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Oral healthcare workers are all familiar with the misery associated with dental caries, yet it can be difficult to appreciate the significant hardship the disease presents on a global scale. While its prevalence varies within a community, region or country, dental caries can be found throughout the world.1 More affluent countries tend to have a higher incidence of caries, due in part to diets higher in sugar. However, less affluent countries are generally experiencing an increasing number of caries as well,1 and it is no coincidence that the amount of sugar consumed is also on the rise in those areas. Without sufficient oral hygiene education and fluoride exposure, the situation will most likely continue to worsen.2 While dental caries is just one component of oral disease, it is the most common. According to the World Health Organization (WHO), dental caries is found in 60 percent to 90 percent of school-aged children throughout the world.3 This article reviews the increasing problem of caries worldwide and discusses the role of fluoride to address it—in particular, silver diamine fluoride, supported for its caries preventive role by both WHO and the U.S. Institute of Medicine (IOM).
There is an unequal distribution of diseases and resources necessary to combat them, dental caries included.2 Access to care is problematic in the majority of developing nations due to insufficient numbers of oral health care facilities and a corresponding shortage of trained oral health care professionals.2 Certain populations of any society are more vulnerable, more disadvantaged and more susceptible to hardship and disease than others.2 Ethnic minorities too often lack health care. The poor and less educated are frequently in this vulnerable group, as well as the very young, the elderly and those who are mentally and/or physically disabled.2 Available caregivers might have inadequate training in oral health practices, thereby unintentionally providing substandard care.4 Without preventive care or intervention, the disease process usually progresses unabated until an emergency occurs, often ending with premature tooth loss due to the necessity of extractions to resolve pain. Long term, these situations can cause reduced quality of life, particularly among the elderly.2 To reduce needless loss of teeth and provide restorative treatment for simple, uncomplicated caries, WHO accepted Atraumatic Restorative Treatment (ART) as a viable option in situations where limited equipment, electricity and materials are available.5 Hand instruments, fluoride-releasing glass ionomer materials, and simple dental supplies/materials are basic components of an oral health care strategy that would allow a health care provider to treat active caries.5 The training is rudimentary, but ART is an effective means of providing care to vulnerable populations. This procedure can be especially helpful in primary dentitions because caries progresses faster into the dentin and threatens the pulp at a faster rate than in the adult dentition.5
World Health Organization
While ART is considered an important secondary intervention, the emphasis of the WHO Oral Health Programme, a technical program within WHO’s Chronic Diseases and Health Promotion Department, is to construct primary intervention policies that promote health, both oral and general, as well as emphasizing the prevention of disease.6 This goal is accomplished by identifying risk factors and developing strategies that allowing people to minimize risks within their control, namely by adjusting personal behavior and lifestyle choices.6 Behavior changes might include incorporating oral hygiene practices, making informed dietary choices and understanding the dental benefits of fluoride. The Oral Health Programme of WHO views fluoride programs as essential in the battle against caries.6
WHO’s strategies target increasing the awareness of specific chronic diseases such as dental caries and their associated risk factors, promoting fluoride delivery systems that work best for a particular community, and providing technical assistance to those communities as they incorporate oral health components into their public health infrastructures.3 The goals are prevention-oriented, especially for portions of the population affected by poverty and greater risk for decreased quality of life and longevity.4 One high-risk group is the world’s growing elderly population.4 This population is challenged with multiple chronic diseases. Oral health and general health are interconnected; to neglect one is to neglect both.
It is estimated that only approximately 20 percent of the global population understands the preventive role of fluoride in dental health.1 Lack of knowledge can be a significant barrier to fluoride use; however, other existing barriers also must be identified and addressed.1 Enlisting the involvement and participation of local schools and nursing homes can be pivotal to success.2 Fluoridated community water systems might not always be feasible. Therefore, promotion of topical fluorides, fluoride salts, toothpastes, rinses, etc. can be part of cost-effective community caries prevention.7 Regardless of its form, fluoride plays a crucial role in caries prevention.
