Subject of clinical cariology.

Oral ecological system, and it’s role in development of dental caries.

Subject of Clinical cariology deals with one of the most prevalent human diseases

dental caries: pathogenesis, management and control. It involves studies of chemical

and biological mechanisms of caries development; recognition of clinical manifestations

of the disease as well as methods of lesion detection and treatment methods.

In daily use the term “caries” usually means a cavity in the hard dental tissues.

A cavity is just a clinical symptom of the disease that can be detected at the advanced stage only!

Dental caries is a disease – a chronical process that can affect quality of life – related to pain, impaired physiological functions; other problems – psychological, professional, communication, etc.

Treatment of this disease is costly both on the individual and population levels. Dental caries is not life-threatening, however, is very prevalent and therefore, requires a lot of professional attention.

Dental caries is prevalent in all populations of the world, and still remains the major reason for tooth loss.

Restorative dentistry was established in 20

century, and was mainly occupied with pain

relief and restorative treatment of decayed

teeth.

Development of high quality of restorative

methods and materials could not guarantee the

cure and control of the disease.

All kinds of restorative procedures are regarded as symptomic treatment; temporary effect with no promise for the disease stabilization.

The treatment of the disease means control of its progression and prevention of clinical manifestations at the erliest stages of the disease development. This requires a thorough knowledge of the mechanisms of caries development and determining factors of the disease.

Restoration of a single cavity does not mean cure of the disease!

19 century – the work of Miller “The microorganisms of the human mouth” is a basis for present understanding of the complexity of human oral ecosystem .

Black (1908 ) published a textbook that became a background for clinical dentistry. According to Black, caries is a chemical dissolution of the calcium salts of the tooth, and transformation into gelatinous body. Such a dissolution can be cause by external damaging factor.

W.D.Miller ir G.V. Black – established dentistry as scientificdiscipline about 100 yrs ago.

Three major discoveries of the 20 century had a tremendous impact on the way cariology and restorative dentistry developed.

I – studies in 30-40ies focusing on the role of nutrition in making teeth more

or less susceptible to caries attacks . A direct correlation between sugar

consumption and dental caries progression was found (Vipeholm study,

Sweden) .

II – late 40 ies, clearly demonstrated the central role of microorganisms in

caries development. Studies with animals showed that caries can be prevented

with penicillin.

The focus on dental caries as an infectious transmittable disease was

established.

The main causative agents were found to be Str.mutans and lactobacilli.

III - late 40ies: T. Dean demonstrated how presence of elevated levels of fluoride in water could significantly reduce number of caries lesions in children.

Major parameters involved in the carious process. (simplified scheme)

CARIES

+Substrate

Teeth and host

Microorganisms

Time

CARIES

-CARIES

-

CARIES

-CARIES

-

This scheme has determined that for many years the efforts in research have been spent on

1) trying to improve resistance of the tooth to acid attack, by incorporating fluoride into the tooth

2) To prove that sugar is the “arch criminal” for dental caries

3) To suggest that caries is caused by specific microorganism. Vaccines against Str. Mutans have been considered as a possible public-health measure.

Can we eradicate microorganisms?

Can we eliminate substrate?

Can we increase host resistance to dental caries?

Can we avoid dental caries?

The tooth is not an isolated anatomical unit, not related to the environment. Oral cavity is a complex ecological system with close response effect between all its elements.The main elements of the oral cavity that can be associated with dental caries development:

1. Saliva; 2. Dental hard tissue – enamel, 3. Dental plaque covering the tooth surfaces

Saliva – oral fluid constantly present in the mouth, with a complex structure – organic and inorganic. The salivary components play major role in maintaining stability and functioning of the oral ecosystem.

Dental enamel -part of the dentition, major functions : mastication, prevention

of inner tissues (dentin and pulp) from injuries. As regards it’s role in the oral

ecosystem, - is a deposit of inorganic materials characterized by active mineral

exchange with the environment.

Enamel is composed of 90% inorg. material – hydroxiapatite consists of

calcium, phosphate, carbon ions, as well as chemically active hydroxyl groups.

About 4% is taken by the organic material and water present in the

intercrystalline spaces. Through these spaces different solutions, ions and

molecules may diffuse to the enamel. Such transportation of minerals is related

to the de- and re-mineralization processes, colour changes, fluoride absorbtion,

etc.

