|Lecture 8 (16 April 07) Application of fluoride and Ca P in caries control measures
Delivery modes of fluoride as caries preventive agents
Fluoride has to be delivered to the microenvironment surrounding the tooth to exert its function in inhibiting or reversing caries development. Two main routes of F administration are systemic fluoridation and topical application. Systemic fluoride has both pre- and post-eruptive effect, topical application is post-eruptive. From previous lectures, we already discussed that the major caries preventive effect of fluoride is post-eruptive. To make it more complicated, systemic fluoride also has topical effect because the ingested fluoride elevates fluoride content of saliva. Water, salt, milk, sugar fluoridation and fluoride supplements are in the systemic category. Topical fluoride application includes professionally-applied fluoride in various forms and over-the-counter products. Fluoride containing restorative materials can be classified as topical form of fluoride as well. Some of these fluoride preparations are community approach, some are individual base, and some has to be delivered by dental personals. They are different in the effectiveness and cost-benefit ratio.
Note: Fluoride works best to prevent/control smooth surface caries, but not as effective on occlusal caries.
Effectiveness of fluoride products
Water fluoridation is effective, but there is antifluoridation campaign against it. When caries prevalence is high, water fluoridation can reduce up to 50% reduction of caries in primary teeth, and up to 60% reduction in permanent teeth. For population with low caries prevalence and receive other forms of F-products, especially F-toothpaste, the effectiveness of water fluoridation is reduced to ~ 20%.
Fluoridated toothpaste is probably the most important means for the topical application of fluoride where they are available. Brushing with F-toothpaste significantly reduce caries incidence. Clinical studies showed caries preventive effect of F-toothpaste to be about 25 %. However, the cariostatic effect in life-long use in population may be much greater due to the cumulative effect.
Fluoride mouthrinse is another form of topical F application that can be prescribed or bought over-the-counter. Fluoride compounds used are NaF, SnF2, amine fluoride. High concentration rinses, 0.1-0.2% (~1000-2000 ppm F), are for weekly basis. 0.025-0.05% (~250-500 ppm F) rinses are for daily basis. The efficacy is highly influenced by caries risk, dental awareness, and access to dental care. The efficacy in high concentration rinse is inconclusive when other fluoride products are used. The daily rinse is useful in subjects with a risk of root caries (10-65% caries reduction).
Fluoride gel: From a review in 1998, caries inhibition ranged from 4 to 37 % (overall = 22%), independent of F toothpaste or fluoridated water. Recall: the amount of APF gel can induce acute or chronic toxicity if it is swallowed.
Fluoride varnishes increase fluoride retention on the tooth surface and produce relatively high surface F level in enamel. Duraphat varnish has the highest F concentration of all products (5%), but the amount of F ingested is not high due to the small amount applied. Meta-analysis study indicated caries reductions of 38% for Duraphat in patients that used F-toothpaste.
F-containing restorative materials. Fluoride can be released from restorative materials as part of the setting reaction or it may be added to the formulation with the specific intention of fluoride release. Glass ionomer may be the only reliable product in terms of fluoride release and substantial clinical effect. Why do we need F-containing restorative materials? Because secondary caries is the main reason for restoration failure. The anticariogenic effect of glass ionomers is remarkably crucial in high-risk patients. Recurrent caries reductions around cervical restorations for conventional and resin-modified glass ionomers relative to composite were greater than 80% in xerostomic patients with less compliance. Similarly, less caries developed at margins of glass ionomer restorations compared with amalgam after 2 years in xerostomic patients who did not routinely use topical fluoride
Milk protein derivative CPP-ACP
Anticariogenic properties of milk and dairy products are known. Studies by the University of Melbourne in Australia showed that a particular part of the casein protein in milk, the casein phosphopeptides (CPP), was responsible for the anticariogenic properties. Casein phosphopeptides can stabilize amorphous calcium phosphate in a solution. CPP binds well to dental plaque. By doing so, calcium and phosphate ions are localized in dental plaque at higher concentration, thus inhibit demin and promote remin.
A sugar-free chewing gum with CPP-ACP significantly increased enamel remineralization compared to control. Tradename of CPP-ACP is Recaldent. Manufacturers have incorporated Recaldent in various products, range from consumer products like chewing gum, to a dentist-prescribed Ca/P topical cream, MI paste. The MI paste is recommended to use in patients with erosion, active caries, or xerostomia.
