Jan Lindhe. Clinical Periodontology

Подождите немного. Документ загружается.

Clean

Molecular

Single

substratum

adsorption

organisms

(Phase 1) (Phase 2)

Multiplication

(

Phase 3)

Sequential adsorption

of organisms

(Phase 4)

Fig. 3-2. Stages in the formation of a biofilm on a clean, hard and non-shedding surface following immersion into a

fluid environment. Phase 1: Molecular adsorption to condition the biofilm formation. Phase 2: Bacterial adhesion

by single organisms. Phase 3: Growth of extracellular matrix production and multiplication of the adhering bacte-

ria. Phase 4: Sequential adsorption of further bacteria to form a more complex and mature biofilm. Adapted from

Marshall (1992).

GENERAL INTRODUCTION TO

PLAQUE FORMATION

Growth and maturation patterns of bacterial plaque

have been studied on natural hard oral surfaces, such

as enamel and dentin, or artificial surfaces, such as

metal or acrylic, using light and electron microscopy

and bacterial culture (Theilade & Theilade 1985). De-

spite differences in surface roughness, free energy and

charge, the most important features of initial plaque

development are similar on all these materials (Sie-

grist et al. 1991).

The ability to adhere to surfaces is a general prop-

erty of almost all bacteria. It depends on an intricate,

sometimes exquisitely specific, series of interactions

between the surface to be colonized, the microbe and

an ambient fluid milieu (Mergenhagen & Rosan 1985).

Immediately upon immersion of a solid substratum

into the fluid media of the oral cavity, or upon cleaning

of a solid surface in the mouth, hydrophobic and

macromolecules begin to adsorb to the surface to form

a conditioning film (Fig. 3-2, Phase 1), termed the

acquired pellicle. This film is composed of a variety of

salivary glycoproteins (mucins) and antibodies. The

conditioning film alters the charge and free energy of

the surface, which in turn increases the efficiency of

bacterial adhesion. Bacteria adhere variably to these

coated surfaces. Some possess specific attachment

structures such as extracellular polymeric substances

and fimbriae, which enable them to attach rapidly

upon contact (Fig. 3-2, Phase 2). Other bacteria require

prolonged exposure to bind firmly. Behaviors of bac-

teria change once they become attached to surfaces.

This includes active cellular growth of previously

starving bacteria and synthesis of new outer mem-

brane components. The bacterial mass increases due

to continued growth of the adhering organisms, adhe-

sion of new bacteria (Fig. 3-2, Phase 4), and synthesis

of extracellular polymers. With increasing thickness,

diffusion into and out of the biofilm becomes more

and more difficult. An oxygen gradient develops as a

result of rapid utilization by the superficial bacterial

layers and poor diffusion of oxygen through the

biofilm matrix. Completely anaerobic conditions

eventually emerge in the deeper layers of the deposits.

Oxygen is an important ecologic determinant because

bacteria vary in their ability to grow and multiply at

different levels of oxygen. Diminishing gradients of

nutrients supplied by the aqueous phase, i.e. the sa-

liva, are also created. Reverse gradients of fermenta-

tion products develop as a result of bacterial metabo-

lism.

Dietary products dissolved in saliva are an impor-

tant source of nutrients for bacteria in the supragingi-

val plaque. Once a deepened periodontal pocket is

formed, however, the nutritional conditions for bacte-

ria change because the penetration of substances dis-

solved in saliva into the pocket is very limited. Within

the deepened pocket, the major nutritional source for

bacterial metabolism comes from the periodontal tis-

sues and blood. Many bacteria found in periodontal

pockets produce hydrolytic enzymes with which they

can break down complex macromolecules from the

host into simple peptides and amino acids. These

enzymes may be a major factor in destructive proc-

esses of periodontal tissues.

