Textbook and Color Atlas of Traumatic Injuries to the Teeth

Textbook and Color Atlas of Traumatic Injuries to the Teeth

Fourth Edition

Edited by

J. O. AndreasenF. M. AndreasenL. Andersson

© 1981, 1994 by Munksgaard, Copenhagen, Denmark© 2007 Blackwell MunksgaardA Blackwell Publishing Company

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Second edition published 1981 by MunksgaardThird edition published 1994 by MunksgaardFourth edition published 2007 by Blackwell Publishing Ltd

ISBN: 978-1-4051-2954-1

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Contributors xPreface xiii

1 Wound Healing Subsequent to Injury 1F. G, S. S J & J. O. A

Definition 1Nature of a traumatic injury 1Wound healing biology 1Dynamics of wound repair 4Types of wound after injury 8Tissues and compounds in wound healing 9Inflammatory phase mediators 13Cells in wound healing 18Angiogenesis 29Wound strength development 32Remodeling phase 35Microenvironnent in wounds 37Factors affecting the wound healing process 39Optimizing oral wound healing 43Essentials 43References 44

2 Response of Oral Tissues to Trauma 62J. O. A & H. L

Repair and regeneration of oral tissues 62Developing teeth 63Teeth with developed roots 72Dentin-pulp complex 84Essentials 95References 96

3 Stem Cells and Regeneration ofInjured Dental Tissue 114H. L, W. V. G,M. J. S, Q. J & J. O. A

Introduction 114The stem cell 114Tissue engineering 121Periodontal tissue regeneration 123Cementum engineering 124

Pulp-dentin regeneration after trauma 126Growing teeth 129Implant/transplant teeth 130Essentials 130References 131

4 Osteoclastic Activity 137S. F. L, C. W. D, A. M. P,M. T & S. S

Osteoclast histogenesis 137Osteoclast morphology 138Odontoclast function 139Regulation of osteoclast activity 143Identification of osteoclasts and odontoclasts 146Osteoclast activity in general 148Inflammation and mediators of hard tissue

resorption 148Essentials 160References 160

5 Physical and Chemical Methods to Optimize Pulpal and Periodontal Healing After Traumatic Injuries 172M. T

Treatment strategies 173General strategies 175Fluoride pre-treatment of the root 189Essentials 194References 194

6 Socio-Psychological Aspects of Traumatic Dental Injuries 197W. M & U. R

Introduction 197Socio-psychological impacts of traumatic dental

injuries 198Stages of psychological development 199Implications for treatment 200Treatment plan 201Talking to children 203

Contents

v

vi Contents

Essentials 204References 205

7 Child Physical Abuse 207R. R. W

Child physical abuse – a definition 207Child physical abuse – historical aspects 207Prevalence 207Etiology 208Diagnosis 208Types of orofacial injuries in child physical abuse 209Bruising 209Human hand marks 209Bizarre bruises 210Abrasions and lacerations 210Burns 211Bite marks 211Dental trauma 211Eye injuries 211Bone fractures 212Differential diagnosis 213The dentist’s role in the management of child

physical abuse 213Essentials 214References 215

8 Classification, Epidemiology and Etiology 217U. G, W. M & J. O. A

Classification 217Epidemiology 223Etiology 228Unintentional traumatic dental injuries 229Intentional traumatic dental injuries 233Mechanisms of traumatic dental injuries 235Essentials 243References 244

9 Examination and Diagnosis of Dental Injuries 255F. M. A, J. O. A & M. T

History 255Clinical examination 258Radiographic examination 267Effect of treatment delay 271Essentials 273References 274

10 Crown Fractures 280F. M. A & J. O. A

Terminology, frequency and etiology 280Clinical findings 281Radiographic findings 282Healing and pathology 282Treatment 285

Provisional treatment of crown fractures 288Definitive treatment of crown fractures 288Reattachment of the original crown fragment 290Laminate veneers in the treatment of crown

fractures 297Prognosis of crown fractures 301Essentials 303References 304

11 Crown-Root Fractures 314J. O. A, F. M. A & M. T

Terminology, frequency and etiology 314Clinical findings 314Radiographic findings 315Healing and pathology 318Treatment 318Essentials 332References 334

12 Root Fractures 337F. M. A, J. O. A & M. C

Terminology, frequency and etiology 337Clinical findings 337Radiographic findings 338Healing and pathology 340Treatment 351Prognosis 358Follow-up 358Orthodontic treatment of root fractured teeth 364Predictors of healing 364Essentials 366References 367

13 Luxation Injuries of Permanent Teeth:General Findings 372F. M. A & J. O. A

Terminology, frequency and etiology 372Clinical findings 372Radiographic findings 373Healing and pathology 374Periodontal ligament (PDL) 374Pulp 374Treatment 376Prognosis 376Pulp necrosis 377Pulp canal obliteration 385Root resorption 386Loss of marginal bone support 393Essentials 395References 397

14 Concussion and Subluxation 404F. M. A & J. O. A

Definitions 404Healing and pathology 404Concussion 404

Contents vii

Subluxation 404Radiographic findings 404Treatment 404Follow-up 405Complications 405Predictors for healing 409Essentials 410References 410

15 Extrusive Luxation and Lateral Luxation 411F. M. A & J. O. A

Definitions 411Healing and pathology 411Clinical findings 411Radiographic findings 411Treatment 412Prognosis 415Pulp necrosis 418Pulp canal obliteration 418Root resorption (external) 418Marginal bone loss 418Predictors of healing 425Tooth survival 425Essentials 426References 427

16 Intrusive Luxation 428J. O. A & F. M. A

Definition 428Healing and pathology 428Clinical findings 428Radiographic findings 429Treatment 432Prognosis 437Diagnosis of healing complications 438Predictors for healing 442Essentials 442References 443

17 Avulsions 444J. O. A & F. M. A

Terminology, frequency and etiology 444Clinical findings 444Radiographic findings 444Healing and pathology 444Treatment of the avulsed tooth 459Prognosis 466Tooth loss 466Pulp necrosis 466Root resorption 470Root development and disturbances in root growth 475Gingival healing and loss of marginal attachment 476Complications due to early loss of teeth 476Essentials 478References 480

18 Injuries to the Supporting Bone 489J. O. A

Terminology, frequency and etiology 489Clinical findings 489Radiographic findings 492Pathology 495Treatment 498Fractures of the mandible or maxilla 500Prognosis 504Fractures of the mandible or maxilla in children 505Fractures of the mandible or maxilla in adults 507Essentials 511References 511

19 Injuries to the Primary Dentition 516M. T. F, G. H, M. B & J. O. A

Introduction 516Epidemiology and etiology 517Clinical and radiographic findings and treatment

of various injury types 523Fractures secondary to chin trauma 533Complications in the primary dentition 533Essentials 537References 539

20 Injuries to Developing Teeth 542J. O. A & M. T. F

Terminology, frequency and etiology 542Clinical, radiographic and pathologic findings 546Treatment 564Essentials 569References 571

21 Soft Tissue Injuries 577L. A & J. O. A

Terminology, frequency and etiology 577Types of soft tissue trauma 578Emergency management 579Wound closure materials and principles 587Antibiotic prophylaxis 592Tetanus prophylaxis 594Essentials 594References 595

22 Endodontic Management and the Use of Calcium Hydroxide in Traumatized Permanent Teeth 598M. C

Crown fractures with dentin exposure 598Crown fractures with pulp exposure 600Clinical evaluation of pulp healing 610Root fractures 611Luxated or avulsed and replanted teeth 615Treatment of immature teeth 621

viii Contents

Timing of endodontic procedure after replantation 625Treatment of mature teeth 632External inflammatory root resorption 632Late external inflammatory root resorption 636Root canal resorption (internal resorption) 638Pulp necrosis following pulp canal obliteration 639Crown malformations 643Discoloration of non-vital teeth 644Essentials 645References 647

23 New Endodontic Procedures using Mineral Trioxide Aggregate (MTA) for Teeth with Traumatic Injuries 658L. K. B

Introduction 658Pulp capping and partial pulpotomy 659Apexification 662Root fractures 663Essentials 666References 666

24 Orthodontic Management of theTraumatized Dentition 669O. M & B. M

Diagnosis and treatment planning 669Factors in treatment planning 670General treatment principles 675Specific treatment principles for various trauma

types 684Replanted teeth 696Prognosis 703Essentials 709References 711

25 Restoration of Traumatized Teeth with Resin Composites 716U. P & J. W. V. V D

Long-term prognosis of composite restorations 716Material considerations 718Clinical implications 721Critical points in the restorative procedure 721Essentials 726References 727

26 Resin-related Bridges and Conventional Bridges in the Anterior Region 729N. H. J. C & C. M. K

Treatment planning 729The ‘dynamic treatment’ concept 729Direct resin-bonded bridges 731Indirect resin-bonded bridges 731Conventional bridges 735Prognosis of resin-bonded bridges and

comparison with alternative prosthodontic treatments 735

Factors influencing the survival of resin-bonded bridges 736

Essentials 736References 737

27 Autotransplantation of Teeth to the Anterior Region 740J. O. A, L. A & M. T

Treatment planning 740Surgical procedure 743Orthodontic treatment of transplanted teeth 749Prognosis 754Essentials 759References 759

