Periodontology E-Book

Hans-Peter Müller

• Herausgeber: Thieme
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 568

Veröffentlichungsjahr: 2015

Beschreibung

Periodontology-The Essentials provides readers with up-to-date information on the anatomy and physiology of the oral cavity as well as the latest methods for diagnosis, prevention, and therapy of periodontal disease. It is specifically designed to help busy dental professionals give their patients the highest level of care. Throughout this book the author stresses the important connections between periodontal disease and the patient's overall health, focusing on preventive care and the consequences of treatment.

Key Features of the Second Edition:

• Expanded and revised coverage, lavishly illustrated by more than 300 four-color photos and drawings
• Updated chapters throughout
• Evidence boxes giving summaries of clinical trials, meta-analyses and other studies, with graded assessment of the findings
• Discussion of the long-suspected association between systemic and periodontal diseases

This book is a remarkably fresh text on the fundamentals of periodontology that will serve as a scientifically grounded yet practical clinical tool for students of dentistry and dental hygiene, private practitioners, hygienists, and periodontists alike.

Leseprobe

If not otherwise noted, tooth identification is according to the two-digit system of the Fédération Dentaire Internationale (FDI). Thus, the first digit denominates the quadrant, clockwise from upper right to lower right, the second, the position of a given tooth in the jaw, numbered from anterior to posterior.

Periodontology

The Essentials

2nd Edition

Hans-Peter Mueller, DDS, PhD

Professor of PeriodontologyInstitute of Clinical DentistryFaculty of Health SciencesUiT–The Arctic University of NorwayTromsø, Norway

311 illustrations

ThiemeStuttgart • New York • Delhi • Rio de Janeiro

Library of Congress Cataloging-in-Publication Data Mueller, Hans-Peter, Prof. Dr. med. dent., author. Periodontology: the essentials / Hans-Peter Mueller. – 2nd edition.

    p.; cm.

Includes bibliographical references and index.

ISBN 978-3-13-138372-3 (alk. paper) –

ISBN 978313164872-3 (e-book)

I. Mueller, Hans-Peter, Prof. Dr. med. dent. Parodontologie.

3rd edition. Based on (expression): II. Title.

[DNLM: 1. Periodontal Diseases—Handbooks. WU 49]

RK361

617.6'32–dc23

                                     2015019401

Illustrator: Karin Baum, Paphos, Cyprus

3rd German edition 20121st English edition 20051st Polish edition 20041st Russian edition 20041st Spanish edition 2006

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Contents

1 Anatomy and Physiology

Development

Crown Development

Root Development

Cementogenesis

Marginal Periodontium

Macroscopic and Microscopic Anatomy

Oral Mucosa

Gingiva

Peri-implant Mucosa

Root Cementum

Periodontal Ligament

Alveolar Bone Proper

Physiology

Turnover Rates

Defense Mechanism

Possibilities of Repair

2 Periodontal Microbiology

Ecology of the Mouth

Biodiversity

The Oral Cavity as a Biotope

Colonization Mechanisms

Biofilm Dental Plaque

Formation of Supragingival Plaque

Colonization of the Subgingival Region

Dental Calculus

Periodontitis: an Infectious Disease

Identification of Periodontal Pathogens

Types of Infection

The Susceptible Host

Presence of Pathogens

Absence of Beneficial Microorganisms

Conducive Environment in the Periodontal Pocket

Transmission

Peri-implantitis

3 Pathogenesis of Biofilm-Induced Periodontal Diseases

Pathogenesis of Dental Biofilm-Induced Gingivitis

Initial Gingivitis

Early Gingivitis

Established Gingivitis

Peri-implant Mucositis

Pathogenesis of Periodontitis

Advanced Lesion

Formal Pathogenesis—Progression

Characteristics of a Multifactorial Disease

Genetic Component

Peri-implantitis

4 Classification of Periodontal Diseases

Current Classification

Plaque-Induced Gingival Diseases

Systemically Modified Gingival Diseases

Drug-Influenced Gingival Diseases

Gingival Diseases Modified by Malnutrition

Gingival Diseases Not Induced by Dental Plaque

Gingival Diseases of Specific Bacterial Origin

Gingival Diseases of Viral Origin

Gingival Diseases of Fungal Origin

Gingival Lesions of Genetic Origin

Gingival Manifestations of Mucocutaneous Diseases

Allergic Reactions

Traumatic Lesions

Foreign Body Reactions

Periodontitis

Chronic Periodontitis

Aggressive Periodontitis

Periodontitis as Manifestation of Systemic Disease

Necrotizing Periodontal Diseases

Necrotizing Ulcerative Gingivitis

Necrotizing Ulcerative Periodontitis

Abscesses of the Periodontium

Gingival Abscess

Periodontal Abscess

Pericoronal Abscess

Combined Periodontal–Endodontic Lesions

Developmental or Acquired Deformities and Conditions

Localized, Tooth-Related Factors that Modify or Promote Plaque-Induced Gingival Diseases/Periodontitis

Mucogingival Deformities and Conditions around Teeth and on Edentulous Alveolar Ridges

