EFFElCT OF A SEALANT, USED IN CONJUNCTION WITH TOPICAL FLUORIDE APPLICATION, ON

FLUORIDE CONCENTRATIONS IN HUMAN TOOTH ENAMEL

M. FRIEDMAN, E. H. M. VAN DER MERWE. J. I. BISCHOFF, L. P. FATTI* and D. H. RETIEF

Dental Research Unit of the South African Medical Research Council and the University of the Witwatersrand. Johannesburg, Republic of South Africa

Summary-A system using acidulated phosphate-fluoride solution (APF) was studied for the topical application of fluoride on acid-conditioned teeth and then coating with a cyanoacrylate varnish. Enamel biopsies for fluoride determination were taken from the six anterior teeth in both arches of 23 subjects. aged 19-23 years. The teeth were acid-conditioned and APF applied. The upper left and lower right segments were varnished while the contralatcral seg- ments were left as controls. The teeth were re-biopsied in groups at 1, 2, 4, 12, 24 and 52 week intervals. At all intervals, fluoride levels after treatment were significantly higher @ < 0.001) regardless of whether they had been coated or not than those before treatment. There was no significant difference between coated and control teeth. When all the data were pooled, however, a significantly greater (p < 0.05) fluoride retention was found in the coated teeth.

INTRODUCTION

The cariostatic action of topically applied fluorides is universally acceptled (Murray and Bennett, 1974) and it has been shown that this action is enhanced by increased fluoride uptake by enamel (Brudevold et al., 1967). Some methods used and recommended to increase the uptake of topically applied fluorides are: cleaning the teeth prior to treatment, prolonging the application time (Richardson. 1967) and reducing the pH of the fluoride solution (Brudevold et al., 1963). It has also been shown that pretreatment of the teeth with mild acid significantly increases the en- amel fluoride uptake (Aasenden, Brudevold and McCann, 1968; De Paola, Aasenden and Brudevold, 1971 ; Mellberg and Loertscher, 1973). Up to two- thirds of the topical y applied fluoride is lost, how- ever, from the surfact: enamel within 24 hr after appli- cation (Mellberg, Laakso and Nicholson, 1966).

Varnishes have therefore been proposed as tempor- ary sealants (Buonocore. 1973) to prevent the initial loss and allow the readily formed calcium fluoride to react to give the more stable fluorapatite over a period of time (Brudevold rt cd., 1967). Essentially two types of varnishes have been used to increase fluoride levels in enamel. These are polyurethane and other varnishes containing fluoride (Lee ef al.. 1972a; Koch and Petersson, 1972) and cyanoacrylate varnishes used as a sealant following topical fluoride treatment (Pugnier, 1972; Dogon. van Leeuwen and Kirklin, 1973).

The purpose of this study was to test the efficacy of sealing topically applied fluoride on pre-etched teeth with a varnish. The fluoride solution was an acidulated phosphate fluoride and the varnish a

* Department of Applied Mathematics, University of the Witwatersrand, Johanxsburg, Republic of South Africa.

2-(2,2,2,-trifluoroethoxy)-ethyl 2-cyanoacrylate (3M Company. St. Paul, Minnesota 55101).

MATERIALS AND METHODS

Twenty-three dental students, aged 19-23 years. were divided into six groups, four of which had three students in each, one had five and one group had six. The six upper and six lower anterior teeth of each subject were used. Enamel biopsies were taken from each tooth prior to treatment,

The enamel biopsy method used was that devel- oped by Hotz, Miihlemann and Schait (1970) and modified by van der Merwe et al. (1974). The teeth were polished with pumice and water and dried. Annular plastic adhesive discs, having an inner dia- meter of 3 mm and an outer diameter of 5 mm. were placed on the buccal surfaces to isolate a known area of enamel (PI. Fig. 1) from which a biopsy was taken. A filter-paper disc of the same area, saturated with IO ~1 of 2 M perchloric acid as demineralizing agent, was pulsated on the isolated area for 8 sec. This disc, together with a second which was used to mop up residual acid, was transferred to 2 ml of TISAB (total ionic strength adjustment buffer) (Orion Research Inc., Cambridge, Mass. 02 139) to which 0.08 ppm fluoride ion was added.

