Composition of saliva and acquired pellicle

Question 1

What are the immune and non-immune defense mechanisms of saliva?

Answer 1

• Protection
• Buffering
• Pellicle formation
• Maintenance of tooth integrity
• Antimicrobial action
• Digestion
• Taste

Question 2

Briefly describe the constituents of saliva

Answer 2

99.5% water and 0.5% electrolytes

Contains the following proteins:

• Enzymes
• Lysozymes
• Defensins
• Mucins
• Histatins
• Statherin
• Lactoferrin
• Small organic molecules

Question 3

Name some enzymes in saliva

Answer 3

‣ amylase, peroxidase, and salivary lipase

Question 4

What are defensins?

Answer 4

proteins of the immune system

‣ Assist in killing phagocytosed microbes by forming pores in membrane to efflux essential nutrients

Question 5

What are mucins and what do they do?

Answer 5

glycosylated proteins produced by epithelial tissues.

‣ Produced by the mucous acinus

‣ They form gel secretions so serve provide lubrication

‣ Protection in oral cavity

‣ Cell signalling

‣ Form chemical barriers – over enamel(pellicle)/mucosa

‣ Aggregation of bacteria

‣ Overexpression of mucin proteins (MUC1) can be associated with cancers e.g. adenocarcinomas and lung diseases

Question 6

What are histatins?

Answer 6

antimicrobial peptides in the oral cavity

‣ Histatin 1 and histatin 2 = wound-closing factors in saliva – enhance initial epithelial cell migration

‣ Secreted by Von Ebners’ glands (minor glands)

‣ Encoded for by 2 genes: HTN1, HTN3

Question 7

What does statherin do?

Answer 7

Prevents calcium-phosphate precipitation in saliva, maintaining high Ca2+ level in saliva for remineralsation/ PO43- for buffering

‣ STATH gene ‣ SIgA (secretory IgA) – antibody in mucous secretions

‣ Tears saliva GIT, respiratory epithelium

Question 8

What does lactoferrin do?

Answer 8

Antimicrobial globular glycoprotein in secretory fluids

‣ Binding and transport of iron ions

‣ Binds to bacterial cell walls, affecting permeability and causing lysis ‣ Binds to viral proteins and stops penetration into cell/ replication

‣ Also anti-fungal and anticarcinogenic

Question 9

Give examples of small organic molecules in saliva

Answer 9

Glucose, urea, lipids, amino acids

Question 11

What is the dental pellicle and when does it form?

Answer 11

Dental pellicle is a protein film that forms on the surface enamel by selective binding of glycoproteins from saliva that prevents continuous deposition of salivary calcium phosphate.

It forms seconds after a tooth is cleaned

Question 12

What does the acquired pellicle protect the tooth from?

Answer 12

It is also protective to the tooth from the acids produced by oral microorganisms after consuming the available carbohydrates

Question 13

What does chlorohexidine do?

Answer 13

Chlorhexidine prevents adhesion of calculus to the tooth

Question 14

What are some of the components of the acquired pellicle?

Answer 14

macromolecules such as lysozyme, alpha-amylase, perioxidase, immunoglobulin A, immunoglobulin G, glycosyltransferase, proline-rich proteins, mucins, albumin and breakdown products from macromolecules from both saliva and bacteria

Question 15

What is ‘plaque’ and what does it contribute to?

Answer 15

Plaque is an adherent microbial biofilm attached to teeth and the primary aetiological agent of dental caries and periodontal disease. 1000-25000 species involved in plaque.

• The microbial composition reflects the site of formation and the host diet

Question 16

Outline the 4 stages of plaque formation

Answer 16

1. Colonisation by pioneer species
2. Outgrowth
3. Secondary colonisation
4. Climax community

Question 17

What are the major sites of plaque formation in the oral cavity?

Answer 17

Major sites of plaque formation are fissures, interproximal areas and the gum margin

Question 18

Which microbes are the early colonisers in plaque formation?

