Interpreting Dental Radiographs E-Book

Keith Horner

• Herausgeber: Quintessence Publishing Co. Ltd.
• Kategorie: Fachliteratur
• Serie: QuintEssentials of Dental Practice
• Sprache: Englisch

Seitenzahl: 169

Veröffentlichungsjahr: 2019

Beschreibung

After clinical history-taking and examination, radiography is the "third way" of diagnosis, and dentists face the daily task of interpreting radiographic images to help in patient management. This book aims to give a comprehensive guide to reading x-ray images in dental practice and concentrates on intraoral radiographs. The text builds on a strong foundation of anatomical knowledge and is reinforced by the authors' experience of the radiological appearances that frequently challenge dentists.

Leseprobe

Quintessentials of Dental Practice – 5Imaging – 1

Interpreting Dental Radiographs

Authors:

Keith Horner

John Rout

Vivian E Rushton

Editors:

Nairn H F Wilson

Keith Horner

Quintessence Publishing Co. Ltd.

London, Berlin, Chicago, Copenhagen, Paris, Milan, Barcelona, Istanbul, São Paulo, Tokyo, New Delhi, Moscow, Prague, Warsaw

British Library Cataloguing in Publication Data

Horner, K. (Keith), 1958 - Interpreting dental radiographs. - (The quintessentials of dental practice) 1. Teeth - Radiography I. Title II. Rout, P. G. J. (Peter Graham John) III. Rushton, V. E. IV. Wilson, Nairn H. F. 617.6'07572

ISBN 1850973164

Copyright © 2002 Quintessence Publishing Co. Ltd., London

All rights reserved. This book or any part thereof may not be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, or otherwise, without the written permission of the publisher.

ISBN 1-85097-316-4

Table of Contents

Tittle Page

Copyright Page

Foreword

Preface

Chapter 1 Basic Principles

Aim

Introduction

What Makes the Image?

The Nature of the Radiation

X-ray energy

X-ray intensity

The Nature of the Object

Atomic number

Physical density

Thickness and shape

The Characteristics of the Image Receptor

How “Accurate” is a Radiographic Image?

Magnification

Image Sharpness

Spatial Perspective

Temporal Perspective

How Should We Interpret the Radiographic Image?

Using the Best Viewing Conditions

Systematic Examination of Radiographs

Summary

Further Reading

Chapter 2 Normal Anatomy

Aim

Introduction

Teeth and the Periodontium

The Tooth

Pulp anatomy

Developing Teeth

Alveolar Bone

The Maxilla

Anterior region

Canine/premolar region

Molar region

Third molar region

The Mandible

Anterior region

Premolar region

Molar region

Sockets and Healing

Further Reading

Chapter 3 Dental Caries

Aim

Introduction

Radiographic technique

Types of caries

Proximal caries

“Pre-radiological”

