Radiology for the Dental Assistant Notes

Introduction to Dental Radiology

• Dental Radiology:
  • The part of dentistry dealing with the use of radiant energy (such as x-radiation) in the diagnosis and treatment of diseases of the head and neck.
• Radiograph:
  • A shadow picture produced by projecting the image of the teeth and their supporting tissues onto an image receptor (film, digital image receptor, etc.) by means of x-radiation.
• Dental Radiography:
  • The art or science of photographically recording images of the teeth and their surrounding structures through the use of x-radiation.

Intra-oral Radiography

• Periapical:
  • Records the entire tooth, including the crown, root apices, and at least 4mm (¼) of the bone surrounding the root apices.
• Interproximal (Bitewing):
  • Records equally the crowns of the maxillary and mandibular teeth and the crestal ⅓ of the alveolar process.
• Occlusal:
  • Demonstrates (or visualizes) a major portion of the maxilla and the mandible on one film.

Extra Oral Radiography

• Panoramic:
  • Presents the entire maxilla, mandible, and the surrounding bony structures and landmarks.
• Cephalometric:
  • Mainly used in Orthodontics to take measurements for tooth movement.
• Water's view:
  • Used in Surgery.
• PA Skull View:
  • Used for Orthodontic treatment and Surgery.

Radiolucent and Radiopaque

• Radiolucent:
  • Medium gray to black areas.
  • Allow more radiation to pass through and strike the film.
  • Examples:
    • Soft tissue
    • Air space
    • Pulp tissue
    • Mental foramen
• Radiopaque:
  • White or light gray structures.
  • Structures absorb the radiation (radiation does not reach the film).
  • Examples:
    • Cement base
    • Enamel
    • Amalgam
    • Bone

Parts of the X-ray Unit

• Control Panel:
  • Adjusts and controls the production of x-radiation.
  • Includes:
    • kVp readout (50-100)
    • mA control (10-15)
    • kVp control
    • Timer (3 impulses - 5 minutes)
• Arm:
  • Movable supporting member for the tubehead.
• Yoke:
  • Movable supporting structure.
• Tubehead:
  • Portion of the unit that produces x-rays.
• Beam Indicating Device (BID):
  • Traditional term used for any extension of the tubehead; intended to indicate the position, direction, and/or size of the radiation field.

How to Position the Tubehead

• Central Ray (CR):
  • An imaginary beam of x-rays traveling through the center of the BID.
• Vertical Angulation:
  • Refers to the position of the x-ray tubehead in a vertical plane with the CR directed from above or below the patient’s occlusal plane.
  • Positive Vertical Angle:
• Occlusal Plane:
  • Is a horizontal plane running from wall to wall between the patient’s maxillary and mandibular teeth parallel to the floor.
• Horizontal Angulation:
  • Refers to the position of the x-ray tubehead in a horizontal plane (from right to left).
• Midsagittal Plane:
  • A vertical plane running from floor to ceiling through the middle of the patient’s head.

Reference Points for Positioning the Head

• Corner of the Mouth - Tragus of the Ear Line:
  • Parallel to the floor when radiographing the mandibular teeth.
• Ala-Tragus Line:
  • A line used to position when radiographing the maxillary teeth.

Radiation Protection Guidelines

• The x-ray operator and the patient should be the only people in the treatment room during the radiographic procedure.
• A thyroid collar and lead apron are required for EVERY PATIENT.
• The operator should stand 6 feet away and not in direct line with the x-ray beam, behind a lead shield, or outside the room.

Infection Control in the Treatment Room

• PPE (Personal Protective Equipment):
  • Gown, Mask, Gloves
• Techniques to prevent cross-contamination:
  • Glove, take out the film and place it in a cup, remove gloves.
  • Re-glove, expose film.
  • Place exposed film on a paper towel on a barrier-covered counter.
  • Change gloves or use over gloves, place film in processor.
  • Remove gloves to mount film.

