The most common fluoride compounds available for topical application are
• NaF (sodium fluoride)
• SnF2 (stannous fluoride)
• APF (acidulated fluoride phosphate)
• Na2FPO3 (sodium monofluorophosphate)
The vehicle most commonly used is a dentifrice but there are other vehicles involving solutions, gels and varnishes. Care must be taken in prescribing. For example, the acidulated gels provide the highest fluoride uptake but at the same time they are likely to remove the glaze from ceramics or roughen the surface of a glass-ionomer or glass filled composite resin if applied too often. Also, the safety factor must be considered when prescribing highly concentrated fluoride products in some age groups.
Fluoride containing dentifricesA dentifrice may contain NaF (1.0%), Na2F PO3 (0.76%), or SnF2 (0.4%) = (% F ion). In general there is approximately 1 mg/gm of available fluoride (1000 ppm). A tooth brush covered in paste holds approximately 1.5 mg of fluoride.
Recent developments include
• lower concentration fluoride dentifrice for young children (400 ppm F ion) which will reduce unintended fluoride ingestion in children up to six years who are unable to control their swallowing reflex,
• higher concentration dentifrices, with 5,000 ppm fluoride ion which should be restricted to adults with a high caries risk.
Concentrated gels
• APF 1.23% gel: contains approximately 12.3mg F ion/gm of gel or 12,300 ppm fluoride ion, at pH 3.5.
• NaF 2%: contains approximately 10mg F ion/gm of gel or 10,000 ppm F ion at pH 7.0.
APF gel is more effective than NaF in providing prolonged protection against caries and in counteracting the effects of strong acids. However, it is contraindicated in the presence of glass based restorative materials such as ceramics, glass ionomers and some glass filled composite resins.
Concentrated solutions
• SnF2 20%: dissolved under heat in glycerine for stabilisation, diluted for topical application as required.
• mouth rinses range from 0.2-0.02% NaF (1000-100 ppm – 1mg F/ml to 1mg F/10ml.) and may be acidulated.
Varnishes
• 1.7% NaF in a viscous resin varnish contains around 1,000ppm fluoride ion.
• 5% NaF in a viscous shellac type of varnish contains around 26,000 ppm fluoride ion.
Varnishes have the advantage of prolonged retention, and through dissolution, allows slow release of the fluoride ion. Gels prolong contact with the enamel for up to a few hours, but if they are swallowed, the fluoride ion is quickly released.
Schedules of application• The minimum use of topical fluoride for all patients, irrespective of the apparent caries risk, should be a morning and evening application of fluoride dentifrice as part of the basic daily oral hygiene routine.
• Retention rate depends on initial concentration applied. Normal retention rate from low concentration mouthrinse is relatively high.
• Use concentrated gels only in the most caries active cases.
• Time of day is important. Application immediately prior to retiring offers prolonged retention because of decrease in resting saliva flow
rate during sleep.
• Duration of application should be at least three minutes.
• Neutral gels work well on porous enamel or exposed dentine and an acid environment will aid in fluoride transport into the tooth structure.
• APF gel provides higher uptake as stored fluoride, therefore a more prolonged period of protection.
• With low caries risk, use an acidulated gel, professionally applied, at 6-12 month intervals.
• With high caries rate use the acidulated gel at six week intervals. This can be applied at home using a custom made stent or tray. However, acidulated gels are not recommended for this application because of the potential for etching ceramic or glass containing restorations.
