Effect of fluoride application on tensile bond strength of self-etching adhesive systems to demineralized dentin

Effect of fluoride application on tensile bond strength of self-etching adhesive systems to demineralized dentin Toshiyuki Itota, DDS, PhD,a Yasuhiro Torii, DDS, PhD,b Satoshi Nakabo, DDS, PhD,c and Masahiro Yoshiyama, DDS, PhDd Okayama University Graduate School of Medicine and Dentistry, Okayama, Japan Statement of problem. It has been reported that the bond strength of composite to demineralized dentin is lower than that to sound dentin. This can be a problem in the success of so-called sealed restorations. Purpose. The aim of this study was to evaluate the effect of fluoride application on the tensile bond strength of self-etching adhesive systems to demineralized dentin. Material and methods. One hundred twenty extracted bovine incisors were ground flat with 600-grit silicone carbide paper. Ninety teeth were then immersed in acetate buffer (pH 4.0) to form demineralized dentin. These teeth were randomly divided into 3 groups of 30 each: surfaces treated with fluoride solution (Group NF), surfaces treated with fluoride solution followed by a water rinse (Group RF), and control surfaces with no pretreatment (Group C). The remaining 30 teeth comprised a group with normal dentin surfaces (Group S). Each group was further divided into 3 subgroups of 10 each to test the bond strength test of Clearfil SE Bond, Unifil Bond, and Mac-Bond II. Tensile bond strengths (in MPa) were measured with a universal testing machine at a crosshead speed of 0.5 mm/min. Mean bond strengths were analyzed by 2-way analysis of variance and Fisher’s PLSD (P ⫽ .05). SEM observations of the surfaces before and after priming and at resin-dentin interfaces in each group were performed. Elemental analysis of the dentin surfaces before priming was also carried out. Results. The bond strengths of the adhesives to demineralized dentin in Groups NF, RF, and C were significantly lower than that of the normal dentin in Group S (P ⬍ .05). The mean bond strengths of the 3 adhesives in Group NF were higher than those in Groups RF and C, but a significant difference was observed only when Clearfil SE Bond was used (P ⬍ .05). In SEM images the open dentinal tubules on the surface and the resin tag formation at the resin-dentin interface were apparent in Group NF but were not observed in Groups RF and C. On elemental analysis, considerable amounts of fluoride and calcium were detected in the surfaces of Group NF. Conclusion. Within the limitations of this study, the surface treatment with fluoride solution supported the resin tag formation at the resin-dentin interface and slightly improved the bond strength of the self-etching adhesive systems tested to demineralized dentin. This result indicated that the fluoride treatment to demineralized dentin might contribute to the success of the sealed restoration. (J Prosthet Dent 2002;88:503-10.)

CLINICAL IMPLICATIONS In this in vitro study, fluoride application to demineralized dentin before application of the self-etching adhesives tested improved the adhesion of the composite tested to demineralized dentin. However, the use of the self-etching adhesive systems tested to demineralized dentin should be avoided, because the bond strengths of the adhesives to demineralized dentin were much lower than that to sound dentin, even with the fluoride treatment.

I

t has been suggested that sealing carious dentin with adhesive resin-based materials can prevent the progression of carious lesions.1 This technique is called sealed restoration and has arrested carious lesions for up to 10 years.2 In addition, Tyas et al3 advocated the concept of minimal intervention dentistry, in which the least invasive operative approach to carious lesions should be carried out to preserve as much demineralized dentin that a

Instructor, Department of Operative Dentistry. Associate Professor, Department of Operative Dentistry. c Instructor, Department of Operative Dentistry. d Professor, Department of Operative Dentistry. b

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could be remineralized as possible. These reports suggested that demineralized dentin could be preserved in these so-called sealed restorations and that sealing with resin-based adhesive materials could inhibit the progress of the lesion by cutting off the nutrition supply to cariogenic microorganisms in the lesion. Recently developed adhesives such as the self-etching adhesive systems have become popular because of their technical simplicity. However, carious dentin is known to lose much of its mineral phase by demineralization, and the organic substrate is degraded by enzymes produced by the infecting microorganisms.4 The soft infected dentin has been called caries-infected dentin, and the underlying noninTHE JOURNAL OF PROSTHETIC DENTISTRY 503

