This lavishly illustrated, practical guide to endodontic treatment covers the latest developments in instrumentation and filling techniques. Ideal for all dental practitioners involved in endodontic therapy [root canal treatment], this new edition has been fully updated throughout and now includes a new author team from the Eastman Dental Institute. Practical approach to the subject takes the reader through every step of the clinical procedures from patient assessment to specific problem solving More than 1500 superb illustrations, including colour coded algorithms, present clinical, diagnostic and practical information in an easy-to-follow manner Offers sensible 'best practice' routes through often conflicting approaches to treatment A full chapter on radiography emphasises its importance in both diagnosis and treatment Includes a chapter on the avoidance of litigation Written at a level which ensures a wide appeal to the general dental practitioner and those commencing specialist training The latest edition is completely restructured to provide a more contemporary approach to the subject area New chapters added, including material on tooth development, endodontic interfaces with orthodontics, general and oral medicine, and orofacial pain Latest research findings integrated into the various endodontic clinical applications Application of new equipment and materials highlighted where appropriate New contributors bring a fresh approach to the subject matter
Front cover 1
Endodontics 2
Copyright page 5
Table of Contents 6
Foreword 7
Preface 8
Acknowledgements 9
Contributors 10
Introduction to endodontology and endodontics 12
Definition of Endodontology and Endodontics 12
Brief introduction to pulpal/periapical disease 12
References 12
1 Rationale for disease management 13
1 Tooth organogenesis, morphology and physiology 13
Tooth development 13
Early development of teeth 13
Primary epithelial band, vestibular band and dental lamina 13
Enamel organs 13
Dental papilla 13
Vestibule formation 14
Changes to and further development of dental lamina for permanent molars 14
Development of successional permanent teeth 15
Differentiation of enamel organs 15
Differentiation of dental papilla, dental follicle and sheath of Hertwig 16
Differentiation and function of the tooth germ 16
Molecular regulation of tooth development 17
Anatomical anomalies 17
Tooth morphology 17
Tooth and root shapes 17
Variation by tooth type 17
Variation by race 17
Variation by time 21
Pulp space and its morphologic patterns 21
Classifications of pulp systems 21
Characteristics of the pulp space 22
Lateral, secondary and accessory canals 24
Dimensions of the pulp space 25
Tooth, root and canal morphology by tooth type 25
Maxillary incisors 25
Mandibular incisors 26
Maxillary and mandibular canines 26
Maxillary premolars 27
Mandibular premolars 27
Maxillary first molars 28
Maxillary second molars 29
Mandibular first molars 29
Mandibular second molars 30
Maxillary and mandibular third molars 30
Clinical interpretation and mental imaging 31
Anatomy and physiology of the pulp–dentine complex 32
The dental pulp 32
The vascular supply 35
Functional aspects of the blood supply 36
The nerve supply 37
Functional aspects of the nerve supply 37
The periradicular tissues 39
Cementum 39
Functions 39
Periodontal ligament 40
Blood supply 41
Nerve supply 41
Functions 41
Alveolar bone 42
References and further reading 42
2 Biological and clinical rationale for vital pulp therapy 44
Functions of the pulp 44
Causes of pulp injury 44
Severe inflammatory and degenerative changes in the pulp 47
Spread of pulpal inflammation 47
Dystrophic pulp calcification 48
Principles of pulp disease prevention and treatment 49
Rationale for vital pulp therapy 49
Regenerative pulp therapy 50
Assessment of success of vital pulp therapy procedures 50
Probability of success of vital pulp therapy procedures 51
Conservative management of caries 51
Fissure sealing of occlusal caries 51
Atraumatic restorative therapy (ART) 51
Indirect pulp capping (one-step versus step-wise excavation) 51
Direct pulp capping 51
Pulpotomy 51
Factors affecting outcome of vital pulp therapy 52
Future approaches to pulp regeneration and vital pulp therapy 52
References and further reading 52
3 Biological and clinical rationale for root-canal treatment and management of its failure 54
Aetiopathogenesis of periapical disease 54
