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PARALLELING TECHNIQUE

Overview

  • Dental Radiography Principles and Techniques 6th Edition: Chapter 19

  • Author: Meghan Tersigni BSc, RDH, Cert. Adult Ed.

LEARNING OBJECTIVES

  • Define key terms associated with the paralleling technique.

  • State the basic principle of the paralleling technique, illustrating the placement of:

    • Receptor

    • Beam alignment device

    • Position Indicating Device (PID)

    • Central ray

  • Discuss how object-receptor distance affects the image and how target-receptor distance compensates for changes.

  • Describe the necessity of a beam alignment device with paralleling.

  • Identify and label parts of the XCP system.

  • Describe different sizes of receptors used with paralleling and how each receptor is placed into the bite-block.

  • State 5 basic rules of paralleling.

  • Describe patient and equipment preparation steps.

  • Discuss recommended exposure sequencing using the paralleling technique and receptor placement with XCP.

  • Summarize guidelines for periapical receptor positioning, including modifications for patients with:

    • Shallow palates

    • Bony growths

    • Sensitive premolar regions

  • List advantages and disadvantages of the paralleling technique.

PARALLELING TECHNIQUE

  • Also referred to as:

    • Extension cone paralleling technique

    • Right-angle technique

    • Long-cone technique

  • Used for exposure of both bitewing and periapical images using a type of receptor holder that is a specific device to maintain alignment.

TERMINOLOGY

  • Parallel: Moving or lying in the same plane, always separated by the same distance and not intersecting.

  • Intersecting: To cut across or through.

  • Perpendicular: Intersecting at or forming a right angle.

  • Right angle: An angle of 90 degrees formed by two lines perpendicular to each other.

  • Long axis of the tooth: An imaginary line that divides the tooth longitudinally into two equal halves.

  • Central ray: The central portion of the primary beam of x-radiation.

PRINCIPLES OF PARALLELING (1 OF 2)

  • The receptor is placed in the mouth parallel to the long axis of the tooth being radiographed.

  • The central ray of the x-ray beam is directed perpendicular to both the film and the long axis of the tooth.

  • A beam alignment device is used to keep the receptor parallel with the long axis of the tooth.

PRINCIPLES OF PARALLELING (2 OF 2)

  • Object-Receptor Distance: The distance between the tooth and receptor must be increased to maintain the receptor parallel to the long axis of the tooth.

  • Target-Receptor Distance: The distance between the source of x-rays and the receptor must be increased to ensure only the most parallel rays are directed at the tooth.

BEAM ALIGNMENT DEVICES AND RECEPTOR HOLDING DEVICES

  • These devices position the receptor in the mouth and retain it during exposure.

  • They must keep the receptor parallel to the long axis of the tooth.

  • How do film holders reduce exposure?

    1. Examples needed.

    2. Examples needed.

COMMERCIALLY AVAILABLE BEAM ALIGNMENT DEVICES

  • Rinn XCP System

  • Rinn XCP Universal Sensor Holder

  • Rinn Snap-A-Ray Holder

  • Stabe Bite-Block

COMPONENTS OF XCP HOLDER

  • AIMING RING: Assists in aligning the beam.

  • BITE-BLOCK: Holds the receptor in place.

  • METAL INDICATOR ARM: Provides measurement guidance for correct positioning.

RECEPTORS USED FOR PARALLELING

  • Size 1 receptor: Used for canine exposures (placed vertically).

  • Size 2 receptor: Used for posterior exposures (placed horizontally) and incisor exposures (placed vertically).

  • DOT IN THE SLOT: Marker for periapicals.

  • DOT DOWN: Marker for bitewings.

5 RULES FOR PARALLELING TECHNIQUE

  1. Receptor placement: Must cover the prescribed area of the teeth.

  2. Receptor position: Receptor must be positioned parallel to the tooth's long axis; receptacle and device need to be placed towards the mouth's center.

  3. Vertical angulation: The central ray must be perpendicular to both the receptor and long axis of the tooth.

  4. Horizontal angulation: The central ray must pass through the contact areas between teeth.

  5. Receptor exposure: The x-ray beam must be centered on the receptor to ensure full area exposure.

FAILURE TO OBSERVE THE 5 RULES

  • Can lead to non-diagnostic images.

