2.0% neutral sodium fluoride and 1.23% acidulated phosphate fluoride. acidulated phosphate fluoride (apf) gel or foam comprises a sodium fluoride solution, paste, or powder that has been acidulated with hydrofluoric acid to ph 3 to 4, buffered with a phosphate, and mixed with a gel or foam vehicle such as carboxymethyl cellulose. 1.23% acidulated phosphate fluoride gel or foam is used for patients without tooth-colored restorations, while 2.0% neutral sodium fluoride is used for patients with composites, porcelain, titanium, sealants or sensitivity. professionally applied fluoride gel or foam is applied through the use of a foam mouth tray which is held in the mouth by gently biting down. the application usually lasts for approximately four minutes, and patients should not rinse, eat, smoke, or drink for 30 minutes after application. the reason for this is to allow the teeth to absorb the fluoride into the tooth structure when it is at its highest concentration, without being interrupted. this aids in the repair of microscopic dental decay. there is no clinical evidence on the effectiveness of one-minute fluoride gel/foam applications. a specific benefit when using foam is that less product is required during application, which results in a lower fluoride dose and lessens the risk of accidental ingestion. additionally, more research regarding the efficacy of fluoride foam is needed as the evidence for its effectiveness is not as strong compared to those of fluoride gels and varnish. some gels are made for home application with the use of a custom tray. a model of a person's teeth can be made by a dental professional, who then uses that to make trays, similar to a sport guard tray, which is put over their teeth. the patient can then use this to hold a fluoride treatment against their teeth overnight or several minutes during the day. the concentration of fluoride in these gels is much lower than in professional products. the self-applied sodium fluoride gel/foam typically contains 0.5% fluoride and stannous fluoride gel/foam contains 0.15%. head and neck radiation treatment may destroy the cells of the salivary gland which can result in dry mouth. patients with reduced salivary flow are at an increased risk of tooth decay. the home application of 1.1% fluoride gel with a custom tray is recommended for patients undergoing or are finished with head and neck radiation treatment and patients with decreased salivary flow. more research is required regarding the efficacy of fluoride gels in treating initial dental decay lesions. varnish fluoride varnish has practical advantages over gels in ease of application and use of smaller volume of fluoride than required for gel applications. the principle of fluoride varnish is to apply fluoride salt in a very high concentration (approximately 50,000 ppm) onto the surface of the teeth. fluoride varnish is a resin-based application that is designed to stay on the surface of the teeth for several hours. as this varnish rests on the tooth's surface, saliva dissolves the fluoride salt, which in turn allows fluoride ions to be released and absorbed by the teeth and soft tissues. later, the fluoride is re-released into the oral cavity from these reservoirs which acts as protection for the teeth against cavities. currently, there is also no published evidence that indicates that professionally applied fluoride varnish is a risk factor for enamel fluorosis. the varnish is applied with a brush and sets within seconds. fluoride varnish has shown to be effective in reducing initial dental decay lesions in both primary and permanent dentition. application of fluoride varnish every six months is effective in preventing dental decay in primary and permanent teeth of children and adolescents. slow-release devices devices that slowly release fluoride can be implanted on the surface of a tooth, typically on the side of a molar where it is not visible and does not interfere with eating. the two main types are copolymer membrane and glass bead. these devices are effective in raising fluoride concentrations and in preventing cavities, but they have problems with retention rates, that is, the devices fall off too often. a 2018 cochrane review found insufficient evidence to determine the effect of slow-release fluoride glass beads in caries-inhibiting when compared to other types of fluoride therapy. lozenges fluoridated lozenges may contain about 1 mg fluoride each, and are meant to be held in the mouth and sucked. the dissolved lozenge is swallowed slowly, so the use of lozenges is both a topical and a systemic therapy. a 1955 study comparing the effects of fluoride lozenges and fluoride pills provided clear evidence early that fluoride acts topically. medical supplements medical fluoride supplements in the form of tablets, lozenges, or liquids (including fluoride-vitamin preparations) are used primarily for children in areas without fluoridated drinking water. the evidence supporting the effectiveness of this treatment for primary teeth is weak. the supplements prevent cavities in permanent teeth. a significant side effect is mild to moderate dental fluorosis. a cochrane review also found no evidence that daily fluoride supplementation in pregnant women was effective in preventing tooth decay or causing fluorosis in their children.