Aetiological factors implicated 54
Bacteria 54
Bacterial products 54
Fungi 54
Archaea 54
Host factors implicated 54
Viruses 58
A synthesized model of pathogenesis and natural history of periapical disease 59
Acute periapical inflammation 61
Chronic periapical inflammation 62
Epithelial proliferation and cysts 62
Chronic suppurative periapical inflammation 64
Acute periapical abscess/cellulitis 64
Periapical osteomyelitis 66
Periapical osteosclerosis or condensing osteitis 66
Nature of the periapical lesion associated with treated teeth 66
Association between root-canal microbiota and periapical lesion development 70
Nature of the root-canal microbiota 73
Species richness or qualitative analysis of microbiota (Table 3.3) 75
Species evenness or quantitative analysis of microbiota (Table 3.4) 76
Distribution and physiological status of intraradicular microbiota 78
Culture studies 78
Microscopy studies 78
In situ hybridization microscopy studies 79
Importance of microbial ecology and biofilm physiology in the treatment of root-canal infection 81
Microbial ecology 81
Biofilm and planktonic physiology 86
Prevention and treatment of periapical disease 87
Biological and clinical perspective on a technically driven chemomechanical procedure 87
Technical aspects of the chemomechanical procedure 89
Effect of chemomechanical and obturation procedures on biological events 91
Effect of persistent bacteria on root-canal treatment outcome 92
Factors affecting outcome of root-canal treatment 94
Causes of root-canal treatment failure 94
Intraradicular microbiota associated with failed root-canal treatment 95
Extraradicular microbiota associated with failed root-canal treatment 95
Cysts and their management 96
Foreign body response and its management 97
Fibrous healing 99
Initial misdiagnosis 99
Management of failed previous treatment and outcome of root-canal retreatment 99
Periapical surgery and retrograde seal 100
Factors affecting the outcome of surgical retreatment 100
Alternative approaches to root-canal treatment 101
References and further reading 101
2 Preparation for delivery of endodontic treatment 104
4 Diagnosis of endodontic problems 104
The nature of endodontic diagnosis 104
The nature of endodontic problems 104
Patient assessment 105
Informed consent and record-keeping 105
The nature of presenting complaints 105
History taking 106
Medical history 106
Dental history 107
Social history 107
Clinical examination 107
Extraoral 107
Ease of oral access 107
Intraoral 108
Soft tissue examination 109
Periodontal examination 109
Tooth examination 110
Pulp testing 111
Electric pulp tester 111
Pulp testing technique 111
Thermal pulp testing 112
Heat 112
Dry heat 112
Hot water 112
Cold 112
Location of source of pain 112
Cutting a test cavity 113
Further tooth evaluation 113
Occlusal examination 113
Imaging techniques 113
Conventional radiographic assessment 114
Conventional films versus digital image recording 114
Comparing the different technologies 115
Film holders 115
Radiation safety and regulations 117
Patients 117
Operators and other staff 117
Viewing and storage equipment 118
Viewers 118
Mounts 118
Radiographic techniques 118
Paralleling periapical projections 118
Bisecting angle periapical projections 119
Parallax techniques 119
Cone-beam computed tomography (CBCT) 120
Quality assurance 122
Interpretation of radiographs 122
Normal radiographic landmarks 123
Enamel, dentine and cementum 123
Cancellous bone 123
Periodontal ligament 123
Lamina dura 123
Pulp space 123
Maxillary antrum 123
The anterior maxillary region 123
Common errors in interpretation 123
False widening of the periodontal ligament space 123
The maxillary antrum 123
Incisive foramen 124
Inferior dental canal 124
Mental foramen 124
Lesions involving the periodontal ligament space 125
Periradicular lesions 125
Lateral periradicular lesions 125
Fractured root lesions 125
Perforation lesions 125
Sclerosing osteitis 125
Lesions not of intrapulpal origin 125
Periodontal lesions 125
Idiopathic osteosclerosis 126
Fibro-cemento-osseous dysplasia 126
Other local and systemic pathosis 127
Diagnostic categories 127
Normal pulp 127
Concussed pulp 127
Reversible pulpitis 127
Irreversible pulpitis 127
Pulpal necrosis 127
Acute periapical inflammation 128
Acute apical abscess 128
Chronic apical periodontitis 128
Resorption 129
Internal 129
External 129
Cracked or fractured teeth 129
