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Effect of Fluoride Varnish on Demineralization Around Orthodontic Brackets
Effect of Fluoride Varnish on Demineralization Around Orthodontic Brackets Robert N. Staley In vitro studies comparing the ability of several fluoride varnishes and sealants to inhibit caries have been reviewed. To truly assess their use in orthodontic patients requires clinical trials. Because fixed orthodontic appliances provide a very favorable environment for the creation of white spot lesions, the sealants that contribute both a physical barrier and fluoride release have the greatest potential to protect enamel in patients during orthodontic treatment. (Semin Orthod 2008;14:194-199.) © 2008 Elsevier Inc. All rights reserved.
he advent of bonded multibracketed fixed appliances in the 1970s brought enamel white spot lesions to the attention of orthodontists. Orthodontists became interested in fluoride varnishes for their potential to prevent or reduce enamel white spot lesions that develop during treatment with bonded fixed appliances. Excellent patient dietary and oral hygiene practices that include topical fluoride agents such as toothpastes and rinses can prevent or minimize the formation of enamel white spot lesions during orthodontic treatment. However, patients with poor dietary and oral hygiene practices can develop white spot lesions within 4 weeks after the beginning of treatment in the absence of fluoride supplementation1 and these lesions can progress to open cavitations.2 The noncarious tooth has on its enamel surface an acquired bio-film, the pellicle, which participates in dynamic physical-chemical equilibrium with the enamel and oral fluids.3,4 When the pH of oral fluids fluctuates below the phys-
T
Department of Orthodontics, College of Dentistry, The University of Iowa, Iowa City, IA. Research supported by the Department of Orthodontics. Address correspondence to Robert N. Staley, DDS, MA, MS, Department of Orthodontics, College of Dentistry, The University of Iowa, Iowa City, IA 52242. Phone: 319-335-7302; E-mail: [email protected] © 2008 Elsevier Inc. All rights reserved. 1073-8746/08/1403-0$30.00/0 doi:10.1053/j.sodo.2008.03.004
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iologic norm, calcium and phosphate ions diffuse from hydroxyapatite mineral in the enamel to the pellicle and into the oral cavity (demineralization). When the pH of oral fluids increases to the norm, calcium and phosphate ions in the saliva are transmitted through the pellicle into the enamel following the laws of chemical equilibrium (remineralization). The remineralization process is greatly enhanced by low levels of fluoride in the saliva and plaque.4 Many theories have been proposed about the mechanisms that cause caries, and research for a better understanding of the caries process continues. The plaque deposited on the surface of a carious tooth contains food debris and microorganisms. In the presence of fermentable carbohydrates, plaque microorganisms produce organic acids that lower the pH in the plaque, which in turn causes a diffusion of calcium and phosphate ions from the enamel through the pellicle and into the plaque fluid. This continues until equilibrium is reached between the enamel and the plaque liquid. Demineralization of the enamel continues when further episodes of low pH levels occur in the plaque. The enamel surface of a white spot carious lesion remains intact while the area below the surface is demineralized.3 Featherstone and coworkers5 hypothesized that as the pH of the plaque lowers the proportion of undissociated acids in the plaque fluid increases. Because these acids are uncharged they can diffuse through the porous
Seminars in Orthodontics, Vol 14, No 3 (September), 2008: pp 194-199
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enamel matrix down a concentration gradient. After they have penetrated the enamel to a depth where the pH is higher, the acids dissociate and release protons that attack the apatite matrix. The released calcium and phosphate ions either diffuse outward into the plaque or precipitate in the surface layer of enamel maintaining an intact surface zone. The first fluoride varnishes were developed in the 1960s (Duraphat® [DPT], 5% sodium fluoride in a colophony base; Colgate Oral Pharmaceuticals Inc., Canton, MA) and in the 1970s (Fluor ProtectorTM [FP], a clear, transparent polyurethane lacquer containing 0.1% weight fluoride ion as difluorosilane; Ivoclar Vivadent, Inc., Amherst, NY) to prevent caries in children.6 Metaanalyses of controlled clinical trials involving DPT7-11 confirmed the clinical effectiveness of this varnish in inhibiting dental caries. The varnish has been widely used in children in Europe and to a lesser extent in North America.6 Four applications each year or three weekly applications once a year are effective. Also two applications a year may be equally effective.6 Results for FP have been inconclusive.6 The cariostatic mechanism of fluoride varnishes is not fully understood, but some possible explanations will be discussed. The colophonybased varnish is a sticky yellowish-brown substance that hardens on contact with saliva producing a temporary cover over the enamel. The patient is instructed to refrain from brushing for 4 hours after application.12 Patients will remove the varnish from the tooth after a few days of tooth brushing. It is speculated that as the varnish is brushed away, fluoride ions depart from the edges of the varnish to join calcium and phosphate ions from the saliva, pellicle, and plaque, and, under favorable conditions, the ions become incorporated into the enamel as fluoridated hydroxyapatite, a less soluble form of apatite. The varnish also leaves calcium fluoride on the surface of the enamel in a CaF2-like material that is less soluble and most likely leaches away from the surface through the pellicle.13 A 1-week in situ exposure of enamel slabs treated with acidulated phosphate fluoride (APF) gel, DPT, and FP showed that only the FP slabs retained a measurable amount of CaF2-like material at the end of the week.13 This finding may be related to the different physical properties of the topical fluoride agents. The APF gel
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and DPT are less likely to persist on the enamel surface 7 days in situ, whereas, FP, a silane sealant, forms a long-lasting durable attachment to the enamel surface. While speculating on the cariostatic mechanism of topical fluoride agents, Ogaard14 commented that fluoride concentration in the enamel structure is not as effective in reducing caries as is the continuous presence of fluoride in the plaque liquid. He thought the fairly insoluble CaF2-like deposits left by topical fluoride agents on the surface of the enamel provide the fluoride ions that diffuse into the plaque liquid and participate in the remineralization of enamel.
