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A comparison of fluoride release from various dental materials
PII:
Journal of Dentistry, Vol. 26, No. 3, pp. 259-265, 1998 Copyright 0 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0300-5712198 $19.00+0.00
so300-5712(97)00011-0
ELSEVIER
A comparison of fluoride various dental materials
release from
S. R. Grobler, R. J. Rossouw and T. J. Van Wyk Kotze Oral and Dental Research
Institute,
University
of Stellenbosch,
Faculty of Dentistry,
Tygerberg,
South Africa
ABSTRACT Objective: The aim of this study was to determine, in vitro, the relative short- and long-term fluoride
releasefrom four resin-modified glass ionomers (Fuji II LC, Vitremer, Enforce & Advance), a polyacid-modifiedcompositeresin (Dyract compomer)and a bonding agent(OptiBond). Methods: All the materials were prepared as outlined by the manufacturers. Circular discsof the materialsmentionedwere suspended in water for up to 300days and the non-cumulative24-h fluoride releasewas determinedpotentiometrically at chosentimes. Results: The amountsof fluoride releasedduring the first day were Vitremer (1.46,~gmm-*), Advance (1.18pgmm-*), Fuji (l.O8,~gmm-‘), Optibond (0.33Ligrnrn-“), Dyract (0.31pg mnP2) and Enforce (0.15pugmm-“). After the secondday the sequencechangedslightly and remainedapproximately the same for the rest of the 300-day period. There was also an increasein the fluoride releaseduring the 60-200-dayperiod relative to the previous period. Conclusion:In generalthe mostfluoride wasreleasedby Advance and not by Fuji II LC or Vitremer. For mostmaterials,fluoride is still releasedafter 300days, Furthermore, even a thin layer of bonding agent releaseda relatively high amount of fluoride (volume-wisethe most) at the beginning.It is deducedthat even the releaseof relatively low amountsof fluoride may result in significantconcentrationsof fluoride in a microleakagegap. 0 1998Elsevier ScienceLtd. All rights reserved KEY WORDS: J. Dent.
1998;
fluoride
release,
26: 259-265
glass
(Received
ionomer,
compomer
20 September
1996;
accepted
INTRODUCTION The major cariostatic mechanism of fluoride is believed to be that it reduces dental caries through promoting remineralization and influencing the morphology of teeth by reducing the solubility of enamel, and through its effect on oral cariogenic bacteria. The beneficial effect of fluoride for the prevention of dental caries is well documented and has prompted the inclusion of fluoride into a host of dental materialsle6. Fluoride-releasing dental restoratives have an effect on secondary carious lesions at the interface of the restoration7-lo, while fluoride adsorption is also found in tooth tissue up to 3 mm away from the restoration Correspondence should be addressed to: S. R. Grobler, Oral and Dental Research Institute, Faculty of Dentistry, Private Bag Xl, Tygerberg, 750.5, Republic of South Africa. Tel: 027-21-931-2246; Fax: 027-21-931-2287; e-mail: srgmaties.sun.ac.za..
3 February
1997)
margins, and may even protect the entire tooth’ l-l4 against dental caries1sm17. Glass-ionomer cements have been suggested as restorative materials”, bases for composites” and amalgam restorations7. The newest generation of glass-ionomer cements have higher cohesive strengths, are light cured and contain more resin (HEMA)20. Other materials are mainly fluoridereleasing resins, such as polyacid-modified composite resins21 (Dyract compomer21). Many studies on fluoride-containing dental materials have shown that fluoride can either be released or absorbed from materials22-25. The aim of this study was to determine, in vitro, the relative short- and long-term fluoride release from four resin-modified glass ionomers (Fuji II LC, Vitremer, Enforce & Advance), a polyacid-modified composite resin (Dyract compomer)21 and a bonding agent (0ptiBond):The hypothesis is that the degree of fluoride release over time would differ amongst
260
J. Dent. 1998; 26: No. 3
1
2
3
4
5
6
7
8
9
11
16
30
60
(A),
Vitremer
200
250 300
(m),
Fuji e), Dyract
DAYS Fig. 7. Plot of 24-hourly Optibond (+).