Fractured crown with vital pulp (cracked tooth syndrome) 129
Fractured crown with non-vital pulp 129
Fractured crown and root with a non-vital pulp 129
Fractured root with a vital or non-vital pulp 129
Periodontal pain 129
Non-odontogenic pain 130
Further reading 130
5 Treatment planning 131
Overall health and oral care of patients and the role of endodontics within it 131
Treatment option selection and treatment planning 131
The ideal treatment-planning scenario 132
The reality of practice, informed consent and medical records 133
Factors influencing treatment planning 134
Illustration of factors affecting treatment decision making using maxillary incisors as an example 134
Scenario 1 134
Scenario 2 134
Scenario 3 135
Scenario 4 135
Scenario 5 136
Scenario 6 137
Scenario 7 137
Summary of factors affecting treatment planning 138
The sequence of treatment delivery 139
Planned initial treatment 139
Immediate relief of symptoms 139
Stabilization 140
Prevention 140
Planned definitive treatment 140
General restorative considerations 140
Strategic importance of teeth 140
Periodontal support 141
Implants 141
Restorability of teeth 142
Access to the tooth and root-canal system 142
Tooth anatomy and orientation 143
Canal anatomy 143
Sclerosed canals 143
Single or multiple visit treatment 143
Previous root-canal treatment 145
Decision-making process for root canal retreatment, surgery or extraction 146
Anatomical considerations for surgical retreatment 147
Systemic consideration for surgical retreatment 147
Root fractures 147
Root resorption 150
Planned review 151
References and further reading 152
6 Pre-endodontic management 153
The clinical area 153
Equipment location, storage and delivery 153
Work surface organization 154
Contamination zones 154
Water supplies 155
Instrumentation and storage 155
The basic instrument pack 156
Operation microscope 156
X-ray machine 156
X-ray viewer 157
Non-surgical retreatment devices 157
Surgical armamentarium 159
Cleaning and sterilization 159
Presterilization cleaning 161
Sterilization 161
Checking successful sterilization 161
Storage 162
File holders and stands 162
Pastes and medicaments 162
Infection control 162
The dental nurse 163
Anticipation 163
Close support 163
Instrument transfer 164
The operator and medico-legal considerations 164
Negligence 165
Dental and medical records 165
Consent 165
Treatment complications 166
Protection of the patient 166
Referral for treatment 166
The patient 166
Education and information 166
Anaesthesia and analgesia 167
Routine root-canal treatment 167
Acute hyperaemic pulp 167
Surgical retreatment 167
Anxious patient 167
Gag reflex 167
Relative analgesia 167
Oral sedation 168
Nasal sedation 168
Intravenous sedation 168
Medication 168
Patients requiring antibiotic cover 168
Patients with HIV/HBV 168
The tooth 168
Removal of calculus and plaque from teeth 168
Removal of caries/restorations 168
Assessment of restorability of teeth 169
Provisional restoration of broken-down teeth 169
Periodontal tissue management 170
Isolation using rubber dam and other devices 170
Rubber dam kits 171
Applying the dam 171
Other devices 173
References and further reading 173
3 Delivery of endodontic treatment 174
7 Vital pulp therapy 174
Management of the primary dentition 174
Morphology of primary teeth 174
Pulp disease in primary teeth 174
Techniques of pulp therapy 174
Indirect pulp capping 174
Direct pulp capping 174
Vital pulpotomy 174
Procedure: quick reference guide 175
Development of alternative approaches to vital pulpotomy in primary teeth 176
Bone morphogenic proteins 176
Other methods 177
Restoration of endodontically treated primary teeth 177
Follow up and complications 177
Management of the secondary or permanent dentition 177
Optimal management of caries 177
Principles of restoration of cavities 177
Smear layer and its management 178
Practical approaches to management of caries and restoration of teeth 179
Treatment of the deep cavity and “compromised” pulp 180
Indirect pulp capping 180
Direct pulp capping 181
Pulpotomy 182
Regenerative pulp therapy 183
Further reading 184
8 Non-surgical root-canal treatment 185
Principles of root-canal system management 185
Principles of mechanical intraradicular preparation 185
Principles of chemical intraradicular preparation and intra-appointment root canal irrigation 185
Principles of chemical intraradicular preparation and interappointment intracanal medication 189