Primary colonization is dominated by facultatively

anaerobic Gram-positive cocci. They adsorb onto the

pellicle-coated surfaces within a short time after me-

chanical cleaning. Plaque collected after 24 h consists

mainly of streptococci; S. sanguis is the most promi-

nent of these organisms. In the next phase, Gram-posi-

tive rods, which are present in very low numbers

DENTAL PLAQUE AND CALCULUS • 83

84 • CHAPTER 3

Fig. 3-3. Primary colonization by

predominantly Gram-positive fac-

ultative bacteria. Ss: Streptococcus

sanguis is most dominant. Av: Acti-

uomyces spp. are also found in 24 h

plaque.

Fig. 3-4. Gram-positive facultative

cocci and rods co-aggregate and

multiply.

Biofilm

Pellicle

Biofilm

Pellicle

Fig. 3-5. Surface receptors on the

Gram-positive facultative cocci

and rods allow the subsequent ad-

herence of Gram-negative organ-

isms, which have a poor ability to

directly adhere to the pellicle.

Fn: Fusobacterium nucleatum.

BI: Prevotella intermedia.

Fig. 3-6. The heterogeneity in-

creases as plaque ages and ma-

tures. As a result of ecologic

changes, more Gram-negative

strictly anaerobic bacteria colonize

secondarily and contribute to an

increased pathogenicity of the

biofilm.

initially, gradually increase and eventually outnumber

the streptococci (Fig. 3-3). Gram-positive filaments,

particularly Actinomyces spp., are the predominating

species in this stage of plaque development (Fig. 3-4).

Surface receptors on the deposited Gram-positive

cocci and rods allow subsequent adherence of Gram-

negative organisms with poor ability to attach directly

to pellicle. Veillonella, fusobacteria and other anaerobic

Gram-negative bacteria can attach in this way (Fig. 3-

5). The heterogeneity of plaque thus gradually

increases and, with time, includes large numbers of

Gram-negative organisms. A complex array of

interrelated bacterial species is the result of this

development. Exchange of nutrients between different

species, but also negative interactions, e.g. the

production of bacteriocins, play a role in the establ-

ishment of a stable bacterial community (Fig. 3-6). Due

to the influences of local environmental factors, struc-

turally different types of plaque evolve at different

locations. Protection of the growing plaque from shear

forces and local availability of certain nutrients are

most important. A distinct composition of mature bac-

terial deposits can eventually be recognized at specific

sites and under specific clinical conditions. Examples

are the plaque on smooth enamel surface versus fis-

sure plaque, or the plaque in shallow and less shallow

gingival crevices.

Accumulation of plaque along the gingival margin

leads to an inflammatory reaction of the soft tissues.

The presence of this inflammation has a profound

DENTAL PLAQUE AND CALCULUS • 85

influence on the local ecology The availability of

blood and gingival fluid components promotes

growth of Gram-negative bacterial species with an

increased periodontopathic potential. Bacterial sam-

ples from established gingivitis lesions have increased

numbers of these bacteria. Because of the capability

enzymatically to digest proteins, many of these organ-

isms do not depend upon a direct availability of die-

tary carbohydrates. Such bacteria do not produce ex-

tracellular polymers and develop only loosely adher-

ent plaque in the developing periodontal pocket. Cul-

tivation of samples from advanced periodontal le-

sions reveals a predominance of Gram-negative an-

aerobic rods. Under the microscope, particularly high

numbers of anaerobic uncultivable spirochetes can be

demonstrated. Further details on the microbial ecol-

ogy of subgingival plaque are discussed in Chapter 4.

In summary, immediately following immersion of

hard, non-shedding surfaces into the fluid environ-

ment of the oral cavity, adsorption of macromolecules

will lead to the formation of a biofilrn. Bacterial adhe-

sion to this glycoprotein layer will first involve pri-

mary plaque formers, such as Gram-positive faculta-

tive cocci and rods. Subsequent colonization onto re-

ceptors of these organisms will involve Gram-nega-

tive, strictly anaerobic bacteria, while the primary

plaque formers also multiply to form colonies. The

heterogeneity of the complex biofilm increases with

time, as the ecologic conditions gradually change.