Two parameters were measured: fluoride ion con- centration using a combination specific fluoride ion electrode (Orion Research. Model 96-09) coupled to a digital pH meter (Orion Research, Model 701). and the calcium concentration by means of atomic absorption spectrophotometry (Carl Zeiss. Qber- kochen, West Germany, Model PMQII with flame attachment FA2). From these values, the depth of etch in micrometers and Ruoride concentration in

237

238 M. Friedman et nl.

Table 1. Mean fluoride concentrations and mean log, fluoride concentrations + S.D. for each group before and after treatment. Values corrected to a depth of 10 LLrn.

Time interval Varnished Control between Before After Before After biopsies WI wm IF-1 mm Fl wm ITI wm (weeks) log,, IF-1 ri- SD. log,. [F-l + SD. log, IF-1 i: SD. log,, [F-J _t SD.

I 321.8 2320.2 33x.5 2006.7 5.28 * 1.04 1.52 f 0.73 5.31 + 1.15 7.31 * 0.81

2 6X7.3 2X89.7 706.6 23 18.9 6.29 & 0.78 7.70 * 0.75 6.33 f 0.71 7.50 * 0.75

4 195.1 716.7 191.5 756.0 4.95 * 0.82 6.42 k 0.57 4.89 k 0.96 6.45 i 0.62

12 733.9 2447.9 783. I 2200.2 6.50 & 0.47 7.60 i 0.65 6.56 & 0.47 7.45 i 0.68

24 351.8 2487.1 356.1 1176.5 5.87 k 0.56 7.59 & 0.68 5.80 f 0.40 7.30 + 0.56

52 334.3 1241.4 302.4 979.4 5.74 f 0.42 6.89 k 0.75 5.64 + 0.41 6.77 If: 0.52

parts per million were calculated according to the method described by Barbakow at al. (1973).

In subsequent treatment of the teeth, a caries-pre- ventive kit (3M Company) was used according to the manufacturer’s instructions. A filter-paper insert positioned in an air-cushion fluoridator tray (Ion Company, Costa Mesa, Calif. 92626) was saturated with 0.05 M phosphoric acid and placed on the teeth for 30 sec. The teeth were washed and dried. The acidulated phosphateefluoride solution supplied with the kit was then applied to the teeth for two minutes, using the same procedure. The teeth vvere dried using compressed air. The cyanoacrylate sealant was then painted on the buccal and lingual surfaces of the upper left and lower right anterior teeth. while the upper right and lower left quadrants were not coated and served as controls. The patients were instructed not to rinse their mouths or eat for 30 min following the fluoride application and to refrain from using Ross silk and from vigorous tooth brushing for two days.

The groups were re-biopsied at determined inter- vals of 1, 2,4. 12. 24 and 52 weeks respectively. Where possible. the second biopsy was taken as close as possible to the first but from an area on the tooth which had not previously been used. The fluoride concentration of the enamel and the depth of etch were again determined.

The effect of the acid pre-conditioning on the en- amel was studied using a scanning electron micro- scope (Cambridge Scientific Instruments Ltd., Cam- bridge, England, Model Stereoscan S4).

RESULTS

In view of the fact that enamel fluoride concen- tration varies exponentially with depth from the tooth surface (Weatherell and Hargreaves. 1966; Barbakow. De Kock and Retief, 1971). and the fact that the bi- opsy depth varied from 4 pm to 14 pm, the fluoride concentrations were all corrected to values at a depth of IO Ltrn by means of the following statistical method: using the model Y = ?emli* for the relation- ship between fluoride concentration in the tooth (Y) and the depth below the surface (.x) at which the

measurement was made, an Analysis of Covariance was performed using log,. Y as dependent variable and Y as concomitant variable, splitting the data into four groups for the four quadrants in the mouth. Sep- arate analyses were performed on the data for each patient obtained before and after fluoride treatment and then the slopes of the regression lines from the separate analyses were compared by means of an F-test. In no case was a significant difference found between the slopes, so a common slope was obtained by pooling and this was used to transform the data to a constant depth of IO I’m.

