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.

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. 

Radiographic films used in Dentistry

1. Intraoral Periapical (IOPA) Film

• Size 0:
  • Dimensions: 22 x 35 mm
  • For: Small children
  • MPD (Maximum Permissible Dose) for whole body: 0.1 Rem in 1 year
• Size 1:
  • MPD for gonads/bone marrow: 0.5 Rem in 1 year
• Size 2:
  • Dimensions: 24 x 40 mm or 32 x 41 mm
  • For: Anterior projections and adults
  • MPD for gestation period in relation to the fetus: 5 Rem
  • MPD for skin: 0.5 Rem in 1 year
• Radiation Exposure:
  • Mean exposure from one IOPA: 300 mR
  • Mean exposure from improved dental X-ray techniques: as low as 110 mR

2. Bitewing Film

• Size 0:
  • For: Very small children
• Size 1:
  • For: Children
• Size 2:
  • For: Adults

3. Occlusal Film

• Size:
  • 3 times larger than size 2 film (57 x 76 mm)
  • Used for capturing larger areas of the dental arch.

4. Screen Film

• Size:
  • 8 x 10 inches
  • Used for extraoral projections in conjunction with an intensifying screen.

Additional Information

• Erythema Dose: The amount of radiation necessary to produce a noticeable skin reaction, typically 300-400 R.
• ALARA Principle: Stands for "As Low As Reasonably Achievable," emphasizing the importance of minimizing radiation exposure.

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.

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