Intra-oral and Extra-oral Radiographic Examination

Components of the Dental X-ray Machine

The dental X-ray machine consists of several fundamental components that facilitate the production and direction of radiation for diagnostic purposes. According to the transcript, these include:

• Tubehead: The primary component containing the X-ray tube that produces the radiation.
• Support Arms: The mechanical system that allows for the movement and positioning of the tubehead.
• Control Panel: The interface used by the operator to adjust exposure settings and activate the X-ray beam.

Position and Beam Indicating Devices

The X-ray tubehead utilizes specific devices to indicate the direction and limit the size of the X-ray beam:

• PID (Position Indicating Device): An extension attached to the tubehead used to direct the X-ray beam. It is sometimes referred to as a "cone."
• BID (Beam Indicating Device): A term used synonymously with PID to describe the apparatus that indicates the path of the X-ray beam.

Angulation in the Bisecting-Angle Technique

Specific vertical angles are required when using the Bisecting-Angle Technique to ensure accurate imaging of different dental regions. These angles are measured in degrees ($^{\circ}$):

Maxilla (Positive Angulation $+$)

• Incisors: $+40^{\circ}$
• Canines: $+45^{\circ}$
• Premolars: $+30^{\circ}$
• Molars: $+20^{\circ}$

Mandible (Negative Angulation $-$)

• Incisors: $-15^{\circ}$
• Canines: $-20^{\circ}$
• Premolars: $-10^{\circ}$
• Molars: $-5^{\circ}$

Consequences of Improper Angulation

Correct angulation is critical for producing a diagnostic image. Errors in tubehead positioning lead to specific geometric distortions:

• Improper Vertical Angle: This results in an incorrect image length. The image may suffer from:
  • Elongation: The image of the tooth appears longer than the actual tooth.
  • Shortening: The image of the tooth appears shorter than the actual tooth.
• Horizontal Angle: This refers to the angle of the X-ray beam in relation to the Mid-Sagittal Plane (MSP). Generally, the more posterior the radiograph, the greater the horizontal angulation required.
• Improper Horizontal Angle: This causes interproximal overlap, where the contact areas of adjacent teeth are superimposed on one another, making the radiograph non-diagnostic for caries detection.

Interaction of X-Rays with Matter

When X-rays exit the tubehead and interact with the patient or matter outside the tube, three primary interactions occur:

1. Transmission: X-rays can pass through the patient without any interaction, reaching the film to create the image.
2. Absorption: X-ray photons can be completely absorbed by the patient's tissues through the photoelectric effect.
3. Scattering: X-ray photons can be scattered in different directions after interacting with matter.

Intra-oral (IO) Radiographic Examination

In intra-oral radiography, the image receptor (film) is placed inside the patient's mouth, while the X-ray source (tubehead) remains outside.

• Film Packet: The standard unit used to hold the film during intra-oral exposures.

Types of Intra-oral Radiographs

1. Periapical (PA): Designed to visualize the entire tooth and surrounding structures. The areas to be seen include:
   • Crown
   • Root
   • Periapex (the area surrounding the root tip)
2. Bitewings (BW): Primarily used to detect interproximal issues. The areas to be seen include:
   • Crowns of both upper and lower teeth.
   • $\frac{1}{3}$ to $\frac{2}{3}$ of both upper and lower roots.
   • Adjacent supporting bone (specifically the alveolar crest).
   • Developing successors located under deciduous (baby) teeth.
3. Occlusal Radiography: Used to visualize larger areas. The areas to be seen include:
   • A large number of teeth.
   • A large segment of the dental arch.
   • Contiguous lateral structures.
   • Commonly used to obtain right-angle views relative to standard periapical views.

Main Indications for Intra-oral Radiographs

Intra-oral radiographs are indicated for the following clinical purposes:

• Detection of caries (dental decay) and apical infections.
• Assessment of periodontal status (bone levels and health).
• Evaluation after trauma to the teeth or supporting structures.
• Assessment of the presence and position of impacted or unerupted teeth.
• Evaluation of tooth morphology before tooth extraction.
• Monitoring during endodontic treatment (root canal therapy).
• Assessment of the position and prognosis of dental implants.

Extra-oral (EO) Radiographic Techniques

In extra-oral radiography, both the X-ray source and the image receptor (which can be a film or an electronic sensor) are positioned outside the patient's mouth.

• Cassette Holders: In this technique, a screen film is "sandwiched" between two intensifying screens of matching size and type. These are then secured within a rigid or flexible cassette holder.

Indications for Extra-oral Radiography

• Evaluation of large areas of the skull and jaws.
• Assessment of growth and development (orthodontic evaluation).
• Evaluation of impacted teeth.
• Detection of lesions, diseases, and conditions affecting the jaws.
• Determining the extent of large lesions.
• Evaluation of trauma (fractures).
• Examination of the maxillary sinuses.
• Evaluation of the Temporomandibular Joint (TMJ) area.
• Evaluation of salivary gland diseases, typically following the injection of contrast media (sialography).

Technical Aspects of Extra-oral Projections

Various projections are used based on the diagnostic need, each requiring specific patient and beam placement:

• Lateral Cephalometric (Ceph): The film is placed parallel to the midsagittal plane. The beam is perpendicular to the film.
• Submentovertex (SMV): The canthomeatal line is positioned parallel to the film. The beam is perpendicular to the film.
• Waters Projection: The canthomeatal line is positioned at a $37^{\circ}$ angle with the film. The beam is perpendicular to the film.
• Posteroanterior (PA) Cephalometric / PA Skull: The canthomeatal line is positioned at a $10^{\circ}$ angle with the film. The beam is perpendicular to the film.
• Reverse Towne Projection: The canthomeatal line is positioned at a $-30^{\circ}$ angle with the film. The beam is perpendicular to the film.
• Body Oblique Lateral: The film is in contact with the cheek at the molar area. The beam aims at the molar-premolar area.
• Ramus Oblique Lateral: The film is in contact with the cheek at the ramus area. The beam aims at the ramus area.

Detailed Indications for Waters Projection

• Primary examination of the maxillary sinus.
• Examination of frontal and ethmoidal sinuses.
• Examination of the sphenoid sinus.
• Examination of the zygomatic bones and arches.
• Assessment of fractures of the nasal bones and the frontal process of the maxilla.

Dental X-ray Image Characteristics

The resulting radiograph displays structures in varying shades based on their density:

• Radiolucent: Refers to the dark or black portions of the radiograph. These sections represent structures that permit the passage of the X-ray beam with little resistance (e.g., pulp, decay, air spaces).
• Radiopaque: Refers to the light or white portions of the radiograph. These sections represent dense structures that absorb or resist the passage of the X-ray beam (e.g., enamel, bone, metal restorations).

Object Localization Techniques

Because a radiograph is a two-dimensional image of a three-dimensional object, dentists must use localization techniques to determine the spatial relationship of objects (e.g., finding the buccal or lingual position of an impacted tooth).

1. Right Angle Technique:

   • Involves taking two projections at right angles (90 degrees) to one another.
   • This method is frequently utilized in the mandible.

2. Tube Shift Technique (Clark's Rule / Buccal Object Rule):

   • This technique relies on the rationale that the relative positions of radiographic images of two separate objects change when the projection angle is changed.
   • SLOB Rule: Same Lingual, Opposite Buccal.
   • If the object in question moves in the same direction as the X-ray tube shift, the object is located on the lingual side.
   • If the object moves in the opposite direction of the tube shift, the object is located on the buccal side.

Questions & Discussion

• The presentation concluded with an invitation for audience questions.