RADT W3 Ch 9, 1, 2: Paralleling Technique, Radiation History and Biology

What are the 3 basic principles of the Paralleling Technique?

1. Film is placed parallel to the long axis of tooth being radiographed

2. Central Ray is directed perpendicular to film and long axis of tooth

3. Film holder must be used to keep film parallel to the long axis of tooth

How does Target-Film Distance (TFD) affect the radiograph?

Increased TFD = less magnification but more definition

• Increased target-film distance (longer cone):

  • Reduces magnification

  • Increases image sharpness

  • Improves image quality

• Short target-film distance:

  • More magnification and distortion

  • Less sharp image

Ideal: Use a longer distance (e.g. 16-inch cone) for better-quality radiographs.

What are some considerations for film selection?

• Palate size

• Torus

• Floor of the mouth

• Arch shape and size

Compare and contrast vertical angulation and horizontal angulation.

Vertical Angulation

• Direction: Up and down; perpendicular to the film

• Affects: Image length

• Incorrect angulation: Foreshortening (too steep) or elongation (too shallow)

• Critical in: Periapical radiographs

Horizontal Angulation

• Direction: Side to side; open contacts

• Affects: Overlapping of contacts

• Incorrect angulation: Proximal/occlusal surfaces appear merged or unclear

• Critical in: Bitewing radiographs

Key Difference:

• Vertical = image height

• Horizontal = contact clarity

What is the suggested paralleling sequence for ANTERIOR exposure?

1. R Max. Canine → L Max. Canine

2. L. Mand. Canine → R Mand. Canine

When using size 2 film, how many exposures are required to cover all the Anterior teeth?

• 3 Max. exposures (2 canine, 1 incisors)

• 3 Mand. exposures (2 canine, 1 incisors)

When using size 1 film, how many exposures are required to cover all the Anterior teeth?

• 4 Max. exposures

• 3-4 Mand. exposures

What is the suggested paralleling sequence for POSTERIOR exposure?

• Start: Q1 premolar → molar

• Q3 premolar → molar

• Q2 premolar → molar

• Q4 premolar → molar

Total exposures: 4 max 4 mand

Due to the shallow nature of the palate, how do we adjust our technique to maintain parallelism between the film and the long axis of the teeth?

Use cotton roll under the bite block (you can use on both sides if required)

How are film placed when a client has bony growths (tori)?

Maxillary tori:

• film should be placed on the far side of the torus; NOT on torus

Mandibular tori:

• film must be placed between the tori and the tongue

How should the film be placed for exposure in the Mandibular premolar region?

• film is placed under the tongue to avoid impinging on muscle attachments

• film is adjusted after the client closes down on the bite-block

What are the advantages and disadvantages of the paralleling technique?

Advantage:

• Accuracy → minimal dimensional distortion if done correctly (good detail and definition)

• Simple and easy to learn

• Easy to standardize

Disadvantages:

• Difficult film placement

• Uncomfortable film-holding device for client

Who was the scientist that discovered xrays?

William C. Roentgen → xrays are sometimes referred as Roentgen rays

Who was the scientist that exposed the early dental radiograph prototype?

Dr. Otto Walkoff

Dr. Edmund Kells was given the credit for what?

First intraoral radiograph made in 1896 on a living person in the US

What is the name of the company that manufactured the first pre-wrapped intraoral radiographic film?

Eastman Kodak Company

Who introduced the bisecting technique?

Weston Price in 1904

Who redefined the original bisecting technique and introduced the BITEWING technique in 1925?

Howard Riley Raper

What was Franklin W. McCormack’s contribution to radiation history?

Applied the paralleling technique in dental radiography during the 1920s.

Define Radiation

A form of energy carried by waves or stream of particles

Define X-Radiation

A high-energy radiation produced by the collision of a beam of electrons with a metal target in an x-ray tube.

Define X-Ray

A beam of energy that has the power to penetrate substances and record image shadows on photographic film.

→ often used to describe a radiograph which is incorrect. It is the beam.

Who is considered to be the father of panoramic radiography?

• Yrjö Paatero (a Finnish dentist) is considered the father of panoramic radiography

• Developed the technique in the 1940s–1950s

What is Radiation Biology?

The study of the effect of ionizing radiation on living tissue so that we can better understand the harmful effects of radiation.

Define Ionization

Ionization is produced through photoelectric effect or Compton scatter

How does radiation cause injury?

• X-rays strike the client causing ionization. Ionization causes chemical changes at the celluilar level which then can cause biological damages.

How do free radical formation cause injury?

• Unstable free radical will want to bind and recombine to regain stability which can create damaging compounds. (ex. H2O2 (hydrogen peroxide)

• Unstable free radical will steal electrons from healthy stable atoms which can damage healthy cells/tissues/dna leading to disease/cancer

Free radicals form when x-ray photon ionizes water (primary component of living cells).

• Water ionization = Hydrogen + hydroxyl free radicals.

• Free radicals are uncharged atoms/molecules that exist with a single unpaired eletron in its outer shell making the atom unstable and highly reactive.

What is the Direct Radiation Theory?

