DENTAL X-RAY TUBE

The dental X-ray tube is surrounded by a glass envelope that houses a vacuum.
The glass prevents low-grade radiation from escaping. The vacuum insures the protection of the equipment from catastrophic failure. Production of X-rays generates enormous amounts of heat; the vacuum prevents the risk of combustion and ensures the proper environment for conduction of electrons.

There are two separate energy sources, one that powers the energy potential between the cathode ?lament and the anode, and the other being
the controls for the cathode ?lament. The latter essentially is the on and off switch of the X-ray unit.

The cathode ?lament is heated which causes electrons to be emitted.

These electrons are then accelerated by the electrical potential of the circuit.

Between the two points is a tungsten target.
When electrons strike the target, X-rays are produced.

HALF-VALUE LAYER

- Property of a material whereas the thickness (mm) reduces 50% of a monochromatic X-ray beam.
- Half-value layer of a beam of radiation from an X-ray unit is about 2 mm of aluminum (Al).

PRIMARY RADIATION

- Is the main beam produced from the X-ray tube. 

SECONDARY RADIATION

- Produced by the collision of the main beam with matter which causes scatter.

Age Groups and Radiographs

• Age 2:

  • Anterior IOPA's: 2
  • Posterior IOPA's: 4
  • Bitewings: 2
  • Total Films: 12

• Age 8:

  • Anterior IOPA's: 8
  • Posterior IOPA's: 4
  • Bitewings: 2
  • Total Films: 14

• Age 8 (another entry):

  • Anterior IOPA's: 8
  • Posterior IOPA's: 8
  • Bitewings: 2
  • Total Films: 20

Summary of Total Films by Type

• Anterior IOPA's:

  • Age 2: 2
  • Age 8: 8
  • Age 8 (another entry): 8
  • Total Anterior IOPA's: 18

• Posterior IOPA's:

  • Age 2: 4
  • Age 8: 4
  • Age 8 (another entry): 8
  • Total Posterior IOPA's: 16

• Bitewings:

  • Age 2: 2
  • Age 8: 2
  • Age 8 (another entry): 2
  • Total Bitewings: 6

Overall Total Films

• Total Films for Age 2: 12
• Total Films for Age 8 (first entry): 14
• Total Films for Age 8 (second entry): 20
• Grand Total Films: 12 + 14 + 20 = 46

Common Problems in Film Processing

1. Light Radiographs

• Causes:
  • Under Development:
    • Temperature too low
    • Time too short
    • Depleted developer solution
  • Under Exposure:
    • Insufficient milliamperage
    • Insufficient kVp
    • Insufficient exposure time
    • Film-source distance too great
    • Film packet reversed in the mouth

2. Dark Radiographs

• Causes:
  • Over Development:
    • Temperature too high
    • Time too long
    • Accidental exposure to light
    • Improper safe lighting
    • Developer concentration too high
  • Over Exposure:
    • Excessive milliamperage
    • Excessive kVp
    • Excessive exposure time
    • Film-source distance too short

3. Insufficient Contrast

• Causes:
  • Improper processing conditions (under or over development)
  • Depleted developer solution
  • Contaminated solutions

4. Film Fog

• Causes:
  • Excessive kVp
  • Improper safe lighting
  • Light leaks in the darkroom
  • Contaminated developer solution

5. Dark Spots or Tines

• Causes:
  • Contaminated solutions
  • Film contaminated with developer before processing
  • Film in contact with tank or another film during fixation

6. Light Spots

• Causes:
  • Insufficient washing
  • Film contaminated with fixer before processing
  • Film in contact with tank or another film during development

7. Yellow or Brown Stains

• Causes:
  • Insufficient washing after fixation
  • Depleted fixer solution
  • Contaminated solutions

8. Blurring

• Causes:
  • Movement of the patient during exposure
  • Movement of the X-ray tube head
  • Double exposure
  • Misalignment of the X-ray tube head (cone cut)

9. Partial Images

• Causes:
  • Top of film not immersed in developing solution
  • Film in contact with tank or another film during processing

10. Emulsion Peel

• Causes:
  • Excessive bending of the film
  • Improper handling of the film

11. Static Discharge

• Causes:
  • Static discharge to film before processing (results in dark lines with a tree-like image)

12. Fingerprint Contamination

• Causes:
  • Fingerprint contamination during handling of the film

13. Excessive Roller Pressure

• Causes:
  • Excessive roller pressure during processing can lead to artifacts on the film.