fluoride
fluoride-containing dental chemical compositions,
MATERIALS
release
(pg mm-‘)
materials
over
with
a 300~day
different
AND METHODS
Four resin-modified glass ionomers (Fuji II LC, Batch No. 071031, GC Intern. Corp., Tokyo, Japan; Vitremer, Batch No. 19940519, 3M Mfg., St. Paul, MN, USA; Advance hybrid21, Batch No. 574013, Caulk/Dentsply International Inc. Milford, DE, USA; Enforce, Batch No. 9412073, Caulk/Dentsply International Inc., Milford, DE, USA), a polyacid-modified composite resin21 (Dyract compomer21, Batch No. C940469, CaulklDentsply International Inc. Milford, DE, USA) and a bonding agent (OptiBond, Batch No. 750985, Kerr Mfg. Co., Romulus, MI, USA) were investigated for their fluoride-releasing ability. All the materials were prepared as outlined by the manufacturers. For each material tested, seven circular copper rings (n=7), of internal diameter 16 mm and 2 mm deep (areaz502.4 mm2), were placed on a glass slab covered with a plastic sheet. The material was mixed and the copper rings half filled. Cotton threads (about 20-cm long) were positioned with one end in the material and the rest extended through an opening (0.5 mm diameter) in the ring. The rings were now further filled by pressing freshly mixed material firmly with glass slabs covered with plastic sheets. When necessary, the material was light-cured for 60 s on both sides, the discs removed from the rings and again light-cured, if necessary, on both sides for 60 s. For the Optibond analysis, discs were prepared from the restorative ZlOO (Batch No. 19940914, 3M
period
for Advance
(*), Enforce
(x) and
Mfg., St. Paul, MN, USA) as outlined above, then coated with a thin layer of Dual Cure OptiBond (mixture of activator 3A and paste 3B) and light cured for 40 s on both sides. Although it is known that fluoride was not added on purpose to the restorative 2100, seven rings with only the restorative were also prepared and tested for fluoride release over 6 days. The discs (seven for each material) were then individually suspended in 10 ml of double glass-distilled water and put in a shaker (Haake, SWB 20, Berlin, Germany) at 37°C for 24 h. The discs were lifted by the thread to just above the water level and rinsed with 10 ml of TISAB with CDTA buffer (Orion Research, Inc., Cambridge, MA, USA). This buffered solution was then analysed for fluoride. The discs were then thoroughly rinsed with distilled water before again being suspended in water. This procedure was repeated every 24 h for the first 9 days, after which the soaking period before each 24-h collection was changed as indicated in Fig. I. In this way a 24-h fluoride release could be determined (non-cumulative F release) after suspension of the discs in water for different periods of time (Fig. I). Fluoride in the buffered solutions was determined with the use of a combination fluoride ion selective electrode (Orion Research, Inc., Cambridge, MA, USA). The potentiometer (Orion Ion Analyser EA 940, Orion Research, Inc., Cambridge, MA, USA) was calibrated with fluoride standard solutions in 50% buffer (TISAB with CDTA) with fluoride concentrations varying between 0.050 ppm and 5 ppm. The fluoride release was expressed in pg F mm-2.
Grobler et a/.: Fluoride release from dental materials Tab/e /. The mean following materials:
fluoride levels (M mm-“) 1, Optibond; 2, Enforce;
of a 24-hourly fluoride 3, Dyract; 4, Vitremer;
release
over
a total period
of 300 days from
seven
SampIeS
261
of each of the
5, Fuji; 6, Advance Materials
Time
Interval
(days)
1
1 2 3 4 5 6 7 8 9 11 16 30 60 200 260 300
0.33 0.05 0.03 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01
Table II. Analysis of the fluoride release Dyract; 4, Vitremer; 5, Fuji; 6, Advance Time interval
by the Bonferroni
2
3
4
5
6
0.15 0.12 0.11 0.05 0.04 0.03 0.02 0.02 0.01 0.02 0.01 0.01 0.01
0.31 0.19 0.19 0.16 0.16 0.16 0.12 0.07 0.08 0.06 0.05 0.05 0.05 0.17 0.17 0.21
1.46 0.52 0.47 0.39 0.39 0.37 0.26 0.23 0.19 0.16 0.14 0.12 0.12 0.26 0.28 0.28
1.08 0.40 0.45 0.37 0.34 0.34 0.27 0.20 0.22 0.16 0.13 0.14 0.14 0.36 0.35 0.34
1.18 0.74 0.58 0.49 0.45 0.38 0.35 0.19 0.22 0.26 0.14 0.20 0.20 0.51 0.58 0.61
multiple
comparison
test at the 5% significant
level:
1, Optibond;
2, Enforce;
Material
(days)
1 2 3
la la 1
2a 2a 2a
3” 3a 3a
4
5
$I
;:
4 5 6 7
1” la ia 1”
2” 2a 2a 2”
6b 3 3 3
;E
5 4b 5b 5b
6 6 6b 3 5 6b 6
89 11 16 30
1” 1” 1” 1” 1”
2” 2a 2” 2” 2a
33 3 3 3
4b 4b 4b
$I
;: 6
;E
5b 5b .cjb
60 200 260 300
1”
2a
3 3a 3 3a
4” 4a 4” 4a
5c 5 5a 5
6 6 6 6
Materials
in the same
3,
horizontal
row with the same
superscript
letter were
RESULTS The plot of the mean values of a 24-hourly fluoride release over a 300-day period for Advance (A), Vitremer (B), Fuji (O), Dyract (*), Enforce ( x ) and Optibond (+) are shown in Fig. 1. Table I gives the mean fluoride levels of 24-hourly fluoride release over a 300-day period from seven samples of each of the following materials: 1, Optibond; 2, Enforce; 3, Dyract; 4, Vitremer; 5, Fuji; 6, Advance. The data were tested for statistically significant differences related to material, time and fluoride using the Kruskal-Wallis one-way ANOVA test. The Bonferroni (all-pairwise) multiple comparison test at the 5% level of significance was used for multiple
4” 4b
not
significantly
;:
different.
comparisons of the means of the different materials (Table 10 for each of the time periods. A Box Whisker plot of the seven samples for each of the five materials was done for every 24-h sampling period for all the different time periods, as indicated in Fig. 1. To summarize, in general it could be deduced that the variation in the amount of fluoride released (within the seven samples) for each material at each time interval was the highest for Vitremer, the second highest for Fuji and the lowest for Optibond. No significant fluoride levels could be found when the restorative ZlOO was soaked alone. Therefore, it could be deduced that when ZlOO is coated with OptiBond all the fluoride released into water came from the bonding agent.
