1. Role of fluoride on dental caries Role of fluoride on the prevalence of dental fluorosis The effect of fluoride on plaque bacteria Objectives: DENT 5302 TOPICS IN DENTAL BIOCHEMISTRY 4 April 2007

2. Outline Overview of fluoride Fluoride, dental caries, and fluorosis: Historical perspective Structural-bound fluoride Calcium fluoride-like material Fluoride in saliva and dental plaque How does fluoride work? (anticaries mechanisms) Effect of fluoride on plaque bacteria

3. Potent inhibitor of many enzymes Elimination by kidneys Avid calcified tissue seeker Inhibit and even reverse the formation of dental caries Fluoride Halogen group The most electronegative element 13th most abundant in the crust of the earth Found in virtually all inanimate and living things F - + H + HF Hydrofluoric acid (pK a ~ 3.4) Fluorine: Fluoride: Fluoride: ionic form of fluorine

4. Remarkable decline in dental caries Systemic and topical fluoride F: The cornerstone of modern preventive dentistry Dental fluorosis Reversible gastric disturbances Skeletal fluorosis Death when large doses are taken acutely when lower doses are taken chronically Fluoride is a hazardous substance Water fluoridation Top 10 great public health achievements of the 20th century (CDC)

5. Regular consumption of drinking water with fluoride Reduction of dental caries Mottled enamel Endemic in several regions of the southwestern USA McKay FS. The relation of mottled enamel to caries. J Am Dent Assoc 15:1429-1437, 1928. “…these mottled enamel cases…are singularly free from caries.” Colorado Springs ? substance in drinking water ? Mottled enamel = Dental fluorosis Fluoride, Dental Caries, and Fluorosis F

6. Dean HT et al., Domestic water and dental caries: V. Additional studies of the relation of fluoride domestic waters to dental caries experience in 4425 white children, aged 12-14 years, of 13 cities in 4 states. Public Health Rep 57:1155-1179, 1942. Water fluoride level ~ 1 ppm Dean et al: various levels of fluoride in most water supplies Caries prevention Low prevalence of dental fluorosis

7. Dental Fluorosis Hypomineralization of enamel from excessive fluoride ingestion during tooth development Mild fluorosis (common)Severe fluorosis (rare) Minor cosmetic defect Increased caries risk: Pitting & Loss outer enamel Overintake of fluoride from 0-6 year old Generally less in primary teeth (develop prenatally) Most critical between 15-30 months of age: maxillary central incisors

8. Optimal water F level (~ 1 ppm) 20 % prevalence of very mild or mild fluorosis Dentistry: Mild fluorosis is an acceptable tradeoff for caries prevention Esthetic: ‘mild’ cosmetic defect ? Why are we concerned about dental fluorosis? The prevalence of fluorosis has increased No fluorosis: 27 % dissatisfied with their tooth color Mild fluorosis: 50% dissatisfied

9. Water Fluoridation EPA (Environmental Protection Agency) Max. Contaminant Level (Primary Drinking Water Standards) = 4 ppm F Naturally existed F in some municipal water & wells : 4-8 ppm F or higher 1945 Grand Rapids Michigan 1948: Grand Rapids had 60% less DMFT than Muskegon ‘control’ city Optimal level: 0.7 - 1.2 ppm F Colder climates drink less water need higher fluoride level

10. USA: 67% (170 millions) on public water system receive fluoridated water Centers for Disease Control and Prevention, 2002 Halo effect Persons not residing in fluoridated communities Foods and beverages produced with fluoridated water The most cost-effective community-based approach for caries prevention Direct annual cost of fluoridation: $ 0.68-3.0 per person per year $1 invested in water fluoridation saves > $38 in treatment costs

11. Discussion: (group of 6-8) 1.The optimal level of fluoride in water as determined by this graph is 1 ppm. What are the rationales? 2.Why in Minnesota the level of added fluoride in water varies from 0.7 to 1.2 ppm?

12. How does fluoride work? Systemic incorporation into enamel during development ‘More perfect’ enamel crystals Less acid soluble Historical perspective The more fluoride incorporated, the better cariostatic effect Shark enamel (100% fluoroapatite) can develop caries lesion! Øgaard B et al. Scand J Dent Res 96:209, 1988. Microradiographic study of demineralization of shark enamel in a human caries model. Cariostatic effect of fluoride

13. The caries-reducing effect of fluoride is primarily achieved by its presence during active caries development at the plaque/enamel interface where it directly alters the dynamics of mineral dissolution and reprecipitation, and to some extent, affect plaque bacteria. Current philosophy Change tooth morphology Effect on plaque bacteria Inhibit demineralization and enhance remineralization process Goal: Try to maximize benefit with minimal adverse effects MORE IS NOT NECESSARILY BETTER! Controversial and not universally accepted Debatable: need much higher concentration of fluoride to be effective Cariostatic Mechanism of Fluoride

14. Effect of fluoride on plaque bacteria 1940: Fluoride inhibited carbohydrate metabolism in pure cultures of streptococci and lactobacilli. Bibby BG, van Kesteren M. The effect of fluoride on mouth bacterial. J Dent Res 1940:19;391-402. Fluoride affects oral bacteria and dental plaque ecology IMPLY a reduced risk of caries

