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The Use of Stannous Fluoride in Oral Care

The Use of Stannous Fluoride in Oral Care

            The search for the new ways of controlling plaque in the oral cavity is one of the main focuses of research in periodontology due to the major role of plaque in the development of periodontal diseases. The main objective of any periodontal therapy is successful plaque control, which can be achieved by physical or chemical means. Although the mechanical removal of plaque is the basis for controlling periodontal diseases, it is impractical or inadequate in certain cases such as deep pockets, non-compliant clients, clients with limited manual dexterity or mentally handicapped, and orthodontic clients or those with fixed prosthesis. Sometimes, the physical removal of plaque is simply not enough due to the high speed of plaque formation, or to the high virulence of plaque. Therefore, the use of chemical agents as an adjunct to routine mechanical tooth cleaning is of interest to dental professionals. The focus of this paper is the use of the stannous fluoride (SnF2) as an antimicrobial agent in oral care.

            What are the clinical uses of SnF2 in dentistry? There are several studies showing that stannous fluoride has anticariogenic, antihypersensitivity, antiplaque and antigingivitis properties (Woodall, 1993, p.459). According to Walton, Thompson, and Seymour (1994), SnF2 is more effective than sodium fluoride as an anticaries agent. It is considered that the fluoride ion exerts its anticaries effect through promoting remineralization of the enamel surface with topical applications, through improving the crystalline structure to decrease enamel solubility, and through altering S. mutans to be less cariogenic. A study by Blank and Carbeneau (1986)( as cited in Woodall, 1993, p.671) indicate that varying concentration of stannous fluoride can reduce dentinal hypersensitivity. SnF2 reduces dentin sensitivity by inactivating enzymatic activity in the odontoblastic process and inducing mineralization within the dentinal tubules (which creates a calcified barrier on the dentin surface) (Walton et al., 1994). As an antimicrobial agent, it belongs to the category of heavy metal salts, and is composed of the two ions: tin (Sn) and fluoride (F). An antimicrobial agent in the oral cavity is the agent capable of killing plaque or interrupting plaque development. Stannous fluoride's anti-plaque and anti-gingivitis properties are attributed to the stannous ion. In regards to the SnF2 mechanism of action, one theory implies that stannous ions bind to lipotechoic acid on the surface of Gram-positive bacteria and reverse the charge on the surface of the cell. Consequently, the ability of the plaque to attach onto the tooth surface is reduced (Walton et al., 1994). However, the effectiveness of stannous fluoride solution in reducing bacterial adhesion is related to the stability of the stannnous ions in aqueous solution and their substantivity. According to Woodall, the accumulation of tin in bacteria may affect the cells’ ability to metabolize polysaccharides (1993, p. 617). Another theory, according to Fine D. (1995), is that tin ions displace calcium ions, altering the enzyme functioning of cells. They also trap thiol compounds, thus rendering cells more vulnerable and less enzymatically active.

            In dentistry, stannous fluoride may be delivered in several ways. As a caries-control agent, stannous fluoride in a form of a 0.8% solution can be applied topically for 4 minutes to reduce caries by up to 78% (Ripa, 1982 cited in Woodall, 1993, p.458). Currently, stannous fluoride is also available in a nonabrasive gel product at a 0.4% concentration. The use of stannous fluoride as an anti-gingivitis agent was studied as well. Boyd and others' study (as cited in Woodall, 1993, p. 620) found that self-administered daily irrigation with 0.02% stannous fluoride resulted in significant improvement in periodontal health. There is also evidence that 0.4% stannous fluoride gel, applied twice daily, can significantly reduce gingivitis by reducing the bacterial populations (Woodall, p.617, Carranza, p.520).

            The known disadvantages of stannous fluoride include its bad taste, its ability to stain demineralized enamel a yellowish-brown color, its ability to irritate the soft tissues, and the fact that it is unstable in solution (Ripa, 1982 as cited in Woodall, 1993, p.617). The agent has been minimally used in mouthrinses due to the difficulty to stabilize it in a mouthwash formulation (Perio 200****). The currently available 0.4% gel is more palatable than the 0.8%, but still could stain teeth, and taste bad.