Enamel Lesion

The Lesion at the Amelodentinal Junction

Dentine Lesion

Lesions at the Pulp

Factors Affecting Radiological Interpretation of Proximal Caries

Monitoring Proximal Caries

Occlusal caries

Factors Affecting Radiological Interpretation of Occlusal Caries

Buccal/lingual caries

Root Surface (Cemental) Caries

Secondary (recurrent) caries

Diagnostic validity of radiology in caries diagnosis

Further Reading

Chapter 4 Radiology of the Periodontal Tissues

Aim

Introduction

Periodontal Disease Classification

Choice of Radiographs

Interpreting Periodontal Bone on Radiographs

Bone Loss

Furcation bone loss

Vertical Bony Defects

Interproximal crater

Infrabony defect

Aggravating Factors

Calculus

Poorly contoured restorations

Tilted teeth

Caries

Other Associated Features

Evidence of occlusal trauma

Bone sclerosis

Maxillary sinus changes

Root resorption

Hypercementosis

Aggressive Periodontitis

Lateral Periodontal Abscess

Periodontal/Endodontic Lesion

Further Reading

Chapter 5 Periapical and Bone Inflammation

Aim

Introduction

Choice of Radiographs

Classification of Inflammatory Lesions

Periapical Inflammatory Disease

Chronic Periapical Periodontitis

Clinical features

Radiological signs

Acute Periapical Periodontitis

Clinical features

Radiological signs

Lesions Associated with Inflammation

External and internal resorption of teeth

Clinical features

Radiological signs

Clinical features

Radiological signs

Hypercementosis

Radiological signs

Pericoronitis

Clinical features

Radiological signs

Osteomyelitis

Clinical features

Radiological signs

Clinical features

Radiological signs

Clinical features

Radiological signs

Clinical features

Radiological signs

Clinical signs

Radiological signs

Further Reading

Chapter 6 Anomalies of Teeth

Aim

Introduction

A Classification of Dental Anomalies

Anomalies of Enamel: Localised or Generalised

Turner’s Hypoplasia

Clinical features

Radiological signs

Amelogenesis Imperfecta

Clinical features

Radiological signs

Clinical features

Radiological signs

Anomalies of Dentine: Generalised

Clinical features

Radiological signs

Clinical features

Radiological signs

Anomalies of Enamel and Dentine

Clinical features

Radiological signs

Altered Crown Morphology

Clinical features

Radiological signs

Anomalies of the Pulp/Root Canals

Pulp Stones/Pulp Sclerosis

Altered Root Morphology

Radiological signs

Supernumerary Roots

Radiological signs

Dilacerated Root

Radiological signs

Shortened Roots

Alteration in Tooth Size

Radiological signs

Radiological signs

Altered Tooth Morphology

Radiological signs

Anomalies Affecting the Number of Teeth

Clinical features

Radiological signs

Additional Teeth (Hyperdontia)

