Pellicle and plaque

Pellicle and plaque

Pellicle A layer directly on top of enamel 1-3μm thick (could reach 10 μm), free from bacteria, and is not removed by a tooth brush, but can be removed by a “prophylaxis”, or scale and polish, with abrasive paste

Plaque • Deposit which forms on the enamel surface if the teeth are not cleaned. • It is removed from the smooth surface (but not always from fissures) by tooth brushing. • It is composed of a matrix and bacteria, and is the source of acids dissolving the teeth in caries, as well as the substances which inflame the gingivae leading to periodontal disease

Composition of Pellicle • Protein high in glu + ala (+gly sometimes) and low in S-containing a.a. • Carbohydrates • The protein resembles proteins from submandibular saliva, precipitated by acetic acid • Old pellicle may contain muramic acid (a constituent of bacterial cell wall)

Mode of formation • Selective adsorption of certain salivary proteins by the apatite of enamel (source not clear yet), but acidic proteins are preferred for their ability to bind to apatite surface

Composition of Plaque Plaque • Composition vary from different areas • Two fractions-Water sol. and Water insol. • 80-85% water (mean 82% of wet weight, 50% in cells & 32% in matrix) B- Bacteria A- Matrix

Water soluble fraction: 1/3 of dry weight. Consist of: • proteins, • peptides, • free amino acids, • sugars and • polysaccharides (mainly glucose derivatives)

Water insoluble fractions: 70% of dry weight consist of insoluble matrix and most of the bacterial content Contains: • 10-14% lipids, 10% minerals • 40% protein of high MW • 11% carbohydrates + some in glyco-proteins (total 13-17%) • 10% mineral matter: mainly calcium, phosphate and fluoride. Differs according to position and type of tooth

- composition changes with age of plaque: • Decrease Ca and Pi between day 1-2, then increase to day 4 • Concentration of carbohydrates follows a reverse pattern

Early plaque (specially in the gingival area) contains some epithelial cell which lyses and provide another source of protein for bacteria.

The Composition of plaque fluid

Note: Plaque fluid is supersaturated with ions. Certain substances in saliva (probably acidic proteins) inhibit precipitation

Hypotheses on the formation of plaque matrix • Iso electric precipitation of salivary proteins: increased pH ppt of salivary proteins • Spontaneous precipitation: Surface action by existing plaque denaturation of some salivary proteins & ppt

Chemical changes in salivary proteins: Bacterial enzymes remove sugars from salivary glyco protein decrease solubility ppt. • Effect of calcium ions: Increase Ca in saliva ppt of protein and agglutination of bacteria.

Possible bacterial contribution to plaque matrix: At least part of matrix comes from bacteria (unproven)

The entry of bacteria into plaque • Factors causing clumping or agglutination of bacteria: • Reduction of pH to < 5.5. • Divalent ions e.g. Ca2+ &Mg2+ • Certain protein constituents of saliva & plaque • All lead to reduction of negative charge (i.e. mutual repulsion) of the bacteria

Summary of findings • A glycoprotein in saliva has agglutination properties & readily adsorbs on to apatite. • This favours adhesion of bacteria to teeth surface • It acts as bridges between the organisms • Calcium ions enhance the effect • Only certain organisms react with agglutinating factor (depend on cell wall composition)

Summary for plaque formation - pH- Ca2+- Bacterial enzyme ppt of some salivary proteins Plaque Agglutinating glycoprotein adsorb onto tooth surface and agglutinate bacteria specially in prescnce of Ca2+

Bacteria of Plaque: Mostly acid producing- some proteolytic (over cavities) • Young plaque (1-2 days old): 70% Gram +ve cocci + 20% rods • Old plaque: after 2 days proportion of cocci & rods decrease to 50% by day 7 the rest are filamentous organisms

Poly saccharide synthesis by plaque bacteria • Dextrans or glucans • Bulky gelatinous mass outside bacterial cells formed from sucrose • Sucrose dextran + fructose • could be ≈ 10% of dry wt of plaque, insoluble, • is metabolized by enzyme in plaque • Link is 1:6 & 1:3 equally • reduce permeability of plaque sucrase dextran

Levans: • Sucrose levans + glucose • Fairly soluble. • Linked in 2:6 position. • Rapidly metabolized by plaque enzyme. • Extra cellular levan sucrase

Intra cellular 1:4 glucans: - Formed by some bacteria (filamentous) - Formed from a variety of sugars (e.g. glu, maltose & sucrose) - Broken down between meals

Properties of plaque: • Insoluble in most reagents • Has low permeability • Firmly held on the tooth surface • Shows a decrease in pH after the ingestion of glucose i.e. acid producing

Factors involved in the rise of pH: • Outward diffusion of lactic acid produced from glycolysis of glucose • Conversion of lactic acid into less ionized acetic and propionic acids • The pH rise factor in saliva (sialin) which is a basic peptide containing Arg. It accelerate glucose uptake by salivary organisms, increase acid production & the formation of CO2& base. The effect is obvious at low sugar conc. At high sugar conc. (>.5%) the effect is masked by increased acid production

Alkali production by plaque • NH2group of urea is used to synthesize a.a. which are deaminated to release NH3 • A.A amines CO2 decarboxylation at pH 5 Increased buffering capacity +

Factors in plaque which influence its caries producing power • The type of bacteria: Plaque from caries – free subjects contain less lactobacillus acidophilus and streptococcus mutans than plaque from caries - active subjects • The fasting plaque pH is higher in caries – free subjects • Acid production after ingesting sugar is greater in caries - active subjects • The plaque calcium and phosphate were inversely related to total caries experience

Note: • Fasting pH is higher in caries – resistant than in caries – prone areas within the same mouth • The calcium and phosphate concentrations are higher in caries – free areas

Pellicle and plaque