Potential of 4 per cent silver fluoride to induce

instruments and local anaesthesia,the procedure reflected a particular philosophy of caries treatment and represented a new approach to caries manage-ment now known as ART (Atraumatic Restorative Treatment).Although ART is practised in several countries,including those which lack traditional dental services,it is not customary with this technique to apply silver fluoride to any residual caries or stained dentine.

Despite the high fluoride level (60,000mg/L according to manufacturer's data),the 40 per cent AgF solution does not appear to have been subjected to controlled laboratory investigation of efficacy or possible adverse effects prior to its introduction for clinical use in the University of Sydney more than 25years ago,as there is no relevant published literature on any such research.

Following publication of the paper by Craig et al .1reporting the slow rate of progression of dentinal caries treated with 40 per cent AgF and 10 per cent stannous fluoride,the School Dental Service in Western Australia adopted a method involving application of 40 per cent AgF followed by restoration with glass ionomer cement as the standard treatment for deep caries in primary teeth (atraumatic technique).

From 1982 to 1991,more than 400,000 school children enrolled in the Western Australian Health Department's dental care program were treated with 40 per cent AgF as part of the atraumatic technique (Lamplough H,personal communication,April 1992).Between 1992 and 1999,a further unknown number of children enrolled in the same program were subjected to similar treatment.As reported by Green,2some Western Australian children aged 5-8years have also received topical applications of 40per cent AgF to permanent first molars for caries prevention.

A study by Gotjamanos 3involving histological evaluation of human primary teeth treated atraumatically by Dental Services staff of the Western Australian Health Department found this

Introduction

In the mid- to late-1970s,paediatric dentistry staff in the Faculty of Dentistry,University of Sydney,adopted a new approach for treating deep caries in primary teeth.Their minimal treatment program involved the use of a 40 per cent silver fluoride (AgF) solution and was aimed at arresting caries progression and preventing exposure of the dental pulp.As removal of unsupported enamel,excavation of soft caries,AgF treatment of residual carious dentine and restoration with glass ionomer cement could be accomplished without use of rotary

Potential of 4 per cent silver fluoride to induce fluorosis in rats:Clinical implications

Theo Gotjamanos,* Philip Ma

technique appeared to preserve the vitality of the dental pulp even when caries had penetrated reparative dentine.However,subsequent analyses for fluoride concentration using both ion selective electrode and ion chromatography techniques revealed that commercial preparations of 40 per cent AgF did not contain the expected 60,000mg/L fluoride,but from 75,000-127,000mg/L fluoride.4-6 Higher than expected fluoride levels have also been detected in more recently produced commercial preparations of 40 per cent AgF,and it has been suggested this could be due to the presence of silver difluoride in the solution rather than the monofluoride.7

Afonso and Gotjamanos4and Gotjamanos8pointed out that the significantly higher than expected levels of fluoride in commercial preparations of AgF may pose a problem with respect to toxicity.This pertains to the use of the 40 per cent solution in children aged 4-7 years whose permanent tooth crowns are still forming and are therefore susceptible to development of fluorosis in the presence of excessive systemic fluoride.

12

45

3

Fig 1.– Incisor teeth of a control rat which received a single topical application of triple distilled

water to two molar teeth.The appearance of these naturally pigmented and continuously growing

teeth is unchanged following treatment.

Fig 2, 3.– Severe localized fluorosis affecting the maxillary incisors of rats which,five

weeks earlier,had received a single topical application of 4 per cent silver fluoride to two

intact molar teeth.

Fig 4.– Development of generalized fluorosis of rat mandibular incisors five-six weeks following

application of 4 per cent silver fluoride to three carious molars (atraumatic technique).The

maxillary incisors are affected to a lesser degree but still show loss of pigment.

Fig 5.– Generalized fluorosis affecting all incisors in a rat following application of 4 per cent

silver fluoride to four carious molars (atraumatic technique).

The clinical and in vitro studies on 40 per cent AgF conducted in the University of Western Australia between 1983 and 1994 have been extended to experimental animal investigations using a 4 per cent AgF solution in order to test whether this lower concentration is effective in preventing caries and not causing fluorosis in developing teeth when used in topically applied form,and also arresting deep caries in molar teeth of rats while preserving vitality of the dental pulp. Results relating to development of fluorosis are now reported in this paper.

Materials and methods

Twenty-five male and female Sprague-Dawley rats aged 21 days,obtained from the Animal Resource Centre at Murdoch University,Western Australia, were anaesthetized with ketamine hydrochloride (25 mg/kg body weight) and their teeth dried with cotton and compressed https://www.wendangku.net/doc/e417943515.html,ing small cotton pellets (size 3 divided into quarters) and removing excess solution by squeezing twice,4 per cent AgF solution was applied for one minute to each of the mandibular and maxillary right first molars.A control group of 22 rats received triple distilled water to the corresponding teeth.

