Cariostatic effect and fluoride release from a visible light-curing adhesive for bonding of orthodontic brackets Bjern ~gaard," Felipe Rezk-Lega," Jan Ruben, b and Joop Arends b Oslo, Norway, attd Groningen, The Netherlands This study was designed to investigate the cariostatic potential in vivo of a visible light-curing adhesive for the bonding of orthodontic brackets. The fluoride release of the adhesive in water and saliva was also measured. Ten orthodontic patients with premolars to be extracted participated. One bracket with Heliosit-Orthodontic (no fluoride) was positioned on the buccal surface of one premolar (control), and another bracket with Orthodontic cement VP 862 (containing fluoride) was positioned on the experimental contralateral premolar. The adhesives were cured with a Heliolux II lamp, and the teeth were extracted after 4 weeks. The patients used a fluoride toothpaste during the experiment. The mineral content of the enamel adjacent to the brackets was determined by quantitative microradiography. The fluoride release from disk-shaped plates of the fluoride adhesive was measured in water for a 6-month period and in human saliva for 24 hours. The fluoride adhesive reduced lesion depths by about 48% than the nonfluoride adhesive (P < 0.05, t test). The largest release of fluoride from the plates in water was observable within the first week. However, a significant amount of fluoride was still released after 6 months. The fluoride release in saliva was significantly lower in human saliva at pH 7 than in water (P < 0.01, t test). When salivary pH was lowered to 4, to mimic a cariogenic challenge, the amount of fluoride released increased up to the value measured in water. It was concluded that the regular use of fluoride toothpastes is insufficient to inhibit lesion development around orthodontic brackets. A fluoride-releasing adhesive reduced lesion development significantly adjacent to brackets compared with a nonfluoride adhesive. The fluoride release was found to be pH dependent and more rational in vivo than may be observed in water. (AM J ORTHOD DENTOFACORTHOP 1992;101:303-7.)

C a r i e s lesion development in association with fixed orthodontic appliances is an extremely speedy process. Visible white-spot lesions may develop within 1 month under ill-fitting bands z or adjacent to brackets. 2 Gorelick et a12 reported that approximately 50% of 121 patients experienced lesions on a tooth during treatment. Lesions on the labial enamel surface remineralize poorly and may represent a clinical problem several years after debonding. 4'5 9Fluoride is known to inhibit lesion development during fixed orthodontic appliance therapy. 2'6 Unfortunately, patient cooperation with topical agents is frequently inadequate or extremely difficult. 7 Fluoridereleasing composite resins for bracket bonding have therefore attracted considerable interest 8'~ and may offer several clinical advantages, such as slow release of low levels of fluoride, site specificity (e.g., adjacent to 'Department of Orthodontics, Dental Faculty, University of Oslo. ~Materia Technica, Dental School, Universityof Groningen. 811127616

bracket-enamel interface), and sufficient time for bracket placement and excess material removal by light curing. The aim of the present study was (1) to examine the cariostatic potential in vivo of a visible light-curing composite adhesive for bracket bonding, and (2) to measure the release of fluoride from the above composite adhesive in water and in saliva. MATERIALS AND METHODS Adhesives

Two visible light-curing orthodontic adhesives were used in this study. The material Heliosit-Orthodontic (Vivadent, Liechtenstein) is a halogen light-curing adhesive without fluoride. The composition is 85% by weight monomer (BISGMA and urethane-dimethacrylate) and 14% by weight pyrolytic silicon dioxide with a maximum particle size of 0.04 g.m as a strengthening agent. The second experimental Orthodontic Cement VP 862 (Vivadent, Liechtenstein) is also a halogen light-curing adhesive, but the fluoride is time released. The composition is based on 30% of a urethane monomer and 65% of a special 303

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A

B

B

A

Fig. i . Schematic drawing of buccal enamel surface with attached bracket. Four enamel sections were prepared as indicated by A and B. The saw blade was orientated perpendicular to the tooth surface along the dashed lines. The two sections marked A refer to bracket periphery, and the two sections marked B refer to bracket center.

glass filler with particle size less than 10 p.m. The glass filler contains fluoride that is very slowly released.

