Chapter 34 Fluorides (Notes)

What is Fluoride?

• Fluoride provides the most effective method for dental caries prevention and control.
• Two general means by which fluoride is made available to teeth:
  • Systemically: through the circulation to developing teeth (pre-eruptive exposure).
  • Topically: directly to exposed tooth surfaces in the oral cavity (post-eruptive exposure).
• Maximum caries-inhibiting effect occurs when there is systemic exposure before tooth eruption and frequent topical fluoride exposure throughout life.

Role of Fluoride in Remineralization

• Fluoride plays a key role in remineralization by promoting formation of fluorapatite, a stronger mineral that replaces hydroxyapatite in enamel.
• Fluorapatite is more resistant to acid attack, providing protection against future decay.

Fluoride Uptake

• Uptake depends on fluoride level in the oral environment and duration of exposure.
• Hypomineralized enamel absorbs fluoride more readily than sound enamel and can incorporate fluoride to form fluorapatite.
• Demineralized enamel remineralized in the presence of fluoride ends up with a higher fluoride concentration than sound enamel.

Fluoride Metabolism

• Sources of fluoride intake:
  • Fluoridated or naturally occurring drinking water.
  • Prescribed dietary supplements.
  • Foods and beverages prepared with fluoridated water.
  • Other small amounts from dentifrices, mouthrinses, and additional fluoride products.
• Absorption:
  • Fluoride is rapidly absorbed as hydrogen fluoride (HF) through passive diffusion in the stomach.
  • Absorption rate depends on the solubility of the fluoride compound and gastric acidity.
  • Most fluoride is absorbed within approximately 60\ \text{min}.
  • Fluoride not absorbed in the stomach is absorbed in the small intestine.
  • Absorption is reduced when fluoride is taken with milk or other food.
• Distribution and blood levels:
  • Plasma carries fluoride for distribution throughout the body and to the kidneys for elimination.
  • Maximum blood levels are reached within \approx 30\ \text{minutes} of intake.
  • Normal plasma fluoride levels are low and rise and fall with intake.
• Excretion:
  • Most fluoride is excreted by the kidneys in urine; smaller amounts are excreted via sweat and feces.
  • Limited transfer from plasma to breast milk for excretion via milk.

Fluoride in Tooth Structures

• Enamel:
  • Fluoride is a natural constituent of enamel.
  • The outer surface has the highest fluoride concentration, which falls toward the interior of the tooth.
• Dentin:
  • Fluoride level may be greater in dentin than in enamel.
  • Higher concentration is present at the pulpal/inner surface where exchanges occur.
  • Newly formed dentin absorbs fluoride rapidly.
• Cementum:
  • Fluoride level in cementum is high and increases with exposure.
  • When clinical attachment level recedes, the root surface is exposed to oral fluids.
  • Fluoride is available to cementum from saliva and all fluoride sources used by the patient (water, dentifrice, mouthrinse).

Effects and Benefits of Fluoridation

• Fluoridated water provides systemic fluoride for developing teeth and topical fluoride for erupted teeth throughout life.
• Appearance of teeth:
  • Optimum or slightly higher fluoride levels yield white, shiny, opaque teeth without blemishes.
  • Slightly higher levels can cause mild enamel fluorosis (white banding or flecks); most fluorosis today is mild and not an esthetic problem.
• Caries reduction and progression:
  • Overall caries reduction with water fluoridation alone (excluding other topical sources): about 27\% across all ages.
  • Anterior teeth tend to receive more fluoride protection than posterior teeth.
  • Caries progression is slowed; first-erupting surfaces benefit from fluoride exposure.
• Root caries: lifelong residents of fluoridated communities have ~50\% less root caries experience.
• Primary teeth: fluoridation from birth reduces caries incidence by up to 40\% in primary dentition.
• Tooth loss: lower incidence of caries-related tooth loss when fluoride is present in drinking water.
• Adults: benefits persist throughout life when living in a fluoridated community.

