Understanding Fluoride's Role in Preventing Dental Caries

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

2. 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

3. Fluorine in nature

4. 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.

5. 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

6. 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

7. 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.

8. History of fluoride in dentistry

9. 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 Fluoride supplement leaflet in 1902 (Pindborg 1965)

10. 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.

11. 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 13.7ppm. • Samples of other endemic areas – similar results.

12. 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.

13. Fluoride’s mechanism of action in caries prevention

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

15. 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.

16. 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.

17. 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.

18. 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)

19. 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.

20. 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 arefluorapatite (Ca10(PO4)6F2). (Posner 1985)

21. 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

22. 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.

23. Stephen’s Curve Critical pH for hydroxyapatite

24. 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.

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

26. 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-

27. 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 causesover-acidification of the cytoplasm. which can also inhibit the mechanism of glucose transport into the cell.

28. Overview of methods for fluoride delivery

29. 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.

30. 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

31. Thank you