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A Perspective On Fluoride

Dimensions of Dental Hygiene speaks with Domenick T. Zero, DDS, MS, about what dental hygienists need to know when using fluoride to prevent caries.

Q. What is the dental hygienist’s role in caries prevention?

A. I see the dental hygienist as the preventive practitioner in most dental practices. I don’t recommend a cookbook approach to prevention because not all treatments are helpful to all patients, especially if they are at low caries risk. Part of a prevention philosophy is carefully evaluating the caries risk status of patients. Hygienists should examine the following during an initial risk assessment: patients’ oral hygiene status, diet, salivary flow, and presence of new caries. Although the dentist provides the formal diagnosis, hygienists can certainly be on the look out for signs of active caries disease process.

Q. What is the first step toward prevention?

A. The biofilm must be disrupted. Plaque is an ecological system. Preventive care has to focus on disrupting the biofilm before it grows into a more pathogenic state. With periodontal disease, the biofilm takes longer to progress to a pathogenic state. With caries, plaque biofilm has the ability to produce acid within a day or two if left undisturbed. When acid formation occurs adjacent to the tooth surface, teeth will start demineralizing and this may result in the net loss of tooth mineral over the course of a day if not counterbalanced by enough remineralization. If this continues over a period of months, a white spot lesion appears first and then eventually cavitation occurs.

Q. Is fluoride effective when plaque is present on the teeth?

A. Several studies have addressed the necessity for removing all of the plaque from teeth before providing acidulated phosphate fluoride (APF) treatment in order for the fluoride to be effective. The results show that the prophy itself is not necessary to gain the benefit of an APF treatment. However, at least cleaning the teeth with a toothbrush as part of oral hygiene instruction before giving a topical fluoride treatment is advised.1-3 APF treatment contains a very high concentration of fluoride that provides an intense driving force, which pushes the fluoride through the plaque to the tooth surface. Also, the high fluoride concentration will actually kill potentially pathogenic bacteria like Streptococcus mutans. The acidic pH of APF intensifies the effect of fluoride because at this low pH, most of the fluoride is in the form of hydrogen fluoride (HF), which can pass more readily through the bacterial cell wall. Once inside it can ionize into free fluoride ion and have a lethal effect on the bacterium.


Q. Are most in-office fluoride treatments APF?

A. Most practices probably still use APF or 2% NaF gel or foam in trays, although there is an increasing trend toward using fluoride varnish “off label” for caries prevention. I do not recommend using the high concentration fluoride rinses or stannous fluorides, which have the same fluoride concentration as fluoride toothpaste (1,000 ppm fluoride) and are not approved by the American Dental Association. I do recommend a full 4 minute treatment time.

Most fluoride varnishes have 22,600 ppm fluoride, which is much higher than the 12,300 ppm fluoride found in APF or the 9,040 ppm fluoride found in NaF gel or foam. The varnish method of delivery tends to hold the fluoride on the tooth surface for a longer period of time than with an APF treatment. The other advantage is that the actual dose of fluoride delivered in fluoride varnishes is lower than in APF treatments. Thus, less fluoride is ingested by the patient. This is an important consideration, especially in young children. While most professionally-applied fluoride treatments are done on children, they should also be given to adults who are at high caries risk.


Q. What about the dosages in take home fluoride products?

A. For patients who don’t show any signs of caries activity and don’t have any risk factors, they may only need monitoring to ensure they are using a fluoride toothpaste. Frequency of use is the main concern with fluoride toothpaste. When a patient is only brushing once or twice per day and active carious lesions or risk factors exist, the frequency of brushing should be increased to three times a day—especially after meals and before going to bed.

The next level up is to incorporate a fluoride rinse after brushing, before going to bed. Using the rinse right before bed has added value because fluoride levels will stay fairly elevated throughout the night. For a high risk patient, products with higher fluoride concentrations should be considered. Gels and pastes can be prescribed, which contain 5,000 ppm. Clear evidence of new caries since the last dental visit is an indicator of high risk. A dramatically decreased salivary flow is another high risk factor. The levels that cause concern are when the unstimulated flow rate is less than 0.1 ml per minute or the stimulated flow rate is less than 0.7 ml per minute.

Q. Most dental hygienists in private practice do not have the ability to quantify the amount of saliva. What are some symptoms that hygienists can look for that indicate low salivary flow?

A. If a patient complains of dry mouth or has difficulty talking or swallowing food, these are all symptoms. When examining the patient, if there is dry mucosa or no pooling of saliva in the floor of the mouth, these are other clinical signs of decreased salivary flow.

Q .Are over-the-counter fluoride toothpastes effective?

A. Yes, for most people fluoride toothpaste is their primary source of topical fluoride. Fluoride toothpaste can still dramatically reduce tooth decay in many people, which is why the rampant caries problems of the past have been improved. However, fluoride toothpaste has its limits so when the caries challenge becomes too great, prescription products with higher fluoride concentrations are indicated.


Q. What are the appropriate uses of fluoride for children by age group?

A. I recommend that parents brush their children’s teeth with fluoride toothpaste at the age when teeth are first erupting. The amount of toothpaste used is key due to the risk of dental fluorosis from ingestion. For a very young child, a child’s sized toothbrush should be used with only a small film of fluoride toothpaste on the brush. As the child gets older, the amount of toothpaste used can be gradually increased. The amount of fluoride given really should be based on the child’s body weight and not age. The lower the body weight, the higher the risk of dental fluorosis. After age 6 or 7, most of the permanent teeth have been formed and parents can be less concerned about fluoride ingestion. Also children are better able to spit out the toothpaste slurry and not swallow as much. Parents need to make note of teeth that are erupting in the mouth before they reach their height of occlusion, particularly at ages 5 and 6 when the permanent teeth are coming. This is when parents should spend extra time brushing their children’s teeth with a fluoride toothpaste. Children shouldn’t be completely relied upon to brush their own teeth until about 10 years old. I still brush my 9-year-old’s teeth, making sure to deplaque them and that the fluoride stays in her mouth for an adequate amount of time by brushing for at least 1 minute. I then let her brush her own teeth for as long as she wants.

I do not recommend professionally-applied fluoride treatments for children under the age of 6, unless there is clear evidence of high caries risk. In considering an in-office fluoride treatment, I need to see evidence of caries, a family history of caries, or high risk diet. If the risk assessment showed that a fluoride treatment was necessary, I would recommend the use of a fluoride varnish and selectively treat the at-risk teeth. This is especially true when teeth are erupting and sealants are difficult or impossible to place. The varnish can be painted on all exposed tooth surfaces. The varnish does not need to come into direct contact with the tooth surface to be effective on interproximal surfaces. High concentrations of fluoride are released into the oral fluids and can benefit adjacent tooth surfaces not directly covered by the fluoride varnish.


  1. Houpt M, Koenigsberg S, Shey Z. The effect of prior toothcleaning on the efficacy of topical fluoride treatment. Two-year results. Clinc Prev Dent . 1983;5:8-10.
  2. Ripa LW, Leske GS, Sposato A, Varma A. Effect of prior toothcleaning on bi-annual professional acidulated phosphate fluoride topical fluoride gel-tray treatments. Results after three years. Caries Res . 1984;18:457-464.
  3. Bijella MF, Bijella VT, Lopes ES, Bastos JR. Comparison of dental prophylaxis and toothbrushing prior to topical APF applications. Community Dent Oral Epidemiol . 1985;13:208-211.

From Dimensions of Dental Hygiene. January 2005;3(1):28-29.

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