In Vitro Studies The purpose of this article is to discuss the results of several in vitro thesis research projects conducted by residents in the Orthodontic Department, College of Dentistry, at The University of Iowa. The studies were conducted in collaboration with cariologists Dr. James S. Wefel and Dr. Kevin J. Donly from the Dows Institute for Dental Research at the College of Dentistry. The cycling of extracted human teeth from artificial saliva to cariogenic solutions mimics the dynamic processes that occur in the oral cavity. The lesions in the control group had to be kept in the white spot lesion stage and not allowed to progress to the stage of open cavitations. The periodic replenishment of artificial saliva and cariogenic solutions and the physical differences between human teeth caused variability in the duration of a study. Extra teeth were put into the control group to monitor the demineralization of the control group, which develops lesions most rapidly. The upper limit on the depth of lesions that still had an intact enamel surface layer was about 150 m. The enamel lesions in the treatment and control groups had an intact enamel layer at the end of the study, which was fragile and often lost during the tooth sectioning process. Orthodontic brackets or tubes were bonded to the teeth. Along the base of the bonded attachment, a window of exposed enamel 1 mm wide and the length of the bracket/ tube base was either treated with a varnish or not treated in the control group. After application of the varnish, the teeth were stored in artificial saliva for 1 day before cycling and tooth brushing began.
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The first fluoride varnish examined in vitro was Duraflor® (DFR; Medicom Inc., Tonawanda, NY). The varnish contains 5% by weight sodium fluoride or 2.26% by weight fluoride ion in a natural colophony base. Todd and coworkers15 compared three groups of extracted human teeth on which brackets were bonded with composite resin: group 1, exposed enamel surface received one application of DFR varnish; group 2, exposed enamel surface received one application of nonfluoridated DFR placebo varnish; and group 3, control, exposed enamel were not treated. The null hypothesis that no differences would be detected between groups was tested. Teeth were cycled between artificial saliva and a cariogenic solution and brushed with a medium bristled toothbrush for 37 days. Analysis of variance (P ⱕ 0.0001) indicated significant differences between groups. The mean areas and depths of lesions in group 1 were significantly smaller than the mean areas and depths in group 2, the placebo varnish, and group 3, the control (Duncan’s test, P ⱕ 0.05). The mean lesion depth in group 1was 50% smaller than the mean depth in the control group. In group 1 the varnish reduced demineralization of the enamel by two mechanisms: (1) physical barrier for 5 days after which all had been removed, and (2) release of fluoride ions. Lesion sizes were similar in the control and placebo varnish groups. Schmit and coworkers16 studied the effect of fluoride varnish DFR on human enamel demineralization adjacent to brackets bonded with an resin modified glass ionomer (RMGI) cement. The study compared four groups: group 1, exposed enamel surface received one application of varnish, brackets bonded with RMGI; group 2, exposed enamel surface not treated, brackets bonded with RMGI; group 3, exposed enamel surface received one application of varnish, brackets bonded with composite resin; and group 4, control, exposed enamel surface not treated, brackets bonded with composite resin. The null hypothesis that no differences would be detected between groups was tested. After 31 days of cycling and brushing, analysis of variance indicated that significant differences existed between groups (P ⱕ 0.0001). Duncan’s test revealed significant group differences. Groups 1 and 2 had similar lesion depths about 50% less than the composite resin control group. Group 3 had lesion depths 35% less deep than the composite resin control group. DFR
appeared less effective in this study compared with that of Todd and coworkers.15 However, the Schmit study was shorter by 6 days. The mean lesion depths were similar: Todd and coworkers,15 83.3 ⫾ 30.4 m, and Schmit and coworkers,16 83.5 ⫾ 26.2 m. The RMGI cement reduced enamel demineralization of the exposed enamel adjacent to the bracket as effectively as the varnish. Joziak and coworkers17 reported that DPT fluoride varnish released significantly more fluoride ions into water and was associated with significantly more fluoride uptake in enamel when compared with DFR varnish. Both varnishes have similar compositions with regard to fluoride content and colophony base. Novak18 compared the ability of the two varnishes to inhibit enamel demineralization. His study included three groups of teeth having brackets bonded with composite resin: group 1, exposed enamel received one application of DPT; group 2, exposed enamel received one application of DFR; and group 3, control received no treatment. The null hypothesis that the varnishes had equal ability to inhibit enamel demineralization was tested. The teeth were brushed and cycled for 33 days. By day 7, all varnish was removed from the teeth. A one-way analysis of variance found a significant difference (P ⱕ 0.0001) between areas and depths of lesions in the three groups. Duncan’s multiple range tests showed that the treated groups had significantly smaller lesion depths than the control group. The lesion depths of the two varnish groups did not differ statistically. On the basis of this study, it appeared that the efficacy of the two fluoride varnishes was similar. The number of applications of a fluoride varnish needed to make it effective in controlling white spot lesions is an important factor. Because the duration of these in vitro studies was short, the results are not comparable to longitudinal in vivo studies that are needed to truly assess effectiveness during orthodontic treatment. Nevertheless, an in vitro study can give some useful information. Using fluoride varnish DPT, Wittenberger19 compared varnish applications to exposed enamel in four groups: group 1 received 1 application of varnish on day 1; group 2 received 2 applications of varnish on days 1 and 7; group 3 received 3 applications of varnish on days 1, 7, and 14; and group 4 was the control and received no
Fluoride Varnish