DENTAL PLAQUE AS A BIOFILM

The term biofilrn describes the relatively undefinable

microbial community associated with a tooth surface

or any other hard, non-shedding material (Wilderer &

Charaklis 1989). In the lower levels of most biofilms a

dense layer of microbes is bound together in a poly-

saccharide matrix with other organic and inorganic

materials. On top of this layer is a looser layer, which

is often highly irregular in appearance and may ex-

tend into the surrounding medium. The fluid layer

bordering the biofilm may have a rather "stationary"

sublayer and a fluid layer in motion. Nutrient compo-

nents may penetrate this fluid medium by molecular

diffusion. Steep diffusion gradients, especially for

oxygen, exist in the more compact lower regions of

biofilms. The ubiquity with which anaerobic species

are detected from these areas of biofilms provides

evidence for these gradients (Ritz 1969).

Accumulation of bacteria on solid surfaces is not an

exclusive dental phenomenon. Biofilms are ubiqui-

tous; they form on virtually all surfaces immersed in

natural aqueous environments. Biofilms form particu-

larly fast in flow systems where a regular nutrient

supply is provided to the bacteria. Rapid formation of

visible layers of microorganisms due to extensive bac-

terial growth accompanied by excretion of copious

amounts of extracellular polymers is typical for

biofilms. Biofilms effectively protect bacteria from an

timicrobial agents. Treatment with antimicrobial

sub-stances is often unsuccessful unless the deposits

are mechanically removed. Adhesion-mediated infec-

tions that develop on permanently or temporarily

implanted materials such as intravascular catheters,

vascular prostheses or heart valves are notoriously

resistant to antibiotics and tend to persist until the

device is removed. Similar problems are encountered

in water conduits, wherein potentially pathogenic

bacteria may be protected from chlorination, or on

ship hulls, where biofilms increase frictional resis-

tance and turbulence (Gristina 1987, Marshall 1992).

In summary, dental plaque as a naturally occurring

microbial deposit represents a true biofilrn which con-

sists of bacteria in a matrix composed mainly of ex-

tracellular bacterial polymers and salivary and/or

gingival exudate products.

STRUCTURE OF DENTAL PLAQUE

Supragingival plaque

Supragingival plaque has been examined in a number

of studies by light and electron microscopy to gain

information on its internal structure (Muhlemann &

Schneider 1959, Turesky et al. 1961, Theilade 1964,

Frank & Brendel 1966, Leach & Saxton 1966, Frank &

Houver 1970, Schroeder & De Boever 1970, Theilade

& Theilade 1970, Eastcott & Stallard 1973, Saxton 1973,

Ronstrom et al. 1975, Tinanoff & Gross 1976, Lie 1978).

The introduction of the electron microscope in dental

research was a significant development for studies of

dental plaque, both because the size of many bacteria

approaches the ultimate resolving power of the light

microscope, and because the resins used for embed-

ding allowed for sections thinner than the smallest

bacterial dimension. Hereby the substructure of

plaque could be identified.

In studies of the internal details of plaque, samples

are required in which the deposits are kept in their

original relation to the surface on which they have

formed. This may be accomplished by removing the

deposits with the tooth. If plaque of known age is the

object of study, the tooth surfaces are cleaned at a

predetermined time before removal (McDouga111963,

Frank & Houver 1970, Schroeder & De Boever 1970).

Pieces of natural teeth or artificial surfaces may also

be attached to solid structures in the mouth and re-

moved after a given interval. This method of plaque

collection was already used at the beginning of the last

century by Black (1911). The systematic use of artificial

surfaces for collection of plaque was reintroduced

during the 1950s. Thin plastic foils of Mylar

were

attached to mandibular incisor teeth for known peri-

ods, after which they were removed for histologic,

histochemical and electron microscopic examination

of the deposited material (Mandel et al. 1957, Muhle-

86 • CHAPTER 3

Fig. 3-8. Electron micrographic illustration of a 4-h den-

tal pellicle with a single bacterium included in the film.