Infection Control in the Dark Room

• Place film or barrier on covered work surface.
• Change gloves or put on overgloves before opening the film packet.
• Remove gloves before handling processed film.

Factors in Image Quality

• Is the image sharp?
• Is the image the same size as the object?
• Is the image the same shape as the object?

Rules of Shadow Casting

• The source of radiation should be as small as possible.
• The source-to-object distance should be as long as practical.
• The object-to-film distance should be as small as possible.
• The object and film should be parallel to each other.
• The source should be directed perpendicular to the object and film.

Production of Radiation

• Radiation is produced by the collision of high-speed electrons with a target, producing x-rays.
• When this happens, high energy is given off: 1% radiation and 99% heat.

Electricity

• To produce x-rays suitable for dental radiograph, it is necessary to convert ordinary electricity into high-energy electrons (x-rays).
• Electricity is the flow of electrons through a wire.
• Electrical current:
  • The number of electrons flowing through the wire.
  • Ampere:
    • The number of electrons flowing through a wire in one second.
• Voltage:
  • Electrical pressure pushes electrons through the wire.
  • Electrical pressure pushing the electrons through the wire to heat it.
• Hertz (HZ):
  • Refers to the frequency or number of fluctuations occurring in the electrical pressure each second.

Production of Radiation - Components

• Cathode:
  • Tungsten wire filament, similar to inside light bulbs.
• Anode:
  • Positively charged to attract electrons.

Terms

• Absorption:
  • The disappearance of x-ray energy.
• Ionization:
  • A process whereby a photon collides with an orbital electron of a neutral atom or molecule and gives up its energy in the collision, causing the electron to be ejected from orbit.
• Quality:
  • The term used to describe the ability of the X-ray beam to penetrate various materials (short wavelength).
• Quantity:
  • A term used to express the amount or intensity of the beam of x-rays (number of positively charged ions in one second).
• Aluminum filter:
  • Selectively absorbs more of the long wavelengths radiation.
• Inverse square laws:
  • The intensity of radiation is inversely proportional to the squares of the distance from the source of radiation to the points of radiation intensity instrument.

Intraoral Film Packet

• Film packet:
  • Made of a water-resistant outer covering with a “pull” tab.
  • Contains a thin lead foil at the back of the packet, with black paper surrounding one or two pieces of film.
• Lead foil:
  • Used to absorb scatter radiation from the patient's head that could cause film fog.
• Embossed dot:
  • The surface of the film has a raised dot called the “embossed dot”.
  • This embossed dot is an aid in mounting the radiograph to determine right or left.

Film Speed

• Film speed:
  • Refers to the sensitivity of the film to x-radiation and is designated by a standardized code; a letter from A-F.
  • Speed group “F” film requires ½ the amount of radiation to produce a diagnostically acceptable radiograph when compared to the “D” speed film.
  • “A” speed film is the least sensitive to x-radiation.
  • “F” speed is the most sensitive.

Film and Emulsion

• The film inside a dental film packet consists of:
  • A flexible plastic (polyester) sheet called the BASE.
  • Photo-sensitive (silver halide) crystals that are sensitive to x-radiation.
  • A gelatin “glue” to stick to silver halide crystals to the base.
  • The silver halide crystals plus the gelatin “glue” make up the emulsion of the film.

Developing Solution

• The developing agent causes the entire crystal to turn into a chunk of metallic silver.
• The 2 main purposes are to:
  • Swell and soften the emulsion of the film.
  • Develop silver halide crystals containing a latent image.
• Developing solution:
  • Activator - swells and softens the emulsion.
  • Restrainer - prevents film fog.
  • Developing Agents - develops the exposed silver halide crystals.
  • Preservative - prevents deterioration of developing agents.