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Table I. Self-etching adhesives used in study Adhesive

Clearfil SE Bond Unifil Bond Mac-Bond II

Composition

Manufacturer

Primer: MDP, hydrophobic dimethacrylate, HEMA, water Bond: MDP, hydrophobic dimethacrylate, HEMA, BIS-GMA Primer: 4-MET, HEMA, ethanol, water Bond: UDMA, HEMA, TEGDMA Primer: MAC-10, phosphate monomer, alcohol, acetone, water Bond: MAC-10, HEMA, BIS-GMA, TEGDMA

Kuraray Co Ltd, Osaka, Japan GC Co, Tokyo, Japan Tokuyama Co, Tokyo, Japan

MDP, 10-Methacryloyloxydecyl dihydrogen phosphate; HEMA, 2-hydroxyethyl methacrylate; 4-MET, 4-methacryloxyethyl-trimellitic acid; UDMA, urethane dimethacrylate; TEGDMA, triethyleneglycol dimethacrylate; MAC-10, carbonic monomer.

fected, partially demineralized dentin has been called caries-affected dentin.5-7 This dentin shows lower mechanical properties than sound dentin.5,8 It has been reported that the bond strength to caries-affected dentin was lower than that to normal dentin, because of the presence of mineral deposits in the tubules that prevent resin tag formation, even when effective adhesive systems, such as All Bond 2, Clearfil Liner Bond II, Single Bond, and FluoroBond, were used.6,7 These findings suggest that the lower bond strength of composite to demineralized dentin was due to the lack of resin tags or to the low mechanical property of this dentin as the result of the loss of mineral support. Laboratory simulations of caries-affected dentin have reported low resin bond strengths.9,10 This was probably due to the collapse of the demineralized matrix during brief air drying during bonding.11 However, mineral reinforcement of demineralized dentin may increase its bond strength to composite and thus may improve the success of sealed restorations.12 Fluoride ions penetrating into the dentin have been shown to enhance mineralization of the dentin.13 However, fluoride treatment to sound dentin has been shown to decrease the bond strength of composite to the dentin.14,15 On the other hand, demineralized dentin has shown enhancement of remineralization after the infiltration of fluoride ions.16 The bond strength of composite to demineralized dentin treated with fluoride solution remains unknown. The presence of fluoride ions during demineralization has been shown to produce deposition or growth of apatite-like crystals within the tooth.17 In addition, mineral crystals containing fluoride are precipitated on and within the demineralized dentin layer.17 This phenomenon has been reported by other authors.18 After remineralization of demineralized root surfaces, the dentin showed no mineral deficit.19 Therefore it is anticipated that fluoride application to demineralized dentin may increase resin-dentin bond strengths by improving the mechanical properties of the dentin. The purpose of this study was to investigate the effect of fluoride application on the tensile bond strength of 504

Table II. Treatment of dentin surface in each group Group

Group S Group NF Group RF Group C

Demineralization

Fluoride application

Rinse with water

No

No

No

Yes Yes Yes

Yes Yes No

No Yes No

self-etching adhesive systems to laboratory-demineralized dentin.

MATERIAL AND METHODS Tensile bond strength test Three commercial self-etching adhesive systems were used in this study (Table I): Clearfil SE Bond, Unifil Bond, and Mac-Bond II. The saturated fluoride solution was made by filtration of a solution with excessive sodium fluoride (Wako Pure Chemical, Kyoto, Japan) dissolved in distilled water. The labial surfaces of 120 extracted bovine incisor teeth were ground through enamel with 600-grit silicone carbide paper to expose flat dentin surfaces. Ninety of these teeth were coated with nail varnish, except for a circular area approximately 4.0 mm in diameter on a flat dentin surface. They were then immersed in acetate buffer (pH 4.0) containing 0.2/mol CH3COONa and 0.2/mol CH3COOH for 5 days at 37°C to form a zone of demineralized dentin. The 90 teeth with demineralized dentin zones, or lesions, were randomly divided into 3 groups of 30 each: Group NF, Group RF, and Group C (Table II). The surfaces of specimens in Group NF were treated by application of the solution saturated with sodium fluoride at room temperature for 1 minute and then dried in a gentle airstream for 30 seconds. In Group RF the same procedure was performed, followed by a water rinse for 1 minute and air drying for 30 seconds. The surfaces in Group C were not subjected to any treatment. The remaining 30 teeth were used as sound dentin specimens (Group S). Ten teeth from each group were used for the tensile bond strength testing of each adhesive system. A VOLUME 88 NUMBER 5