Principles of root-canal system obturation 189
Coronal access cavities 190
Principles of cutting a coronal access cavity 190
Cutting the coronal access cavity 191
Outline shape 192
Location of the canal terminus and determination of canal and working length 192
Point of termination of canal preparation 192
Clinical location of the root-canal system terminus/termini 194
Radiographic method 194
Electronic apex-locator method 195
Tactile method 198
Paper-point method 198
Combined method for determining position of canal terminus 198
Determination of working length 198
Maintaining canal instrumentation to its terminus 199
Relationship between the radicular access, its dimensions and root-canal anatomy 200
Simple canal systems (types a, b and c) 200
Complex canal systems 201
Mechanical preparation of the tapered radicular access cavity 203
Mechanical preparation of the radicular access by hand instrumentation 203
Rotary motion 204
Push–pull filing 205
Design of hand instruments 205
Twisted instruments 206
Machined instruments 206
Mechanical preparation of the radicular access by automated devices 206
Nickel–titanium rotary instruments 207
Radial lands 207
Flutes 207
Safety tip 208
Unconventional instrument design 208
Preparation of the radicular access in curved canals 209
Maintaining curvature with a push–pull filing mode of instrument manipulation 209
Reducing the restoring force 210
Reducing or controlling the length or area of file actively engaged in cutting 212
Maintaining curvature with a rotational mode of hand instrument manipulation 213
Maintenance of double curves 213
Preparing a regularly tapered radicular access and gauging it 214
Recommended approach to preparing the radicular access 215
Coronal preflaring 215
Negotiation to the full length of canal and length verification 216
Negotiation to the full length of canal and its apical enlargement 216
Final shaping of the radicular access 216
Chemical treatment of root-canal systems and root-canal irrigation 217
Mechanics of root-canal irrigant delivery and its actions 219
Dynamic irrigation after mechanical preparation of the canal system is complete 223
Photoactivated disinfection 226
Interappointment intracanal medication 226
Phenol-based agents 226
Phenol and camphorated monochlorophenol (CMCP) 226
Metacresyl acetate or cresatin 227
Aldehydes 227
Halides 227
Antibiotics 227
Steroids 228
Calcium hydroxide 228
Calcium hydroxide preparations 230
Placement of calcium hydroxide 230
Removal and replacement of calcium hydroxide 230
Temporary coronal access cavity seal 231
Zinc oxide/eugenol cement 232
Glass ionomer cements 232
Other materials 232
Root-canal system obturation 232
When should the root-canal system be obturated? 233
Where should the root filling terminate in relation to the apex? 233
The ideal root-filling material 234
Solid cores 234
Pastes 234
Gutta-percha 235
Alternative materials 235
Resilon® 235
SmartSeal® 235
Experimental materials 235
Sealers 236
Obturation techniques 237
Principles of obturation 237
Preparation of canal surface 237
Dry canal 237
Controlled apical placement 237
Efficient and effective backfill 239
Coronal seal 239
Lateral compaction 239
Warm vertical compaction 242
Injection of thermoplasticized gutta-percha 244
Thermoplasticized gutta-percha carriers 244
Thermomechanical compaction technique 245
Hybrid technique 246
Coronal seal 246
Post-preparation/restorative considerations 246
Further reading 247
9 Management of non-surgical root-canal treatment failure 248
Diagnosis of non-surgical root-canal treatment failure 248
Decision-making process 248
Non-surgical root-canal retreatment 248
Indications for non-surgical root-canal retreatment 248
Principles of root-canal retreatment 250
Removal of coronal restorations 250
Removal of bridges 250
Removal of posts 250
Removing gutta-percha 252
Removing gutta-percha with a central core (Thermafil®) 253
Removing cement material 253
Negotiating a ledge 253
Packed dentine debris 253
Sclerosed canals 253
Removal of metal instruments and silver points 254
Perforations 256
Surgical root-canal retreatment 256
Indications and classification of endodontic surgical procedures 256
Emergency surgery 257
Incision and drainage 257
Trephination 257
Biopsy 258
Periapical surgery and root-end management 258
Flap design 258
Full mucoperiosteal flaps 259
Limited mucoperiosteal flaps 259
Incisions 261
Flap elevation 261
