An Introduction to Orthodontics PDF

an introduction to orthodontics This page intentionally left blank an introduction to orthodontics F OURTH ED IT IO N Laura Mitchell MBE MDS, BDS, FDSRCPS (Glasg), FDSRCS (Eng), FGDP (UK), D. Orth RCS (Eng), M. Orth RCS (Eng)...

an introduction to orthodontics This page intentionally left blank an introduction to orthodontics F OURTH ED IT IO N Laura Mitchell MBE MDS, BDS, FDSRCPS (Glasg), FDSRCS (Eng), FGDP (UK), D. Orth RCS (Eng), M. Orth RCS (Eng) Consultant Orthodontist, St. Luke’s Hospital, Bradford Honorary Senior Clinical Lecturer, Leeds Dental Institute, Leeds With contributions from Simon J. Littlewood MDSc, BDS, FDS (Orth) RCPS (Glasg), M. Orth RCS (Edin), FDSRCS (Eng) Consultant Orthodontist, St. Luke’s Hospital, Bradford Honorary Senior Clinical Lecturer, Leeds Dental Institute, Leeds Zararna L. Nelson-Moon MSc, PhD, BDS, FDS (Orth) RCS (Eng), M. Orth RCS (Eng) Consultant Orthodontist and Honorary Senior Clinical Lecturer Leeds Dental Institute, Leeds Fiona Dyer MMedSci, BChD, FDS (Orth) RCS (Eng), M. Orth RCS (Eng), FDS RCS (Eng) Consultant Orthodontist and Honorary Clinical Lecturer Charles Clifford Dental Hospital, Sheffield 1 Great Clarendon Street, Oxford OX2 6DP, United Kingdom Oxford University Press is a department of the University of Oxford. It furthers the University’s objective of excellence in research, scholarship, and education by publishing worldwide. Oxford is a registered trade mark of Oxford University Press in the UK and in certain other countries © Laura Mitchell, 2013 The moral rights of the authors have been asserted This edition published 2013 First edition published 1996 Second edition published 2001 Third edition published 2007 Impression: 1 All rights reserved. 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Readers must therefore always check the product information and clinical procedures with the most up-to-date published product information and data sheets provided by the manufacturers and the most recent codes of conduct and safety regulations. The authors and the publishers do not accept responsibility or legal liability for any errors in the text or for the misuse or misapplication of material in this work. Except where otherwise stated, drug dosages and recommendations are for the non-pregnant adult who is not breastfeeding. Links to third party websites are provided by Oxford in good faith and for information only. Oxford disclaims any responsibillty for the materials contained in any third party website referenced in this work. Preface for fourth edition I would like to thank the readers of previous editions and in particular those that have passed on their suggestions for this the fourth edition. Online Resource Centre References for this chapter can also be found at: www.oxfordtextbooks.co.uk/orc/mitchell4e/. Where possible, these are presented as active links which direct you to the electronic version of the work, to help facilitate onward study. If you are a subscriber to that work (either individually or through an institution), and depending on your level of access, you may be able to peruse an abstract or the full article if available. Acknowledgements It is difficult to know where to start in terms of thanking those that have assisted with this new edition. How- ever, without the help and hard work of my co-authors, in particular Simon Littlewood, a fourth edition would not have been possible. I should also mention our colleagues and the support staff of the units at which we work for their assistance in getting good quality illustrations and also for their forbearance during the time of writing. I would like to acknowledge Joanne Birdsall who kindly assisted Fiona Dyer with the preparation of Chapter 15. The functional appliances illustrated in Chapter 19 were produced by the Senior Orthodontic technician at St. Luke’s Hospital Bradford, Nigel Jacques and are testament to his consistently good laboratory work. I would also like to thank the staff of Oxford University Press for their help and patience. Finally, once again, I have to pay tribute to the support and encouragement of my husband without which, another edition would not have been possible. Thank you. This page intentionally left blank Brief contents 1 The rationale for orthodontic treatment 1 2 The aetiology and classification of malocclusion 9 3 Management of the developing dentition 17 4 Craniofacial growth, the cellular basis of tooth movement and anchorage (Z. L. Nelson-Moon) 33 5 Orthodontic assessment (S. J. Littlewood) 53 6 Cephalometrics 73 7 Treatment planning (S. J. Littlewood) 85 8 Class I 101 9 Class II division 1 113 10 Class II division 2 127 11 Class III 137 12 Anterior open bite and posterior open bite 149 13 Crossbites 159 14 Canines 169 15 Anchorage planning (F. Dyer) 179 16 Retention (S. J. Littlewood) 193 17 Removable appliances 207 18 Fixed appliances 219 19 Functional appliances (S. J. Littlewood) 235 20 Adult orthodontics (S. J. Littlewood) 251 21 Orthodontics and orthognathic surgery (S. J. Littlewood) 263 22 Cleft lip and palate and other craniofacial anomalies 283 23 Orthodontic first aid 295 Definitions 302 Index 305 This page intentionally left blank Detailed contents 1 The rationale for orthodontic treatment 1 5.6 Diagnostic records 63 5.7 Forming a problem list 65 1.1 Definition 2 1.2 Prevalence of malocclusion 2 1.3 Need for treatment 2 6 Cephalometrics 73 1.4 Demand for treatment 4 6.1 The cephalostat 74 1.5 The disadvantages and potential risks of orthodontic 6.2 Indications for cephalometric evaluation 75 treatment 4 6.3 Evaluating a cephalometric radiograph 76 1.6 The effectiveness of treatment 5 6.4 Cephalometric analysis: general points 77 1.7 The temporomandibular joint and orthodontics 6 6.5 Commonly used cephalometric points and reference lines 77 2 The aetiology and classification of malocclusion 9 6.6 Anteroposterior skeletal pattern 78 6.7 Vertical skeletal pattern 81 2.1 The aetiology of malocclusion 10 6.8 Incisor position 81 2.2 Classifying malocclusion 11 6.9 Soft tissue analysis 82 2.3 Commonly used classifications and indices 11 6.10 Assessing growth and treatment changes 83 2.4 Andrews’ six keys 15 6.11 Cephalometric errors 83 6.12 3D Cephalometric analysis 84 3 Management of the developing dentition 17 3.1 Normal dental development 18 7 Treatment planning (S. J. Littlewood) 85 3.2 Abnormalities of eruption and exfoliation 20 3.3 Mixed dentition problems 22 7.1 Introduction 86 3.4 Planned extraction of deciduous teeth 29 7.2 General objectives of orthodontic treatment 86 3.5 What to refer and when 30 7.3 Forming an orthodontic problem list 86 7.4 Aims of orthodontic treatment 87 4 Craniofacial growth, the cellular basis of tooth 7.5 Skeletal problems and treatment planning 88 7.6 Basic principles in orthodontic treatment planning 89 movement and anchorage (Z. L. Nelson-Moon) 33 7.7 Space analysis 90 4.1 Introduction 34 7.8 Informed consent and the orthodontic 4.2 Craniofacial embryology 34 treatment plan 95 4.3 Mechanisms of bone growth 36 7.9 Conclusions 96 4.4 Postnatal craniofacial growth 39 4.5 Growth rotations 42 8 Class I 101 4.6 Craniofacial growth in the adult 43 4.7 Growth of the soft tissues 44 8.1 Aetiology 102 4.8 Control of craniofacial growth 45 8.2 Crowding 102 4.9 Growth prediction 46 8.3 Spacing 105 4.10 Biology of tooth movement 46 8.4 Displaced teeth 110 4.11 Cellular events associated with loss of anchorage 50 8.5 Vertical discrepancies 111 4.12 Cellular events during root resorption 50 8.6 Transverse discrepancies 111 4.13 Summary 51 8.7 Bimaxillary proclination 111 5 Orthodontic assessment (S. J. Littlewood) 53 9 Class II division 1 113 5.1 Introduction to orthodontic assessment 54 9.1 Aetiology 114 5.2 Taking an orthodontic history 54 9.2 Occlusal features 117 5.3 Clinical examination in three dimensions 56 9.3 Assessment of and treatment planning 5.4 Extra-oral examination 56 in Class II division 1 malocclusions 117 5.5 Intra-oral examination 61 9.4 Early treatment 120 xii Detailed contents 9.5 Management of an increased overjet associated 16 Retention (S. J. Littlewood) 193 with a Class I or mild Class II skeletal pattern 120 16.1 Introduction 194 9.6 Management of an increased overjet 16.2 Definition of relapse 194 associated with a moderate to severe Class II 16.3 Aetiology of relapse 194 skeletal pattern 120 16.4 How common is relapse? 