The microbe appears attached to the surface. The den-

tal pellicle varies in thickness but has a homogeneous

morphology From Brecx et al. (1981).

mann & Schneider 1959, Zander et al. 1960, Schroeder

1963, Theilade 1964). Other types of plastic materials

Fig. 3-7. Electron micrographic illustration of a 4-h den-

tal pellicle. The pellicle has formed on an artificial sur-

face of plastic, which was painted on to the surface of

the tooth. The plastic surface was exposed to the envi-

ronment for a 4-h period. A thin condensed layer of or-

ganic material is covering the film. The material has a

relatively homogeneous appearance but varies in thick-

ness over the surface. From Brecx et al. (1981).

Fig. 3-9. Electron micrographic illustration of a 4-h den-

tal pellicle, formed on a plastic surface attached to the

buccal surface of a tooth. A condensed layer of organic

material is observed on the surface and cell remnants

are embedded in the film. From Brecx et al. (1981).

such as Westopal

, Epon

, Araldite

, and spray plast

have since been employed for this purpose (Berthold

DENTAL PLAQUE AND CALCULUS • 87

Fig. 3-10. High power electron micrographic illustra-

tion of a 4-h pellicle with bacteria residing in the pelli-

cle at a distance of around one micron from the con-

densed organic material. The pellicle is rather even in

composition and, at the oral side, an irregular con-

densed organic material is seen close to the bacteria.

From Brecx et al. (1981).

et al. 1971, Kandarkar 1973, Lie 1975, Listgarten et al.

1975, Rdnstrom et al. 1975). Results from several such

studies indicate that plaque formed on natural or

artificial surfaces does not differ significantly in struc-

ture or microbiology (Hazen 1960, Berthold et al. 1971,

Nyvad et al. 1982, Theilade et al. 1982a, b), indicating

that at least some of the principal mechanisms in-

volved in plaque formation are unrelated to the nature

of the solid surface colonized. However, there are

small, but important, differences in the chemical com-

position of the first layer of organic material formed

on these artificial surfaces compared with that formed

on natural tooth surfaces (Sonju & R611a 1973, Sonju

& Glantz 1975, Oste et a1.1981). Tooth surfaces, enamel

as well as exposed cementum, are normally covered by

a thin acquired pellicle of glycoproteins (Fig. 3-7). If

removed, e.g. by mechanical instrumentation, it

reforms within minutes. The pellicle is believed to

play an active part in the selective adherence of bacte-

ria to the tooth surface (Fig. 3-8). For details of the

proposed mechanisms, see Chapter 4.

The first cellular material adhering to the pellicle on

the tooth surface or other solid surfaces consists of

coccoid bacteria with numbers of epithelial cells and

polymorphonuclear leukocytes (Fig. 3-9). The bacteria

are encountered either on (Fig. 3-10) or within the

pellicle as single organisms (Fig. 3-11) or as aggregates

of microorganisms (Fig. 3-12). Larger numbers of mi-

Fig. 3-11. High power electron micrographic illustra-

tion of a 4-h pellicle with an embedded bacterium. Th(

bacterium is deposited on the film surface together

with the dental pellicle. Around the bacterium empty

;paces are observed representing the radius of extru-

sions of filaments radiating from the microorganisms.

From Brecx et al. (1981).

Fig. 3-12. Electron micrographic illustration of a 4-h

dental pellicle with bacteria attached to a plastic sur-

face, which had been adhering to a buccal tooth sur-

face and was exposed to the oral environment. A singl

row of bacteria attached to the surface is seen to the

left. On top of the bacteria, a layer of condensed or-

ganic material representing the oral lateral portion of

+ho rlortfnl oollirlo is nn+orl From Rrory o+ a1 (1QR11

88 • CHAPTER 3

Fig. 3-13. Thin section of plaque colony consisting of

morphologically similar bacteria deposited on plastic

film (F) applied to the buccal surface of a premolar dur-

ing an 8-h period. Magnification x 35 000. Bar: 0.2 µm.

From Brecx et al. (1980).