Clinical features

Radiological signs

Further Reading

Chapter 7 Trauma to the Teeth and Jaws

Aim

Introduction

Choice of Radiographs

Trauma to the dentition

Dentoalveolar Fractures

Fractures of the Mandible

Trauma to the Teeth and Supporting Tissues

Luxation

Tooth Fracture

Fractures of the crown

Fractures of the root

Sequelae of Tooth Trauma

Fractures Involving Bone

Dentoalveolar fractures

Fracture of the maxillary tuberosity

Fracture of the genial tubercles

Fracture of the mandible

Further Reading

Chapter 8 Assessment of Roots and Unerupted Teeth

Aim

Introduction

Choice of Radiographs

Mandibular Third Molars

Radiographic Assessment of Mandibular Third Molars

Type and angulation of the impaction

The crown

The roots

Bone factors

Other teeth

Maxillary Canines

Radiographic Assessment of Maxillary Canines

Position

Crown and root form

Follicular size

Condition of other teeth

Retained Roots

Further Reading

Chapter 9 Radiolucencies in the Jaws

Aim

Introduction

Choice of Radiographs

Assessing Radiolucencies in the Jaws

The Site of the Lesion

The Shape of the Lesion

The Margin and Lumen of the Lesion

The Presence/Absence of Expansion

Multiplicity of Lesions

The Presence of a Periosteal Reaction

The Effect of the Lesion on Other Structures

Radiolucencies in the Jaws

Radiological signs

Radicular Cyst and Residual Cyst

Clinical features

Radiological signs

Dentigerous Cyst

Clinical features

Radiological signs

Lateral Periodontal Cyst

Clinical features

Radiological signs

Keratocyst

Clinical features

Radiological signs

Nasopalatine Cyst

Clinical features

Radiological signs

Solitary Bone Cyst

Clinical features

Radiological signs

Ameloblastoma

Clinical features

Radiological signs

Metastatic Deposits

Clinical features

Radiological signs

Surgical (Fibrous Healing) Defect

Radiological signs

Giant Cell Granuloma

Clinical features

Radiological signs

Hyperparathyroidism

Clinical features

Radiological signs

Further Reading

Chapter 10 Mixed Density and Radiopaque Lesions

Aim

Introduction

Choice of Radiographs

Assessing Mixed Density/Radiopaque Lesions

The site of the lesion

The radiopacity of the lesion

The margin of the lesion

Multiplicity of lesions

The effect of the lesion on other structures

Position

Mandibular and maxillary tori

Clinical features

Radiological signs

Compound odontome

Clinical features

Radiological signs

Complex odontome

Clinical features

Radiological signs

Sclerosing osteitis

Socket sequestrum

Clinical features

Radiological signs

Osteomyelitis

Osteosclerosis

Clinical features

Radiological signs

Fibro-Cemento-Osseous Lesions

Clinical features

Radiological features

Fibrous Dysplasia

Clinical features

Radiological signs

Paget’s Disease of Bone

Clinical features

Radiological signs

Osteoma

Clinical features

Radiological signs

Metastatic carcinoma

Radiopacities in the Soft Tissues

Clinical features

Radiological signs

Antroliths and Rhinoliths

Clinical features

Radiological signs

Gingival Inflammatory Hyperplasia

Foreign Bodies

Dental materials

Accidental implantation

Further Reading

Foreword

What proportion of procedures in general dental practice includes the interpretation of radiographs? All but a small percentage. It therefore follows that practitioners of all ages should be skilled in interpreting dental x-rays. This very readable book – Volume 5 in the Quintessentials for General Dental Practitioners Series – has been written to help the hard-pressed practitioner maintain and enhance these skills.

A mine of clinically relevant information, generously illustrated with high-quality radiographic images, Interpreting Dental Radiographs provides an authoritative and comprehensive guide to reading x-ray images. With an emphasis on those radiographic appearances that most frequently challenge even the most experienced of practitioners, this book is an invaluable aid to improved diagnosis. Exposing patients to ionising radiation and obtaining good-quality x-rays is to no avail if the information included in the images cannot be accurately interpreted. All those who read or possibly only dip into this book will without doubt gain new insight and understanding of the information included in dental x-rays – an outcome which can only enhance diagnostic acumen and patient care. Interpreting Dental Radiographs is an excellent addition to the Quintessentials for General Dental Practitioners Series, filled from cover to cover with information for immediate chairside application.

Nairn Wilson Editor-in-Chief

Preface

Radiography is an essential tool in dental practice and almost all patients will need a radiograph at some point during a course of treatment. Successful radiography requires well-maintained and safe equipment, careful film handling, accurate technique and controlled processing. Once a radiograph is produced it must be interpreted correctly. This book aims to provide a guide to successful radiological interpretation.

In preparing the book, we made an early decision to focus principally upon the more common radiological diagnostic tasks. While the choice of subjects making up the chapters is fairly predictable, the content was influenced heavily by the correspondence each of us has had with dentists in general practice over the years. General dental practitioners frequently send radiographs to us for an opinion, a service we are happy to provide. Time has informed us that certain conditions, anomalies and lesions recur as diagnostic problems and we have used this experience to help design the book.

Radiology is an expanding clinical discipline, with new technologies adding to the traditional armamentarium of x-ray set and film or cassette. However, in this book we make no apologies for sticking with the more traditional images that make up the overwhelming workload of the average dentist. In particular, we have decided to concentrate upon intraoral radiography, although there are some exceptions. In some places we refer to “image receptor”, to acknowledge the increasing use of digital radiographic systems in dentistry.

Keith Horner John Rout Vivian E Rushton

Chapter 1

Basic Principles

Aim

The aims of this foundation chapter are threefold: first, to give an understanding of the nature of the radiographic image and the factors that govern its formation; second, to recognise the limitations of radiographs; finally, to describe a systematic approach to image interpretation.

Introduction

Our eyes constantly expose our brain to “images”. Our binocular vision allows us to cope with three-dimensions while our colour vision helps to characterise the subtle variations of the objects around us. In contrast, radiographs seem to present a far simpler view on things: x-ray images are two-dimensional and consist of black, white and shades of grey. Interpretation of radiographic images, however, poses very different challenges from those presented by everyday vision. An understanding of these is essential to interpretation.

What Makes the Image?

Image formation begins with a pattern of x-rays hitting the image receptor (film, intensifying screen/film combination or digital receptor). This pattern is recorded, either chemically (film) or electronically (digital radiography), and displayed as a pattern of densities. The image you see is dictated principally by three factors:

the nature of the radiation

the nature of the objects lying between the x-ray source and the receptor

the characteristics of the image receptor.

The Nature of the Radiation

X-ray energy and intensity are the important factors here.

X-ray energy

X-rays are high-energy, high frequency, short wavelength electromagnetic radiation. However, “x-rays” cover a band within the electromagnetic spectrum ranging from lower energy (lower frequency, longer wavelength) to higher energy (higher frequency, shorter wavelength). How the radiation that comes out of your x-ray set fits into this range of energies depends principally upon the kilo Voltage (kV). Most modern dental x-ray sets in the UK are in the 65 to 70kV band. Previously, many sets were manufactured to operate at 50kV. While the kV affects radiation dose, in this chapter we are concerned with the radiographic image. In this context, lower kV leads to high-contrast “black and white” images with few intermediate grey tones. Relatively higher kV produces images with more subtle variation in grey tones (longer grey scale) and lower overall contrast (Fig 1-1).

