Fluoride & Caries Prevention

• Fluoride's role in oral and dental science involves understanding its properties. Understanding its application is key to patient management, preventative education, and overall oral health.
• GDC learning outcomes include applying appropriate preventative measures, health promotion, and evidence-based prevention.

Pre-Reading for the Topic

• Aetiology of dental caries and histology of enamel and dentine lectures are recommended. Aetiology of dental caries involves the interaction of susceptible tooth surfaces, time, plaque bacteria, and fermentable carbohydrates.

Intended Learning Outcomes Regarding Fluoride

• Key milestones in the history of fluoride and its use in caries prevention are outlined. The stages in fluoride deposition and modes of action are described. The learning outcomes include being able to explain how fluorosis occurs, and to identify fluorosis and assess its severity.

Refresher Session: Enamel Composition

• Normal enamel is primarily made of hydroxyapatite, comprising 96% of enamel's composition. Enamel has a lattice structure and primarily consists of phosphate and calcium ions. At a critical pH of 5.5 for hydroxyapatite, the tooth surface demineralizes, breaking down into its component ions.
• If pH remains low and is not neutralized over time, extensive demineralization leads to caries. Infrequent attacks result in lower caries risk, while frequent attacks increase demineralization and higher caries risk.

Fluoride Relevance

• Before linking fluoride to dentistry, understanding its properties and history is important to understanding its value as a dental professional

Fluorine Fundamentals

• Fluorine is a halogen within the periodic table, has the symbol F and atomic number 9. It is highly reactive with metals, forming salts or halides referred to as fluoride. Fluorine is found naturally in water, rocks, soil, and tea.

Key Historical Events in Fluoride Research and Application

• 1874: Dr. Erhardt.
• 1892: Sir James Crichton-Browne
• 1901: Frederick McKay
• 1902: Sale of fluorine compound.
• 1909: Investigation of Colorado Stain.
• 1912: McKay investigates similar staining in Naples, Italy.
• 1916: GV Black paper published on Colorado Stain.
• 1930: Dr. HT Dean conducts 'shoe leather'/'21 cities' studies.
• 1931: Staining on teeth is noted in Bauxite, Arkansas
• 1932: McKay links mottling and caries reduction.
• 1933: Ainsworth conducts UK water fluoride comparison studies.
• 1940: Fluoride research continues
• 1945: First experiment of artificial water fluoridation.
• 1955: Artificial water fluoridation is attempted in the UK
• 1960: Anti-fluoride campaigns emerge.
• 1964: Birmingham is fluoridated.
• 1976: The Royal College of Physicians' enquiry into water fluoridation
• 1980: Mrs. McColl opposes water fluoridation.
• 1985: The KNOX report is released.
• 2000: The York Study is conducted.

Summary of Fluoride History

• 1916: Dr Frederik McKay documented a 'stain' on teeth in Colorado Springs and enlisted GV Black's help to investigate and GV Black published a paper.
• 1931: Churchill, a chemist in Arkansas, noticed a similar effect in local children with changes in their water source, identified higher fluoride content and advised there was no definitive link to mottling.
• 1932: McKay suggested the compound causing mottling may reduce caries.
• 1930-1940: Dr H Trendley-Dean researched links between fluoride, mottling, and caries reduction
  • Results showed an increase in mottling with increased fluoride. They also showed decreased caries if water was fluoridated. 1ppm fluoride was found to be the optimal level. An Index for Fluorosis' was developed to classify severity of tooth mottling
• 1985: The Knox Report reviewed papers, and concluded has no link and fluoridated drinking water is safe.
• 2000: The York Report reviewed evidence, and found no association between water fluoridation and fractures, or cancer.
• Cochrane Review 2015: Fluoridation increased no decay in baby teeth by 15% and no decay in permanent teeth by 14%. Fluoridated water reduces caries by 26% in permanent teeth and reduces these in baby teeth by 35%.
  • 0.7ppm gives a 12% chance of Fluorosis, and 73% of studies focused on natural fluoridation.

Relevance Today

• Currently, water fluoridation benefits are well researched but it is not universal and remains controversial. In the UK, around 10% of the population has fluoride in their water.

Fluoride Uptake

• Fluoride absorbed into the tooth surface makes it resistant to demineralization. This occurs at pre-eruptive (systemic fluoride) and post-eruptive (topical fluoride) stages.

Matrix Secretion Stage

• Fluoride is absorbed from systemic sources and travels to developing tooth buds via blood. It deposits fluoroapatite during enamel formation, replacing hydroxyapatite. Excess fluoride inhibits ameloblast activity, potentially causing fluorosis.

