.

  • Radioactivity: Process by which unstable atoms or elements undergo spontaneous disintegration or decay to achieve a more balanced nuclear state.

  • Ion: A charged particle that can be positive or negative.

    • Positive ion: An atom missing an electron.

    • Negative ion: An ejected electron.

Ionization

  • Ionization: Process by which an atom gains or loses electrons, becoming positively or negatively charged.

  • Ionizing radiation: Radiation that is high in energy and capable of producing ions.

    • Classified into: Particulate and electromagnetic radiation.

Types of Radiation
Particulate Radiation

  • Has mass and travels in straight lines at high speeds.

  • Includes:

    • Neutrons, protons, electrons, beta particles, gamma particles.

    • Cannot reach the speed of light and may carry a charge (except neutrons).

Electromagnetic Radiation

  • Has no mass or charge and travels at the speed of light.

  • Includes:

    • Radio waves, microwaves, visible light, UV rays, X-rays, gamma rays (ranked from low to high energy).

  • Only high-energy electromagnetic waves have ionizing capacities.

Electromagnetic Spectrum

  • Photons: Bundles of energy with no mass.

  • Wave Properties:

    • Velocity: Speed of the wave.

    • Wavelength: Distance between the crest of one wave and the crest of the next wave.

    • Frequency: Number of wavelengths that pass a certain point in a given length of time.

  • Longer wavelengths have lower penetrating power.

  • Shorter wavelengths have higher penetrating power and higher energy.

Characteristics of X-Rays

  • Invisible.

  • Travel at the speed of light.

  • High frequency and short wavelengths.

  • Capable of penetrating objects.

  • Can change cells.

Chapter 2: Part 2: X-ray Machine

X-ray Machine Components

  • Control Panel:

    • Contains on/off switch, milliamperage (mA), time, kilovoltage (kVp) settings.

    • Ampere (A): Number (quantity) of electrons.

    • Increase in amperage increases the number of electrons produced (typical dental machine operates at 5-8 mA, most are 7 mA).

    • Volt (V): Force moving electrons from cathode to anode.

    • Kilovoltage peak (kVp): Peak voltage of alternating current, determining speed and penetrating power of the X-ray beam.

X-ray Tube Components

  • Cathode (-):

    • Contains a tungsten filament which emits electrons.

    • Molybdenum cup/focusing cup directs electrons.

  • Anode (+):

    • Contains a tungsten target where electrons hit to produce X-rays.

    • Focal spot where X-rays originate.

    • Copper stem dissipates heat (X-ray production is 1% X-ray and 99% heat).

Electrical Currents

  • Direct Current (DC): Electrons flow in one direction through a conductor.

  • Alternating Current (AC): Electrons flow in two opposite directions.

  • Rectification: Conversion of AC to DC.

Transformers

  • Transformers: Devices used to adjust voltage.

    • Step-down Transformer: Decreases voltage for the filament circuit to 3-5 volts.

    • Step-up Transformer: Increases incoming voltage to 65,000-100,000 volts for the high-voltage circuit.

    • Autotransformer: Acts as a voltage compensator.

Types of X-rays Produced

  • Bremsstrahlung (General) Radiation:

    • Produced when an electron hits or passes close to the nucleus of a tungsten atom; constitutes about 70% of produced X-rays.

  • Characteristic Radiation:

    • Produced when a high-speed electron dislodges an inner-shell electron from a tungsten atom causing rearrangement of remaining electrons, occurring at 70 kV and above.

Definitions of X-Radiation

  1. Primary Radiation: The penetrating X-ray beam produced at the anode target.

  2. Secondary Radiation: X-radiation that results from the interaction of primary radiation with matter.

  3. Scatter Radiation: A form of secondary radiation that has been deflected from its original path.

Interactions of X-Radiation

  • No Interaction: X-ray passes through atom without affecting it.

  • Photoelectric Effect: Absorption of energy from X-ray, resulting in ejected photoelectrons.

  • Compton Scatter: Interaction resulting in a scattered photon and an electron, causing ionization of atoms.

  • Coherent Scatter: Low-energy photons passing through without ionization but can change the direction of the photon.

Chapter 16: Infection Prevention

Infection Prevention Basics

  • Importance of understanding the purpose of infection prevention protocols among dental professionals.

Rationale for Infection Prevention

  • Purpose: Prevent transmission of infectious diseases.

  • Transmission Routes:

    • Patient to dental professional.

    • Dental professional to patient.

    • Patient to patient.

Pathogen Definition

  • Pathogen: A microorganism capable of causing disease.

Conditions for Infection

  • For infection to occur, the following must be present:

    1. Susceptible host.

    2. Pathogen with sufficient infectivity and numbers.

    3. Portal of entry for the pathogen.

Guidelines for Prevention Practices

  1. Personal Protective Equipment (PPE):

    • Includes protective clothing, gloves, masks, eyewear.

  2. Hand Hygiene:

    • Routine washing, antiseptic rubs, antiseptic handwashing.

  3. Sterilization and Disinfection:

    • Addresses critical, semicritical, and noncritical instruments.

  4. Cleaning and Disinfection:

    • Use of intermediate and low-level disinfectants.

Infection Prevention Procedures

Before Exposure

  • Preparation of the treatment area, including equipment and supplies (e.g., dental chair, X-ray machine, lead apron).

  • Preparing the patient and radiographer (headrest adjustments, hygiene procedures, glove use, etc.).

During Exposure

  • Drying exposed receptors, collecting exposed items, and using beam alignment devices.

After Exposure

  • Disposal of contaminated items, handling of lead aprons, surface disinfection, and continuation of hand hygiene.

Procedures for Digital Imaging

  • Different protocols for wired sensors and PSP sensors in terms of infection control.