Fixing Solution

• The fixing solution stops all development of the image and leaves only the black and silver deposits in the emulsion.
• The 2 main purposes of the fixing solution:
  • Remove all undeveloped silver halide crystals from the emulsion.
  • Shrink and re-harden the emulsion to prevent scratching.
• Fixing solution:
  • Acidifier - stops development of the image.
  • Fixing agent - removes undeveloped silver halide.
  • Hardener - shrinks and re-hardens the emulsion.
  • Preservative - prevents deterioration of the fixing agent.

Manual Processing

• Develop for 5 minutes @68-70°F.
• Rinse for 20 seconds in water.
• Fix for 10 minutes.
• Wash for 20 minutes in water.
• Dry.

Manual Processing / Dip Method - What is needed

• Thermometer:
  • To determine developer temperature.
• Timer:
  • To accurately time processing intervals.
• Time-temperature processing chart:
  • Provides proper developing instructions.
• Stirring rods (2):
  • One for each developing & fixer, thoroughly mix/stir processing chemicals BEFORE films are processed.
• Tank cover:
  • Prevents exposure of chemicals to air and light.

Film Processing Steps

• Develop → Squeegee → Fixing → Squeegee → Wash → Dry
  • Squeegee: film passes between rollers that squeeze excess developer or fixer from the film emulsion

Automatic Film Processors

• Solution in the automatic processors must be changed and/or replenished at appropriate intervals depending on the number and size of films processed in the unit.
• ALWAYS FILL THE FIXER COMPARTMENT FIRST!!! FILL THE DEVELOPER COMPARTMENT LAST.
• Contamination of processing solutions results in a radiograph that is not fully developed, fixed, or washed.
• Such radiographs have poor contrast and tend to rapidly discolor with a characteristic brownish discoloration.

Digital Imaging in Dentistry

• The conventional radiographic image, such as a periapical or panoramic radiograph or photographic image captured on films is called “analog image”.
• Analog image:
  • Is one in which the various shades of gray blend smoothly from one to another.
• Digital image:
  • Has no existence outside of the computer where the image information exists only as a series of numerical values.

Types of Digital Systems

• Wired system:
  • CCD Based systems - charge-coupled device
  • CID based system - Charge injections device
  • CMOS Based systems - complimentary metal-oxide semiconductor
  • CMOS/APS - active pixel sensor
• Wireless System:
  • PSP Based system - photostimulable phosphor

Image Control Features

• Change image contrast
• Reverse the image (positive to negative)
• Apply special filters (Control image sharpness)
• Rotate the image
• Zoom/magnify the image
• Make linear & angular measurements
• Color enhanced (substitute color values for gray scales)
• The amount of radiation required to produce a digital image is significantly lower than absorbed dose for a conventional intraoral film.

Advantages of Digital Radiography

• Almost “instant” image visualization - less than 1 second
• The ability to manipulate the image in various ways
• Reduce patient exposure
• Elimination of the darkroom - reduce OSHA & EPA compliance issues
• Potential integration of the radiographic information into electronic data bases/ patient record system

Disadvantages of Digital Radiographs

• Small image detector size relative to conventional film sizes
• High implementation cost - equipment is expensive
• Storage of each Digital image requires a lot of disk space, or optical disk storage (write once read many WORM)
• Emerging technology - no standardized format, equipment becomes obsolete quickly
• Legal status of Digital Images is not clearly established

Quality Assurance in Dental X-Rays

• First step is to evaluate the darkroom:
  • White light leaks
  • Take some masking tape into darkroom
  • Turn out all lights, as your eyes adjust to darkroom, they will become sensitive to light
  • Tape all leaks with masking tape, around the door, plumbing fixtures, etc
  • Elimination of is a critical first step
• Second step:
  • Drain the old developing and Fixing solutions, clean the tanks and mix fresh solution to the manufacturers recommendations.

Safelight

• Safelight:
  • A low intensifying “white” light bulb placed behind a colored filter of some kind.
  • Safelights work because x-ray film emulsions are not sensitive to certain wavelengths of visible light.
  • Not every safelight is “safe” for all films. Consult the manufacturer’s recommendations for the appropriate safelight to be used in your office.
  • Remember the plastic cover/lid on the daylight loader of an automatic processor IS the safelight.