Fig 1-1 These images of a tooth and a small aluminium step wedge were produced at 50kV (top) and 90kV (bottom). The difference is subtle but the 50kV image shows greater contrast, seen most easily on the stepwedge.

X-ray intensity

The greater the intensity of x-rays the more radiation hits the film. This produces a higher-density (“darker”) image.

The Nature of the Object

The factors included in the “nature” of the objects are as follows.

Atomic number

Fig 1-2 The most striking example of the effect of atomic number upon x-ray absorption is seen with an everyday radiograph. This bitewing shows the enormous contrast difference between metallic restorations (high atomic number) and everything else. The gold crown is very radiopaque because of its very high atomic number, while the composite restorations in a number of teeth are comparatively radiolucent. The bone and teeth (moderately high atomic number elements) are, in turn, substantially more radiopaque than areas showing soft tissues (low atomic number elements).

Physical density

Atomic size is not the only factor of importance in x-ray attenuation. Physical density also plays a significant role. The most practical example of this is the contrast between air and soft tissues. While the mean atomic numbers of these are quite small, the relatively low density of air means that there is a very obvious contrast on radiographs at air/soft tissue boundaries (Fig 1-3).

Fig 1-3 Air/soft tissue interfaces. Despite the fairly small difference in average atomic number between soft tissues and air, a visible contrast is present due to the large difference in density. The tongue outline is shown by white arrows, the soft palate posterior surface with black arrows.

Thickness and shape

Thicker objects absorb more x-rays than thinner ones of the same material. Of course, in nature, objects are of variable thickness and usually have rounded margins. This means that in a two-dimensional radiograph the object will vary in its radiopacity according to its shape.

In practice, these three factors (atomic number, density and thickness) combine to govern the absorption of x-rays. However, the radiographic image depends upon the ability of the receptor (film, intensifying screen/film combination or digital receptor) to record and display the information in the attenuated x-ray beam.

The Characteristics of the Image Receptor

The important characteristics of the image receptor are:

density

contrast

size of silver halide grains.

Density and contrast are partly governed by the characteristics of the objects in the x-ray beam (atomic number, physical density and thickness, as described above) but are also profoundly influenced by the radiographic process itself. In particular, image receptors all have individual “characteristic curves”, that relate the density to the x-ray exposure. This relationship is only linear for some digital systems, all others being non-linear (Fig 1-4). The reasons for this, and the details of the curves for different image receptors, are not relevant to this book. The important point is that changing the image receptor (e.g. changing from one manufacturer of film to another) will have effects upon the character of the image you see, all other factors being equal.

Fig 1-4 Characteristic curve for dental x-ray film(s). Optical density (vertical axis) indicates the “darkness” of the film. For the same density, film A requires less exposure than film B. Film A is, therefore, the faster film.

The size of the silver halide grains in the emulsion has a strong influence upon the ability of a radiograph to differentiate between structures that lie close together (resolution). Resolution is objectively measured by radiographing test objects containing very fine metal wires of decreasing thickness and intervening distance. It can be expressed as the number of line pairs per millimetre (l.p. mm-1). Dental intraoral film has very high resolution – around 20 l.p.mm-1 – greater than the detail visible to the unaided human eye. This explains why magnification of intraoral (periapical, bitewing) radiographs not only increases image size but also improves the detail that can be perceived. Most intensifying screen/film cassette combinations, such as would be used for panoramic radiography, have a resolution of around 5 to 6 l.p. mm-1, explaining why radiographs produced using cassettes can never reproduce detail as well as intraoral film. The resolution of digital receptors used for intraoral radiography has been estimated at between 6 and 15 l.p. mm-1, depending on the system used. This, in part, may explain research findings that reveal that some intraoral digital systems are less effective at demonstrating fine root canal systems and fine endodontic files than conventional film. Three images of the same object on different image receptors that demonstrate resolution differences are shown in Fig 1-5. Using larger grain sizes is one way of increasing film speed. Thus, higher speed to reduce dose to patients involves a trade-off in terms of a reduction in sharpness of the image. Image sharpness is discussed in more detail below.

