Dentin Bond Strength of Light-cured Glass-ionomer Cements K. HINOURA, M. MIYAZAKI, and H. ONOSE Department of Operative Dentistry, Nihon University School of Dentistry, 1-8 Kanda-Surugadai, Chiyoda-ku, Tokyo, 101, Japan The purpose ofthis study was to investigate the influence of surface XR Ionomer, and GC Light VL-1 (GC) for Fuji Lining LC. treatments and irradiation conditions on the bond strength of lightThe incisal surfaces of bovine incisors were ground on wet No. cured glass-ionomer cements to dentin. The light-cured glass- 240-grit SiC paper mounted on a metallurgical grinder until apionomer cements used in this study were Vitrabond, XR Ionomer, proximately 2 mm remained coronal to the nearest pulp horn. The and Fuji Lining LC. Three experiments were designed to study the roots were removed, and each tooth was then mounted in coldinfluence of the following factors on bond strength to dentin: (1) curing acrylic resin so that the flattened area was exposed. The effect of the surface treatment of the dentin, (2) effect of the teeth were stored in distilled water at 0C until ready to be polished irradiation time, (3) effect of an increase in the interval between and were not re-used. Final finish was accomplished by grinding on mixingofthe cement and irradiation. Samples were stored in water wet No. 600-grit SiC paper until a 4-mm-diameter area of dentin for 24 hours, after which shear bond testing was performed at a was exposed. These surfaces were washed and dried with comcross-head speed of 1 mm/min. For Vitrabond, the Scotchprep and pressed air. Gluma 2 treatments gave the greatest shearbond strengths. ForXR The following surface treatments were applied: Ionomer and Fuji Lining LC, the Scotchprep treatment gave the (A) no treatment (smear layer intact); greatest shear bond strengths. The bond strengths for all cements (B) dentin surface was conditioned with 10% polyacrylic acid increased with prolonged irradiation time. Bond strengths de(Dentin Conditioner; GC) for 20 s and washed with tap water creased with a longer elapsed time between mixing and lightfor 20s; curing. This means that light-curing should be done soon after the (C) dentin surface was etched with EDTA (Gluma 2; Bayer) for cement is placed. The failure mode was found to be cohesive in the 30 s and washed with tap water for 20 s; and ionomer. (D) dentin surface was conditioned with Scotchprep (3M) for 30s. All specimens were dried with compressed air. J Dent Res 70(12):1542-1544, December, 1991 A Teflon mold, 1.5 mm high and 4 mm in diameter, was used to form and hold the materials to the dentin surface. Each ionomer Introduction. cement was mixed, placed into the mold, compressed with a 500-g weight for 10 s, and irradiated with the appropriate curing light. Glass-ionomer cements have certain characteristics that are attracThree experiments were designed for study of the influence of tive to the dentist. They bond adhesively to both enamel and dentin the following factors on bond strength to dentin: (Powis et al., 1982; Hinoura et al., 1986; Mitra, 1991a), release (1) effects of the dentin surface treatments-The dentin surface fluoride ions over a prolonged period of time (Swartz et al., 1984; was treated with treatments (A) to (D). The curing light Mitra, 1991b), are biocompatible (Wilson and McLean, 1988), and exposure time was 30 s, and the time interval between the have approximately the same coefficient of thermal expansion as cement mixing and light irradiation was one mi; does enamel. However, the handling properties of these materials (2) effect of the irradiation time-No dentin surface treatment make them especially technique-sensitive because of their suscepwas used. The irradiation time was five, 10, 20, 30, 40, or 60 tibility to moisture contamination or dehydration during the early s, and the time interval between cement mixing and light stages ofthe setting reaction. They also have short working times irradiation was one min; and and rather long setting times. (3) effect of time interval between the start of cement mixing Recently, light-cured glass-ionomer cements have become availand light irradiation-No dentin surface treatment was able which offer improved handling characteristics. A reduction in used, and the irradiation time was 30 s. The time elapsed setting time because of photocuring within the cavity preparation between cement mixing and light exposure was one, three, may assist in decreasing the moisture contamination and dehydrafive, 10, 20, 30, or 60 min. tion difficulties associated with the early stage of the setting The finished specimens were allowed to set for 30 min at room reaction. temperature, at which time all assembled specimens were transThe purpose of this study was to investigate the influence of ferred to distilled water and stored in 370C water for 24 h after the surface treatments and irradiation conditions on the bond strength start of cement mixing. Ten specimens per group were tested in a of light-cured glass-ionomer cements to dentin. shear mode in an Instron Testing Machine (Instron Corporation, Canton, MA 02021) at a cross-head speed of 1 mm/min. Shear bond strength values (MPa) were calculated from the peak load at failure Materials and methods. divided by the specimen surface area (0.1256 cm2). The light-cured glass-ionomer cements used in this study were Vitrabond Light-Cure Glass Ionomer Liner/Base (Batch No. liquid 82, powder 8W3; P/L Ratio of 1.4:1; 3M Dental Products), XR Results. Ionomer (Batch No. liquid 9-1289, powder 9-5256; P/L Ratio of1.2:1; The results of the bond strength tests for various surface treatKerr/Sybron), and Fuji Lining LC (Batch No. liquid 240301, powder ments are presented in Table 1. These results were subjected to 110503; P/L Ratio of 1.4:1; GC). They are intended for use in lining analysis of variance followed by Tukey's test. In the Tables, values and basing applications under composite or metal restorations. connected lines are not significantly different (p > 0.05). by These light-cured glass-ionomer cements were cured by exposure to For Vitrabond, the Scotchprep and Gluma 2 treatment groups an Optilux (3M) for Vitrabond, Command II Light (Kerr/Sybron) for were the strongest, followed by no treatment. The Dentin Conditioner treatment gave the weakest bond strength. For XR Ionomer and Fuji Lining LC, the Scotchprep treatment group was signifiReceived for publication April 8, 1991 cantly stronger than with the other surface treatment groups. Accepted for publication June 26, 1991