Testing the Safelight

• The coin-test:
  • A simple test used to determine whether films are being fogged by an improper safelight.
  • Room lights off and safelight on, unwrap a non-screen (pa) film and place the film on the countertop under the safelight.
  • Place a coin on top of the film and let the safelight expose the film for about 5 minutes.
  • Process the film.
  • If an image of the coin appears on the test, the film is fogged.
  • The safelight should be at least 4 feet away from where the films are being tested.

X-Ray Checker

• Checking Quality and Density Of X-Rays
  • An x-ray checker is an object that can be exposed to x-rays instead of a patient.
  • X-ray checker is used to identify when to change solutions.
  • As the film or checker film becomes light, solutions should be replenished.

Problem Solving - The PT Gags

• Be Calm
• Always start with the easiest film first
• Don't try to sneak the x-ray film
• Gagging is the normal is a normal reflex
• Distraction helps
• Place a small amount of salt on tip of tongue
• Use topical anesthetic (gel or liquid)
• Be Patient

Problem Solving - The PT is Tongue Tied

• Pt who are tongue tied have Ankyloglossia which means that the tip of the tongue is attached to the lingual surface of the mandible by a band of soft tissue.
• Solution:
  • Use a stiff film holding device and press the film down into the top of the tongue

Problem Solving - Missing Teeth

• This is an easy problem to solve: tear or cut a cotton roll to the width of the space and wedge the cotton roll onto the empty space.
• The Cotton Roll Serves as a substitute for the tooth and prevents the film holder from tipping into the space

Problem Solving - The PT has Tori

• Tori are normal bony growths usually found in the middle of the hard palate in the maxilla or in the canine-premolar region of the mandible.
• Place the film farther into the mouth to avoid the film contacting the sensitive tissue covering the torus.

Familiar Terms

• Density:
  • Overall darkness or lightness of a processed radiograph.
• Central Ray:
  • Imaginary stream of x-rays in the middle/center of the beam.
• Vertical Angulation:
  • The position of cone is up and down.
• Horizontal Angulation:
  • The position of cone is side to side.
• Wet Readings:
  • Radiographs that have been developed for the proper length of time and fixed for a few minutes.

Radiation Biology

• Radiation Biology:
  • Portion of science that studies the effect of ionizing radiation on living organisms.
• Atoms:
  • LEGO BLOCKS used to make the world. Everything in the world is made out of ATOMS.
• Molecules:
  • Can be small or big and can have a variety of different shapes and functions.
• Biologic Effects:
  • The result of damage to the biologically active molecules within a cell.
• Tissues:
  • Groups of the same kind of cell.
• Nucleus:
  • Considered to be more radiosensitive than the cytoplasm.
• Cell:
  • Smallest unit where these chemical reactions of life can occur is within the cell.

Factors Influencing Radiation Effects

• Host Factors:
  • Species of Animals
  • Type & sensitivity of tissues
  • Rate of Cell division
  • Phase of cell cycle
  • Intrinsic resistance
  • Nutrition
• Radiation Factors:
  • Type of Radiation
  • Total Dose
  • Penetrating Ability
  • Acute Vs. Chronic Exposure
  • Local area Vs. Whole body exposure
  • Ability to repair damage

Latent Period

• The Latent Period is the time between exposure to radiation and the time the biological effect becomes visible.
• It is important to remember that every “normal” cell has the ability to repair radiation damage to DNA or the cytoplasm. The lower the dose of radiation to the cell, the more the cell is in repairing the damage