General guidelines for vertical angulations for common dental radiographs in children:

Anterior Teeth

1. Maxillary Central Incisors:
   • Vertical Angulation: +40 to +50 degrees
2. Maxillary Lateral Incisors:
   • Vertical Angulation: +40 to +50 degrees
3. Maxillary Canines:
   • Vertical Angulation: +45 to +55 degrees
4. Mandibular Central Incisors:
   • Vertical Angulation: -10 to -20 degrees
5. Mandibular Lateral Incisors:
   • Vertical Angulation: -10 to -20 degrees
6. Mandibular Canines:
   • Vertical Angulation: -15 to -25 degrees

Posterior Teeth

1. Maxillary Premolars:
   • Vertical Angulation: +30 to +40 degrees
2. Maxillary Molars:
   • Vertical Angulation: +20 to +30 degrees
3. Mandibular Premolars:
   • Vertical Angulation: -5 to -10 degrees
4. Mandibular Molars:
   • Vertical Angulation: -5 to -10 degrees

Digital Radiology

Advances in computer and X-ray technology now permit the use of systems that employ sensors in place of X-ray ?lms (with emulsion). The image is either directly or indirectly converted into a digital representation that is displayed on a computer screen. 

DIGITAL IMAGE RECEPTORS

- charged coupled device (CCD) used
- Pure silicon divided into pixels.
- Electromagnetic energy from visible light or X-rays interacts with pixels to create an electric charge that can be stored.
- Stored charges are transmitted electronically and create an analog output signal and displayed via digital converter (analog to digital converter). 

ADVANTAGES OF DIGITAL TECHNIQUE

Immediate display of images.

Enhancement of image (e.g., contrast, gray scale, brightness).

Radiation dose reduction up to 60%.

Major disadvantage: High initial cost of sensors. Decreased image resolution and contrast as compared to D speed ?lms.

DIRECT IMAGING

- CCD or complementary metal oxide semiconductor (CMOS) detector used that is sensitive to electromagnetic radiation.

- Performance is comparable to ?lm radiography for detection of periodontal lesions and proximal caries in noncavitated teeth.

INDIRECT IMAGING

- Radiographic ?lm is used as the image receiver (detector). 

- Image is digitized from signals created by a video device or scanner that views the radiograph.

Sensors

STORAGE PHOSPHOR IMAGING SYSTEMS

Phosphor screens are exposed to ionizing radiation which excites BaFBR:EU+2 crystals in the screen storing the image.

A computer-assisted laser then promotes the release of energy from the crystals in the form of blue light.

The blue light is scanned and the image is reconstructed digitally.

ELECTRONIC SENSOR SYSTEMS

X-rays are converted into light which is then read by an electronic sensor such as a CCD or CMOS.

Other systems convert the electromagnetic radiation directly into electrical impulses.

Digital image is created out of the electrical impulses. 

1. Postero-Anterior (PA) View of Skull

• Head Position: Centered in front of the cassette; canthomeatal line parallel to the floor. For cephalometric applications, the canthomeatal line is 10° above the horizontal, and the Frankfort plane is perpendicular to the film.
• Projection of Central Ray: Passes posterior to anterior, perpendicular to the film.
• Important Features:
  • Used to examine the skull for disease, trauma, and sinuses.
  • Best for viewing the coronoid process; a PA view with a 10° tilt is called the Caldwell projection.

2. Lateral Skull or Cephalometric View

• Head Position: Left side of the face near the cassette; midsagittal plane parallel to the film.
• Projection of Central Ray: Directed towards the external auditory meatus, perpendicular to the film and midsagittal plane.
• Important Features:
  • Assesses facial growth.
  • Reveals soft tissue profile.
  • Surveys skull and facial bones for disease and trauma.

3. Water's Projection

• Head Position: Sagittal plane perpendicular to the film; chin raised so the canthomeatal line is 37° above horizontal.
• Projection of Central Ray: Passes through the maxillary sinus.
• Important Features:
  • Also known as Occipito-mental projection (variation of PA view).
  • Best for demonstrating zygoma fractures, paranasal sinuses, and nasal cavity.
  • Shows the position of the coronoid process between the maxilla and zygomatic arch.

4. Submentovertex (SMV) View

• Head Position: Head and neck extended backward; vertex of the skull at the center of the cassette.
• Projection of Central Ray: Directed towards the vertex of the skull.
• Important Features:
  • Also called BASE, FULL AXIAL, or JUG HANDLE VIEW.
  • Best for viewing the base of the skull and zygomatic arch fractures.
  • Contraindicated in patients with cervical spondylitis.
  • For viewing zygomatic arches, exposure time is reduced to one-third of that used for the skull.

5. Reverse Towne's View

• Head Position: Canthomeatal line oriented 25-30° downward.
• Projection of Central Ray: Directed towards the occipital bone.
• Important Features:
  • Frankfort plane vertically oriented and parallel to the film.
  • Best for viewing condylar neck fractures.
  • Condyles are better visualized if the patient opens their mouth widely.

6. Lateral Oblique Mandibular Body Projection

• Head Position: Tilted towards the side being examined; mandible protruded.
• Projection of Central Ray: Directed towards the first molar region.
• Important Features:
  • Demonstrates the premolar and molar region.
  • Best for viewing the inferior border of the mandible.

7. Lateral Oblique Mandibular Ramus Projection

• Head Position: Tilted towards the side being examined; mandible protruded.
• Projection of Central Ray: Directed posteriorly towards the center of the ramus.
• Important Features:
  • Often used for examining third molar regions of the maxilla and mandible.
  • Provides a view of the ramus from the angle to the condyle.