Fig. 3-14. Electron micrographic illustration of early

plaque formation. The film surface on which the pelli-

cle and bacteria adhere is located to the left. Bacteria of

varying morphology are attached to the film. They are

surrounded by organic pellicle material. An epithelial

cell remnant is seen in close vicinity to the microbes.

From Brecx et al. (1981).

Fig. 3-15. Electron micrographic illustration of 24-h den-

tal plaque formed on a plastic film surface attached to the

buccal surface of the tooth. A multilayer bacterial plaque

is noted. A remnant of an epithelial cell has been trapped

in the microbial mass. From Brecx et al. (1981).

Fig. 3-16. Thin section of old plaque stained for the

demonstration of polysaccharides by reacting them

with electron-dense material appearing dark in the il-

lustration. Many bacteria contain large amounts of in-

tracellular polysaccharide, and the intermicrobial ma-

trix contains extracellular polysaccharides. Magnifica-

tion x 7000. Bar: 1µm. From Theilade & Theilade (

1970).

DENTAL PLAQUE AND CALCULUS • 89

Fig. 3-17. High power electron micrographic illustra-

tion of a single bacterium attached to the pellicle by

filaments which extend from the bacterial surface to

the tooth surface. The surface had been exposed to the

oral environment for an 8-h period. From Brecx et al.

(1981)

Fig. 3-19. Thin section of plaque with a region predomi-

nated by Gram-negative bacteria. Between them, ves-

icles are surrounded by a trilaminar membrane (two

thin electron-dense layers with an electron-lucent layer

in between). This substructure is also seen in the outer-

most endotoxin containing cell wall layer of the adja-

cent Gram-negative bacteria. Magnification x 110 000.

Bar: 0.1 µm. From Theilade & Theilade (1970).

croorganisms may be carried to the tooth surface by

epithelial cells.

The number of bacteria found on the surface a few

hours after cleaning depends on the procedures applied

to the sample before examination, the reason being that

adherence to the solid surface is initially very weak. If

no special precautions are taken during the preparatory

processing, the early deposits are easily lost (Brecx et

al. 1980). Apparently the adherence

of microorganisms to solid surfaces takes place in two

steps:

1. a reversible state in which the bacteria adhere

loosely, and later

2. an irreversible state, during which their adherence

becomes consolidated (Gibbons & van Houte 1980).

Fig. 3-18. Thin section of plaque with granular or ho-

mogeneous intermicrobial matrix. Magnification x

20 000. Bar: 0.1 µm. From Theilade & Theilade (1970).

90 • CHAPTER 3

Another factor which may modify the number of bac-

teria in early plaque deposits is the presence of gingi-

vitis, which increases the plaque formation rate so that

the more complex bacterial composition is attained

earlier (Saxton 1973, Hillam & Hull 1977, Brecx et al.

1980). Plaque growth may also be initiated by micro-

organisms harbored in minute irregularities in which

they are protected from the natural cleaning of the

tooth surface.

During the first few hours, bacteria that resist de-

tachment from the pellicle may start to proliferate and

form small colonies of morphologically similar organ-

isms (Fig. 3-13). However, since other types of organ-

isms may also proliferate in an adjacent region, the

pellicle becomes easily populated by a mixture of

different microorganisms (Fig. 3-14). In addition,

some organisms seem able to grow between already

established colonies (Fig. 3-15). Finally, it is likely that

clumps of organisms of different species will become

attached to the tooth surface or to the already attached

microorganism, contributing to the complexity of the

plaque composition after a few days. At this time,

different types of organisms may benefit from each

other. One example is the corncob configurations re-

sulting from the growth of cocci on the surface of a

filamentous microorganism (Listgarten et al. 1973).

Another feature of older plaque is the presence of dead

and lysed bacteria which may provide additional nu-

trients to the still viable bacteria in the neighborhood

(Theilade & Theilade 1970).

The material present between the bacteria in dental

plaque is called the intermicrobial matrix and ac-

counts for approximately 25% of the plaque volume.

Three sources may contribute to the intermicrobial

matrix: the plaque microorganisms, the saliva, and the

gingival exudate.