            As new formulations are being developed to increase the stability of stannous fluoride, the product is being used more as an antimicrobial agent. The review of the past studies shows that despite the evidence of plaque reduction by stannous fluoride during the short-term studies, the long-term improvement in gingival health has not been proved (Carranza, & Newman, 1996, p.505, Periodontology 2000****). Several studies suggest that stannous fluoride is effective in reducing gingivitis and plaque accumulation. Specifically, the stannous ions affect the ability of cells to metabolize polysaccharides, which results in inhibited bacterial growth (Woodall, 1993, p.617). Binney, Addy, Owens, and Faulkner (1997) found that stannous fluoride as well as other toothpastes such as triclosan with zinc citrate and triclosan with copolymer toothpastes was more effective in inhibiting plaque compared to the control, namely water. However, it is difficult to determine if the results are of any merit because this study only investigated the short-term chemical action of the formulation in a greater dosage (3g of toothpaste mixed into a slurry of 10 ml water) than that normally delivered on a toothbrush, and did not account for the undetermined variable of toothbrushing. In another study by Addy, Greenman, Renton-Harper, Newcombe, and Doherty (1997), different stannous fluoride formulations were found to be significantly better than saline in reducing salivary bacteria count and plaque accumulation. In particular, stannous fluoride combined with stannous pyrophosphate toothpastes showed the most inhibitory action. The authors claimed that the findings suggest that the plaque inhibitory activity of SnF2 is largely derived from the stannous moiety and is dose-dependant. The evidence for increased availability of stannous ions in the pyrophosphate formulation was also revealed in a vivo study measuring tea staining on specimen with different formulations (Wade, Addy, Hughes, Milsom, & Doherty, 1997).

            The series of long-term studies and some short-term studies have been conducted to investigate the effectiveness of amine/stannous fluoride containing products in reducing plaque and preventing gingivitis. The results of comparing the effectiveness of the AmF/SnF to the other agents were inconsistent. Some studies ( Laine et al, 1993; Sgan-Cohen, Gat, Schwartz, 1996) found AmF/SnF more effective than NaF, while other studies (Mengel, Wissing, Schmitz-Habben, Flores-de-Jacoby, 1996) did not discover any differences between the two agents, suggesting that the positive results could be attributed to the Hawthorne effect. The study by Riep, Bernimoulin, & Barnett (1999) found the reduction of plaque by AmF/SnF not significant when compared to NaF. Also, the study by Laine et al (1993) found a significant decrease in gingival bleeding, while the other study that measured bleeding did not find any differences (Sgan-Cohen et al., 1996). Only one study reported more side effects in a AmF/SnF group compared to the NaF control, but this difference was significant (52% versus 6%). Generalization of the results from these studies is difficult due to high variability of methods used. For example, Sgan-Cohen et al. (1996) and Riep et al. (1999) conducted their studies on healthy individuals, while Mengel et al. (1996) used subjects with chronic gingivitis and early signs of periodontitis, and Laine et al. (1993) did their study on lymphoma patients undergoing cancer chemotherapy, all of which could affect the results. However, the stannous fluoride was combined with amide fluoride. Moreover, because all these studies used a combination agent (AmF/SnF), which combines the antimicrobial effect of stannous fluoride with the caries-preventive potential of amide fluoride, it is even harder to judge the effectiveness of SnF2 in it, especially considering the evidence showing that the activity of stannous fluoride is greatly affected by the rest of the ingredients in a health product (Wade et al, 1997). The summary of the above studies reveals the non-unanimous results.

            In another long-term (18 weeks) home use study on 143 volunteers, Owens, Addy, and Faulkner (1997) found no significant differences between stannous fluoride toothpaste and other test agents for the gingival index and plaque index at 6 or 18weeks. However, there was a consistent pattern for decreasing gingivitis and plaque scores in all groups. This is not to say that there is a lack of clinical superiority of the test products compared to stannous fluoride agents. More likely, the home use methodology could be insensitive to detect actual differences, primarily because subjects may perform additional antiplaque activities, which were masked by the Hawthorne effect.