Occlusal Trauma

Peri-implant Mucositis, Peri-implantitis

5 Epidemiology of Periodontal Diseases

Epidemiological Terminology

Periodontal Epidemiology

Examination Methods

Assessment of Gingival Inflammation

Bacterial Deposits

Combined Indices

Attachment Loss

Case Definitions

Epidemiology of Plaque-Induced Periodontal Diseases

Natural History

Periodontitis in the United States

Europe

Global Trends

Early-Onset (Aggressive) Periodontitis

Prevalence, Extent, and Severity of Gingival Recession

Peri-implant Diseases

6 Diagnosis of Periodontal Diseases

Anamnesis

Medical History

Dental History

Clinical Examination

Extraoral Examination

Intraoral Examination

Functional Examination

Periodontal Examination

Clinical Peri-implant Diagnosis

Mucogingival Examination

Oral Hygiene

Radiologic Examination

Panoramic Radiographs

Full-Mouth Radiographic Survey

Computed Tomography

Intraoperative Diagnosis of Defect Morphology

Osseous Defects

Furcation Involvement

Advanced Diagnostic Techniques

Diagnostic Test Systems

Microbiological Tests

Markers of Specific and Nonspecific Host Response

Saliva Diagnostics

Human Genetic Tests

Halitosis

Diagnosis

General Diagnosis

Tooth-Related Diagnosis

Prognosis

Treatment Planning

Case Presentation

7 Prevention of Periodontal Diseases

Prevention-Oriented Dentistry

Karlstad Study

Possibilities of Prevention

Measures at the Population Level

Secondary and Tertiary Prevention

Preferential Treatment of High-Risk Groups

8 General Medical Considerations

Systemic Phase

Infectious Patients

Increased Risk of Infective Endocarditis

Further Indications for Antibiotic Prophylaxis

Bleeding Disorders, Anticoagulant Therapy

Atherosclerosis, Cardiovascular Diseases

Associations between Periodontitis and Cardiovascular Diseases

Pulmonary Diseases

Diabetes Mellitus

Obesity, Metabolic Syndrome

Pregnancy

Osteopenia, Osteoporosis

Smoking

Alcohol Consumption

Impact of Periodontal Therapy on General Health

9 Emergency Treatment

Periodontal Emergencies

Traumatic Injury

Necrotizing Ulcerative Periodontal Diseases

Herpetic Gingivostomatitis

Periodontal Abscess

Combined Periodontal–Endodontic Lesions

10 Phase I—Cause-Related Treatment

Mechanical Plaque Control

Toothbrushing Techniques

Interdental Hygiene

Chemical Plaque Control

Chlorhexidine

Essential Oils

Cetylpyridinium Chloride

Triclosan

Metal Salts

Other Additives

Local Anesthesia

Adverse Effects of Local Anesthetics

Regional Infiltration and Block Anesthesia

Supragingival and Subgingival Scaling and Root Planing, Subgingival Curettage

Definitions

Aims

Indication

Contraindication

Instruments

Procedure

Critical Assessment

One-Stage, Full-Mouth Disinfection

Photodynamic Therapy, Laser

Re-evaluation

Sharpening of Instruments

Sickle Scalers

Universal Curettes

Area-Specific Curettes

11 Phase II—Corrective Procedures

Periodontal Surgery

Gingivectomy

Aims

Indications

Contraindications

Instruments

Procedure

Postoperative Care

Critical Assessment

Gingivoplasty

Definition

Aim

Indications

Contraindications

Instruments

Electrosurgery

Procedure

Critical Assessment

Flap Operations

Aims

Indications

Contraindications

Instruments

Various Techniques

Procedure for the Modified Widman Technique

Postoperative Care

Critical Assessment

Periodontal Wound Healing

Presence of Progenitor Cells

Re-establishment of a Biocompatible Root Surface

Exclusion of Epithelium

Wound Stabilization

Bone and Bone Substitutes

Growth and Differentiation Factors

Root Surface Conditioning with Enamel Matrix Proteins

Guided Tissue Regeneration

Membranes

Indications

Contraindications

Procedure

Postoperative Care

Critical Assessment

Minimally Invasive Surgical Techniques

Treatment of Furcation-Involved Teeth

Fundamental Morphological Terms

Structures within the Furcation

Conservative Furcation Therapy

Root Amputation and Hemisection

Premolarization

Tunnel Preparation

Regenerative Procedures

Possible Treatment Strategies

Mucogingival Surgery

Widening of the Zone of Keratinized Tissue with a Free Gingival Graft

Gingival Recessions

Lateral Sliding Flap

Coronally Advanced Flap after Vestibular Extension with Free Gingival Graft

Coronally Advanced Flap with Connective Tissue Graft

Semilunar Coronally Repositioned Flap

Envelope Technique

Guided Tissue Regeneration

Critical Assessment

Frenectomy

Occlusal Therapy

Occlusal Splint

Occlusal Adjustment

Semipermanent Splinting

Perio-Prosthetic Aspects

Treatment of Peri-implant Infections

12 Phase III—Supportive Periodontal Therapy

Risk Assessment, Risk Communication, Risk Management

Risk Assessment

Local Risk Factors

Dentition-Related Risk Factors

General Risk Factors

Communication

Risk Management

13 Medication and Supplements

Antibiotic and Antimycotic Therapy

Systemically Administered Antibiotics

Topical Administration of Antimicrobial Substances

Local Antimycotic Therapy

Modulation of the Host Response

Inhibitors of Tissue Collagenase

Modulation of Bone Metabolism

Omega-3 Polyunsaturated Fatty Acids

Anti-inflammatory Drugs

Nonsteroidal Anti-inflammatory Drugs

Local Glucocorticoids

Nutritional Supplements, Probiotics

Vitamins

Calcium

Probiotics

14 References

Index

Preface

For half a century, periodontology has spearheaded scientific progress in dentistry. A tiny portion of the vast body of literature that has shaped modern periodontology has recently been listed by the American Academy of Periodontology on the occasion of its centennial.1 What has kept us clinicians, teachers, and scientists busy was, for example, the discovery that bacteria of the oral cavity, which play a critical role in most periodontal diseases, organize themselves in a biofilm; and that the pathogenesis of periodontitis, like that of any chronic disease, is complex and multifactorial. Opportunities and constraints of guided tissue and other forms of periodontal regeneration have been developed in painstakingly designed animal and clinical experiments, and the somewhat ailing implant dentistry has finally got a firm scientific foundation. Not least, a century-old suspicion that periodontal infections interact, in a bidirectional way, with other systemic diseases and conditions has been revived, and new intervention studies address the possible beneficial effects of periodontal therapy on general health.

The true revolution is, however, the application of well-defined evidence in daily practice. Despite the claim that, in particular, periodontists practice their profession up-to-date, dentists had long been inclined to pursue commercial interests, be it their own or those of providers of new and fancy developments.

That won't be so any longer. Since electronic search engines and, in particular, biomedical data bases are generally available, and electronic access to original articles including all back files is possible, new generations of practitioners will be in the position to quickly identify, critically assess, and filter the exploding amount of new data and retrieve relevant information as regards a specific clinical question or problem, both online and in real time. Dentists are more and more inclined to ask the crucial question, “Is there any evidence?”

The recent surge of systematic reviews of, in particular, well-designed intervention studies has proved that our profession has a sound scientific foundation. The available evidence has to be graded, though, and recommendations should address patient-relevant issues. Real evidence-based medicine does include a strong interpersonal relationship between the patient with chronic disease and the therapist. Thus, continuity of care and emphatic listening is of paramount importance for conjoint decision-making, which does not entirely rely on the available scientific evidence but, to a large extent, also on individual circumstances.

As before, the second edition of Periodontology—The Essentials attempts to condense latest developments and concepts in an easily searchable volume. Although undergraduate dentistry and dental hygienist students are again the main target audience for the compendium, general dental practitioners and specialists in other fields of dentistry may benefit from quickly checking specific periodontal details in their daily practice as well.

Hans-Peter Mueller, DDS, PhD

1 Kornman KS, Robertson PB, Williams RC. The literature that shaped modern periodontology. J Periodontol 2014; 85: 3—9.

1 Anatomy and Physiology

The periodontium (from the Greek terms περι, around, and ωδωνσ, tooth) denotes the soft and hard tissues that anchor the teeth to the bones of the jaws, provide interdental linkage of the teeth within the dental arch, and facilitate epithelial lining of the oral cavity in the region of the erupted tooth.1–3

It is a developmental, biological, and functional unit that is comprised of four different types of tissue:

Gingiva—that is, the marginal periodontium

Root cementum

Alveolar bone proper

Periodontal ligament

The gingiva, a keratinized soft tissue, surrounds the tooth at the cervical level together with parts of the alveolar process. The desmodontal fiber apparatus connects the various mineralized forms of root cementum, which are in some ways similar to bone tissue, and the alveolar bone proper, which is part of the alveolar process.

The majority of fibers consist of collagen. They insert partly in the inner cortical plate of the alveolar bone and partly in root cementum. The fibers of the periodontal ligament are functionally oriented. During and after tooth eruption they undergo continuous renewal and remodeling, which is mainly controlled by fibroblasts. Those fibers, which are anchored either in root cementum or in alveolar bone proper, are called Sharpey's fibers. Oxytalan fiber bundles, which run parallel to the tooth axis, may also be observed. Their function is largely unknown.

Development

The development of the periodontium is essentially linked to tooth development (Fig. 1.1). The number and shape of the teeth are strictly genetically determined. Tooth development is initiated by epithelial thickening of the ectodermal epithelial lining of the primitive oral cavity (stomodeum) between the fifth and sixth week of embryogenesis. This odontogenic epithelium is called the dental plate or dental lamina. Originating from the dental lamina, tooth development is controlled by a chain of cell–cell and cell–matrix interactions. Both ectodermal and ectomesenchymal cells reach increasingly higher degrees of differentiation and eventually develop into highly differentiated ameloblasts and odontoblasts which produce enamel matrix and predentin.

Fig. 1.1 The development of the periodontium is part of tooth development. Interactions between epithelium and ectomesenchymal tissue (E & M) of the neural crest beneath lead to the initiation of crown development (enamel, pulp, and dentin). Tissues of the periodontium proper (cementum, alveolar bone proper, periodontal ligament) derive from the dental follicle proper. Proliferation of Hertwig's epithelial root sheath (HER) leads to root formation. JE: junctional epithelium; AEFC: acellular extrinsic fiber cementum; CMSC: cellular mixed stratified cementum. (Adapted from MacNeil and Somerman.4)

Crown Development

Between weeks 6 and 8 after ovulation, cells of the dental lamina proliferate in distinct regions (the later positions of deciduous teeth) into the mesenchymal tissue beneath. They induce a condensation of the ectomesenchymal tissue, which derives from the neural crest. This tissue is now called determinate dental mesenchyme.