The bacteria may release various metabolic prod-

ucts. Some bacteria may produce various extracellular

carbohydrate polymers, serving as energy storage or

as anchoring material to secure their retention in

plaque (Fig. 3-16). Degenerating or dead bacteria may

also contribute to the intermicrobial matrix. Different

bacterial species often have distinctly different meta-

bolic pathways and capacity to synthesize extracellu-

lar material. The intermicrobial matrix in plaque,

therefore, varies considerably from region to region.

A fibrillar component is often seen in the matrix be-

tween Gram-positive cocci (Fig. 3-17) and is in accord

ance with the fact that several oral streptococci syn-

thesize levans and glucans from dietary sucrose. In

other regions, the matrix appears granular or homo-

geneous (Fig. 3-18). In parts of the plaque with the

presence of Gram-negative organisms, the intermicro-

bial matrix is regularly characterized by the presence

of small vesicles surrounded by a trilaminar mem-

brane, which is similar in structure to that of the outer

envelope of the cell wall of the Gram-negative micro-

organisms (Fig. 3-19). Such vesicles probably contain

endotoxins and proteolytic enzymes, and may also be

involved in adherence between bacteria (Hofstad et al.

1972, Grenier & Mayrand 1987).

It must be remembered, however, that the transmis-

sion electron microscope does not reveal all organic

components of the intermicrobial matrix. The more

soluble constituents may be lost during the proce-

dures required prior to sectioning and examination of

the plaque sample. Biochemical techniques may be

used to identify such compounds (Silverman & Klein-

berg 1967, Krebel et al. 1969, Kleinberg 1970, Hotz et

al. 1972, Rolla et al. 1975, Bowen 1976). Such studies

indicate that proteins and carbohydrates constitute the

bulk of the organic material while lipids appear in

much lower amounts.

The carbohydrates of the matrix have received a

great deal of attention, and at least some of the poly-

saccharides in the plaque matrix are well charac-

terized: fructans (levans) and glucans. Fructans are

synthesized in plaque from dietary sucrose and pro-

vide a storage of energy which may be utilized by

microorganisms in time of low sugar supply. The

glucans are also synthesized from sucrose. One type

of glucan is dextran, which may also serve as energy

storage. Another glucan is mutan, which is not readily

degraded, but acts primarily as a skeleton in the ma-

trix in much the same way as collagen stabilizes the

intercellular substance of connective tissue. It has been

suggested that such carbohydrate polymers may be

responsible for the change from a reversible to an

irreversible adherence of plaque bacteria.

The small amount of lipids in the plaque matrix are

as yet largely uncharacterized. Part of the lipid content

is found in the small extracellular vesicles, which may

contain lipopolysaccharide endotoxins of Gram-nega-

tive bacteria.

Subgingival plaque

Owing to the difficulty of obtaining samples with

subgingival plaque preserved in its original position

between the soft tissues of the gingiva and the hard

tissues of the tooth, there are only a limited number of

studies on the detailed internal structure of human

subgingival plaque (Schroeder 1970, Listgarten et al.

1975, Listgarten 1976, Westergaard et al. 1978). From

these it is evident that in many respects subgingival

plaque resembles the supragingival variety, although

the predominant types of microorganisms found vary

considerably from those residing coronal to the gingi-

val margin.

Between subgingival plaque and the tooth an elec-

tron-dense organic material is interposed, termed a

cuticle (Fig. 3-20). This cuticle probably contains the

remains of the epithelial attachment lamina originally

connecting the junctional epithelium to the tooth, with

the addition of material deposited from the gingival

exudate (Frank & Cimasoni 1970, Lie & Selvig 1975,

Eide et al. 1983). It has also been suggested that the

cuticle represents a secretory product of the adjacent

DENTAL PLAQUE AND CALCULUS • 91

Fig. 3-20. Semithin section of subgingival plaque. An

electron-dense cuticle bordering the enamel space is

visible to the left. Filamentous bacteria are less than in

supragingival plaque. The surface toward the gingival

tissue contains many spirochetes (between arrows).