Clinical study Six patients with 10 pairs of premolars to be extracted as part of the orthodontic treatment, participated voluntarily in this investigation. The buccal enamel surfaces of the premolars were pumiced, washed and dried, etched with 37% phosphoric acid for 1 minute, and then dried again with compressed air. Saliva contamination was prevented with lip expanders. The adhesives, Heliosit-Orthodontic or Orthodontic Cement VP 862, were applied directly on the bracket base (Ormesh, Ormco, Ormco Corp., Glendora, Calif.). One bracket with the Heliosit-Orthodontic was positioned on the buccal surface of one premolar (control), and another bracket with Orthodontic cement VP 862 was positioned on the experimental contralateral premolar in a random order. Excess adhesive was removed with a scaler. The adhesive was cured with polymerization light from a Heliolux II lamp (Vivadent, Liechtenstein). The adhesive was cured for 20 seconds along the tangential side of the tooth surface from the cervical part and subsequently for 20 seconds along the tangential side of the tooth surface from the incisal part, according to the manufacturers' recommendations. The patients were allowed to use a normal fluoridated toothpaste durihg the experimental period. After a 4-week period, the teeth were extracted and stored for analysis on wet cotton in closed test tubes at 4 ~ C.

Microradiography To quantify the results of plaque action near the bracket during the study, microradiography was used. To determine the mineral content in volume percent in enamel near the br.hcket, microradiographs were made of the enamel both under the central part of the bracket and at the bracket periphery

(Fig. 1). The sections were placed together with an aluminum stepwedge placed on a high resolution photographic film (Kodak high-speed hol~raphic film SO-253). The x-ray irradiation of the samples was done by means of monochromatic roentgen rays from a Philips PW 1730 x-ray generator (Philips N.V., Eindhoven, the Netherlands) at 20 kV and 15 mA. Details of the microradiography technique have been published previously."-" The volume percentages of mineral in the enamel sections were estimated densitometrically with the formula of Angmar et el." The slit dimensions of the microdensitometer were 6 x 73 I.tm-';the films were moved with respect to the slit with a speed of 2.7 I.tm S-L In microradiography experiments there are two important parameters, lesion depth (Ij) in micrometers and the total mineral loss in the lesion (AZ). Delta Z is expressed in volume percent times micrometer (vol% x p.m). Lesion depth is the distance between the outer enamel surface and a point where the mineral content is 5% less than in sound enamel. Delta Z is the mineral loss and is the surface area between the microradiographic tracing of sound enamel and the tracing of demineralized (or carious) enamel.

Fluoride release of the orthodontic cement in water Disk-shaped plates (8.5 mm in diameter and 3.5 mm thick) of the Orthodontic cement VP 862 were prepared in teflon molds; the adhesive was cured with polymerization light as previously described. Once polymerized, the specimens were removed from the mold, trimmed, and weighed. Six plates were placed in separate small plastic containers, each holding 10 ml of distilled water (pll 7). The fluoride content in the water was determined with a fluoride selective electrode (Model 9409) coupled to an ion meter (Orion Research Inc., Cambridge, Mass:) after addition to TISAB (total ionic strength adjustment buffer, Orion cat. no. 94-09-09). Fluoride was measured after 1 hour, 24 hours, 1 week, 2 weeks, 1 month, 3 months, and 6 months. After each fluoride measurement, the plates were washed in distilled water and placed in new plastic tubes containing 10 ml of distilled water. During the experiment the temperature was 20~ C; the solutions were slowly agitated. The technique has recently been described by Rezk-Lega and ~gaard. ~5

Fluoride release from orthodontic cement in human saliva Disks of the Orthodontic cement VP 862, prepared as previously described, were also studied in saliva. Six series of disks were placed in separate plastic containers, each holding 10 ml of unstimulated human saliva. The fluoride concentrations were measured, as described, after 1 hour. Saliva ptl was subsequently lowered to 4.0 by adding hydrochloric acid, and the fluoride content of the saliva was measured. 16

RESULTS Microradiography. The total mineral loss and lesion depths under the central part of the brackets and at the bracket periphery are presented in Table I. The fluoride-containing ad-

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F c o n t e n t In ppm

l ,~

o

0-1 h

24 h - I wk 1-24 h

I-2 wk8

2 wks-1 mnth 8 - 0 mntha I--3 mnth8

D time Fig. 2. Fluoride release from orthodontic adhesiveas a function of time in water.