262
J. Dent. 1998; 26: No. 3
DISCUSSION The fact that fluoride-releasing materials may prevent/ influence secondary caries 7-10,15-17is one of the reasons why these dental materials became so popular. All the products evaluated in this study released fluoride. In general, the pattern of fluoride release by the glass ionomers is in agreement with findings of many other authors5,22,23’26-41. However, less research was done on the fluoride release from composites4,5z42 and others. Fuji II LC powder is a strontium-containing fluoroaluminosilicate glass. The liquid consists of an aqueous solution of polyacrylic acid and maleic acid, HEMA, water, camphorquinone and an activator. This material is dual-cure43. Vitremer tri-cure glass-ionomer powder is composed44 of a radiopaque, fluoroaluminosilicate glass. It also contains micro-encapsuled potassium persulfate and ascorbic acid as redox catalyst, and pigments. The liquid consists of an aqueous solution of a modified polycarboxylic acid, copylymer, water, HEMA and photo-initiators. Enforce cement with fluoride is a dual-cure high strength resin filled cement. The resin is Bis-GMA based and the filler is barium glass with a fumed silica component. The fluoride is silanated to the glass filler particle and when a fluoride ion is released an hydroxyl replaces it in the matrix. Enforce also contains45 a photo-initiator and a chemical curer. The restorative Dyract consists45 of the following: UDMA resin, TCB resin (containing both carboxylic acidic and methacrylate groups and patented), strontium fluoro-silicate glass, initiators and stabilizers. The polyacid-modified composite resin21 (Dyract compomer21) contains 72% (w/w) reactive filler of strontium-aluminium-fluoro-silicate-glass of which 9% (w/w) is fluoride. Furthermore, the polymerizable molecules of the UDMA and TCB resins are interconnected in a three-dimensional network which is reinforced by means of the enclosed filler particles. Dyract can only be hardened through photopolymerization. The new generation of polyacid-modified composite resin21 (corn p omers) are alleged to shrink much less and compensate for internal stresses due to elasticity. The polyacid-modified composite resins2r also expand in the mouth with the absorption of water and therefore have the potential to overcome/minimize the initial shrinkage due to polymerization. Through the innovation of a new resin system (according to the manufacturers) it has been possible to establish a new class of dental material which combines the major benefits of both composite and glass-ionomer chemistry. The dentine bonding agent OptiBond46 dual-cure A (catalyst resin) and dual cure B (accelerator paste) is used in this study. The catalyst resin A contains bispheno1 glycidyl dimethacrylate, 2-HEMA and chemical and light cured catalysts. The dual-cure accelerator paste B contains barium aluminium borosilicate glass, fumed silica, disodium hexafluorosilicate, barium borosilicate,
2-HEMA and glycerol dimethacrylate. Advance47 hybrid is a resin-modified glass ionomer21. It is claimed by the manufacturers to have one patented acid monomer structure (OEMA), with acid groups that participate in a glass-ionomer reaction and a monomer structure which participates in a resin polymerization reaction. It is claimed not to be a blend of part glass ionomer and part resin, like other competitive products. The liquid contains polymerizable dicarboxylic acid monomer, water and a diluent monomer. The powder is a fluoride leachable glass ionomer containing free radical polymerizable initiators. In general, the pattern of F release (Fig. I) was similar among the various materials tested. The highest release of fluoride occurred during the first week, with the most rapid release during the first 24 h. During the second week the fluoride release levelled off significantly for all the materials tested. Tay and Braden (1988)48 followed the long-term elution of fluoride ions over 2.5 years. They also reported two elution processes, one short-term and rapid, the other more gradual or prolonged. However, during the period from 60 to 200 days there was a significant increase in the F release for Advance (from 0.20 to 0.51 pgmmM2), Fuji (from 0.14 to 0.34pg mme2), Vitremer (from 0.12 to 0.26,ug mme2) and Dyract (from 0.05 to 0.17,~~g mmp2), which then stayed about the same for up to 300 days, except for Advance where a slightly further increase/fluctuation was observed after 300 days (Fig. I). The same type of increase/fluctuation was reported6 for FluorEver OBA after 33 weeks and for a number of glass ionomers39 when comparing the levels at 7 days and at 3-month periods. The increases mentioned could probably be due to the time period of exposure to water and the diffusion of water into the materials, with the resultant release of fluoride from the bulk of the materials. Some of the materials contain a hydrophilic group like HEMA, which forms poly-HEMA which has strong affinity to water with its hydrophilic hydroxyl group. Pedley et al. (1980)49 reported that the equilibrium water content of poly-HEMA is typically 40 wt%. It is apparent that the water sorption and solubility of composite resins is dependent on the resin system used and the generic type of composite5’. It was also found that the water sorption is diffusion controlled49. It is stated that Dyract45 has the ability to absorb water in a moist environment and that the absorption continues for several months until the entire filling material contains about 3% water. From the stage that Dyract comes into contact with water the ion diffusion mechanism, including fluoride release, is able to take place. Differences may also be explained by the mechanism of release, as fluoride release occurs partly by diffusion through pores and cracks.51 Therefore, it could be expected that fluoride release will differ between different materials, as was found in this study.