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Table III. Tensile bond strength of self-etching adhesives to dentin (n ⫽ 10) in each group

Group Group Group Group

S NF RF C

Clearfil SE Bond (MPa)

Unifil Bond (MPa)

Mac-Bond II (MPa)

20.3 ⫾ 6.4 a 5.2 ⫾ 1.1 b 2.7 ⫾ 1.0 c 2.9 ⫾ 0.5 c

16.1 ⫾ 4.6 a 2.6 ⫾ 0.8 cd 1.5 ⫾ 0.5 d 2.1 ⫾ 1.0 cd

15.5 ⫾ 5.2 a 3.2 ⫾ 1.8 c 2.1 ⫾ 1.5 cd 2.9 ⫾ 1.2 c

Values are given as mean ⫾ SD. Values with the same letter are not significantly different (analysis and Fisher PLSD; P ⬎ .05).

Teflon cylindrical ring with an inner diameter of 3.7 mm and a height of 3.0 mm was attached with adhesive tape to the 90 demineralized and 30 sound dentin surfaces, and the surfaces inside of the ring were treated with each self-etching adhesive system according to each manufacturer’s instruction. Each primer was applied on the surfaces for 20 seconds and dried in a gentle airstream. The respective adhesive was applied and polymerized for 10 seconds with a visible light-polymerizing unit (Visilux 2; 3M Dental Products, St. Paul, Minn.) at 400 mW/cm2. Three light-polymerized composites from each manufacturer, Clearfil AP-X (Kuraray Co Ltd, Osaka, Japan), Estio LC (GC Co, Tokyo, Japan), and Palfique Estelite (Tokuyama Co, Tokyo, Japan), were placed after polymerization of the adhesive and were light-polymerized from the top for 40 seconds. After polymerization, the ring and the adhesive tape were removed gently and the specimens were stored in distilled water at 37°C for 24 hours. The tensile bond strength was measured by a universal testing machine (10kND, Autograph AGS; Shimadzu, Kyoto, Japan) at a crosshead speed of 0.5 mm/min. The fractured surfaces of debonded specimens were observed through use of a stereoscopic microscope (SMZ-10; Nikon, Tokyo, Japan) to determine the failure mode.

SEM The morphologic changes in the surfaces of 30 specimens before and after application of each primer in each group were observed with an SEM (DS-720; Topcom, Tokyo, Japan) at 15 kV to examine the effect of the priming on the pretreated surfaces. The specimens were dried in air at 37°C overnight, gold-coated with the use of an ion sputter (JFC-1100E; JEOL, Tokyo, Japan), and observed at the orifices of the dentinal tubules and the form of the intertubular dentin surface. For observation of the resin-dentin interfaces, 5 specimens in each group were applied with each adhesive system and were sectioned through the resin-dentin interfaces by a low-speed rotary cutting machine (Isomet; Buehler Ltd, Evanston, Ill.). After the cut surface of the specimens was polished with 2000-grit silicone carbide paper, it was etched with 40% phosphoric acid for 30 seconds to remove the inorganic substrate and rinsed under a stream of water. The specimens were then immersed in 10% sodium hypochlorite solution (Neo NOVEMBER 2002

Cleaner; Neo Dental Chemical Products, Tokyo, Japan) for 10 minutes to dissolve the organic substrate and were rinsed with water. The specimens were dehydrated in ascending concentrations of ethanol, subjected to critical point drying, and then gold-coated. The hybrid layer and the resin tags at the resin-dentin interfaces of these specimens were observed with an SEM.

Qualitative microanalysis of dentin surface Elemental analysis of the dentin surfaces before priming was carried out by energy-dispersive spectrometry with an electron probe apparatus (Voyager; Noran Instruments Inc, Middleton, Wis.).