Table I. Total mineral loss (AZ) and lesion depths (!,3 at the central part under the br;tckets and at the bracket perii'ery for a fluoride-containing adhesive and a no nfluoride-containing adhesive after 4 weeks bonding Under bracket center

Adhesive Heliosit-Orthodontic (no fluoride) Orthodontic Cement VP 862 (fluoride)

Mineral loss AZ bz vol% • Izm • SD

Bracket periphery

Lesion depth la in I~m • SD

696 __+ 66

24 •

2

761 • 210

22 • 4

Mhzeral loss AZ in vol% x I l m • SD 1365 • 200 1 9

/

981 + 2 8 0 "

Lesion depths 1~ in lain • SD 61 •

12 ] 9

32 _ 8

1

9 Significantly different from the nonfluoride adhesive at the 5% level.

hesive (Orthodontic Cement VP 862) reduced lesion depths during a 4-week period by about 48% than the nonfluoride adhesive (Ileliosit Orthodontic). The differences between Id and AZ are statistically significant at the 5% level (t test). As might be expected, no significant differences are observed whether Ij or AZ are compared under the center of the brackets. Fluoride release in water or in human saliva

Fig. 2 shows the fluoride release from the orthodontic cement VP 862 into 10 ml of distilled water as a function of time. The largest release of fluoride is observable within the first week. However, a significant amount of fluoride is still released after 6 months. In Table II the released fluoride from the adhesive in 10 ml of distilled water after I hour is compared with the release of fluoride in 10 ml of human saliva. The fluoride released is significantly lower in human

saliva at pH 7.0 than in water (p < 0.01, t test). When the salivary pH is lowered to 4.0, the amount of fluoride released increases up to the value measured in water. DISCUSSION

Fluoride-releasing composite resins systems have attracted substantial interest in restorative dentistry because of low-dose long-term release of fluoride ions. The release of fluoride is very beneficial for composite resins, but they must be accompanied with long-term mechanical properties. 17.~s Recent research indicates that low-level fluoride doses may have clinical advantages compared with single high-level doses, t9"21 This study has shown that a fluoride-releasing visible light-curing adhesive .reduces lesion development adjacent to orthodontic brackets significantly than a nonfluoridated adhesive (Table I) supporting observations by Sonis and Snell s and Underwood et a l . 9 All

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Table II. Fluoride released from the fluoride-containing adhesive within 1 hour in 10 mL distilled water (pH 7.0), human saliva (pH 7.0), or human saliva (pH 4.0) Fluoride adhesive Distilled water lluman saliva truman saliva

I I

pH 7.0 7.0 4.0

Fluoride concentration in ppm F0.96 - 0.4 ] 9 0.2 § 0.3 1.2 +-- 0.3 NS

*Significantly different from distilled water at the 5% level. NS. not significantlydifferent from distilled water.

the patients were requested to brush daily with a fluoride-containing toothpaste. In spite of this topical application of fluoride by toothpaste, significant lesions develdped immediately adjacent to the brackets bonded with the nonfluoride adhesive. This parallels a recent study by O'Reilly and Featherstone 2 showing that regular use of fluoride toothpastes during 9 applianc e therapy was not sufficient to inhibit lesion develoPment. The caries inhibition observed with the fluoride adhesive is comparable with that obtained with glass ionomer cements for cementation of orthodontic bands, z2 A fluoride-releasing adhesive for bracket bonding or bonding of retainers may therefore offer significant caries protection independent of patient cooperation. In this study homologous premolars to be extracted for Orthodontic purposes were used. In this way each patient had an internal control. This is an important aspect since caries susceptibility is known to differ strongly between patients. Plaque was not scored in this study in general or adjacent to the brackets; the participants were given proper oral hygiene instruction. Glatz and Featherstone 2~ did not find any correlation between the amount of demineralization occurring around orthodontic appliances in 1 month and the plaque index scored weekly. Scheie et al. 24 showed that a cariogenic environment rapidly develops around orthodontic appliances even in the presence of an oral hygiene regimen. A major mechanism for the cariostatic effect of fluoride is intimately related to the fact that fluoride must be present dttrh~g the demineralization and remineralization processes. For highly concentrated fluoride agents (toothpastes, rinses, gels) a calcium fluoride-type material (CaF2) is the major reaction product on the enamel or in lesions. It has been suggested that CaF2 forms a pH controlled reservoir for release of low levels of fluoride during cariogenic challenges. 25 The released fluoride ions may then adsorb onto the enamel crystals and inhibit further dissolution or increase remineralization of enamel. '~ Composite adhe-