Flap retraction 261
Osteotomy 261
Curettage 262
Root-end resection 262
Root-end cavity preparation 263
Haemostasis 264
Root-end filling 265
Through and through surgery 266
Wound closure 267
Wound healing 268
Corrective surgery 268
Perforation repair 268
Root resection 269
Hemisection 270
Intentional replantation and transplantation 270
Regenerative procedures 271
Decompression 273
References and further reading 274
10 Management of acute emergencies and traumatic dental injuries 275
Principles of management of pain 275
Diagnostic accuracy 275
Effective intraoperative pain control 275
Local analgesic agents and their actions 275
Local analgesic agent delivery 276
Gow–Gates technique 276
Akinosi technique 276
Intraligamental injections 277
Intrapulpal injections 277
Intraosseous technique 277
Management of the “hot” pulp 277
Effective postoperative pain control 278
Emergency scenarios 279
Preoperative emergencies 279
Emergencies of pulpal origin 279
Diagnosis 279
Treatment 280
Medication 281
Emergencies of periradicular origin 281
Diagnosis 281
Treatment 283
Medication 284
Emergencies resulting from acute dentoalveolar trauma 285
Triage 285
Acute management 286
Crown fractures 286
Crown–root fractures 286
Root fractures 286
Treatment of luxated teeth 288
Intraoperative emergencies 288
Medical emergencies 288
Sodium hypochlorite 289
Interappointment and postoperative emergencies 290
Medium- to long-term management of dentoalveolar injuries 291
Healing patterns, trends and salient features 292
Template for wound healing, repair and regeneration 292
Pulp 292
Periodontal ligament 292
Root fracture and apical development 292
Alveolar bone 292
Clinical data for prognostication on outcomes of traumatic injuries 293
References and further reading 295
11 Management of tooth resorption 296
Aetiology and pathogenesis 296
Internal resorption 296
Transient internal resorption 296
Progressive internal resorption 296
External resorption 299
Transient external resorption 299
Progressive external resorption without persistent inflammation of the periodontal tissue 299
Progressive external resorption with persistent inflammation of the periodontal tissue sustained by 300
1. Root-canal infection 300
2. Pressure 301
3. Irritation by foreign material 303
4. Subgingival plaque 303
Progressive external resorption associated with systemic disease 308
Progressive external resorption associated with no obvious local or systemic disease (idiopathic) 308
References and further reading 309
4 Multidisciplinary aspects of endodontic management 310
12 The perio–endo interface 310
Comparison of apical and marginal periodontitis 310
Preceding disease states in apical or marginal periodontitis 310
Progression, clinical manifestation and measurement of apical and marginal periodontitis 310
Cell profiles in apical and marginal periodontitis 312
Microbiota associated with apical or marginal periodontitis 312
Risk factors for progression of apical or marginal periodontitis 313
Natural history of apical and marginal periodontitis 313
Association of apical and marginal periodontitis with systemic diseases 313
Pathways of communication between pulp and periodontium 314
Lateral and accessory canals 314
Dentinal tubules 314
Development defects 314
Cementum coverage defects 315
Iatrogenic perforations and root fracture 315
Effect of pulp disease and its treatment on the periodontium 316
Pulpo-periapical inflammation and bone loss 316
Pulpo-periapical inflammation and periodontal wound healing 316
Effect of iatrogenic problems 316
Effect of periodontal disease and its treatment on the pulp 317
Effect of periodontal disease on the pulp 317
Effect of periodontal treatment on the pulp 317
Definition and classification of perio–endo lesions 317
Definition of perio–endo lesions 318
Classification of perio–endo lesions 318
Diagnosis of perio–endo lesions 318
History of dentinal, pulpal and periapical pain 318
History of periodontal symptoms 318
Signs of pulpal or periapical disease 318
Periodontal charting including the probing profile of the tooth 318
Radiographic pattern of bone loss 320
Causes of perio–endo lesions and their aetiology-based management 321
Single isolated perio–endo lesion 321
Root-canal infection 321
Root cracks or fractures 322
Root perforation 324
Root resorption 327
Anatomical tooth anomalies 328
Orthodontic treatment 331
Tooth transplantation and replantation 331
