Bonding stability and shelf life of GLUMA T. Hasegawa* A. Manabe K. Itoh S. Wakumoto *Department of Operative Dentistry School of Dentistry Showa University 2-1-1 Kitasenzoku, Ohta-ku Tokyo 145, Japan Received February 19, 1988 Accepted July 18, 1988 *To whom correspondence should be addressed Dent Mater 5:150-152, May, 1989
Abstract-The long-term bonding stability and shelf life of the two dentin-bonding systems-GLUMA combined with Clearfil New Bond and HEMA combined with Clearfil New Bond-were evaluated by measurement of the tensile bond strength and the wall-to-wall polymerization contraction in the cylindrical dentin cavity. The tensile bond strengths of the two bonding systems did not decrease significantly after the specimens were stored in water at room temperature for a maximum period of 24 weeks. Since the bonding efficiency of the two bonding systems was not affected by the storing of these solutions in a refrigerator for a maximum period of 24 weeks, the shelf life of these agents is considered to be longer than 24 weeks.
LUMA is an aqueous solution of glutaraldehyde and hydroxyethyl methacrylate (HEMA) which has been reported to improve the bonding between dentin and resin materials (Munksgaard et al., 1984; Munksgaard and Asmussen, 1984; J~rgensen et al., 1985). The efficiency of the bonding system can be evaluated by measurement of (a) its ability to prevent contraction gap formation during polymerization of the composite, and (b) the long-term stability of bond strength. Munksgaard and Asmussen (1985) have reported that GLUMA satisfied these two requirements; however, the authors found that the glutaraldehyde in this bonding agent had no effect when combined with the marketed bonding agent (Clearfil New Bond, Kuraray Co., Osaka, Japan) (Itoh et al., 1985; Itoh and Wakumoto, 1986), because the combined use of an aqueous solution of 35% HEMA and the two marketed bonding agents (Clearffl New Bond, Kuraray; Pyrofll Bond, Sankin Co., Tokyo, Japan) showed a bonding ability comparable with that of GLUMA. Furthermore, authors reported that the combined use of 35% HEMA solution and Clearfil New Bond should be recommended clinically because of the possible pulp irritation caused by the glutaraldehyde in GLUMA (Watanabe et al., 1986). This suggestion was supported by the fact that the fingertip of the operator always became discolored, becoming brown by direct contact with GLUMA, although HSrstedBindslev (1987) reported that only a slight inflammation was observed in the pulp when the cavity was restored by the use of GLUMA. The purpose of the present study was to investigate the long-term stability and the shelf life of the GLUMA-Clearffl New Bond and the HEMA-Clearfil New Bond systems (both from Kuraray, Osaka).
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MATERIALS AND METHODS To evaluate tensile bond strength measurement after long-term storage, we embedded freshly extracted human teeth in epoxy resin and prepared a flat dentin surface perpendicular to the tooth axis by grinding on a wet carborundum paper, ending with No. 1000. The exposed dentin surface was cleaned with neutralized 0.5M EDTA solution (pH 7.4) for 60 sec by means of a small sponge pellet. After the samples were washed and dried, the 5-35 GLUMA (aqueous solution of 5% glutaraldehyde and 35% HEMA by volume), or the 35% HEMA solution prepared by use of a fresh bottle of glutaraldehyde and HEMA, was applied for 60 sec, and the dentin surface was dried completely. In the control group, pretreatment by GLUMA or HEMA was omitted. A split Teflon mold (inner diameter, 3.6 mm; outer diameter, 20 mm) was fixed to the dentin, and the autocuring bonding agent (Clearfil New Bond) was applied through the central hole. The light-curing composite (Silux, 3M Co.) was poured into the mold, forming a layer of less than 2 mm, and the composite was then polymerized by a lamp unit (Focus Activator Light, Teledyne Getz, USA). A chemically cured composite (P-10, 3M Co.) was poured into the upper half of the mold, and a #6 round bur was inserted into the unpolymerized composite. The specimens for the tensile bond strength measurement were then stored in water at room temperature of 24 +_ I°C for a maximum period of 24 weeks. After 24 hours and 1, 4, 12, and 24 weeks of storage in water, the tensile bond strengths of ten specimens for each storage period and each bonding system were measured by means of a universal testing machine (TCM-200, Minebea Co., Tokyo, Japan) with a crosshead speed of 5 mm/min.