During morphogenesis of the tooth germ, the tooth bud develops between the 8th and 12th weeks into the caplike enamel organ. The odontogenic mesenchyme divides into two cell lines:

The dental papilla, containing progenitor cells of odontoblasts and later the pulp.

The dental follicle, which surrounds the tooth germ and develops into the periodontium.

Cells of the enamel organ differentiate into four cytologically and functionally defined strata:

Outer enamel epithelium

Stratum reticulare

Stratum intermedium

Inner enamel epithelium

Finally, the bell stage of the tooth germ develops, which already gives an indication of the later shape of the crown. The enamel–dentin border is defined when odontoblasts and later ameloblasts differentiate and start, in the region of the later cusps and incisal edges of the teeth, secreting predentin and enamel matrix, respectively. The dental papilla and enamel organ are surrounded by the dental follicle, which demarcates the dental papilla from the surrounding mesenchyme.

During further odontogenesis the dental lamina of the deciduous molars proliferates distally and becomes committed to the development of the molars of the permanent dentition, which therefore belong to the first dentition.

The tooth germs of the permanent first molars arise between the 13th and 15th week of embryogenesis. The germs of succedaneous teeth arise between the 5th prenatal (central incisors) and 10th postnatal months (second premolars), and develop from an apically prolonged secondary dental lamina lingually and palatally to the deciduous germs.

Root Development

Root formation starts when dentin and enamel formation reaches the connection between inner and outer enamel epithelium, viz. the later cementoenamel junction. The final shape of the crown has now been determined.

Due to further proliferation of the enamel epithelium, an epithelial root sheath (Hertwig's root sheath) develops, which is located between the dental papilla and the dental follicle proper:

Apically, it bends inwards to form the epithelial diaphragm.

The double-layered epithelium (outer and inner stratum) is responsible for differentiation of root dentin-forming odontoblasts.

It thus represents the “mold” for the later tooth root.

Tooth eruption depends on the prolongation of the dentinal tube, while the diaphragm remains in the same location. Coronally, Hertwig's epithelial root sheath loses contact with the root surface. The sheath disintegrates into a loose mesh of epithelial strands, namely the epithelial rests of Malassez.

Cementogenesis

In contrast to the inner enamel epithelium of the enamel organ, the inner enamel epithelium of Hertwig's root sheath does not differentiate into enamel-producing ameloblasts:

Cell–cell interactions lead to differentiation of cells of the neighboring ectomesenchymal tissue of the dental papilla into odontoblasts, which start forming predentin.

Immediately afterwards an enamel-like material is deposited on the surface of predentin.

This material probably induces differentiation of cementoblasts derived from the dental follicle and mediates anchorage of the cementum to the dentin surface.

Following disintegration of the epithelial root sheath, cells of the dental follicle proper come into contact with the newly formed root surface (cell–matrix interaction). They then start formation of root cementum (Fig. 1.2). Cells and fiber bundles of the periodontal ligament and alveolar bone proper are also derived from cells of the dental follicle proper.

These traditional views of cementogenesis have been challenged5:

The presence of mesenchymal cells among disintegrated cells of Hertwig's epithelial root sheath is usually interpreted as a sign of cell migration from the dental follicle proper towards the root surface.

Alternatively, cells of the root sheet may have completed epithelial–mesenchymal transformation.

Thus, cementoblasts may originate from Hertwig's epithelial root sheath itself.

In multirooted teeth, shortly after dentin and enamel formation have commenced in the cusp region, two or three epithelial knots are formed in the region of the cervical loop of the enamel epithelium.

Tongues of epithelium proliferate across the dental papilla in a central direction.

While the size of the enamel organ increases, these epithelial tongues meet and fuse in the region of the future fornix of the furcation.

In this way, the future dentin floor of the furcation is created.

This means that the formation of the furcation is part of crown development.

The epithelial root sheath initiates the formation of tooth roots. It determines their shape. In case of multirooted teeth it divides into two or three branching tubes. The presence of enamel epithelium also explains frequent formation of enamel paraplasias in the furcation area, such as enamel projections, enamel tongues, and enamel pearls.

Epithelial tongues lie within the connective tissue of the dental papilla and exclude parts of ectomesenchymal tissue from the developing tooth germ. That is why cementum deposits (ridges and bulges) are frequently found in the region of fusing epithelial tongues.

Marginal Periodontium

The epithelial part of the gingiva is of ectodermal origin. Three epithelia can be distinguished:

Junctional epithelium

Oral sulcular epithelium

Oral gingival epithelium

Fig. 1.2 Traditional view of the initial stages of formation of acellular extrinsic fiber cementum (AEFC). Fibroblasts of the dental follicle come into contact with predentin in the region of the apical edge after disintegration of the epithelial root sheet, where they attach and, after differentiation into cementoblasts, start to produce collagen fibrils. This results in an initial fiber fringe with maximum fiber density. The mineralization front reaches the base of the fibers and proceeds into the initial fiber fringe. MER: Malassez epithelial rests. (Adapted from MacNeil and Somerman.4)

The junctional epithelium derives from the reduced enamel epithelium which surrounds, in a preeruptive stage, the tooth crown. The reduced enamel epithelium consists of:

ameloblasts, which are reduced in height,

cells of the previous stratum intermedium of the enamel epithelium.

The epithelium attaches to the enamel in a form of primary epithelial attachment by hemi-desmosomes. During tooth eruption, reduced enamel epithelium gradually transforms, from coronal to apical, into junctional epithelium (secondary epithelial attachment):

Reduced cuboid ameloblasts change shape and become elongated cells of junctional epithelium.

The cells of stratum intermedium regain their ability to divide and become basal cells of junctional epithelium.

Posteruptively, junctional epithelium is a selfrenewing tissue with specific structures and functions. In addition, de novo formation of junctional epithelium is facilitated:

Following, for example, a gingivectomy procedure (see Chapter 11), cells of oral gingival epithelium migrate first to the dentogingival region.

Influenced by the underlying connective tissue (i.e., the periodontal ligament), these cells develop characteristics of junctional epithelium:

– Stratified, two-layered epithelium

– No keratinization

– Ability to attach to the tooth surface

Macroscopic and Microscopic Anatomy

Oral Mucosa

Traditionally, oral mucosa is classified according to function as lining, specialized, and masticatory mucosa.6

The nonkeratinized lining mucosa comprises alveolar mucosa, the mucosa of the oral vestibule, the cheeks and lips, the floor of the mouth and ventral sides of the tongue, and the mucosa of the soft palate. The lining mucosa has a stratified, three-layered epithelium consisting of:

Stratum basale

Stratum filamentosum

Stratum distendum

The lining mucosa contains a distinctive submucosa with a loose arrangement of collagen and elastic fibers.

The specialized mucosa of the dorsum of the tongue mediates touch, temperature, and taste sensations.

The keratinized masticatory mucosa comprises the gingiva and the mucosa of the hard palate:

Gingiva surrounds the teeth at the cementoenamel junction and the alveolar bone and extends to the mucogingival border. Palatally, it consists of a small rim, which continues into the mucosa of the hard palate.

The structural characteristics of the gingival epithelium are essentially the same as those of the mucosa of the hard palate:

– Gingiva possesses a nonhomogeneous stratum corneum of variable thickness, in which most cells contain a pyknotic nucleus, a sign of parakeratinization.

– Mucosa of the hard palate possesses a regularly orthokeratinized epithelium with a uniformly thick stratum corneum without pyknotic cell nuclei.