28 Implants in the Anterior Region 761J. O. A, J. Ö, C. H,D. B, T. V A, J. J, S. E. N & O. S

Indications for implants in trauma patients 761Treatment with implants in a trauma situation –

when to give up? 761Treatment planning 763Timing of implant insertion in relation to jaw

growth 763Timing of implant placement following tooth

extraction 764Biologic and surgical aspects for implant therapy

after loss of traumatized teeth 767Ideal implant position in esthetic sites 769The concept of comfort and danger zones 770To create and maintain a normal appearing gingiva 771To create and maintain a normal appearing alveolar

process 771Preoperative evaluation 772Standard insertion in single gaps with good bone

volume 773Surgical procedure in single tooth gaps with

doubtful bone volume 773Horizontal augmentation 776GBR technique: simultaneous approach 777GBR technique: staged approach 777Rationale for the described techniques 779Vertical augmentation by bone transplantation 781Vertical augmentation by alveolar distraction

osteogenesis 783Long-term results 785Causes and predictors of failure 785Patient satisfaction 789Essentials 789References 790

29 Esthetic Considerations in Restoring the Traumatized Dentition: a Biologic Approach 798B. U. Z & S. T

Replacement of a missing maxillary central incisor 798Orthodontic space closure treatment 798

Contents ix

Autotransplantation of premolars 803Single-tooth implants 805Fixed prosthetics 807Replacement of a missing maxillary lateral incisor 807Replacement of a canine 808Replacement after loss of multiple maxillary

anterior teeth 809Restoring fractured teeth 809The Toreskog/Myrin concept 810Essentials 811References 812

30 Prevention of Dental and Oral Injuries 814A. S

Introduction 814Means to prevent dental maxillofacial injuries 817Appliances to prevent dental injuries 817Fabrication of custom mouthguards 823Special considerations for mouthguards 826Care of mouthguards 827Use of mouthguards and other protective

appliances in various sports activities 828Cost–benefit of impact protecting devices 829Other applications for the use of mouthguards 829Prevention of oral injury from traffic accidents 830Essentials 830References 832

31 Prognosis of Traumatic Dental Injuries:Statistical Considerations 835P. K. A, F. M. A & J. O. A

Identifying prognosis related factors 835Expressing prognosis quantitatively 835Comparing life tables 839Essentials 840References 840

32 Splinting of Traumatized Teeth 842K. S. O

Influence of splinting on dental tissues 842Requirements for an acceptable splint 842Splinting methods 843Testing the mechanical properties of various

splinting types 843

Recommendations for splinting type and duration 848

Essentials 850References 850

33 Bleaching of the Discolored Traumatized Tooth 852J. E. D & U. P

Etiology of discoloration 852Medicaments 852Intracoronal bleaching 853External tooth bleaching 857Clinical recommendations 857Essentials 858References 858

34 Economic Aspects of Traumatic Dental Injuries 861U. G, L. A & J. O. A

Costs of traumatic dental injuries 861Time and costs 862Essentials 866References 866

35 Information to the Public, Patients andEmergency Services on Traumatic Dental Injuries 869M. T. F

Developing a public awareness campaign 869Recommendations for specific groups 871Prevention of sports-related dental trauma 871Guidelines to the public: first aid and treatment

of trauma to primary teeth 871Guidelines to the public: first aid and treatment of

trauma to permanent teeth 872Information to emergency services 872Information to patients 872Essentials 874References 875

Appendix 1 876Appendix 2 880Appendix 3 881Appendix 4 882

Index 883

PER KRAGH ANDERSEN, Cand.Stat., PhD, Med.Dr.ProfessorDepartment of BiostatisticsUniversity of CopenhagenDenmark

LARS ANDERSSON, DDS, PhD, Odont.Dr.Professor of Oral and Maxillofacial SurgeryDepartment of Surgical SciencesFaculty of DentistryHealth Sciences CenterKuwait UniversityKuwait

FRANCES M. ANDREASEN, DDS, Odont.Dr.Research AssociateDepartment of Oral and Maxillofacial Surgery andCenter for Rare Oral DiseasesUniversity Hospital, CopenhagenDenmark

JENS O. ANDREASEN, DDS, Odont.Dr, HC, FRCSDepartment of Oral and Maxillofacial Surgery andCenter for Rare Oral DiseasesUniversity Hospital, CopenhagenDenmark

THOMAS VON ARX, PD.Dr.Med.Dent.Associate ProfessorDepartment of Oral Surgery and StomatologySchool of Dental MedicineUniversity of BerneSwitzerland

LEIF K. BAKLAND, DDSProfessor and ChairDepartment of EndodonticsSchool of DentistryLoma Linda UniversityUSA

METTE BORUM, DDS, PhDDirectorMunicipal Pediatric Dental ServiceHoeje-Taastrup CommunityTaastrupDenmark

DANIEL BUSER, DDS, Dr.Med.Dent.Professor and ChairmanDepartment of Oral Surgery and StomatologySchool of Dental MedicineUniversity of BerneSwitzerland

NICO H.J. CREUGERS, DDS, PhDProfessor and ChairmanDepartment of Oral Function and Prosthetic DentistryNijmegen Medical Centre, Dental SchoolRadboud UniversityThe Netherlands

MIOMIR CVEK, DMS, Odont.Dr.ProfessorFaculty of StomatologyUniversity of ZagrebCroatia, andDepartment of PedodonticsEastman Dental Institute, StockholmSweden

JON E. DAHL, DDS, Dr.Odont., DScSenior Scientist and ProfessorNordic Institute of Dental MaterialsHaslumNorway

JAN W.V. VAN DIJKEN, DDS, Odont.Dr.ProfessorDental Hygienist EducationDental School UmeåUmeå UniversitySweden

Contributors

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Contributors xi

CRAIG W. DREYER, PhD, MDS, BDSSenior LecturerSchool of DentistryUniversity of AdelaideAustralia

MARIA T. FLORES, DDSProfessor of Pediatric DentistryFaculty of DentistryUniversity of ValparaisoChile

WILLIAM V. GIANNOBILE, DDS, D.Med.Sci.Najjar Professor of Dentistry and DirectorMichigan Center for Oral Health ResearchUniversity of Michigan Clinical CenterUSA

ULF GLENDOR, DDS, PhD, Med.Dr.Research AssociateDivision of Social Medicine and Public Health ScienceDepartment of Health and SocietyUniversity of LinköpingSweden

FINN GOTTRUP, MD, DMSciProfessor of SurgeryHead of the University Center of Wound HealingDepartment of Plastic SurgeryOdense University HospitalDenmark

CHRISTOPH HÄMMERLE, DMD, Dr.Med.Dent.ProfessorClinic for Fixed and Removable ProsthodonticsCenter for Dental and Oral Medicine and Cranio-Maxillofacial SurgeryUniversity of ZurichSwitzerland

GIDEON HOLAN, DMDDirector of Postgraduate ProgramDepartment of Pediatric DentistryThe Hebrew UniversityHadassah School of Dental MedicineIsrael

JOHN JENSEN, DDS, PhDAssociate Professor and ChairmanDepartment of Oral and Maxillofacial SurgeryAarhus University HospitalDenmark

QIMING JIN, DDS, PhDResearch InvestigatorDepartment of Periodontics and Oral MedicineUniversity of MichiganUSA

CEES M. KREULEN, DDS, PhDAssociate ProfessorDepartment of Oral Function and Prosthetic DentistryNijmegen Medical Centre, Dental SchoolRadboud UniversityThe Netherlands

SVEN F. LINDSKOG, DDS, Odont.Dr.Professor and Senior ConsultantDepartment of Oral PathologyDental SchoolKarolinska InstituteSweden

HENRIK LØvSCHALL, DDS, PhDAssociate ProfessorDepartment of Dental Pathology, Operative Dentistry andEndodonticsSchool of DentistryUniversity of AarhusDenmark

BARBRO MALMGREN, DDS, Med.Dr.Senior ConsultantPediatric DepartmentKarolinska University HospitalSweden

OLLE MALMGREN, DDS, Odont.Dr.Associate ProfessorOrthodontic ClinicUppsalaSweden

WAGNER MARCENES, DDS, Odont.Dr.Professor of Oral EpidemiologyInstitute of DentistryQueen Mary’s School of Medicine and DentistryBarts and the LondonLondonUK

SVEN ERIK NØRHOLT, DDS, Ph.Dr.Consultant in Oral and Maxillofacial SurgeryDepartment of Oral and Maxillofacial SurgeryAarhus University HospitalDenmark

JAN ÖDMAN, DDS, Odont.Dr.Consultant OrthodontistCopenhagen Municipal Pedodontic ServiceTrollhättanSweden

xii Contributors

KYÖSTI S. OIKARINEN, DDS, Odont.Dr.Professor and ChairmanDepartment of Oral and Maxillofacial SurgeryUniversity of OuluFinland

