A DENTAL PRACTITIONER HANDBOOK SERIES EDITED BY DONALD D. DERRICK, D.D.S., L.D.S., R.C.S. ORTHODONTIC DIAGNOSIS W. J. B. HOUSTON F.D.S. R.C.S. Edin., Ph.D., D.ORTH. Professor of Orthodontics Royal Dental Hospital of London School of Dental Surgery COPYRIGHT NOTICE © JOHN WRIGHT & SONS, LTD., 1975 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 other wise, without the prior permission of the Copyright owner. ISBN 0 7236 0380 4 PRINTED IN GREAT BRITAIN BY HENRY LING LTD., A SUBSIDIARY OF JOHN WRIGHT & SONS LTD., AT THE DORSET PRESS, DORCHESTER PREFACE IT is ten years since a book of this title first appeared in the Dental Practitioner Handbook series under the authorship of Dr. J. S. Beresford. When I was asked to revise it, 1 felt that the style was so characteristic of its first author that modification by another would not produce a satisfactory result. An entirely new version was decided upon and the opportunity was taken to update the content and to revise the layout. However, the objectives of the book remain unchanged: to present to undergraduate students and dental practitioners the basis of modern orthodontic diagnosis. The publication of a text on orthodontic diagnosis without a corresponding section on treatment methods is unusual but has a number of advantages: orthodontic treatment methods vary but the factors to be taken into account in formulating a treatment plan should be common to all systems; and furthermore, this diagnostic procedure should form the basis of the dental examination of any patient. The advanced diagnostic aids, such as cephalometric radiographs, of the specialist orthodontist are not dealt with in depth for two reasons: firstly because a thorough exposition of the uses and limitations of these methods would have occupied a disproportionate part of the text; and secondly because these aids are not usually available to the general dental practitioner for whom this text was primarily written. The examination of a patient's facial morphology and function and of the occlusal pattern need take little extra time once experience has been gained. This is time well spent because it should lead to a more adequate appreciation of the patient's dental problems and it can greatly add to the interest of dental practice. A number of colleagues have made helpful and constructive comments on this work but I cannot mention them all by name. I would particularly like to thank Mr. K. G. Isaacson for his help. Mr. B. J. Webber prepared the models and Mr. K. F. Taylor was responsible for the photography. Finally, I wish to record my appreciation to Miss A. Taylor for her expert secretarial assistance. January, 1975 W.J.B.H. CONTENTS 1. Normal Occlusion .. .. .. .. 1 2. Malocclusion .. .. .. .. .. 9 3. Orthodontic Records .. .. .. .. 24 4. Dental Base Relationship .. .. .. .. 31 5. Soft Tissue Morphology and Activity .. .. 40 6. Mandibular Positions and Paths of Closure .. .. 47 7. Intra-oral Examination .. .. .. .. 54 8. Objectives of Orthodontic Treatment .. .. 58 9. Treatment Planning .. .. .. .. 62 Conclusion .. .. .. .. .. .. 73 Glossary of Terms .. .. .. .. .. 74 Index .. .. .. .. .. .. 79 CHAPTER 1 NORMAL OCCLUSION A DISCUSSION of normal occlusion is an appropriate starting point for a work on orthodontic diagnosis because 'malocclusions' are judged as departures from the 'normal'; and orthodontic treatment is designed to produce a more 'normal' relationship of the teeth. It is important to distinguish 'normal occlusion' from 'ideal occlusion'. Ideal occlusion is a theoretical concept based on the morphology of the teeth, but it is almost never found in nature and it is not a realistic treatment goal because few patients will have the full complement of 32 teeth in perfect occlusion at the end of ortho dontic treatment. The value of ideal occlusion is as a theoretical standard by which other occlusions can be judged. Being a theoret ical concept based on the anatomy of the unworn teeth, ideal occlusion does not take account of the changes that occur with age. In contrast with ideal occlusion, there can be no precise description of normal occlusion. Normal occlusion allows for minor variations from the ideal which are aesthetically and functionally satisfactory. Thus normal occlusion includes slight irregularities of tooth align ment and relationship. More severe tooth malpositions and mal- relationships between the arches are described as 'malocclusions'. This rather vague description of the normal may seem unsatis factory but it is in conformity with other usages of 'normal': it is not possible to specify the limits of normal height or intelligence any more exactly than it is to demarcate the limits of normal occlusion. Because the boundaries between normal occlusion and malocclusion are unclear, it is possible to find disagreement even between experts on the categorization of borderline cases. FEATURES OF NORMAL OCCLUSION IN THE DECIDUOUS DENTITION Arch Form and Alignment {Fig. la) The arches are regular in form and all deciduous teeth must be present, of normal form and in correct alignment. Unlike the per manent dentition, spacings of two types may be present: (1) Spacings between the incisors. (2) So-called 'primate' spacings mesial to the upper canine and distal to the lower canine. Arch Relationship (Fig. lb) The upper arch is wider and longer than the lower. Thus the buccal 1 ORTHODONTIC DIAGNOSIS cusps of the upper molars should overlap the lower molars and the upper incisors should overlap the lower incisors establishing a normal overjet relationship. The overjet in the ideal deciduous dentition Fig. 1.