Grobler
After 60 days Enforce and Optibond could only release 0.01 pg mm-2 over a 24-h period. It should, however, be remembered that the fluoride release from Optibond was only from one thin layer of bonding resin coated on a non-fluoride-containing composite (2100). Therefore, the amount of fluoride released from Optibond cannot be directly compared to that released by the other materials. From a thin layer of Optibond, 0.33 pg mmp2 fluoride is released during the first day, which would be the highest amount of fluoride per volume of all materials, where the fluoride could be released from the bulk of the discs. It should be remembered that, in practice, Optibond is also used in a very thin layer as bonding agent. As no significant fluoride levels could be found when the restorative ZlOO was soaked alone, it can be deduced that when coated with OptiBond all the fluoride came from the bonding agent. The sequence for the fluoride release after the first day was Vitremer (1.46 pugmmp2) Advance (1.18pg mmp2) Fuji (1.08 pg mmM2) Optibond (0.33 pg mme2)=Dyract (0.31 pg mme2) Enforce (0.15 pg mm2). After the second day the sequence changed slightly and stayed approximately the same for the rest of the period. It was Advance (0.74,~g mm-‘) Vitremer (0.52,~g mmd2) Fuji (0.40 ,ug mmp2) Q Dyract (0.19 pg mm-2) Enforce (0.12pg mm-2) Optibond (0.05 ,ug mme2). It is interesting to note that also in this study the resin-modified glass ionomers (except for Enforce) gave the highest fluoride release (Fig. I, Table I), with the highest value for Advance (hybrid) with its patented acid monomer (OEMA). In other studies5,38 which included glass ionomers and composite, glass ionomers also released the most fluoride. The polyacid-modified composite resin21 Dyract gave the most even release of fluoride over the whole period of 300 days (Fig. 1), starting with 0.31 pugmmp2 and ending with 0.21 pg mme2 after 300 days. Ideally, fluoride should be released slowly by a diffusion process without deterioration of the physical properties of the material. Although fluoride release by some of the materials has been reported elsewhere23,38’40, it is not possible to compare our values directly because of the differences in the way of expressing them. It still remains debatable as to which is the best way to express fluoride release, because none of them are 100% accurate. Ppm fluoride in the solution is one way, but is only acceptable for that specific study by comparing the relative amounts. Others are mass fluoride/area and mass fluoride/ volume. They all have their disadvantages unless the area and volume could be both taken into account in the calculations, which is not possible. Furthermore, it
et a/.: Fluoride
release
from dental materials
263
was shown24,52 that the sample dimension
has a significant effect on the amount of fluoride release and uptake. This could also have an effect on the calculations in this study after the outer-most fluoride has been released (say during the first 60 days, Fig. I) and fluoride is then released from the inner bulk (say after 200 days, Fig. I), which means that the area of release which could not be included in the calculation actually increased. From the Box Whisker plots of the seven samples for each of the five materials for every 24-h sampling period for the different time periods indicated in Fig. 1, it could be deduced that the prepared samples (n=7) of Advance, Optibond, Enforce and Dyract were quite homogenous while Vitremer, Fuji and were nonhomogeneous, namely the deviation in the fluoride release between the samples of a material is high. The relevance of the levels of fluoride release can be explained by considering ex. a microleakage gap of a restoration with a diameter of 3 mm and a depth of 1.5 mm. Let it be assumed that the whole restoration is surrounded by an enclosed microleakage space of lOOpurn in diameter. For the material with the lowest fluoride release, i.e. 0.15 pugmmp2 (Enforce during the first day), the fluoride level in the microleakage space could then be - 1500 ppm. While for the material with the highest fluoride release, i.e. 1.46 pg mmp2 (Vitremer during the first day, Table l), the fluoride concentration in the space could reach a level of as high as - 14000 ppm F. Even during a very low fluoride release (from a restorative material) of 0.05 ppm (Fig. 1), the fluoride concentration in the space will be - 500 ppm. With smaller gaps the fluoride levels will increase substantially. It is reported53 that a fluoride concentration of 900-6000 ppm will be bactericidal, depending on the type of species. The minimum growth inhibiting concentration of fluoride was found to be 0.019 ppm at pHz5.0 and 0.14ppm at pH 7.0. Furthermore, it was found54 that low concentrations of fluoride (as low as 0.01 ppm), particularly when present continually, actively enhance lesion remineralization and/or lesion arrestment. Therefore, this study shows that most of the fluoridecontaining dental materials released significant amounts of fluoride, some over many days. The fluoride release would be even more significant in the case of enclosed microleakage gaps as far as de/remineralization and caries development are concerned. Furthermore, considerable differences amongst the materials were found concerning the fluoride release. References 1. Norman,
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54.
265
Tay, W. M. and Braden, M., Fluoride ion diffusion from polyalkenoate (glass-ionomer) cements. Biomaterials 1988; 9: 454456. Pedley, D. G., Skelly, P. J. and Tighe, B. J., Hydrogels in biomedical application. British Polymer Journal 1980; 12: 99-109. Yoshiki, O., Hashem, A. and Elsalawy, R., Some mechanistic observation on water-deteriorated dental composite resins. Biomedical Material Engineering 1995; 5: 93-l 15. Kuhn, A. T. and Wison, A. D., The dissolution mechanisms of silicate and glass ionomer dental cements. Biomaterials 1985; 6: 378-382. Yip, H. K., The effect of sample dimension on the fluoride uptake and release from light-cured glass ionomer cements. Caries Research, 1995, 29, 316 (abstr. 85). Maltz, M. and Emilson, C. G., Susceptibility of oral bacteria to various fluoride salts. Journal of Dental Research 1982; 61: 786-791. Ten Cate, J. M. and Featherstone, J. D. B., Physiochemical aspects of fluoride-enamel interactions. In Fluoride in Dentistry, 2nd edn, ed. 0. Fejerskov, J. Ekstrand and B. A. Burt. Munsgaard, Copenhagen, 1996, pp. 252-272.