Answer 18

The species most able to colonise are: Streptococcus oralis, Steptococcus mitis and Streptococcus sanguis = 90% of the flora in the first few hours. Replicate in oxygen rich environment

‣ Actinomyces and Neisseria – early colonisers

Question 19

What occurs in ‘outgrowth’?

Answer 19

multiplies spreads in the plane of the surface and then upwards

Question 20

What happens during secondary colonisation?

Answer 20

• Secondary colonisation occurs by gram positive and gram negative, by the process of co-aggregation (aggregation between different species) leading to an increase in diversity. Proportion of streptococci decreases

‣ Co-aggregation occurs when colonising microbes attach to cells part of the developing biofilm.

‣ At 24 hours plaque contains a wide variety of bacteria and interspecies associations

Question 21

What occurs during the ‘climax community’ stage?

Answer 21

Plaque matures to form a stable climax community – bacterial succession. Colonies->corncobs->anaerobic environment

Question 22

What is the adhesion of a microbe to a surface governed by?

Answer 22

The adhesion of a microbe to a surface including another microbe is governed by shear force which sweeps bacteria away from a surface, and electrostatic repulsion with Van de Waal’s forces that provide areas of weak attraction

Question 23

Define asaccharolytic

Answer 23

Bacteria that can’t breakdown charbohydrates, so instead break down proteins

Question 24

What are the predominant species in supragingival plaque?

How do they contribute to the formation of dental caries?

Answer 24

Streptococcus and Actinomyces species are predominant in the supra gingival area. They can adhere the saliva-coated tooth surface by attachment between adhesins (located on bacterial cell surfaces) and receptors (contained mainly in the salivary coating on tooth surfaces) and are known to utilise salivary components as nutrients.

These bacteria are saccharolytic and degrade carbohydrates derived from foods to form lactic, formic acid, acetic, succinic and other organic acids, and concomitantly consume oxygen by NADH oxidase. Taken together, these activities create acidic and anaerobic conditions. The acidification is rapid and the supragingival pH can reach around 4 within several minutes

Question 25

Where do subgingival bacteria get their nutrients from?

Answer 25

• Subgingival sites (stable tooth and unstable epithelial surface) are bathed with a continuous efflux of gingival crevicular fluid (GCF), derived from blood plasma and thus nutritionally rich in nitrogenous compounds such as amino acids, peptides and proteins

Question 26

What species of bacteria are located subgingivally and what are the conditions of their environment?

Answer 26

As a gingival crevice deepens, the environmental factors in the subgingival site become more stable, i.e. neutral pH and anaerobic.

‣ Under these conditions, asaccharolytic and anaerobic and/or proteolytic bacteria such as Fusobacterium, Eubacterium, Campylobacter, Prevotella and Porphyromonas are found.

Question 27

How do saccharolytic and assacharolytic bacteria differ?

Answer 27

Saccharolytic bacteria share the same main metbaolic pathway, whereas assacharolytic bacteria have different metabolic pathways

Question 28

What is GCF?

Answer 28

Fluid/exudate occurring in the gingival crevice with a composition similar to saliva

• Associated with inflammatory response against infection – it is not a product of healthy tissue. Calculus can form from it.
• Contains leukocytes, lymphocytes, monocytes + organic ions
• Functions: ‣ Clearance of bacteria/cleansing of sulcus ‣ Antimicrobial action of antibodies

Question 29

What are the names of the three plaque hypotheses?

Answer 29

1. non-specific
2. specific
3. ecological

Question 30

What is the non-specific plaque hypothesis?

Answer 30

Disease results from interactions among all bacterial species of plaque. More plaque -> more disease. QUANTITY not quality

Question 31

What is the specific plaque hypothesis?

Answer 31

Limited number of pathogens are responsible for disease so therapies can target them (non-specific was abandoned in 20th century)

Question 32

What is the ecological plaque hypothesis?

Answer 32

Environmental factors controlling flora and disease results from shift in balance of resident species