    1. Examples needed.

    2. Examples needed.

LET’S THINK…

  • Q: What radiographic error occurs if the central ray is not directed through the contact areas?

    • A: Examples needed.

  • Q: How can we correct this?

    • A: Examples needed.

STEP-BY-STEP PROCEDURES

  1. Client preparation

  2. Equipment preparation

  3. Exposure sequence for receptor placement

  4. Receptor placement for paralleling technique

CLIENT PREPARATION

  • Procedure:

    • Explain the procedures to the client.

    • Adjust the chair and headrest for comfort.

    • Place and secure the lead apron with a thyroid collar.

    • Remove all objects from the mouth (removable dentures, tongue piercings, retainers).

    • Advise the client to remove eyewear as it may interfere with XCP and PID placements.

EQUIPMENT PREPARATION

  • Set the exposure control factors.

  • Open and assemble the sterilized packages containing beam alignment devices over a clean work area.

EXPOSURE SEQUENCE FOR RECEPTOR PLACEMENT

  • Anterior exposure sequence: Less likely to cause gag reflex; uses both size 1 and size 2 receptors.

    • Total of 6 anterior placements; all placed vertically:

    1. 4 canine exposures using size 1 receptor.

    2. 2 incisor exposures using size 2 receptor.

  • Posterior exposure sequence: Only size 2 receptor used; 8 placements total, placed horizontally:

    • 4 premolar exposures.

    • 4 molar exposures.

  • For a full mouth series (FMS) including bitewings, these should be exposed at the end of the sequence to enhance the client's experience.

TIPS FOR EXPOSURE SEQUENCE

  • Maintain a consistent routine from client to client.

  • Consider positioning the PID before receptor placement to minimize the time the receptor is in the client’s mouth.

  • For posterior sequencing, consider placing premolar images before molar images to optimize assembly time.

RECEPTOR PLACEMENT FOR PARALLELING TECHNIQUE - ANTERIORS

  • Detailed guidance needed.

RECEPTOR PLACEMENT FOR PARALLELING TECHNIQUE - POSTERIORS

  • Detailed guidance needed.

MODIFICATIONS IN PARALLELING TECHNIQUE

  • Clinicians must be adept at handling variations such as:

    • Shallow palate

    • Bony growths (torus)

    • Mandibular premolar region

SHALLOW PALATE

  • Place cotton rolls on either side of the bite block.

  • Increase vertical angulation by 5 to 15 degrees (maximum 20 degrees) to limit distortion.

BONY GROWTHS - TORUS

  • Maxillary torus: Place the receptor on the far side of the torus for exposure.

  • Mandibular tori: Place the receptor between the tori and the tongue for exposure.

MANDIBULAR PREMOLAR REGION

  • The receptor must be placed under the tongue; soften the film edge to minimize discomfort (avoid creasing).

  • Ensure quick exposure by pre-positioning the PID nearby, reducing time spent in the client's mouth.

  • Present images of the exposure of mandibular premolar periapical:

    • Image A: Receptor tipped away from the tongue during bite-block placement.

    • Image B: Adjusted position when the patient closes on the bite-block.

ADVANTAGES VS. DISADVANTAGES OF PARALLELING TECHNIQUE

ADVANTAGES

  • Accuracy: Images are free from distortion.

  • Simplicity: Eliminates the need for determining horizontal and vertical angulation.

  • Duplication: Facilitate valid comparison of serial images.

DISADVANTAGES

  • Receptor placement: May be challenging.

  • Discomfort: Beam alignment devices may lead to patient discomfort.

LET’S THINK…

  • Q: Which type of client may have difficulties with the paralleling technique?

    • A: Examples needed.

  • FYI (for now): Q: What alternative exposure technique might be recommended?

    • A: Examples needed.

HELPFUL HINTS

  • Effective communication: Clients are more likely to tolerate discomfort when they understand why the receptor placement is necessary.

  • Use polite language such as "open, please" and "close gently, please."

  • Avoid negative wording such as