In the subsequent results. the values given are the means of the corrected fluoride concentrations of all experimental or all control teeth in each group. The mean fluoride concentrations for each group of the sealed and control teeth before and after treatment are given in Table I. The differences of these mean fluoride concentrations at each time interval are represented graphically in Text Fig. 2. This represents the fluoride uptake, and hence retention, by enamel. In all cases, excepting after the four-week interval, the coated teeth retained more fluoride than the con- trols. Text Fig. 3 shows the magnitude of the increases in the fluoride concentration of the sealed and control teeth. These values range from 2.8 for the control teeth after the 12-week interval to 7.2 for the coated teeth after one week. The fluoride uptake of the six

Fig. 2. Differences of the mean fluoride concentrations before and after topical fluoride application.

Effect of a sealant on enamel fluoride 239

- 1

Not varnIshed

Perlod between blopsles. weeks

Fig. 3. The ratio of mean fluoride concentration after topi- cal application of flucride to the mean baseline fluoride

concentration at specified time intervals.

upper teeth is compared with that of the six lower teeth at each period in Text Fig. 4. In all cases, the lower teeth retained more fluoride than the upper teeth.

Two sample t-tests were performed on the trans- formed data to test for differences in fluoride levels (corrected for depth) before and after fluoride treat- ment as well as for differences in the fluoride retention in coated and uncoated teeth and in the lower and upper teeth. This analysis was repeated separately for the six groups of p,-ltients with 1, 2, 4, 12. 24 and 52 weeks delay between fluoride treatment and second measurement, respectively.

At each time interval and regardless of whether the teeth had been varnished or not, the fluoride levels after treatment were significantly higher (p <O.OOl) than those before treatment, but in no case was there any significant difference between the fluoride reten- tion in the coated and control teeth. However. taking the data from all six groups together, a significant difference (p ~0.05) in fluoride retention between coated and uncoated teeth was found, the fluoride retention in the coated teeth being higher. In all except the four-weeks case, the fluoride retention in the lower teeth was significantly higher (p <O.OOl) than that in the upper teeth.

The scanning electron micrographs showed the relatively featureless, appearance of normal enamel (Pl. Fig. 5). The etching by the 0.05 M phosphoric acid conditioning agent produced only a slightly roughened appearance of the enamel (PI. Fig. 6).

DISCUSSION

Aasenden, Brudevold and McCann (1968) demon- strated greater retention of fluoride after a topical fluoride application when the enamel had been condi- tioned with dilute H3P04 prior to application of the fluoride solution. In their in ai~o and in citro studies, they showed enhanced fluoride deposition when en-

amel was pre-treated with 0.01 M or 0.05 M H3P04, the 0.05 M acid being more effective. This was later confirmed by De Paola, Aasenden and Brudevold (1971) who conducted a one-year clinical trial. They found a significant difference in caries experience in favour of subjects exposed to the mild etching pro- cedure prior to a topically applied acidulated phos- phate-fluoride (APF) solution. Mellberg and Loertscher (1973) compared the Ruoride uptake from APF solutions by normal and acid-etched human en- amel. They found that etched enamel acquired about five times more fluoride than un-etched enamel. Our results. where in all cases the fluoride levels after treatment were significantly increased (p <O.OOl), clearly support the use of the acid-conditioning tech- nique used in conjunction with topical fluoride ther-

apy. The modification of the enamel surface by acid con-

ditioning possibly renders it more receptive to bond- ing with an adhesive sealant. Comparing the scanning electron micrographs of normal enamel with enamel conditioned with 0.05 M phosphoric acid, this pre- conditioning alters the enamel surface minimally. The characteristic prism-end structure of enamel which is apparent after etching with stronger acids (Lee et ul., 1972b; Retief. 1975) was not produced.

The reaction between fluoride and human enamel is complex and not yet fully understood. Generally it is thought that the reaction between fluoride and hydroxyapatite gives one of two products, CaFz and fuorapatite (McCann, 1968). McCann showed further that fluorapatite is relatively insoluble when com- pared with CaF2. It is fluorapatite which increases enamel resistance to acid demineralization (Young and Elliot, 1966). Richardson (1967) found that pro- longing the exposure of enamel to fluoride solutions leads to greater Ruoride fixation by the enamel in the form of fluorapatite. He proposed the use of various agents to seal fluoride into contact with the enamel and thus prolong the exnbsure time. Some of the most successful agents .h\: tested in vitro were polyoxyethylene soya amirle and silicone grease.

