THE ORAL ENVIRONMENT
I-INTRODUCTION:
For many decades, the oral cavity was simply considered the entrance to the digestive tract. Then, based on the wealth of new data establishing a bidirectional and reciprocal relationship between general health and the ubiquitous bacteria of the Oropharyngeal sphere, the concept of the Oral Ecosystem was introduced.
II-TERMINOLOGY:
1-Ecology: science which studies the conditions of existence of living beings among themselves and with the outside world.
2-The ecosystem: can be defined as a set of elements whose reciprocal effects ensure the stability of the oral environment.
At the oral level we distinguish (the oral ecosystem)
III-DEFINITION OF THE ORAL ECOSYSTEM:
The oral ecosystem is the set of interactions between the oral flora, saliva, mucous membranes and the dental organ taking place at the level of the oral cavity, and whose reciprocal effects form a balanced and stable system.
The latter encompasses: a plethora of organized microbial communities. This microbial cosmos in the oral cavity is called Oral Microbiota and an Oral Microbiome which is composed of the different anatomical microniches of the oral cavity and its bath fluid, saliva and gingival fluid.
- THE ORAL MICROBIOME (the abiotic environment):
A-SALIVA:
The salivary glands secrete approximately 1 to 2 liters of saliva per 24 hours, the mixture of parotid, submaxillary, sublingual and accessory saliva is called mixed saliva: It is a stringy, tasteless, bland-smelling, colorless and transparent liquid.
A-1-COMPOSITION:
The average composition of saliva per 1000g of oral fluid is 995g of water, 2g of mineral matter and 3g of organic substances.
- Mineral substances:
-dissolved gaseous elements such as: O2, N2, CO2.
-non-gaseous elements: anions: chlorides, bicarbonates, phosphates, and, to a lesser extent, fluorine, iodides and bromides.
-cations: represented essentially by Ca++ which plays an essential role in the formation of the acquired film and bacterial adhesion, K+, Mg+ and incidentally Zn, Fi, Mn and cobalt.
- organic substances:
– carbohydrates: in small quantities coming either from food or from salivary glycoproteins.
-lipids: mainly triglycerides, fatty acids and phospholipids are found. They play an important role in the formation of dental plaque and its transformation into tartar.
-proteins: we distinguish several:
– mucins: these are salivary glycoproteins which give saliva its viscosity, they form an adherent film on the dental surface allowing the attachment of microbial germs.
– enzymes: example: amylase, lysozyme, peroxidases, lactoferrin.
-secretory immunoglobulins A.
– elements represented in the form of traces: leukocytes, epithelial cells, food debris, bacteria and fungi.
B- GINGIVAL FLUID:
1- DEFINITION:
Fluid of serum origin that oozes from the gingivodental sulcus, the fluid comes from the diffusion of liquid from the small gingival vessels due to the permeability of the gingival tissue, it crosses the junctional epithelium to flow into the gingivodental sulcus.
The amount of gingival fluid increases with the degree of inflammation.
2- COMPOSITION:
-proteins: immunoglobulins, glycoproteins, albumin, fibrinogen, complement factors.
– enzymes: most are released by polymorphonuclear cells: collagenases, cathepsins, alkaline and acid phosphatases.
-prostaglandins PGE2 which increase during periodontal inflammation.
3- The roles of gingival fluid:
– Positive roles:
- Purification of the sulcus by washing and rejection of toxins
- Antimicrobial action: by polymorphonuclear cells, macrophages, lysozymes and IgA, IgG, IgM
- Fibrinolytic action.
- Epithelial attachment (biochemical bond between tooth and epithelium)
- Bactericidal and bacteriostatic.
– Negative roles:
- Bacteria development: (nutritional substrate)
- Inflammation maintenance
C- THE DENTAL ORGAN:
The enamel surface is covered with salivary mucins facilitating bacterial adhesion, whereas the external gingival surface presents variable degrees of keratinization and desquamation, from which bacteria do not find a stable base to attach themselves.
D-BUCCAL MUCOUS MEMBRANES:
Desquamation involves the elimination of germs that attach to the surface of the epithelium.
We also have the back of the tongue which seems to house one of the most complex bacterial niches in human ecology (morphology characterized by irregularities such as cracks, depapillated areas, papillae which promote the accumulation of debris and microorganisms.
- THE ORAL MICROBIOTA :
Otherwise called the biotic community, which encompasses a plethora of microbial communities (10 14 of microorganisms) including commensal, symbiotic bacteria called “Holobiont” (Simon et al. 2019 ) and a conglomerate of pathogenic bacteria, fungi, archaea as well as parasites.
A-Lifestyle of microbial germs:
- Mutualism: This is a symbiotic relationship from which two populations benefit.
- Commensalism : one population benefits while the other does not.
- Parasitism: one organism benefits at the expense of another.
B- The conditions necessary for the growth of microorganisms:
- Physicochemical factors:
- Temperature :
-constant 34 to 36°C.
-Allows the growth of a very large number of species.
-May vary during feeding, for a short period of time.
- PH:
-Close to neutral 6.7 to 7.3
-may vary during feeding or by bacterial metabolism.
-in the particular area of the subgingival site, pH = 7.5 to 8.8
- Presence of oxygen:
– The great diversity in O2 concentrations allows the growth of aerobic, microaerophilic, facultative aerobic-anaerobic, strict anaerobic bacteria.
- Humidity:
– the oral cavity is permanently bathed in saliva and gingival fluid, which allows the multiplication of micro-organisms.