196 9.7 Retention 122 16.5 Informed consent and relapse 196 16.6 Retainers 197 10 Class II division 2 127 16.7 Adjunctive techniques used to 10.1 Aetiology 128 reduce relapse 200 10.2 Occlusal features 129 16.8 Conclusions about retention 201 10.3 Management 130 17 Removable appliances 207 11 Class III 137 17.1 Mode of action of removable appliances 208 11.1 Aetiology 138 17.2 Designing removable appliances 208 11.2 Occlusal features 139 17.3 Active components 209 11.3 Treatment planning in Class III 17.4 Retaining the appliance 210 malocclusions 139 17.5 Baseplate 212 11.4 Treatment options 140 17.6 Commonly used removable appliances 213 17.7 Fitting a removable appliance 214 12 Anterior open bite and posterior open bite 149 17.8 Monitoring progress 215 17.9 Appliance repairs 216 12.1 Definitions 150 12.2 Aetiology of anterior open bite 150 18 Fixed appliances 219 12.3 Management of anterior open bite 152 12.4 Posterior open bite 156 18.1 Principles of fixed appliances 220 18.2 Indications for the use of fixed appliances 222 18.3 Components of fixed appliances 222 13 Crossbites 159 18.4 Treatment planning for fixed appliances 227 13.1 Definitions 160 18.5 Practical procedures 228 13.2 Aetiology 160 18.6 Fixed appliance systems 228 13.3 Types of crossbite 161 18.7 Demineralization and fixed appliances 231 13.4 Management 163 18.8 Starting with fixed appliances 232 14 Canines 169 19 Functional appliances (S. J. Littlewood) 235 14.1 Facts and figures 170 19.1 Definition 236 14.2 Normal development 170 19.2 History 236 14.3 Aetiology of maxillary canine displacement 170 19.3 Overview 236 14.4 Interception of displaced canines 172 19.4 Case study: functional appliance 236 14.5 Assessing maxillary canine position 172 19.5 Timing of treatment 240 14.6 Management of buccal displacement 173 19.6 Types of malocclusion treated with 14.7 Management of palatal displacement 175 functional appliances 241 14.8 Resorption 176 19.7 Types of functional appliance 241 14.9 Transposition 177 19.8 Clinical management of functional appliances 247 19.9 How functional appliances work 248 15 Anchorage planning (F. Dyer) 179 19.10 How successful are functional appliances? 249 15.1 Introduction 180 20 Adult orthodontics (S. J. Littlewood) 251 15.2 Assessing anchorage requirements 180 15.3 Classification of anchorage 183 20.1 Introduction 252 15.4 Intra-oral anchorage 183 20.2 Specific problems in adult orthodontic 15.5 Extra-oral anchorage 186 treatment 252 15.6 Monitoring anchorage during treatment 189 20.3 Orthodontics and periodontal disease 253 15.7 Common problems with anchorage 190 20.4 Orthodontic treatment as an adjunct to 15.8 Summary 190 restorative work 254  Detailed contents xiii 20.5 Aesthetic orthodontic appliances 257 22.3 Classification 284 20.6 Obstructive sleep apnoea and mandibular 22.4 Problems in management 285 advancement splints 260 22.5 Co-ordination of care 287 22.6 Management 288 21 Orthodontics and orthognathic surgery 22.7 Audit of cleft palate care 291 (S. J. Littlewood) 263 22.8 Other craniofacial anomalies 291 21.1 Introduction 264 23 Orthodontic first aid 295 21.2 Indications for treatment 264 21.3 Objectives of combined orthodontics 23.1 Fixed appliance 296 and orthognathic surgery 266 23.2 Removable appliance 298 21.4 The importance of the soft tissues 266 23.3 Functional appliance 298 21.5 Diagnosis and treatment plan 266 23.4 Headgear 299 21.6 Planning 271 23.5 Miscellaneous 299 21.7 Common surgical procedures 272 21.8 Sequence of treatment 274 Definitions 302 21.9 Retention and relapse 278 Index 305 21.10 Future developments in orthognathic surgery: 3D surgical simulation 278 22 Cleft lip and palate and other craniofacial anomalies 283 22.1 Prevalence 284 22.2 Aetiology 284 This page intentionally left blank 1 The rationale for orthodontic treatment Chapter contents 1.1 Definition 2 1.2 Prevalence of malocclusion 2 1.3 Need for treatment 2 1.3.1 Dental health 3 1.3.2 Psychosocial well-being 4 1.4 Demand for treatment 4 1.5 The disadvantages and potential risks of orthodontic treatment 4 1.5.1 Root resorption 4 1.5.2 Loss of periodontal support 5 1.5.3 Demineralisation 5 1.5.4 Soft tissue damage 5 1.5.5 Pulpal injury 5 1.6 The effectiveness of treatment 5 1.7 The temporomandibular joint and orthodontics 6 1.7.1 Orthodontic treatment as a contributory factor in TMD 6 1.7.2 The role of orthodontic treatment in the prevention and management of TMD 6 Principal sources and further reading 7 2 The rationale for orthodontic treatment Learning objectives for this chapter Gain an understanding of the differences between need and demand for treatment Gain an appreciation of the benefits and risks of orthodontic treatment Gain an understanding of the limitations of orthodontic treatment 1.1 Definition Orthodontics is that branch of dentistry concerned with facial growth, with development of the dentition and occlusion, and with the diagno- sis, interception, and treatment of occlusal anomalies. 1.2 Prevalence of malocclusion Numerous surveys have been conducted to investigate the prevalence of malocclusion. It should be remembered that the figures for a particu- Table 1.1 UK child dental health survey 2003 lar occlusal feature or dental anomaly will depend upon the size and In the 12-year-old age band: composition of the group studied (for example age and racial charac- teristics), the criteria used for assessment, and the methods used by the Children undergoing orthodontic treatment at the time of the examiners (for example whether radiographs were employed). survey 8% The figures for 12-year-olds in the 2003 United Kingdom Child Dental Children not undergoing treatment – in need of treatment Health Survey in are given in Table 1.1. It is estimated that in the UK (IOTN dental health component) 26% approximately 45% of 12-year-olds have a definite need for orthodontic treatment. No orthodontic need (NB includes children who have had treatment in past) 57% Now that a greater proportion of the population is keeping their teeth for longer, orthodontic treatment has an increasing adjunctive role prior to restorative work. In addition, there is an increasing acceptability of orthodontic appliances with the effect that many adults who did not have treatment during adolescence are now seeking treatment. 1.3 Need for treatment It is perhaps pertinent to begin this section by reminding the reader that The decision to embark upon a course of treatment will be influenced malocclusion is one end of the spectrum of normal variation and is not by the perceived benefits to the patient balanced against the risks of a disease. appliance therapy and the prognosis for achieving the aims of treatment Ethically, no treatment should be embarked upon unless a demon- strable benefit to the patient is feasible. In addition, the potential advan- tages should be viewed in the light of possible risks and side-effects, Box 1.1 Decision to treat including failure to achieve the aims of treatment. Appraisal of these The decision to treat depends upon factors is called risk–benefit analysis and, as in all branches of medicine Benefits of treatment versus Risks and dentistry, needs to be considered before treatment is commenced Improved function Worsening of dental for an individual patient (Box 1.1). In parallel, financial constraints cou- health (e.g. caries) pled with the increasing costs of health care have led to an increased focus upon the cost–benefit ratio of treatment. Obviously the threshold Improved aesthetics Failure to achieve aims of treatment for treatment and the amount of orthodontic intervention will differ between a system that is primarily funded by the state and one that is Psychological benefits private or based on insurance schemes.  