Poorly designed restorations 331
Localized periodontal disease 331
Multiple perio–endo lesions 332
Isolated lesion(s) superimposed upon generalized periodontitis 332
Chronic periodontitis 332
Aggressive periodontitis (juvenile periodontitis [JP] rapidly progressive periodontitis [RPP])
Management of perio–endo lesions 334
Estimation of prognosis 334
Treatment of perio–endo cases 334
Root amputation 335
Role of regenerative techniques in treatment of perio–endo lesions 336
References and further reading 339
13 The ortho–endo interface 340
The nature of contemporary orthodontic management 340
Effect of orthodontic tooth movement on the pulp 340
Effect of orthodontic tooth movement on root resorption 341
Effect of orthodontic tooth movement on resorption of vital, non-vital or root-treated teeth 342
Effect of previous traumatic injuries on orthodontically-mediated resorption and tooth movement 342
Effect of orthognathic/orthodontic treatment on teeth and their pulps 343
Effect of orthodontic tooth movement on endodontic treatment and its outcome 343
Role of orthodontics in endodontic-restorative treatment planning 343
References and Further Reading 344
14 The restorative–endo interface 345
Principles of restoration of root-treated teeth 345
Restorability of the tooth 345
When to restore after endodontic treatment 349
How to restore teeth after endodontic treatment 349
Restoration of anterior teeth 349
Relatively intact teeth 349
Teeth with proximal cavities 349
Teeth with inadequate tissue for retention without auxiliary aids 351
Characteristics of dowels or posts 353
Material of composition 353
Shape 353
Length 354
Determinants of dowel length 354
Diameter 355
Surface configuration 356
Diaphragm 357
Restoration of posterior teeth 357
Relatively intact teeth 357
Teeth with proximo-occlusal cavity 358
Teeth with MOD (mesio-occluso-distal) cavities 360
Teeth with inadequate tissue for retention without auxiliary aids 363
Core materials 365
Amalgam 365
Composite 365
Cermets 366
Cast cores 366
Root-treated teeth as abutments 366
Occlusal loading 366
Restoration of a tooth with a resected root 368
Restoration of a hemisected tooth 368
Treatment of tooth discoloration 368
Vital bleaching 368
Non-vital bleaching 368
Composite or porcelain veneers 370
Ceramometal or ceramic crowns 370
Extraction of root-treated teeth and replacement with implant-retained crowns 370
References and further reading 371
15 The medical–endo interface and patients with special needs 372
Overall patient care and the role of endodontics 372
Patient assessment 372
Management of the medically-compromised patient 373
Cardiovascular disease 373
Infective endocarditis 373
Stroke 373
Bleeding disorders 373
Respiratory disease 374
Latex allergy 374
Diabetes 374
Bisphosphonate-related osteonecrosis 375
Multiple sclerosis 375
Cerebral palsy 376
Parkinson’s disease 376
Dementia 376
Endodontics and patients with learning disability 376
Down’s syndrome 377
Autistic spectrum disorders 377
Epilepsy 377
Consent 377
Best interest meetings 378
Independent mental capacity advocates (IMCA) 378
Endodontics and the management of anxiety 378
The gag reflex 378
Endodontics and conscious sedation 379
Assessment 379
Inhalation sedation 379
Intravenous sedation with midazolam 379
Oral and intranasal sedation 379
References and further reading 379
16 The orofacial pain–endo interface 380
Definition of pain 380
Orofacial pain prevalence 380
Neurophysiological basis of orofacial pain 380
Classification of orofacial pain 380
Diagnosis of orofacial pain 380
Characteristics of orofacial pain 381
Orofacial pain and endodontics 382
Case histories of typical orofacial/endodontic pain dillemas 383
Concluding remarks 383
References and further reading 383
17 The oral medicine and oral surgery–endo interface 385
Differential diagnosis of orofacial lumps and bumps 385
Soft tissue swellings 385
Hard tissue swellings 385
Differential diagnosis of radiolucent and radiopaque lesions 385
Cysts 385
Bone lesions 385
Idiopathic osteosclerosis 385
Fibro-cemento-osseous dysplasia 385
Odontogenic tumours 385
Metastases to the jaws 386
Differential diagnosis of mucosal lesions 386
Further reading 392
Index 393
A 393
B 393
C 393
D 394
E 394
F 394
G 395
H 395
I 395
J 395
K 395
L 395
M 395
N 396
O 396
P 396
Q 397
R 397
S 399
T 399
U 399
V 399
W 399
X 399
Z 399
Tooth organogenesis, morphology and physiology
K Gulabivala and Y-L Ng