Healthy People Program
The U.S. government also recognizes the importance of promoting health, hence the creation of the Healthy People initiative over 20 years ago. Healthy People 2020 is the most recent version of the objectives and goals the government has set to gradually improve its citizens’ health. Healthy People 2020 aims to increase the percentage of the population with access to an oral health care system, increase the number of schools with health centers addressing oral health, and increase preventive oral health care for low-income children.8 Also, the U.S. government has targeted an increase in the number of public water systems having an optimal level of fluoride.8 Fluoridated community water systems are still recognized as the most effective means of caries prevention.7
Role of Fluoride and Silver
No matter what the form of fluoride, it has a deleterious effect on oral biofilm. It changes plaque development and structure, as well as its metabolism of carbohydrates, thus reducing the quantity of acid production.7 It is well-known for its role in preventing demineralization and promoting remineralization. During demineralization, loss of calcium phosphate from sound enamel begins at a pH of 5.5; however, the presence of fluoride can reduce the pH to 4.5 at which demineralization of enamel occurs, thus having a protective effect.7 As fluoride is gradually taken up by the tooth structure, the enamel transforms from hydroxyapatite (Ca10(PO4)6(OH)2) to fluorapatite (Ca10(PO4)6F2).9 This latter mineral is less acid-soluble.9
As stated earlier, fluoride sources can take various forms. One such compound is silver diamine fluoride (Ag(NH3)2F). This material has been used throughout Asia and in portions of South America to prevent and arrest caries.7 Both WHO and IOM in the U.S. have determined that silver diamine fluoride (abbreviated SDF), is a beneficial material to be used in the fight against dental caries.7 Applying SDF is simpler, faster, cheaper and easier than most other treatments,9 and the potential for use in dental public health is tremendous. At this point in time, however, it can be used in the U.S. only for research purposes while the U.S. Food and Drug Administration gathers more evidence on its effectiveness and safety.
As its name implies, there are two main components to SDF: the silver part and the fluoride part. The benefits of fluoride are well-documented. The silver component of SDF comprises silver ions (Ag+), which have been shown to have an antimicrobial effect in preventing infections and in coverings for severe burns,9 as well as reducing biofilms from tubing, such as catheters.10 Silver also has been used in purification of drinking water.10 According to the critical review by Rosenblatt, Stamford and Niederman,9 “Studies have indicated that silver interacts with sulfhydryl groups of proteins and with DNA, altering hydrogen bonding and inhibiting respiratory processes, DNA unwinding, cell-wall synthesis, and cell division.”9 Through this mechanism, biofilm formations are impeded and pathogens destroyed.
Silver diamine fluoride has been the subject of various randomized clinical studies because of the anti-infective properties of silver coupled with the benefits of fluoride. Over the last few decades, scientists and health professionals have sought to determine if SDF is an effective material to combat dental caries.11 Since its first use in 1969, SDF has been compared to other preventive treatments for dental caries in high-risk populations.11 Results supporting its effectiveness follow.
Many nations have reported root caries as common among their institutionalized elderly.12 As many as half of the elderly residents in group homes have been reported to currently experience or have previously experienced root caries.12 Generally, oral health and hygiene are more compromised for residents than for individuals living independently or with family members.12 Therefore, prevention and treatment of root caries are prioritized by WHO and advocacy groups for the elderly.4
Due to their mineral composition, exposed root surfaces are naturally softer and more susceptible to demineralization than is enamel. While enamel is the most mineralized material in the body, dentin is only 70 percent mineralized.13 Additionally, dentin’s hydroxyapatite contains more magnesium and carbonate than the enamel’s hydroxyapatite; therefore, the hydroxyapatite in dentin is less stable and more easily dissolved when exposed to acidogenic plaque.13 Furthermore, the organic portion of dentin, primarily collagen fibers, can be denatured by the acids and enzymes produced by the adhering biofilm.13 These physical qualities of permit demineralization of dentin at a higher oral pH than enamel—6.5 versus 5.5.13 This translates to a caries progression rate approximately twice as fast for dentin than for enamel.13 However, if sufficient mineral salts remain in the dentin, remineralization can occur.13 The metabolic activity of the oral bacteria must be altered to modify the progression of caries.14 Several investigations have studied the effectiveness of SDF against caries due to the antibacterial properties of silver ions12 and fluoride’s ability to reduce bacterial production of polysaccharides, which are critical to plaque adhesion, and to decrease bacteria’s capacity to metabolize carbohydrates.13