Journal of Dentistry, Vol. 26, No. 3, pp. 259-265, 1998 Copyright 0 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0300-5712198 $19.00+0.00
so300-5712(97)00011-0
ELSEVIER
A comparison of fluoride various dental materials
release from
S. R. Grobler, R. J. Rossouw and T. J. Van Wyk Kotze Oral and Dental Research
Institute,
University
of Stellenbosch,
Faculty of Dentistry,
Tygerberg,
South Africa
ABSTRACT Objective: The aim of this study was to determine, in vitro, the relative short- and long-term fluoride
releasefrom four resin-modified glass ionomers (Fuji II LC, Vitremer, Enforce & Advance), a polyacid-modifiedcompositeresin (Dyract compomer)and a bonding agent(OptiBond). Methods: All the materials were prepared as outlined by the manufacturers. Circular discsof the materialsmentionedwere suspended in water for up to 300days and the non-cumulative24-h fluoride releasewas determinedpotentiometrically at chosentimes. Results: The amountsof fluoride releasedduring the first day were Vitremer (1.46,~gmm-*), Advance (1.18pgmm-*), Fuji (l.O8,~gmm-‘), Optibond (0.33Ligrnrn-“), Dyract (0.31pg mnP2) and Enforce (0.15pugmm-“). After the secondday the sequencechangedslightly and remainedapproximately the same for the rest of the 300-day period. There was also an increasein the fluoride releaseduring the 60-200-dayperiod relative to the previous period. Conclusion:In generalthe mostfluoride wasreleasedby Advance and not by Fuji II LC or Vitremer. For mostmaterials,fluoride is still releasedafter 300days, Furthermore, even a thin layer of bonding agent releaseda relatively high amount of fluoride (volume-wisethe most) at the beginning.It is deducedthat even the releaseof relatively low amountsof fluoride may result in significantconcentrationsof fluoride in a microleakagegap. 0 1998Elsevier ScienceLtd. All rights reserved KEY WORDS: J. Dent.
1998;
fluoride
release,
26: 259-265
glass
(Received
ionomer,
compomer
20 September
1996;
accepted
INTRODUCTION The major cariostatic mechanism of fluoride is believed to be that it reduces dental caries through promoting remineralization and influencing the morphology of teeth by reducing the solubility of enamel, and through its effect on oral cariogenic bacteria. The beneficial effect of fluoride for the prevention of dental caries is well documented and has prompted the inclusion of fluoride into a host of dental materialsle6. Fluoride-releasing dental restoratives have an effect on secondary carious lesions at the interface of the restoration7-lo, while fluoride adsorption is also found in tooth tissue up to 3 mm away from the restoration Correspondence should be addressed to: S. R. Grobler, Oral and Dental Research Institute, Faculty of Dentistry, Private Bag Xl, Tygerberg, 750.5, Republic of South Africa. Tel: 027-21-931-2246; Fax: 027-21-931-2287; e-mail: srgmaties.sun.ac.za..
3 February
1997)
margins, and may even protect the entire tooth’ l-l4 against dental caries1sm17. Glass-ionomer cements have been suggested as restorative materials”, bases for composites” and amalgam restorations7. The newest generation of glass-ionomer cements have higher cohesive strengths, are light cured and contain more resin (HEMA)20. Other materials are mainly fluoridereleasing resins, such as polyacid-modified composite resins21 (Dyract compomer21). Many studies on fluoride-containing dental materials have shown that fluoride can either be released or absorbed from materials22-25. The aim of this study was to determine, in vitro, the relative short- and long-term fluoride release from four resin-modified glass ionomers (Fuji II LC, Vitremer, Enforce & Advance), a polyacid-modified composite resin (Dyract compomer)21 and a bonding agent (0ptiBond):The hypothesis is that the degree of fluoride release over time would differ amongst
260
J. Dent. 1998; 26: No. 3
1
2
3
4
5
6
7
8
9
11
16
30
60
(A),
Vitremer
200
250 300
(m),
Fuji e), Dyract
DAYS Fig. 7. Plot of 24-hourly Optibond (+).