applications of varnish. The brushing and cycling study lasted 21 days. Analysis of variance showed significant differences between the groups (P ⱕ 0.0001). Tukey’s test showed differences between the groups (P ⱕ 0.05). The mean lesion depths in group 1 (one application of varnish) were significantly less than the control group mean. In groups 2 and 3, the mean lesion depths were significantly less than in the control group and group 1. Lesion depth was similar in groups 2 and 3. Multiple applications are recommended for this varnish when used in orthodontic patients with poor dietary and hygiene practices. Patients with moderately poor dietary and hygiene practices may benefit from regular applications of a fluoride varnish, perhaps at every appointment throughout orthodontic treatment. A clinical trial is needed to make reliable recommendations about the role of this varnish in reducing white spot formation in orthodontic patients. Juhlin20 compared the ability of fluoride varnishes DPT and FP to inhibit enamel demineralization in teeth on which brackets were bonded with composite resin. She compared three groups: group 1, exposed enamel received one application of DPT varnish; group 2, exposed enamel received one application of FP varnish; and group 3, control teeth were not treated. The cycling study involving tooth brushing lasted 27 days. A one-way analysis of variance (P ⱕ 0.0001) and the Bonferroni test showed significant differences between groups. Mean lesion depths for the teeth treated with the varnishes were significantly less than the lesion depths in the control group. The mean lesion depth of the FP group was significantly less than the depth of the DPT group. Much of the FP varnish remained on the enamel surfaces at the end of the study, whereas 100% of the DPT varnish was removed by the 9th day of the study. FP varnish created a durable physical barrier in addition to providing fluoride to the enamel surface during this short study. Loucks and coworkers21 compared the ability of FP varnish Delton® (D) sealant and Pro Seal™ (PS) to resist toothbrush abrasion and, afterward, enamel demineralization from a single 96-hour exposure to a cariogenic solution. No brackets were bonded to the teeth. She compared four groups of teeth: group 1, exposed enamel received one application of fluoride varnish FP; group 2, exposed enamel received one application of sealant D; group 3, exposed enamel re-
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ceived one application of sealant PS; and group 4, control teeth were not treated. Each tooth was brushed 15,000 times in a slurry of nonfluoridated toothpaste and water to simulate a 2 year duration. Sealant D is a light-cured nonfluoridated unfilled resin used in sealing occlusal surfaces. A clinical trial has shown sealant D was effective in reducing occlusal caries.22 According to the manufacturer, sealant PS is a filled resin with glass ionomer powder as the filler. The proprietary catalyst induces a complete polymerization of the material without an oxygeninhibited layer, resulting in a nonporous resin matrix. Analysis of variance showed that significant differences existed between the lesion depths of the four groups (P ⱕ 0.0001). Tukey’s HSD test showed that the control group had significantly greater lesion depths than the three treatment groups, with all four groups differing significantly from one another. The FP group lesion depths were greater than D group lesion depths, and D group lesion depths were greater than lesion depths in the PS group. Reductions in lesion depths compared with control were: group FP (47%), group D (72%), and group PS (92%). The lesions detected in the PS group were caused by small air bubbles trapped in the sealant that were exposed by toothbrush abrasion that, in turn, allowed the cariogenic solution to reach the enamel surface. Care must be exercised in applying PS to the etched enamel surface. Two thirds of the PS teeth did not have any detectable demineralization. The average lesion depth in the PS treated teeth was 11.4 ⫾ 10.7 m, compared with the control lesions at 139 ⫾ 34 m. To give some perspective, when 37% phosphoric acid etches the enamel, it dissolves about 5 to 10 m of the enamel surface and creates a zone of etched enamel rods 15 to 25 m deep.23 It is apparent that all three materials tested created a durable physical barrier between the enamel surface and the cariogenic solution. Varnish FP is a silane lacquer that has very low viscosity and good wetting action, allowing it to penetrate porosities in the enamel surface mimicking the tagging effect of composite resins.24 A randomized prospective clinical trial found that varnish FP applied once every 3 months during orthodontic treatment resulted in a 27% reduction in the occurrence of white spot lesions compared with control patients.25 Repeated applications of varnish FP are recommended during
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treatment, perhaps at each appointment. The most durable material was sealant PS that resisted 2 years of simulated toothbrush wear well. The durability of PS is related to the composition of its glass ionomer powder, which contains glass particles formed by fusing quartz, alumina, calcium fluoride, cryolite, aluminum fluoride, and aluminum phosphate.26 These results support an earlier study that also subjected sealant PS to 2 years of simulated tooth brushing.27 Two of the materials, varnish FP and sealant PS, also contained fluoride that contributed to the reduction of caries. A recent in vitro study reported that sealant PS released fluoride during a 17-week period in a sustained but significantly decreasing amount.28 Sealant PS also had the ability to be recharged with fluoride ions.28
Conclusion The varnishes and sealants discussed in this article may be helpful in reducing white spot lesions in orthodontic patients who have poor oral hygiene and dietary practices. Clinical trials with these materials are needed to determine their efficacy. At present the varnishes still await approval from the US Food and Drug Administration for use as caries preventive agents. Their use is considered “off label.”29 Fixed bonded orthodontic brackets create an oral environment conducive to rapid development of white spot carious lesions. Patients with a moderate cariogenic threat may benefit from repeated applications of a fluoride varnish. The clear or white varnishes are accepted best by patients. The sealant products appear to have the best ability to reduce and prevent white spot lesions in patients with a high cariogenic threat. The varnishes and sealants can be introduced at the beginning of treatment, at any time during treatment, or after removal of the fixed appliance.
