Typical commercial acidulated phosphate-fluoride (APF, 12,300 ppm fluoride) gels contain 2% sodium fluoride, 0.34% hydrogen fluoride, and 0.98% phosphoric acid with thickening, flavoring, and coloring agents in an aqueous gel. Some commercial gels, however, contain more sodium fluoride (2.6%) but less hydrogen fluoride (0.16%). The fluoride-ion concentration of most gels ranges from 1.22% to 1.32%. Examples of office and prescription fluoride treatments are listed in Table 3-1. APF products are contraindicated for patients with tooth hypersensitivity—they can cause erosion and worsen the hypersensitivity.

Neutral sodium fluoride foams, gels, and rinses are available. One product is thixotropic, which contains sodium fluoride and thickening agents (polyacrylic acid and a gum). The pH is adjusted to between 6 and 8. Values of pH in this range should minimize acid etching of restorative materials, such as composites, compomers, resin-modified glass ionomers (hybrid ionomer), glass ionomers, and ceramics, caused by more acidic APF gels.

Varnishes containing 5% sodium fluoride (22,600 ppm fluoride) are available (Duraflor Halo 5% Sodium Fluoride White Varnish, Medicom, Tonawanda, NY; Kolorz ClearShield Fluoride Varnish, DMG America, Englewood, NJ). Some products (Enamel Pro Varnish, Premier Dental Products, Plymouth Meeting, PA) also contain amorphous calcium phosphate (ACP), which contributes to remineralization of enamel.

Stannous fluoride products are effective in providing fluoride but can cause staining of tooth surfaces and restorations.

Characteristics of different types of fluoride treatments are compared in Table 3-2. The clinical effectiveness of acidulated phosphate-fluoride gels varies, which depends in part on the method and frequency of application. Reductions in dental caries of 37% and 41% were observed in two studies of 2 years’ duration in which the gel was applied annually. A reduction of 26% was observed at the end of 3 years in another study. A reduction of 80% after 2 years was observed in a study in which a gel with lower fluoride content (0.5% versus 1.23%) and higher pH (pH 4.5 versus pH 3) than that used in the aforementioned studies was self-applied each school day. One clinical study showed no significant reduction in the incidence of dental caries after 2 years. The typical 4-minute application appears to be more effective than a 1-minute application.

Varnish containing 5% sodium fluoride has been found to be effective in reducing caries in primary and permanent dentition. Caries reduction (Eecayed, Missing, Filled Surfaces – DMFS) ranged from 19% to 48% in primary dentition and from 30% to 63% in permanent dentition. Five percent sodium fluoride varnish is also effective in reducing orthodontic decalcification.

Most commercial pit and fissure sealants, examples of which are listed in Table 3-3, are resins in which polymerization is activated by light. The chemistry of sealants is similar to that of the composite restorative materials that are discussed in Chapter 4. The principal difference is that sealants are more fluid to penetrate the pits and fissures in addition to the etched areas produced on the enamel, which provide for retention of the sealant.

Sealants polymerized by visible light (490-nm wavelength) are one-component systems that require no mixing. The resin is a diluted dimethacrylate monomer (bisphenol A-glycidyl methacrylate [Bis-GMA] or urethane dimethacrylate [UDMA]), the polymerization of which is initiated by activation of a diketone in the presence of an organic amine with the visible light. Several sealants contain up to 50% by weight of inorganic filler to improve durability, and many contain a white pigment to improve the contrast between the sealants and enamel. The sealants polymerize in the mouth when exposed to a curing light to become a cross-linked polymer, as indicated in the following simplified reaction:

< ?xml:namespace prefix = "mml" ns = "http://www.w3.org/1998/Math/MathML" />Dimethacrylate+Diluent+Activator+Light=Sealant

The sealants polymerized by an organic amine accelerator are supplied as two-component systems. One component contains a monomer and a benzoyl peroxide initiator, and the second component contains a diluted monomer with 5% organic amine accelerator. The two components are mixed thoroughly before being applied to the prepared teeth.

Physical and mechanical properties of commercial pit and fissure sealants are listed in Table 3-4. Additional properties of clinical importance include retention and efficacy.

Retention of a sealant in a fissure is the result of mechanical bonding caused by penetration of the sealant into the fissure and the etched areas of enamel to form tags. Filling the fissure completely is difficult because air frequently is trapped in the bottom of the fissure (Figure 3-2, A), or the accumulation of debris at the base of the fissure prevents it from being sealed completely (Figure 3-2, B). Acid etching of the enamel surface improves the retention of the sealant by cleaning the area to be sealed, improving the wettability of the enamel, increasing the surface area, and forming spaces into which the sealant can penetrate to form tags (Figure 3-3).

Penetration of a sealant into the fissure must occur before the sealant has polymerized. The rate of penetration is determined by the configuration (length and radius) of the pit or fissure and by the penetration coefficient (PC) of the sealant (see more details in Appendix 3-1). The penetration coefficient is related to the surface tension and viscosity of the sealant and the contact angle of the sealant on the enamel.

The containers in which the sealant components are supplied must be kept closed tightly during storage to minimize the evaporation of volatile monomers, which would cause the sealant to become more viscous and limit its penetration into the pit or fissure.

Many clinical studies have been reported. However, caution is warranted when comparing some of these studies because materials, techniques, teeth studied, and clinical criteria for judging success or failure vary from study to study. Three parameters important in the evaluation of a clinical study of a sealant are (1) a statistical test of the significance, (2) the net gain as a result of treatment, and (3) the percentage of effectiveness. When pairs of teeth are studied, the net gain is the number of pairs in which the treated tooth is sound and the untreated tooth is decayed minus the number of pairs in which the treated tooth is decayed and the untreated tooth is sound. The percentage of effectiveness is the net gain divided by the total number of carious controls expressed as a percentage. A summary of a 5-year clinical study on schoolchildren is listed in Table 3-5. The effectiveness of a single application of a sealant clearly decreases with time.