- Host factors:
– Food
– host defense mechanics
– Hormonal changes : pregnancy in the 2nd trimester
- Genetic factors : Genetic factors appear to influence intestinal and oral flora.
- Age:
- – From the age of 70: the increase in the prevalence of staphylococci (S. aureus), lactobacilli
– From the age of 80: increase in the number of yeasts (candida albicans)
C – Acquisition of oral flora :
The oral cavity is sterile at birth.
A first contamination occurs during childbirth by bacteria from the vaginal flora.
It is only from the 3rd to 5th day that the oral flora will form (mothering ++). Essentially salivary Streptococcus attaches mainly to the epithelial surfaces, we also find the genus Actinomyces which colonizes the saliva, the mucous membrane, the tongue and the tonsillar crypts.
Mixed dentition:
Appearance of anaerobic phenomena.
Permanent dentition:
Biotic and abiotic factors are put in place.
We find: supra-gingival flora, sub-gingival flora, tongue flora, and saliva.
| cheeks | language | saliva | Supragingival plaque | Subgingival plaque | |
| S.mutans S.sanguis S.mitis S.anginosus S.salivarius | ND +++ +++ + + | ND 0 +++ ++ ++ | + ++ +++ ++ ++ | ++ ++ ++ ++ + | + + + +++ ND |
IV- MEANS OF DEFENSE OF THE ORAL ENVIRONMENT:
1- NON-SPECIFIC MEANS OF DEFENSE:
- The gingival mucosa: it ensures the protection of the underlying elements thanks to epithelial obliteration reinforced by keratinization, thickness and cellular cohesion and rapid turnover.
- Action of peripheral muscles: the tongue, cheeks and lips which allow the cleaning of the mouth.
- Physicochemical factors:
– salivary flow: it has a detergent action and eliminates bacteria.
-the role of purification of the gingival sulcus provided by the gingival fluid .
– salivary pH: this is an important factor in the regulation of the different elements of the oral flora (5.5-6.5): an acidic pH promotes the growth of acidophilic lactobacilli, while an alkaline pH promotes the transformation of bacterial plaque into tartar and the development of periodonto-pathogenic germs.
- Cellular factors: Represented by phagocytic cells originating from the gingival lamina propria via the epithelial intercellular spaces leading to the SGD and saliva. During phagocytosis, polymorphonuclear cells and monocytes release several lytic enzymes and their prolonged release can cause tissue damage within the host.
- Antimicrobial products present in saliva and gingival fluid:
– Lysozyme: enzyme discovered by FLEMING in 1922; it is a polypeptide that inhibits bacterial growth, synthesized by polymorphonuclear neutrophils and acinar cells of the salivary glands. Lysozyme binds selectively to streptococcus mutans and salivary mucins. The bacterial lysis it causes is increased in the presence of an acidic pH. It inhibits the aggregation of streptococci and the fermentation of glucose.
– Histatins: Group of 12 cationic proteins rich in histidine found mainly in parotid saliva. Some of them inhibit the growth of streptococci mutans and candida albicans. They are strongly absorbed on the surface of the enamel and bind strongly to Porphyromonas gingivalis. They have a bacteriostatic and fungistatic role.
– Lactoferin: This is a glycoprotein that has bacteriostatic activity on many germs. Its role is to capture and fix iron, because it depletes the environment of iron, which deprives bacteria of iron essential for their growth.
– Defensins: These are antimicrobial peptides isolated from polymorphonuclear cells, some of which have a bactericidal effect on gram-negative bacteria and a fungicidal effect on candida albicans, without really knowing their mechanism of action.
2- SPECIFIC MEANS OF DEFENSE:
They are contained in the blood, saliva and gingival fluid which are represented by immunoglobulins, complement and specific immunity cells.
A- IMMUNOGLOBULINS:
They come from the blood except for salivary IgA and are found in saliva and gingival fluid:
1- Ig G: monomeric form, they represent 75% of serum Ig and they have 4 forms (IgG 1, 2,3,4). They activate the complement, and they can attach to macrophages and to the membrane of mast cells. They neutralize bacterial toxins by attaching to microorganisms, thus causing their phagocytosis.
2- Ig M: pentameric form (5 identical monomers), they represent 10% of serum Ig, they bind to B lymphocytes and they are the first to appear in the antibody response. They are opsonizing.
3- Ig D: they exist in trace amounts, they are mainly present on the surface of lymphocytes located on the periphery of the germinal centers, they can play an important role in triggering the stimulation of lymphocytes by the antigen, thus initiating the immune reaction.
4- Ig E: they represent 0.004% of serum Ig, fixed on the membrane of mast cells, and they can fix on basophils. Their encounter with the specific antigen leads to the degranulation of the cells that carry them.
5-Serum IgA: monomeric form, most present in the gum and gingival fluid, it prevents bacterial adhesion to mucosal structures.
6- secretory Ig A: dimeric form, it inhibits bacterial adhesion to dental surfaces and mucous membranes, they are not very specific.
B- THE SUPPLEMENT:
It is a protein complex made up of 11 proteins called factors initiated by the letter C and numbered from 1 to 9, of which C1 contains 3 factors C1q C1r C1s (recognition site) whose activation of this entire system leads to the lysis of the target cell.
C- SPECIFIC IMMUNITY CELLS:
-B lymphocytes by differentiating into plasma cells which in turn synthesize antibodies.
-T lymphocytes which can release lymphokines (set of chemical mediators of inflammation or by returning directly with the antigen by effector cells.
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