References 1. Ogaard B, Rolla G, Arends J: Orthodontic appliances and enamel demineralization. Part I. Lesion development. Am J Orthod Dentofacial Orthop 94:68-73, 1988 2. Mitchell L: An investigation into the effect of fluoride releasing adhesive on the prevalence of enamel surface changes associated with directly bonded orthodontic attachments. Br J Orthod 19:207-214, 1992 3. Zero DT: Dental caries process. Dent Clin North Am 43:635-664, 1999
4. ten Cate JM, van Loveren C: Fluoride mechanisms. Dent Clin North Am 43:713-742, 1999 5. Featherstone JD, Duncan JF, Cutress TW: A mechanism for dental caries based on chemical processes and diffusion phenomena during in-vitro caries simulation on human tooth enamel. Arch Oral Biol 24:101-112, 1979 6. Seppa L: Fluoride varnishes in caries prevention. Med Princ Pract 13:307-311, 2004 7. Helfenstein U, Steiner M: Fluoride varnishes (Duraphat): a meta-analysis. Community Dent Oral Epidemiol 22:1-5, 1994 8. Helfenstein U, Steiner M: A note concerning the caries preventive effect of Duraphat. Community Dent Oral Epidemiol 22:6-7, 1994 9. Strohmenger L, Brambilla E: The use of fluoride varnishes in the prevention of dental caries: a short review. Oral Dis 7:71-80, 2001 10. Marinho VC, Higgins JP, Logan S, et al: Fluoride varnishes for preventing dental caries in children and adolescents. Cochrane Database Syst Rev 3:CD002279, 2002 11. Marinho VC, Higgins JP, Logan S, et al: Topical fluorides (toothpastes, mouthrinses, gels or varnishes) for preventing dental caries in children and adolescents. Cochrane Database Syst Rev 4:CD002782, 2003 12. Retief DH, Harris BE, Bradley EL: In vitro enamel fluoride uptake from topical fluoride agents. Dent Materials 1:93-97, 1985 13. Dijkman TG, Arends J: The role of “CaF2-like” material in topical fluoridation of enamel in situ. Acta Odontol Scand 46:391-397, 1988 14. Ogaard B: The cariostatic mechanism of fluoride. Compend Contin Educ Dent 20(1 Suppl):10-17, quiz 34, 1999 15. Todd MA, Staley RN, Kanellis MJ, et al: Effect of a fluoride varnish on demineralization adjacent to orthodontic brackets. Am J Orthod Dentofacial Orthop 116: 159-167, 1999 16. Schmit JL, Staley RN, Wefel JS, et al: Effect of fluoride varnish on demineralization adjacent to brackets bonded with RMGI cement. Am J Orthod Dentofacial Orthop 122: 125-134, 2002 17. Joziak MT, Schemehorn BR, Tavss EA, et al: Comparison of enamel fluoride uptake and release from fluoride varnishes [abstract]. J Dent Res 77(Spec Issue):1684, 1998 18. Novak BA: Effect of fluoride varnishes (Duraflor®/ Duraphat®) on demineralization adjacent to orthodontic brackets. MS thesis, University of Iowa, 2002 19. Wittenberger DA: Multiple applications of a fluoride varnish (Duraphat®) on demineralization adjacent to orthodontic brackets. MS thesis, University of Iowa, 2003 20. Juhlin TL: The effect of two fluoride varnishes Duraphat® and Fluor ProtectorTM on the inhibition of enamel demineralization adjacent to orthodontic brackets. MS thesis, University of Iowa, 2004 21. Loucks JL, Staley RN, Wefel JS, et al: Inhibition of enamel demineralization by an enamel sealant Pro SealTM: an in vitro study. Am J Orthod Dentofacial Orthop 133:S88-94, 2008 22. Bravo M, Montero J, Bravo JJ, et al: Sealant and fluoride varnish in caries: a randomized trial. J Dent Res 84:11381143, 2005
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23. Powers JM, Messersmith ML: Enamel etching and bond strength, in Brantley WA, Eliades T, eds: Orthodontic Materials, Scientific and Clinical Aspects. Stuttgart, Thieme, 2001, pp 105-122 24. Arends J, Lodding A, Petersson LG: Fluoride uptake in enamel: in vitro comparison of topical agents. Caries Res 14:403-413, 1980 25. Ogaard B, Larsson E, Henriksson T, et al: Effects of combined application of antimicrobial and fluoride varnishes in orthodontic patients. Am J Orthod Dentofacial Orthop 120:28-35, 2001
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26. Kakaboura A, Vougiouklakis G: Cements in orthodontics, in Brantley WA, Eliades T, eds: Orthodontic Materials, Scientific and Clinical Aspects. Stuttgart, Thieme, 2001, pp 221-240 27. Hu W, Featherstone JD: Prevention of enamel demineralization: an in vitro study using light-cured filled sealant. Am J Orthod Dentofacial Orthop 128:592-600, 2005 28. Soliman MM, Bishara SE, Wefel J, et al: Fluoride release rate from an orthodontic sealant and its clinical implications. Angle Orthod 76:282-288, 2006 29. Vaikuntam J: Fluoride varnishes: should we be using them? Pediat Dent 22:513-516, 2000
he advent of bonded multibracketed fixed appliances in the 1970s brought enamel white spot lesions to the attention of orthodontists. Orthodontists became interested in fluoride varnishes for their potential to prevent or reduce enamel white spot lesions that develop during treatment with bonded fixed appliances. Excellent patient dietary and oral hygiene practices that include topical fluoride agents such as toothpastes and rinses can prevent or minimize the formation of enamel white spot lesions during orthodontic treatment. However, patients with poor dietary and oral hygiene practices can develop white spot lesions within 4 weeks after the beginning of treatment in the absence of fluoride supplementation1 and these lesions can progress to open cavitations.2 The noncarious tooth has on its enamel surface an acquired bio-film, the pellicle, which participates in dynamic physical-chemical equilibrium with the enamel and oral fluids.3,4 When the pH of oral fluids fluctuates below the phys-