Type and Sensitivity of Tissues

• Radiation biologists divide the human body into 2 basic types of tissues
  • Somatic Tissue:
    • Tissues of the body that are not passed from parent to children. EX: muscles, bones, salivary glands, kidneys, skin, etc. Basically any tissue that is not egg or sperm.
  • Genetic/Reproductive Tissues:
    • Include the female egg and the male sperm, which are passed from parent to offspring.
• Genetic radiation damage may be inherited by many generations of offspring with potentially greater effect

Tissue & Organ Radiation Sensitivity

• Radiation Sensitive - most sensitive
  • Blood forming {hematopoietic}
  • Small Lymphocytes
  • Reproductive tissue {ovaries & testes}
• Intermediate Sensitivity - a little less sensitive
  • Blood vessels
  • Glands
  • Connective tissues
  • Bone
• Radiation Resistant - least sensitive
  • Muscle
  • Nerve

Radiation Units and Measurement

• Exposure:
  • Refers to the amount of radiation received by an individual;
  • Amount of radiation that comes out of the x-ray unit and the person being irradiated.
• Dose:
  • The amount of energy actually absorbed or deposited within the cells of the body may be referred to as the “dose,” or “absorbed dose,” or equivalent dose.
• Absorbed Dose:
  • Typically used as an indication of potential harm.
• Equivalent Dose:
  • Special unit used to compare the biological effect of one kind of ionizing radiation relative to another kind.

Units of Radiation and Measurement

Effective Dose

• The effective dose:
  • An attempt to determine the “total body” risk of developing cancer and birth defects when a localized exposure to ionizing radiation has taken place.
• For dental radiographs, this effective dose is VERY, VERY SMALL.
• Effective Dose is measured in sievert {Sv}.
• The use of Long Rectangular BID results in an 80% lower risk compared to using a short BID.

Radiation Protection Concepts

• The goal of radiation protection:
  • To minimize the public health to excessive exposure to ionizing radiation.
• Maximum Permissible Dose [M.P.D.]
  • Radiation protection concept for people who work with various kinds of radiation. By definition M.P.D. is the amount of radiation that WILL NOT produce any serious or harmful effects in the person receiving it.

Radiation Protection Concepts - Exposure

• Occupationally Exposed:
  • Those people who are normally expected to use or work around radiation as a normal part of their job. [Dentists, Assistant, or Hygienists.]
• Non-Occupationally Exposed:
  • Those persons who do not work with radiation. [Receptionist]
• Note:
  • In the event of pregnancy, an occupationally exposed female would be permitted to receive the same dose as a non-occupationally exposed person.

Maximum Permissible Dose Whole body/ Genetic Exposure Limits

• Occupationally Exposed
  • 50 mSv or 5 rem/yr.
• Non-Occupationally Exposed
  • 5 mSv/yr or 0.5 rem/yr
• Pregnant Occupationally Exposed
  • 5 mSv/yr or 0.5 rem/yr

A.L.A.R.A.

• A.L.A.R.A. - As Low As Reasonably Achievable
  • Means that every reasonable measure will be taken to assure that occupationally and non-occupationally persons will receive the smallest amount of radiation possible.
• Background Radiation:
  • Every day we are exposed to radiation from within our environment.
  • Background radiation comes from outer space (cosmic radiation) from the earth (terrestrial radiation) and from the food we eat (internally deposited radioactivity.)

Radiation Protection - Patient

• Use “F” speed film. It requires 50% less radiation
• Use Time - Temperature Processing
• Properly Filter The Beam Of Radiation
• Properly Collimate The Beam Of Radiation
  • Rectangular collimation is preferred because it reduces the area of the patient’s face exposed to radiation compared to a round open cylinder.