In order to determine the shelf life of GLUMA and HEMA, we measured the bond strength and the wallto-wall polymerization contraction in the cylindrical dentin cavity after storage of these solutions. The GLUMA and 35% HEMA solutions were used in the same way for tensile bond strength measurement after long-term storage, and stored in a refrigerator at 8 --- 2°C. Immediately after these solutions were prepared and every four weeks up to 24 weeks, we measured the tensile bond strength after 24 hours by the technique described above. The same storage period as stated above was used for measurement of the wall-to-wall polymerization contraction of these solutions, as follows: The proximal surface of each freshly extracted human molar was ground, and the dentin surface was flattened on a wet 220-grit carborundum paper. A cylindrical cavity (3 ram, diameter; 1.5 mm, depth) was prepared in the exposed dentin, and the cavity, including the surrounding dentin surface, was cleaned with 0.5 M EDTA (pH 7.4) for 60 seconds. After the sample was washed and dried, the G L U M A or 35% HEMA was applied for 60 seconds (by use of a small brush) and dried completely. After applying a drop of the mixture of Clearfil New Bond and blowing away the excess bonding agent, we poured a light-cured composite into the cavity so that it overflowed. The composite resin surface was covered with a plastic matrix and pressed gently onto a glass plate. The resin was irradiated for 40 seconds, and the specimens were stored in water for 10 minutes. The cavity margin was polished on a linen cloth with an alumina slurry and observed under a light microscope at a magnification of 1024 ×. The width of the contraction gap was measured at intervals of 45 degrees along the cavity margin by a screw micrometer, mounted on the ocular lens. The maximum contraction was measured in percentage of the cavity diameter. Ten specimens were prepared for each storage period and each bonding system. RESULTS
The tensile bond strength after the specimens were stored in water for
TABLE 1 TENSILE BOND STRENGTH OF EXPERIMENTAL BONDING SYSTEMS TO HUMAN DENTIN AFTER SPECIMENS WERE STORED IN WATER FOR UP TO 24 WEEKS (MN/m 2) Storage Period 24 hours 1 week 4 weeks 12 weeks 24 weeks
C.N.B.* 11.9 ± 5.2 14.1 ± 7.3 11.6 ± 3.9 7.0 __ 5.4 7.1 ± 2.8
(4) (5) (5) (4) (2)
HEMA** 16.8 ± 21.4 ± 13.7 ± 14.5 ± 19.1 ±
+ C.N.B.* 4.1 (6) 5.0 (10) 4.9 (9) 6.6 (7) 8.5 (8)
GLUMA*** 15.2 ± 17.2 ± 11.4 ± 16.7 ± 19.0 ±
+ C.N.B.* 6.1 (4) 6.4 (7) 5.2 (6) 5.0 (7) 9.2 (9)
Mean ± S.D. n = 10. * C.N.B., Clearfil New Bond. ** HEMA, Aqueous solution of 35% HEMA. *** GLUMA, Aqueous solution of 35% HEMA and 5% glutaraldehyde. The dentin surface was treated with 0.5 M EDTA for 60 sec prior to the application of the bonding systems. GLUMA and HEMA were applied for 60 sec before the C.N.B. application. The number of specimens fractured inside the resin material is indicated in parentheses.
TABLE 2 MAXIMUM CONTRACTION GAP OF EXPERIMENTAL BONDING SYSTEMS IN CYLINDRICAL DENTIN CAVITY (%) HEMA** + C.N.B.* GLUMA*** Immediately after 0.03 ± 0.04 (7) 0.08 ± 4 weeks after 0 (10) 0.04 ± 8 weeks after 0.01 ± 0.03 (9) 0.04 ± 12 weeks after 0.03 ± 0.05 (7) 0.02 ± 0.01 ± 16 weeks after 0.01 ± 0.02 (8) 20 weeks after 0.03 ± 0.05 (7) 0.07 ± 24 weeks after 0.02 ± 0.06 (9) 0.02 ± Mean ± S.D. n = 10. * C.N.B., Clearfil New Bond. ** HEMA, Aqueous solution of 35% HEMA. *** GLUMA, Aqueous solution of 35% HEMA and 5% glutaraldehyde. HEMA and GLUMA were stored in a refrigerator for up to 24 weeks. The number in parentheses indicates the number of gap-free specimens.