T
Department of Orthodontics, College of Dentistry, The University of Iowa, Iowa City, IA. Research supported by the Department of Orthodontics. Address correspondence to Robert N. Staley, DDS, MA, MS, Department of Orthodontics, College of Dentistry, The University of Iowa, Iowa City, IA 52242. Phone: 319-335-7302; E-mail: [email protected] © 2008 Elsevier Inc. All rights reserved. 1073-8746/08/1403-0$30.00/0 doi:10.1053/j.sodo.2008.03.004
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iologic norm, calcium and phosphate ions diffuse from hydroxyapatite mineral in the enamel to the pellicle and into the oral cavity (demineralization). When the pH of oral fluids increases to the norm, calcium and phosphate ions in the saliva are transmitted through the pellicle into the enamel following the laws of chemical equilibrium (remineralization). The remineralization process is greatly enhanced by low levels of fluoride in the saliva and plaque.4 Many theories have been proposed about the mechanisms that cause caries, and research for a better understanding of the caries process continues. The plaque deposited on the surface of a carious tooth contains food debris and microorganisms. In the presence of fermentable carbohydrates, plaque microorganisms produce organic acids that lower the pH in the plaque, which in turn causes a diffusion of calcium and phosphate ions from the enamel through the pellicle and into the plaque fluid. This continues until equilibrium is reached between the enamel and the plaque liquid. Demineralization of the enamel continues when further episodes of low pH levels occur in the plaque. The enamel surface of a white spot carious lesion remains intact while the area below the surface is demineralized.3 Featherstone and coworkers5 hypothesized that as the pH of the plaque lowers the proportion of undissociated acids in the plaque fluid increases. Because these acids are uncharged they can diffuse through the porous
Seminars in Orthodontics, Vol 14, No 3 (September), 2008: pp 194-199
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enamel matrix down a concentration gradient. After they have penetrated the enamel to a depth where the pH is higher, the acids dissociate and release protons that attack the apatite matrix. The released calcium and phosphate ions either diffuse outward into the plaque or precipitate in the surface layer of enamel maintaining an intact surface zone. The first fluoride varnishes were developed in the 1960s (Duraphat® [DPT], 5% sodium fluoride in a colophony base; Colgate Oral Pharmaceuticals Inc., Canton, MA) and in the 1970s (Fluor ProtectorTM [FP], a clear, transparent polyurethane lacquer containing 0.1% weight fluoride ion as difluorosilane; Ivoclar Vivadent, Inc., Amherst, NY) to prevent caries in children.6 Metaanalyses of controlled clinical trials involving DPT7-11 confirmed the clinical effectiveness of this varnish in inhibiting dental caries. The varnish has been widely used in children in Europe and to a lesser extent in North America.6 Four applications each year or three weekly applications once a year are effective. Also two applications a year may be equally effective.6 Results for FP have been inconclusive.6 The cariostatic mechanism of fluoride varnishes is not fully understood, but some possible explanations will be discussed. The colophonybased varnish is a sticky yellowish-brown substance that hardens on contact with saliva producing a temporary cover over the enamel. The patient is instructed to refrain from brushing for 4 hours after application.12 Patients will remove the varnish from the tooth after a few days of tooth brushing. It is speculated that as the varnish is brushed away, fluoride ions depart from the edges of the varnish to join calcium and phosphate ions from the saliva, pellicle, and plaque, and, under favorable conditions, the ions become incorporated into the enamel as fluoridated hydroxyapatite, a less soluble form of apatite. The varnish also leaves calcium fluoride on the surface of the enamel in a CaF2-like material that is less soluble and most likely leaches away from the surface through the pellicle.13 A 1-week in situ exposure of enamel slabs treated with acidulated phosphate fluoride (APF) gel, DPT, and FP showed that only the FP slabs retained a measurable amount of CaF2-like material at the end of the week.13 This finding may be related to the different physical properties of the topical fluoride agents. The APF gel
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and DPT are less likely to persist on the enamel surface 7 days in situ, whereas, FP, a silane sealant, forms a long-lasting durable attachment to the enamel surface. While speculating on the cariostatic mechanism of topical fluoride agents, Ogaard14 commented that fluoride concentration in the enamel structure is not as effective in reducing caries as is the continuous presence of fluoride in the plaque liquid. He thought the fairly insoluble CaF2-like deposits left by topical fluoride agents on the surface of the enamel provide the fluoride ions that diffuse into the plaque liquid and participate in the remineralization of enamel.
