Lec 5: Fluorides in Prevention and Controlling Dental Caries (PDF)

Lec 5 ‫ايمان عالء‬. ‫م‬.‫م‬ Fluorides in prevention and controlling dental caries Mechanism of action of fluoride By the early 1990s it was well understood that fluoride is most effective in caries prevention. It is accepted that fl...

Lec 5 ‫ايمان عالء‬. ‫م‬.‫م‬ Fluorides in prevention and controlling dental caries Mechanism of action of fluoride By the early 1990s it was well understood that fluoride is most effective in caries prevention. It is accepted that fluoride action in preventing caries is multifactorial. It is seen that anti caries effect is most pronounced when a low level fluoride is constantly maintained in the oral cavity, though the respective roles of pre eruptive and post-eruptive fluoride continues to be debated. Systemically ingested fluoride, when it is absorbed in the alimentary tract, either is excreted in urine or incorporated into calcified tissues, such as bone and teeth. It is well established that fluoride is incorporated into dental apatite crystals during tooth development forming fluoroapatite (FAP). Today the most important anti-caries effect is claimed to be due to the formation of calcium fluoride (CaF2) in plaque and on the enamel surface during and after rinsing or brushing with fluoride (topical fluoride). CaF2 serves as a fluoride reservoir. When the pH drops, fluoride and calcium are released into the plaque fluid. Fluoride diffuses with the acid from plaque into the enamel pores and forms fluoroapatite (FAP). Ca10 [PO4]6[OH] 2 + 20F– ↔ 10 CaF2 + 6[HPO4–] 3 + 2[OH] Hydroxyapatite Calcium fluoride Fluoroapatite (FAP) incorporated in the enamel surface is more resistant to a subsequent acid attack. Eman Alaa Scientists have proposed that fluoride has several functions : 1. Increased enamel resistance or reducing enamel solubility [acid dissolution]. 2. Interferes in the formation and functioning of dental plaque microorganisms. 3. Increases the rate of post-eruptive maturation. 4. Remineralization of incipient lesions. 5. Improves tooth morphology. Eman Alaa Increased enamel resistance Fluoride reduces the solubility of dental enamel by both systemic and topical action. - Fluoride ingested prior to tooth eruption enhances the development of fluorapatite at the enamel surface and that this fluorapatite is resistant to the demineralizing acids that initiate the carious process. - The topical effect of fluoride in reducing enamel solubility occurs during the repeated cycles of demineralization and remineralization in the early stages of carious lesion. The presence of low levels of in the plaque leads to a gradual establishment of well-crystallized and more acid resistant apatite in enamel surface. Fluoride’s effect on tooth mineral Enamel is composed primarily (~95%) of hydroxyapatite (HA) crystals in which are substituted a number of other ions including fluoride. Well-formed HA crystals have a hexagonal configuration of phosphate and calcium ions with a central hydroxyl ion. Eman Alaa  Crystals can incorporate a wide range of extraneous ions from the surrounding enviroment substituting for calcium, phosphate and hydroxyl groups. Extraneous ions incorporation can occur as crystals form during tooth development or by interaction with the enviroment after tooth formation. The incorporation of magnesium and carbonate because of a poor fit in the crystal tends to destabilize the crystal, making it more susceptible to acid dissolution. In developing enamel, carbonate will substitute for phosphate ions and if the concentration is high enough for hydroxyl ions. Magnesium can substitute to a limited extent for calcium but often resides at the crystal surfaces. Fluoride, however, substituting for the hydroxyl group fits extremely well and stabilizes the HA molecule forming fluoridated apatite. If all of the hydroxyl ions are substituted fluorapatite (FA) forms. The fluoride ion is extremely electronegative and forms very strong hydrogen bonds with hydroxyl and acid phosphate groups in the HA crystal rendering the enamel surface more difficult to protonate. Essentially this makes the enamel more difficult to demineralize, and it also favors the remineralization process. Eman Alaa This is the primary chemical mechanism of fluoride’s action to protect the tooth against acids produced by plaque metabolism, as follows: Ca10(PO4)6(OH)2 + Mg++ = magnesium whitlockite Ca10(PO4)6(OH)2 + CO3− = carbonated apatite Ca10(PO4)6(OH)2 + 2F− = Ca10(PO4)6(F)2(fluorapatite) +2(OH−) Fluoridated apatite and/or fluorapatite are generally found in the surface layers of enamel that contains high fluoride