Need for treatment 3 successfully. In this chapter we consider each of these areas in turn, of periodontal support. This may also occur in a Class III malocclusion starting with the results of research into the possible benefits of ortho- where the lower incisors in crossbite are pushed labially, contributing to dontic treatment upon dental health and psychological well-being. gingival recession. Traumatic overbites can also lead to increased loss of periodontal support and therefore are another indication for orthodon- 1.3.1 Dental health tic intervention (see also Box 1.2). Finally, an increased dental awareness has been noted in patients Caries following orthodontic treatment, and this may be of long-term benefit Research has failed to demonstrate a significant association between to oral health. malocclusion and caries, whereas diet and the use of fluoride toothpaste are correlated with caries experience. However, clinical experience sug- Trauma to the anterior teeth gests that in susceptible children with a poor diet, malalignment may Any practitioner who treats children will confirm the association reduce the potential for natural tooth-cleansing and increase the risk between increased overjet and trauma to the upper incisors. A system- of decay. atic review found that individuals with an overjet in excess of 3 mm had more than double the risk of injury. Periodontal disease Overjet is a greater contributory factor in girls than boys even though The association between malocclusion and periodontal disease is weak, traumatic injuries are more common in boys. Other studies have shown as research has shown that individual motivation has more impact than that the risk is greater in patients with incompetent lips. tooth alignment upon effective tooth brushing. Certainly, good tooth- brushers are motivated to brush around irregular teeth, whereas in the Masticatory function individual who brushes infrequently their poor plaque control is clearly Patients with anterior open bites (AOB) and those with markedly of more importance. Nevertheless, it would seem logical that in the increased or reverse overjets often complain of difficulty with eating, middle of this range that, irregular teeth would hinder effective brush- particularly when incising food. Classically patients with AOB complain ing. In addition, certain occlusal anomalies may prejudice periodontal that they have to avoid sandwiches containing lettuce or cucumber. support. Crowding may lead to one or more teeth being squeezed buc- Patients with severe hypodontia also may experience problems with cally or lingually out of their investing bone, resulting in a reduction eating. Speech Box 1.2 Those occlusal anomalies for which there The soft tissues show remarkable adaptation to the changes that occur is evidence to suggest an adverse effect upon the during the transition between the primary and mixed dentitions, and longevity of the dentition, indicating that their when the incisors have been lost owing to trauma or disease. In the correction would benefit long-term dental health main, speech is little affected by malocclusion, and correction of an Increased overjet occlusal anomaly has little effect upon abnormal speech. However, if a patient cannot attain contact between the incisors anteriorly, this may Increased traumatic overbites contribute to the production of a lisp (interdental stigmatism). Anterior crossbites (where causing a decrease in labial periodontal support of affected lower incisors) Tooth impaction Unerupted impacted teeth (where there is a danger of pathology) Unerupted teeth may rarely cause pathology (Fig. 1.1). Unerupted Crossbites associated with mandibular displacement impacted teeth, for example maxillary canines, may cause resorption of the roots of adjacent teeth. Dentigerous cyst formation can occur (a) (b) (c) Fig. 1.1 Patient aged 11 years with asymptomatic resorption of the upper left first permanent molar by the upper left second premolar. Following extraction of the first permanent molar the second premolar erupted uneventfully (a); (b) at presentation; (c) 6 months after the extraction of the upper first permanent molar. 4 The rationale for orthodontic treatment around unerupted third molars or canine teeth. Supernumerary teeth A patient’s perception of the impact of dental variation upon his or may also give rise to problems, most importantly where their presence her self-image is subject to enormous diversity and is modified by cul- prevents normal eruption of an associated permanent tooth or teeth. tural and racial influences. Therefore, some individuals are unaware of marked malocclusions, whilst others complain bitterly about very minor Temporomandibular joint dysfunction syndrome irregularities. This topic is considered in more detail in Section 1.7. The dental health component of the Index of Orthodontic Treat- ment Need was developed to try and quantify the impact of a particular 1.3.2 Psychosocial well-being malocclusion upon long-term dental health. The index also comprises an aesthetic element which is an attempt to quantify the aesthetic While it is accepted that dentofacial anomalies and severe malocclu- handicap that a particular arrangement of the teeth poses for a patient. sion do have a negative effect on the psychological well-being and self- Both aspects of this index are discussed in more detail in Chapter 2. esteem of the individual, the impact of more minor occlusal problems The psychosocial benefits of treatment are however countered to a is more variable and is modified by social and cultural factors. Research degree by the visibility of appliances during treatment and their effect has shown that an unattractive dentofacial appearance does have a upon the self-esteem of the individual. In other words a child who negative effect on the expectations of teachers and employers. How- is being teased about their teeth will probably also be teased about ever, in this respect, background facial appearance would appear to braces. have more impact than dental appearance. 1.4 Demand for treatment After working with the general public for a short period of time, it can With the increasing dental awareness shown by the public and the readily be appreciated that demand for treatment does not necessarily increased acceptability of appliances, the demand for treatment is reflect need for treatment. Some patients are very aware of mild rota- increasing rapidly, particularly among the adult population who may tions of the upper incisors, whilst others are blithely unaware of mark- not have had ready access to orthodontic treatment as children. This edly increased overjets. It has been demonstrated that awareness of has also been fuelled by the increased availability of less visible appli- tooth alignment and malocclusion, and willingness to undergo ortho- ances including ceramic brackets and lingual fixed appliances. In addi- dontic treatment, are greater in the following groups: tion, increased dental awareness also means that patients are seeking a higher standard of treatment result. These combined pressures place females considerable strain upon the limited resources of state-funded systems higher socio-economic families/groups of care. As it appears likely that the demand for treatment will continue in areas which have a smaller population to orthodontist ratio, pre- to escalate, some form of rationing of state-funded treatment is inevi- sumably because appliances become more accepted table and is already operating in some countries. In Sweden for exam- ple, the contribution made by the state towards the cost of treatment is One interesting example of the latter has been observed in countries based upon need for treatment as determined by the Swedish Health where provision of orthodontic treatment is mainly privately funded, Board’s Index (see IOTN in Chapter 2). for example, the USA, as orthodontic appliances are now perceived as a ‘status symbol’. 1.5 The disadvantages and potential risks of orthodontic treatment Like any other branch of medicine or dentistry, orthodontic treatment is not without potential risks (see Table 1.2). Box 1.3 Recognized risk factors for root resorption during orthodontic treatment 1.5.1 Root resorption Shortened roots with evidence of previous root resorption It is now accepted that some root resorption is inevitable as a conse- Pipette-shaped or blunted roots quence of tooth movement (see also Box 1.3). On average, during the Teeth which have suffered a previous episode of trauma course of a conventional 2-year fixed-appliance treatment around 1 Iatrogenic – use of excessive forces; intrusion; prolonged treat- mm of root length will be lost (this amount is not clinically significant). ment time However, this mean masks a wide range of individual variation, as some patients appear to be more susceptible and undergo more marked root resorption. Evidence would suggest a genetic basis in these cases.  