In Vitro Studies The purpose of this article is to discuss the results of several in vitro thesis research projects conducted by residents in the Orthodontic Department, College of Dentistry, at The University of Iowa. The studies were conducted in collaboration with cariologists Dr. James S. Wefel and Dr. Kevin J. Donly from the Dows Institute for Dental Research at the College of Dentistry. The cycling of extracted human teeth from artificial saliva to cariogenic solutions mimics the dynamic processes that occur in the oral cavity. The lesions in the control group had to be kept in the white spot lesion stage and not allowed to progress to the stage of open cavitations. The periodic replenishment of artificial saliva and cariogenic solutions and the physical differences between human teeth caused variability in the duration of a study. Extra teeth were put into the control group to monitor the demineralization of the control group, which develops lesions most rapidly. The upper limit on the depth of lesions that still had an intact enamel surface layer was about 150 m. The enamel lesions in the treatment and control groups had an intact enamel layer at the end of the study, which was fragile and often lost during the tooth sectioning process. Orthodontic brackets or tubes were bonded to the teeth. Along the base of the bonded attachment, a window of exposed enamel 1 mm wide and the length of the bracket/ tube base was either treated with a varnish or not treated in the control group. After application of the varnish, the teeth were stored in artificial saliva for 1 day before cycling and tooth brushing began.
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The first fluoride varnish examined in vitro was Duraflor® (DFR; Medicom Inc., Tonawanda, NY). The varnish contains 5% by weight sodium fluoride or 2.26% by weight fluoride ion in a natural colophony base. Todd and coworkers15 compared three groups of extracted human teeth on which brackets were bonded with composite resin: group 1, exposed enamel surface received one application of DFR varnish; group 2, exposed enamel surface received one application of nonfluoridated DFR placebo varnish; and group 3, control, exposed enamel were not treated. The null hypothesis that no differences would be detected between groups was tested. Teeth were cycled between artificial saliva and a cariogenic solution and brushed with a medium bristled toothbrush for 37 days. Analysis of variance (P ⱕ 0.0001) indicated significant differences between groups. The mean areas and depths of lesions in group 1 were significantly smaller than the mean areas and depths in group 2, the placebo varnish, and group 3, the control (Duncan’s test, P ⱕ 0.05). The mean lesion depth in group 1was 50% smaller than the mean depth in the control group. In group 1 the varnish reduced demineralization of the enamel by two mechanisms: (1) physical barrier for 5 days after which all had been removed, and (2) release of fluoride ions. Lesion sizes were similar in the control and placebo varnish groups. Schmit and coworkers16 studied the effect of fluoride varnish DFR on human enamel demineralization adjacent to brackets bonded with an resin modified glass ionomer (RMGI) cement. The study compared four groups: group 1, exposed enamel surface received one application of varnish, brackets bonded with RMGI; group 2, exposed enamel surface not treated, brackets bonded with RMGI; group 3, exposed enamel surface received one application of varnish, brackets bonded with composite resin; and group 4, control, exposed enamel surface not treated, brackets bonded with composite resin. The null hypothesis that no differences would be detected between groups was tested. After 31 days of cycling and brushing, analysis of variance indicated that significant differences existed between groups (P ⱕ 0.0001). Duncan’s test revealed significant group differences. Groups 1 and 2 had similar lesion depths about 50% less than the composite resin control group. Group 3 had lesion depths 35% less deep than the composite resin control group. DFR
appeared less effective in this study compared with that of Todd and coworkers.15 However, the Schmit study was shorter by 6 days. The mean lesion depths were similar: Todd and coworkers,15 83.3 ⫾ 30.4 m, and Schmit and coworkers,16 83.5 ⫾ 26.2 m. The RMGI cement reduced enamel demineralization of the exposed enamel adjacent to the bracket as effectively as the varnish. Joziak and coworkers17 reported that DPT fluoride varnish released significantly more fluoride ions into water and was associated with significantly more fluoride uptake in enamel when compared with DFR varnish. Both varnishes have similar compositions with regard to fluoride content and colophony base. Novak18 compared the ability of the two varnishes to inhibit enamel demineralization. His study included three groups of teeth having brackets bonded with composite resin: group 1, exposed enamel received one application of DPT; group 2, exposed enamel received one application of DFR; and group 3, control received no treatment. The null hypothesis that the varnishes had equal ability to inhibit enamel demineralization was tested. The teeth were brushed and cycled for 33 days. By day 7, all varnish was removed from the teeth. A one-way analysis of variance found a significant difference (P ⱕ 0.0001) between areas and depths of lesions in the three groups. Duncan’s multiple range tests showed that the treated groups had significantly smaller lesion depths than the control group. The lesion depths of the two varnish groups did not differ statistically. On the basis of this study, it appeared that the efficacy of the two fluoride varnishes was similar. The number of applications of a fluoride varnish needed to make it effective in controlling white spot lesions is an important factor. Because the duration of these in vitro studies was short, the results are not comparable to longitudinal in vivo studies that are needed to truly assess effectiveness during orthodontic treatment. Nevertheless, an in vitro study can give some useful information. Using fluoride varnish DPT, Wittenberger19 compared varnish applications to exposed enamel in four groups: group 1 received 1 application of varnish on day 1; group 2 received 2 applications of varnish on days 1 and 7; group 3 received 3 applications of varnish on days 1, 7, and 14; and group 4 was the control and received no
Fluoride Varnish