ULLA PALLESEN, DDSDirector of Clinical TeachingDepartment of Cariology and EndodonticsSchool of DentistryCopenhagen UniversityDenmark

ANGELA M. PIERCE, MDS, Odont.Dr., FRACDS, FFOP(RCPA)Honorary Consultant in Oral PathologyDivision of Tissue PathologyInstitute of Medical and Veterinary ScienceAdelaideAustralia

ULLA RYDÅ, Med. Dr.Consultant Child PsychiatristJönköping County CouncilJönköpingSweden

OLE SCHWARTZ, DDS, PhDChairmanDepartment of Oral and Maxillofacial SurgeryUniversity Hospital, CopenhagenDenmark

SHAHROKH SHABAHANG, DDS, MS, PhDAssociate ProfessorDepartment of EndodonticsSchool of DentistryLoma Linda UniversityUSA

ASGEIR SIGURDSSON, Cand.Odont, MSAdjunct Associate ProfessorDepartment of EndodonticsUniversity of North Carolina School of Dentistry, USA, andPrivate Endodontic PracticeReykjavikIceland

MARTHA J. SOMERMAN, DDS, PhDDeanSchool of DentistryUniversity of WashingtonSeattleUSA

SIMON STORGÅRD JENSEN, DDS, PhDConsultant Oral and Maxillofacial SurgeonDepartment of Oral and Maxillofacial SurgeryCopenhagen University HospitalGlostrupDenmark

MAHMOUD TORABINEJAD, DMD, MSD, PhDProfessor and Advanced Education Program DirectorDepartment of EndodonticsSchool of DentistryLoma Linda UniversityUSA

SVERKER TORESKOG, DDSPrivate PracticeGöteborgSweden

MARTIN TROPE, DDSJ. B. Freedland ProfessorDepartment of EndodonticsSchool of DentistryUniversity of North CarolinaUSA

MITSUHIRO TSUKIBOSHI, DDS, PhDPrivate Practice, General DentistryAichiJapan

RICHARD R. WELBURY, MB, BS, PhD, FDSRCS, FRCPCHProfessor of Paediatric DentistryGlasgow Dental School and HospitalUK

BJÖRN U. ZACHRISSON, DDS, MSD, PhDProfessor and Private Practice in OrthodonticsDepartment of OrthodonticsUniversity of OsloNorway

More than thirty years has elapsed since the publication ofthe first edition of this textbook in 1972. At that time, tableclinics were being held, where the theme of treatment was to extract traumatized teeth at the time of injury,and then the problem was solved. Since then, the biology ofacute dental trauma has been elucidated through clinicaland experimental research and in subsequent editions of thisbook used as the guiding light in defining treatment strategy.

A disturbing finding from several recent studies is thatacute treatment of dental injuries can sometimes lead toinferior healing. This naturally leads to a rethinking of strat-egy for treatment of the injured patient. Until now, acceptedtreatment has been to reposition traumatically displacedteeth or bone fragments into an anatomically correct posi-tion. However, this procedure itself may further damagealready traumatized tissues. This might explain the negativeeffect of many forceful reductions, as after luxation injuries,particularly upon periodontal healing. Likewise, the ideathat an exposed pulp is a diseased and infected pulp whichrequires immediate or delayed extirpation has not been substantiated in real life. On the contrary, given the righthealing conditions, exposed pulp is a survivor. Similarly,root fractured incisors are often removed due to a lack of understanding of the healing capacity of the pulp andperiodontium and their respective roles in the healingprocess.

Previously, acute dental trauma was considered an eventencompassing certain treatment problems that could beadequately resolved by proper endodontic, surgical ororthodontic intervention. However, recent new research hasaltered this view. Now we know that most healing compli-cations following trauma are related to pre-injury or injuryfactors, and that treatment should be very specific andrestricted in order to optimize healing. This edition isdevoted to a biologic approach in understanding the natureof trauma and subsequent healing events and how theseevents can be assisted by treatment interventions.

The study and understanding of healing in hard and softtissues after trauma is probably one of the most serious chal-

lenges facing the dental profession. That this task presentlyrests with only a handful of researchers is out of proportionwith the fact that perhaps half of the world’s populationtoday has suffered oral or dental trauma – a paradox thatdental trauma is dentistry’s stepchild.

In the decade that has elapsed since the third edition ofthis textbook, the impact of dental implants has been felt. Inthe wake of esthetically and functionally successful implanttherapy, there is a growing tendency towards the approachof: ‘If in doubt, take it out’ and replace with a dental implant.This mind-set has seriously colored many professionals’ per-ception of conservative therapy, be it active observation orinterceptive endodontic therapy. Moreover, it has led to anexplosion in the cost of treatment following dental trauma.For the sake of completeness, the chapter on dental implantshas therefore been expanded with respect to primary biologic principles, with particular emphasis on problemsrelated to the use of implants following dental trauma. Inthis regard, it should be borne in mind that trauma patientsare most often young patients in whom the placement of animplant is contraindicated because it interferes with growthand development of the jaw. Furthermore, the fact thatmany families in the world today may live on a few dollarsa day brings the cost–benefit aspect of treatment into focus.In such a world, sophisticated treatment modalities that arenow available may only be realistic for very few. And thenwhat? This reality is also described.

The enormous impact of a traumatic event on the mentalhealth of the patient has long been ignored. In some situa-tions, the loss of a tooth or parts of teeth may result in a difficult psychological situation, which so far has been com-pletely underplayed and neglected in dental traumatology.This void is addressed in this new edition by a chapter onthe psychological impact of dental trauma on the patient.Moreover, a traumatic event, whether crown fracture ortooth loss, usually results in severe esthetic problems. Afurther chapter is now devoted specifically to esthetic rehabilitation of the traumatized patient.

In this edition, an evidence-based approach to treatmenthas been chosen. This implies that any treatment procedure

Preface

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xiv Preface

must be carefully screened for its effect upon healingprocesses. Due to the fact that treatment approaches, bytheir very nature, are usually traumatogenic, treatment prin-ciples for traumatized teeth become critical. Randomizedclinical studies would be desirable, but inevitably there arepractical and ethical problems with this: it would be diffi-cult to ask for signed patient approval to place the patientin group A or B to test the difference between acute treat-ment procedures.

Acute dental trauma implies severe pain and psychologi-cal impact for many of us. There may also be severe eco-nomic consequences for trauma victims, especially in lessprivileged social groups. The dental profession must copewith these problems. One approach could be prevention ofdental injuries, but previous efforts in this direction have notalways been cost-effective. In this fourth edition, accident-prone sports activities have been identified where mouth-guards could be of value.

Statistics from most countries show that one third of allpreschool children have suffered a dental trauma involvingthe primary dentition and 20–25% have suffered a trauma

to the permanent dentition. With such statistics it is likelythat more than 3 billion of the world’s population aretrauma victims and, considering the general lack of con-tinuing and serious research into dental trauma, the importance of this area of dentistry cannot be overstated.

It is the authors’ hope that a better knowledge of thebiology of dental trauma and wound healing will lead to amore intelligent treatment strategy, where the slogan ‘Handsoff where you can!’ to save teeth could mean that the trau-matic episode might be a short-lived one and not a pro-tracted story of treatment and re-treatment – not only for the victim of dental trauma, but also for the dental practitioner.

The aim of this textbook is to ignite interest in thisstepchild of dentistry, a discipline where all the skills of den-tistry are needed to help victims of dental trauma. Please beinvolved!

Jens O. Andreasen, DDS, Odont. dr. h.c, CopenhagenFrances M. Andreasen, DDS, dr. odont., CopenhagenLars Andersson, DDS, dr. odont., Kuwait

F. Gottrup

Definition

The generally accepted definition of wound healing is: ‘areaction of any multicellular organism on tissue damage inorder to restore the continuity and function of the tissue ororgan’. This is a functional definition saying little about theprocess itself and which factors are influential.

Traumatic dental injuries usually imply wound healingprocesses in the periodontium, the pulp and sometimesassociated soft tissue. The outcome of these determines thefinal healing result (Fig. 1.1). The general response of softand mineralized tissues to surgical and traumatic injuries isa sensitive process, where even minor changes in the treat-ment procedure may have an impact upon the rate andquality of healing.

In order to design suitable treatment procedures for atraumatized dentition, it is necessary to consider the cellu-lar and humoral elements in wound healing. In this respectconsiderable progress has been made in understanding ofthe role of different cells involved.

In this chapter the general response of soft tissues toinjury is described, as well as the various factors influencingthe wound healing processes. For progress to be made in thetreatment of traumatic dental injuries it is necessary to beginwith general wound healing principles. The aim of thepresent chapter is to give a general survey of wound healingas it appears from recent research. For more detailed infor-mation about the various topics the reader should consulttextbooks and review articles devoted to wound healing(1–23, 607–612).

Nature of a traumatic injury

Whenever injury disrupts tissue, a sequence of events is ini-tiated whose ultimate goal is to heal the damaged tissue. The

sequence of events after wounding is: control of bleeding;establishing a line of defense against infection; cleansing the wound site of necrotic tissue elements, bacteria orforeign bodies; closing the wound gap with newly formedconnective tissue and epithelium; and finally modifying theprimary wound tissue to a more functionally suitable tissue.