Tooth development
Many readers approach human embryology with a view to satisfying academic test requirements and may even believe such academic knowledge to be far removed from clinical practice. Yet this book begins with this fascinating subject, not merely to lay an academic foundation for the knowledge of endodontics but because contemporary practice recognizes that these biological processes hold the key to future therapeutic strategies. Regenerative treatment approaches depend upon insight from developmental processes to engineer the growth of new tissues to replace those that are diseased or damaged. The ultimate may even be to grow whole replacement teeth on demand, in situ or for implantation. Among the clinicians involved should be endodontists in whose field of knowledge and practice these procedures should lie. Any clinician involved in delivering procedures that even border on regenerative techniques should have a basic understanding of tooth development and its associated structures.
The “intelligence” or “activating force” that directs the precise coordination of multiple cell line activity, growth, migration, induction, fusion and disintegration with such control and symphonic grace, still eludes us. In our current state of knowledge, we are left merely to describe the observable and timed changes gleaned through various biological studies. Experimental studies also give us some insight about the genomic and proteomic involvement in the process, even though the picture is far from complete. Yet there is already sufficient intuitive knowledge to enable the culture of tooth tissues and whole teeth in the laboratory, albeit in a neophytic way (Fig. 1.1).
Fig. 1.1 Something to chew on (courtesy of Takashi Tsuji, Tokyo University of Science)
Early development of teeth
The primitive mouth cavity is evident as a slit-like space lined by ectoderm in the 3–4-week-old human embryo. It is located under the surface of the brain capsule and above the pericardial sac where the heart forms. The mouth cavity is still separated from the primitive pharynx by the oropharyngeal membrane. The mandibular processes grow ventrally on each side of the head to meet gradually in the midline, where they form the lower border of the mouth opening. The maxillary processes arise from the upper surfaces of the origin of the mandibular process and likewise grow towards the midline, to form the upper border of the mouth below the brain capsule (Fig. 1.2). The maxillary and mandibular processes are essentially extensions of mesenchyme tissue covered by ectoderm. The ectoderm is a layer of low columnar epithelial cells, resting on a basal lamina which separates them from the mesenchymal tissue, which originates from the neural crest cell line. In some regions, such as the tooth-bearing part, the epithelium has a more superficial part, which consists of 2–3 layers of flattened cells. At this stage, the maxillary and mandibular processes do not show separate lip or gum regions; the development of the lips, cheeks and gum regions is closely associated with the development of the dental lamina, from which teeth arise.
Fig. 1.2 Maxillary and mandibular processes in the head of human embryo (approx. 5 weeks)
Primary epithelial band, vestibular band and dental lamina
The first indication of formation of tooth development structures becomes evident at 6 weeks of embryonic life when the oral epithelium in the lateral regions of the maxillary and mandibular processes proliferate and then spread towards the midline where they become continuous into horseshoe-shaped bands. These bands are not evident on the surface but project into the underlying mesenchyme and are called the primary epithelial bands.
During the seventh week of embryonic life, the primary epithelial band divides on its deep surface into two processes; the outer, thicker one becomes the vestibular lamina (responsible for the later separation of lips/cheeks from gums) and the inner, smaller one becomes the dental lamina (which later gives rise to the teeth) (Fig. 1.3). As the dental lamina grows in length, it penetrates deeper into the mesenchyme; at the front of the mouth in a lingual direction, to form a shelf-like projection and at the back of the mouth remaining more vertical (Fig. 1.4). It is not known whether this results from active invagination of the lamina or upward proliferation of the mesenchyme.