Various host tissue cells can be seen on the right side.

Magnification x 775. Bar: 10 µm. From Listgarten (

1976).

Fig. 3-21. (a) Light microscopic image of the

dentogingi- val region of a dog with experimental

gingivitis. A thin layer of dentogingival plaque can be

seen, extending from the supragingival region

approximately

/2 mm into the gingival sulcus. (b)

Higher magnification of a region of the plaque shown

in (a). The subgingival plaque has a varying thickness

and the epithelial cells are separated from the surface

by a layer of leukocytes. There are also numerous

leukocytes in the superficial portion of the sulcus

epithelium. The apical termina- tion of the plaque is

bordered by leukocytes separating the epithelium from

direct contact with the plaque bac- teria.

epithelial cells (Schroeder & Listgarten 1977). Infor-

mation is lacking concerning its chemical composi-

tion, but its location in the subgingival area makes it

unlikely that salivary constituents contribute to its

formation.

The subgingival plaque structurally resembles su-

pragingival plaque, particularly with respect to

plaque associated with gingivitis without the forma-

Fig. 3-22. Semithin section of supragingival plaque

with layer of predominantly filamentous bacteria ad-

hering to the enamel (to the left). Lighter staining indi-

cates calcification of part of the plaque close to the

tooth. Magnification x 750. Bar: 10 µm. From Listgarten

(1976).

tion of deep pockets (Fig. 3-21a). A densely packed

accumulation of microorganisms is seen adjacent to the

cuticular material covering the tooth surface (Fig. 3-22).

The bacteria comprise Gram-positive and Gram-

negative cocci, rods and filamentous organ-isms.

Spirochetes and various flagellated bacteria may also be

encountered, especially at the apical extension of the

plaque. The surface layer is often less densely

92 • CHAPTER 3

Fig. 3-23. Light microscopic image of a smear sample

taken from the dentogingival region in a subject who

had abstained from mechanical oral hygiene during 3

weeks. Numerous leukocytes can be observed embed-

ded in a dense accumulation of bacteria.

Fig. 3-24, 3-25. Semithin section of supragingival plaque on enamel (E), which has been dissolved prior to section

ing. Filamentous organisms predominate. At the surface some of these organisms are surrounded by cocci. This

configuration resembles a corncob. Magnification x 750 and x 1400. Bars: 10 µm and 1 µm. From Listgarten (1976).

Fig. 3-26. The corncob formations seen at the plaque

surface in Fig. 3-24 and 3-25. Magnification x 1300. Bar:

1 µm. From Listgarten (1976).

packed and leukocytes are regularly interposed be-

tween the plaque and the epithelial lining of the gin-

gival sulcus (Fig. 3-23).

When a periodontal pocket has formed, the appear-

ance of the subgingival bacterial deposit becomes

much more complex. In this case the tooth surface may

either represent enamel or cementum from which the

periodontal fibers are detached. Plaque accumulation

on the portion of the tooth previously covered by

periodontal tissues does not differ markedly from that

observed in gingivitis (Fig. 3-24). In this layer, filamen-

tous microorganisms dominate (Figs. 3-25, 3-26, 3-27),

but cocci and rods also occur. However, in the deeper

parts of the periodontal pocket, the filamentous or-

ganisms become fewer in number, and in the apical

portion they seem to be virtually absent. Instead, the

dense, tooth-facing part of the bacterial deposit is

dominated by smaller organisms without particular

orientation (Listgarten 1976) (Fig. 3-28).

The surface layers of microorganisms in the peri-

odontal pocket facing the soft tissue are distinctly

different from the adherent layer along the tooth sur-

face, and no definite intermicrobial matrix is apparent

(Figs. 3-28, 3-29). The microorganisms comprise a

larger number of spirochetes and flagellated bacteria.

Gram-negative cocci and rods are also present. The

multitude of spirochetes and flagellated organisms are

motile bacteria and there is no intermicrobial ma-