This healing process is basically the same in all tissues, butmay vary clinically according to the tissues involved. Thuswound healing after dental trauma is complicated by themultiplicity of cellular systems involved (Fig. 1.2).

During the last two decades, significant advances havebeen made in the understanding of the biology behindwound healing in general and new details concerning theregulating mechanisms have been discovered.

While a vast body of knowledge exists concerning thehealing of cutaneous wounds, relatively sparse informationexists concerning healing of oral mucosa and odontogenictissues. This chapter describes the general features of woundhealing, and the present knowledge of the cellular systemsinvolved. Wound healing as it applies to the specific odon-togenic tissues will be described in Chapter 2.

Wound healing biology

Wound healing is a dynamic, interactive process involvingcells and extracelluar matrix and is dependent on internal aswell as external factors. Different schemes have been used inorder to summarize the wound healing process. Withincreasing knowledge of the involved processes, cell typesetc., a complete survey of all aspects will be hugely difficultto overview. The authors have for many years used a modi-fication of the original Hunt flow diagram for woundhealing (19) (Fig 1.2). This diagram illustrates the mainevents in superficial epithelialization and production ofgranulation tissue.

The wound healing process will be described in detail inthe following section.

1Wound Healing Subsequent to InjuryF. Gottrup, S. Storgård Jensen & J. O. Andreasen

1

2 Chapter 1

Fig. 1.1 Cells involved in the healing event after a tooth luxation. Clockwise from top: endothelial cell and pericytes; thrombocyte (platelet); erythro-cyte; fibroblast; epithelial cell; macrophage; neutrophil; lymphocytes; mast cell.

Wound Healing Subsequent to Injury 3

Repair versus regeneration

The goal of the wound healing process after injury is torestore the continuity between wound edges and to re-estab-lish tissue function. In relation to wound healing, it is appro-priate to define various terms, such as repair andregeneration. In this context, it has been suggested that theterm regeneration should be used for a biologic process bywhich the structure and function of the disrupted or losttissue is completely restored, whereas repair or scar forma-tion is a biologic process whereby the continuity of the dis-rupted or lost tissue is regained by new tissue which doesnot restore structure and function (14). Throughout thetext, these terms will be used according to the above defini-tions. The implication of repair and regeneration as theyrelate to oral tissues is discussed in Chapter 2.

Cell differentiation

Cell differentiation is a process whereby an embryonic non-functional cell matures and changes into a tissue-specificcell, performing one or more functions characteristic of thatcell population. Examples of this are the mesenchymal par-avascular cells in the periodontal ligament and the pulp, andthe basal cells of the epithelium. A problem arises as towhether already functioning odontogenic cells can revert toa more primitive cell type. Although this is known to takeplace in cutaneous wounds, it is unsettled with respect todental tissues (see Chapter 2). With regard to cell differen-tiation, it appears that extracellular matrix compounds, suchas proteoglycans, have a significant influence on cell differ-entiation in wound healing (25).

Progenitor cells (stem cells)

Among the various cell populations in oral and other tissues,a small fraction are progenitor cells. These cells are self-per-

petuating, nonspecialized cells, which are the source of newdifferentiating cells during normal tissue turnover andhealing after injury (17–19). The role of these in woundhealing is further discussed in Chapter 3.

Cell cycle

Prior to mitosis, DNA must duplicate and RNA be synthe-sized. Since materials needed for cell division occupy morethan half the cell, a cell that is performing functional syn-thesis (e.g. a fibroblast producing collagen, an odontoblastproducing dentin or an epithelial cell producing keratin)does not have the resources to undergo mitosis. Conversely,a cell preparing for or undergoing mitosis has insufficientresources to undertake its functions. This may explain whyit is usually the least differentiated cells that undergo prolif-eration in a damaged tissue, and why differentiated cells donot often divide (15).

The interval between consecutive mitoses has beentermed the cell cycle which represents an ordered sequenceof events that are necessary before the next mitosis (Fig. 1.3):The cell cycle has been subdivided into phases such as G1,the time before the onset of DNA synthesis. In the S phasethe DNA content is replicated, G2 is the time between the Sphase and mitosis, and M the time of mitosis (Fig. 1.3). Thecumulative length of S, G2 and M is relatively constant at10–12 hours, whereas differences occur among cell types inthe duration of G1 (26).

Cells that have become growth arrested enter a restingphase, G0, which lies outside the cell cycle. The G0 state isreversible and cells can remain viable in G0 for extendedperiods.

In vivo, cells can be classified as continuously dividing(e.g. epithelial cells, fibroblasts), non-dividing post-mitotic(e.g. ameloblasts) and cells reversibly growth arrested in G0

that can be induced to re-enter the proliferative cycle.

Coagulation

Blood platelets

Inflammation

LymphocytesMacrophagesGranulocytes

Resistance toinfection

Epithelium

Collagenlysis

Remodeling

HEALED WOUND

Collagensynthesis

Contraction

ProteoglycansynthesisAngiogenesis

Fibroblasts

TRAUMA

Fig. 1.2 Modified Hunt flow diagramfor wound healing.

4 Chapter 1

Factors leading to fibroblast proliferation have beenstudied in the fibroblast system. Resting cells are made com-petent to proliferate (i.e. entry of G0 cells into early G1 stage)by so-called competence factors (i.e. platelet derived growthfactor (PDGF), fibroblast growth factor (FGF) and calciumphosphate precipitates). However, there is no progressionbeyond G1 until the appearance of progression factors suchas insulin-like growth factor-1 (IGF-1), epidermal growthfactor (EGF) and other plasma factors (26) (Fig. 1.3).

Cell migration

Optimal wound repair is dependent upon an orderly influxof cells into the wound area. Directed cell motion requirespolarization of cells and formation of both a leading edgethat attaches to the matrix and a trailing edge that is pulledalong. The stimulus for directional cell migration can be asoluble attractant (chemotaxis), a substratum-bound gradi-ent of a particular matrix constituent (haptotaxis) or thethree-dimensional array of extracellular matrix within thetissue (contact guidance). Finally there is a free edge effectwhich occurs in epithelial wound healing (see p. 36) (27, 28).

Typical examples of cells responding to chemotaxis are cir-culating neutrophils and monocytes and macrophages (seep. 23). The chemoattractant is regulated by diffusion of theattractant from its source into an attraction-poor medium.

Cells migrating by haptotaxis extend lamellipodia more orless randomly and each of these protruding lamellipodiacompetes for a matrix component to adhere to, whereby aleading edge will be created on one side of the cell and a new membrane inserted into the leading edge. In thatcontext, fibronectin and laminin seem to be important foradhesion (27).

Contact guidance occurs as the cell is forced along pathsof least resistance through the extracellular matrix. Thus,migrating cells align themselves according to the matrix

configuration, a phenomenon that can be seen in theextended fibrin strands in retracting blood clots (see p. 9),as well as in the orientation of fibroblasts in granulationtissue (29). In this context it should be mentioned thatmechanisms also exist whereby spaces are opened within theextracellular area when cells migrate. Thus both fibroblastsand macrophages use enzymes such as plasmin, plasmino-gen and collagenases for this purpose (30).

During wound repair, a given parenchymal cell maymigrate into the wound space by multiple mechanismsoccurring concurrently or in succession. Factors related tocell migration in wound healing are described later for eachparticular cell type.

Dynamics of wound repair

Classically the events taking place after wounding can bedivided into three phases, namely the inflammation, the pro-liferation and the remodeling phases (5, 13, 20–23, 31). Theinflammation phase may, however, be subdivided into ahemostasis phase and an inflammatory phase. But, it shouldbe remembered that wound healing is a continuous processwhere the beginning and end of each phase cannot be clearlydetermined and phases do overlap.

Tissue injury causes disruption of blood vessels andextravasation of blood constituents. Vasoconstriction pro-vides a rapid, but transient, decrease in bleeding. The extrinsic and intrinsic coagulation pathways are also imme-diately activated. The blood clots together with vasocon-striction re-establish hemostasis and provide a provisionalextracellular matrix for cell migration. Adherent plateletsundergo morphological changes to facilitate formation ofthe hemostatic plug and secrete several mediators of woundhealing such as platelet derived growth factor, which attractand activate macrophages and fibroblasts. Other growthfactors and a great number of other mediators such aschemoattractants and vasoactive substances are alsoreleased. The released products soon initiate the inflamma-tory response.

Inflammation phase

Following the initial vasoconstriction a vasodilatation takesplace in the wound area. This supports the migration ofinflammatory cells into the wound area (Fig. 1.4).

These processes take place in the coagulated blood clotplaced in the wound cavity. When prothrombin changes tothrombin, cleaving the fibrinogen molecule to fibrin, theclot turns into a fibrin clot, which later becomes the woundcrust in open wounds. Fibronolytic activity is, however, alsopresent in this early stage of healing. From plasminogen isproduced plasmin which digests fibrin leading to theremoval of thrombi. Fibrin has its main effect when angio-genesis starts and the restoration of vascular structurebegins.