Statistical analysis Tensile bond strength data for self-etching adhesives in each group were statistically analyzed by 2-way analysis of variance and Fisher PLSD for comparison between means at a significance level of .05.

RESULTS Table III shows the tensile bond strengths of selfetching adhesives to dentin in Group S (normal dentin surfaces without the demineralized dentin), Group NF (demineralized dentin surfaces applied with the fluoride solution), Group RF (demineralized dentin surfaces rinsed with water after application of the fluoride solution), and Group C (demineralized dentin surfaces without pretreatment). The mean bond strength of the Clearfil SE Bond in Group NF was 5.2 ⫾ 1.1 MPa, significantly higher than that in Group RF (2.7 ⫾ 1.0 MPa) and Group C (2.9 ⫾ 0.5 MPa). There was no significant difference in the bond strength between Group RF and Group C. For Unifil Bond, there were no significant differences in the bond strength among the 3 groups, Group NF (2.6 ⫾ 0.8 MPa), Group RF (1.5 ⫾ 0.5 MPa), and Group C (2.1 ⫾ 1.0 MPa), although the mean bond strength in Group NF was the highest of the 3 groups with demineralized dentin. The mean bond strength of the Mac-Bond II in Group NF (3.2 ⫾ 1.8 MPa) was also higher than that in Group RF (2.1 ⫾ 1.5 MPa) and Group C (2.9 ⫾ 1.2 MPa), but there were no significant differences among the 3 groups. Although the mean bond strengths of the Clearfil SE Bond, Unifil Bond, and Mac-Bond II to 505

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Fig. 1. SEM images of dentin surfaces before (left) and after (right) application of Clearfil SE Bond primer in Group S (A and B), Group NF (C and D), Group RF (E and F), and Group C (G and H).

demineralized dentin in Group NF were higher than those in Groups RF and C, these bond strengths were far 506

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Fig. 2. SEM images of resin-dentin interfaces applied with Clearfil SE Bond: Group S (A), Group NF (B), Group RF (C), and Group C (D). H, Hybrid-like layer; R, adhesive resin layer.

tively high, but there was no significant difference among them (20.3 ⫾ 6.4 MPa, 16.1 ⫾ 4.6 MPa, and 15.5 ⫾ 5.2 MPa, respectively). When the failure mode under tensile loading was analyzed, cohesive fracture in dentin was found in all demineralized dentin specimens, whereas sound dentin specimens showed cohesive fracture of the resin. Figure 1 shows typical SEM images of the dentin surfaces before and after the application of primer of the Clearfil SE Bond in all groups. The sound dentin surface was covered with a smear layer before the application of primer (Fig. 1, A). In contrast, after application of the acidic primer, the surface had many open dentinal tubules and was covered with a resinous layer (Fig. 1, B). In Group NF, many open dentinal tubules were seen in the demineralized dentin treated with saturated sodium fluoride, and crystal-like deposits were found on the dentin surface before priming in Group NF (Fig. 1, C). After application of Clearfil SE Bond primer, the crystallike deposits were no longer apparent and the surface texture became smooth (Fig. 1, D). In specimens from Group RF, the orifices of most dentinal tubules were not apparent, although those that were observed contained granular material. No crystal-like deposits were observed on the surface (Fig. 1, E). After application of NOVEMBER 2002

Clearfil SE Bond primer, the dentinal tubules were still not apparent and the surface was covered with a layer of fine crystal (Fig. 1, F). In Group C, most of the tubule orifices were not apparent, and an amorphous structure was observed at the intertubular dentin (Fig. 1, G). After application of Clearfil SE Bond primer, the surface became covered with granular deposits (2-3 ␮m in size) (Fig. 1, H). When Unifil Bond and Mac-Bond II were used, the morphologic changes at the surfaces after the application of each primer were similar (not shown) to that of the Clearfil SE Bond. Figure 2 shows typical SEM images of the resindentin interfaces in all groups applied with the Clearfil SE Bond. At the resin-sound dentin interface in Group S, many resin tags and a thin hybrid layer were observed (Fig. 2, A). In specimens from Group NF, resin tags formed in the demineralized dentin layer, but their appearance was irregular (Fig. 2, B). A hybrid layer-like structure was also observed underneath the resin, but its undulating appearance was different from that of the hybrid layer observed in Group S. In specimens from Group RF, a hybrid layer-like structure was observed at the surface, underneath which was a 10-␮m-thick layer of resin (Fig. 2, C). No taglike structure was formed beneath the hybrid-like 507