Fig. 1.3 The dental lamina
Fig. 1.4 The primary enamel organ
Enamel organs
A short while after formation, the dental lamina thickens into small rounded swellings, involving the whole thickness from free edge to the base of attachment to the oral epithelium. These are the enamel organs of the deciduous teeth with four in each quadrant (2 incisors, canine and first deciduous molar) (see Fig. 1.4). The dental lamina continues to grow backwards, giving rise to further enamel organs for the second deciduous molar (10-week embryo), and the permanent molars (first permanent molar at 16-week embryo; second and third permanent molars after birth). At 10 weeks of embryonic life, the enamel organs and dental lamina conform to a catenary curve. As the tooth germs grow, the spacing between them is reduced. There is at this early stage no indication of the successional permanent teeth, which develop later by budding off from the lingual aspects of each deciduous enamel organ.
Dental papilla
The mesenchymal tissue surrounding the developing enamel organ responds by proliferation to form a dense mass of cellular tissue. This gives rise to the dental papilla (primitive pulp) and the follicular sac for each tooth bud. The enamel organ in the “bud” stage appears as a simple, spherical to ovoid, epithelial condensation that is poorly morpho- and histo-differentiated. The epithelial component is separated from the adjacent mesenchyme by a basement membrane. The combination of enamel organ, dental papilla and follicular sac are collectively known as the tooth germ (Fig. 1.5). The enamel organ becomes concave on its papillary surface and begins to grow at the rims so as to encircle the dental papilla, which, at this stage, is partly capped by the enamel organ (hence “cap” stage) (Fig. 1.6) and progressively embraces a greater volume of it, to be called the “bell” stage (Fig. 1.7). At the cap stage, the centre of the concavity develops a projection of epithelium called the enamel knot (Fig. 1.6), which soon disappears by programmed cell death (apoptosis) and seems to contribute cells to the enamel cord. The enamel knot represents an important regulatory signalling centre during tooth development by producing bone morphogenetic proteins (BMP-2, BMP-7), fibroblast growth factor (FGF–p21 cyclin-dependent kinase inhibitor), sonic hedgehog (Shh), WNT and transcription factors. These signals regulate growth and development of the epithelial folds that correspond to the cusp pattern of the mature tooth. The primary enamel knot also determines the position of the secondary enamel knots corresponding to the site of the future cusps. The enamel cord is a strand of cells seen at the early bell stage of development. When present, it overlies the incisal margin of a tooth or the apex of the first cusp to develop. It has been suggested that the enamel cord may be involved in the process, by which the cap stage is transformed into the bell stage or that it is a focus for the origin of stellate reticulum cells.
Fig. 1.5 The tooth germ
Fig. 1.6 The enamel organ at “cap” stage
Fig. 1.7 The enamel organ at “bell” stage
Vestibule formation
Concurrent with the enamel organ development, the vestibular band growth continues apace. At around the time of the cap stage, a vertical cleft becomes established in the vestibular band, separating the formative lips and cheeks from the formative gums (Fig. 1.8). As for the dental lamina, the vestibular band development progresses backwards.
Fig. 1.8 The formative lips and cheeks separated from the formative gums at the advanced “bell” stage
Changes to and further development of dental lamina for permanent molars
As the enamel organ is reaching the cap stage, so the dental lamina lengthens and divides into buccal and lingual parts, though the function of this is unknown. By the time the enamel and dentine formation begins during early bell stage, the dental lamina connecting the tooth germs to the oral epithelium starts to degenerate leaving a network of strands and clumps of epithelial cells. At the same time, the dental lamina continues to grow backwards to give rise to the permanent molars but, by this stage, is separated from the oral epithelium.
Development of successional permanent teeth
The enamel organs for the successional teeth arise so differently from the permanent molars that it raises...
| Erscheint lt. Verlag | 26.1.2014 |
|---|---|
| Sprache | englisch |
| Themenwelt | Medizin / Pharmazie ► Gesundheitsfachberufe |
| Medizin / Pharmazie ► Zahnmedizin | |
| ISBN-10 | 0-7020-5425-9 / 0702054259 |
| ISBN-13 | 978-0-7020-5425-9 / 9780702054259 |
| Haben Sie eine Frage zum Produkt? |
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