Neutrophils, lymphocytes and macrophages are the firstcells to arrive at the site of injury. Their major role is to guard

DNA synthesis

G2

G1G0

S

M mitosis

PDGFFGFCalcium phosphateprecipitate

IGF-1EGF

Fig. 1.3 Cell cycle. G0 = resting phase; G1 = time before onset of DNAsynthesis; S = replication of DNA; G2 = time between DNA replication andmitosis; M = mitosis.

Wound Healing Subsequent to Injury 5

PLATELETSandFIBRIN

PDGFTGF-βTGF-αEGF

NEUTROPHIL

ATTRACTIONACTIVATION

ANGIOGENESIS

MACROPHAGE

ATTRACTIONACTIVATION

PDGFTGF-βVEGFTNFbFGF

FIBROBLAST

ATTRACTIONACTIVATIONMITOGENESIS

TGFVEGF

PLASMALEAKAGE

IGF-I

DAMAGEDCELLSandMATRIX

bFGF

OXYGEN

Low pO2

LACTATE

High lactate

ENDOTHELIALCELL

PDGFFGF

Fig. 1.4 Cellular components and mediators in the wound healing module. Signals for wound healing are released by platelets, fibrin, plasma leakage,damaged cells and matrix. Furthermore low oxygen tension and a high lactate concentration in the injury site contribute an important stimulus forhealing.

6 Chapter 1

against the threat of infection, as well as to cleanse thewound site of cellular matrix debris and foreign bodies.The macrophages appear to direct the concerted action ofthe wound cell team (Fig. 1.4).

Proliferative phase (fibroplasia)

This is called the fibroplasia phase or regeneration phase andis a continuation of the inflammatory phase, characterizedby fibroblast proliferation and migration and the produc-tion of connective tissue. It starts about day 2 after the tissuetrauma and continues for two to three weeks after thetrauma in the case of a closed wound. This phase can beextended significantly in the case of an open wound withsevere tissue damage, where complete closure will requireproduction of a large amount of connective tissue.

In response to chemoattractants created in the inflam-mation phase, fibroblasts invade the wound area and thisstarts the proliferation phase. The invasion of fibroblastsstarts at day 2 after injury and by day 4 they are the majorcell type in normal healing. Fibroblasts are responsible forreplacing the fibrin matrix (clot) with collagen-rich newstroma often called granulation tissue. In addition, fibrob-lasts also produce and release proteoglycans and gly-cosaminoglycan (GAG), which are important componentsof the extracellular matrix of the granulation tissue. Vascu-lar restoration uses the new matrix as a scaffold and numer-ous new capillaries endow the new stroma with a granularappearance (angiogenesis). Macrophages provide a contin-uing source of growth factors necessary to stimulate fibro-plasia and angiogenesis. The structural molecules of newlyformed extracellular matrix, termed provisional matrix,produce a scaffold or conduit for cell migration. These mol-ecules include fibrin, fibronectin and hyaluronic acid.Fibronectin and the appropriate integrin receptors bindfibronectin, fibrin or both on fibroblasts appearing to limitthe rate of formation of granulation tissue.

Stimulated by growth factors and other signals, fibroblastsand endothelial cells divide, and cause a capillary networkto move into the wound site which is characterized byischemic damaged tissue or a coagulum.

The increasing numbers of cells in the wound area inducehypoxia, hypercapnia and lactacidosis, due to the increasedneed for oxygen in an area with decreased oxygen deliverybecause of the tissue injury (32, 33).

At cellular level oxygen is an essential nutrient for cellmetabolism, especially energy production. This energy issupplied by the coenzyme adenosine triphosphate (ATP),which is the most important store for chemical energy onthe molecular/enzymatic level and is synthesized in mito-chondria by oxidative phosphorylation. This reaction isoxygen dependent.

NADPH-linked oxygenase is the responsible enzyme forthe respiratory burst that occurs in leukocytes. During the inflammatory phase of the healing process NADPH-linked oxygenase produces high amounts of oxidants byconsuming high amounts of oxygen (34). Successful woundhealing can only take place in the presence of the enzyme,

because oxidants are required for prevention of woundinfection.

Not only phagocytes, but almost every cell in the woundenvironment is fitted with a specialized enzyme to convertO2 to reactive oxygen species (ROS), including oxidizingspecies such as free radicals and hydrogen peroxide (H2O2)(35, 36). These ROS act as cellular messengers to promoteseveral important processes that support wound healing.Thus O2 has a role in healing beyond its function as nutri-ent and antibiotic. Given the growth factors, such as platelet-derived growth factor (PDGF), require ROS for their actionon cells (35, 37), it is clear that O2 therapy may act as aneffective adjunct. Clinically this has been found in chronicgranulomatous disease (CGD) where there are defects ingenes that encode NADPH oxidase. The manifestations ofthis defect are increased susceptibility to infection andimpaired wound healing (625).

Simultaneously, the basal cells in the epithelium divideand move into the injury site, thereby closing the defect.Along with revascularization, new collagen is formed which, after 3–5 days, adds strength to the wound. The highrate of collagen production continues for 10–12 days,resulting in strengthening of the wound. At this time healing tissue is dominated by capillaries and immature collagen.

The fibroblasts are responsible for the synthesis, deposi-tion and remodeling of the extracellular matrix, which con-versely can have an influence on the fibroblast activities. Cellmovements at this stage into the fibrin clot or tightly wovenextracellular matrix seem to require an active proteolyticsystem that can cleave a path for cell migration. Fibroblastderived enzymes (collagenase, gelatinase A, etc.) and serumplasmin are potential candidates for this task (23).

After fibroblast migration into the wound cavity the pro-visional extracellular matrix is gradually replaced with col-lagenous matrix. Once an abundant collagen matrix hasbeen deposited in the wound, the fibroblasts stop producingcollagen, and the fibroblast rich granulation tissue isreplaced by a relatively acellular scar. Cells in the woundundergo apoptosis (cell death) triggered by unknownsignals, but doing so the fibroblast dies without raising aninflammatory response. Deregulation of these processesoccurs in fibrotic disorders such as keloid formation,morphea and scleroderma. Collagen synthesis and secretionrequires hydroxylation of proline and lysine residues. Suffi-cient blood flow delivering adequate molecular oxygen ispivotal for this process.

Collagen production/deposition and development ofstrength of the wound is directly correlated to the partialpressure PO2 of the tissue (PtO2) (38–40). Synthesis of col-lagen, cross-linking and the resulting wound strength relieson the normal function of specific enzymes (41, 42). Thefunction of these enzymes is directly related to the amountof oxygen present, e.g. hydrolyzation of proline and lysineby hydroxylase enzymes (43).

Recently it has been shown that oxygen also may triggerthe differentiation of fibroblasts to myofibroblasts, cellsresponsible for wound contraction (44).

Wound Healing Subsequent to Injury 7

Neovascularization/angiogenesis

Early in the healing process there is no vascular supply tothe injured area, but the stimulus for angiogenesis is present:growth factors released by especially macrophages, lowoxygen and elevated lactate. The angiogenesis starts the dayafter the lesion. Angiogenesis is complicated, involvingendothelial cells and activated epidermal cells. Proteolyticenzymes degrade the endothelial basement membraneallowing endothelial cells from the surroundings of thewound area to proliferate, migrate and form new vessels.The establishment of new blood vessels occurs by thebudding or sprouting of intact venoles and the sprouts meetin loops (259, 377; see p. 30). The presence of capillary loopswithin the provisional matrix provides the tissue with a redgranular appearance. Once the wound is filled with newgranulation tissue angiogenesis ceases and many of theblood vessels disintegrate as a result of apoptosis. Angio-genesis is dependent upon the extracellular matrix (ECM)(623, 624).

While hypoxia can initiate neovascularization, it cannotsustain it. Supplementary oxygen administration acceleratesvessels’ growth (35, 45). Vascular endothelial growth factor(VEGF) has been established as a major long-term angio-genetic stimulus at the wound site. Recently the cell responseto hypoxia has been further elucidated. Hypoxia induciblefactor 1 (HIF-1) has been identified as a transcription factorthat is induced by hypoxia (46, 48).

In the presence of normal oxygen tensions HIF-1 tran-scriptional activity is ubiquinated and degraded (47). HIF-1seems to upregulate genes involved in glucose metabolismand angiogenesis under hypoxia and in a model of myocar-dial and cerebral ischemia the factor seems to protect cellsfrom damage. The exact molecular mechanisms of howhypoxia is sensed by the cells are still unknown.

The arrangement of cells in the proliferative phase hasbeen examined in rabbits using ear chambers where woundsheal between closely approximated, optically clear mem-branes (33, 49). It appears from these experiments thatmacrophages infiltrate the tissue in the dead space, followedby immature fibroblasts. New vessels are formed next tothese fibroblasts which synthesize collagen. This arrange-ment of cells, which has been termed the wound healingmodule, continues to migrate until the tissue defect is oblit-erated. The factors controlling the growth of the woundhealing module are described on p. 38.