—Normal occlusion in the deciduous dentition. should be about 2 mm. and the overbite should be about one third of the height of the lower incisor crowns. Each lower tooth (except for the lower central incisor), should occlude both with the corresponding upper tooth and with the upper tooth in front (Fig. lb). However, because the lower second deci- NORMAL OCCLUSION duous molar is longer than the upper the terminal surfaces of the deciduous arches should be flush. FEATURES OF NORMAL OCCLUSION IN THE PERMANENT DENTITION Arch Form and Alignment The arches are regular in form. All teeth must be present, of normal form and in correct alignment. There should be correct approximal contacts between each of the permanent teeth. The permanent incisors, particularly the uppers, are more proclined than the deciduous incisors. Arch Relationship (Fig. 2) As in the deciduous dentition, the buccal cusps of the upper cheek teeth should overlap the lowers and the upper incisors should overlap the lower incisors both horizontally (overjet) and vertically (overbite). Fig. 2.—Normal occlusion in the permanent dentition. The lower incisor edges should occlude with the middle part of the palatal surface of the upper incisors. Provided that the angulation between the upper and lower incisors is average, this will ensure a normal overjet and overbite. Each lower tooth should occlude both with the corresponding upper tooth and, apart from the central incisor, with the upper tooth anterior to it. As in the deciduous dentition, the arches should terminate in the same plane because the lower third molar is longer than the corresponding upper molar. ORTHODONTIC DIAGNOSIS THE DEVELOPMENT OF NORMAL OCCLUSION It is important to recognize that there are considerable variations in both the timing and sequence of eruption of the teeth. The Deciduous Dentition The upper gum pad is wider than the lower and overlaps it laterally and anteriorly {Fig. 3). In the infant the gum pads are rarely brought Birth 3 years 6 years years Fig. 3.—Stages in the development of normal occlusion. into contact and the tongue lies between them in contact with the lips and cheeks. Deciduous incisors often start to erupt at about 6 months of age and the usual order and times of eruption of the deciduous teeth are indicated in Table I. By the age of 3 years the deciduous dentition should be complete and the features at this stage have already been described. Changes in the Deciduous Occlusion Between the ages of 3 and 6 years changes may occur in the deciduous 4 NORMAL OCCLUSION occlusion. These commonly include an increase in intercanine width so that spacing develops or increases between the deciduous incisors and, provided that occlusal wear of the deciduous teeth has flattened Table 1. TYPICAL AGES OF ERUPTION AND MESIODISTAL WIDTHS OF THE DECIDUOUS TEETH Time of eruption Mesiodistal width in months in mm. Maxillary Teeth Central incisor 8 6-5 Lateral incisor 9 50 Canine 18 6-5 First molar 14 70 Second molar 24 8-5 Mandibular Teeth Central incisor 6 40 Lateral incisor 7 4-5 Canine 16 5-5 First molar 12 80 Second molar 20 9-5 Note: Eruption times vary considerably—up to 6 months earlier or later than the times given is not unusual. Mesiodistal widths vary by up to 20 per cent on either side of the figures given. Table 2. TYPICAL AGES OF ERUPTION AND MESIODISTAL WIDTHS OF THE PERMANENT TEETH Time of eruption Mesiodistal width in years in mm. Maxillary Teeth Central incisor 7-5 8-5 Lateral incisor 8-5 6-5 Canine 11-5 80 First premolar 100 70 Second premolar 110 6-5 First molar 60 100 Second molar 120 9-5 Mandibular Teeth Central incisor 6-5 5-5 Lateral incisor 7-5 60 Canine 100 70 First premolar 10-5 70 Second premolar 110 70 First molar 60 110 Second molar 120 10-5 Note: The figures given both for eruption times and for mesiodistal widths commonly vary by up to 20 per cent on either side of the figures given. off" the cusps and reduced the crown height of the deciduous incisors, the lower arch may move forwards in relation to the upper so that the incisors occlude edge-to-edge {Fig. 3). This change in arch relationship reflects a change in dental base relationship due to