Radiation Protection - Patient - Continued

• Do not use pointed plastic cones / PID - produce twice as much scatter radiation
• Long Bid- LONG RECTANGULAR BID ARE PREFERRED
• Use High Kilovoltage- in the range of 75-90 kVp will reduce skin exposure by 40-50% compared to units operating at 60 kVp or less

Radiation Protection - Patient - Continued Again

• Use Electronic Timers- Do not use Mechanical / Spring wound timer
• Use Film Holding Devices
• Use Leaded “BODY” Aprons will reduce genetic exposure by 90% - 98%
• Leaded “Thyroid Collar” will reduce thyroid exposure by 50%

Radiation Protection - Operator

• Stand at least 6 feet away from beam of radiation & the patient’s head during exposure.
• Stand outside the room during exposure IF YOU CAN NOT GET 6 FEET AWAY.
• Never stand in direct line with the beam radiation.
• Never hold films in the patient's mouth.
• Never hold or stabilize the tubehead during exposure.
• Don’t forget you also have a DNA damage repair system within your cell.

Panoramic Radiograph

• Panoramic x-ray units produce a radiograph of the entire maxilla and mandible on one film. The panoramic unit requires that the source of radiation be motionless and the film move around the patient’s head.
• Panoramic Radiograph:
  • Beam of radiation - narrow slit, exposes very small portion of film and patient at one time.
  • Film - requires intensifying screens
  • Film placement - extra-oral
  • Object to film distance - varies
  • Source to film distance - fixed distance
  • Exposure - depends on unit
  • Image quality - fair to moderate

Panoramic Anatomic Landmarks

• Mental Foreman
• Nasal Fossa
• Mandibular Canal
• Zygomatic Arch
• Coronoid Process
• Incisive Foramen
• Internal Oblique Line
• Lateral Pterygoid Plate
• Styloid Process
• Palate
• Hamular Process

Processing Errors

• Too dark (fogging)
• Mottle “noise”
• Dark rectangular area on film
• Dark edge on film
• Fingerprints
• Dark spots
• White spots
• Clear streaks, splotches, or scratches
• Dark spots in random or comet pattern
• Dark spots in a pattern
• Under-developed:
  • Lighter than normal.
• Over-developed:
  • Darker than normal.
• Under-fixed:
  • Results in an incomplete removal of undeveloped silver halide crystals from the emulsion of the film.
• Over-fixed:
  • Results in a clear film.

Correcting Processing Errors

• Under-developed:
  • Lighter than normal film
  • To correct - use fresh developing solution, process for the correct amount of time, and the proper temperature.
• Over-developed:
  • Darker than normal film
  • To correct - use proper time temperature and follow the manufacturer's instructions.

Correcting Over and Under Fixing Errors

• Over-fixing:
  • Results in an incomplete removal of undeveloped silver halide crystals from the emulsion of the film producing a film that appears washed out.
  • To correct, place film in the fixer for the proper time.
• Under-fixing:
  • Produces an image that is milky- that is not transparent
  • To correct-place film in the fixer twice as long as that of the developer.

Other Processing Errors

• Chemical Stains:
  • Improper processor maintenance may lead to the production of irregular stains on the film.
• Debris on Film:
  • Improper processor maintenance may lead to the deposition of chemical debris by the rollers of the film processor on the surface of the film.
• Films Stick Together:
  • Feeding films into the automatic processor to quickly
• Black Paper on Film:
  • Failure to concentrate on the task at hand may lead to processing the film with the black paper still on it.

Review of Exposure Errors

Exposure Errors - Double Exposure and Backward Film

• Double Exposure:
  • When an x-ray has been exposed twice - showing two images
  • Correction - be careful keeping exposed and unexposed films separate.
• Backward Film:
  • Herringbone effect or tire track pattern on the film
  • To correct, look at the film packet and ensure the white or plain surface is facing the BID.

Exposure Errors - Bent Film

• Bent Film:
  • Result of excessive pressure on the film in one area of the x-ray film
  • To correct, careful placement of the film tells the patient to close slowly and lightly, placing a cotton roll under the film holder if necessary to hold film in place

Cone Cut

• Partial image
• Caused by improper vertical angulation and not proper posting of the BID

Overlapped

• Caused by not directing the BID/PID between contact point. Horizontal angulation error.