Immediately following the topical fluoride application,the animals were inoculated orally with an actively growing culture of Streptococcus mutans (sobrinus)6715-17 and placed on Diet 2000 and 10 per cent sucrose water.They were reinoculated with S.sobrinus24 hours later,housed in groups of four or five,and monitored daily for normal communal behaviour and weight gain.The control animals were inoculated in a similar manner and maintained on the same diet and sucrose water.After 12 weeks,all animals were euthanased by an overdose of nitrous oxide and the jaws defleshed.

In the second experiment,100 Sprague-Dawley female rats aged 19 days were inoculated with S. sobrinus in the same manner as described above and fed Diet 2000 and 10 per cent sucrose water.They were divided randomly into four groups and six weeks later,one,two,three or four carious mandibular molar teeth from each animal of a particular group were treated with 4 per cent AgF as part of the atraumatic technique.A control group of 25 rats that had been inoculated with S.sobrinus and maintained on the same cariogenic diet as the experimental animals received triple distilled water via cotton pellet to four of their carious molar teeth. All animals were euthanased six-seven weeks following AgF treatment.

Results

While the 25 experimental animals which received a single topical AgF application and all control animals from both series of experiments survived until the end of observation periods,not all test animals from the second experiment survived.In the group of 100 subjected to the atraumatic technique, 91 survived.Although the cause(s) of death in the nine non-surviving animals was not established, none died within a few hours or days after receiving applications of silver fluoride to deep carious lesions; nor did they exhibit any spasm of the extremities, tetany or convulsions suggestive of acute fluoride toxicity.However,the possibility exists that they suffered a degree of fluoride toxicity which interfered with some body function,restricting their capacity to eat and/or drink and leading to death.Alternatively, they may have become debilitated due to other unknown causes which contributed to premature death.

Control animals which received topically applied triple distilled water to two molar teeth showed no alteration to the clinical appearance of their maxillary or mandibular incisors (Fig.1).In the group which received topically applied 4 per cent AgF solution to two intact molars,discrete regions of moderate to severe fluorosis (Fig.2 and 3) were detected five weeks later in the continually growing maxillary incisor teeth of six rats (T able 1).The proportion of animals which developed fluorosis (24 per cent) was significantly higher in the 4 per cent AgF group compared to controls (overall chi-squared test:?2=6.05;Fisher’s exact test:p=0.023). Application of 4 per cent AgF solution to carious dentine as part of the atraumatic technique resulted in marked alterations to the clinical appearance of the incisors in 16 (73 per cent) out of 22 surviving rats which received applications to three carious teeth (Fig.4),and in 21 (88 per cent) out of 24 surviving rats which received applications of AgF solution to four carious teeth (Fig.5).The altered appearance was noted five-six weeks following treatment and was characterized by pigment loss and opaqueness consistent with generalized fluorosis. Similar changes in incisors were detected in only one

(4 per cent) of 23 surviving rats which had received

a single application of AgF to one carious molar,and Table 1. Development of fluorosis in rats following topical application of 4 per cent AgF solution to two intact molar teeth

Fluorosis

Group Positive Negative T otal 4% AgF61925 Control*0 2020 T otal63945 *Control animals received topically applied triple distilled water.

in two (9 per cent) of 22 surviving rats which had received applications of 4 per cent AgF solution to two carious teeth.Control animals showed no alteration to the appearance of their incisor teeth following application of triple distilled water to carious cavities in molar teeth.

Analysis of these results showed there was a highly significant positive trend for fluorosis risk with increasing applications of AgF (overall chi-squared test:?2=51.37,with Fisher’s exact test:p<0.0001;test for trend:p<0.001),the risk of developing fluorosis with four applications being 123 times greater than that for a single treatment (Fig.6).Discussion

Experimental dental fluorosis produced by administration of large doses of fluoride (for example,by a peritoneal injection) has been reported to produce horizontal bands of pigment-free areas of rat incisor enamel;histologic changes in the ameloblasts of such teeth can be seen one hour after fluoride administration.9The pattern of fluorosis observed in the present study differs somewhat from previous descriptions in that discrete localized areas of pigment loss and opacity were seen in incisors of rats which had received a single topical application of AgF to two molar teeth,while rats which received AgF to carious dentine of three or four of their molars showed generalized pigment loss and opacity of incisor teeth.