concentrations of fluoride. This can arise both during development and from topical exposure Inhibition of bacterial enzyme system Fluoride interferes with oral bacteria in two ways: In high concentrations it acts as bactericidal and in low concentration it decreases acid production. Fluoride inhibits glycolysis(the process by which fermentable carbohydrates are metabolized by cariogenic bacteria to produce acids). Plaque fluoride can inhibit the production of extracellular polysaccharides by cariogenic bacteria—this is necessary for plaque adherence to smooth enamel surfaces. Eman Alaa  Fluoride inhibits enolase, an enzyme necessary for the bacteria to metabolize carbohydrates and produce acids necessary to cause demineralization. As fluoride is trapped in the cell, the process becomes cumulative Increased rate of post-eruptive maturation At the time of tooth eruption the enamel is not completely calcified and undergoes a post-eruptive period of approximately 2 years during which enamel calcification continues. Throughout this period-period of enamel maturation’ there is continuous accumulation of fluoride as well as other elements in the superficial part of enamel. Improves tooth morphology It has been reported by a number of investigators, although not universally accepted that posterior teeth from fluoridated areas have a distinct gross morphology. This is shown in Figure: - the cusps are rounder; the fissures are more shallow and the fissure approximation abrupt and tight. Eman Alaa - In contrast, fluoride-deficient teeth have less rounded cusps, steep inclines, and unfavorable fissure approximation. The latter is troublesome, because the less well-fused fissures serve as an excellent trap for food debris, bacteria and bacterial byproducts. Enhancing remineralization As the saliva flows over the plaque and its components neutralize the acid, raising the pH, demineralization is stopped and reversed. The saliva is supersaturated with calcium and phosphate, which can drive mineral back into the tooth. The partially demineralized crystal surfaces within the lesion act as "nucleators”, and new surfaces grow on the crystals. These processes constitute remineralization ( the replacement of mineral in the partially demineralized regions of the carious lesion of enamel or dentine including the tooth root). After repeated cycles of dissolution and reprecipitation, enamel crystals may be completely different from their original state Summary As summary we can considered three stages for fluoride effect: - Pre-eruptive Systemic Effects - Post-eruptive Systemic Effects - Post-eruptive Topical Effects Eman Alaa Pre-eruptive Systemic Effects During tooth development, fluoride is incorporated into the developing tooth’s mineralized structure. Although this is no longer believed to be the most important reason for the effect of fluoride in dental caries, the presence of fluoride in the dental enamel probably increases resistance to demineralization when the tooth surface is exposed to organic acids. Systemic fluoride may enhance the resistance of the tooth by way of: 1. An alteration in tooth morphology, and 2. A conversion of the hydroxyapatite mineral to a fluoridated state with an attendant reduction in solubility Post-eruptive Systemic Effects After tooth eruption, fluoride is no longer involved systemically in tooth formation. However, consumed fluoride is excreted through the saliva and can aid in tooth protection throughout the lifetime. Post-eruptive Topical Effects Providing fluoride only before tooth eruption does not afford maximum protection against caries. In fact, topical mechanisms are now considered the primary means by which fluoride imparts protection to teeth. Thus, topical fluorides are now considered important in caries prevention independent of the provision of systemic fluorides. Eman Alaa  The post-eruptive beneficial effect of fluoride likely occurs primarily from the presence of fluoride in the fluid phase at the tooth surface. Fluoride is responsible for decreasing demineralization when the tooth is exposed to organic acids and for increasing the rate of remineralization. The frequency of fluoride exposure to the tooth surface is of prime importance to maintain the high fluoride concentration that is necessary in the fluid phase of enamel surfaces to prevent caries and enhance the remineralization of early carious lesions. Goals of Fluoride (F) Administration 1. Do not harm the patient. 2. Prevent decay on intact dental surfaces. 3. Arrest active decay. 4. Remineralize decalcified tooth surfaces. Eman Alaa Fluoride administration Fluoride can be administered systemically or applied topically for preventive effect A. Systemic. B. Topical. 