fluoride
fluoride-containing dental chemical compositions,
MATERIALS
release
(pg mm-‘)
materials
over
with
a 300~day
different
AND METHODS
Four resin-modified glass ionomers (Fuji II LC, Batch No. 071031, GC Intern. Corp., Tokyo, Japan; Vitremer, Batch No. 19940519, 3M Mfg., St. Paul, MN, USA; Advance hybrid21, Batch No. 574013, Caulk/Dentsply International Inc. Milford, DE, USA; Enforce, Batch No. 9412073, Caulk/Dentsply International Inc., Milford, DE, USA), a polyacid-modified composite resin21 (Dyract compomer21, Batch No. C940469, CaulklDentsply International Inc. Milford, DE, USA) and a bonding agent (OptiBond, Batch No. 750985, Kerr Mfg. Co., Romulus, MI, USA) were investigated for their fluoride-releasing ability. All the materials were prepared as outlined by the manufacturers. For each material tested, seven circular copper rings (n=7), of internal diameter 16 mm and 2 mm deep (areaz502.4 mm2), were placed on a glass slab covered with a plastic sheet. The material was mixed and the copper rings half filled. Cotton threads (about 20-cm long) were positioned with one end in the material and the rest extended through an opening (0.5 mm diameter) in the ring. The rings were now further filled by pressing freshly mixed material firmly with glass slabs covered with plastic sheets. When necessary, the material was light-cured for 60 s on both sides, the discs removed from the rings and again light-cured, if necessary, on both sides for 60 s. For the Optibond analysis, discs were prepared from the restorative ZlOO (Batch No. 19940914, 3M
period
for Advance
(*), Enforce
(x) and
Mfg., St. Paul, MN, USA) as outlined above, then coated with a thin layer of Dual Cure OptiBond (mixture of activator 3A and paste 3B) and light cured for 40 s on both sides. Although it is known that fluoride was not added on purpose to the restorative 2100, seven rings with only the restorative were also prepared and tested for fluoride release over 6 days. The discs (seven for each material) were then individually suspended in 10 ml of double glass-distilled water and put in a shaker (Haake, SWB 20, Berlin, Germany) at 37°C for 24 h. The discs were lifted by the thread to just above the water level and rinsed with 10 ml of TISAB with CDTA buffer (Orion Research, Inc., Cambridge, MA, USA). This buffered solution was then analysed for fluoride. The discs were then thoroughly rinsed with distilled water before again being suspended in water. This procedure was repeated every 24 h for the first 9 days, after which the soaking period before each 24-h collection was changed as indicated in Fig. I. In this way a 24-h fluoride release could be determined (non-cumulative F release) after suspension of the discs in water for different periods of time (Fig. I). Fluoride in the buffered solutions was determined with the use of a combination fluoride ion selective electrode (Orion Research, Inc., Cambridge, MA, USA). The potentiometer (Orion Ion Analyser EA 940, Orion Research, Inc., Cambridge, MA, USA) was calibrated with fluoride standard solutions in 50% buffer (TISAB with CDTA) with fluoride concentrations varying between 0.050 ppm and 5 ppm. The fluoride release was expressed in pg F mm-2.
Grobler et a/.: Fluoride release from dental materials Tab/e /. The mean following materials:
fluoride levels (M mm-“) 1, Optibond; 2, Enforce;
of a 24-hourly fluoride 3, Dyract; 4, Vitremer;
release
over
a total period
of 300 days from
seven
SampIeS
261
of each of the
5, Fuji; 6, Advance Materials
Time
Interval
(days)
1
1 2 3 4 5 6 7 8 9 11 16 30 60 200 260 300
0.33 0.05 0.03 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01
Table II. Analysis of the fluoride release Dyract; 4, Vitremer; 5, Fuji; 6, Advance Time interval
by the Bonferroni
2
3
4
5
6
0.15 0.12 0.11 0.05 0.04 0.03 0.02 0.02 0.01 0.02 0.01 0.01 0.01
0.31 0.19 0.19 0.16 0.16 0.16 0.12 0.07 0.08 0.06 0.05 0.05 0.05 0.17 0.17 0.21
1.46 0.52 0.47 0.39 0.39 0.37 0.26 0.23 0.19 0.16 0.14 0.12 0.12 0.26 0.28 0.28
1.08 0.40 0.45 0.37 0.34 0.34 0.27 0.20 0.22 0.16 0.13 0.14 0.14 0.36 0.35 0.34
1.18 0.74 0.58 0.49 0.45 0.38 0.35 0.19 0.22 0.26 0.14 0.20 0.20 0.51 0.58 0.61
multiple
comparison
test at the 5% significant
level:
1, Optibond;
2, Enforce;
Material
(days)
1 2 3
la la 1
2a 2a 2a
3” 3a 3a
4
5
$I
;:
4 5 6 7
1” la ia 1”
2” 2a 2a 2”
6b 3 3 3
;E
5 4b 5b 5b
6 6 6b 3 5 6b 6
89 11 16 30
1” 1” 1” 1” 1”
2” 2a 2” 2” 2a
33 3 3 3
4b 4b 4b
$I
;: 6
;E
5b 5b .cjb
60 200 260 300
1”
2a
3 3a 3 3a
4” 4a 4” 4a
5c 5 5a 5
6 6 6 6
Materials
in the same
3,
horizontal
row with the same
superscript
letter were
RESULTS The plot of the mean values of a 24-hourly fluoride release over a 300-day period for Advance (A), Vitremer (B), Fuji (O), Dyract (*), Enforce ( x ) and Optibond (+) are shown in Fig. 1. Table I gives the mean fluoride levels of 24-hourly fluoride release over a 300-day period from seven samples of each of the following materials: 1, Optibond; 2, Enforce; 3, Dyract; 4, Vitremer; 5, Fuji; 6, Advance. The data were tested for statistically significant differences related to material, time and fluoride using the Kruskal-Wallis one-way ANOVA test. The Bonferroni (all-pairwise) multiple comparison test at the 5% level of significance was used for multiple
4” 4b
not
significantly
;:
different.
comparisons of the means of the different materials (Table 10 for each of the time periods. A Box Whisker plot of the seven samples for each of the five materials was done for every 24-h sampling period for all the different time periods, as indicated in Fig. 1. To summarize, in general it could be deduced that the variation in the amount of fluoride released (within the seven samples) for each material at each time interval was the highest for Vitremer, the second highest for Fuji and the lowest for Optibond. No significant fluoride levels could be found when the restorative ZlOO was soaked alone. Therefore, it could be deduced that when ZlOO is coated with OptiBond all the fluoride released into water came from the bonding agent.