Epithelialization

Re-epithelialization of wounds begins within hours afterinjury. If parts of dermis layers are intact, epidermal cellsfrom skin appendages such as hair follicles quickly removeclotted blood and damaged stroma and cover the woundspace. This results in fast epithelialization. If dermis is totallydestroyed the epithelialization only takes place from thewound edges and epithelialization can continues for a con-siderable time dependent on wound area.

During epithelialization the cells undergo considerablephenotypic alteration including retraction of intracellular

tonofilaments, dissolution of most intercellular desmo-somes and formation of peripheral cytoplasmatic actin fila-ments, which allow cell movement. Furthermore the cells nolonger adhere to one another and the basement membrane.This allows migration of the cells dissecting the wound andseparating scar from viable tissue. Integrin expression of themigrating epidermal cells appears to determine the path ofdissection (23). Epidermal cell migration between collage-nous dermis and the fibrin scar requires degradation ofextracellular matrix. This is achieved by production of pro-teinases (collagenases, e.g. MMP-1) and activation ofplasmin by activators produced by epidermal cells. In welladapted, non-complicated surgical incisional wounds thefirst layers of epidermal cells move over the incisional line1–2 days after suturing. At the same time epidermal cells atthe wound margin in open wounds begin to proliferatebehind the actively migrating cells. The stimulus for migra-tion and proliferation of epidermal cells is unknown, but theabsence of neighbor cells at the margin of the wound (freeedge effect), local release of growth factors and increasedexpression of growth factor receptors may be a suggestion.

During dermal migration from the wound margin a base-ment membrane reappears in a ziplike fashion andhemidesmosomes and type VII collagen anchoring fibrilsform. Epidermal cells firmly attached to the basement mem-brane and underlying dermis revert to normal phenotype.

The production of epithelial tissue is primarily dependenton the degree of hydration and oxygen. While a moist woundenvironment increases the rate of epithelialization by a factorof 2–3 (50, 51), the optimal growth of epidermal cells isfound at an oxygen concentration of 10–50% (52–54).

Wound contraction

Wound contraction is a complex process, beneficial becausea portion of the lesion is covered by skin despite scar tissueand thus it decreases complications by decreasing the openskin wound area. During the second week of healing, fibrob-lasts assume a myofibroblast phenotype characterized bylarge bundles of actin containing microfilaments (55). Thestimulus for contraction probably is a combination ofgrowth factors, integrin attachment of the myofibroblasts tocollagen matrix and cross-links between collagen bundles(23). Wound contraction seems to be related to the earlywound healing period and the effect decreases in time; inchronic unclosed wounds no wound contraction exists.

Scar contracture

As opposed to the process of wound contraction of skinedges, this is a late pathological process in wound healing. Itconsists of a contraction of large amounts of scar tissue fol-lowed by immobilization of the affected area (e.g. a joint). Inscar contracture, the wound area as well as adjacent tissueshrink as opposed to contraction where only the wound area is involved. The morbidity of scar contracture is a majorproblem in the rehabilitation of severely injured patients.

8 Chapter 1

Remodeling phase

The remodeling phase is also called the moderation phase orthe scar phase.

In closed wounds this phase starts 2–3 weeks after closure,while it does not start in open wounds before the wound hashealed. Granulation tissue covered by epidermis is known toundergo remodeling earlier than uncovered granulationtissue. The length of this is unknown; some have argued one year but others have claimed the rest of the patient’s life.

During this phase the granulation tissue is remodeled andmatured to a scar formation. When granulation tissue iscovered by epithelium it undergoes remodeling. Similarly awound covered by a graft will continue the remodelingphase. This results in a decrease in cell density, numbers ofcapillaries and metabolic activity (55). The collagen fibrilswill be united into thicker fiber bundles. There is a majordifference between dermis and scar tissue in the arrange-ment of collagen fiber bundles. In scar tissue, as in granula-tion tissue, they are organized in arrays parallel to thesurface, while in dermis more in basket weave pattern (21).This difference results in a more rigid scar tissue. The colla-gen composition change from granulation tissue to scartissue where there is collagen type III decreases from 30% to10%. In the remodeling phase the biomechanical strength ofa scar increases slightly, despite no extra collagen being pro-

duced. This increase relates primarily to a better architec-tural organization of the collagen fiber bundles.

The epidermis of a scar differs from normal skin bylacking the rete pegs, which are anchored within the under-lying connective tissue matrix (21). Furthermore there is noregeneration of lost subepidermal appendages such as hairfollicles or sweat glands in a scar.

Types of wound after injury

Wounds can be divided into different types, according tohealing and associated wound closure methods (56–58)(Fig. 1.5). This distinction is based on practical treatmentregimens while the basic biological wound healingsequences are similar for all wound types.

Primary healing, or healing by first intention, occurs whenwound edges are anatomically accurately opposed andhealing proceeds without complication. This type of woundheals with a good cosmetic and functional result and with aminimal amount of scar tissue. These wounds, however, aresensitive to complications, such as infection.

Secondary healing, or healing by second intention, occursin wounds associated with tissue loss or when wound edgesare not accurately opposed. This type of healing is usually

A B C

D E F

G H I

J K L

Fig. 1.5 Wound healing eventsrelated to the type of wound and sub-sequent treatment. A–C: incisionalwound with primary closure; D–F:open and non-sutured wound; G–I:delayed primary closure; J–L: second-ary closure. From GOTTRUP (56) 1991.

Wound Healing Subsequent to Injury 9

the natural biological process that occurs in the absence ofsurgical intervention. The defect is gradually filled by gran-ulation tissue and a considerable amount of scar tissue willbe formed despite an active contraction process. The result-ing scar is less functional and often sensitive to thermal andmechanical injury. Furthermore, this form of healingrequires considerable time for epithelial coverage and scarformation, but is rather resistant to infection, at least whengranulation tissue has developed.

Surgical closure procedures have combined the advan-tages of the two types of healing. This has led to a techniqueof delayed primary closure, where the wound is left open fora few days but closure is completed before granulation tissuebecomes visible (usually a week after wounding) and thewound is then healed by a process similar to primary healing(59, 60, 435, 614). The resulting wound is more resistant tohealing complications (primarily infection) and is function-ally and cosmetically improved. If visible granulation tissuehas developed before either wound closure or wound con-traction has spontaneously approximated the defect, it iscalled secondary closure. This wound is healed by a processsimilar to secondary healing and scar formation is morepronounced than after delayed primary closure. The differ-ent closure techniques are shown in Fig. 1.5. The followingsection describes the sequential changes in tissue compo-nents and their interactions seen during the wound healingprocess.

Tissues and compounds in wound healing

Hemostasis phase and coagulation cascade

An injury that severs the vasculature leads to extravasion ofplasma, platelets, erythrocytes and leukocytes. This initiatesthe coagulation cascade that produces a blood clot usuallyafter a few minutes and which, together with the alreadyinduced vascular contraction, limits further blood loss (Fig.1.6). The tissue injury disrupts the endothelial integrity ofthe vessels, and exposes the subendothelial structures andvarious connective tissue components. Exposure of type IVand V collagen in the subendothelium promotes bindingand aggregation of platelets and their structural proteins(61, 62). Exposure of collagen and other activating agentsprovokes endothelial cells and platelets to secrete severalsubstances, such as fibronectin, serotonin, platelet derivedgrowth factor (PDGF), adenosine diphosphate (ADP)thromboxane A and others. Following this activation,platelets aggregate and platelet clot formation begins withina few minutes. The clot formed is impermeable to plasmaand serves as a seal for ruptured vasculature as well as toprevent bacterial invasion (62). In addition to platelet aggre-gation and activation, the coagulation cascade is initiated(Fig. 1.6).

The crucial step in coagulation is the conversion of fib-rinogen to fibrin which will create a threadlike network to

entrap plasma fractions and formed elements. This fibrinblood clot is formed both intravascularly and extravascu-larly and supports the initial platelet clot (Fig. 1.6). Extrin-sic and intrinsic clotting mechanisms are activated, eachgiving rise to cascades that will convert prothrombin tothrombin, and in turn cleave fibrinogen to fibrin which thenpolymerizes to form a clot (63).

The extrinsic coagulation pathway is initiated by tissuethromboplastin and coagulation Factor VII, whereas the ini-tiator of the intrinsic coagulation cascade consists ofHageman factor (Factor XII), prekallikrein and HMW-kinogen. The extrinsic coagulation pathway is the primarysource of clotting, while the intrinsic coagulation pathway isprobably most important in producing bradykinin, avasoactive mediator that increases vascular permeability(64).

Products of the coagulation cascade regulate the cells inthe wound area. Thus intact thrombin serves as a potentgrowth stimulator for fibroblasts and endothelial cells (65, 66) whereas degraded thrombin fragments stimulatemonocytes and platelets (67–69). Likewise plasmin acts as a growth factor for parenchymal cells (69). Fibrin acts asa chemoattractant for monocytes (70) and induces angio-genesis (64). Other mediators created by blood coagulationfor wound healing include kallikrein, bradykinin, and C3aand C5a through a spillover activation of the complementcascade and most of these factors act as chemoattractantsfor circulating leukocytes. Thus apart from ensuring hemo-stasis, the clot also initiates healing (Fig. 1.4).