– The epithelium of both the gingiva and the mucosa of the hard palate is about 0.3 mm thick, on average.

Gingiva

Clinically, a healthy gingiva is characterized by certain features of shape, color, and consistency (Fig. 1.3):

Its narrow band follows the scalloped contour of the necks of the teeth and the cementoenamel junction, which is normally covered by gingival tissue. This gives rise to distinct interdental papillae, their vestibular and oral parts being connected by a saddlelike interdental col.

Gingiva of individuals with a northern European heritage is usually pale pink, coral, or mauve in color. In Mediterranean, African, and Asian populations, melanocytes may give a more or less dark color to the gingiva (Fig. 1.3b).

Orange-peel-type stippling of the surface of the attached gingiva results from indentations lying at the crossing points of rete ridges of the oral gingival epithelium.

Fig. 1.3 Clinical characteristics of healthy gingiva.

a Note clinical signs of slight inflammation (cf. Chapter 6) as redness, swelling, and gingival exudate mesiobuccally at tooth 31.

b Melanin pigmentation of attached gingiva of a southern European individual.

A frequently observed gingival groove separates the free gingiva, which adheres to the enamel surface, from the attached gingiva. The free gingiva ends 1 to 2 mm on the enamel surface at a narrow angle.

A small depression at the tooth surface of 0.1 to 0.5 mm is called the gingival sulcus:

– The sulcus is bordered by the tooth surface, the oral sulcular epithelium, and the junctional epithelium.

– Note: The depth of the gingival sulcus cannot be determined clinically, for example, by using a periodontal probe (see Chapter 6).

The mucogingival border demarcates the gingiva apically.

Histologically, three different epithelia may be differentiated:

Oral gingival epithelium on the outer surface of the free and attached gingiva.

Oral sulcular epithelium, lateral to the gingival sulcus.

Nonkeratinized junctional epithelium, which is located at the inner surface of the free gingiva covering enamel and, in certain situations, root cementum.

Oral sulcular epithelium and oral gingival epithelium are keratinized, stratified, fourlayered epithelia (Fig. 1.4a) comprised of:

Stratum basale

Stratum spinosum

Stratum granulosum

Stratum corneum

Oral gingival epithelium always contains certain nonepithelial cells:

Melanocytes

Antigen-presenting Langerhans cells

Merkel cells, which operate as sensory mechanoreceptors for touch and pressure reception

Small lymphocytes, especially cytotoxic T cells, and to a minor extent T helper cells (see Chapter 3)

Junctional epithelium is not keratinized. It consists of two strata:

Stratum basale

Stratum suprabasale

Oral gingival epithelium and oral sulcular epithelium are as much as 70 to 80 % parakeratinized; that is, pyknotic cell nuclei are still found in the stratum corneum. In 20 to 30 % of cases, the attached gingiva is orthokeratinized (Fig. 1.4a); that is, the densely packed horny scales do not contain cell nuclei.

Junctional epithelium facilitates epithelial lining of the oral cavity during and after tooth eruption. The mechanism by which junctional epithelium is attached to different structures of the tooth surface (enamel, cementum, dental cuticle) or implant surfaces is mediated by an internal basal lamina consisting of glycoproteins and collagen, and hemidesmosomes.

Fig. 1.4 Tissues of the periodontium.

a Lamina propria (to left) and oral gingival epithelium with stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. In this case, the epithelium is orthokeratinized.

b Cellular mixed stratified fiber cementum with layers of cellular intrinsic fiber cementum (CIFC) and acellular extrinsic fiber cementum (AEFC), which covers the surface.

c Periodontal ligament between the alveolar bone proper and AEFC.

d Alveolar bone proper appears on radiographs as lamina dura (e.g., mesial surface of tooth 17).

Table 1.1 Composition of the supra-alveolar fiber apparatus of the lamina propria

Primary fiber apparatus

Secondary fiber apparatus

Dentogingival fibers

Transgingival fibers

Dentoperiosteal fibers

Intergingival fibers

Alveologingival fibers

Interpapillary fibers

Circular fibers

Periosteal-gingival fibers

Transseptal fibers

Intercircular fibers

Semicircular fibers

Apart from epithelium, gingiva consists of a firm fibrous connective tissue, the lamina propria. There is no submucosa. The supra-alveolar fiber apparatus of the lamina propria is composed of primary and secondary fibers (Table 1.1). The fibers of the secondary fiber apparatus connect primary fiber bundles.

Peri-implant Mucosa

The peri-implant mucosa is attached to the surface of titanium implants in two ways:

An epithelial barrier about 2 mm long, which adheres to the implant by hemidesmosomes, corresponding to the junctional epithelium.

Apically, a 1 to 1.5 mm wide zone of fibrous connective tissue can be found. Collagen fibers run parallel to the implant surface and insert partly in the periosteum of the alveolar bone.

In the connective tissue, two zones can be differentiated:

A fibroblast-rich zone with few vessels, about 40 μm wide, which is in direct contact with the implant surface.

Laterally, a zone with few cells and dense collagen fibers and more vessels is seen.

Since a periodontal ligament is missing, blood supply is exclusively facilitated by larger supraperiosteal vessels.7

Root Cementum

Root cementum originates pre-eruptively during root development and throughout life after completion of root growth.3 Formation of cementum is effected by daughter cells of the ectomesenchymal cells of the dental follicle:

Cementoblasts

Cementocytes

Fibroblasts

Various kinds of root cementum have been described depending on histological features and function (Table 1.2):

Acellular afibrillar cementum (AAC) is found only on enamel, as tongues or islands, when enamel has come into contact with connective tissue after conclusion of crown development. Its function, if any, is unknown.

The laminar acellular extrinsic fiber cementum (AEFC), thickness 20 to 250 μm, is found in the cervical and middle third of the root:

– AEFC consists of densely packed (30,000/mm2), perpendicularly oriented collagen fiber bundles (Sharpey's fibers), each about 4 μm thick.

– Fibers extend into the periodontal ligament and connect the root with the alveolar bone.

– AEFC is produced first by fibroblasts of the dental follicle proper and is thus of ectomesenchymal origin (Fig. 1.2).

– Later it is produced by fibroblasts of the periodontal ligament.

– Note: AEFC is committed entirely to anchorage of the tooth in its socket.

Cellular intrinsic fiber cementum (CIFC) is a product of cementoblasts of the dental follicle proper, the later periodontal ligament:

– CIFC contains cementocytes.

– Collagen fibers run circularly or helically around the root, that is, parallel to the root surface. CIFC does not contain Sharpey's fibers.

– CIFC is repair cementum, but it also forms part of the cellular mixed stratified cementum (CMSC).

Cellular mixed stratified cementum (CMSC) is a stratified tissue with alternate layers of AEFC and CIFC/AIFC (Fig. 1.4b): – It is inhomogeneously mineralized, partly porous, and of variable thickness (100 to > 600 μm).

– CMSC is mainly found in the apical third of the root and the furcation area of multi-rooted teeth.

– It is committed to functional adaptation, that is, dynamic change of the outer shape of the root during movements of the tooth, mesial shift, and occlusal drift.

– If it is covered by AEFC, it anchors the tooth in its socket.

– Infrequently, acellular intrinsic fiber cementum (AIFC) is found in CMSC.

Periodontal Ligament

The periodontal ligament is a cell- and fiberrich, firm connective tissue which anchors the tooth via root cementum and alveolar bone proper in its socket (Fig. 1.4c)3:

Developmentally, it derives from ectomesenchymal cells of the dental follicle proper.

The periodontal space is narrower in the middle of the root (0.12–0.17 mm) than at the alveolar crest (0.17–0.23 mm) or the tooth apex (0.16–0.24 mm). Higher values are found in adolescents and lower values in older adults.

Functional strain may lead to a widening of the periodontal space and increasing thickness of collagen fiber bundles.