262
J. Dent. 1998; 26: No. 3
DISCUSSION The fact that fluoride-releasing materials may prevent/ influence secondary caries 7-10,15-17is one of the reasons why these dental materials became so popular. All the products evaluated in this study released fluoride. In general, the pattern of fluoride release by the glass ionomers is in agreement with findings of many other authors5,22,23’26-41. However, less research was done on the fluoride release from composites4,5z42 and others. Fuji II LC powder is a strontium-containing fluoroaluminosilicate glass. The liquid consists of an aqueous solution of polyacrylic acid and maleic acid, HEMA, water, camphorquinone and an activator. This material is dual-cure43. Vitremer tri-cure glass-ionomer powder is composed44 of a radiopaque, fluoroaluminosilicate glass. It also contains micro-encapsuled potassium persulfate and ascorbic acid as redox catalyst, and pigments. The liquid consists of an aqueous solution of a modified polycarboxylic acid, copylymer, water, HEMA and photo-initiators. Enforce cement with fluoride is a dual-cure high strength resin filled cement. The resin is Bis-GMA based and the filler is barium glass with a fumed silica component. The fluoride is silanated to the glass filler particle and when a fluoride ion is released an hydroxyl replaces it in the matrix. Enforce also contains45 a photo-initiator and a chemical curer. The restorative Dyract consists45 of the following: UDMA resin, TCB resin (containing both carboxylic acidic and methacrylate groups and patented), strontium fluoro-silicate glass, initiators and stabilizers. The polyacid-modified composite resin21 (Dyract compomer21) contains 72% (w/w) reactive filler of strontium-aluminium-fluoro-silicate-glass of which 9% (w/w) is fluoride. Furthermore, the polymerizable molecules of the UDMA and TCB resins are interconnected in a three-dimensional network which is reinforced by means of the enclosed filler particles. Dyract can only be hardened through photopolymerization. The new generation of polyacid-modified composite resin21 (corn p omers) are alleged to shrink much less and compensate for internal stresses due to elasticity. The polyacid-modified composite resins2r also expand in the mouth with the absorption of water and therefore have the potential to overcome/minimize the initial shrinkage due to polymerization. Through the innovation of a new resin system (according to the manufacturers) it has been possible to establish a new class of dental material which combines the major benefits of both composite and glass-ionomer chemistry. The dentine bonding agent OptiBond46 dual-cure A (catalyst resin) and dual cure B (accelerator paste) is used in this study. The catalyst resin A contains bispheno1 glycidyl dimethacrylate, 2-HEMA and chemical and light cured catalysts. The dual-cure accelerator paste B contains barium aluminium borosilicate glass, fumed silica, disodium hexafluorosilicate, barium borosilicate,
2-HEMA and glycerol dimethacrylate. Advance47 hybrid is a resin-modified glass ionomer21. It is claimed by the manufacturers to have one patented acid monomer structure (OEMA), with acid groups that participate in a glass-ionomer reaction and a monomer structure which participates in a resin polymerization reaction. It is claimed not to be a blend of part glass ionomer and part resin, like other competitive products. The liquid contains polymerizable dicarboxylic acid monomer, water and a diluent monomer. The powder is a fluoride leachable glass ionomer containing free radical polymerizable initiators. In general, the pattern of F release (Fig. I) was similar among the various materials tested. The highest release of fluoride occurred during the first week, with the most rapid release during the first 24 h. During the second week the fluoride release levelled off significantly for all the materials tested. Tay and Braden (1988)48 followed the long-term elution of fluoride ions over 2.5 years. They also reported two elution processes, one short-term and rapid, the other more gradual or prolonged. However, during the period from 60 to 200 days there was a significant increase in the F release for Advance (from 0.20 to 0.51 pgmmM2), Fuji (from 0.14 to 0.34pg mme2), Vitremer (from 0.12 to 0.26,ug mme2) and Dyract (from 0.05 to 0.17,~~g mmp2), which then stayed about the same for up to 300 days, except for Advance where a slightly further increase/fluctuation was observed after 300 days (Fig. I). The same type of increase/fluctuation was reported6 for FluorEver OBA after 33 weeks and for a number of glass ionomers39 when comparing the levels at 7 days and at 3-month periods. The increases mentioned could probably be due to the time period of exposure to water and the diffusion of water into the materials, with the resultant release of fluoride from the bulk of the materials. Some of the materials contain a hydrophilic group like HEMA, which forms poly-HEMA which has strong affinity to water with its hydrophilic hydroxyl group. Pedley et al. (1980)49 reported that the equilibrium water content of poly-HEMA is typically 40 wt%. It is apparent that the water sorption and solubility of composite resins is dependent on the resin system used and the generic type of composite5’. It was also found that the water sorption is diffusion controlled49. It is stated that Dyract45 has the ability to absorb water in a moist environment and that the absorption continues for several months until the entire filling material contains about 3% water. From the stage that Dyract comes into contact with water the ion diffusion mechanism, including fluoride release, is able to take place. Differences may also be explained by the mechanism of release, as fluoride release occurs partly by diffusion through pores and cracks.51 Therefore, it could be expected that fluoride release will differ between different materials, as was found in this study.