Topical Fluoride Applications

• Topical fluorides are essential for patients of all ages.
• Primary sources:
  • Fluoridated water
  • Fluoride toothpaste
• Additional topical sources may be professionally applied and/or self-applied by patients at elevated caries risk.

Topical Fluoride Formulations

• Self-applied topical fluorides (OTC and Rx): toothpastes, mouthrinses, and gels.
• Professional topical fluorides: higher-strength rinses, gels, foams; varnishes; and silver diamine fluoride (SDF).
• Neutral NaF foam:
  • pH: \text{pH} \approx 7.0 (neutral)
  • Fluoride concentration: \approx 2\%\ \text{NaF} (≈ 9{,}040\ \text{ppm})
  • Advantages: safe for all restorations, gentler on exposed root surfaces
  • Disadvantages: slightly lower immediate fluoride uptake compared with APF foam
  • Best for: restorations, erosion, recession, sensitivity, and young children
• APF foam (Acidulated Phosphate Fluoride):
  • pH: \text{pH} \approx 3.0{-}3.5 (acidic)
  • Fluoride concentration: \approx 1.23\%\ \text{NaF} \quad(\approx 12{,}300\ \text{ppm})
  • Advantages: acidic environment enhances fluoride uptake, especially on smooth enamel surfaces; effective in short applications (1–4 minutes)
  • Disadvantages: can etch and dull porcelain, composite, and glass ionomer restorations; not ideal for patients with many esthetic restorations
  • Best for: older children and adults with natural teeth, minimal restorations, and high caries risk
• APF gels/foams are commonly used in professional settings; APF gel is frequently recommended in higher-risk patients.

Comparison of Fluoride Treatments (Typical Characteristics)

• Stannous Fluoride (SnF₂):
  • Typical concentration: home gel 0.4\%; in-office solution up to 8\% (≈ 19{,}000\ \text{ppm})
  • pH: \text{acidic} \ (\approx 2.8{\text{ to }}5.0)
  • Mechanism: antimicrobial; fluoride remineralization; adheres to rough root surfaces
  • Advantages: antimicrobial effects; reduces gingivitis; useful for high caries risk and gingivitis
  • Disadvantages: metallic taste; tooth/restoration staining; unstable shelf life
  • Use: high caries risk with gingivitis; root surface caries
• Sodium Fluoride (NaF):
  • Typical concentrations: OTC toothpaste 2\% NaF; in-office gel variants around 2\% (varies by product)
  • pH: Neutral (~7.0)
  • Mechanism: promotes remineralization; inhibits demineralization; sticks to rough root surfaces
  • Advantages: neutral pH safe for restorations; well‑tolerated across ages
  • Disadvantages: less antimicrobial activity than SnF₂
  • Use: broad, all-ages caries prevention; common in toothpaste and water
• Comparison takeaway: APF generally offers greater enamel uptake in short contact times; SnF₂ has antimicrobial benefits; NaF is versatile and restoration-friendly.

Professionally Applied Topical Fluorides

• 38% Silver Diamine Fluoride (SDF):
  • Indications: extreme caries risk; behavior/medical management challenges; lesions that cannot be treated in one visit; difficult-to-treat lesions; limited access to care
  • Advantages: noninvasive; cariostatic; reduces caries risk on adjacent teeth; reduces dentinal hypersensitivity
  • Contraindications: allergy to silver; pregnancy/breastfeeding
  • Application: neutral, staining of carious lesions black while healthy tissue remains unaffected
  • Dosing and procedure: approximately 1 drop (≈ 25 μL) covers up to five surfaces per visit; apply to lesion for absorption; reevaluation in 2–4 weeks
• ADA recommendations (professional applications):
  • 5% NaF varnish and 1.23% APF gel supported for caries prevention
  • For children under 6 years: varnish only (avoid gels due to swallowing risk)
  • For patients 6 years and older with elevated risk: either varnish or gel
  • Frequency: every 3–6 months depending on risk
  • Note: limited evidence for twice-yearly APF foam preventing cavities, especially in permanent teeth; not generally recommended for permanent dentition
• Varnish: 5% NaF varnish
  • Available in unit-dose wells or packets; typical unit dose ~0.25, 0.4, or 0.5 mL for primary, mixed, and permanent dentitions