90% of the human body consists of resident microflora which is very important for maintaining the stability of ecosystem. Acquisition of this resident microflora occurs from birth, and is a natural process, during which all environmentally exposed surfaces of the body become colonized.

The resident microflora of a site contributes to the normal development and physiology of the host.

The mouth of the newborn baby is sterile. The transmission of microorganisms occurs through water, food via saliva.For.ex., oral streptococci and gram- bacteria can be derived by vertical transmission to the child from the mother.

The variety of oral microflora increases during first years of life.The eruption of the dentition creates new habitats for microbialColonisation: teeth provide new sites for bacterial adhesion. This results in the undisturbed accumulation of large masses of bacteria, especially at stagnant places (plaques accumulation).

At some stage the acquisition of new bacteria stops, the stable situation isreached, a “microbial homeostasis”: a dinamic equilibrium between the resident microflora and local environmental conditions.

Out of 300 different species, only a few a able to colonize in large numbers,due to specific biological and physical properties.A certain surface-specific distribution of different m/organisms exists in the oral cavity.

Bakterijos Burna

Staphylococcus epidermidis ++

Staphylococcus aureus*  +

Streptococcus mitis  ++ 

Streptococcus  salivarius ++ 

Streptococcus mutans* ++

Enterococcus faecalis* +

Streptococcus pneumoniae* +

Streptococcus pyogenes* +

Neisseria sp. +

Neisseria meningitidis* +

Veillonellae sp. +

Enterobacteriaceae* (Escherichia coli) +

Proteus sp. +

Pseudomonas aeruginosa*

+/-

Haemophilus influenzae* (11)

+

Bifidobacterium bifidum (12)

Lactobacillus sp. (13) ++

Clostridium sp.* (14)  +/- 

Clostridium tetani (15)

Corynebacteria (16) +

Mycobacteria

Actinomycetes + 

Spirochetes ++

Mycoplasmas  +

Temperature (optimal 36-38°C).

pH level (optimal salivary pH 6,5-7,5;for acidophylics – more acidic)

Amount of oxygen (aerobai anaerobai)

Nutritional elements (carbohydrates, amino acids, peptides)

Specific and nonspecifc imuno factors regulating growth

ir kt.

Environmental factors determinating the activity of microbial community:

Community of oral microflora is organized in a specific way, in order to survive in homeostasis (microbial biofilm).

“Cariogenic” bacteria – part of the community, their activity depends noton their absolute numbers, but rather on the interaction between other bacteria.

Principles of microbial biofilm formation and survival

Primary m/o – “pioniers” ( Streptococcus) create favorable environment for adhesion and accumutalion of secondary microorganisms.Second colonizers adhere to the primary ones by co- aggregation and co-adhesion.

Consumption of major elements of nutrition determines selection of the m/o.

By increasing the layer of the plaque, concentration of oxygen decrease, therefore, facultative and obligate anaerobs replace the aerobic flora. (actinomyces, corynebacterium, veillonella, fusobacterium).

The newly formed community of microorganisms has a variety of species,Is very stable, and rejects the outsider species (specific inhibitors – bakteriocines, hydrogen peroxyde, acid release).

Bacteria present in the biofilm, are genotypically different from the same species growing separately.

Streptococcus mutans

For cariogenic bacteria to grow, the environmental conditions should become favourable; i.e., an ecological shift should occur in the community.

The diet rich in carbohydrates promotes growth of many oral bacteria. It has been shown that the plaque of several days can differ by weight, covering area, depending on how much sugar has been in the diet.

Because of high level of acids in the plaque, acidophylic bacteria prevail.

sugar is desintegrated into glucans and fructans, these promote plaque accumulation and adhesion on the tooth surfaces, and can be used as a food reserve.

Lactobacilli

Dental plaque: structure and characteristics

dental pellicle, thin organic sheet, formed from salivary

mucopolishacharides, adheres firmly to the dental enamel, and penetrates

to the enamel 3m.

Pellicle regulates: • transport of inorganic materials form enamel, • is a basis for adhesion of the plaque;• adhesion of organic materials and m/organisms form saliva.