sives releasing low levels of fluoride most likely are effective by the same mechanism. Fig. 2 shows that relatively high amounts of fluoride are released in water within the first week and continued to decline during the 6-month experiment. Chan et al. 1~also observed a decline in fluoride release in water for an orthodontic adhesive during a 6-week period. Arends and van der Zee ~7 showed that fluoride released from a composite resin was subsequently taken up by the surrounding hard tissue. Table II compares the release of fluoride from the adhesive in water and human saliva at neutral and low pH. The experimental period was limited to 1 hour in vitro a longer treatment time with saliva is not possible. The data clearly show that significantly less fluoride is released in saliva than in water at neutral pH. However, when salivary pH is lowered to a value of 4, to mimic a severe caries challenge, the amount of fluoride increases up to the level measured in water. This shows that fluoride release from the adhesive is deftnitely pH controlled in the same way as shown with 9CaF2 and glass ionomer cements.16"22 The effect is probably due to adsorption of proteins and secondary phosphate at neutral pH and desorption of proteins and phosphate at lower pH. 16This indicates that fluoride release from adhesives is much more economical than may be expected from dissolution experiments of adhesives in water. CONCLUSIONS

This study showed that during the experimental period, regular use of fluoride toothpastes was not sufficient to inhibit lesion development around orthodontic brackets. However, fluoride released from a visible light-curing adhesive inhibited lesion development adjacent to orthodontic brackets significantly, although no complete inhibition was noted. The reason may be that during severe cariogenic conditions like that prevailing around brackets and underneath bands, fluoride may have a limited effect unless it is directly present at the dissolution site. Improved oral hygiene and the use of prophylactic fluoride during orthodontic treatment with fixed appliances may thus be essential since the two procedures probably have a synergistic effect. 26'27 The fluoride release from the adhesive was found to be pH dependent; more fluoride was released during cariogenic challenges (low pH) than at neutral pH. Further clinical studies are in progress to examine the long-term effect of the fluoride adhesive on white-spot lesion development and the mechanical properties. REFERENCES

1. OgaardB, RollaG, ArendsJ. Orthodonticappliancesand enamel demineralization. Part I. Lesion development9AM J ORTItOD DL'croFAr OaTllOV1988;94:68-73.