Box 34-2 Indications for Professional Fluoride Application (Summary)

• Indications include: active or secondary caries; exposed root surfaces; orthodontic appliances; low or no fluoride exposure; xerostomia
• Varnish can provide protective coating and slow fluoride release for uptake

Procedure: Topical Gel/Foam Tray Application

• Determine need based on caries risk assessment; APF preferred for certain risk profiles
• Tray selection: APF or NaF gel/foam; APF gel commonly supported by data
• Patient positioning: upright; explain procedure and duration (about 4 minutes); do not swallow
• Tray coverage and fit: ensure full coverage of complete dentition; check recession areas; if root coverage cannot be achieved, plan varnish for those areas
• Tray preparation: fill tray with minimum gel (1/3 full for gel); fully fill but avoid overfilling foam
• Drying: dry teeth before insertion; use saliva ejector during drying
• Insertion: place trays in mouth; may require two-step procedure (one tray at a time); patient may not rinse between trays
• Timing: total 8 minutes if two-step; remove trays by tilting head forward; have patient expectorate after removal to avoid swallowing; wipe excess gel/foam; use high-power suction as needed
• Post-procedure instructions: do not place anything in mouth for 30 minutes; avoid rinsing, eating, drinking, or brushing immediately after treatment

Varnish Technique (5% NaF)

• Pre-application considerations:
  • Determine need based on caries risk; professional fluoride preferred for children <6 years
  • Review medical history for rosin/colophony allergy; if present, use rosin-free varnish or alternative topical fluoride (e.g., tray method with 1.23% APF for 6+ years and adults for root caries)
  • Explain procedure; seat patient supine; for infants/toddlers, have parent seated knee-to-knee; ensure patient does not swallow
• Application:
  • Dispense varnish from tube or single-dose packet; mix on applicator brush
  • Apply thin, systematic coat over all tooth surfaces; for infants/toddlers, apply maxillary anterior teeth first if cooperative; otherwise begin with mandibular teeth and proceed in a systematic sequence
  • Coverage should include exposed cervical areas, recession, facial/lingual/palatal surfaces, and occlusal surfaces
  • Application time: approximately 1–3 minutes
• Post-application instructions:
  • Teeth may feel coated; avoid hard foods, hot/alcoholic drinks, brushing, and flossing until the next day or 4–6 hours post-application to allow uptake

Post-Op Fluoride Instructions

• Tray application:
  • Do not rinse, eat, drink, brush, or floss for at least 30 minutes after gel/foam
• Varnish application:
  • Avoid hot drinks and alcoholic beverages; delay brushing/ flossing and hard, sticky, or crunchy foods for 4–6 hours or until the next morning
  • Varnish residue can be removed with toothbrushing and flossing the next day