Mikroorganizsm colonies. Plaque m/o population is from 70 to 100 mln / 1

mg of plaque weight per day, and after 3 days reachesa 130 mln m/o.

Dominating m/o - gram-positive cocci - Str. mitis, Str. sanguis ir Str.

mutans. Furthermore, Actinomicetes, lactobacilli.

Products of nutrition and bacterial metabolism; Minerals form saliva; Cells of desquamated epitheium.

Dental plaque is a huge laboratory, characterized by constantly ongoing chemical processes: dissolution, formation, adhesion, release, etc.

I XIX century it was demonstrated by Miller, that fermentation of carbohydrates occurs in the microbial plaque, and as a result, a lactic acid is formed. This acid promotes pH drop in the environment, and, consequently, the dissolution of enamel minerals.The modern research showed that metabolic processes in the plaque are considerably more complex to be able to induce caries. M/o colonies are active all the time, even if there is no nutrition coming from the diet.

As a result of this metabolism, pH drop in the plaque.

Stephan curve showes changes in the environmental pH, due to fermentation of the carbohydrates.

Pathogenic characteristic of microorganisms (Loesche, 1986)

Ability to transport fermentable carbohydrates, and to metabolise them to acids.

Collection of extracellular and intracellular polischarides (glucans, fructans) Utilization of intermediate toxic products of metabolism

Suppression of certain enzymes participating in sugar metabolism.

Ability to metabolize sugar in extremal conditions for ex, in very acidic environment ( lactobacilli).

Every pH drop is able to disturb chemical equilibrium between the elements present in enamel and in the oral environment; when pH drops, minerals are dissolved, when it increases , minerals are taken up from the environment.

Summary or, cumulative result of these reactions determines whether cariesLesion will develop on a tooth surface.

Dental caries can develop on any tooth surface, covered by sufficient amount of microbial biofilm.

-----------------------------------------------------------------------------Threshold for clinical detection

Time

Mineral loss

Mineral gain

PH changes on the dental enamel-plaque interface

Oral ecosystem is formed to maintain the homogenicity and stability of itselements.

The acids are neutralized by salivary buffering systems.

certain species, pvz, Veilonela, Neiseria, propionobacteria are able to metabolize the lactic acid,, and to stabilize the pH shifts.

certain bacteria release carbamide that can neutralize acidicį pH (Str.salivarius, Str.sanguis).

The bacterial symbiosis favours maintaing of ral homeostasis, and makes the environment more resistant to external damage.

Maintaining of Homeostasis

By definition, dental caries is a dynamic process taking place in the microbial

deposits (dental plaque on the tooth surfaces) which results in disturbance of

the equilibrium between tooth substance and the surrounding plaque fluid so,

that over the time, the result is a loss of mineral from the tooth surface .

Microbial Deposit, pH

Tooth

Maintainance of ecological equilibrium is the main prerequisite to control the disease.

(The nonspecific plaque hypothesis – dental caries is caused by shifts in homeostasis of resident oral microflora that occur due to various environmental factors).

Can we eliminate microorganisms?

microorganisms and their activity – is an inherent part of a human being as a biological individuum.

Summary

Summary

(Nonspecific plaque hypothesis – dental caries is caused by shifts in homeostasis of resident oral microflora that occur due to various environmental factors).

Potential cariogens are always present in the plaque, however, in case of neutral pH, they are not capable to compete with other m/o in the community.When the diet is balanced, clinical relevance of these bacteria is not significant, and the de- ir re- mineralization processes in the oral cavity are in balance.If the oral conditions are favourable for growth of acidogenic bacteria, their number is increased, and other species are displaced from the biofilm.This is the ecological shift in the biofilm, that favours the condition for caries development.

A correlation between macro-organism ir microflora egsists: some factors of macroorganism can be helpful in maintaining the homeostasis of the oral environment (e.g. salivary factors).

Microbial deposit pH

Tooth

Microbial Deposit pH

Tooth

Time

Bufer capasity

Sugar clearance rate

Saliva composition

Saliva flow rate

Fluoride

Diet, Composition and frequency

M/crobial species

Social class

Attitudes

Knowledge

IncomeEducation

Behavior

Determinants of the caries process

Adaptuota pagal Fejerskov&Manji, 1990