A Textbook of Orthodontics 3rd ed. - T. Foster (Blackwell, 1990) WW

351 Pages·1990·5.77 MB·English

A Textbook of Orthodontics

T. D. FOSTER
DDS, FDS, DOrthRCS
Emeritus Professor of
Children's Dentistry and Orthodontics,
University of Birmingham;
Honorary Consultant in
Children's Dentistry and Orthodontics,
Central Birmingham
Health Authority (Teaching)

THIRD
E D I T I O N

BLACKWELL SCIENTIFIC PUBLICATIONS

OXFORD LONDON

EDINBURGH BOSTON MELBOURNE

To my wife

© 1975, 1982, 1990 by
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First published 1975
Second edition 1982
Third edition 1990

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British Library
Cataloguing in Publication Data

Foster, T. D. (Thomas Donald)
A textbook of orthodontics. — 3rd ed.
1. Dentistry. Orthodontics
L Title
617.6'43

ISBN 0-632-02654-5

Contents

Preface to third edition, vii

Preface to first edition, ix

1
Postnatal growth of the skull and jaws, 1

2
The occlusion of the teeth, 24

3
The development of the occlusion of the teeth, 44

4
Skeletal factors affecting occlusal development, 75

5 Muscle factors affecting occlusal development, 109

6
Dental factors affecting occlusal development, 129

7
Localized factors affecting the development of the occlusion, 147

8
The need for orthodontic treatment, 179

9
Orthodontic tooth movement, 183

10 The planning of orthodontic treatment, 202

11 The extraction of teeth in orthodontic treatment, 209

12
Principles of orthodontic appliances, 231

13 Principles of removable appliance treatment, 245

14 Principles of fixed appliance treatment, 260

15 Principles of functional appliance treatment, 274

16 Principles of treatment in Class 1 occlusal relationship, 283

17 Principles of treatment in Class 2 occlusal relationship, 286

18 Principles of treatment in Class 3 occlusal relationship, 310

19 Orthodontic treatment related to growth, 324

20
Orthodontics and preventive dentistry, 337

Index, 343

v

Preface to third edition

The science and art of orthodontics continues to receive a vigourous
input, both from research and from clinical development. There is a
growing emphasis on the quality of treatment results, particularly from
the aspect of functional occlusion, and a growing awareness that treat-
ment of the more complex problems requires careful evaluation and
sophisticated appliances in skilled hands. Nevertheless, there remains a
need for all dentists to understand the background to the natural occlu-
sion and its variations, and to the rationale of orthodontic treatment,
and this remains the aim of the book.

In preparing this third edition, once again the relevant literature
of the past six years has been reviewed, and there has been a general
updating. Most of the older references have been replaced, though refer-
ence to some of the 'classic' historical work remains. The sections on
occlusion and on cephalometrics have been largely rewritten, and addi-
tions and amendments have been made to all sections of the book in
accordance with the most recent research findings. A further change has
been the inclusion of a list of references at the end of each chapter,
where it is felt they may be more useful than at the end of the book.

I am again indebted to my colleagues and my students for their help,
both direct and indirect, and particularly to Dr W. P. Rock, Mr R. I. W.
Evans, Dr A. P. Howat and Mr S. Weerakone for the provision of illustra-
tions, and to Miss Jennifer Moses for the preparation of the typescript.

vii

Preface to first edition

Orthodontics is a subject which has aroused a good deal of healthy con-
troversy. Much of the knowledge on the subject has been gained from
clinical experience, though there is an increasing emphasis on scientific
investigation as a background to clinical methods.

The practice of orthodontics needs to be learned clinically, by prac-
tical experience, but a knowledge of the theoretical background is
essential for successful practice. This book has been written in order to
present the background to current orthodontic practice. It is not
intended as a recipe book; rather it is hoped that it provides the student
with a rational explanation of the aetiology of the occlusion and position
of the natural dentition, and of the treatment of occlusal discrepancies.

Orthodontic practice deals very largely with the wide range of
normal variation. For this reason, pathological abnormalities have been
excluded and variation has been emphasized. In those areas of the
subject where there is difference of opinion, an attempt has been made
to put forward the various views where these are supported by evidence
from published work, and, where possible, to draw some rational line in
the light of personal experience.

In producing this book, I am conscious of the help given, both
directly and indirectly by my colleagues. I would like to acknowledge
the assistance of those who have made available clinical records and
who have helped with the preparation of illustrative material. In
particular, I wish to thank Mr M. R. Sharland and Mr M. C. Walker for
the production of the photographs, and Miss Jennifer Jones for the
preparation of the typescript.

ix

1

Postnatal growth of the skull and jaws

Most orthodontic treatment at the present time is carried out during the
growth period, between the ages of 10 and 15 years. The occlusion and
position of the teeth is also established during the growth period, and
changes after growth has finished are of relatively minor degree. It is
probable that interference with the occlusion in the early stages of
growth, for example by extraction of teeth, produces some alteration in
occlusal development. Furthermore, patterns of growth of the jaws and
development of the occlusion, which vary between individuals, may
have a bearing on the need for orthodontic treatment and the timing
and type of treatment prescribed.