If the blood clot is exposed to air it will dry and form a scabwhich serves as a temporary wound dressing. A vast networkof fibrin strands extends throughout the clot in all directions(Fig. 1.6). These strands subsequently undergo contractionand become reoriented in a plane parallel to the wound edges(71, 72). As the fibrin strands contract, they exert tensionalforces on the wound edges whereby serum is extruded fromthe clot and the distance between wound edges is decreased.Contraction and reorientation of the fibrin strands laterserve as pathways for migrating cells (see p. 29).

If proper adaptation of the wound edges has occurred theextravascular clot forms a thin gel filling the narrow spacebetween the wound edges and gluing the wound edgestogether with fibrin.

If hemostasis is not achieved, blood will continue to leakinto the tissue, leading to a hematoma and a coagulumwhich consists of serum plasma fraction, formed elementsand fibrin fragments. The presence of such a hematoma willdelay the wound healing and increase the risk of infection(77).

Coagulation

More extensive blood clot formation is undesirable in mostwounds as the clots present barriers between tissue surfacesand force wounds that might have healed without a clot toheal by secondary intention. In oral wounds such as extrac-tion sockets, blood clots are exposed to heavy bacterial col-onization from the saliva (74). In this location neutrophil

10 Chapter 1

leukocytes form a dense layer on the exposed blood clot andthe most superficial neutrophils contain many phagocytosedbacteria (75).

The breakdown of coagulated blood in the wound releases ferric ions into the tissue which have been shown to

decrease the nonspecific host response to infection (76). Furthermore, the presence of a hematoma in the tissuemay increase the chance of infection (77).

Clot adhesion to the root surface appears to be importantfor periodontal ligament healing. Thus an experiment has

INTRINSIC PATHWAY

Exposure of platelets tosubendothelial collagen

EXTRINSIC PATHWAY

Exposure of blood totissue thromboplastin

Fibrinogen

ProthrombinThrombin

Factor XIIFactor XIIFactor XII

Fibrin

VII

X

Fig. 1.6 Extrinsic and intrinsic coagulation cascade.

Wound Healing Subsequent to Injury 11

shown that heparin impregnated root surfaces, which pre-vented clot formation, resulted in significantly less connec-tive tissue repair and an increase in downgrowth of pocketepithelium after gingival flap surgery (78).

Fibrin

During the coagulation process, fibrinogen is converted tofibrin which, via a fishnet arrangement with entrapped ery-throcytes, stabilizes the blood clot (Figs 1.6 and 1.7).

In the early acute inflammatory period extravasation of aserous fluid from the leaking vasculature accumulates as an edema in the tissue spaces. This transudate contains fib-rinogen which forms fibrin when acted upon by thrombin(Fig. 1.7). Fibrin plugs then seal damaged lymphatics andthereby confine the inflammatory reaction to an area imme-diately surrounding the wound.

Fibrin has been found to play a significant role in woundhealing by its capacity to bind to fibronectin (63). Thusfibronectin present in the clot will link to both fibrin and toitself (79, 80).

Fibrin clots and fibrinopeptides are weak stimulators offibroblasts (81), an effect which is prevented by depletion offibronectin (82). It has also been proposed that an interac-tion may take place between hyaluronic acid and fibrinwhich creates an initial scaffold on which cells may migrateinto the wound (83).

The extravascular fibrin forms a hygroscopic gel that facil-itates migration of neutrophils and macrophages, an effectwhich possibly reflects a positive interaction between themacrophage surface and the fibrin matrix. Fibrin has alsobeen shown to elicit fibroblast migration and angiogenesis,both of which initiate an early cellular invasion of the clot(63, 64, 84–86).

Fibrin clots are continuously degraded over a 1–3 weekperiod (73, 87, 88). This occurs during the fibrinolysiscascade which is activated by the plasminogen present indamaged endothelial cells and activated granulocytes andmacrophages (87–89; Fig. 1.7).

In experimental replantation of teeth in monkeys it hasbeen found that collagen fiber attachment to the root surfacewas preceded by fibrin leakage, and that this leakage was aninitial event in the wound healing response (90).

In summary, the blood clot, apart from being responsiblefor hemostasis, also serves the purpose of initiating woundhealing including functioning as a matrix for migrating con-nective cells.

Fibronectin

Fibronectin is a complex glycoprotein, which can be presentas soluble plasma fibronectin, produced by hepatocytes, orstromal fibronectin, found in basal laminae and loose con-nective tissue matrices where it is produced by fibroblasts,

Fig. 1.7 Schematic illustration of thepresence of fibrin in experimental skinwounds in guinea pigs. The scale issemiquantitative, graded from 0 to 3.From ROSS & BENDITT (73) 1961.

12 Chapter 1

macrophages and epithelial cells (91, 92). During woundhealing, fibronectin is also produced locally by fibroblasts(93), macrophages in regions where epidermal cell migra-tion occurs (92), endothelial cells (94, 95), and by epidermalcells (96).

Fibronectin plays many roles in wound healing, includingplatelet aggregation, promotion of re-epithelialization, cellmigration, matrix deposition and wound contraction (92, 97).

In wound healing, fibronectin is the first protein to bedeposited in the wound (98) and therefore, together withfibrin, serves as a preliminary scaffold and matrix formigrating cells (99) (see p. 29). Thus plasma fibronectin islinked to fibrin which has been spilled from damaged vesselsor from highly permeable undamaged vessels (see p. 29) (97,100). The fibrin–fibronectin complex forms an extensivemeshwork throughout the wound bed which facilitatesfibroblast attachment and migration into the clot (80,101–103). Furthermore, soluble fibronectin fragments arechemotactic for fibroblasts and monocytes (104).

Fibronectin appears also to guide the orderly depositionof collagen within the granulation tissue. Thus fibronectinserves as the scaffold for deposition of types III and I collagen (105–109) as well as collagen type VI (109). Asdermal wounds age, bundles of type I collagen become more prominent at the expense of type III collagenfibronectin (106). Finally, fibronectin seems to represent anecessary link between collagen and fibroblasts which makesit possible to generate the forces in wound contraction (92, 110).

In endothelium during wound healing, fibronectin isfound in the basement membrane and reaches a maximumat approximately the same time as the peak in endothelialcell mitosis occurs, indicating a possible role of fibronectinin endothelial cell migration (111).

In epithelialization, it has been found that fibronectin isimplicated in epidermal cell adhesion, migration and differ-entiation (96, 111–114). Thus migrating epithelial cells aresupported by an irregular band of fibrin–fibronectin matrixwhich provides attachment and a matrix for prompt migra-tion (87, 108).

Clinically, fibronectin has been used to promote attach-ment of connective tissue to the exposed root and surfaces,and thereby limiting epithelial downgrowth (117–123). Fur-thermore fibronectin has been shown to accelerate healingof periodontal ligament fibers after tooth replantation (120).This effect has also been shown to occur in experimentalmarginal periodontal defects in animals (121, 122) as wellas in humans (123).

Complement system

The complement system consists of a group of proteins thatplay a central role in the inflammatory response. One of theactivated factors, C5a, has the ability to cleave its C-termi-nal arginine residue by a serum carboxypeptidase to form

C5a-des-arg which is a potent chemotactic factor for attract-ing neutrophils to the site of injury (124, 125).

Necrotic cells

Dead and dying cells release a variety of substances that maybe important for wound healing such as tissue factor, lacticacid, lactate dehydrogenase, calcium lysosomal enzymes andfibroblast growth factor (FGF) (126).

Matrix

Proteoglycans and hyaluronic acid

All connective tissues contain proteoglycans. In sometissues, such as cartilage, proteoglycans are the major con-stituent and add typical physical characteristics to the matrix(127).

Chondroitin sulfate proteoglycansChondrocytes, fibroblasts and smooth muscle cells are allable to produce these proteoglycans. Chondroitin sulfateimpairs the adhesion of cells to fibronectin and collagen andthereby promotes cell mobility. Skin contains proteoglycans,termed dermatan sulfates, which are involved in collagenformation.

Heparin and heparan sulfate proteoglycansHeparins are a subtype with an anticoagulant activity.Heparan sulfates are produced by mast cells and adhere tocell surfaces and basement membranes.

Keratan sulfates are limited to the cornea, sclera and car-tilage. Their role in wound healing is unknown.

Hyaluronic acid is a ubiquitous connective tissue compo-nent and plays a major role in the structure and organiza-tion of the extracellular matrix. Hyaluronic acid has beenimplicated in the detachment process of cells that allowscells to move. Furthermore hyaluronic acid inhibits cell dif-ferentiation. Because of its highly charged nature, hyaluronicacid can absorb a large volume of water (128).

The role of proteoglycans during wound healing is notfully understood (129). Heparin may play a role in thecontrol of clotting at the site of tissue damage. Proteogly-cans are also suspected of playing an important role in theearly stages of healing when cell migration occurs. Thushyaluronic acid may be involved in detachment of cells sothat they can move (130). Furthermore, proteoglycans mayprovide an open hydrated environment that promotes cellmigration (129, 131, 133).