I3 LOWW

UPPer

Period between blopsles, weeks

Fig. 4. The fluoride uptake by the six upper teeth com- pared to the fluoride uptake of the six lower teeth at each

time interval.

240 M. Friedman (‘r al

Another method used to prolong fluoride contact

with enamel is the incorporation of unbound fluoride into a varnish. In this case, the fluoride is available for reaction with enamel (Murray and Bennett, 1974). A polyurethane varnish containing 10 per cent w/w disodium monofluorophosphate (Epoxylite CPF 9070, Lee Pharmaceuticals, South El Monte, Calif. 91733) has been shown to increase enamel fluoride concentrations at least until 30 days after application (Lee et (II., 1972a). A modified varnish containing 2.26 per cent fluoride as sodium fluoride (Duraphat. Woelm. Eschwege. Germany) has also been used in this way and has been found to increase fluoride levels in teeth (Koch and Petersson. 1972; Bang and Kim. 1973; Stamm, 1974).

Alternatively. cyanoacrylate resins have been used as temporary sealants to prevent loss of fluoride from enamel surfaces after topical application, to maintain intimate contact of the topical fluoride and CaF, with the hydroxyapatite and to ensure fixation of fluoride in the enamel as fluorapatite (Buonocorc. 1973: Dogon et LI/., 1973). Although the sealant used in those studies contains fluoride, it is covalently bonded to carbon atoms and not available for reaction in the oral environment.

Dogon c’t (11. (1973). using the same technique and material as employed in our investigation. found con- sistently higher fluoride concentrations in the resin- sealed teeth. Two years after treatment, the fluoride concentrations were still significantly higher in the sealed teeth. Our results do not support these find- ings. In no single group did we find a significant dif- ference between coated and unvarnished teeth. How- ever, when all our data were pooled, the fluoride retention in the coated teeth was significantly higher than the fluoride levels in the uncoated teeth (p <0.05). This finding may have emerged as a result of the increase in the sample size when the data are pooled. Although we accept that the principle of seal- ing topically applied fluoride to enamel surfaces has merit, we would have expected a greater difference in the fluoride uptake between the varnished and con- trol teeth.

A result which emerged during the present investi- gation was that the lower teeth retained significantly more fluoride than the upper teeth, in both the con- trol and coated teeth. A possible reason for this may be that the labial surfaces of the lower anterior teeth were protected for longer periods by the varnish as the labial surfaces of the upper, anterior teeth are more vulnerable to abrasion than the labial surfaces of the corresponding lower teeth.

Our study clearly shows that the uptake of fluoride by enamel is greatly enhanced by acid etching the tooth surfaces prior to topical fluoride therapy. It would appear, however, that the subsequent use of temporary sealants has no additional benefit on fluor- ide retention.

REFERENCES

Aasenden R., Brudevold F. and McCann H. G. 1968. The response of intact and experimentally altered human en- amel to topical fluoride. Archs orul Biol. 13. 543-552.

Bang S. and Kim Y. J. 1973. Electron microprobe analysis of human tooth enamel coated in ciro with fluoride-var- nish. fir/r. odmr. Am 17. 84-88.

Barbakow F. H.. De Kock A. C. and Retlet” D. H. IY71. The fluoride concentration in the enamel of permanent central incisors. J. rkwt. AS,Y S. Afr. 26. I34- i3X.

Barbakow F. H.. van der Merwe E. H. M.. Scnnes S. G.. Retief D. H. and Fatti L. P. 1973. An ijl riro evaluation of an iontophoretic technique for increasing the surface fluoride content in enamel. J. dmt. Ass. S. /ilk. 28. 624-629.

Brudevold F.. McCann H. G.. Nilsson R.. Richardson B. and Coklica V. 1967. The chemistry of caries inhibition problems and challenges in topical treatments. J. tl~lt. Rex 46, 37-45.