Grobler
After 60 days Enforce and Optibond could only release 0.01 pg mm-2 over a 24-h period. It should, however, be remembered that the fluoride release from Optibond was only from one thin layer of bonding resin coated on a non-fluoride-containing composite (2100). Therefore, the amount of fluoride released from Optibond cannot be directly compared to that released by the other materials. From a thin layer of Optibond, 0.33 pg mmp2 fluoride is released during the first day, which would be the highest amount of fluoride per volume of all materials, where the fluoride could be released from the bulk of the discs. It should be remembered that, in practice, Optibond is also used in a very thin layer as bonding agent. As no significant fluoride levels could be found when the restorative ZlOO was soaked alone, it can be deduced that when coated with OptiBond all the fluoride came from the bonding agent. The sequence for the fluoride release after the first day was Vitremer (1.46 pugmmp2) Advance (1.18pg mmp2) Fuji (1.08 pg mmM2) Optibond (0.33 pg mme2)=Dyract (0.31 pg mme2) Enforce (0.15 pg mm2). After the second day the sequence changed slightly and stayed approximately the same for the rest of the period. It was Advance (0.74,~g mm-‘) Vitremer (0.52,~g mmd2) Fuji (0.40 ,ug mmp2) Q Dyract (0.19 pg mm-2) Enforce (0.12pg mm-2) Optibond (0.05 ,ug mme2). It is interesting to note that also in this study the resin-modified glass ionomers (except for Enforce) gave the highest fluoride release (Fig. I, Table I), with the highest value for Advance (hybrid) with its patented acid monomer (OEMA). In other studies5,38 which included glass ionomers and composite, glass ionomers also released the most fluoride. The polyacid-modified composite resin21 Dyract gave the most even release of fluoride over the whole period of 300 days (Fig. 1), starting with 0.31 pugmmp2 and ending with 0.21 pg mme2 after 300 days. Ideally, fluoride should be released slowly by a diffusion process without deterioration of the physical properties of the material. Although fluoride release by some of the materials has been reported elsewhere23,38’40, it is not possible to compare our values directly because of the differences in the way of expressing them. It still remains debatable as to which is the best way to express fluoride release, because none of them are 100% accurate. Ppm fluoride in the solution is one way, but is only acceptable for that specific study by comparing the relative amounts. Others are mass fluoride/area and mass fluoride/ volume. They all have their disadvantages unless the area and volume could be both taken into account in the calculations, which is not possible. Furthermore, it
et a/.: Fluoride
release
from dental materials
263
was shown24,52 that the sample dimension
has a significant effect on the amount of fluoride release and uptake. This could also have an effect on the calculations in this study after the outer-most fluoride has been released (say during the first 60 days, Fig. I) and fluoride is then released from the inner bulk (say after 200 days, Fig. I), which means that the area of release which could not be included in the calculation actually increased. From the Box Whisker plots of the seven samples for each of the five materials for every 24-h sampling period for the different time periods indicated in Fig. 1, it could be deduced that the prepared samples (n=7) of Advance, Optibond, Enforce and Dyract were quite homogenous while Vitremer, Fuji and were nonhomogeneous, namely the deviation in the fluoride release between the samples of a material is high. The relevance of the levels of fluoride release can be explained by considering ex. a microleakage gap of a restoration with a diameter of 3 mm and a depth of 1.5 mm. Let it be assumed that the whole restoration is surrounded by an enclosed microleakage space of lOOpurn in diameter. For the material with the lowest fluoride release, i.e. 0.15 pugmmp2 (Enforce during the first day), the fluoride level in the microleakage space could then be - 1500 ppm. While for the material with the highest fluoride release, i.e. 1.46 pg mmp2 (Vitremer during the first day, Table l), the fluoride concentration in the space could reach a level of as high as - 14000 ppm F. Even during a very low fluoride release (from a restorative material) of 0.05 ppm (Fig. 1), the fluoride concentration in the space will be - 500 ppm. With smaller gaps the fluoride levels will increase substantially. It is reported53 that a fluoride concentration of 900-6000 ppm will be bactericidal, depending on the type of species. The minimum growth inhibiting concentration of fluoride was found to be 0.019 ppm at pHz5.0 and 0.14ppm at pH 7.0. Furthermore, it was found54 that low concentrations of fluoride (as low as 0.01 ppm), particularly when present continually, actively enhance lesion remineralization and/or lesion arrestment. Therefore, this study shows that most of the fluoridecontaining dental materials released significant amounts of fluoride, some over many days. The fluoride release would be even more significant in the case of enclosed microleakage gaps as far as de/remineralization and caries development are concerned. Furthermore, considerable differences amongst the materials were found concerning the fluoride release. References 1. Norman,
R. D., Phillips, R. W. and Swartz, M. C., Fluoride uptake by enamel from certain dental materials. Journal of Dental Research 1960; 39: 11-16. 2. Rawls, H. R. and Zimmerman, B. F., Fluoride exchanging resins for caries prevention. Caries Research 1983; 17: 3243.
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