The effectiveness of treatment 5 Table 1.2 Potential risks of orthodontic treatment Problem Avoidance/Management of risk Demineralisation Dietary advice, improve oral hygiene, increase availability of fluoride Abandon treatment Periodontal Improve oral hygiene. Avoid moving teeth out attachment loss of alveolar bone Root resorption Avoid treatment in patients with resorbed, blunted, or pipette-shaped roots Loss of vitality If history of previous trauma to incisors, counsel patient Relapse Avoidance of unstable tooth positions at end Fig. 1.2 Demineralization. of treatment Retention predisposes to plaque accumulation as tooth cleaning around the components of the appliance is more difficult. Demineralisation during treatment with fixed appliances is a real risk, with a reported prevalence 1.5.2 Loss of periodontal support of between 2 and 96 per cent (see Chapter 18, Section 18.7). Although there is evidence to show that the lesions regress following removal of As a result of reduced access for cleansing, an increase in gingival the appliance, patients may still be left with permanent ‘scarring’ of the inflammation is commonly seen following the placement of fixed appli- enamel (Fig. 1.2). ances. This normally reduces or resolves following removal of the appli- ance, but some apical migration of periodontal attachment and alveolar 1.5.4 Soft tissue damage bony support is usual during a 2-year course of orthodontic treatment. In most patients this is minimal, but if oral hygiene is poor, particularly Traumatic ulceration can occur during treatment with both fixed and in an individual susceptible to periodontal disease, more marked loss removable appliances, although it is more commonly seen in associa- may occur. tion with the former as a removable appliance which is uncomfortable Removable appliances may also be associated with gingival inflam- is usually removed. mation, particularly of the palatal tissues, in the presence of poor oral hygiene. 1.5.5 Pulpal injury Over-enthusiastic apical movement can lead to a reduction in blood 1.5.3 Demineralisation supply to the pulp and even pulpal death. Teeth which have undergone Caries or demineralisation occurs when a cariogenic plaque occurs in a previous episode of trauma appear to be particularly susceptible, association with a high-sugar diet. The presence of a fixed appliance probably because the pulpal tissues are already compromised. 1.6 The effectiveness of treatment The decision to embark upon orthodontic treatment must also consider There is a wealth of evidence to show that orthodontic treatment the effectiveness of appliance therapy in correcting the malocclusion of is more likely to achieve a pleasing and successful result if fixed the individual concerned. This has several aspects. appliances are used, and if the operator has had some postgraduate training in orthodontics. Are the tooth movements planned attainable? This is considered in more detail in Chapter 7 but, in brief, tooth movement is only feasi- Patient co-operation. A successful outcome is dependent upon ble within the constraints of the skeletal and growth patterns of the patient compliance with attending appointments, looking after individual patient. The wrong treatment plan, or failure to anticipate their teeth and appliance and with wearing auxiliaries e.g. elastics. adverse growth changes, will reduce the chances of success. In addi- A patient is more likely to co-operate if they fully understand the tion, the probable stability of the completed treatment needs to be process and their role in it from the outset i.e. during the consent considered. If a stable result is not possible, do the benefits conferred process. by proceeding justify prolonged retention, or the possibility of relapse? 6 The rationale for orthodontic treatment The likelihood that orthodontic treatment will benefit a patient is Table 1.3 Failure to achieve treatment objectives increased if the malocclusion is severe, the patient is well-motivated and appliance therapy is planned and carried out by an experienced Operator factors Patient factors orthodontist. The likelihood of gain is reduced if the malocclusion is Errors of diagnosis Poor oral hygiene/diet mild and treatment is undertaken by an inexperienced operator. In essence, it may be better not to embark on treatment at all, rath- Errors of treatment planning Failure to wear appliances/elastics er than run the risk of failing to achieve a worthwhile improvement Anchorage loss Repeated appliance breakages (Table 1.3). Technique errors Failed appointments 1.7 The temporomandibular joint and orthodontics The aetiology and management of temporomandibular joint dys- The consensus view is that orthodontic treatment, either alone or in function syndrome (TMD) have aroused considerable controversy in combination with extractions, does not ‘cause’ TMD. all branches of dentistry. The debate has been particularly heated regarding the role of orthodontics, with some authors claiming that 1.7.2 The role of orthodontic treatment in the orthodontic treatment can cause TMD, whilst at the same time oth- prevention and management of TMD ers have advocated appliance therapy in the management of the condition. Some authors maintain that minor occlusal imperfections lead to abnor- There are a number of factors that have contributed to the confusion mal paths of closure and/or bruxism, which then result in the develop- surrounding TMD. The objective view is that TMD comprises a group ment of TMD. If this were the case, then given the high incidence of of related disorders of multifactorial aetiology. Psychological, hormo- malocclusion in the population (50–75 per cent), one would expect a nal, genetic, traumatic, and occlusal factors have all been implicated. higher prevalence of TMD. A number of carefully controlled longitu- Recent research has shown that depression, stress and sleep disor- dinal studies have been carried out in North America, and these have ders are major factors in the aetiology of TMD. It is also accepted that found no relationship between the signs and symptoms of TMD and the parafunctional activity, for example bruxism, can contribute to muscle presence of non-functional occlusal contacts or mandibular displace- pain and spasm. Success has been claimed for a wide assortment of ments. However, other studies have found a weak association between treatment modalities, reflecting both the multifactorial aetiology and TMD and some types of malocclusion including Class II skeletal pat- the self-limiting nature of the condition. Given this, it is wise to try irre- tern (especially associated with a retrusive mandible); Class III; anterior versible approaches in the first instance. The reader is directed to look at open bite; crossbite and asymmetry. two recent Cochrane reviews (see Relevant Cochrane reviews and Fur- A review of the current literature would indicate that orthodontic ther reading) on the use of stabilization splints and occlusal adjustment. treatment does not ‘cure’ TMD. It is important to advise patients of this, particularly those who present reporting TMD symptoms, and to note 1.7.1 Orthodontic treatment as a contributory this in their records. Whilst current evidence indicates that orthodontic treatment is not factor in TMD a contributory factor and also does not cure the TMD, it is advisable to A survey of the literature reveals that those articles claiming that ortho- carry out a TMD screen for all potential orthodontic patients. At the dontic treatment (with or without extractions) can contribute to the very least this should include questioning patients about symptoms; an development of TMD are predominantly of the viewpoint (based on examination of the temporomandibular joint and associated muscles the authors’ opinion) and case report type. In contrast, controlled longi- and recording the range of opening and movement (see Chapter 5). If tudinal studies have indicated a trend towards a lower incidence of the signs or symptoms of TMD are found then it may be wise to refer the symptoms of TMD among post-orthodontic patients compared with patient for a comprehensive assessment and specialist management matched groups of untreated patients. before embarking on orthodontic treatment. Key points The decision to undertake orthodontic treatment or not is essentially a risk–benefit analysis where the perceived benefits in commencing treatment at that time outweigh the potential risks. If there is any uncertainty as to whether the patient will co-operate and/or benefit from treatment, then it is advisable not to proceed at that time.  