The theory that cell damage occurs as a direct result of ionizing radiation targeting critical areas.

• Ex. Xray photon directly striking DNA cell causing injury to irradiated organism

• Occurs infrequently but is more severe damage (most xray photons just pass through cells and cause little damage)

What is the Indirect Radiation Theory?

The theory that x-ray photons are being absorbed within the cell causing “toxins” therefore damaging the cell.

• Ex. Free radicals combine to form toxins causing cellular dysfunction and biological injury

• Occurs frequently because of the high water content in the cells (70-80%)

What is the Dose-Response-Curve?

The correlation between the response and damage of tissues with the dose or amount of radiation received.

• Graph showing the relationship between radiation dose and biological effect

• Helps determine how much damage occurs at different exposure levels

Explain the Threshold Curve

A type of Dose-Response curve that indicates that below a certain level (threshold) no response is evident.

Explain the Linear Curve

A type of Dose-Response Curve that indicates that the response (injury) is proportional to the dose.

Explain the Linear Non-Threshold curve.

A type of Dose-Response Curve that indicates that a response is seen at any dose.

Define Stochastic

randomly determined; having a random probability distribution or pattern that may be analysed statistically but may not be predicted precisely.

Define Stochastic effects in relation to radiation injury.

Defn: Stochastic effects are random biological injuries caused by radiation. The severity of stochastic effects is not dependent on the magnitude of the absorbed dose (there is no threshold). These effects are believed to result from ionizing radiation damaging chromosomes—potentially leading to conditions such as cancer.

Define Non-Stochastic effects in relation to radiation injury.

Defn: Non-stochastic effects are biological injuries caused by radiation that have a threshold dose. The severity of non-stochastic effects increases with the magnitude of the absorbed dose. These effects occur only when exposure exceeds a certain level and often result from extensive cell damage or death. (ex. erythema (redness), hair loss, cataracts, infertility)

What is Latent Period?

The time that elapses between exposure and observable clinical signs.

• More radiation = faster the dose rate = shorter latent period

• Basically a measure for how quickly clinical signs appear

Define Injury period

Injury period follows latent period in which cellular damage may be the result of the duration of exposure.

Define Recovery Period

Recovery period is the phase following the latent and injury periods of radiation exposure during which cells repair sublethal damage.

• Damaged tissues may heal partially or fully (not all cellular radiation are permanent)

• Depends on radiation dose, tissue type, and cell turnover rate

• Some injuries may be permanent or cumulative if repair is incomplete

  • damage that remains unrepaired accumulates in the tissues which then can lead to cancer, cataracts, birth defects

What are the 5 factors that contribute to severity of Radiation Injury

1. Total dose → how much radiation received/being absorbed by cells

2. Dose Rate → the rate at which exposure to radiation occurs (cells take time to heal)

3. Area Exposed → larger area, more injury

4. Cell Sensitivity → some cell types are more sensitive

5. Age → younger individuals more susceptible; elderly have thinner body tissue and less capable of repair

What types of cells are Radiosensitive? are Radioresistant?

Radiosensitive → small lymphocyte, bone marrow, reproductive cells

Radioresistant → muscles, nerve, mature bone

What is the difference between short-term and long-term effects in relation to Radiation?

Short-term = large amounts of radiation over short period of time

Long-term = small amounts of radiation repeated over long period of time (dentistry risk)

What is Background Radiation?

Naturally occurring background radiation that emits from radioactive materials present in the earth and air. (i.e potassium, uranium)

What are the OLD units of measurement for Radiation? (3)

1. Roentgen (R) - exposure

2. Radiation Absorbed Dose (RAD)

3. Radiation Equivalent (in Man) = rem

What are the NEW units of measurement for Radiation? (3)

1. Coulombs/kg (C/kg)

2. Gray (Gy)

3. Sievert (Sv)

What does Roentgen (Coulomb) measure?

• Measure the energy produced by gamma radiation in a cubic centimetre of air AKA measures radiation exposure

• Abbrev. R or mR (milli)

What does Radiation Absorbed Dose - RAD (Gray) measure?

• Amount of energy absorbed by tissue

• amount of radiation energy transferred to some mass of material (i.e. humans)

• 1 R of gamma radiation exposure = 1 Rad of Absorbed dose.

What does Roentgen Equivalent Man - REM (Sievert) measure?

• Unit that relates the dose of any radiation to the biological effects of that dose

• Measures the biological effect of ionizing radiation on human tissue.

• Used to assess radiation risk to health

• Gamma rays/beta particles → 1 RAD of exposure = 1 REM of dose

What are the 4 critical organs at risk when performing Dental Radiography?

1. Thyroid Gland

2. Bone Marrow

3. Skin

4. Eyes

What are the 4 variables that contributes to the quantity of xray exposure to clients.

1. Film speed → faster films reduces absorbed dose by 60%

2. Collimation → Rectangular shape instead of round reduced absorbed dose by 60-70%

3. Technique → Long cone paralleling and longer TFD reduces skin dose

4. Exposure → Higher kVp reduces skin dose. (high kvp=more penetrating=less absorbed)