Maturation Stage

• Fluoride is absorbed from systemic sources, occurs after calcification but before eruption, deposition continues with more fluoride, and fluoroapetite is formed.

Post-Eruptive Stage

• Healthy tooth surfaces experience a drop in pH due to bacterial acid, leading to loss of calcium and phosphate. This demineralizes the tooth. An increase in pH and fluoride addition with calcium and phosphate remineralizes the tooth with fluoroapetite

Key Points

• The most fluoride is acquired in the 2-3 years post-eruption. Demineralized enamel absorbs fluoride more readily because it is more porous. A regular supply of low-level fluoride is essential.
• Fluoride is more effective at reducing progression once the process has started because it is more readily absorbed.

Fluoroapetite Importance

• Fluoroapetite is formed by fluoride replacing hydroxyl ions during remineralisation and is less soluble due to a lower critical PH of 4.5. This newly formed molecule is more stable due to improved stronger hydrogen bonds. It also helps inhibit demineralisation. Fluoroapetite makes the tooth more resistant to acid attacks, and this reduces the caries incidence.

Fluoride Sources

• Fluoride is derived from topical applications that create a reservoir of fluoride in saliva and bonds to calcium in saliva forming CaF2.

Maintaining Fluoride Supply

• Topical fluoride sources that help ensure a supply include; toothpastes, mouthwashes, glass ionomer cements, fluoride varnishes and tablets, and also fluoride in water. Prescription is required for toothpastes if they contain 2800 or 5000ppm of fluoride, and for fluoride tablets.

Fluoride's action

• At concentrations over 1%, fluoride has a bactericidal effect. It can be toxic to bacteria like strep mutans. It can inhibit glycolysis by preventing glucose uptake through the cell wall/its breakdown and inhibits transport of sugars. Bacteria's food supply is cut, so it can't metabolize sugars. When PH drops, H+ and F- bond to form HF, and this diffuses across the bacterial cell wall.

Fluoride Action on Enamel Surface

• Fluoride reduces enamel surface energy by reducing wettability, preventing pellicle formation. This reduces plaque and bacterial adhesion, lowering the likelihood of caries.

Fluoride's Impact on Tooth Morphology

• Some evidence suggests that systemic fluoride may alter tooth morphology during development, such as shallower pits, reduced fissure depth, and lower cusp height can make the teeth more cleansable.

Fluoride on Dentine and Cementum

• Root caries occurs in the surfaces of dentine and cementum when the gums recede. They are more common in xerostomia patients and progress more quickly than normal caries because they're less mineralized. Fluoride helps by incorporating into the surface during remineralisation, reducing surface wettability, and antibacterial effects.
• Proffesional and self aplications of fluorides are essential.

What does the research say about fluoride for Root Caries?

• Professionally applied fluoride reduces risk of root caries at 2 years and self-applied fluoride reduces risk of root caries at 1 year
• Professionally and self-applied fluoride is essential for caries prevention in exposed root surfaces and will become more of an issue as the population gets older.

Fluorosis Explained

• Fluorosis occurs due to excess ingestion of fluoride: resulting in changes in tooth enamel, varying from white opacities to severe brown-yellow mottling. The dose of fluoride and age a person was exposed to it can affect how the teeth are affected.

How Does Fluorosis Occur?

• It is thought that fluoride inhibits ameloblast activity during matrix formation and maturation, resulting in hypomineralised enamel. The caused hypomineralisation causes enamel to become more porous, leading to discoloration. Enamel defects are not always a sign of flurosis, they can be caused by trauma, disease, drugs and genetics.

Aetiological Agents of Fluorosis

• Dietary fluoride supplements, drinking water, toothpaste and topical applications can cause fluorosis primarily between the ages of 0-8 years depending on the development stage of the teeth.

Identifying Fluorosis

• Characteristics of mild fluorosis include: the affected area near the tips of cusp, incremental lines pencil shading,. Affected teeth calcify slowly and are usually bilateral. Non-fluoride enamel opacities are centered in one area and affect the whole tooth. An enamel surface that is etched is not fluorosis.

Indices for Recording

• The two main indices are the Dean Index from 1942, and the Thylstrup and Fejerskov index from 1978. When recording, a score of 0 means that enamel has normal translucency and scores of 1-4 have increasing levels of fluorosis with no loss of the outermost Enamel. Scores of 5-9 mean the tooth has loss of enamel..

Summary: Stages of Action and Fluoride Deposition

• There are multiple stages of fluoride deposition: calcification stage systemic, post-eruption stage topical, and maturation stage systemic.

Summary: Actions of Fluoride

• Modes of action of fluoride: effects on tooth morphology, action on hydroxyapatite, action on enamel surfaces, and action on bacteria.