Immunization Against *Streptococcus mutans*

• Colonization of Streptococcus mutans (MS) can be reduced through methods involving whole cells, glucosyltransferases, or cell wall-associated proteins.
• Research shows protection has been achieved in rodents and primates.
• There is no approval yet on human trials for immunization.

Passive Immunization

• Tooth surfaces are coated with antibodies or synthetic antibody fragments.
• This process reduces MS colonization in humans and primates.
• It is a targeted (for site, bacterial/multiple species), safe, acceptable, non-invasive method.
• There is no cross-reaction with human tissues or side effects.

Chemistry of Enamel

Enamel Crystals

• Enamel is composed of millions of crystals with approximately hexagonal outlines.
• Individual crystals are organized into bundles called enamel prisms (or rods).
• The prisms interweave with alternating prisms in opposing directions.
• Crystals appear as elongated hexagons with a column of hydroxyl groups in the center.
• Mineral crystals consist of hydroxyapatite, an inorganic calcium phosphate salt.
• Biological hydroxyapatite differs from non-biological forms (e.g., in granite) due to variations in crystal size, morphology, and the presence of other crystals.
• Pure hydroxyapatite's stoichiometry is Ca10(PO4)6(OH)2, but tooth and bone apatite contains other ions like carbonate, magnesium, and fluoride.
• Apatite variations include missing calcium and hydroxyl ions (hydroxyl is reported to be 20-30% lower in enamel).
• Extraneous ions (impurities) like carbonate, fluoride, magnesium, and sodium are often present, with significant amounts of carbonate and acid phosphate. Fluoride replaces hydroxyl to some extent.

Fluoride Substitution

• Hetero-ionic substitution occurs when an endogenous ion is replaced.
• Fluoride substitutes for hydroxyl ions and fits better in the hydroxyl position, thus stabilizing crystal structure.
• Fluoride's electronegativity pulls ions together, lowers lattice energy.
• The hydrogen bonds point toward the fluoride ion, further stabilizing the structure.
• Fluoridated crystals are harder to dissolve in acid & easier to re-deposit at lower concentrations.

Carbonate Substitution

• Carbonate replaces hydroxyl or phosphate/acid phosphate.
• The poorer fit of carbonate in the lattice leads to a less stable, more acid-soluble apatite phase.
• Carbonate substitutions and ion vacancies increase the solubility of enamel.

Magnesium Substitution

• Magnesium can replace calcium to a limited extent.
• Magnesium has a destabilizing effect on the apatite lattice, similar to carbonate.
• Carbonate and magnesium have a synergistic effect, increasing their incorporation and the acid solubility of apatite.

Density Distribution

• Apatite crystal density varies throughout enamel.
• Density decreases from the tooth surface toward the dentine, while porosity, water, and organic content increase.
• Low mineral density exists near occlusal fissures with complicated prismatic structures due to poorer prismatic packing.
• Inner enamel regions have more water, space, and protein due to less prismatic packing.
• Low mineral density exists in cervical regions, with higher density in areas like cusps.

Ion Incorporation

• Carbonate incorporation occurs during tissue development.
• Carbonate rises from 2% at the enamel surface to 4-6% towards the dentine.
• High concentrations of carbonate may be found in areas like fissures in molars.
• Magnesium is incorporated during enamel formation (about 1/10th the concentration of carbonate), showing a similar distribution pattern.
• Magnesium concentrations increase towards the dentine surface, from 0.2% at the enamel surface to 0.5% close to dentine, exhibiting isolated pockets of high concentration.
• Fluoride distribution is highest in the outermost enamel, decreasing dramatically towards the interior.
• Unerupted enamel scavenges fluoride ions from tissue fluids.
• Excessive fluoride ingestion during amelogenesis leads to fluorotic enamel (enamel fluorosis).
• Fluorosis may show bands with high or low fluoride and hypomineralized bands with sub-superficial porosities.

Fluorosis

• Enamel is more caries-resistant due to high fluoride content.
• Severe cases might have pits due to loss of fragile areas upon tooth eruption.

Apatite Crystals in Dentine

• Dentine crystals have similar chemistry to, but are smaller than, those in enamel.
• Dentine contains higher levels of carbonate and magnesium.
• Hydroxyapatite crystals are arranged along and between collagen fibril meshwork, which makes up most of the organic matrix.
• Dentine collagen is highly cross-linked and stable, with the organic matrix ≈ 20% of dentine's weight.