Rationale for clinical use of fluoride
It is no doubt that fluoride can prevent caries, but which method is the most suitable, and how much is needed? More is not necessarily better. Before you prescribe or deliver fluoride to patients, there are factors to be considered: caries risk, product efficacy, patient compliance, cost-effective ratio, background F exposure, access to dental care, and safety issue.
Which delivery method? Most of the methods available are extensively study and shown to be effective in reducing caries. In general, frequently exposure to low level of fluoride is more effective than those that are infrequently used. Patient’s compliance to the proper use may be more effective than the product per se.
Cost-benefit ratio should be considered. This is related to caries risk. In many European countries without water fluoridation, children maintain their low caries prevalence just by using fluoride toothpaste. So, in the area with water fluoridation plus children use fluoride toothpaste, additional fluoride supplement is not recommended.
A recent reviews show that twice a year application of fluoride gel reduced caries 22 %. In low caries population, a mean caries incidence can be 0.25 DMFS per year. This means that 22% reduction save 0.055 DMFS per year, therefore the cost-benefit ratio is unfavorable in this group.
The amount of fluoride exposed and the related safety is one of the most important issues. Acute toxicity should not happen in normal practice. Chronic toxicity or long-term effect in terms of dental fluorosis is more likely to occur, especially by multiple F exposure.
Attributable risk for dental fluorosis
This study determined the attributable risk for mild to moderate enamel fluorosis in two groups of children 10-14 years old. 429 grew up in nonfluoridated community, 234 grew up in optimally fluoridated community. Attributable risk is the proportion of cases of mild to moderate enamel fluorosis associated with exposure to specific fluoride sources. Note that the numbers do not add up to 100 % because the child can have more than one way of F exposure.
In the optimally fluoridated community, the highest attributable risk is using more than pea-size amount of toothpaste in young children. If the pea-size amount of toothpaste was used, the attributable risk is small even the child brushed more than once per day. Also noted that formula reconstituted with fluoridated water contributed to 9 % of the attributable risk.
In the non-fluoridated community, the highest attributable risk is fluoride supplement. But that was before the recommendation was changed to the current one. The next highest attributable risk is using more than pea-size amount of toothpaste in young children, and the frequency of brushing in toddler.
Risk factors for dental fluorosis
Tooth brushing behavior with F toothpaste: US national data showed that 32% of children under age 2 brushed with F toothpaste, the figure increased to 91% among 4-year-olds. Parents have to supervise when they brush because children tend to swallow a lot of toothpaste. Preschoolers frequently swallowed 55-79% of the toothpaste, but as high as 90% was found.
A study found that about 34% of fluorosis cases in non-fluoridated area were associated with children younger than 2 years old using F toothpaste. And 68% of the fluorosis cases in areas with optimally water fluoridation were from children younger than 1 year old ingested F toothpaste. Odds ratio for risk of developing fluorosis with the use of F-toothpaste is 1.6-1.8.
Toothpastes with flavor for children also tend to be swallowed more. Special toothpastes for young children have lower F concentration, 500 ppm F in comparison to 1000 ppm F in regular toothpastes. A small pea-sized amount of toothpaste is recommended for children younger than 6 years old, unless fully developed swallowing reflex. ADA recommends not using fluoride toothpaste in toddlers (under 24 months of age). There is a warning label for use in children the back of toothpaste tube. Manufacturers of toothpastes recommend that children under 6 years old should use only a pea-size amount of toothpaste.
Risk factor - Fluoride supplements:
The inappropriate use of fluoride supplements is one of the significant causes of fluorosis. Fluoride supplements in the form of tablets or vitamins are prescribed for use in children by dentists and physicians. Before prescribe fluoride supplements, dentists and physicians have to test the child’s water supplies for fluoride content. And be aware that there are several other sources of fluoride than drinking water from the tap, like juice or bottle water.
Animal studies showed a threshold plasma F level for dental fluorosis. One ‘spike’ of 0.2 ppm/day for 1 week can cause dental fluorosis. One or two ‘spikes’ of 0.1 ppm/day for 1 week is fine. If a child (5 kg,10 lb) is given 0.5 mg F, equivalent to 0.1 mg/kg, plasma F can exceed 0.2 ppm, a threshold level that can cause dental fluorosis.