Desmodontal fiber bundles have been described as supracrestal, horizontal, oblique, interradicular, and apical fibers. Cellular elements of the periodontal ligament are:

Fibroblasts

Cementoblasts and dentoclasts

Osteoblasts and osteoclasts

Epithelial cells (Malassez rests)

Immune defense cells and neurovascular elements

The periodontal ligament is heavily vascularized. Blood supply is facilitated via:

the gingival plexus of postcapillary venules, and

a desmodontal blood vessel basket comprised of lateral branches of the alveolar and infraorbital arteries in the maxilla, and the lingual and mental arteries in the mandible.

Lymph vessels form a dense, basketlike network, which anastomoses with lymph vessels of the gingiva and septa of the alveolar bone.

Both sensory and autonomic nerve fibers are found:

Somatosensory, afferent fibers reach the periodontal ligament as terminal branches of the dental nerve. Some of them appear apically as lateral branches of the dental nerve whereas others pass through foramina and the cribriform lamina.

Free nerve endings of sensory fibers are responsible for pain perception.

Ruffini-like endings are mechanoreceptors for proprioceptive stimuli, that is, pressure. Pressure sensitivity is extraordinarily refined.

Nonmyelinated sympathetic fibers are responsible for the local regulation of desmodontal vessels.

Alveolar Bone Proper

Deriving from cells of the dental follicle, the alveolar bone proper is also of ectomesenchymal origin.3 On radiographs it appears as lamina dura (Fig. 1.4d). Alveolar bone proper contains Sharpey's fibers, which are connected to fibers of the periodontal ligament.

Alveolar bone may be absent on the vestibular aspects of teeth positioned prominently in the jaw. This condition is termed fenestration if marginal bone is present and dehiscensce if marginal bone is missing.

Three cell types may be distinguished:

Osteoblasts: a mixed population composed of preodontoblasts with large nuclei and fibroblastlike cells with small nuclei and desmodontal progenitor cells of osteoblasts.

Osteocytes, which arise from osteoblasts and become entrapped in their own product, namely bone. Osteocytes are located in bony lacunae and are connected by long cell projections. Young osteocytes are smaller than osteoblasts but have a similar structure. Older osteocytes have a reduced set of organelles.

Osteoclasts are multinucleated giant cells, which are located in surface pits of the bone (Howship's lacunae). They arise by fusion of hematopoietic, mononuclear precursor cells of bone marrow. An organelle-poor, brushlike cytoplasmatic border consisting of microvilli is characteristic. Resorption of bone is facilitated by acidic phosphatases and other hydrolytic enzymes.

Physiology

Soft (gingiva, periodontal ligament) and hard tissues (root cementum, alveolar bone proper) of the periodontium are committed to various tasks:

Anchoring of the teeth in their bony sockets

Keeping teeth together within the jaw as a dental arch

Adaptation to functional and topographic alterations

Enabling change in tooth position

Repair of the effects of traumatic injury

Maintenance of the epithelial lining of the oral cavity

Provision of peripheral defense mechanisms against infection

Perception of pain and pressure, sensing of touch

Turnover Rates

In junctional epithelium, the ratio between the basal cell area and the area of exfoliation results in an extremely high tissue turnover.3 It is 50 to 100 times higher than for oral gingival epithelium.

Tissue turnover of gingival connective tissue is higher than that of dermis:

Gingival fibroblasts synthesize larger amounts of new collagen than would be necessary for mature collagen replacement.

The resulting excess seems to be available for tissue repair.

Cementogenesis:

Formation of AEFC is extremely slow. In humans, thickening amounts to about 0.005 to 0.01 μm per day.

Initial CIFC is formed considerably faster (0.4–3.1 μm per day). Further layers are built up at a rate of 0.1 to 0.5 μm per day, which is still faster than AEFC.

Growth rates are comparable with those of crown and root dentin, and growth is only slightly slower than the growth of alveolar bone proper.

The turnover rate of the periodontal ligament is about twice that of the gingiva and four times that of the dermis. There is a marked capacity for tissue remodeling. Tissue turnover keeps the structural organization of the tissue constant. During remodeling, an adaptation of the three-dimensional organization of the desmodontal fiber apparatus to an altered position or functional strain occurs:

Both processes are accompanied by decomposition and synthesis of collagen fibers and are at times indistinguishable.

Collagen is removed by phagocytosing fibroblasts.

Physiological rates of renewal and removal of collagen fibers are balanced.

Physiologic forces during chewing stimulate these processes. During aging, turnover decreases.

Bony remodeling occurs in the alveolar process during growth of the jaw, eruption of the teeth, and during tooth replacement. Apposition of bone predominates:

Growth starts from periosteum and endosteum.

The renewal rate seems to be higher than in other bones.

Remodeling of the alveolar bone proper commences with the tooth's functional period, as soon as it comes into occlusal contact with the antagonist.

Occlusal forces are transferred to the bone by the periodontal ligament.

The direction, frequency, duration, and magnitude of the forces largely determine the extent and rate of remodeling.

The complicated post-eruptive tooth movement is characterized by an oblique tilting with a vertical and horizontal component:

Occlusal drift

Mesial migration

Eruption following extraction of the antagonist

Defense Mechanism

The gingiva is protected against mechanical, thermal, and chemical injury by the firm consistency of the supra-alveolar fiber apparatus and keratinization of the oral gingival epithelium.

In most circumstances, specific compartments of the peripheral host defense of the gingiva efficiently prohibit bacterial invasion of the dentogingival region (see Chapter 3):

Protection against bacterial infection is provided by both the epithelial and connective tissue components of the gingiva.

Although junctional epithelium does not keratinize, its extreme turnover rate and the presence of resident leukocytes make it relatively resistant to bacterial invasion.

The lamina propria of the gingiva provides cellular and humoral components of the immune system.

Particularly in young individuals, inflammatory cell infiltrates in the gingiva provide some protection against periodontal destruction.

Possibilities of Repair

Replantation or transplantation of teeth is only successful if cells and fibers of the periodontal ligament on the root surface and the inner surface of the alveolar socket are maintained. Otherwise, ankylosis and/or root resorption will occur. Reparative replacement of desmodontal fibers is carried out by cell populations of the periodontal ligament. The regenerative potential is, however, essentially limited8:

Reparative, cellular intrinsic fiber cementum may be formed rapidly during wound healing.

However, this bonelike type of cementum should probably not be regarded as odontogenic tissue.

The true tissues of the tooth-supporting apparatus (i.e., alveolar bone proper, periodontal ligament, acellular extrinsic fiber cementum) all derive from the dental follicle proper, which has its origin in the ectomesenchymal tissue of the neural crest. Differentiation during odontogenesis is dependent on a cascade of genetic signals and growth factors.

Regeneration of the tooth-supporting apparatus in the proper sense of restoration of the normal tissue architecture should therefore not be expected.

Note: The mere reparative deposition of cellular cementum has no functional relevance.

2 Periodontal Microbiology

Ecology of the Mouth

Biodiversity

Whereas the human body consists of about 10 trillion somatic cells (1013), 10 times more microorganisms,1 about 100 trillion (1014), colonize the different surfaces of skin, mucous membranes of the oral cavity, the gastrointestinal tract (the vast majority), respiratory and genitourinary tracts, as well as the teeth, dental implants, and dental prostheses.

Currently, the Human Oral Microbiome Database (HOMD) consists of 16S rRNA gene sequences (see below) of more than 700 different taxa of oral bacteria.2

Taxa have been assigned to 14 phyla.

About 66 % of these taxa have been cultivated in recent years.