Chemistry of Enamel Caries

Saturation

• Ionic materials precipitate when the surrounding solution is above the saturation point.
• Ionic materials dissolve when the surrounding solution is below the saturation point.
• Saturation is achieved when the solubility product (Ksp) reaches a certain value.
• For calcium hydroxyapatite: Ksp = [Ca]10 x [PO4]6 x [OH]2
• Dissolution leads to caries if fluid is not supersaturated.
• Remineralization (repair) requires supersaturated solutions.
• pH changes affect the nature of phosphate anion, altering the solubility product equation.
• Incorporation of fluoride decreases the solubility product, but carbonate and magnesium increase it.
• Crystalline hydroxyapatite dissolves in plaque fluid only if pH is reduced to less than 5.5.
• Lower pH reduces PO43- concentration; adding H+ shifts the equilibrium, reducing the ability to maintain Ca2+ bonds. Dissolution occurs.
• Above pH 5.5, HPO42- dominates; below pH 5.5, H2PO4- dominates.
• H+ from bacterial metabolism binds to PO43-, reducing its ionic bond to calcium.
• At pH ≤ 5.5, the H2PO4- ionic bond weakens, leading to hydroxyapatite dissolution.

Demineralization and Remineralization

• Undersaturation below pH 5.5 leads to mineral dissolution.
• Higher pH & presence of fluoride leads to biofilm fluid supersaturation and reprecipitation of minerals in enamel, reducing net demineralization.
• Acid is converted to salts by saliva after sugar exposure ceases, increasing pH.
• Biofilm becomes supersaturated with fluorapatite and hydroxyapatite.
• Lost calcium and phosphate are efficiently recovered with the aid of fluoride.
• Fluoride ions are shift towards an more sustainable equilibrium in an acidic environment because they are less soluble.

White Spot Lesions

• Lesions are an early clinical sign of caries seen as white spots.
• Bacterial acid dissolves the mineral, creating tiny pores that dry out, causing light scatter.

Carious Lesion of Enamel

Translucent Zone

• The deepest part is adjacent to sound enamel.

Dark Zone

• Region superficial to the Translucent one, and shows increased porosity of small holes that are inaccessible. Possible reprecipitation has occurred.

Body Of Lesion

• Shows significant porosity with large pores.

• Initially soluble carbonate and magnesium-rich components are removed.

• Removal of minerals is not characteristic of hydroxyapatite at first.

Tooth Surface Fluoride

• Fluoride is found in enamel surface affected by non-cavitated caries lesions.
• Sound enamel has a higher fluoride content than sound subsurface enamel.
• Higher fluoride content is measured overlying the lesion compared to the surrounding enamel.
• Fluoride content in the zones of the caries lesion is also higher versus the sound enamel.

Chemical Changes

• Soluble components and magnesium carbonate are first removed.
• Accompanied by a slight increase in fluoride
• Loss of destabilizing ions and addition of fluoride shifts environment toward precipitation of those ions, which can be seen in the Dark Zone for example after initial dissolution.
• Dissolution continues in the lesion by removing reprecipitated minerals because a lower pH is obtained nearer Enamel, making a mineral of greater stability become soluable

Enhancing Fluoride

• Fluoride's effectiveness is limited by intrinsic salivary Ca2+ and PO43-.
• Supplements of bioavailable calcium and phosphate into oral cavity may facilitate fluoride.
• Increasing CaF2 assists persistence of Calcium and therefore Fluoride near surfaces of Enamel with Ca addition when using Fluoride treatments
• Patients with these treatments should brush with fluoride and not rinse afterward as well

Biomimetic Remineralization

• Remineralization occurs via Casein phosphopeptide: amorphous calcium phosphate

CPP

• Stabalizes high Concentrations of Calcium and Phosphate ions near the surface as it binds them from nanoclusters
• These Complexes bind with Biofilm to maintain supersaturation with calcium and phosphate ions close to surfaces as they establish Buffered environments
• Precipitation is encouraged alongside ion presence across surface layers on the tooth

SAP

• Self Assembling Peptides can be synthesised from Natural amino acids yielding many benefits
  • Increases net mineral gain by inhibiting demineralization, instead promoting remineralization
  • Nucleate hydroxyapatite de novo
  • Mimic enamel matrix proteins which control initial mineral deposition (nucleation) and subsequent crystal growth
  • Capable of infiltrating white spot lesions
  • Candidate fill material in areas of no drilling

Colonization of Streptococcus mutans can be reduced through immunization methods. Passive immunization involves coating tooth surfaces with antibodies or synthetic antibody fragments to reduce MS colonization. This method is targeted, safe, and non-invasive, with no cross-reaction with human tissues or side effects.