1. Water fluoridation. 1. Those applied by professional. a. Community water a. Topical solutions and gels. fluoridation. b. Fluoride containing varnishes. b. School water fluoridation. c. Fluoride prophylaxis paste. d. Restorative materials 2. Dietary supplements. containing fluoride. a. Fluoride tablets and drops. e. Fluoride containing devices b. Fluoridized salts. (Slow Release). c. Fluoride vitamins preparation. 2. Self applied fluoride agents. d. Fluoridized milk and fruit a. Fluoride dentifrices. juices. b. Fluoride rinses. c. Fluoride gels. Fluoride Tablets, Lozenges and Drops Fluoride supplements were intended as a substitute for fluoridated water for children in non-fluoridated areas. They are also called as ‘fluoride supplements’ because they are manufactured as tablets or drops for swallowing. Eman Alaa  However fluoride supplements should be: 1. Prescribe for children ages 6 months to 16 years who are at high risk for tooth decay and, 2. Whose primary drinking water has a low fluoride concentration. 3. Prescribed only by dentists where there is clear evidence for high risk of caries and non-compliance with using other fluoridated products; and the parents must be cooperative. Fluoride tablets became the method of choice for fluoride supplementation. Supplements contain a measured amount of fluoride typically 0.25mg, 0.5mg, and 1mg usually as sodium fluoride. Fluoride tablets are commercially available as NaF tablets of 2.2. 1.1 and 0.5 mg. 2.2 mg sodium fluoride tablet gives 1mg ion fluoride, 1.1 mg sodium fluoride tablet gives 0.5mg ion fluoride. 0.5 mg sodium fluoride tablet gives 0.25 mg ion fluoride. The American Dental Association (ADA) Recommended Fluoride Supplementation Schedule: Eman Alaa  Instruction to use fluoride supplement (tablet or lozenges or drop): if fluoride level is unknown, drinking water should be tested for fluoride content before supplements are prescribed. Fluoride supplement indicated to children living in area with none or low level of fluoride in water. Especially children with high risk to dental caries, children with chronic systemic disease and handicapped children. Fluoride supplement is daily used from 6months to 16 years to give their maximum effect (To obtain the benefits from fluoride supplements, long-term compliance on a daily basis is required). To maximize the topical effect of fluoride, tablets and lozenges are intended to be chewed or sucked for 1–2 minutes before being swallowed. Before considering supplementing fluoride, it is relevant to take into account the natural sources of fluoride in food and drinking water. It has also been shown that when exposure to fluoride is discontinued, its caries- reducing effect gradually wanes. This is entirely logical, because fluoride is affecting the dynamics of lesion formation. Fluoride supplement Should not be given with milk. Fluoride during pregnancy Fluoride may be supplemented during pregnancy until dental formation is completed through pharmaceutical products, i.e. tablets or drops, according to variable doses (0.25 and 1 mg). During pregnancy and breast feeding, mothers should take 1 mg a day. Eman Alaa  In fact, theoretically, during intrauterine life, the fluoride taken by the mother may work in the pre-eruptive phase, during the amelogenesis of deciduous teeth with a consequent beneficial effect on the newborn’s deciduous teeth. Fluoride passes through the placenta freely, until it reaches excessively high levels in the mother’s blood, and thus triggers this passage (barrier effect) to protect the fetus from excessive doses. The threshold concentration that pushes the placenta to trigger this function is 0.4 ppm of fluoride in maternal blood. Some Authors consider the systemic administration of fluoride as a further supplement during pregnancy, as it is identified as the first step to caries prevention Fluoride Drops they are available as 0.125mg,0.25mg,0.50mg drops.The drops are prescribed to the children until they are old enough to swallow 10 drops equal to 1mg,if 10 drops placed in a liter of water the result concentration of 1ppm of fluoride. It may be given with multivitamins drops for young children. Note : ‫لالطالع فقط‬ There continues to be controversy concerning the use of dietary fluoride supplements, and now they are not generally recommended Fluoride supplements should only be prescribed by dentists where there is clear evidence for high risk of caries and non-compliance with using other fluoridated products (reference : comprehensive preventive dentistry book) Eman Alaa