DRAD

Incomplete

What type of radiation are X-rays?

High-energy electromagnetic radiation with short wavelength and high frequency

Properties of x-rays

• high frequency, high energy electromagnetic energy

• no mass or charge

• naturally present in nature and produced by sun

• similar to gamma rays

• absorbed by atmosphere

• travel in straight lines

• obey the inverse square law

• energy of an x-ray can be attenuated by matter

• capable of causing biological damage in living tissue (ionisation)

• undetectable by human senses

• range of different wavelengths which dictates the energy they have

• similar to light waves - all are packaged as energy particles called photons and is equivalent to one quantum of energy

What determines the energy of an X-ray photon?

Its frequency (higher frequency = higher energy)

How does wavelength relate to energy?

Shorter wavelength = higher energy = greater penetration

How do X-rays travel?

In straight lines, at the speed of light, and they diverge

What does the inverse square law state?

Intensity ∝ 1 / distance².

The inverse square law states that a specified physical quantity or intensity—such as light, sound, or gravity—is inversely proportional to the square of the distance from its source

Why is the inverse square law important clinically?

Reduces operator radiation exposure with distance

What are the two main components of an X-ray tube?

Cathode (−) and Anode (+)

What is the function of the cathode?

Produces electrons via thermionic emission

Describe thermionic emission of electrons at the cathode

1. Tungsten filament is heated by low voltage current mA

2. Excites outer electrons of tungsten atoms

3. Electrons are released into an electron cloud at the cathode

4. The number of electrons is related to electric current mA

5. Electrons are accelerated at high speed towards anode

6. Negatively charged focusing cup helps direct electron cloud towards the anode

What is the cathode filament made of and why?

Tungsten

• high melting point

• high atomic number

Function of the anode

Contains tungsten target - converts electron energy into x-rays and heat

Why is copper used in the anode?

To dissipate heat efficiently (99% of energy released as heat)

What percentage of energy becomes X-rays?

~1% X-rays, 99% heat

Which type of radiation is most common in dentistry?

Bremsstrahlung radiation

What is Bremsstrahlung radiation and how is it produced?

• high-speed electron passes close to nucleus of tungsten atom and is slowed or deflected

• causes loss of kinetic energy that is emitted as an x-ray photon

• produces a continuous spectrum of x-ray energies

• energy of photon depends on how close the electron gets to the nucleus

What is Characteristic radiation and how is it produced?

• incoming electron ejects an inner-shell electron (usually from the K shell) of a tungsten atom

• outer-shell electron drops down to fill vacancy, releasing energy as an x-ray photon

• produces specific energy levels

• energy depends on difference between electron shell energies

• requires sufficient incoming energy to remove inner-shell electron

What determines total X-ray output?

mA × time

Describe the photoelectric effect

Process resulting in pure absorption

1. x-ray photon travels at high speed towards the object

2. high-speed x-ray photon transfers energy and ejects inner shell electron

3. Outer shell electron fills vacant space, emitting energy in the form of light (characteristic radiation)

4. Emitted inner shell electron continues to interact with other atoms until it loses all of its energy

Describe the Compton effect

1. x-ray photon interacts with outer-shell electron and transfers only part of its energy

2. photoelectron is emitted

3. scattered photon still has a fraction of energy of the incoming photon and can still travel through the patient

Describe the term radiolucency and radiopacity

• radiopaque shadows represent various dense structures within an object that have totally stopped the beam

• radiolucent shadows represent areas where the beam has passed through the object and has not been stopped at all

• grey shadows represent areas where the x-ray beam has been stopped to varying degrees

What is image sharpness (resolution) and what affects it?

refers to clarity of the image

• focal spot size

• movement

• distance relationships

What is magnification and what increases it?

occurs when the image appears larger than the object

• object is farther from receptor (increased OID)

• source is closer to object (decreased SOD)

What is filtration and why is it important?

• removal of low-energy x-rays that would otherwise be absorbed by the patient without contributing to the image

• reduces patient dose

What is collimation and which collimation is best?

• restricting beam size

• rectangular (reduces exposure most)

What happens when kVp increases?

