Fractures of the Zygomatic Arch

• Structures: Zygomatic arch, zygomatic bone.
• Best Views:
  • Submento-Vertex View: Provides a clear view of the zygomatic arch and helps assess fractures.
  • Waters View: Useful for visualizing the zygomatic bone and maxillary sinus.
  • Reverse Townes View: Can also be used to visualize the zygomatic arch.

Base of Skull

• Structures: Base of the skull, cranial fossae.
• Best Views:
  • Submento-Vertex View: Effective for assessing the base of the skull and related fractures.

Maxillary Sinus

• Structures: Maxillary sinus, zygomatic bone.
• Best Views:
  • Waters View: Excellent for visualizing the maxillary sinus and any associated fractures.

Fractures of Zygoma

• Structures: Zygomatic bone, zygomatic arch.
• Best Views:
  • Waters View: Good for assessing zygomatic fractures.
  • PA View: Provides a frontal view of the zygomatic bone.
  • Reverse Townes View: Useful for visualizing the zygomatic arch.

Nasal Septum

• Structures: Nasal septum, nasal cavity.
• Best Views:
  • PA View: Useful for assessing the nasal septum and any associated fractures.

Condylar Neck Fractures

• Structures: Mandibular condyle, neck of the condyle.
• Best Views:
  • Lateral Oblique View (15°): Good for visualizing condylar neck fractures.
  • Transpharyngeal View: Useful for assessing the condylar region.

Medially Displaced Condylar Fractures

• Structures: Mandibular condyle.
• Best Views:
  • Lateral Oblique View (30°): Effective for visualizing medially displaced condylar fractures.

Coronoid Process of Mandible

• Structures: Coronoid process.
• Best Views:
  • PA View of Skull: Can help visualize the coronoid process.

Fractures of Ramus and Body of Mandible

• Structures: Mandibular ramus, body of the mandible.
• Best Views:
  • Lateral Oblique View (15°): Useful for assessing fractures of the ramus and body of the mandible.

Horizontal Favorable and Unfavorable Fractures of Mandible

• Structures: Mandible.
• Best Views:
  • Lateral Oblique View (30°): Effective for evaluating horizontal fractures.

Bony Ankylosis of TMJ

• Structures: Temporomandibular joint.
• Best Views:
  • CT Scan: Provides detailed imaging of bony structures and ankylosis.

Fibrous Ankylosis of TMJ

• Structures: Temporomandibular joint.
• Best Views:
  • CT Scan: Useful for assessing fibrous ankylosis.

Internal Derangement of the Disk

• Structures: TMJ disk.
• Best Views:
  • MRI: The best modality for evaluating soft tissue structures, including the TMJ disk.

Disk Perforation

• Structures: TMJ disk.
• Best Views:
  • MRI: Effective for diagnosing disk perforation.

Arthrography

• Structures: TMJ.
• Best Views:
  • Arthrography: Can be used to assess the TMJ and visualize the disk and joint space.

Radiation Biology

-X- and g -rays are called sparsely ionizing because along the tracks of the electrons set in motion, primary ionizing events are well separated in space.

Alpha-particles and neutrons are densely ionizing because the tracks consist of dense columns of ionization.

X-rays, gamma rays, electrons, and protons are all low LET forms of radiation in that their density of ionization is sparse. In general, they penetrate tissues deeply and result in less intracellular radiation injury.

High LET forms of radiation, such as heavy nuclear particles (e.g. fast neutrons), penetrate tissues less deeply and cause more radiation injury to biologic material.

Cells are most sensitive to Radiation when:

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.

RELATIVE RADIO SENSITIVITY OF THE TISSUES

Radiosensitive (2500 r or less kills or seriously injures many cells)

Lymphocytes and lymphoblasts
Bone marrow (myeloblastic and erythroblastic cells)
Epithelium
Germ cells (testes and ovary)

Radioresponsive (2500-5000 r kills or seriously injures many cells)

Epithelium of skin and many appendages.
Endothelium of blood vessels
Salivary glands
Growing bone and cartilage.
Conjunctiva, cornea and lens of eye
Collagen and elastic tissue(fibroblasts themselves are resistant)

Radioresistant (over 5000 r are required to kill or injure many cells)

Kidney
Liver
Thyroid
Pancreas
Pituitary
Adrenal and parathyroids
Mature bone and cartilage
Muscle
Brain and other nervous tissue.

The numbers represent the minimum damaging doses; a gray and a sievert represent roughly the same amount of radiation:
• Fetus--2 grays (Gy).
• Bone marrow--2 Gy.
• Ovary--2-3 Gy.
• Testes--5-15 Gy.
• Lens of the eye--5 Gy.
• Child cartilage--10 Gy.
• Adult cartilage--60 Gy.
• Child bone--20 Gy.
• Adult bone--60 Gy.
• Kidney--23 Gy.
• Child muscle--20-30 Gy.
• Adult muscle--100+ Gy.
• Intestines--45-55 Gy.
• Brain--50 Gy.
 

Bisecting angle technique 

Bisecting angle technique is a method used in dental radiography to obtain radiographs of teeth and surrounding structures. This technique involves positioning the X-ray beam perpendicular to an imaginary line that bisects the angle formed by the long axis of the tooth and the film or sensor. Here are the general guidelines for angulations when using the bisecting angle technique:

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: -15 to -25 degrees
5. Mandibular Lateral Incisors:
   • Vertical Angulation: -15 to -25 degrees
6. Mandibular Canines:
   • Vertical Angulation: -20 to -30 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: -10 to -15 degrees
4. Mandibular Molars:
   • Vertical Angulation: -5 to -10 degrees

Key Points

• Positioning: The film or sensor should be placed as close to the tooth as possible, and the X-ray beam should be directed perpendicular to the bisecting line.
• Patient Comfort: Ensure that the patient is comfortable and that the film or sensor is properly stabilized to avoid movement during exposure.
• Technique Variability: The exact angulation may vary based on the individual patient's anatomy, so adjustments may be necessary.

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.