The role of fluoride in dental caries prevention Dr Ahmad Aljafari BDS, MFDS RCSEd, MSc, PhD

Lecture outline Fluorine in nature History of fluoride use in dentistry Fluoride’s mechanism of action in caries prevention Overview of methods for fluoride delivery

Fluorine in nature

Fluorine Fluorine (F),has an atomic number of 9. Part of the halogen group. At room temperature, it is a gas of diatomic molecules (F2) The gas is pale, yellow- green, pungent, and poisonous. Used in aluminum refining, refrigerants and cookware manufacturing, and pharmaceuticals.

Fluorine in nature The 24th most abundant element in the universe. The 13th in earth crust. Highly reactive. Hence, combines with other elements (e.g., calcium, sodium) in nature and is found only in mineral form. Fluorite (CaF2) is the primary mineral source of fluorine, although other forms, such as fluorapatite (Ca5(PO4)3F) and cryolite (Na3AlF6) are also used. Fluorite

What is fluoride? The ionic form of Fluorine. An inorganic, monatomic anion (F-). In terms of charge and size, the fluoride ion resembles the hydroxide ion

Fluoride in nature Mineral form in earth crust (e.g. fluorite). Seawater (1.1 ppm). Fresh water (highly variable). Fish (0.2-0.4mg/100g). Tea: (0.1 – 0.6mg/100ml). Other foods might contain fluoride in very low concentrations.

History of fluoride in dentistry

1874: Carl Erhadt suggested potassium fluoride supplements to preserve teeth. 1892: Sir James Crichton Browne noted an increased susceptibility to caries when switching from brown (higher in Fluoride) to white bread First mentioned Fluoride supplement leaflet in 1902 (Pindborg 1965)

1901: Dr Fredrick McKay noticed permanent white flecks, or yellow or brown spots on the teeth of his patients (Colorado stain). Called the stain “Mottled enamel”. Noted it was not more susceptible to caries than normal l enamel The distribution of the condition made him conclude it was related to water supply, but couldn’t define cause.

Samples of other endemic areas – similar results. 1931: High incidence of ‘mottled enamel’ in Bauxite, Arkansas. An aluminum mining town. Mr H.V Churchill noted Fluoride was present in their water at a level of 13.7 ppm. Samples of other endemic areas – similar results. Similar occurences recorded in

1931: Dr H.T Dean looked into the issue of enamel mottling and fluoride in water across the USA. Concluded that increased Fluoride concentration in water leads to higher prevalence of mottling Noted reduced caries prevalence in children with access to fluoridated water in comparison to with non-fluoridated water. Fluoride in water in the US and

Fluoride’s mechanism of action in caries prevention

Mechanism of Action Pre-eruptive (Systemic): Less important Post-eruptive (Topical): More important

Pre-eruptive (systemic) Used to be the focus of research prior to the 1980s. Nowadays we know that its impact is minimal. It is insufficient for caries prevention.

Pre-eruptive (systemic) Earlier work suggested that: It improves tooth morphology : More rounded cusps. Shallower inclines. More favourable fissure patterns. Is incorporated into enamel to make it more resistant to the demineralization process. More recent work demonstrated that fluoride incorporated during tooth development does not reduce solubility.

Post-eruptive (topical) The relevant mode of action nowadays. The outcome is the result of three processes: 1. Reduction of susceptibility to demineralization. 2. Encouragement of enamel remineralization. 3. Inhibition of cariogenic bacteria metabolism.

Reduction of susceptibility to demineralization Enamel is constituted of 95% mineral, 4% water, and 1% protein and lipid. The minerals form hydroxyapatite crystals (Ca10(PO4)6OH2). The crystals form enamel rods extending from the DEJ to the surface Robinson (2009)

Reduction of susceptibility to demineralization Conditions during tooth development and after formation frequently lead to mineral substitutions within the crystals. Ions such as carbonate and magnesium tend to replace calcium in the crystals. This disrupts crystal structure. In turn, this facilitates demineralization upon acid attacks and makes remineralization more difficult.

Reduction of susceptibility to demineralization In the presence of Fluoride surrounding enamel, it replaces the hydroxyl ion (OH-) Substitution occurs mostly on enamel surface (5-10 µm). New crystals formed are fluorapatite (Ca10(PO4)6F2). (Posner 1985)

Reduction of susceptibility to demineralization The resultant crystals are more resistant to demineralization (critical pH for Fluorapatite is 4.7) Due to fluoride’s high electro- negativity and symmetrical charge distribution. Lussi 2012

Encouragement of enamel remineralization At a pH of 7, calcium and phosphate ions in the enamel and the surrounding plaque fluid are in an equilibrium. Acids produced by cariogenic bacteria in the dental plaque mean there is a release of H+ and a drop in pH. H+ decreases the OH– concentration and interacts with the phosphate ions in the plaque fluid. At a pH of 5.5 (critical pH), the calcium and phosphate ions concentrations in the plaque fluid are not sufficient to maintain the enamel in a stable equilibrium and hydroxyapatite crystals start to dissolve.

Stephen’s Curve Critical pH for hydroxyapatite

Encouragement of enamel remineralization During remineralization, calcium and phosphate ions move from the supersaturated plaque fluid to the enamel. When fluoride is present in the plaque fluid, it gets absorbed to the enamel crystals and attracts the calcium and phosphate ions. It also reduces the uptake of carbonate. The resultant crystals (fluorapatite) are less soluble. F at low levels among enamel crystals inhbiits dissolution of tooth mineral by enhancing the formation of a more stable structure with a lower solubility. Solubility boundary shift to a lower ph

Encouragement of enamel remineralization 0.03 ppm in solution around enamel leads to remineralization enhancement 0.08 ppm – optimum concentration.

Inhibition of cariogenic bacteria metabolism Fluoride in its ionic form is unable to cross the cell membrane. In a lower pH some of the fluoride becomes in the form of hydrofluoric acid (HF). HF can rapidly diffuse into cariogenic bacterial cells. Inside the cell, HF dissolves back to H+ and F-

Inhibition of cariogenic bacteria metabolism Fluoride presents an antimicrobial effect in two possible mechanisms: Interacting with the enzyme enolase to reduce acid production directly.  Interacting with phosphotransferase system (PTS) pathway to decrease the amount of sugar entering the cell reducing acid production indirectly. The H+ accompanying the fluoride into the cell causes over-acidification of the cytoplasm. which can also inhibit the mechanism of glucose transport into the cell.

Overview of methods for fluoride delivery

Overview of methods for fluoride delivery The ideal method to deliver fluoride should: Provide a long-term source for fluoride in the solution surrounding the enamel. Lead to only a minimal amount of fluoride being systemically ingested. Be cost-effective.

Overview of methods for fluoride delivery Fluoride supplements: Drops Tablets Fluoridated water Fluoridated foods (salt, milk) Home applied fluoride: Toothpaste Mouthwash Fluoride in dental materials Professionally applied fluoride Gels Varnish Slow release devices

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