The temporomandibular joint and orthodontics 7 Relevant Cochrane reviews: Occlusal adjustment for treating and preventing temporomandibular joint disorders Koh, H. et al. (2009) http://onlinelibrary.wiley.com/o/cochrane/clsysrev/articles/CD003812/frame.html The authors concluded that there is an absence of evidence, from RCTs, that occlusal adjustment treats or prevents TMD. Occlusal adjust- ment cannot be recommended for the management or prevention of TMD. Orthodontics for treating temporomandibular joint (TMJ) disorders Luther, F. et al. (2010). http://onlinelibrary.wiley.com/o/cochrane/clsysrev/articles/CD006541/frame.html The conclusion was there are insufficient research data on which to base our clinical practice on the relationship of active orthodontic inter- vention and TMD. Stabilisation splint therapy for temporomandibular pain dysfunction syndrome. Al-Ani, M.Z. et al. (2009). http://onlinelibrary.wiley.com/o/cochrane/clsysrev/articles/CD002778/frame.html There is insufficient evidence either for or against the use of stabilisation splint therapy for the treatment of temporomandibular pain dysfunc- tion syndrome. Principal sources and further reading American Journal of Orthodontics and Dentofacial Orthopedics, 101(1), Luther, F. (2007).TMD and occlusion part II. Damned if we don’t? (1992). Functional occlusal problems: TMD epidemiology in a wider context. This is a special issue dedicated to the results of several studies set up British Dental Journal, 13, 202. by the American Association of Orthodontists to investigate the link These 2 articles are well worth reading. between orthodontic treatment and the temporomandibular joint. Maaitah, E. F., Adeyami, A. A., Higham, S. M., Pender, N. and Harrison, J. E. Chestnutt, I. G., Burden, D. J., Steele, J. G., Pitts, N. B., Nuttall, N. M., and (2011). Factors affecting demineralization during orthodontic treatment: Morris, A. J. (2006). The orthodontic condition of children in the United A post-hoc analysis of RCT recruits. American Journal of Orthodontics Kingdom, 2003. British Dental Journal, 200, 609–12. and Dentofacial Orthopedics, 139, 181–91. Davies, S. J., Gray, R. M. J., Sandler, P. J., and O’Brien, K. D. (2001). A useful study which concludes that pre-treatment age, oral hygiene Orthodontics and occlusion. British Dental Journal, 191, 539–49. and status of the first permanent molars can be used as a guide to the likelihood of decalcification occurring during treatment. This concise article is part of a series of articles on occlusion. It contains an example of an articulatory examination. Mizrahi, E. (2010). Risk management in clinical practice. Part 7. Dento-legal aspects of orthodontic practice. British Dental Journal, Egermark, I., Magnusson, T., and Carlsson, G. E. (2003). A 20-year follow-up 209, 381–90. of signs and symptoms of temporomandibular disorders in subjects with and without orthodontic treatment in childhood. Angle Orthodontist, Murray, A. M. (1989). Discontinuation of orthodontic treatment: a study of 73, 109–15. the contributing factors. British Journal of Orthodontics, 16, 1–7. A long-term cohort study which found no statistically-significant Nguyen, Q. V., Bezemer, P. D., Habets, L., and Prahl-Andersen, B. (1999). difference in TMD signs and symptoms between subjects with or A systematic review of the relationship between overjet size and without previous experience of orthodontic treatment. traumatic dental injuries. European Journal of Orthodontics, 21, Holmes, A. (1992). The subjective need and demand for orthodontic 503–15. treatment. British Journal of Orthodontics, 19, 287–97. Office for National Statistics (2004). Children’s dental health in the United Joss-Vassalli, I., Grebenstein, C., Topouzelis, N., Sculean, A. and Katsaros, Kingdom 2003. Office for National Statistics, London. C. (2010). Orthodontic therapy and gingival recession: a systematic Shaw, W. C., O’Brien, K. D., Richmond, S., and Brook, P. (1991). Quality review. Orthodontics and Craniofacial Research, 13, 127–41. control in orthodontics: risk/benefit considerations. British Dental Luther, F. (2007).TMD and occlusion part I. Damned if we do? Occlusion the Journal, 170, 33–7. interface of dentistry and orthodontics. British Dental Journal, 13, 202. A rather pessimistic view of orthodontics. 8 The rationale for orthodontic treatment Weltman, B., Vig, K. W., Fields, H. W., Shanker, S. and Kaizar, E. E. (2010). See also: Root resorption associated with orthodontic tooth movement: Readers’ forum (December 2011) American Journal of Orthodontics and a systematic review. American Journal of Orthodontics and Dentofacial Dentofacial Orthopedics, 138, 690–6. Orthopedics, 137, 462–76. An interesting and informative read on decalcification during Wheeler, T. T., McGorray, S. P., Yurkiewicz, L., Keeling, S. D., and King, orthodontic treatment. G. J. (1994). Orthodontic treatment demand and need in third and The British Orthodontic Society also do an excellent Advice Sheet entitled fourth grade schoolchildren. American Journal of Orthodontics and ‘Temporomandibular disorders (TMD) and the orthodontic patient’ Dentofacial Orthopedics, 106, 22–33. which unfortunately is only available to members (so you may need to Contains a good discussion on the need and demand for treatment. track down a BOS member and ask nicely!). References for this chapter can also be found at: www.oxfordtextbooks.co.uk/orc/mitchell4e/. Where possible, these are presented as active links which direct you to the electronic version of the work, to help facilitate onward study. If you are a subscriber to that work (either individually or through an institution), and depending on your level of access, you may be able to peruse an abstract or the full article if available. 2 The aetiology and classification of malocclusion Chapter contents 2.1 The aetiology of malocclusion 10 2.2 Classifying malocclusion 11 2.2.1 Qualitative assessment of malocclusion 11 2.2.2 Quantitative assessment of malocclusion 11 2.3 Commonly used classifications and indices 11 2.3.1 Angle’s classification 11 2.3.2 British Standards Institute classification 11 2.3.3 Summers occlusal index 11 2.3.4 Index of Orthodontic Treatment Need (IOTN) 13 2.3.5 Peer Assessment Rating (PAR) 13 2.3.6 Index of Complexity, Outcome and Need (ICON) 13 2.4 Andrews’ six keys 15 Principal sources and further reading 16 10 The aetiology and classification of malocclusion Learning objectives for this chapter Be aware of current understanding of the aetiology of malocclusion Gain an understanding of approaches to classifying malocclusion Be aware of the commonly used classifications and indices 2.1 The aetiology of malocclusion The aetiology of malocclusion is a fascinating subject about which not the whole story, as a change from a rural to an urban life-style there is still much to elucidate and understand. At a basic level, maloc- can also apparently lead to an increase in crowding after about two clusion can occur as a result of genetically determined factors, which generations. are inherited, or environmental factors, or more commonly a combina- Although this discussion may at first seem rather theoretical, the aeti- tion of both inherited and environmental factors acting together. For ology of malocclusion is a vigorously debated subject. This is because if example, failure of eruption of an upper central incisor may arise as a one believes that the basis of malocclusion is genetically determined, result of dilaceration following an episode of trauma during the decidu- then it follows that orthodontics is limited in what it can achieve. How- ous dentition which led to intrusion of the primary predecessor – an ever, the opposite viewpoint is that every individual has the potential for example of environmental aetiology. Failure of eruption of an upper ideal occlusion and that orthodontic intervention is required to elimi- central incisor can also occur as a result of the presence of a supernu- nate those environmental factors that have led to a particular maloc- merary tooth – a scenario which questioning may reveal also affected clusion. Research suggests that for the majority of malocclusions the the patient’s parent, suggesting an inherited problem. However, if in aetiology is multifactorial with polygenic inheritance, and orthodon- the latter example caries (an environmental factor) has led to early tic treatment can effect only limited skeletal change. Therefore, as a loss of many of the deciduous teeth then forward drift of the first per- patient’s skeletal and growth pattern is largely genetically determined, if manent molar teeth may also lead to superimposition of the additional orthodontic treatment is to be successful clinicians must recognize and problem of crowding. work within those parameters (see also Box 2.1). While it is relatively straightforward to trace the inheritance of syn- When planning treatment for an individual