Fig 1-5 Three radiographs of the same tooth, taken using conventional dental film (right), an intensifying screen/film cassette combination (centre) and a digital intra-oral x-ray system (left). The difference in image sharpness is obvious, with conventional dental film being best. Indeed, at this magnification the grains of this fast emulsion (F-speed) dental film are visible.

How “Accurate” is a Radiographic Image?

We tend to rely a lot on radiographs in dentistry. This reliance is based upon a trust that the image represents the truth accurately. In reality, no radi-ographic image can be a perfect representation of life. Some of the factors that should be considered are:

magnification

image sharpness

spatial perspective

temporal perspective.

Magnification

All conventional radiographic images are magnified. Radiographs are “shadow pictures” and the size of the shadow depends upon the relative relationship of x-ray source, object and image receptor.

But we can use simple geometry (Fig 1-6) to redefine magnification as:

Fig 1-6 Magnification (M) can be defined as the size of the image divided by the size of the object. It is easier to measure in practice, however, by dividing the source to film distance by the source to object distance.

Thus, to produce an image with as little magnification as possible, we would choose an arrangement where the object was as close to the film as possible and where the x-ray source was far away from both. Many old dental x-ray machines used a very short x-ray source-to-skin distance (10cm). These gave relatively high magnifications compared to the modern machines using a 20cm or 30cm x-ray source-to-skin distance. Because magnification cannot be eliminated in conventional radiography we should use reference markers of known length when measuring distances, e.g. files in endodontic working length estimation.

In digital radiography, images are displayed on the computer monitor at various stated magnifications. However, it is important to remember that a “life-size” image (x 1 magnification) refers to the size of the object as recorded on the digital receptor surface, and will still have some magnification depending on the geometric relationship of x-ray source/object/receptor described above.

Image Sharpness

A radiographic image is always less “sharp” in its outline and its internal detail than the original object. In part, this is related to the fact that, inside the x-ray machine, the radiation derives from an area (the focal spot) rather than an infinitely small point (Fig 1-7). Thus, the “umbra” (= “shadow”) of an object will be surrounded by a “penumbra”, or peripheral blur. Clearly, the bigger the focal spot of the x-ray machine, the greater the blurring. Most dental x-ray sets have a focal spot about 1 mm in width. Focal-spot size tends to increase over years of use. Therefore, at least in theory, years of use will lead to a gradual reduction in image sharpness.

Fig 1-7 x-rays are produced in an x-ray tube (inset image). The main picture shows a close-up of the anode. The focal spot is visible as a small rectangular area on the anode surface.

Penumbra size increases as the distance from focal spot to object decreases and that from object to image receptor increases, as shown in Fig 1-8. Thus, for intraoral radiography the “ideal” situation is to have a very long distance from x-ray source to the patient, with the image receptor as close to the tooth as possible (exactly the same “ideal” as that for reducing magnification). With the paralleling technique for intraoral periapical radiography, the film has to be placed at a distance from the tooth and a longer focus-to-skin distance is needed compared to the old bisecting angle technique, where the film could be pressed closely to the tooth. This is why the paralleling technique is sometimes called the “long-cone” technique.

Fig 1-8 Penumbra, or peripheral blurring, is produced by the fact that x-rays are produced not from a point source but from an area (A). The size of the penumbra is reduced by moving the object closer to the film, or by increasing the distance from the source to the object and film (B).

Sharpness is also influenced by the characteristics of the image receptor (as discussed above).

Spatial Perspective

On radiographs the three dimensions (height, width and depth) are converted to just two (height and width). Inevitably, therefore, the observed image depends upon perspective.

In the dental context, an appreciation of depth in an image is often gained by prior knowledge of normal anatomy. For example, we know that the incisive (nasopalatine) foramen lies to the palatal side of the upper central incisors. However, where anatomical knowledge is not helpful, three-dimensional appreciation can only be restored to radiography by viewing two radiographs with a differing perspective. At its simplest, this will involve taking two images at right angles (Fig 1-9). However, two images with only marginal differences in perspective allow interpretation of three dimensions by using the principle of parallax.

Fig 1-9