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DENTIN BOND OF LIGHT-CURED GLASS IONOMER

Vol. 70 No. 12

1543

TABLE 1 EFFECTS OF THE DENTIN SURFACE TREATMENTS ON THE BOND STRENGTH

Surface Treatment Vitrabond None

6.79 (1.22)

Dentin Conditioner

5.02 (1.81)

Gluma 2 (EDTA)

8.30 (0.72)

8.68 (1.27) Scotchprep Values connected by vertical lines are not significantly different (p > 0.05).

Bond Strength, mean (S.D.), MPa XR Ionomer 4.48 (0.61) 3.60 (1.41) 4.58 (0.91) 5.82 (0.98)

Lining LC

5.39 (1.66)

4.53 (1.70) 5.62 (1.58) 8.30 (1.55)

TABLE 2 EFFECT OF THE IRRADIATION TIME ON THE BOND STRENGTH

Irradiation Time (s)

Vitrabond 5 4.07 (0.70) 10 4.59 (0.67) 20 6.58 (1.07) 30 6.79 (1.22) 40 6.89 (1.36) 60 6.97 (1.60) Values connected by vertical lines are not significantly different (p > 0.05).

Bond Strength, mean (S.D.), MPa XR Ionomer

Lining LC

2.29 (1.02)

3.18 (0.96)

2.86 (1.05)

4.74 (1.02)

3.00 (0.86)

5.18 (1.80)

4.48 (0.61)

5.39 (1.66)

4.92 (0.94)

5.60 (1.34)

4.92 (1.12)

5.90 (1.75)

TABLE 3 EFFECT OF TIME INTERVAL BETWEEN THE START OF CEMENT MIXING AND LIGHT IRRADIATION ON THE BOND STRENGTH

Time after Mixing (min)

Vitrabond

1

6.69 (1.15)

3

6.29 (1.17)

5

6.23 (1.05)

10

3.47 (0.86)

20

3.05 (0.89)

30

2.30 (0.69)

60

2.36 (0.87)

Bond strength, mean (S.D.), MPa XR Ionomer 4.27 (0.73) 2.80 (0.80) 2.26 (0.84) 2.19 (0.77) 1.61 (0.55) 1.39 (0.50) 1.27 (0.74)

Lining LC 5.37 (1.29) 5.34 (1.54)

5.18 (1.22) 4.22 (1.15)

3.99 (1.45) 3.45 (1.75) 2.21 (0.52)

Values connected by vertical lines are not significantly different (p > 0.05).

Table 2 shows the bond strengths of the glass-ionomer cements to dentin for various irradiation times. The bond strengths for all

cementsincreasedwithprolongedirradiationtimes. ForVitrabond,

the bond strength values separated into two groups: Groups with irradiation times of 20, 30, 40, and 60 s were significantly stronger than those with five and 10 s. The bond strength values of XR Ionomer fell into three groups: The 40- and 60-second groups were the strongest, followed by 30 s, with the shorter times grouped

together. For Fuji Lining LC, only the five-second irradiation group was significantly weaker than the others. Table 3 shows the bond strengths of the glass-ionomer cements to dentin with various time intervals elapsing between the start of cement mixing and light irradiation. In general, for all cements, bond strengths decreased with a longer elapsed time between mixing and light-curing. For Vitrabond, the bond strength values were separated into several groups: One-, three-, and five-minute

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1544

HINOURA et al.