A study of institutionalized elderly patients concluded that the annual application of SDF demonstrated a greater benefit than oral hygiene instructions alone or the application of chlorhexidine varnish or sodium fluoride varnish every three months. All treatment groups received oral hygiene instruction. The number of root caries was significantly higher in the instruction-only group.13 The root caries reduction for patients treated with SDF was similar or improved compared to the chlorhexidine and sodium varnish groups. The main benefit of using SDF is needing only one application annually versus four applications for the varnishes.13 This, and the fact that SDF is easy, inexpensive and minimally invasive, makes it a good option for situations where nontraditional dental treatment is necessary.13 For these same reasons, SDF can be beneficial to special needs populations who have physical or mental conditions limiting their ability for oral self-care or access to care.13
Fluoride Options and Availability
Although water fluoridation is viewed as the most equitable and cost-effective means for fluoride delivery,7 there are only approximately 355 million people in the whole world who receive fluoride in this manner.15 As many as 86 percent of Chinese adults were unaware of the benefits of fluoride.15 While special needs populations might need specific attention and care, the general populations of most nations can also benefit from augmented fluoridation when existing levels are inadequate. A Cochrane review found that even though a fluoridated water system might be in place, topical sources of fluoride are a useful complement in caries prevention.15 Since the 1960s, SDF has been recognized as an effective topical material in the fight against dental caries.16
Glass Ionomers Material
Glass ionomer cements are known for their fluoride-releasing properties and are frequently used as a restorative material for reducing the risk of secondary caries.17 The lower the pH in the oral environment, the more fluoride is released from the material.17 Glass ionomer cements are used in ART for this purpose because the fluoride released from the material is absorbed by the surrounding tooth structure, thus the restored tooth is strengthened against additional acid attacks.5
SDF can be used in conjunction with glass ionomer material during ART. When SDF has been placed in cavity preparations prior to a glass ionomer restoration, the quantity of fluoride and the depth of absorption increased significantly compared to the glass ionomer alone.18 Formation of reparative dentin also is promoted by placing silver fluoride beneath a glass ionomer cement restoration in deciduous teeth.19 This procedure is especially beneficial for people at high risk for caries.17
The Pros of SDF
After conducting a critical review of research studies regarding SDF, Rosenblatt and associates concluded that it has the ideal product qualities the IOM and WHO advocate for the 21st century.9 SDF is effective in the treatment and prevention of dental caries, inexpensive and easy to use with minimal training necessary for personnel, as well as having a minimal treatment time and invasiveness.9 SDF can be painted on with a micro brush or dabbed on with a small cotton ball in only a minute.9 The armamentarium for SDF application is simple, without the need for plumbed water sources, electricity or expensive equipment.20 These qualities make it an excellent candidate for inclusion in WHO’s and IOM’s arsenal against caries,9 especially in disadvantaged populations.7
Although SDF has many appealing qualities, there are some drawbacks that must be discussed. By far the most commonly mentioned negative aspect is the black staining that accompanies its use when applied to active caries,9-13,16-20 as well as the possible staining of neighboring glass ionomer cements.18 Intact tooth surfaces do not discolor,9 and blackened, arrested caries are not due exclusively to SDF alone—discoloration also occurs in arrested caries having had no intervention or after sodium fluoride varnish treatment. However, the SDF treated samples had a higher percentage of blackening.20 After the application of SDF to a carious lesion, excess silver and phosphate components react chemically to form silver phosphate, which acts as a hard, insoluble layer forming a barrier, limiting the solubility of tooth structure and arresting the caries process.13 The unattractive appearance of this blackened silver phosphate layer is the most common undesirable effect to which patients object.9-13, 16-20 Another undesirable trait is SDF’s unappealing metallic taste.20
All in all, the information on silver fluoride is interesting and promising. The potential benefit of SDF is remarkable: its purported ability to arrest dental caries; minimal requirements for training, supplies and personnel; and reduced cost of treatment when compared to restorative care. Physical and emotional trauma experienced by the patient can also be reduced by having caries treatment that is less invasive, less potentially painful, and preventive rather than restorative. A solution to the global dental caries problem is necessary to address the unmet dental needs of millions of people. With further research, the establishment of a protocol for SDF application can be determined. Without question, more research is needed, especially in vivo studies with long-term results reported for the use of SDF on humans. Dental hygienists are waiting for the day when this medicament can be included in the standard of care they provide their patients.
