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

351 Pages·1990·5.77 MB·English
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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 Blackwell Scientific Publications Editorial Offices: Osney Mead, Oxford OX2 OEL 25 John Street, London WC1N 2BL 23 Ainslie Place, Edinburgh EH3 6AJ 3 Cambridge Center, Suite 208 Cambridge, Massachusetts 02142, USA 107 Barry Street, Carlton Victoria 3053, Australia All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior permission of the copyright owner First published 1975 Second edition 1982 Third edition 1990 Set by Best-Set Typesetter Ltd, Hong Kong Printed and bound in Great Britain by William Clowes Limited, Becclcs and London DISTRIBUTORS Marston Book Services Ltd PO Box 87 Oxford 0X2 ODT (Orders: Tel: (0865) 791155 Fax:(0865)791927 Telex: 837515) USA Year Book Medical Publishers 200 North LaSalle Street Chicago, Illinois 60601 (Orders: Tel: (312) 726-9733) Canada The C. V. Mosby Company 5240 Finch Avenue East Scarborough, Ontario (Order: Tel: (416) 298-1588) Australia Blackwell Scientific Publications (Australia) Pty Ltd 107 Barry Street Carlton, Victoria 3053 (Orders: Tel: (103) 347-0300) 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.

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