Brudevold F.. Savory A., Gardner D. E.. Spinelli M. and Speirs R. 1963. A study of acidulated fluoride solu- tions-1. Irl vitro effects on enamel. ilrrhs orul Biol. 8. 167-177.

Buonocore M. G. 1973. Adhesives in the prevention of caries. J. Am. drnt. 4s.~. 87. lOO& 1005.

De Paola P. F., Aasenden R. and Brudevold F. 1971. The use of topically applied acidulated phosphateefluoride preceded by mild etchmg of the enamel: A one-year clinical trial. Arc/~ orcd Biol. 16. I 155 1163.

Dogon I. L., van Leeuwcn M. and Kirklin M. 1973. !,I vioo studies on the “scaling” of fluoride in teeth: Two- year clinical results. Internat. Ass. for Dent. Res. Pre- printed abstracts. 51st General Meeting, Abstract 240.

Hotz P.. Miihlemann H. R. and Schait A. 1970. A new method of enamel biopsy for fluoride determination. Hrlv. odmt. Actcr 14. 26-29.

Koch G. and Petersson L. G. 1972. Fluoride content of enamel surface treated with a varnish containing sodium fluoride. O&t. Rwy 23. 437 446.

Lee H.. Ocumpaugh D. E.. Shaffcr J. and Sheble A. M. 1972a. Sealing of developmental pits and fissures: IV. Measurement of ~1 rice fluoride pickup by electron mic- roprobe X-ray spectrophotometry. J. drut. Re.s. 51. 634-639.

Lee H.. Stoffey D.. Orlowski J.. Swartz M. L.. Ocumpaugh D. and Neville K. 1972b. Scaling of developmental pits and fissures: III. Effects of fluoride on adhesion of rigid and flexible sealers. J. u’rjlt. Rex 51. 191-201.

McCann H. G. 1968. The solubility of fluorapatite and its relationship to that of calcium fluoride. Arch orcrl Biol. 13. 987-1001.

Mellberg J. R., Laakso P. V. and Nicholson C. R. 1966. The acquisition and loss of Ruoride by topically fluori- dated hum&n tooth enamel. Archs orul Biol. 11. 1213-1220.

Mellberg J. R. and Loertscher K. L. 1973. Fluoride acqul- sition in vitro by etched enamel from acidulated phos- phate Huoride preparations. J. drrlt. Rcs. 52. 447-450.

Murray J. J. and Bennett D. L. 1974. Topical iluorldes and dental caries: A review. J. Dent. 2. I I 17.

Pugnier V. A. 1972. Cyanoacrylate resins in caries preven- tion: A two year study. J. An). drnt. ilss. 84. 829-831.

Retief D. H. 1975. A comparative study of three etching solutions: Effects on enamel surface and adhesive-ena- mel interface. J. orctl R&h. 2. 75-96.

Richardson B. 1967. Fixation of topically apphed fluoride in enamel. J. dcvtt. Rcs. 46 (SuppI. to k-0. I). X7-Y I.

Stamm J. W. 1974. Fluoride uptake from tonical sodium fluoride varnish measured b; an irl rice enamel biopsy. J. Can. dent. Ass. 40. 501-505.

Van der Merwe E. H. M.. Retief D. H.. Barbakow F. H. and Friedman M. 1974. An evaluation of an 111 t+ro en- amel acid etch biopsy technique for fluoride determina- tion. J. drnt. Ass. 5’. Afi. 29. 81-87.

Weatherell J. A. and Hargreaves J. A. 1966. The fluoride content of surface enamel from permanent and deci- duous teeth. Ado. Fluor. Res. 4. 181~191.

Young R. A. and Elliott J. C. 1966. Atomic-scale bases for several properties of apatites. .Archs oral Biol. 11. 699-707.

Effect of sealant on ename fluoride 241

Fig. 1. Annular plastic adhesive discs used to define biopsy area on six upper anterior teeth

Fig. 5. Scanning electron micrograph showing featureless appearance of normal enamel surface. x 1000

Fig. 6. Scanning electron micrograph showing appearance of enamel after etching with 0.05 M H3P04 % 1000