This table is the latest recommended fluoride supplement schedule. Currently it is recommended that F supplement should never been used in areas with water fluoridation. These numbers may change again when you are in pediatric clinic, or in your practice. Make sure you are up to date.
How much fluoride is in my water? The information of community water fluoridation level in the US can be found at http//apps.nccd.cdc/gov/MWF/Index.asp. This is the National Center for Chronic Disease Prevention and Health Promotion, Center for Disease Control and Prevention website. (My Water’s Fluoride, Oral Health Resources).
Where to send water to test fluoride content? You can order the water kits from Doug Magne 612-624-9123. This is done here - Fluoride Testing Service, School of Dentistry, University of Minnesota. MN Department of Health no longer has the fluoride test service. There are some private companies that do the testing (about double the fee charged by the Dental School). Inside there is a form to fill and a plastic test tube for the water to be tested. You have to send a check (20 $ per sample), and the results will be sent back to both the dentist and patient. More question contact Doug or Dr. Robert Ophaug 612-625-5198.
What if the child has multiple sources of drinking water? For example, a 5-year old boy drinks about 50-50 % water at home and school. Home water has 0.25 ppm F, school water is 1 ppm F. Calculate the Effective F concentration from fractional fluoride concentration of each water source. Home water = 0.25 x 0.5 = 0.125 ppm F. School water = 1.0 x 0.5 = 0.5 ppm F. Therefore, the Effective F concentration that the boy receives per day is 0.5 + 0.125 = 0.625 ppm F. According to the supplementation schedule for the effective F concentration, the child does not need any F supplement. However, if you base the recommendation according to home water fluoride level alone, the child will get 0.5 mg F supplement, which will be too much and increase risk of dental fluorosis.
Risk factor - Fluoride in water: Drinking optimally F water by itself is not a risk factor for dental fluorosis. A person lives in a community without water fluoridation can get fluoride in drinking water from other sources such as child care or school. There is also a halo effect from water fluoridation somewhere else. Now we also drink a lot of bottle waters, most of them contain less than 0.3 ppm, but 10% contain close to 0.7 ppmF. Home filtration systems (distillation and reverse osmosis) remove 90 % or more F from water, but the carbon/charcoal systems do not. Juices had upto 2.8 ppm F, 42% had more than 0.6 ppm. Fluoride level in soft drinks ranged from 0.02 to 1.28 ppmF depend on the plant they were made. Overall, 77% of soft drinks had more than 0.6 ppmF.
These are some data of fluoride content in bottled water from an USDA website. A distillation or reverse osmosis removed fluoride from water, so most of the bottled water does not have optimal level of fluoride. Some bottled water has added fluoride, for example, Dannon F to go.
Risk factor - Infant formula reconstituted with fluoridated water:
Breast milk and cow milk are very low in fluoride (0.01-0.04 ppm). In the 80’s US manufacturers voluntarily reduced F in infant formula to 0.15 to 0.3 ppm. Powder concentrates infant formula plus fluoridated water can have 1 ppm, and liquid concentrates infant formula plus fluoridated water can have 0.5 ppm. This is a significant source of fluoride, especially when more than 1 L is ingested. (5 kg infant will pass the threshold of dental fluorosis which is 0.1 mg/kg/day). Infant formula reconstituted with fluoridated water is responsible for 9% of dental fluorosis in fluoridated community.
In November 2006, ADA has issued an Interim Guidance on Fluoride Intake for Infants and Young Children, stated that for infants who get most of their nutrition from formula during the first 12 months, ready-to-feed formula is preferred to help ensure that infants do not exceed the optimal amount of fluoride intake. If liquid concentrate or powdered infant formula is the primary source of nutrition, it can be mixed with water that is fluoride free or contains low levels of fluoride to reduce the risk of fluorosis. Examples of water that has low level of fluoride are those labeled purified, demineralized, deionized, distilled or reverse osmosis filtered water.
If we believe in the concept that the major caries prevention effect of fluoride is from topical application, there is no benefit in infant younger than 6 months old, before the first teeth erupted. A different point of view: Permanent maxillary incisors form between 22-26 months old. Therefore any excessive fluoride during the first 6 months, or even 1 year, is unlikely to affect the most esthetic teeth.
Note: Infant chicken product can have as high as 8 ppm F due to the deboning process which add fluoride from chicken bone into the product. The amount of fluoride in infant chicken product can be 20 times higher than infant fruit products.