Voturne lOt Number 4 2. O'Reilly MM, Featherstone JDB. Demineralization and remineralization around orthodontic appliances: an in vivo study. AM J ORTHODDF.NIOFACORrHoP 1987;92:33-40. 3. Gorelick L, Geiger AM, Gwinnett AJ. Incidence of white spot formation after bonding and banding. AM J OR'nIOD 1982;81: 93-8. 4. /~rtun J, Thylstrup A. A 3-year clinical and SEM study of surface changes of carious enamel lesions after inactivation. AM J OR"roOD DF-',"roFAcOR'rHOP 1989;95:327~ 5. Ogaard B. Prevalence of white spot lesions in 19-year-olds: a study on untreated and orthodontically treated persons 5 years after treatment. AM J OR'I'HOD DENTOFAC ORTHOP 1989;96: 423-7. 6. Ogaard B, R011a G, Arends J, ten Cate JM. Orthodontic appliances and enamel demineralization. Part 2. Prevention and treatment of lesions. AM J ORTIIOD DENTOFACOR'IItOP 1988;94: 123-8. 7. Geiger AM, Gorelick L, Gwinnett AJ. Reducing white spot lesions in orthodontic populations with fluoride rinsing. J Dent Res 1990;69:236. 8. Sonis AL, S~nell W. An evaluation of a fluoride-releasing, visible light-activated bonding system for orthodontic bracket placement. AM J OR'r]IODDENTOFACOR'lqtOP 1989;95:306-1 I. 9. Underwood ML, Rawls ttR, Zimmermann BF. Clinical evaluation of a fluoride-exchanging resin as an orthodontic adhesive. AM J OR'IHODDENTOFACOR'I-HOP1989;96:93-9. 10. Chan DCN, Swift EJ, Bishara SE. In vitro evaluation of a fluoride-releasing orthodontic resin. J Dent Res 1990;69: 1576-9. II. Gelhard TBI-~I, Arends J. Microradi~raphy of in vivo remineralized lesions in human enamel. J Biol Buccale 1984; 12:59-65. 12. De Josselin de Jong, ten Bosch JJ. Error analysis of the microradiographic determination of mineral content in mineralized tissue slices. Phys Med Biol 1985;10:1067-75. 13. Arends J, Ruben J, Jongebloed WL. Dentin caries in vivo: combined scanning electron microscopic and microradiographic investigation. Caries Res 1989;23:36-41. 14. Angmar B, Carlstr6m D, Glas JE. Studies on the ultrastructure of enamel. J UItrastruct Res 1963;8:i2-23. 15. Rezk-Lega F, Ogaard B, R011a G. Availability of fluoride from glass-ionomer cements in human saliva. Scand J Dent Res 1991; 99:60-3.

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16. R011aG, Ogaard B. Studies on the solubility of calcium fluoride in human saliva. In: Leach SA, ed. Factors relating to demineralization and remineralization of the teeth. Oxford: Information Retrieval Ltd, 1986:191-9. 17. Arends J, van der Zee Y. Flouride uptake in bovine enamel and dentin from a fluoride-releasing composite resin. Quintessence lnt 1991;21:541-4. 18. Arends J, Ruben J, Dijkman AG. The effect of fluoride release from a fluoride-containing composite resin on secondary caries: an in vivo study. Quintessence lnt 1990;21:671-4. 19. Borsboom P, van der Met HC, Arends L Enamel lesion formation with and without 0.12 ppm F in solution. Caries Res 1985;19:396-402. 20. Arends J, Christoffersen J. Nature and role of loosely bound fluoride in dental enamel. J Dent Res 1990;69:601-5. 21. Margolis HC, Moreno EC, Murphy BJ. Effect of low levels of fluoride in solution on enamel demineralization. J Dent Res 1986;65:23-9. 22. Rezk-Lega F, Ogaard B, Arends J. An in vivo study on the merits of two glass ionomers for the cementation of orthodontic bands. AM J OR'mOP DE,',rrOrACORmOP 1991;99:162-7. 23. Glatz EMG, Featherstone JDB. Demineralization related to orthodontic bands and brackets--a clinical study. AM J OR'mOP !985;87:87. 24. Scheie. AAa, Arneberg P, Krogstad O. Effect of orthodontic treatment on prevalence of Streptococcus mutans in plaque and saliva. Scand J Dent Res 1~84;92:211-7. 25. Ogaard B. Effects of fluoride on caries development and progression in vivo. J Dent Res 1990;69:813-9. 26. Glass RL. Fluoride dentifrice: the basis for the decline in caries prevalence. J R Med Suppl 1986;79:!5-7. 27. Rr G, Ogaar d B, Cruz R de Almeida. Fluoride containing toothpastes, their clinical effect and mechanism of cariostatic action--a review, lnt Dent J 1991 [in press].

Reprint requests to: Dr. Bjorn Ogaard Department of Orthodontics Dental Faculty University of Oslo P.O. Box 1109, Blindem 0317 Oslo 3

Cariostatic effect and fluoride release from a visible light-curing adhesive for bonding of orthodontic brackets.

This study was designed to investigate the cariostatic potential in vivo of a visible light-curing adhesive for the bonding of orthodontic brackets. T...
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