In the case of silver fluoride solution applied topically to intact teeth,some of the fluoride can spill out from the cotton pellet,mix with saliva and enter the systemic circulation via absorption from the gastrointestinal tract.On the other hand,when silver fluoride solution is used as part of the

atraumatic technique and applied via a small cotton pellet to carious cavities on occlusal and proximal surfaces,systemic entry of fluoride would occur predominantly via pulpal blood vessels after passage through carious dentine and entry into the pulp chamber;however,the potential exists for some spillage of solution to occur into saliva.As demonstrated in the present study,either method of applying 4 per cent AgF to rat teeth appears to result in sufficient fluoride entering the systemic circulation to adversely affect ameloblast cells of continually forming incisors and produce marked fluorotic changes in enamel.

These findings have implications for paediatric dentistry,particularly with respect to the Western Australian Health Department’s use of 40 per cent AgF as a topical solution for caries prevention in first permanent molars 2and the Department’s standard treatment of deep caries in primary teeth (atraumatic technique).The clinical protocols employed in the present study were designed to follow closely those used on children by the Health Department in Western Australia,in that AgF was applied using small cotton pellets from which excess solution had been removed.Despite the precautions taken to avoid administration of excess AgF solution when applying the solution to tooth surfaces and carious cavities,both procedures induced fluorosis in developing incisor teeth of the experimental animals.T aking into consideration differences between fluoride doses for young rats and young children due to their differing body masses and size of molar teeth,intra- and inter-operator variations in the amount of residual AgF solution that would be left in cotton pellets handled by the principal investigator of the present study and between different dental auxiliaries who participate in Western Australia’s Dental Health Services program for children,and the tenfold difference in fluoride concentration between the full strength solution used on children and the 4per cent solution tested on rats,the dose of AgF administered to experimental animals in the present study may have been higher than that normally administered to https://www.wendangku.net/doc/e417943515.html,ing data obtained from an in vitro study on human primary teeth,8and taking into account the fact that the size of cotton pellets used in the present study on rat molars was much smaller (25 per cent of size 3),it can be estimated that the F dose administered to rats which had four carious teeth treated atraumatically was up to 10mg/kg body weight.This falls within the ‘acute fluoride administration’range of 10-20mg/kg body weight used by Fejerskov et al.9in Wistar rats which were given sodium fluoride.

As the threshold value for human dental fluorosis is significantly lower than that required to produce fluorosis in the rat,9human ameloblasts could be

Fig 6.- Development of fluorosis in rats which received 4 per cent AgF solution to one-four carious molar teeth as part of the atraumatic technique.Control animals received four applications of

triple distilled water to four carious molars.

Atraumatic technique %developed fluorosis

expected to be more sensitive to equivalent doses of fluoride reaching the systemic circulation following administration of silver fluoride solution – either through topical application to intact teeth for caries prevention or direct application to carious dentine as part of the atraumatic technique.This raises the possibility that clinical protocols relating to 40 per cent AgF use in young children may place them at risk of developing fluorosis.

The clinical study by Green2involved topical application of 40 per cent AgF to first molars of children aged 5-8 years.While crown formation of permanent maxillary and mandibular central incisors,maxillary lateral incisors,and mandibular canines would be expected to be complete by 5 years of age,the crowns of mandibular lateral incisors and maxillary canines may still be forming along with crowns of all premolar teeth and those of second and third molars.Therefore,the potential exists for fluorosis to be induced in children aged 5 years and for some anterior and most posterior teeth to be affected following topical application of 40 per cent AgF solution to first molars.

There is equal probability that the atraumatic technique,which has been used in Western Australian children as young as 4 years,contributes to fluorosis,particularly in cases where three or four carious teeth are treated with 40 per cent AgF at the same appointment.In the present study,while fluorotic changes were observed in less than 10 per cent of animals which had one or two carious molars treated atraumatically,between 73-88 per cent of rats which had three or four carious teeth treated in this manner developed fluorosis.The risk of fluorosis was 123 times greater in rats which received four applications of AgF during one treatment session. The results of the present investigation confirm the potential of silver fluoride to induce fluorosis when administered to rats as a 4 per cent solution. They also indicate that the previously expressed concerns over the possible toxicity of 40 per cent AgF in young children4,6,8were justified.Further-more,the findings do not support the position adopted by those consulted by the Health Department of Western Australia and asked to comment on concerns over possible toxicity of AgF. International consultants have expressed the view that fluorosis is unlikely to result from single applications of AgF.11However,such opinions do not appear to have been based on any controlled laboratory or clinical research investigations on silver fluoride conducted by the consultants themselves or by other investigators.