For comparison, the proportion of cultivable taxa is less than 1 % in most other natural habitats.3

More is to be expected.4 About twice as many taxa could already be identified in the oral cavity. After validation probably more than 400 new taxa will soon be added to the HOMD.5 The composition of the flora of, in particular, a visceral cavity (e. g., gastrointestinal, genitourinary and respiratory tracts, oral cavity) is remarkably specific:

Between 500 and 1,000 different taxa have been described in the gastrointestinal tract.6

However, few (< 10 %) have been found in both gastrointestinal tract and oral cavity.

Fig. 2.1 Cloning and sequencing of bacterial 16S rRNA genes. Identification of cultivable and currently not cultivable bacterial species. (Modified after Leys et al,7 courtesy of the American Society for Microbiology.)

a Sampling of subgingival bacteria.

b Isolating and denaturing DNA.

c Amplification of 16S rRNA gene with polymerase chain reaction (PCR).

d Ligation of 16S rRNA gene fragments in plasmids (vectors) of Escherichia coli and transfection into competent

E. coli cells.

e Colonies of successfully transformed E. coli cells can be identified on agar plates.

f Sequencing of DNA of transformed cells; identification of inserts. Species identification in gene data banks (BLAST).

Some oral bacteria (e. g., streptococci, Veillonella spp.), can be found in virtually all humans and do colonize most mucous membranes of the oral cavity.

The majority of oral species, however, are very selective8 and may colonize either periodontal pockets, the dorsum of the tongue, or carious lesions, for example.

By amplifying conserved and highly variable regions of 16S rRNA genes using the polymerase chain reaction (PCR), transferring amplicons to competent cells of Escherichia coli (cloning), and subsequently sequencing the respective DNA strands (Fig. 2.1, Box 2.1),7 bacteria of the oral cavity have been presently assigned to 14 phyla (Fig. 2.2 and Table 2.1).5 Of special importance are:

Bacteroidetes: Gram-negative bacteria of the genera Prevotella, Bacteroides, Porphyromonas, Tannerella, and Capnocytophaga.

Proteobacteria: Neisseria, Eikenella, Kingella, Aggregatibacter, Campylobacter; all gram-negative.

Firmicutes: Gram-positive bacteria; three classes:

– Bacilli-class: Streptococcus, Lactobacillus, Staphylococcus, Gemella.

– Clostridia-class: Eubacterium, Parvimonas, Veillonella, Dialister, Selenomonas.

– Erysipelotrichia: Bulleidia extructa, Solobacterium moorei, Erysipelothrix tonsollarum, Lactobacillus [XVII] catenaformis.

Tenericutes (formerly class Mollicutes within the phylum Firmicutes): Mycoplasma.

Actinobacteria: Actinomyces, Rothia, Corynebacterium, Propionibacterium; all gram-positive.

Fusobacteria: Fusobacterium, Leptotrichia; gram-negative.

Spirochaetes: All treponemes; gram-negative.

Box 2.1 Basic principles of bacterial phylogenetics

In order to compare and determine the phylogenetic similarities of different bacteria, whether or not they are currently cultivable, certain characteristics of genes may be used which decode ribosomal RNA.

After transcription of the genome by messenger (m) RNA, the genetic code is translated into an amino acid sequence on the ribosomes. Prokaryotes (for instance, bacteria) have 70S ribosomes, which consist of rRNA and protein. Each ribosome is composed of a large (50S) and a small (30S) subunit. The latter contains the specific 16S rRNA.

Since accurate transcription of the genetic code and its translation into the amino acid sequence (and, ultimately, the protein) is of utmost importance, a few crucial regions of ribosomal DNA are highly conserved, while less critical regions are variable. The presence of both highly conserved and variable regions enables differentiation at species level, so it is possible to distinguish similar species phylogenetically.

Highly conserved and variable regions are amplified by PCR and transferred via plasmid vectors into competent cells of E. coli. Subsequently, the respective DNA strands may be sequenced (Fig. 2.1).

Currently, more than 125,000 sequences of bacterial 16S rDNA can be called up in gene data banks. Unknown bacteria can thus be identified and compared with the sequences of known species. Highly conserved regions of different species are used to align the sequences in question. The number of differences in variable regions is then determined, which can be used in cluster analyses to construct a phylogenetic tree (Fig. 2.2) which displays evolutionary relationships graphically.

Fig. 2.2 Phylogenetic tree of 10 of the 14 currently identified different bacterial phyla of the oral cavity. (After Paster et al,3 modified after Dewhirst et al5; courtesy of the American Society for Microbiology.) In phyla TM7 (Saccharibacteria) and SR1 so far no cultivable organisms were detected. Other phyla with very few phylotypes in the oral cavity (< 1 %) are Chlamydia, Chloroflexi, GN02 and Euryarchaeota.

The Oral Cavity as a Biotope

In order to describe a certain biotope, the following terms may be used:

Habitat—a place where bacteria grow. Different bacteria form a bacterial community.

Ecosystem—microbes in their environment.

Niche—function of a bacterium in its habitat. Different bacteria compete for the same niche.

Resident flora—microorganisms which are commonly found in a habitat. Equivalent terms are normal flora or commensals.

Opportunistic infection—under certain circumstances, commensals can cause disease.

The oral cavity is a unique, complex biotope in the organism. Hard structures (teeth, dental implants) interrupt the mucosal lining. Teeth provide widely differing ecosystems which allow colonization by specific bacteria:

Pits and fissures

Smooth surfaces

Cervical region of the teeth

Root canal system

Carious dentin

Further ecosystems, each with a special flora, include:

Periodontal pockets

Dorsum of the tongue

Tonsils

The various habitats are colonized by very different bacterial communities8,9:

Buccal mucosa: Streptococcus mitis, Gemella haemolysans

Dorsum of the tongue: S. mitis, Streptococcus parasanguinis, Streptococcus salivarius, Granulicatella adiacens, G. haemolysans

Masticatory mucosa of the hard palate: S. mitis, Streptococcus infantis, Granulicella elegans, G. haemolysans, Neisseria subflava

Palatal tonsils: S. mitis, Granulicalla adiacens, G. haemolysans; in some cases also Prevotella spp., Porphyromonas spp.

Crown of the tooth: Streptococcus sanguinis, Streptococcus gordonii, Streptococcus mutans, Actinomyces oris, Rothia dentocariosa, G. haemolysans, Granulicella adiacens.

Carious lesions: Lactobacillus spp.

Subgingival region: Predominantly obligately anaerobic, gram-negative bacteria including spirochetes and motile rods

Root canal system: Obligately anaerobic, gram-negative bacteria

Note: Changes in the ecosystem may have a considerable influence on bacterial populations and thus a decisive therapeutic effect. For instance:

Subgingival administration of oxygen (e. g., by applying 3 % H2O2) may kill anaerobic bacteria.

Complete pocket elimination of periodontal pockets by excision (see Chapter 11) may impede recolonization with anaerobic pathogens.

Sealing of fissure systems, which establishes anaerobic conditions and prevents further supply of substrates, may render streptococci and lactobacilli metabolically inactive.

Colonization Mechanisms

The oral cavity provides, for many bacteria, very comfortable living conditions10:

Warm (about 36°C) and humid environment

Frequent nutritional supply

Solid surfaces to adhere to

On the other hand, host defense mechanisms may interfere with colonization. Bacteria must have certain capabilities if they are to establish themselves in the oral cavity:

Various mechanical obstacles put up by the host have to be overcome:

– Saliva flow

– Gingival crevicular fluid flow, which is directed outwards from the gingival sulcus or periodontal pocket (see Chapter 3)

– Epithelial desquamation

– Self-cleansing during mastication

– Personal oral hygiene

Both the bacteria and the surface to be colonized are electronegatively charged. Protons (in an acidic environment) and other cations may bridge electrostatic forces.

The adhesion of bacteria to the surface is mostly quite specific:

– Lectinlike (i.e., proteins that recognize carbohydrate structures of the pellicle, see below) and hydrophobic adhesins react with complementary receptor molecules of the host surface.