The proliferative phase of healing involves cell duplica-tion, differentiation and synthesis of extracellular matrixcomponents. Thus hyaluronidate has been found to keepcells in an undifferentiated state which is compatible withproliferation and migration (127). At this stage chondroitinand heparan sulfates are apparently important in collagenfibrillogenesis (127) and mast cell heparin promotes capil-lary endothelial proliferation and migration (132). Further-

Wound Healing Subsequent to Injury 13

more, when endothelium is damaged, a depletion of growth-suppressing heparan sulfate may allow PDGF or otherstimuli to stimulate angiogenesis (133).

The combined action of substances released fromplatelets, blood coagulation and tissue degradation results in hemostasis, initiation of the vasculatory response andrelease of signals for cell activation, proliferation and migration.

The role of the anticoagulant heparin is to temporarilyprevent coagulation of the excess tissue fluid and bloodcomponents during the early phase of the inflammatoryresponse.

Inflammatory phase mediators

The sequence of the inflammatory process is directed by dif-ferent types of chemical mediators which are responsible forvascular changes and migration of cells into the wound area(Fig 1.6).

Mediators responsible for vascular changes

Inflammatory mediators such as histamine, kinins and sero-tonin cause vasodilatation unless autonomic stimulationoverrules them.

The effect of these mediators is constriction of smoothmuscles. This influences endothelial and periendothelialcells, providing reversible opening of junctions between cellsand permitting a passage of plasma solutes across the vas-cular barrier. These mediators are released primarily during

the process of platelet aggregation and clotting. The bestknown mediators related to the vascular response are shownin Table 1.1.

Histamine

The main sources of histamine in the wound appear to beplatelets, mast cells, and basophil leukocytes. The histaminerelease causes a short-lived dilation of the microvasculature(137) and increased permeability of the small venules. Theendothelial cells swell and separations occur between theindividual cells. This is followed by plasma leaking throughthe venules and the emigration of polymorphonuclearleukocytes (137–141).

Serotonin

Serotonin (5-hydroxytryptamine) is generated in the woundby platelets and mast cells. Serotonin appears to increase thepermeability of blood vessels, similarly to histamine, butappears to be more potent (139, 140). Apart from causingcontraction of arterial and venous smooth muscles and dila-tion of arterioles, the net hemodynamic effect of serotoninis determined by the balance between dilation and contrac-tion (137, 142).

Prostaglandins

Other mediators involved in the vascular response areprostaglandins (PG). These substances are metabolites ofarachidonic acid and are part of a major group calledeicosanoids, which are also considered primary mediators inwound healing (143). Prostaglandins are the best knownsubstances in this group and are released by cells via arachi-donic acid following injury to the cell membrane. Theseinclude PGD2, PGE2, PGF2, thromboxane A2 and prostacy-cline (PGI2). These components have an important influ-ence on vascular changes and platelet aggregation in theinflammatory response and some of the effects are antago-nistic. Under normal circumstances, a balance of effects isnecessary. In tissue injury, the balance will shift towardsexcess thromboxane A2, leading to a shutdown of themicrovasculature (143).

New research suggests that prostaglandins, and especiallyPGF2, could be endogenous agents that are able to initiaterepair or reconstitute the damaged tissue (144). Thusbiosynthesis of PGF2 has been shown to have an importanteffect on fibroblast reparative processes (145), for whichreason this prostaglandin may also have an important influ-ence on later phases of the wound healing process. The effectof prostaglandins on the associated inflammatory responseelicited subsequent to infection is further discussed inChapter 2.

Bradykinin

Bradykinin released via the coagulation cascade relaxes vas-cular smooth muscles and increases capillary permeability

Table 1.1 Mediators of vascular response in inflammation. Modified fromVENGE (136) 1985.

Mediator Originating cells

Humoral ComplementKallikrein–Kinin systemFibrin

Cellular Histamine ThrombocytesMast cellsBasophils

Serotonin ThrombocytesMast cells

Prostaglandins Inflammatory cells

Thromboxane A2 ThrombocytesNeutrophils

Leukotrienes Mast cellsBasophilsEosinophilsMacrophages

Cationic peptides Neutrophils

Oxygen radicals NeutrophilsEosinophilsMacrophages

14 Chapter 1

leading to plasma leakage and swelling of the injured area.

Neurotransmitters (norepinephrine, epinephrine and acetylcholine)

The walls of arteries and arterioles contain adrenergic andcholinergic nerve fibers. In some tissue the sympatheticadrenergic nerve fibers may extend down to the capillarylevel. Tissue injury will stimulate the release of neurotrans-mitters which results in vasoconstriction.

Mediators with chemotactic effects

These mediators promote migration of cells to the area ofinjury and are thus responsible for the recruitment of thevarious cells which are involved in the different phases ofwound healing (Fig. 1.4).

The first cells to arrive in the area are the leukocytes. Thechemotactic effects are mediated through specific receptorson the surface of these cells. Complement activated prod-ucts like C5a, C5a-des-arg, and others cause the leukocytesto migrate between the endothelial cells into the inflamma-tory area. This migration is facilitated by the increased cap-illary permeability that follows the release of the earliermentioned mediators. Further leukocyte chemoattractantsinclude kallikrein and plasminogen activator, PDGF andplatelet factor 4.

Other types of chemotactic receptors are involved whenleukocytes recognize immunoglobulin (Ig) and complementproteins such as C3b and C3bi. The mechanism appears to be that B lymphocytes, when activated, secreteimmunoglobulin which again triggers the activation of thecomplement system resulting in production of chemoat-tractants such as C5a-des-arg (146).

Other mediators involved in chemoattraction will bementioned in relation to the cell types involved in thewound healing process.

S. Storgård Jensen

Growth factors

Growth factors are a group of polypeptides involved in cel-lular chemotaxis, differentiation, proliferation, and synthe-sis of extracellular matrix during embryogenesis, postnatalgrowth and adulthood.

All wound healing events in both hard and soft tissues areinfluenced by polypeptide growth factors, which can bereleased from the traumatized tissue itself, can be harboredin the quickly formed blood clot or brought to the area byneutrophils or macrophages.

Growth factors are local signaling molecules. They can actin a paracrine manner where they bind to receptors on thecell surface of neighboring target cells, leading to initiationof specific intracellular transduction pathways; or they canact in an autocrine manner, whereby the function is elicited

on the secreting cell itself. Additionally, elevated serum levelshave been demonstrated for a few growth factors which mayindicate an endocrine effect. Complex feedback loops regu-late the production of the individual growth. The effect ofeach growth factor is highly dependent on the concentrationand on the presence of other growth factors. A growth factor can have a stimulatory effect on a specific cell type,whereas an increased concentration may inhibit the exactsame cell type. Two different growth factors with a knownstimulatory effect on a cell type can in combination resultin both an agonistic, synergistic, and even an antagonisticeffect.

Growth factors may have the potential to improve healingof traumatized tissues in several ways. First, some growthfactors have the ability to recruit specific predetermined celltypes and pluripotent stem cells to the wounded area bychemotaxis. Second, they may induce differentiation of mes-enchymal precursor cells to mature secreting cells. Third,they often stimulate mitosis of relevant cells, and therebyincrease proliferation. Fourth, several growth factors havethe ability to increase angiogenesis, the ingrowth of newblood vessels. Finally, they can have a profound effect onboth secretion and breakdown of extracellular matrix(ECM) components.

The most important growth factors are listed in Table 1.2and a brief summary of their characteristics, including theirpresumed role in wound repair and regeneration is givenbelow.

Dentoalveolar traumas may involve a multitude of tissueslike oral mucosa, periodontal ligament, root cementum,dentin, dental pulp, bone, skin, blood vessels and nerves.Only a few clinical studies have evaluated the use of growthfactors specifically for oral and maxillofacial traumas (p. 16).

Platelet derived growth factor (PDGF) consists of twoamino acid chains and comes in homo- and heterodimericisoforms (AA, AB, BB, CC, and DD, where AA, AB, and BBare the best documented) (147). PDGF binds to two specificreceptors: α and β. Differential binding of the different iso-forms to the receptors contributes to the varying effects of PDGF. As the name implies, PDGF is released fromplatelets, where it is present in large amounts in α-granules.Platelets are activated by thrombin or fibrillar collagen.Other sources of PDGF are macrophages, endothelial cellsand fibroblasts. PDGF was the first growth factor shown tobe chemotactic for cells migrating into the wound area, suchas neutrophils, monocytes, and fibroblasts. Additionally,PDGF stimulates proliferation and ECM production offibroblasts (148) and activates macrophages to debride thewound area (149).

Transforming growth factors (TGFs) comprise a largefamily of cytokines with a widespread impact on the for-mation and development of many tissues (among those, theBMPs, which are described separately). This factor hasearlier been divided into α and β subtypes, where the latteris the most important for the wound healing process (150).TGF-β is mainly released from platelets and macrophages asa latent homodimer that must be cleaved to be activated.This latent form is present in both wound matrix and saliva.