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Fig. 3. Qualitative microanalysis of dentin surfaces before application of primer in all groups.

layer in specimens in Group RF. In specimens from Group C, the resin layer was thicker (approximately 20-␮m thickness) than those in Group RF, but no tag-like structure was formed (Fig. 2, D). In specimens bonded with Unifil Bond and Mac-Bond II, the SEM images of the resin-dentin interfaces in Groups S, RF, and C were similar (not shown) to that of the Clearfil SE Bond specimens. However, the irregular tag-like structures formed in Group NF were more irregular than those obtained with the use of Clearfil SE Bond. Figure 3 shows the results of qualitative microanalysis of the dentin surfaces before application of primer in all groups. In Group NF, considerable amounts of fluoride and calcium were detected in the surfaces. In contrast, fluoride was not detected in Group RF, C, or S.

DISCUSSION Adhesion of resin-based materials to carious dentin is considered to be an important factor for the success of sealed restorations.2 In this study, however, the bond strength to laboratory-demineralized dentin was significantly lower (P ⬍ .05) than that to sound dentin, regardless of the presence or absence of fluoride application. These results agree with some previous reports that the bond strength of composite to caries-affected dentin is lower than that to sound dentin.6,7 This low bond strength to demineralized dentin may be due to lower mechanical property of such dentin. It was hypothesized that the reinforcement of demineralized dentin by fluo508

ride application might increase the bond strength of composite to such dentin. In this study the application of sodium fluoride solution to laboratory-demineralized dentin produced a small but consistent increase in the bond strength of self-etching adhesives to demineralized dentin. When fluoride solution was applied on demineralized dentin, calcium fluoride or apatites containing calcium fluoride were precipitated on the surface.17,18 These precipitations arose from the reaction of fluoride, calcium, and phosphate ions contained in the demineralized dentin layer. Indeed, energy-dispersive spectrometry analysis in this study showed that a relatively high amount of calcium ions were still present on the dentin surface after demineralization (Fig. 3, Group C). It was considered that the deposition of apatites occurred not only on the dentin surface but also within the demineralized dentin layer. The precipitation of microcrystals in the exposed collagen layer of the demineralized dentin might partially restore dentin structure. The SEM observations of the surface texture of the demineralized dentin treated with fluoride solution differed from those in specimens that were treated with fluoride and then rinsed with water. The surface structures in Group NF specimens showed a relatively well-preserved dentin structure, whereas the surfaces in Group RF and Group C specimens seemed more amorphous. SEM observation of the resin-dentin interface suggested that fluoride application facilitated the infiltration of resin monomer into the demineralized dentin. It was considered that the mainVOLUME 88 NUMBER 5

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tenance of the dentin structure was beneficial for the penetration of primer and adhesive resin into demineralized dentin. The infiltration of adhesive resin into the demineralized dentin in Group NF specimens resulted in the formation of a hybrid layer and tag-like structure, as shown in Figure 2, B. On the other hand, Group RF specimens showed lower bond strengths that were not significantly different compared with Group C specimens. Rinsing with water after fluoride application apparently removed mineral deposits from the demineralized dentin. This was confirmed by the absence of crystal-like deposits (Fig. 1, E) and the inability of the electron probe to detect any surface fluoride (Fig. 3, Group RF). The loss of mineral may have permitted collapse of collagen fibrils during air drying. Collapsed collagen does not take up resin monomers. This was confirmed by the absence of individual resin tag formation and by the SEM images in Figure 1, E and Figure 2, C, which showed few open dentinal tubules. It appeared as if the resin monomer could not penetrate very deeply into the demineralized dentin layer (Fig. 2, C). In control specimens without fluoride application, the bond strength was low because of the loss of mineral support in the demineralized dentin layer and the lack of resin infiltration. Although mineral deposition did not occur because of the absence of fluoride ions, some amounts of calcium and phosphate ions existed on the demineralized dentin. SEM observation of the control surface revealed many granular deposits on the demineralized dentin surface after application of Clearfil SE Bond primer. These deposits might be reaction products from the interaction of the acidic primer with subsurface mineralized dentin.20,21 However, SEM observations of these bonded interfaces showed relatively shallow resin penetration (Fig. 2, D). Although fluoride application produced a small increase in the adhesion of the self-etching adhesives to laboratory-demineralized dentin, the bond strength was much lower than that to sound dentin, even when the fluoride solution was applied and not rinsed. Moreover, the bond strengths to laboratory-demineralized dentin were lower than resin bond strengths to caries-affected dentin.6,7 Unlike true caries-affected dentin, the tubules in laboratory-demineralized dentin were completely open. It was hoped that resin tag formation would increase resin-dentin bond strength. The fact that the mode of failure of resin-bonded, laboratory-demineralized dentin involved cohesive failure of the dentin matrix suggests that prolonged exposure to acetic acid may weaken collagen. The results of this study cannot directly relate to bonding to clinical carious dentin. Further investigations will be necessary to increase the bond strength to carious dentin for establishment of sealed restorations, as NOVEMBER 2002