J Dent Res December 1991

groups were significantly stronger, followed by 10- and 20-minute decreased with a longer interval. This means that light-curing groups, and finally the 20-, 30-, and 60-minute groups. For XR should be done soon after placement of the cement. XR Ionomer was Ionomer, only the one-minute group separated completely, with a the most sensitive in this regard and showed a marked decrease in 35% decrease in the bond strength between the one- and three- bond strength between one and three min. Both Vitrabond and minute groups. For Fuji Lining LC, none of the groups separated Lining LC would permitbetween five and 10 min to elapse before the completely. In particular, there was no significant difference among bond strengths were significantly lowered. the one-, three-, five-, 10-, and 20-minute groups. The most signifiHinoura et al. (1986) have reported the average bond strength of cant decreases in bond strength were seen after one min for XR conventional glass-ionomer cements to be approximately 2 MPa. The measured bond strengths were almost three times higher for Ionomer, and after five min for Lining LC and Vitrabond. these light-cured cements. The light-cured glass-ionomer cements have several other advantages over conventional glass ionomers, Discussion. including the convenience of a rapid set by exposure of the mixed It is interesting to note that the highest bond strengths were cement to the curing light. Two of the cements studied, Vitrabond obtained for dentin surfaces treated with Scotchprep. Scotchprep and Lining LC, also offer extended working time after the cement is contains HEMA, as do Vitrabond and Fuji Lining LC. HEMA may mixed. Further studies are needed to define the mechanisms by help develop an affinity between the dentin surface and these which these hybrid resin/glass-ionomer materials bond to dentin in cements. On the other hand, Dentin Conditioner (PAA) treatment order for the influence of variables-such as surface treatment, lowered the bond strengths of all the cements. Polyacrylic acid exposure time, and elapsed time before light-curing--on the bond removes the smear layer and reveals the cut dentinal tubules strength of these visible-light-cured glass ionomers to be fully without opening the tubules. Powis et al. (1982) reported that understood. polyacrylic acid treatment produced improved adhesion compared with no treatment for chemically-cured glass-ionomer cements. REFERENCES Several other investigators (Erickson and Glasspoole, 1985; Retief et al., 1986) have shown that the adhesion of Scotchbond to dentin is greater when the smear layer is left intact. The light-cured glass- ERICKSON, R.L. and GLASSPOOLE, EA (1985): Effect ofAcid Rinsing on Dentin Smear Layer, J Dent Res 64:276, Abst. No. 914. ionomer cements in this study are actually hybrid systems, combining conventional glass ionomer and visible-light-cured resin chem- HINOURA, K; MOORE, B.K.; and PHILLIPS, R.W. (1986): Influence of Dentin Surface Treatments on the Bond Strengths of Dentin-lining istries. In this case, the adhesion behavior appears to be more like Cements, Oper Dent 11:147-154. that ofthe resin Scotchbond than like a conventional glass ionomer. The bond strengths increasedwith longer irradiation times. The HINOURA, K; MOORE, B.K; and PHILLIPS, R.W. (1987): Tensile Bond Strength Between Glass Ionomer Cements and Composite Resins, JAm failure mode for light-cured glass-ionomer cements was found to be Dent Assoc 114:167-172. cohesive in the ionomer. The bond strength improvement was most likely due to an increase in the cohesive strength of the cements. MITRA, S.B. (199la): Adhesion to Dentin and Physical Properties ofa Lightcured Glass-ionomer Liner/Base, J Dent Res 70:72-74. Hinoura et al. (1987) reported that etching of a glass-ionomer cement with H3PO4 for 60 s greatly increased the tensile bond MITRA, S.B. (1991b): In vitro Fluoride Release from a Light-cured Glass Ionomer Liner/Base, J Dent Res 70:75-78. strengths of resin composite to glass ionomer, and that bond failure at such surfaces occurred cohesively within the glass ionomer. In MIYAZAKI, M.; MATSUZAKI, T.; AKIYAMA, Y.; SAITO, H.; HINOURA, K; and ONOSE, H. (1989): Study on Light Cured Composite Resins. this study, cohesive failure mode may also be related to the tensile Effect of the Elongation of the Irradiation Time on the Bond Strength, properties of light-cured glass ionomer. Miyazaki et al. (1989) Jpn J Conserv Dent 32:1331-1337. reported that the physical properties of light-cured resins improved with increased irradiation time up to some maximum value. The POWIS, D.R.; FOLLERAS, T.; MERSON, S.A.; and WILSON, A.D. (1982): Improved Adhesion of a Glass Ionomer Cement to Dentin and Enamel, irradiation times after which no significant increases in bond JDent Res 61:1416-1422. strength occurred were 20-second irradiation for Vitrabond, 40second irradiation for XR Ionomer, and 10-second irradiation for RETIEF, D.H.; GROSS, J.D.; BRADLEY, E.L.; and DENYS, F.R. (1986): TensileBondStrengthsof DentinBondingAgentstoDentin,DentMater Fuji Lining LC. It should be pointed out that these results were for 2:72-77. a 1.5-mm thickness of cement, which is relatively thick for a lining application. It is likely that the times indicated are conservative SWARTZ, M.L.; PHILLIPS, R.W.; and CLARK, H.E. (1984): Long-term F Release from Glass Ionomer Cements, J Dent Res 63:158-160. estimates for the time required to reach optimal bond strength for WILSON, A.D. and McLEAN, J.W. (1988): Biocompatibility. In: Glass a thinner liner. lonomer Cement. Chicago, IL: Quintessence Publishing Co., Inc., pp. The interval between the start of cement mixing and light 125-130. irradiation also affected the bond strength. The bond strengths

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