15. F inhibits bacterial adsorption F reduces proportion of cariogenic bacteria in dental plaque F decreases acid production In vitro: 9500 ppm F in solution inhibit bacterial adsorption to hydroxyapatite Clinical: rinses & toothpaste with Sn or amine F reduce plaque deposit Clinical: only high concentration of fluoride works! No difference in subjects from area upto 21 ppm F in water Reduced MS in plaque after daily use of APF gel (12,300 ppm F) Chemostat: 19 ppm F prevent MS from growing to a larger proportion Fluoridated water or daily rinse with 0.2% (~900 ppm) NaF solution Reduce 0.1 - 0.2 unit in pH drop after a sucrose challenge No effect after 0.05 % (~200 ppm) rinse Effect on dental plaque bacteria

16. Bound to enzymes - Enolase - Proton-extruding ATPase Cytoplasmic acidification H + + F - HF HF HF forms when external pH is lower than pK a (3.4) H + + F - Accumulation of H+ Accumulation of fluoride Fluoride enters cell as HF (not F - ) Antimicrobial effect of F 1 1 2 2

17. ‘Fluoride has inhibitory effects on plaque metabolism’ In vitro: 9500 ppm F in solution inhibit bacterial adsorption to hydroxyapatite Reduced MS in plaque after daily use of APF gel (12,300 ppm F) Fluoridated water or daily rinse with 0.2% (~900 ppm) NaF solution reduced 0.1 - 0.2 unit in pH drop after a sucrose challenge No effect in pH drop after 0.05 % (~200 ppm) NaF rinse No reduction of MS in plaque in subjects from area upto 21 ppm F in drinking water How much fluoride is needed for antimicrobial effect? To what extent do these effects contribute to caries prevention?

18. Effective at a few ppm F ppm F to reduce solubility << ppm F for antimicrobial effect At pH 4-5 Fluoride in solution reduces the amount of enamel dissolved The most important cariostatic mechanism of F: De- and Remineralization How much fluoride is needed to reduce enamel solubility?

19. Lower dissolution rate F - substitute OH - Decrease crystal dimension (F- is smaller) Strong attraction with calcium (F: the most electronegative) Stabilize the lattice structure Hydroxyapatite lattice structure F OH Ca Improve the crystallinity F - fill vacancy H-bond with O H-bond F Fluoride in HAP crystal: Structurally-bound F ‘Fluorhydroxyapatite’ ‘Fluoridated hydroxyapatite’ ‘Fluoroapatite-like material’

20. Range from 5-50 ppm wet weight 1% is available as fluoride ion 15-75% is ionizable Some firmly-bound fluoride (bacterial uptake?) Plaque matrix concentrate fluoride from saliva: How much fluoride is in dental plaque? +ve charges in matrix & on bacterial surface attract Ca 2+ Ca 2+ bind fluoride.

21. Calcium fluoride Oral mucosa? Plaque fluid F and Saliva F after 1-min rinse with NaF ( 900 ppm) or MFP ( 1000 ppm) Plaque fluid F Saliva F F decreases exponentially Elevated for ~ 3 hours Clinical study: F level in saliva and plaque remained for 18 h F reservoir Ekstrand J. Enhancing effects of fluoride. Cariology for the nineties, 409-420.

22. ten Cate JM, van Loveren C. Fluroide Mechanisms. Dent Clin N Am 1999;43:713-742. Adapted from Sjögren T, Birkhed D. Caries Res 1993;27:474. Age 26 + 8 24 + 8 Male / female 9 / 14 13 / 11 Salivary flow (ml/min) 1.5 + 0.3 1.5 + 0.5 MS (log CFU/ml saliva) 4.2 + 1 5.3 + 1 Lactobacilli (log CFU/ml saliva) 3.8 + 0.8 4.5 + 1.2 Brushing time (min) 2.8 + 1.6 2.6 + 2 Amount of toothpaste (g) 1.1 + 0.5 1.2 + 0.6 DMFT 4.8 + 5 * 18.9 + 7.3 Decay surface 0 * 3.8 + 3.1 Rinse frequency1.5 + 0.7 * 3.6 + 1.9 Amount of water to rinse (ml) 70 + 60 * 190 + 10 F in saliva (immediate) (mM)0.6 + 0.4 * 0.3 + 0.3 F in saliva (accumulate) (mM·min) 6.9 + 3.9 * 3.9 + 2.9 Characteristics Low Caries-Active High Caries-Active Discussion: (group of 6-8) What characters affect caries development?

23. Discussion: (group of 6-8) I believe that the main anticaries effect of fluoride is by changing the equilibrium towards remineralization, not antimicrobial effect. Why?

24. Recommended references 1. Ten Cate JM, van Loveren C. Fluoride Mechanisms. Dent Clin North Am 1999;43(4):713-742. 2. Featherstone JD. The science and practice of caries prevention. J Am Dent Assoc 2000;131:887-899. 3. Gordon Nikiforuk. Understanding Dental Caries 1. Etiology and Mechanisms, Basic and Clinical Aspects. Basel; New York: Karger 1985. Chapters 4. 4. Gordon Nikiforuk. Understanding Dental Caries 2. Prevention, Basic and Clinical Aspects. Basel; New York: Karger 1985. Chapters 3. 5. van Loveren C. Antimicrobial activity of fluoride and its in vivo importance: Identification of research questions. Caries Res 2001;35(suppl 1):65-70. 6. Fejerskov O. Changing paradigms in concepts on dental caries: Consequences for oral health care. Caries Res 2004;38:182-191. 7. Ten Cate JM. Review on fluoride, with special emphasis on calcium fluoride mechanisms in caries prevention. Eur J oral Sci 1997;105:461-465.