patient it is often helpful dromes such as cleft lip and palate (see Chapter 22), it is more difficult to to consider the role of the following in the aetiology of their malocclu- determine the aetiology of features which are in essence part of normal sion. Further discussion of these factors will be considered in the forth- variation, and the picture is further complicated by the compensatory coming chapters covering the main types of malocclusion: mechanisms that exist. Evidence for the role of inherited factors in the (1) Skeletal pattern – in all three planes of space aetiology of malocclusion has come from studies of families and twins. The facial similarity of members of a family, for example the prognathic (2) Soft tissues mandible of the Hapsburg royal family, is easily appreciated. However, (3) Dental factors more direct testimony is provided in studies of twins and triplets, which Of necessity, the above is a brief summary, but it can be appreci- indicate that skeletal pattern and tooth size and number are largely ated that the aetiology of malocclusion is a complex subject, much of genetically determined. which is still not fully understood. The reader seeking more information Examples of environmental influences include digit-sucking habits is advised to consult the publications listed in the section on Further and premature loss of teeth as a result of either caries or trauma. Soft reading. tissue pressures acting upon the teeth for more than 6 hours per day can also influence tooth position. However, because the soft tissues includ- ing the lips are by necessity attached to the underlying skeletal frame- work, their effect is also mediated by the skeletal pattern. Crowding is extremely common in Caucasians, affecting approxi- Box 2.1 Functional occlusion mately two-thirds of the population. As was mentioned above, the size of the jaws and teeth are mainly genetically determined; An occlusion which is free of interferences to smooth gliding however, environmental factors, for example premature deciduous movements of the mandible with no pathology tooth loss, can precipitate or exacerbate crowding. In evolutionary Orthodontic treatment should aim to achieve a functional terms both jaw size and tooth size appear to be reducing. However, occlusion crowding is much more prevalent in modern populations than it was BUT lack of evidence to indicate that if an ideal functional in prehistoric times. It has been postulated that this is due to the occlusion is not achieved that there are deleterious long-term introduction of a less abrasive diet, so that less interproximal tooth effects on the TMJs wear occurs during the lifetime of an individual. However, this is  Commonly used classifications and indices 11 2.2 Classifying malocclusion The categorization of a malocclusion by its salient features is helpful for describing and documenting a patient’s occlusion. In addition, clas- Box 2.2 Important attributes of an index sifications and indices allow the prevalence of a malocclusion within Validity — Can the index measure what it was designed to a population to be recorded, and also aid in the assessment of need, measure? difficulty, and success of orthodontic treatment. Malocclusion can be recorded qualitatively and quantitatively. How- Reproducibility — Does the index give the same result when recorded on two different occasions and by different ever, the large number of classifications and indices which have been examiners? devised are testimony to the problems inherent in both these approach- es. All have their limitations, and these should be borne in mind when they are applied (Box 2.2). 2.2.1 Qualitative assessment of malocclusion was devised by Angle in 1899, but other classifications are now more Essentially, a qualitative assessment is descriptive and therefore this cat- widely used, for example the British Standards Institute (1983) classifi- egory includes the diagnostic classifications of maloccusion. The main cation of incisor relationship. drawback to a qualitative approach is that malocclusion is a continu- ous variable so that clear cut-off points between different categories do 2.2.2 Quantitative assessment of malocclusion not always exist. This can lead to problems when classifying borderline In quantitative indices two differing approaches can be used: malocclusions. In addition, although a qualitative classification is a help- ful shorthand method of describing the salient features of a malocclu- Each feature of a malocclusion is given a score and the summed total sion, it does not provide any indication of the difficulty of treatment. is then recorded (e.g. the PAR Index). Qualitative evaluation of malocclusion was attempted historically The worst feature of a malocclusion is recorded (e.g. the Index of before quantitative analysis. One of the better known classifications Orthodontic Treatment Need). 2.3 Commonly used classifications and indices 2.3.1 Angle’s classification 2.3.2 British Standards Institute classification Angle’s classification was based upon the premise that the first perma- This is based upon incisor relationship and is the most widely used nent molars erupted into a constant position within the facial skeleton, descriptive classification. The terms used are similar to those of Angle’s which could be used to assess the anteroposterior relationship of the classification, which can be a little confusing as no regard is taken of arches. In addition to the fact that Angle’s classification was based molar relationship. The categories defined by British Standard 4492 are upon an incorrect assumption, the problems experienced in categoriz- shown in Box 2.3 below (see also Figs 2.2, 2.3, 2.4, 2.5): ing cases with forward drift or loss of the first permanent molars have As with any descriptive analysis it is difficult to classify borderline resulted in this particular approach being superseded by other classi- cases. Some workers have suggested introducing a Class II intermediate fications. However, Angle’s classification is still used to describe molar category for those cases where the upper incisors are upright and the relationship, and the terms used to describe incisor relationship have overjet increased to between 4 and 6 mm. However, this suggestion has been adapted into incisor classification. not gained widespread acceptance. Angle described three groups (Fig. 2.1): 2.3.3 Summers occlusal index Class I or neutrocclusion — the mesiobuccal cusp of the upper first molar occludes with the mesiobuccal groove of the lower first molar. This index was developed by Summers, in the USA, during the 1960s. In practice discrepancies of up to half a cusp width either way were It is popular in America, particularly for research purposes. Good also included in this category. reproducibility has been reported and it has also been employed to determine the success of treatment with acceptable results. The index Class II or distocclusion — the mesiobuccal cusp of the lower first scores nine defined parameters including molar relationship, overbite, molar occludes distal to the Class I position. This is also known as a overjet, posterior crossbite, posterior open bite, tooth displacement, postnormal relationship. midline relation, maxillary median diastema, and absent upper incisors. Class III or mesiocclusion — the mesiobuccal cusp of the lower first Allowance is made for different stages of development by varying the molar occludes mesial to the Class I position. This is also known as a weighting applied to certain parameters in the deciduous, mixed, and prenormal relationship. permanent dentition. 12 The aetiology and classification of malocclusion Box 2.3 British Standards incisor classification Class I — the lower incisor edges occlude with or lie immedi- ately below the cingulum plateau of the upper central incisors. Class II — the lower incisor edges lie posterior to the cingulum plateau of the upper incisors. There are two subdivisions of this category: Division 1 — the upper central incisors are proclined or of average inclination and there is an increase in overjet. Division 2 — The upper central incisors are retroclined. The overjet is usually minimal or may be increased. Class III — The lower incisor edges lie anterior to the cingulum Fig. 2.2 Incisor classification — Class I. plateau of the upper incisors. The overjet is reduced or reversed. Fig. 2.3 Incisor classification — Class II division 1. Fig. 2.4 Incisor classification — Class II division 2. Fig. 2.1 Angle’s classification. Fig. 2.5 Incisor classification — Class III.  