– Adhesins are located in threadlike pili or fimbriae, which can also bridge electrostatic forces and enable contact to the surface of the substrate.

Secretory immunoglobulin A (sIgA) of the host and so-called agglutinins may recognize antigenic properties in fimbriae and specifically block them.

Colonization of many bacteria further depends on:

– Redox potential

– Oxygen tension

– Antagonisms and synergisms between microorganisms

Biofilm Dental Plaque

Among different bacteria, a multitude of interactions may exist, for instance complex food webs, metabolic cooperation, etc. (Fig. 2.3). This might be the main reason for the organization of microorganisms of the dental surface in a highly complex biofilm:

Note that biofilms comprise the typical bacterial population colonizing solid surfaces in a humid environment,11 which can be found, for example, on any object and on the ground beneath standing or flowing water or in any sewage installation.

Fig. 2.3 Bacterial interactions in subgingival biofilms. (Modified after Carlsson.10)

Extracellular structures of a multitude of very different bacteria, such as capsule polysaccharides or glycocalyx, surround the bacterial population as a matrix:

– It maintains the structure of the biofilm by formation of networked, cross-linked macromolecules. Biofilm bacteria are thus largely protected from external influences.

– Glycocalix facilitates survival and growth within the community.

– During periods of ceased nutrient supply, many bacteria can degrade exopolysaccharides.

Another characteristic feature is defined microenvironments with different pH, oxygen tension, and redox potential.

Bacteria may produce β-lactamase which cleaves the β-lactam ring of certain antibiotics; or catalase, or superoxide dismutases catalyzing dismutation of oxidizing ions released by phagocytes.

A primitive circulation system supplies substrates and eliminates waste products and metabolites.

As compared to planktonic cultures where bacteria live individually in a fluid culture, bacterial communities in a biofilm (Fig. 2.4) exert remarkable properties,12 which include:

Close metabolic cooperation

Fig. 2.4 Scanning electron microscopic image of the dental biofilm.

A primitive communication system with exchange of genetic information13

Resistance against phagocytosis and killing by neutrophil granulocytes, irrespective of presence of specific antibodies and complement.

Resistance against antibiotics due to incorporation of bacteria in a matrix. Note: Minimum inhibitory concentrations (MICs) are determined for bacteria living in a planktonic environment. More realistic minimum biofilm eradication concentrations may be 100 or even up to 1,000 times higher.

Accumulation of signaling compounds may mediate a sort of communication, so-called quorum sensing. For instance, gene expression for antibiotic resistance may be activated after reaching a certain threshold level of respective molecules (quorum cell density).

In general, as a community, the capacity for increased pathogenicity might be drastically increased. Examples of biofilm-associated body infections, which are often serious, are:

Catheter infection

Infectious endocarditis in patients with prosthetic heart valves

Infection of artificial joints

Conjunctivitis in patients wearing contact lenses

In particular, dental caries, periodontal disease, peri-implantitis and denture stomatitis are typical biofilm (i.e., plaque-induced) infections (see Chapter 13), which are characterized by delayed onset and a chronic course. Causative agents are endogenous microorganisms. Note: Localization of bacterial masses more or less outside of the host organism essentially determine the treatment:

Mechanical disruption of the biofilm

Adjunctive use of antiseptics

Changes in the ecosystem

Formation of Supragingival Plaque

With the commencement of plaque formation, that is, aggregation of bacteria on the tooth surface, microorganisms of the oral cavity may become pathogenic. Within minutes up to two hours of undisturbed plaque formation, an organic deposition of glycoproteins from the saliva is formed on the tooth surface and other hard structures of the oral cavity, the so-called acquired pellicle. On this pellicle, pioneer bacteria are seen after about four hours10:

Streptococci, especially Streptococcus mitis, S. sanguinis, and S. oralis

Small proportions of gram-positive rods such as Actinomyces oris. These plaque bacteria adhere loosely to start with but soon become firmly attached.

Interestingly, most of the bacteria that adhere first to the pellicle are dead.

The primary adhesion of Streptococcus mutans onto the acquired pellicle is partly due to lectinlike adhesins binding to α-galactoside receptors of salivary glycoproteins.

Subsequent production of extracellular glucans promotes further accumulation of these bacteria.

Dental plaque is stabilized by extracellular polysaccharides, in particular the extremely insoluble 1,3-α-glucan (mutan), which are synthesized by S. mutans, S. sanguinis, S. oralis, and Streptococcus salivarius.

Aggregations between streptococci and Actinomyces spp. are particularly important for further plaque formation.

Salivary bacteria colonize the plaque surface, while bacteria that are only loosely attached are washed away.

Irregularities of the tooth surface are preferentially colonized and rapidly leveled.

With a generation time of about 1 to 2 hours, the main reason for increase of plaque mass during the first 24 hours is bacterial proliferation.14

If plaque is allowed to further accumulate undisturbed, its composition becomes more complex15:

The proportions of streptococci decrease while proportions of facultative or obligate anaerobic Actinomyces spp. increase.

Among gram-negative bacteria, Veillonella spp. predominate.

Gram-negative anaerobic rods of the genera Fusobacterium, Prevotella, and Porphyromonas appear in small proportions in supragingival flora. Note: Fusobacterium nucleatum plays a key role in dental biofilm formation because of its multigeneric coaggregation properties.13

After about one week of undisturbed plaque growth, spirochetes and motile rods may be observed in plaque.

Thus, plaque formation and its maturation go through four phases:

Minutes to two hours: Pellicle formation (specific adsorption of salivary glycoproteins).

First day: Gram-positive (Streptococcus mitis, S. sanguinis, S. oralis) and gram-negative cocci (Veillonella parvula, Neisseria mucosa) and rods (Actinomyces odontolyticus, A. viscosus, A. oris). Extracellular polysaccharide production (e. g., mutan: 1,3-α-glucan) of S. mutans. Leveling of surface irregularities.

Second to fourth day: Decrease of streptococci, increase of Actinomyces spp., gram-negative cocci and rods.

After one week: Spirochetes and motile rods.

Colonization of the Subgingival Region

Deepening of the sulcus as well as edematous swelling of the gingiva, as a response to supragingival plaque accumulation, ultimately leads to formation of a subgingival space. Later this space may further increase when junctional epithelium proliferates apically as the result of loss of connective tissue attachment.

As mentioned above, cloning in Escherichia coli and subsequent sequencing of 16S rDNA (Box 2.1) has revealed that the oral cavity is colonized by more than 700 different bacterial species, many of which are currently not yet cultivable. Most periodontal pathogens of the subgingival region are gram-negative and obligately anaerobic. Some exceptions are gram-positive Parvimonas micra (formerly Micromonas micra, Peptostreptococcus micros), Streptococcus intermedius and Eubacterium spp. as well as facultative anaerobic Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans, Eikenella corrodens, and Capnocytophaga spp. (Table 2.1).

The subgingival region provides comfortable conditions for many bacteria,10 which are very different from those found in supragingival areas:

Bacteria are protected from oral hygiene measures and saliva flow. This results in selective colonization of bacteria that are not able to adhere on solid surfaces—in particular, spirochetes and motile rods.

Gingival exudate contains nutrients and essential growth factors for numerous periodontal pathogens:

– Amino and fatty acids as energy source.

– α2-globulin is essential for Treponema denticola.

– Hemin, iron, and vitamin K, which are all essential for the black-pigmenting, gram-negative anaerobes of the genera Prevotella and Porphyromonas.

– Prevotella intermedia, P. nigrescens and members of the P. melaninogenica group can substitute vitamin K for steroid hormones such as estradiol and progesterone. For that reason, an excessive increase of these microorganisms in gingival pockets is often observed during pregnancy, possibly leading to so-called pregnancy gingivitis.

Favorable conditions for obligately anaerobic bacteria in deep periodontal pockets include a low redox potential and low oxygen tension.