            SnF2 has low to moderate substantivity, which is the sustained retention of the agent in the mouth (Mosby’s Comprehensive Review, 1993). Another study looked at substantivity of stannous fluoride toothpaste (Elworthy, Greenman, Doherty, Newcombe, Addy, 1996), and found stannous fluoride toothpaste to be similar in effectiveness to its non-stannous fluoride-containing control at all time points up to 5hours, and significantly more effective after 5 hours. In comparison to water, stannous fluoride was significantly more effective at all times.

            With regards to the effectiveness of stannous fluoride in subgingival irrigation for enhancing the beneficial effects of debridement, Krust, Drisko, Gross, Overman, and Tira (1991) investigated this method. Their pilot study of eight patients exhibiting 32 sites with moderate periodontal disease found no significant changes in bleeding tendency, probing depth, attachment level and levels of Bacteroides porphyromonas after four weeks of subgingival irrigation with 1.64% stannous fluoride in addition to debridement. Interestingly, the same results were found with 0.12% chlorohexidine and sterile saline. However, the sample size used in this study may have been too small to discriminate significant differences resulting among the groups. A larger sample will minimize the effects of extreme scores and increase the representativeness of the sample. It is difficult to compare results between these studies since they use different irrigation delivery system, which varies the duration of action in the periodontal pockets.

            Very interesting results were showed by the in vitro study by Shapria, Shchatzker, Gedalia, Borinski, and Sela (1997). They discovered that AmF, SnF2 or AmF/SnF2 enhanced the superoxide release from neutrophils by two- to three- fold. This suggests that AmF and SnF2 enhance the oxygen-dependent antibacterial activity of neutrophils.

            Along with the studies supporting the effectiveness of stannous fluoride, there are studies that stand against its use. Sjostrom,& Kalfas (1999) described a case of extensive periodontal tissue necrosis and permanent loss of alveolar bone after irrigation of newly debrided periodontal pockets with a 2% stannous fluoride solution. The authors of the article claim stannous fluoride solution to be the most probable cause of tissue necrosis, although the paper does not discuss the possibility of a local allergic reaction to stannous fluoride, or reaction to the topical anesthetic. However, even with so many undecided points, this case presents with the possibility of serious long-standing side effects of stannous fluoride use that should not be left unattended.

            There are equivocal and sometimes-conflicting results among clinical studies on the effects of stannous fluoride administered in oral care; however, significant reductions in bacterial plaque and gingivitis have been documented along with the potential side effects. Partly, the difficulty lies in that stannous fluoride can hydrolyze within formulations and this instability may explain why not all studies demonstrate increased plaque inhibition by stannous fluoride. Its antimicrobial effect is more of a qualitative than a quantitative one; since studies showed a decrease in gingivitis without reduction in the amount of plague. The side effects are most probable to be minor with topical use, but there is a possibility of the more serious long-standing side effects if delivered into the newly debrided periodontal pocket. In order to draw a final conclusion regarding the effectiveness and possible risks of stannous fluoride use, the more thorough literature review should be performed, and obviously more studies are needed to test the properties of the agent. The studies must be conducted in vivo as much as possible, and should be as unanimous as possible regarding the methods used, the number, age and state of health of subjects, as well as the measurements used to describe one or another property. It is very important that stannous fluoride is investigated both in a pure form, and as a part of different formulations used in treatment and prevention of disease (e.g. toothpastes, mouthrinses, subgingival irrigation solutions etc). With regards to its use in subgingival irrigation, it is difficult to compare results between studies since different irrigation delivery systems were utilized, which varied the duration of chemical action in the periodontal pockets. Further research is necessary to explore the use of sustained release devices and varied application intervals on the effectiveness of stannous fluoride used subgingivally in oral irrigation. Currently, there is consensus in that chemical management of plaque can enhance mechanical removal, especially for individuals who are unable to brush and floss, mentally handicapped, have deep pockets, orthodontic clients. Since stannous fluoride has been shown to have anticaries, anti-hypersensitivity, anti-plaque and anti-gingivitis properties, then individuals who need who may need caries prevention, remineralization, hypersensitivity treatment and reduction in plaque and gingivitis would benefit from stannous fluoride the most. An example of such case would be an elderly client with recession, root caries dentinal hypersensitivity, and limited manual dexterity living in non-fluoridated community. However, when considering stannous fluoride use a clinician should weigh the benefits over the potential side effects of the agent.


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