Commonly used classifications and indices 13 2.3.4 Index of Orthodontic Treatment Need component has been criticized for being subjective – particular diffi- culty is experienced in accurately assessing Class III malocclusions or (IOTN) anterior open bites, as the photographs are composed of Class I and The Index of Orthodontic Treatment Need was developed as a result Class II cases, but studies have indicated good reproducibility. of a government initiative. The purpose of the index was to help deter- mine the likely impact of a malocclusion on an individual’s dental health 2.3.5 Peer Assessment Rating (PAR) and psychosocial well-being. It comprises two elements. The PAR index was developed primarily to measure the success (or oth- Dental health component erwise) of treatment. Scores are recorded for a number of parameters This was developed from an index used by the Dental Board in Sweden (listed below), before and at the end of treatment using study mod- designed to reflect those occlusal traits which could affect the function els. Unlike IOTN, the scores are cumulative; however, a weighting is and longevity of the dentition. The single worst feature of a malocclu- accorded to each component to reflect current opinion in the UK as to sion is noted (the index is not cumulative) and categorized into one of their relative importance. The features recorded are listed below, with five grades reflecting need for treatment (Table 2.1): the current weightings in parentheses: Grade 1 — no need crowding — by contact point displacement (×1) Grade 2 — little need buccal segment relationship — in the anteroposterior, vertical, and transverse planes (×1) Grade 3 — moderate need Grade 4 — great need overjet (×6) Grade 5 — very great need overbite (×2) centrelines (×4) A ruler has been developed to help with assessment of the dental health component (reproduced with the kind permission of UMIP Ltd. The difference between the PAR scores at the start and on com- in Fig. 2.6), and these are available commercially. As only the single pletion of treatment can be calculated, and from this the percentage worst feature is recorded, an alternative approach is to look consecu- change in PAR score, which is a reflection of the success of treatment, tively for the following features (known as MOCDO): is derived. A high standard of treatment is indicated by a mean per- centage reduction of greater than 70 per cent. A change of 30 per Missing teeth cent or less indicates that no appreciable improvement has been Overjet achieved. The size of the PAR score at the beginning of treatment Crossbite gives an indication of the severity of a malocclusion. Obviously it is difficult to achieve a significant reduction in PAR in cases with a low Displacement (contact point) pretreatment score. Overbite 2.3.6 Index of Complexity, Outcome and Need Aesthetic component (ICON) This aspect of the index was developed in an attempt to assess the aes- thetic handicap posed by a malocclusion and thus the likely psycho- This new index incorporates features of both the Index of Orthodontic social impact upon the patient – a difficult task (see Chapter 1). The Need (IOTN) and the Peer Assessment Rating (PAR). The following are aesthetic component comprises a set of ten standard photographs (Fig. scored and then each score is multiplied by its weighting: 2.7), which are also graded from score 1, the most aesthetically pleas- Aesthetic component of IOTN (×7) ing, to score 10, the least aesthetically pleasing. Colour photographs are available for assessing a patient in the clinical situation and black-and- Upper arch crowding/spacing (×5) white photographs for scoring from study models alone. The patient’s Crossbite (×5) teeth (or study models), in occlusion, are viewed from the anterior Overbite/open bite (×4) aspect and the appropriate score determined by choosing the photo- Buccal segment relationship (×3) graph that is thought to pose an equivalent aesthetic handicap. The scores are categorized according to need for treatment as follows: The total sum gives a pretreatment score, which is said to reflect the need for, and likely complexity of, the treatment required. A score of score 1 or 2 — none more than 43 is said to indicate a demonstrable need for treatment. score 3 or 4 — slight Following treatment the index is scored again to give an improvement score 5, 6, or 7 — moderate/borderline grade and thus the outcome of treatment. Improvement grade = pre-treatment score – (4 × post-treatment score) score 8, 9, or 10 — definite This ambitious index has been criticized for the large weighting An average score can be taken from the two components, but the given to the aesthetic component and has not yet gained widespread dental health component alone is more widely used. The aesthetic acceptability. 14 The aetiology and classification of malocclusion Table 2.1 The Index of Orthodontic Treatment Need (Reproduced with the kind permission of UMIP Ltd.) Grade 5 (Very Great) 5a Increased overjet greater than 9 mm 5h Extensive hypodontia with restorative implications (more than one tooth missing in any quadrant) requiring pre-restorative orthodontics 5i Impeded eruption of teeth (with the exception of third molars) due to crowding, displacement, the presence of supernumerary teeth, retained deciduous teeth, and any pathological cause 5m Reverse overjet greater than 3.5 mm with reported masticatory and speech difficulties 5p Defects of cleft lip and palate 5s Submerged deciduous teeth Grade 4 (Great) 4a Increased overjet 6.1–9 mm 4b Reversed overjet greater than 3.5 mm with no masticatory or speech difficulties 4c Anterior or posterior crossbites with greater than 2 mm discrepancy between retruded contact position and intercuspal position 4d Severe displacement of teeth, greater than 4 mm 4e Extreme lateral or anterior open bites, greater than 4 mm 4f Increased and complete overbite with gingival or palatal trauma 4h Less extensive hypodontia requiring pre-restorative orthodontic space closure to obviate the need for a prosthesis 4l Posterior lingual crossbite with no functional occlusal contact in one or both buccal segments 4m Reverse overjet 1.1–3.5 mm with recorded masticatory and speech difficulties 4t Partially erupted teeth, tipped and impacted against adjacent teeth 4x Supplemental teeth Grade 3 (Moderate) 3a Increased overjet 3.6–6 mm with incompetent lips 3b Reverse overjet 1.1–3.5 mm 3c Anterior or posterior crossbites with 1.1–2 mm discrepancy 3d Displacement of teeth 2.1–4 mm 3e Lateral or anterior open bite 2.1–4 mm 3f Increased and complete overbite without gingival trauma Grade 2 (Little) 2a Increased overjet 3.6–6 mm with competent lips 2b Reverse overjet 0.1–1 mm 2c Anterior or posterior crossbite with up to 1 mm discrepancy between retruded contact position and intercuspal position 2d Displacement of teeth 1.1–2 mm 2e Anterior or posterior open bite 1.1–2 mm 2f Increased overbite 3.5 mm or more, without gingival contact 2g Prenormal or postnormal occlusions with no other anomalies; includes up to half a unit discrepancy Grade 1 (None) 1 Extremely minor malocclusions including displacements less than 1 mm Copyright © The University of Manchester 2005. All rights reserved  Andrews’ six keys 15 Fig. 2.6 IOTN ruler (Copyright © The University of Manchester 2005. All rights reserved). Fig. 2.7 Aesthetic component of IOTN (the Aesthetic Component was originally described as ‘SCAN’ and was first published in 1987 by Evans, R. and Shaw, W. C. (1987). A preliminary evaluation of an illustrated scale for rating dental attractiveness. European Journal of Orthodontics, 9, 314–8. 