1. World Health Organization. Global consultation on oral health through fluoride. 2006. Available at: www.who.int/oral_health/events/Global_consultation/en/index.html.
2. Petersen PE. (World health organization global policy for improvement of oral health – world health assembly 2007. Int Dent J. 2008; 58(3): 115-21.
3. World Health Organization. Media centre: oral health. 2007. Available at: www.who.int/mediacentre/factsheets/fs318/en/index.html.
4. World Health Organization. Oral health in ageing societies: integration of oral health and general health. Available at: www.who.int/oral_health/events/Ageing_societies/en/index.html.
5. Dental Health International Nederland. Manual for the ART approach to control dental caries. Available at: www.dhin.nl/art_manual.
6. World Health Organization. The objectives of the WHO global oral health programme (ORH). Available at: www.who.int/oral_health/objectives/en/index.html.
7. Chu CH, Mei ML, Lo ECM. Use of fluorides in dental caries management. Gen Dent. 2010; 58: 37-43.
8. Healthy People 2020. Summary of objectives: oral health. Available at:www.healthypeople.gov/2020/topicsobjectives2020/pdfs/OralHealth.pdf .
9. Rosenblatt A, Stamford TCM, Niederman R. Silver diamine fluoride: a caries “silver-fluoride bullet.” 2009. J Dent Res. 88(2): 116-25.
10. Hiraishi N, Yiu CKY, King NM, et al. Antimicrobial efficacy of 3.8% silver diamine fluoride and its effect on root dentin. J Endodont. 2010; 36(6): 1026-29.
11. Yee R, Holgren C, Mulder J, et al. Efficacy of silver diamine fluoride for arresting caries treatment. J Dent Res. 2009; 88(7): 644-7.
12. Tan HP, Lo ECM, Dyson JE, et al. A randomized trial on root caries prevention in elders. J Dent Res. 2010; 89(10): 1086-90.
13. Tan H. Prevention and arrest of root surface caries in Chinese elders living in residential homes. 2006; Doctoral thesis, University of Hong Kong. Available at: hub.hku.hk/bitstream/10722/50947/2/Abstract.html.
14. Kidd EAM. How ‘clean’ must a cavity be before restoration? Caries Res. 2004; 38: 305-13.
15. Petersen PE, Kwan S, Zhu L, et al. Effective use of fluorides in the People’s Republic of China –a model for WHO mega country initiatives. Commun Dent Health. 2008; 25(4): 257-67.
16. Braga MM, Mendes FM, Benedetto MS, Imparato JCP. Effect of silver diammine fluoride on incipient caries lesions in erupting permanent first molars: A pilot study. J Dent Child. 2009; 76(1): 26-33.
17. Ariffin Z, Ngo H, McIntyre J. Enhancement of fluoride release from glass ionomer cement following a coating of silver fluoride. Aust Dent J. 2005; 51(4): 328-32.
18. Knight GM, McIntyre JM, Craig GG, Mulyani. Ion uptake into demineralized dentine from glass ionomer cement following pretreatment with silver fluoride and potassium iodide. Aust Dent J. 2006; 51(3): 237-41.
19. Knight GM, McIntyre JM, Craig GG, et al. An in vitro model to measure the effect of a silver fluoride and potassium iodide treatment on the permeability of demineralized dentine to Streptococcus mutans. Aust Dent J. 2005; 50(4): 242-5.
20. Lo ECM, Chu CH Lin HC. A community-based caries control program for pre-school children using topical fluorides: 18-month results. J Dent Res. 2001; 80(12): 2071-4.
Monika Alcorn, RDH, BSDH
Ellen J. Rogo, RDH, PhD
Associate Professor Idaho State University