• ↑ Penetration

• ↓ Image contrast (more gray)

• ↑ Scatter radiation

• Slight ↑ in X-ray quantity

How does kVp affect contrast?

• Low kVp → high contrast

• High kVp → low contrast

Which setting is the primary controller of contrast?

kVp

What does mA control?

Number of electrons → quantity of X-rays produced

What happens when mA increases?

• ↑ X-ray quantity

• ↑ Image density (darker)

• ↑ Patient dose

What does exposure time control?

Duration of X-ray production → affects total quantity

What happens when exposure time increases?

• ↑ Image density (darker)

• ↑ Patient exposure

What controls beam quality?

kVp

What controls beam quantity?

mA and time (mAs)

What is image density?

Degree of darkness on radiograph

What is contrast?

Visual difference between the various black, white, and grey shadows

What is high contrast useful for?

caries detection

What is low contrast useful for?

Bone/periodontal assessment

What factors increase patient dose?

• ↑ mA

• ↑ exposure time

• High kVp (indirectly via scatter)

• Retakes

How can patient dose be reduced?

• Use lowest effective mAs

• Optimise kVp - not too high, not too low

• Use digital sensors

• Avoid retakes

What does kVp control?

Beam quality (energy) and penetrating power of X-rays

What does mA control?

Number of electrons → quantity of X-rays produced

What does exposure time control?

Duration of X-ray production → affects total quantity

How are dental radiographs broadly classified?

• Intraoral radiographs (film/sensor inside mouth)

• Extraoral radiographs (film/sensor outside mouth)

Which type of radiograph generally provides the highest detail?

Intraoral radiographs

What factors determine which radiograph is selected?

• Diagnostic purpose

• Area being examined

• Patient comfort/cooperation

• Radiation dose considerations

What structures are seen on a periapical radiograph?

• Crown

• Entire root

• Root apex

• Surrounding alveolar bone

What is a periapical radiograph best used for?

• Periapical lesions

• Root fractures

• Root morphology

• Bone loss

• PDL space

• Lamina dura

• Endodontic working length

Why is the paralleling technique preferred?

• More accurate

• Minimal distortion

• Better reproducibility

• Better dimensional accuracy

What is the paralleling technique?

• Receptor is placed parallel to long axis of tooth

• central ray of x-ray beam is aimed perpendicular to long axis of tooth and receptor

What is the main disadvantage of the paralleling technique?

Can be less comfortable and difficult in shallow palates/small mouths

What is the bisecting angle technique?

Beam directed perpendicular to an imaginary bisector between tooth and receptor

Advantages of bisecting angle technique

• Easier placement

• More comfortable in difficult anatomy

Disadvantages of bisecting angle technique

• more distortion

• less reproducible

• greater magnification risk

Common errors from using bisecting angle technique

• Foreshortening - too much vertical angling makes teeth appear shorter

• Elongation - too little vertical angling makes teeth appear longer

• Cone-cutting - x-ray beam fails to cover the entire receptor

Common periapical radiograph errors

• Cone cutting

• Elongation

• Foreshortening

• Overlap

• Missing apex

What does a bitewing radiograph show?

Crowns of maxillary + mandibular teeth and crestal bone on same image

Diagnostic uses of bitewings

• Detecting interproximal caries

• Recurrent caries

• Monitoring caries progression

• Open margins

• Overhangs

• Calculus

• Assess periodontal status

Difference between uses of horizontal and vertical bitewings

• Horizontal → routine caries detection

• Vertical → better for periodontal bone loss

Major limitation of bitewings

Do not show root apices

Diagnostic uses of occlusal radiograph

• Impacted teeth

• Sialoliths - salivary stones

• Fractures

• Large cysts/tumors

• Supernumerary teeth

• Foreign bodies

What is an occlusal radiograph?

• Large receptor lies flat on occlusal plane; beam directed through chin/nose depending on view

• Captures a large, ‘bird’s-eye’ view of the floor of the mouth and roof of the mouth/palate

Advantages of occlusal radiographs

• Large field of view

• Helpful when intraoral placement difficult

• Well-tolerated in children

Disadvantages of occlusal radiographs

• Lower detail than periapicals

• Less commonly used routinely

What does a panoramic radiograph show?