Specific relationships between periodontal pathogens and beneficial bacteria of the oral cavity (synergisms and antagonisms) may play an important role in the colonization of the subgingival space as well (see Fig. 2.3).

Note: In contrast to colonization of supragingival tooth surfaces, an individual's diet (frequency and composition of meals) has no apparent influence on the colonization of the subgingival space.

Dental Calculus

Dental calculus is mineralized bacterial plaque. It is not the primary cause of destructive periodontal disease. However, since it is always covered by vital plaque, its removal remains a cornerstone of all periodontal therapy (see Chapter 10).

Mineralization of supragingival and subgingival plaque is brought about by minerals dissolved in saliva and gingival exudate, respectively16:

– After secretion from large sublingual, submandibular and parotid salivary glands, partial pressure of CO2 in the saliva decreases rapidly in the oral cavity.

– As a result, pH rises and dissolved minerals precipitate. Therefore, supragingival calculus is mainly located adjacent to the excretion ducts of the large salivary glands, lingually at mandibular incisors, and buccally at the first and second molars in the maxilla. Note: the pH may also rise following production of ammonia and urea.

– Subgingival calculus covers the tooth/root surface within a gingival/periodontal pocket. Under the antibacterial influence of gingival exudate, a zone at the bottom of the pocket about 0.5 mm wide appears always to be plaque- and calculus-free.

Various crystalline structures of calcium phosphate may be found in calculus (Table 2.2).

Note: The tendency to develop dental calculus and plaque differs greatly among individuals.

Periodontitis: an Infectious Disease

Identification of Periodontal Pathogens

As most diseases of the oral cavity are caused by bacteria, traditional concepts of prevention have been based on the idea of largely reducing bacterial masses (see Chapter 7). However, both dental caries and inflammatory periodontal diseases are probably not caused by the total bacterial mass or plaque in general. Both have characteristics of endogenous/opportunistic infections (see below) which depend on certain preconditions:

Presence of a specific habitat.

Certain changes in the external conditions which promote the increase of particular segments of the complex flora.

A change in the host's defense system which may lead to loss of control over the pathogenic flora in the habitat.

For most of the second part of the last century, periodontal diseases were assumed to be caused by specific microorganisms (specific plaque hypothesis). In order to ultimately identify a specific pathogen as cause of a particular infectious disease, the traditional Koch-Henle's postulates have to be applied:

Table 2.2 Crystalline structures of calcium phosphate in dental calculus

Name

Sum formula

Occurrence

Brushite

CaHPO4 × 2H2O

Recent calculus

Octacalciumphosphate

Ca4H (PO4)3 ×2H2O

Mostly in outer layers of supragingival calculus

Hydroxyapatite

Ca10(OH)2(PO4)6

Mostly in inner layers of supragingival plaque

Whitlockite

Ca3(PO4)2

Main component of subgingival calculus; contains small amounts of Mg

The pathogen occurs without exception in every case of the disease and under circumstances which can account for the pathological changes and clinical course of the disease.

It does not emerge in any other disease as a fortuitous and nonpathogenic entity.

After being completely isolated from the body and repeatedly grown in pure culture, the pathogen can induce the disease anew and can be recovered from the experimentally infected host.

Lack of applicability of these postulates to oral infections prompted Socransky17 to modify (and, in fact, considerably weaken) them as follows:

An oral pathogen is associated with diseased sites. It should be absent in healthy sites or in different forms of the disease.

Elimination of the pathogen should lead to healing of the lesion.

Presence of abnormal cellular and/or humoral immune responses to the potential pathogen while responses to other microorganisms are normal.

Further evidence for pathogenicity may arise from animal experimentation and identification of virulence factors.

Based on these criteria, in particular in the 1980s and 1990s, the following periodontal pathogens were identified18,19:

Pathogens which are strongly associated with periodontal disease:

– Aggregatibacter actinomycetemcomitans

– Porphyromonas gingivalis

– Tannerella forsythia (formerly Bacteroides forsythus)

– Eubacterium nodatum

– Treponema denticola

Potential pathogens moderately associated with periodontal disease:

– Prevotella intermedia

– Campylobacter rectus

– Parvimonas micra (formerly Micromonas micra, Peptostreptococcus micra)

– Eikenella corrodens

– Fusobacterium nucleatum

– Other Eubacterium spp.

– β-hemolytic streptococci

Significant in certain cases:

– Staphylococcus spp.

– Pseudomonas spp.

– Enterococci, enteric rods

– Candida spp.

It should be critically emphasized that, in epidemiologic research of complex diseases, such as periodontitis, rather Sir Bradford Hill'scriteria20 of causal association are to be applied (see Chapter 5). Hill's criteria include:

Strength, consistency and specificity of the association: What is the relative risk? Is there agreement among repeated observations in different places, at different times, using different methodology, by different researchers, under different circumstances? Is the outcome unique to the exposure?

Temporality: Does exposure precede the outcome?

Experimental evidence: Does controlled manipulation of the exposure change the outcome?

Biological gradient: Is there evidence of a dose–response relationship?

A remaining set of criteria may support a hypothesis but is not regarded as evidence for causality:

Plausibility: Does the causal relationship make biological sense?

Coherence: Is the causal association compatible with present knowledge of the disease?

Analogy: Does the causal relationship conform to a previously described relationship?

Further developments in molecular biology have even led to the formulation of molecular guidelines, namely the presence or absence of a specific nucleic acid sequence21, for establishing microbial disease causation.

The breadth of bacterial diversity in the oral cavity, which became evident only after the application of novel, open-ended molecular methods, has led to critical revision of current concepts of the causative role of specific bacteria in the pathogenesis of periodontal diseases, which had been identified with traditional means such as cultivation of biofilm samples. Modern tools for a better characterization of the entire microbiota sampled at numerous periodontal sites in a given patient include:

Checkerboard DNA-DNA hybridization of, say, 40 (or even 74) predominant species in subgingival biofilm22

Microarrays with oligonucleotide probes for about 300 cultivable and yet not cultivable species in oral biofilm (Human Oral Microbe Identification Microarray, HOMIM).23Note: Possible cross-reactions and nonspecific target binding has been described with both methods, and this has currently not been settled satisfactorily.

Next-generation sequencing4 (e.g., HOMINGS, species-level identification of nearly 600 oral bacteria taxa):

– For further studies on microbial diversity in the oral cavity

– To determine metabolic activities in dental biofilm

– Sequencing of functional genes

– Whole genomic analyses of certain species

After several decades of intensive research in periodontal microbiology it is presently unclear whether the flood of information from these novel techniques will ultimately lead to a paradigm shift of clinical concepts as regards diagnosis and treatment of inflammatory periodontal diseases.

Types of Infection

It is possible that periodontal diseases comprise different kinds of infections which should then be differentiated (Fig. 2.5):

Endogenous/opportunistic infection with bacteria that belong to the resident flora of the skin, nose, oral cavity, or intestinal and urogenital tracts. Opportunistic pathogens are usually not especially virulent. On the other hand, members of the resident flora at one site may cause life-threatening infections in other organ systems.

– If oral hygiene is poor, or there are alterations within the habitat or drastic changes in the local or systemic host defense, some of these commensals—that is, potentially pathogenic bacteria found in every oral cavity—may increase disproportionately.

– This may lead to periodontitis.

Exogenous infection with microorganisms that are usually not members of the resident microflora:

– Infections with enterobacteria, pseudomonads, or staphylococci are possible. These bacteria may negatively influence established periodontitis as superinfection.

– Among periodontal pathogens, in particular a highly virulent clone of Aggregatibacter actinomycetemcomitans, JP2 (see below), may be considered an exogenous pathogen.

A. actinomycetemcomitans, P. gingivalis, T. forsythia, aswellas E. nodatum and T. denticola