On the basis of results of previous studies conducted in the University of Western Australia3-8 and on the findings of the present investigation, there is no justification for the Health Department of Western Australia or for private dental practitioners to continue to use 40 per cent AgF solution in children under any circumstances.This solution should be withdrawn from clinical use in accord with previous recommendations 5,7-8

The case for abandoning 40 per cent AgF is strengthened by the fact that the company which first produced this solution for use by paediatric dentistry staff in the University of Sydney used as a reference the 40 per cent concentration of silver nitrate that had been introduced by Howe in 1917 as a sterilizing agent for treatment of deep dentinal caries.12The 1970s decision to set the concentration of AgF at the same level as had been used for silver nitrate was not only an empirical one but also surprising considering the fact that by 1960 silver nitrate at 40 per cent concentration was no longer being widely used in clinical dentistry because of scientific findings regarding its lack of efficacy and concerns over its potential toxicity.12

Adoption of 40 per cent AgF for routine use in children’s dentistry by the University of Sydney and the Western Australian Health Department without prior laboratory testing for efficacy and safety was even more surprising and difficult to understand in the light of the higher clinical safety standards that have been in place for the past 25 years.

As discussed previously,7,8the debate concerning the use of 40 per cent AgF in children should focus on the most likely mechanism of cariostatic action of silver fluoride and rely on existing scientific literature for data that would assist in the formulation of an AgF solution at a strength that would be effective in arresting dentinal caries and protecting the dental pulp,but carry no risk of toxicity.

There is a lack of scientific evidence that fluoride in solution has the capacity to inactivate or destroy microorganisms in carious dentine in vivo,inhibit the progression of caries through dentine and prevent carious exposure of the dental pulp.On the other hand,evidence exists for silver ions having a bactericidal effect on oral bacteria,including S. mutans,at concentrations in the range 20-200ppm.13 In view of its bactericidal properties,coupled with its physical effect of occluding carious and intact dentinal tubules following precipitation,silver is likely to be the key component of AgF that exerts a cariostatic action and thereby prevents or delays penetration of reparative dentine by caries and subsequent exposure of the dental pulp.

As the amount of silver in 40 per cent AgF is in the order of 340,000ppm,there is wide scope for the concentration of AgF to be lowered significantly to a level where it would still be effective against caries in primary teeth but would not carry a risk for fluorosis or other form of toxicity.If a silver ion concentration

in the order of 4,000-4,500ppm can be shown to be cariostatic,an AgF solution at a concentration of 0.5 per cent,that is one-eightieth of that currently used clinically,might prove to be effective and appropriate for treatment of primary tooth caries in children aged 4-7 years.The fluoride level in such a solution would be in the order of 1,000-1,500ppm which,if used with caution,should not present any risk of toxicity.

Laboratory and clinical testing of AgF solutions at concentrations between 0.5-2 per cent might be found to be effective for treatment of deep caries in permanent teeth prior to placement of a permanent restoration with satisfactory marginal sealing properties.If this could be confirmed,it raises the possibility of such AgF solutions becoming a routine part of ART.

Conclusion

While scientific evidence does not support continued clinical use of highly concentrated solutions of silver fluoride in paediatric or other areas of clinical dentistry,the evidence suggests low concentrations of AgF may have a role in the management of dental caries in both primary and permanent teeth,not only for those who have ready access to private and government dental services, but also for children and adults in areas which lack such services and who must rely on auxiliaries for their dental care.Protocols involving low strength AgF solutions should be developed and evaluated in controlled clinical trials before wider implementation in dentistry for children and adults is contemplated. Acknowledgement

The authors appreciate the assistance of Max Bulsara,Biostatistical Consulting Service,Department of Public Health,University of Western Australia.References

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prevention in newly-erupted first permanent molars.Aust Dent J 1989;34:407-409.

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commercial preparations of silver fluoride.Aust Dent J 1997;42:52-53.

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paediatric dentistry.Aust Dent J 1997;42:166-168.

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Pindborg JJ.Pathology of the dental hard tissues,Copenhagen: WB Saunders 1970:163-165.

10.Fejerskov O,Y aeger JA,Thylstrup A.Microradiography of the

effect of acute and chronic administration of fluoride on human and rat dentine and enamel.Arch Oral Biol 1979;24:123-130. 11.Neesham DC.Fluoride concentration in AgF and dental

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nitrate on human dentin and pulp.J Am Dent Assoc 1958;57:621-630.

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Address for correspondence/reprints:

Associate Professor Theo Gotjamanos,

University of Western Australia,

Department of Pathology,

Queen Elizabeth II Medical Centre,

Nedlands,Western Australia 6907.