Broad image of:

• Maxilla

• Mandible

• Teeth

• TMJ region

• Maxillary sinuses

• Surrounding structures

Diagnostic uses of panoramic radiography

• Impacted teeth

• Fractures

• Missing teeth

• Large lesions

• Developmental anomalies

• Third molar assessment

Advantages of panoramic radiographs

• Large coverage

• Quick

• Useful screening tool

• Comfortable

• Lower dose than full mouth series

Disadvantages of panoramic radiographs

• Lower resolution

• Magnification/distortion

• Overlapping structures

• Not ideal for caries detection

What is a cephalometric radiograph primarily used for?

Orthodontic diagnosis and treatment planning

What is a cephalometric radiograph?

Standardised skull radiographs

What does a cephalometric radiograph evaluate?

• Jaw relationships

• Growth patterns

• Craniofacial skeletal relationships

• Airway space

What is CBCT?

3D radiographic imaging using a cone-shaped X-ray beam

Diagnostic uses of CBCTs

• Implant planning

• Impacted tooth localization

• TMJ evaluation

• Root fractures

• Endodontic anatomy

• Bone defects

• Pathology assessment

Advantages of CBCTs

• 3D visualisation

• No superimposition

• High diagnostic value

Disadvantages of CBCTs

• Higher radiation dose than conventional films

• More expensive

• Greater artifact risk

Best radiograph for interproximal caries

BW

Best radiograph for periapical lesion

PA

Best radiograph for broad jaw screening

Panoramic

Best radiograph for orthodontic skeletal analysis

Cephalometric

Best radiograph for implant planning / 3D localization

CBCT

Best radiograph for salivary stones or large area localization

Occlusal

What principle guides radiograph selection?

ALARP (As Low As Reasonably Practicable)

Radiation considerations following ALARA principles

• Use lowest dose possible

• Select appropriate radiograph

• Avoid unnecessary repeat exposures

• Prefer conventional radiographs before CBCT unless a 3D image is required

What are the two main methods of dental radiographic image capture?

• Conventional film radiography

• Digital radiography

What do both film and digital radiography rely on?

Differential absorption of X-rays as they pass through oral structures

What is the major difference between film and digital radiography?

• Film uses chemical processing

• Digital uses electronic capture and computer processing

What are the main layers of dental X-ray film?

• Base (polyester support)

• Adhesive layer

• Emulsion layer

• Protective coating

What is found in the emulsion layer in film and what is its role?

Silver halide crystals (light-sensitive material) - react to X-ray exposure and form the latent image

What is a latent image?

An invisible image formed after X-ray exposure but before chemical processing

Film Image Formation

1. X-rays hit film → interact with silver halide crystals

2. Creates a latent image

3. Film undergoes chemical processing → visible image formed

Chemical processing of film

1. Developing - converts exposed crystals → black metallic silver

2. Rinsing - stops developer action

3. Fixing - removes unexposed crystals, hardens and stabilises image

4. Washing and drying → removes residual chemicals and preserves radiograph

Advantages of film radiography

• High spatial resolution (sharp detail)

• No electronic system

• Lower initial equipment cost

Disadvantages of film radiography

• Chemical processing required

• Time-consuming

• Higher radiation dose

• No image enhancement

• Physical storage needed

• Processing errors possible

What replaces film in digital radiography?

Electronic image receptors (digital sensors)

Advantages of digital radiography

• Lower radiation dose (~50-80% reduction)

• Instant image (CCD/CMOS)

• Ability to adjust brightness/contrast, zoom, measure

• Easy storage and sharing

• No chemical processing

Disadvantages of digital radiography

• Higher initial cost

• Sensors are bulky, less comfortable

• Risk of damage to sensors

• Lower spatial resolution than film (but still clinically acceptable)

What are the two main digital imaging systems?

• Direct digital (CCD / CMOS)

• Indirect digital (PSP)

What does CCD stand for?

Charge-Coupled Device

What does CMOS stand for?

Complementary Metal-Oxide Semiconductor

Mechanism of direct digital imaging

1. X-rays hit sensor

2. Energy converted into electrical signal

3. Signal processed into digital mage

4. Image appears immediately on screen