Silver Diamine Fluoride (SDF) Details

• 38% SDF is a liquid used to stop tooth decay and strengthen teeth without drilling.
• Composition and effect:
  • Contains silver ions (antimicrobial) and fluoride ions (remineralizing)
  • May stain decayed areas black while healthy portions remain unchanged
  • Stops cavities by killing decay-causing bacteria
• Indications for SDF use:
  • Extreme caries risk (xerostomia, severe early childhood caries, cancer treatments)
  • Behavior/medical management challenges; lesions not all treatable in a single visit
  • Limited access to dental care; difficult-to-treat carious lesions
• Advantages: noninvasive; cariostatic; reduces caries risk on neighboring teeth; reduces dentinal hypersensitivity
• Limitations/contraindications:
  • Contraindicated in silver allergy; caution in pregnancy/breastfeeding
  • Aesthetic concerns due to black staining of carious tissue
• Application procedure:
  • Each treatment visit uses approximately 1 drop in a dappen dish to treat up to five surfaces (max 25 μL per visit)
  • Protect the operatory environment; isolate tongue/cheek to prevent staining; dry the lesion; apply SDF for 1–3 minutes; allow to dry 60 seconds; dispose of materials properly
  • Post-placement: reevaluate lesion in 2–4 weeks
• SDF staining mechanism:
  • SDF composition 38\%\ \text{SDF} (~44{,}800\ \text{ppm fluoride})
  • Silver reacts with carious dentin and bacterial by-products to form dark silver compounds, yielding a black stain on demineralized tissue
  • Healthy enamel/dentin does not permanently stain; temporary surface staining on healthy tissue may fade
• Important notes:
  • There are no postplacement instructions beyond reevaluation; routine follow-up is recommended

Self-Applied Fluorides (OTC and Rx)

• Available forms: dentifrices, mouthrinses, gels
• Concentrations ≤ 1500\ \text{ppm} fluoride are generally OTC; some products under 1500 ppm are Rx only
• Indications:
  • Indicated based on caries risk assessment and overall care plan
• Methods of self-application:
  • Tray methods (custom-made or disposable): fully cover the teeth; avoid overfilling
  • Mouthrinses: swish for about 1 minute with a measured amount; spit; some patients need to learn to rinse to force solution between teeth
  • Toothbrushing with fluoride toothpaste: after breakfast and before bed; do not eat after brushing; optional brush-on gels for additional benefits; interdental brushes can apply fluoride to proximal surfaces or open furcations

Fluoride Mouthrinses

• Indications:
  • Beneficial for individuals at moderate-to-high caries risk
  • Can be used as part of an individual care plan or school-based program
• Age considerations:
  • Not recommended for children aged 6 years or younger or for those unable to rinse adequately
• Benefits:
  • Documented reduction in caries incidence with frequent rinsing at low fluoride concentrations
  • Greatest benefits for newly erupted teeth and smooth surfaces; also helps with root caries
• Typical rinse strength:
  • 0.05\%\ \text{NaF} (the maximum strength available over the counter)

Fluoride Mouthrinse Indications and Procedures

• Indications include:
  • Moderate-to-rampant caries risk in fluoridated or nonfluoridated communities
  • Biofilm-retentive appliances (orthodontics, partial dentures, space maintainers)
  • Xerostomia from radiation, medications, or other causes
  • Hypersensitivity of exposed root surfaces
• Procedure for fluoride mouthrinse:
  • Use a 0.05% sodium fluoride rinse
  • Rinse and spit per product instructions; avoid swallowing

Fluoride Rinse Benefits (Evidence Snapshot)

• Frequent rinsing with low-concentration fluoride yields caries reduction across ages
• In school-aged children with primary dentition, reductions up to 42.5\% in caries incidence have been reported
• Greater benefits for smooth surfaces; notable benefit for newly erupted teeth
• Benefits are additive in communities with water fluoridation and in combination with other fluoride sources
• Effective in preventing and reversing root caries

Brush-On Gels

• Fluoride brush-on gels strengthen enamel and increase resistance to decay
• Strongly recommended for higher-risk individuals, including older adults

ADA Recommendations for Professional Applied Fluoride

• Product types and fluoride ppm:
  • 1.23% Acidulated Phosphate Fluoride (APF Gel): 12{,}300\ \text{ppm} fluoride equivalent
  • 2% Sodium Fluoride (NaF Gel): 9050\ \text{ppm} fluoride equivalent
  • 5% NaF Varnish: 22{,}600\ \text{ppm} fluoride equivalent
  • 38% Silver Diamine Fluoride (SDF): ~44{,}800\ \text{ppm fluoride} plus silver content
• Indications by age and risk level:
  • Children under 6 years: varnish preferred; gels with swallowing risk avoided
  • 6 years and older with elevated risk: varnish or gel
  • Frequency: every 3–6 months depending on risk
  • Some formulations (e.g., APF foam) have limited or mixed evidence for permanent dentition and may not be routinely recommended
• Documentation and product selection should consider patient age, caries risk, restorations, and compliance