a maximum period of 24 weeks is shown in Table 1. The measurements on each bonding system were analyzed statistically by Student's t test. The two bonding systems-Clearfll New Bond-GLUMA and Clearfil New Bond-HEMA- showed a constant tensile bond s t r e n g t h after storage in water for a maximum period of 24 weeks, whereas that of Clearfil New Bond alone decreased significantly (p < 0.05) after 24 weeks compared with storage after 24 hours. The bond strength of Clearfll New Bond increased significantly (p < 0.05) by pretreatment with GLUMA or HEMA in the 12-to-24-week storage group. The bond strength between the dentin and resin produced by these bonding systems, however, was considered to be greater than the
+ C.N.B.* 0.06 (3) 0.06 (7) 0.04 (3) 0.03 (6) 0.02 (8) 0.06 (2) 0.06 (9)
bond strength measured, because over 60% of the 150 specimens fractured inside the resin cylinder. The wall-to-wall polymerization contraction and tensile bond strength exhibited by the two bonding systerns are shown in Tables 2 and 3. The polymerization contraction in the cylindrical dentin cavity pretreated with GLUMA or HEMA was not affected by the storing of these two solutions in a refrigerator for up to 24 weeks. In all periods tested, seven or more of the ten specimens in the group pretreated with HEMA showed complete marginal adaptation. The number of gap-free specimens in the group of GLUMA combined with Clearfil New Bond varied from two to nine, which differed from the group pretreated with HEMA.
Dental Materials~May 1989 151
TABLE 3 TENSILE BOND STRENGTHS OF EXPERIMENTAL BONDING SYSTEMS MEASUREDAFTER 24 HOURS (MN/m2) Immediately after 4 weeks 8 weeks 12 weeks 16 weeks 20 weeks 24 weeks
after after after after after after
HEMA** + C.N.B.* 20.9 _+ 8.3 (6) 17.8 21.8 18.5 20.0 21.4 21.5
_+ 2.9 _ 5.2 +_ 4.6 _+ 5.4 __ 8.3 ± 6.6
(10) (10) (7) (9)
GLUMA***+ C.N.B.* 16.4 +_ 6.1 (8) 20.2 17.6 13.2 15.1
__ 4.2 (8) __+_5.3 (9) _+ 4.6 (10)
_ 4.6 (8) 20.1 __ 4.4 (8)
21.3 _+ 9.6 (10)
Mean _+ S.D. n=lO. * C.N.B., Clearfil New Bond. ** HEMA, Aqueous solution of 35% HEMA. *** GLUMA, Aqueous solution of 35% HEMA and 5% glutaraldehyde. HEMA and GLUMA were stored in a refrigerator for up to 24 weeks. The number of specimens fractured inside the resin material is indicated in parentheses.
The difference in the tensile bond strength after 24 hours was insignificant (p<0.05) b e t w e e n the two bonding systems, and the difference was signficant (p<0.05) after 12 weeks. DISCUSSION The most important requirement for a dentin-bonding agent is that it compensate for the contraction force of the composite and prevent contraction gap formation. If a complete adaptation between the dentin and resin is obtained just after polymerization of the composite, it would be ensured by the subsequent hygroscopic expansion of the composite. However, it is also important that the long-term stability of bonding be evaluated, because the bonding may be deteriorated by the chemical and physical stresses in the oral environment. Therefore, the efficiency of the
dentin-bonding agent was determined by measurement of the polymerization contraction and tensile bond strength after long-term storage. The stability of bonding by Clearfil New Bond was improved by p r e t r e a t m e n t with G L U M A or HEMA for up to 24 weeks. The effect of the chemical exchange of the two components in GLUMA on the bonding might be negligible in this study, because the differences in tensile bond strength and maximum contraction gap were insignificant (p < 0.05) for the experimental period of 24 weeks. This result may be explained by the fact that the oxidation of glutaraldehyde and the solubility of HEMA in water are insignificant up to 24 weeks of storage in a refrigerator at 8 -+ 2°C. CONCLUSION It is possible to conclude that pretreatment with 35% HEMA prior to
152 H A S E G A W A et al./BONDING S T A B I L I T Y A N D S H E L F L I F E OF GLUMA
Clearffl New Bond application satisfies the requirements of prevention of the polymerization contraction gap and long-term bonding stability. REFERENCES
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