2.4 Andrews’ six keys Andrews analysed 120 ‘normal’ occlusions to evaluate those features Andrews used this analysis to develop the first pre-adjusted brack- which were key to a good occlusion (it has been pointed out that these et system, which was designed to place the teeth (in three planes of occlusions can more correctly be described as ‘ideal’). He found six fea- space) to achieve his six keys (see Box 2.4). This prescription is called tures, which are described in Box 2.4. These six keys are not a method of the Andrews’ bracket prescription. For further details of pre-adjusted classifying occlusion as such, but serve as a goal. Occasionally at the end systems see Chapter 18. of treatment it is not possible to achieve a good Class I occlusion – in such cases it is helpful to look at each of these features in order to evaluate why. 16 The aetiology and classification of malocclusion Box 2.4 Andrews’ six keys Correct molar relationship: the mesiobuccal cusp of the upper first Correct crown inclination: incisors are inclined towards the buc- molar occludes with the groove between the mesiobuccal and middle cal or labial surface. Buccal segment teeth are inclined lingually. In buccal cusp of the lower first molar. The distobuccal cusp of the upper the lower buccal segments this is progressive first molar contacts the mesiobuccal cusp of the lower second molar No rotations Correct crown angulation: all tooth crowns are angulated No spaces mesially Flat occlusal plane Principal sources and further reading Andrews, L. F. (1972). The six keys to normal occlusion. American Journal of (Peer Assessment Rating): reliability and validity. European Journal of Orthodontics, 62, 296–309. Orthodontics, 14, 125–39. Angle, E. H. (1899). Classification of malocclusion. Dental Cosmos, 41, 248–64. The PAR index, part 1. British Standards Institute (1983). Glossary of Dental Terms (BS 4492), BSI, Richmond, S., Shaw, W. C., Roberts, C. T., and Andrews, M. (1992). The PAR London. index (Peer Assessment Rating): methods to determine the outcome of orthodontic treatment in terms of improvements and standards. Daniels, C. and Richmond, S. (2000). The development of the Index of Com- European Journal of Orthodontics, 14, 180–7. plexity, Outcome and Need (ICON). Journal of Orthodontics, 27, 149–62. The PAR index, part 2. Harradine, N. W. T., Pearson, M. H., and Toth, B. (1998). The effect of Summers, C. J. (1971). A system for identifying and scoring occlusal disor- extraction of third molars on late lower incisor crowding: A randomized ders. American Journal of Orthodontics, 59, 552–67. controlled clinical trial. British Journal of Orthodontics, 25, 117–22. For readers requiring further information on Summers’ occlusal Markovic, M. (1992). At the crossroads of oral facial genetics. European index. Journal of Orthodontics, 14, 469–81. Shaw, W. C., O’Brien, K. D., and Richmond, S. (1991). Quality control in A fascinating study of twins and triplets with Class II/2 malocclusions. orthodontics: indices of treatment need and treatment standards. British Mossey, P. A. (1999). The heritability of malocclusion. British Journal of Dental Journal, 170, 107–12. Orthodontics, 26, 103–13, 195–203. An interesting paper on the role of indices, with good explanations of the IOTN and the PAR index. Proffit, W. R. (1978). Equilibrium theory revisited: factors influencing posi- tion of the teeth. Angle Orthodontist, 48, 175–186. Tang, E. L. K. and Wei, S. H. Y. (1993). Recording and measuring malocclu- Further reading for those wishing to learn more. sion: a review of the literature. American Journal of Orthodontics and Dentofacial Orthopedics, 103, 344–51. Richmond, S., Shaw, W. C., O’Brien, K. D., Buchanan, I. B., Jones, R., Stephens, C. D., et al. (1992). The development of the PAR index Useful for those researching the subject. References for this chapter can also be found at www.oxfordtextbooks.co.uk/orc/mitchell4e/. Where possible, these are presented as active links which direct you to the electronic version of the work, to help facilitate onward study. If you are a subscriber to that work (either individually or through an institution), and depending on your level of access, you may be able to peruse an abstract or the full article if available. 3 Management of the developing dentition Chapter contents 3.1 Normal dental development 18 3.1.1 Calcification and eruption times 18 3.1.2 The transition from primary to mixed dentition 18 3.1.3 Development of the dental arches 19 3.2 Abnormalities of eruption and exfoliation 20 3.2.1 Screening 20 3.2.2 Natal teeth 20 3.2.3 Eruption cyst 21 3.2.4 Failure of/delayed eruption 21 3.3 Mixed dentition problems 22 3.3.1 Premature loss of deciduous teeth 22 3.3.2 Retained deciduous teeth 23 3.3.3 Infra-occluded (submerged) primary molars 23 3.3.4 Impacted first permanent molars 23 3.3.5 Dilaceration 23 3.3.6 Supernumerary teeth 24 3.3.7 Habits 27 3.3.8 First permanent molars of poor long-term prognosis 27 3.3.9 Median diastema 28 3.4 Planned extraction of deciduous teeth 29 3.4.1 Serial extraction 29 3.4.2 Indications for the extraction of deciduous canines 29 3.5 What to refer and when 30 Principal sources and further reading 31 18 Management of the developing dentition Learning objectives for this chapter Gain an appreciation of normal development Be able to recognize deviations from normal development Gain an understanding of the management of commonly occurring mixed dentition problems Many dental practitioners find it difficult to judge when to intervene in a decisions to intercede are often made in response to pressure exerted by developing malocclusion and when to let nature take its course. This is the parents ‘to do something’. It is hoped that this chapter will help impart because experience is only gained over years of careful observation and some of the former, so that the reader is better able to resist the latter. 3.1 Normal dental development It is important to realize that ‘normal’ in this context means average, Table 3.1 Average calcification and eruption times rather than ideal. An appreciation of what constitutes the range of nor- mal development is essential. One area in which this is particularly per- Calcification tinent is eruption times (Table 3.1). commences (weeks in utero) Eruption (months) 3.1.1 Calcification and eruption times Primary dentition Central incisors 12–16 6–7 Knowledge of the calcification times of the permanent dentition is inval- uable if one wishes to impress patients and colleagues. It is also helpful Lateral incisors 13–16 7–8 for assessing dental as opposed to chronological age; for determining Canines 15–18 18–20 whether a developing tooth not present on radiographic examination First molars 14–17 12–15 can be considered absent; and for estimating the timing of any possible Second molars 16–23 24–36 causes of localized hypocalcification or hypoplasia (termed in this situ- ation chronological hypoplasia). Root development complete 1–11⁄2 years after eruption Calcification Eruption 3.1.2 The transition from primary to mixed commences (months) (years) dentition Permanent dentition The eruption of a baby’s first tooth is heralded by the proud parents as a Mand. central incisors 3–4 6–7 major landmark in their child’s development. This milestone is described Mand. lateral incisors 3–4 7–8 in many baby-care books as occurring at 6 months of age, which can lead Mand. canines 4–5 9–10 to unnecessary concern as it is normal for the mandibular incisors to erupt at any time in the first year. Dental textbooks often dismiss ‘teeth- Mand. first premolars 21–24 10–12 ing’, ascribing the symptoms that occur at this time to the diminution of Mand. second premolars 27–30 11–12 maternal antibodies. Any parent will be able to correct this fallacy! Mand. first molars Around birth 5–6 Eruption of the primary dentition (Fig. 3.1) is usually completed Mand. second molars 30–36 12–13 around 3 years of age. The deciduous incisors erupt upright and spaced – a lack of spacing strongly suggests that the permanent successors will be Mand. third molars 96–120 17–25 crowded. Overbite reduces throughout the primary dentition until the Max. central incisors 3–4 7–8 incisors are edge to edge, which can contribute to marked attrition. Max. lateral incisors 10–12 8–9 The mixed dentition phase is usually heralded by the eruption of Max. canines 4–5 11–12 either the first permanent molars or the lower central incisors. The lower labial segment teeth erupt before their counterparts in the upper Max. first premolars 18–21 10–11 arch and develop lingual to their predecessors. It is usual for there to be Max. second premolars 24–27 10–12 some crowding of the permanent lower incisors as they emerge into the Max. first molars Around birth 5–6 mouth, which reduces with intercanine growth. As a result the lower Max. second molars 30–36 12–13 incisors often erupt slightly lingually placed and/or rotated (Fig. 3.2), but will usually align spontaneously if space becomes available. If the Max. third molars 84–108 17–25 arch is inherently crowded, this space shortage will not resolve with Root development complete 2–3 years after eruption. intercanine growth.  Normal dental development 19 The upper permanent incisors also develop lingual to their predeces- erupt, the lateral incisors usually upright themselves and the spaces