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minimal intervention is an important concept in clinical restorative dentistry.

CONCLUSIONS Within the limitations of this in vitro study, very low bond strengths were caused by application of self-etching primer adhesive systems to carious dentin demineralized in the laboratory. Application of fluoride-containing solutions produced a slight improvement in bond strength. REFERENCES 1. Mertz-Fairhurst EJ, Schuster GS, Williams JE, Fairhurst CW. Clinical progress of sealed and unsealed caries. Part I: depth changes and bacterial counts. J Prosthet Dent 1979;42:521-6. 2. Mertz-Fairhurst EJ, Curtis JW Jr, Ergle JW, Rueggeberg FA, Adair SM. Ultraconservative and cariostatic sealed restorations: results at year 10. J Am Dent Assoc 1998;129:55-66. 3. Tyas MJ, Anusavice KJ, Frencken JE, Mount GJ. Minimal intervention dentistryCa review. FDI Commission Project 1-97. Int Dent J 2000;50:112. 4. Tjaderhane L, Larjava H, Sorsa T, Uitto VJ, Larmas M, Salo T. The activation and function of host matrix metalloproteinases in dentin matrix breakdown in caries lesions. J Dent Res 1998;77:1622-9. 5. Kimochi T, Yoshiyama M, Urayama A, Matsuo T. Adhesion of a new commercial self-etching/self-priming bonding resin to human caries-infected dentin. Dent Mater 1999;18:437-43. 6. Nakajima M, Sano H, Burrow MF, Tagami J, Yoshiyama M, Ebisu S, et al. Tensile bond strength and SEM evaluation of caries-affected dentin using dentin adhesives. J Dent Res 1995;74:1679-88. 7. Yoshiyama M, Urayama A, Kimochi T, Matsuo T, Pashley DH. Comparison of conventional vs self-etching adhesive bonds to caries-affected dentin. Oper Dent 2000;25:163-9. 8. Sano H, Ciucchi B, Matthews WG, Pashley DH. Tensile properties of mineralized and demineralized human and bovine dentin. J Dent Res 1994;73:1205-11. 9. Ehudin DZ, Thompson VP. Tensile bond strength of dental adhesives bonded to simulated caries-exposed dentin. J Prosthet Dent 1994;71:16573. 10. Perdiga˜ o J, Swift EJ Jr, Deinehy GE, Wefel JS, Donly KJ. In vitro bond strengths and SEM evaluation of dentin bonding systems to different dentin substrates. J Dent Res 1994;73:44-55. 11. Nakaoki Y, Nikaido T, Pereira PN, Inokoshi S, Tagami J. Dimensional changes of demineralized dentin treated with HEMA primers. Dent Mater 2000;16:441-6. 12. Nakajima M, Ogata M, Harada N, Tagami J, Pashley DH. Bond strengths of self-etching primer adhesives to in vitro-demineralized dentin following mineralizing treatment. J Adhes Dent 2000;2:29-38. 13. Damen JJ, Buijs MJ, ten Cate JM. Fluoride-dependent formation of mineralized layers in bovine dentin during demineralization in vitro. Caries Res 1998;32:435-40. 14. Nystrom GP, Holtan JR, Douglas WH. Effects of fluoride pretreatment on bond strength of a resin bonding agent. Quintessence Int 1990;21:495-9. 15. Takahashi Y, Arakawa Y, Matsukubo T, Takeuchi M. The effect of sodium fluoride in acid etching solution on sealant bond and fluoride uptake. J Dent Res 1980;59:625-30. 16. ten Cate JM, van Duinen RNB. Hypermineralization of dentinal lesions adjacent to glass-ionomer cement restorations. J Dent Res 1995;74:126671. 17. Featherstone JD, Glena R, Shariati M, Shields CP. Dependence of in vitro demineralization of apatite and remineralization of dental enamel on fluoride concentration. J Dent Res 1990;69:620-5. 18. Christoffersen J, Christoffersen MR, Arends J, Leonardsen ES. Formation of phosphate-containing calcium fluoride at the expense of enamel, hydroxyapatite and fluorapatite. Caries Res 1995;29:223-30. 19. Heilman JR, Jordan TH, Warwick R, Wefel JS. Remineralization of root surfaces demineralized in solutions of differing fluoride levels. Caries Res 1997;31:423-8.