applications of varnish. The brushing and cycling study lasted 21 days. Analysis of variance showed significant differences between the groups (P ⱕ 0.0001). Tukey’s test showed differences between the groups (P ⱕ 0.05). The mean lesion depths in group 1 (one application of varnish) were significantly less than the control group mean. In groups 2 and 3, the mean lesion depths were significantly less than in the control group and group 1. Lesion depth was similar in groups 2 and 3. Multiple applications are recommended for this varnish when used in orthodontic patients with poor dietary and hygiene practices. Patients with moderately poor dietary and hygiene practices may benefit from regular applications of a fluoride varnish, perhaps at every appointment throughout orthodontic treatment. A clinical trial is needed to make reliable recommendations about the role of this varnish in reducing white spot formation in orthodontic patients. Juhlin20 compared the ability of fluoride varnishes DPT and FP to inhibit enamel demineralization in teeth on which brackets were bonded with composite resin. She compared three groups: group 1, exposed enamel received one application of DPT varnish; group 2, exposed enamel received one application of FP varnish; and group 3, control teeth were not treated. The cycling study involving tooth brushing lasted 27 days. A one-way analysis of variance (P ⱕ 0.0001) and the Bonferroni test showed significant differences between groups. Mean lesion depths for the teeth treated with the varnishes were significantly less than the lesion depths in the control group. The mean lesion depth of the FP group was significantly less than the depth of the DPT group. Much of the FP varnish remained on the enamel surfaces at the end of the study, whereas 100% of the DPT varnish was removed by the 9th day of the study. FP varnish created a durable physical barrier in addition to providing fluoride to the enamel surface during this short study. Loucks and coworkers21 compared the ability of FP varnish Delton® (D) sealant and Pro Seal™ (PS) to resist toothbrush abrasion and, afterward, enamel demineralization from a single 96-hour exposure to a cariogenic solution. No brackets were bonded to the teeth. She compared four groups of teeth: group 1, exposed enamel received one application of fluoride varnish FP; group 2, exposed enamel received one application of sealant D; group 3, exposed enamel re-
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ceived one application of sealant PS; and group 4, control teeth were not treated. Each tooth was brushed 15,000 times in a slurry of nonfluoridated toothpaste and water to simulate a 2 year duration. Sealant D is a light-cured nonfluoridated unfilled resin used in sealing occlusal surfaces. A clinical trial has shown sealant D was effective in reducing occlusal caries.22 According to the manufacturer, sealant PS is a filled resin with glass ionomer powder as the filler. The proprietary catalyst induces a complete polymerization of the material without an oxygeninhibited layer, resulting in a nonporous resin matrix. Analysis of variance showed that significant differences existed between the lesion depths of the four groups (P ⱕ 0.0001). Tukey’s HSD test showed that the control group had significantly greater lesion depths than the three treatment groups, with all four groups differing significantly from one another. The FP group lesion depths were greater than D group lesion depths, and D group lesion depths were greater than lesion depths in the PS group. Reductions in lesion depths compared with control were: group FP (47%), group D (72%), and group PS (92%). The lesions detected in the PS group were caused by small air bubbles trapped in the sealant that were exposed by toothbrush abrasion that, in turn, allowed the cariogenic solution to reach the enamel surface. Care must be exercised in applying PS to the etched enamel surface. Two thirds of the PS teeth did not have any detectable demineralization. The average lesion depth in the PS treated teeth was 11.4 ⫾ 10.7 m, compared with the control lesions at 139 ⫾ 34 m. To give some perspective, when 37% phosphoric acid etches the enamel, it dissolves about 5 to 10 m of the enamel surface and creates a zone of etched enamel rods 15 to 25 m deep.23 It is apparent that all three materials tested created a durable physical barrier between the enamel surface and the cariogenic solution. Varnish FP is a silane lacquer that has very low viscosity and good wetting action, allowing it to penetrate porosities in the enamel surface mimicking the tagging effect of composite resins.24 A randomized prospective clinical trial found that varnish FP applied once every 3 months during orthodontic treatment resulted in a 27% reduction in the occurrence of white spot lesions compared with control patients.25 Repeated applications of varnish FP are recommended during
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treatment, perhaps at each appointment. The most durable material was sealant PS that resisted 2 years of simulated toothbrush wear well. The durability of PS is related to the composition of its glass ionomer powder, which contains glass particles formed by fusing quartz, alumina, calcium fluoride, cryolite, aluminum fluoride, and aluminum phosphate.26 These results support an earlier study that also subjected sealant PS to 2 years of simulated tooth brushing.27 Two of the materials, varnish FP and sealant PS, also contained fluoride that contributed to the reduction of caries. A recent in vitro study reported that sealant PS released fluoride during a 17-week period in a sustained but significantly decreasing amount.28 Sealant PS also had the ability to be recharged with fluoride ions.28
Conclusion The varnishes and sealants discussed in this article may be helpful in reducing white spot lesions in orthodontic patients who have poor oral hygiene and dietary practices. Clinical trials with these materials are needed to determine their efficacy. At present the varnishes still await approval from the US Food and Drug Administration for use as caries preventive agents. Their use is considered “off label.”29 Fixed bonded orthodontic brackets create an oral environment conducive to rapid development of white spot carious lesions. Patients with a moderate cariogenic threat may benefit from repeated applications of a fluoride varnish. The clear or white varnishes are accepted best by patients. The sealant products appear to have the best ability to reduce and prevent white spot lesions in patients with a high cariogenic threat. The varnishes and sealants can be introduced at the beginning of treatment, at any time during treatment, or after removal of the fixed appliance.