For these reasons a knowledge of growth of the skull and jaws and of
occlusal development should be of importance in orthodontic practice.
Although at present much orthodontic treatment is carried out on the
basis of a snapshot picture of the occlusion, without knowledge of pre-
vious growth, there is an increasing awareness that a knowledge of
previous growth changes may be important in planning treatment, and
that the timing of treatment in relation to growth may facilitate the
progress of such treatment.

There are many growth studies in progress in various parts of the
world which have particular emphasis on dental occlusion. There is also
much research on growth of the skull and jaws in more general terms.
In spite of this, such growth is far from being completely understood,
particularly because a great deal of variation exists in the detail of
growth changes. This variation makes it difficult to formulate general
rules about growth changes, except in very broad terms.

In this chapter it is proposed to outline the present knowledge on
postnatal skull and jaw growth, asking the questions when, where, how
and why does growth proceed.

The skull and jaws at birth

At birth, the skull is far from being merely a small version of the adult
skull. There are differences in shape, in proportion of the face and the
cranium and in the degree of development and fusion of the individual
bones. Some bones, which in the adult are single bones, are still in
1
separate constituent parts at birth. Other bones, which in the adult are

2
CHAPTER 1

closely joined to their neighbours at sutures, are, at birth, widely
separated from neighbouring bones. Bones which have developed from
cartilage, mainly those at the base of the skull, still have a cartilaginous
element actively growing. Bones which have developed from mem-
brane, mainly those of the calvarium and face, still have wide
membranous areas at their margins actively forming bone. The main
features of the skull at birth can be summarized as follows (Figs. 1.1, 1.2,
1.3).

Bones in separate component parts

1 At the base of the skull the sphenoid bone is in three parts, the
central body with its two lesser wings, and on each side the greater wing
and its attached pterygoid process.
2
The occipital bone is in two parts, the condylar part which carries
the occipital condyles, and the squamous part, much of which has
developed from membrane and forms part of the calvarium.
3
The temporal bone on each side is in two parts, the petromastoid
component which has developed from the cartilaginous neurocranium,

Fig. 1.1. Side view of the skull at birth, showing the wide separation of the cranial bones
and the fontanelles at the corners of the parietal bone (P). The main components of the
occipital bone are still ununited.

3
POSTNATAL GROWTH OF THE SKULL AND JAWS

Fig. 1.2. Front view of the skull
at birth. The frontal bone and the
mandible are in two parts; divided
in the mid-line.

Fig. 1.3. Diagrammatic representation of the base of the skull at birth. The sphenoid bone
is in three component parts, the temporal bones in two parts and the occipital bone in two
parts.

4
CHAPTER 1

and the squamous component which has developed from the mem-
branous neurocranium.
4
The frontal bone and the mandible, which will eventually become
single bones, are each in two parts at birth, the parts being separated in
the mid-sagittal plane.

Bones widely separated from neighbouring bones

In general, the sutures of the skull are wider at birth than in the adult,
being areas of active bone formation. This separation is particularly
noticeable at the four corners of the parietal bone where the areas of
membrane between the parietal bone and neighbouring bones form the
six fontanelles. These are the anterior and posterior fontanelles in the
mid-sagittal plane where the parietal bones meet the frontal and
occipital bones respectively, and the antero-lateral and postero-lateral
fontanelles on each side, at the junction of parietal, sphenoid and frontal
bones and parietal, temporal and occipital bones respectively.

The sphenoid and occipital bones, which eventually will become
fused at the base of the skull, are still separated at birth by a cartilaginous
area, the spheno-occipital synchondrosis.

Relative sizes of the face and the cranium

The relationship in size between the face and the cranium is notice-
ably different at birth from that in the adult. The cranium, or more
properly the neurocranium, has grown rapidly in the prenatal period,
accommodating the rapidly developing brain. The face, or vis-
cerocranium, has developed less towards its adult size than has the
cranium, with the result that at birth the face appears small in the
vertical dimension in relation to the total size of the head when
compared with the proportions in the adult (Fig. 1.4). The main reasons
for this lie in the form of the maxilla and mandible. These bones, which
form the main contribution to the vertical dimension of the face, are
relatively small at birth. The maxillary antrum is little more than a flat
space, compared with its much greater vertical depth in the adult (Fig.
1.5). The mandible is relatively straight, with a more obtuse gonial angle
than in the adult. In both bones there are no erupted teeth, and
consequently little vertical development of alveolar bone. The articular
fossae for the mandible on the temporal bones are relatively flat, giving
possibility for a wide range of mandibular movement.