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20. Grandini R, Novelli C, Pierleoni P. Dentin adhesives. An update [in Italian]. Minerva Stomatol 1991;40:751-8. 21. Hanaizumi Y, Maeda T, Takano Y. Distribution of calcium ions at the interface between resin bonding materials and tooth dentin. Use of commercially available adhesive systems. J Electron Microsc 1998;47:227-41. Reprint requests to: DR TOSHIYUKI ITOTA DEPARTMENT OF OPERATIVE DENTISTRY OKAYAMA UNIVERSITY GRADUATE SCHOOL 2-5-1 SHIKATA-CHO

ITOTA ET AL

OKAYAMA 700-8525 JAPAN FAX: 81-86-235-6674 E-MAIL: [email protected] Copyright © 2002 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2002/$35.00 ⫹ 0 10/1/129079

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MEDICINE

AND

Noteworthy Abstracts of the Current Literature

DENTISTRY doi:10.1067/mpr.2002.129079

Three-year performance of a resin composite releasing calcium, fluoride, and hydroxyl ions. van Dijken JW. Acta Odontol Scand 2002;60:155-9

Purpose. Cross-sectional studies have shown that the primary reason for the replacement of restorations is secondary dental caries. A desirable quality of a restoration would be its ability to prevent demineralization. Multiple authors have suggested that ion-releasing materials may prevent this problem. The aim of this study was to evaluate a new posterior ion-releasing composite over a 3-year period. Material and Methods. A new composite (Ariston pHc; Ivoclar-Vivadent, Schaan, Liechtenstein), which releases calcium, fluoride, and hydroxyl ions, was tested and evaluated over a 3-year period. A total of 69 Class I (n ⫽ 6) and Class II (n ⫽ 63) posterior restorations were placed in premolar and molar teeth of 36 patients (12 men and 24 women, mean age 50.7 years). These restorations were evaluated by USPHS criteria at baseline, 6 months, 1, 2, and 3 years after restoration placement by 2 calibrated evaluators. The following parameters were evaluated: anatomical form, marginal adaptation, color stability, marginal discoloration, surface roughness, and secondary dental caries. An adhesive bonding technique was not used in the restoration placement, which contributed to postoperative sensitivity in 10 of the 69 restorations. The characteristics of the restorations were described at the recall schedule by using relative cumulative frequency distributions of the scores. Results. A total of 26% failures were observed at the follow-up: 13 cusp fractures, 2 partial fractures of the composite, 1 secondary dental caries, and 1 endodontic therapy needed due to continued post restoration sensitivity. Eight cusp fractures occurred between 24 and 36 months. The cusp fractures were repaired with composite during the study period and, of the repaired teeth, an additional 4 fractured again. The author speculates that the high rate of cusp fracture may have resulted from expansion of the composite over time or hydrolytic degradation of the alkaline glass filler. The low secondary caries formation against this ion-releasing composite may be due to the short length of this clinical study. Conclusion. The author concludes that, despite the promise of pH stabilizing properties of the material, this material has a clinically unacceptable high failure rate. 39 references.—RP Renner

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