Dental Radiography - Panoramic Imaging

Dental Radiography: Principles and Techniques - Panoramic Imaging

Chapter Overview

  • Authors: Joen M. Iannucci, DDS, MS, Laura Jansen Howerton, RDH, MS

  • Copyright ©2022, by Elsevier Inc. All Rights Reserved.

  • Total Chapters in the Text: 25 (Specifically focused on Chapter 25: Panoramic Imaging)

Lesson Objectives

  • Define key terms associated with panoramic imaging.

  • Describe the purpose and uses of panoramic imaging.

  • Describe the fundamentals of panoramic imaging.

  • Describe the equipment used in panoramic imaging.

  • Describe patient preparation, equipment preparation, and patient positioning procedures needed before exposing a panoramic projection.

  • Describe a diagnostic panoramic image.

  • Identify and discuss common patient preparation and positioning errors associated with panoramic imaging, including causes and solutions.

  • Discuss the advantages and disadvantages of panoramic imaging.

Introduction

  • Purpose of the Chapter:

    • To present basic concepts of panoramic imaging.

    • To describe patient preparation, equipment preparation, and patient positioning procedures necessary for conducting panoramic imaging procedures effectively.

Basic Concepts

Purpose and Use

  • Panoramic imaging provides an overall image of the maxilla and mandible, serving to:

    • Supplement bite-wing and selected periapical images.

    • Note that images on a panoramic projection are generally not as defined or sharp as those obtained through intraoral projections.

Fundamentals of Panoramic Imaging

  • In panoramic imaging, the x-ray receptor and tubehead move around the patient simultaneously:

    • The x-ray tubehead rotates around the patient’s head in one direction, while the receptor rotates in the opposite direction.

    • The patient maintains a stationary position, either sitting or standing.

Tomography

  • Definition:

    • An imaging technique allowing visualization of one body layer or section while blurring structures in other planes, thus producing distinct images of anatomy in focus.

Rotation Center

  • Defined as the pivotal point, or axis, around which the cassette carrier and x-ray tubehead rotate.

    • Modern systems utilize a continuously moving center of rotation as opposed to multiple fixed locations.

Focal Trough

  • Defined as a three-dimensional curved zone in which anatomical structures appear clearly on a panoramic image.

    • This theoretical concept determines the positioning needed for dental arches to achieve the sharpest image.

Resultant Images in Panoramic Imaging

  • Real Image: Resulting when a structure lies between the receptor and the moving rotation center.

  • Double Image: Produced when an anatomical structure behind the rotation center is penetrated twice by the x-ray beam.

  • Ghost Image: Appears when an anatomical structure located outside the focal plane and near the x-ray source is penetrated, rendering it indistinct, larger, and positioned higher than its actual counterpart.

Equipment Used in Panoramic Imaging

Panoramic X-Ray Units

  • Features of panoramic x-ray units include:

    • X-ray tubehead

    • Head positioner

    • Exposure controls

X-Ray Tubehead

  • Similar in function to an intraoral x-ray tubehead but uses a different collimator shape:

    • Instead of a traditional collimator, a lead plate with an opening in a narrow vertical slit is utilized in panoramic x-ray machines.

Image Receptors

  • Panoramic x-ray units utilize image receptors such as:

    • Direct digital sensors

    • PSP plates

    • Film, specifically screen film, which is sensitive to light from an intensifying screen and is positioned between two screens in a cassette holder.

    • Extraoral screen film is also used in panoramic imaging.

Intensifying Screens

  • Two types of intensifying screens:

    • Calcium Tungstate: Emits blue light and generally requires higher x-ray exposure.

    • Rare Earth: Emits green light and necessitates lower x-ray exposure than calcium tungstate.

Cassette

  • A light-tight device used to hold the extraoral film and intensifying screens.

    • Can be either rigid or flexible, and may be curved or straight.

Step-by-Step Procedures

Equipment Preparation

  • The dental radiographer must complete the necessary equipment preparations before preparing patients for exposure, which may vary depending on the receptor used.

Patient Preparation

  1. Explain the imaging procedures to the patient.

  2. Place a lead apron (without a thyroid collar) on the patient and secure it (a double-sided lead apron is preferred).

  3. Remove all objects from the head and neck area that might interfere with the procedure.

Patient Positioning

  1. Instruct the patient to sit or stand “as tall as possible” with a straight back.

  2. Instruct the patient to bite on the plastic bite block.

  3. Ensure the midsagittal plane is perpendicular to the floor.

  4. Adjust the Frankfort plane to be parallel to the floor.

  5. Instruct the patient to position their tongue on the roof of the mouth, keeping it there during the exposure.

  6. Ensure the patient closes their lips around the bite block.

  7. Instruct the patient to remain still during the rotation for exposure.

  8. Proceed with receptor processing after exposure.

Characteristics of a Diagnostic Panoramic Image

  • A diagnostic panoramic image results when:

    • These preparations have been executed correctly.

    • The image should be free of errors; it must accurately depict relevant anatomical features and exhibit proper exposure with correct density and contrast.

Anatomic Features

  • The panoramic image should effectively visualize the maxillofacial anatomy, ensuring the dentition and bone structures are represented adequately.

Density and Contrast

  • The density, or overall darkness, of a panoramic image should not be excessive, allowing for good contrast that enables identification of anatomical structures, such as the junction between enamel and dentin in the molar region.

Common Patient Preparation and Positioning Errors Associated with Panoramic Imaging

  • Errors:

    • Patient movement during exposure may lead to blurred images.

    • Incorrect positioning of the patient can result in misrepresentation of anatomical structures.

    • The patient's plane of occlusion not aligned may result in distortion in image.

  • Causes:

    • Inadequate communication or explanation of procedures to the patient.

    • Failure to properly instruct the patient on tongue positioning or lip closure.

  • Solutions:

    • Clear explanation of procedures and what the patient should expect.

    • Instructions should be repeated to ensure understanding.

Advantages and Disadvantages of Panoramic Imaging

  • Advantages:

    • Provides a comprehensive view of the maxillofacial region in a single image.

    • Useful for evaluating bone structure, including impacted teeth and fractures.

    • Reduction in patient radiation exposure compared to multiple intraoral films.

    • Greater patient comfort since fewer images are needed.

  • Disadvantages:

    • Limited image resolution compared to intraoral radiography, making certain pathologies less visible.

    • Superimposition of anatomical structures can complicate interpretation.

    • Not ideal for detecting caries or periodontal disease precisely due to lower detail.