This article explains fluoride’s role in caries prevention, its mechanism, and methods of systemic and topical administration. It also covers fluoridation benefits, drawbacks, and supporting studies.

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Mechanism of Action

• Increased enamel resistance (or) reduction in enamel solubility
• Increased rate of post-eruptive maturation
• Remineralisation of incipient lesions

1. Fluoride enhances the remineralisation process of enamel by following the mechanism - Fluorohydroxyapatite has lower solubility than hydroxyapatite.
2. Thus for given calcium and phosphate levels in saliva, the degree of supersaturation to fluorohydroxyapatite is larger than hydroxyapatite.
3. The crystal lattice of hydroxyapatite + fluoride = fluorohydroxyapatite.

• Interference with plaque microorganisms
• Modification in tooth morphology

Under cariogenic conditions, carbohydrates are converted to acids by bacteria in plaque biofilm. When pH drops below 5.5, biofilm fluid becomes undersaturated with phosphate ions and enamel dissolves to restore balance. When fluoride (F-) is present, fluorapatite is incorporated into demineralised enamel and subsequent demineralisation is inhibited.

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Modes of Fluoride Administration

1. Systemic Fluorides

• Community water fluoridation
• School water fluoridation
• Milk fluoridation
• Salt fluoridation
• Fluoride supplements

2. Topical Fluorides

• Professionally applied
• Sodium fluoride preparation
• Stannous fluoride preparation
• Acidulated phosphate fluoride (APF)
• Fluoride varnish
• Fluoride-impregnated floss and prophylactic paste
• Fluoride-containing dental materials and devices

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Self-applied

1. Fluoridated dentifrice

2. Fluoride mouth rinse

1. Systemic Fluorides

A. Community Water Fluoridation

It is defined as a controlled adjustment of the concentration of fluoride in the communal water supply so as to achieve a maximum caries reduction and clinically insignificant level of fluorosis.

Studies on community water fluoridation:

• Grand Rapids–Muskegon study
• Newburgh–Kingston study
• Evanston–Oak Park study
• Tiel and Culemborg–Dutch study
• Brantford, Sarnia, Stratford–Canadian study
• Hastings–New Zealand study

For community water systems that add fluoride to their water U.S. Public Health Service recommends a fluoride concentration of 0.7 mg/L (parts per million [ppm]) to maintain caries prevention benefits and reduce the risk of dental fluorosis.

The optimal level of fluoride in water:

This is usually calculated by a formula given by Galagan and Vermillion in 1957.

ppm F = 0.34/E

• E – Estimated daily water intake of children in oz/lb of body weight
• T– Mean maximum daily air temperature in degrees Fahrenheit of area

Diffusion/ halo effect

1. If the residents of fluoridated communities consume numerous foods and beverages manufactured in communities with fluoridated water, fluoride from this fluoridated water becomes incorporated into these products leading to a net increase in fluoride ingestion in fluoridated communities. This leads to mild enamel hypoplasia in those communities.
2. However, in non-fluoridated communities, the benefits of fluoridation are indirectly received by consuming foods and beverages processed from the fluoridated communities. This is termed as diffusion or halo effect that spreads some benefit of fluoridated water to non-fluoridation communities.

Fluoride compounds used for water fluoridation

Chemicals used as a fluoride source should be preferably highly soluble. Chemicals used most frequently are:

• Sodium fluoride
• Hydrofluorosilicic acid
• Sodium silicofluoride
• Ammonium silicofluoride
• Calcium fluoride
• Fluorspar

Types of equipment for water fluoridation

Various types of equipment used for fluoridating water are:

• The saturator system
• The dry feeder system
• The solution feeder system
• Venturi fluoridator system
• Saturation suspension cone

Advantages of water fluoridation

1. A large number of people are benefited.
2. Consumption is regular.
3. Fluoridated drinking water not only acts systemically during tooth formation to make dental enamel more resistant to dental decay but also has a topical effect through the release in saliva after ingestion.
4. Fluoridation of community water is the least expensive and most effective way to provide fluoride to a large group of people.

Disadvantage of water fluoridation

• Interfere with human rights
• Other modes are not considered
• There might not be a common water supply source

B. School Water Fluoridation

1. This procedure was first started in 1954 in St Thomas vs the Virgin Islands by the US Public Health Service Division.
2. The current recommended regimen for school water fluoridation is adding 4.5 times more fluoride.
3. When community water fluoridation is not practical, school water fluoridation is a good substitute.
4. The amount of fluoride added to school drinking water should be greater than normal because children have to stay in school for a short time of the day to compensate for holidays and vacations.

Advantages

• Good results in reducing caries
• Minimal equipment
• Not expensive

Disadvantages

• The benefit does not start for kids until they start school
• Not all children go to school in poor countries like India
• The amount of water drunk can not be regulated

C. Milk Fluoridation

1. Ziegler in 1956 was the first person to mention milk fluoridation as a method of systemic fluoridation.
2. The concentration of fluoride in a 250 mL milk bottle was 0.625 mg.
3. The mode of action of fluoride is both systemic as well as topical.
4. The amount of fluoride to be added depends upon the age of the child and the fluoride concentration in water.
5. This is further complicated by the fact that different children consume varying quantities of milk per day.

Compounds used for milk fluoridation

• Calcium fluoride
• Sodium fluoride
• Disodium monofluorophosphate
• Disodium silicofluoride.

Disadvantages

1. Fluoride is incompletely ionised in milk.
2. Fluoride absorption from milk is lower than from water.
3. There is a wide variation in the intake of milk by children.
4. It requires parental or school efforts.
5. Technical difficulties in implementing the programme.
6. Problems of distribution to children in schools.
7. High cost of fluoridated milk.

D. Salt Fluoridation

• Salt fluoridation began in Switzerland in 1955
• Commonly used slats are sodium fluoride (225mg/kg) and potassium fluoride(250mg/kg)
• Fluoride concentrations (IDEAL): 250-300mg/kg
• A concentration of 200 mg/kg of fluoride is regarded as the minimal acceptable level of fluoride in salt

Advantages

• Fluoridated salt is safe
• Theoretically, fluoridated salt works both topically and systemically to prevent oral cavities
• No supervision of set up or distribution system
• Low cost
• Depends on individual acceptance and rejection

Disadvantages

• There is no exact control over the recommended intake because everyone's salt intake is different
• International efforts to reduce sodium uptake
• When the requirement for fluorides is highest, the use of fluoridated salt is lowest: early in life

E. Fluoride Supplements

1. Examples of supplements are Tablets or drops (to be swallowed); Lozenges (to be sucked or dissolved in the mouth) and Tablets for chewing (fluoritab liquid, Vi-Daylin/F ADC drops, pediaflor drops, etc.).
2. A measured quantity of fluoride, usually in the form of sodium fluoride, is present in supplements in amounts of 0.25 mg, 0.5 mg, or 1.0 mg.
3. Fluoride supplements extend their cariogenic effect by acting both locally and systemically. For its local or topical effect, fluoride must either contact the tooth surface before it is swallowed or pass through the circulation and be secreted in saliva.

Disclaimer- The views and opinions expressed in this article are those of the author and do not necessarily reflect the official policy or position of M3 India.

About the author of this article: Dr Neha Kalantri is a practising dentist from Nashik.