Boxed Indications and Practical Considerations

• Indications for professional fluoride applications include:
  • Active or secondary caries, exposed root surfaces, orthodontic appliances, very low fluoride exposure, xerostomia
• Varnish provides a quick, protective layer and slow fluoride release; convenient for young children and difficult patients

Tray Placement and Procedure (Fluoride Tray Technique)

• General workflow:
  • Assess need and select appropriate fluoride (APF vs NaF)
  • Prepare patient and materials; protect patient and clinical environment
  • Fill trays with the recommended amount; avoid overflow
  • Instruct patient on duration and post-treatment precautions
  • Execute a careful, full-arch coverage; monitor for patient comfort
  • Post-procedure instructions include not rinsing for 30 minutes and avoiding eating or drinking immediately after, depending on product used

Post-Placement Follow-Up and Documentation

• Aftercare varies by product (tray vs varnish vs SDF)
• Schedule reevaluation as indicated (e.g., SDF reassessment in 2–4 weeks; routine fluoride follow-ups per risk assessment)
• Documentation should include indications, product used, coverage, and patient compliance with post-operative instructions

SDF Staining and Aesthetic Considerations

• Staining explains why SDF is chosen in certain patients despite esthetic concerns
• Stains only demineralized carious dentin and not healthy enamel or dentin
• Staining is black/gray and may be temporary on surrounding tissues but is generally permanent on carious tissue

Practical Implementation Summary

• Tailor fluoride therapy to age, caries risk, esthetic considerations, and access to care
• Use combination of systemic (water supply), topical (toothpaste, mouthrinses), and professional applications to maximize caries prevention
• Consider alternatives (APF vs NaF vs SnF₂) based on restorations, patient tolerance, and clinical goals
• Monitor and reevaluate periodically to adjust preventive strategies

Key Formulas and numeric references

• Fluoride concentrations and equivalents:
  • APF gel/foam: 1.23\% \text{ NaF} \approx 12{,}300\ \text{ppm}
  • NaF varnish: 5\% \text{ NaF} \approx 22{,}600\ \text{ppm}
  • SnF₂: (home gel) 0.4\%; in-office solution 8\% (≈ 19{,}000\ \text{ppm})
  • SDF: 38\%\ \text{SDF} (≈ 44{,}800\ \text{ppm fluoride})
• pH values:
  • NaF neutral: \text{pH} \approx 7.0
  • APF: \text{pH} \approx 3.0{-}3.5
  • SnF₂: \text{pH} \approx 2.8{\text{ to }}5.0
• Clinical outcomes:
  • Caries reduction with fluoridated water: \approx 27\% across age groups
  • Primary teeth caries reduction with birth fluoridation: up to 40\%
  • Anterior teeth receive more fluoride protection than posterior teeth; progression slowed with fluoride exposure
  • Root caries reduction in lifelong fluoridated communities: ~50\%

Connections and Implications

• Fluoride acts on multiple levels: systemic prevention during tooth development and topical protection after eruption.
• The balance between benefits and esthetic concerns (e.g., fluorosis, SDF staining) guides product choice.
• Community fluoridation has a broad public health impact by reducing caries incidence and progression across populations.
• Ethical and practical considerations include patient consent for SDF staining, high-risk groups, and ensuring safe use in children and special populations.

References to Practice and Real-World Relevance

• Fluoride therapies should be integrated into individualized prevention plans across ages and risk levels.
• Regular assessment of caries risk, dietary habits, and fluoride exposure informs therapy selection and frequency.
• Public health policies on fluoridation influence community-level caries outcomes and access to preventive care.