References 1. Ogaard B, Rolla G, Arends J: Orthodontic appliances and enamel demineralization. Part I. Lesion development. Am J Orthod Dentofacial Orthop 94:68-73, 1988 2. Mitchell L: An investigation into the effect of fluoride releasing adhesive on the prevalence of enamel surface changes associated with directly bonded orthodontic attachments. Br J Orthod 19:207-214, 1992 3. Zero DT: Dental caries process. Dent Clin North Am 43:635-664, 1999
4. ten Cate JM, van Loveren C: Fluoride mechanisms. Dent Clin North Am 43:713-742, 1999 5. Featherstone JD, Duncan JF, Cutress TW: A mechanism for dental caries based on chemical processes and diffusion phenomena during in-vitro caries simulation on human tooth enamel. Arch Oral Biol 24:101-112, 1979 6. Seppa L: Fluoride varnishes in caries prevention. Med Princ Pract 13:307-311, 2004 7. Helfenstein U, Steiner M: Fluoride varnishes (Duraphat): a meta-analysis. Community Dent Oral Epidemiol 22:1-5, 1994 8. Helfenstein U, Steiner M: A note concerning the caries preventive effect of Duraphat. Community Dent Oral Epidemiol 22:6-7, 1994 9. Strohmenger L, Brambilla E: The use of fluoride varnishes in the prevention of dental caries: a short review. Oral Dis 7:71-80, 2001 10. Marinho VC, Higgins JP, Logan S, et al: Fluoride varnishes for preventing dental caries in children and adolescents. Cochrane Database Syst Rev 3:CD002279, 2002 11. Marinho VC, Higgins JP, Logan S, et al: Topical fluorides (toothpastes, mouthrinses, gels or varnishes) for preventing dental caries in children and adolescents. Cochrane Database Syst Rev 4:CD002782, 2003 12. Retief DH, Harris BE, Bradley EL: In vitro enamel fluoride uptake from topical fluoride agents. Dent Materials 1:93-97, 1985 13. Dijkman TG, Arends J: The role of “CaF2-like” material in topical fluoridation of enamel in situ. Acta Odontol Scand 46:391-397, 1988 14. Ogaard B: The cariostatic mechanism of fluoride. Compend Contin Educ Dent 20(1 Suppl):10-17, quiz 34, 1999 15. Todd MA, Staley RN, Kanellis MJ, et al: Effect of a fluoride varnish on demineralization adjacent to orthodontic brackets. Am J Orthod Dentofacial Orthop 116: 159-167, 1999 16. Schmit JL, Staley RN, Wefel JS, et al: Effect of fluoride varnish on demineralization adjacent to brackets bonded with RMGI cement. Am J Orthod Dentofacial Orthop 122: 125-134, 2002 17. Joziak MT, Schemehorn BR, Tavss EA, et al: Comparison of enamel fluoride uptake and release from fluoride varnishes [abstract]. J Dent Res 77(Spec Issue):1684, 1998 18. Novak BA: Effect of fluoride varnishes (Duraflor®/ Duraphat®) on demineralization adjacent to orthodontic brackets. MS thesis, University of Iowa, 2002 19. Wittenberger DA: Multiple applications of a fluoride varnish (Duraphat®) on demineralization adjacent to orthodontic brackets. MS thesis, University of Iowa, 2003 20. Juhlin TL: The effect of two fluoride varnishes Duraphat® and Fluor ProtectorTM on the inhibition of enamel demineralization adjacent to orthodontic brackets. MS thesis, University of Iowa, 2004 21. Loucks JL, Staley RN, Wefel JS, et al: Inhibition of enamel demineralization by an enamel sealant Pro SealTM: an in vitro study. Am J Orthod Dentofacial Orthop 133:S88-94, 2008 22. Bravo M, Montero J, Bravo JJ, et al: Sealant and fluoride varnish in caries: a randomized trial. J Dent Res 84:11381143, 2005
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23. Powers JM, Messersmith ML: Enamel etching and bond strength, in Brantley WA, Eliades T, eds: Orthodontic Materials, Scientific and Clinical Aspects. Stuttgart, Thieme, 2001, pp 105-122 24. Arends J, Lodding A, Petersson LG: Fluoride uptake in enamel: in vitro comparison of topical agents. Caries Res 14:403-413, 1980 25. Ogaard B, Larsson E, Henriksson T, et al: Effects of combined application of antimicrobial and fluoride varnishes in orthodontic patients. Am J Orthod Dentofacial Orthop 120:28-35, 2001
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26. Kakaboura A, Vougiouklakis G: Cements in orthodontics, in Brantley WA, Eliades T, eds: Orthodontic Materials, Scientific and Clinical Aspects. Stuttgart, Thieme, 2001, pp 221-240 27. Hu W, Featherstone JD: Prevention of enamel demineralization: an in vitro study using light-cured filled sealant. Am J Orthod Dentofacial Orthop 128:592-600, 2005 28. Soliman MM, Bishara SE, Wefel J, et al: Fluoride release rate from an orthodontic sealant and its clinical implications. Angle Orthod 76:282-288, 2006 29. Vaikuntam J: Fluoride varnishes: should we be using them? Pediat Dent 22:513-516, 2000