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Investigation of self-etching dentin primers
Investigation of self-etching dentin primers T. Hasegawa* A. Manabe K. Itoh S. Wakumoto Department of Operative Dentistry School of Dentistry, Showa University 2-1-1 Kitasenzoku Ohta-ku Tokyo, Japan 145 Received March 6, 1989 Accepted August 8, 1989 *Corresponding author Dent Mater 5:408-410, November, 1989
Abstract- In order to simplify the dentin bonding procedures by combining the dentin cleansing and dentin primer steps, we investigated the efficacy of the four acidic monomers-monomethacryloxyethyl succinate (MES), dimethacryloxyethyl phosphate (DMEP), tertiary butylacrylamide sulfonic acid ('rBAS), and 4-methacryloxyethyl trimellitic anhydride (4-META), diluted in 35% hydroxyethyl methacrylate (HEMA) solution- by measuring the maximum contraction gap of the visible-light-curing composite (Silux 3M, St. Paul, MN, USA) in the cylindrical dentin cavity mediated by the bonding agent (Clearfil New Bond, Kuraray Co., Osaka, Japan). More than five of the ten specimens which were pre-treated with an aqueous mixture of 35% HEMA and four functional monomers at the concentrations of 0.1 M, 0.2 M, and 0.3 M showed a complete marginal adaptation, and this result was the same as in the control group in which the cavities were cleansed and pre-treated with 0.5 M EDTA and 35% HEMA, respectively. Moreover, the procedures were simpler. Therefore, these four monomers are considered to be effective as self-etching primers.
he adaptation of the composite to the dentin cavity wall is affected not only by the ability of the bonding agent used but also by the combination of the dentin cleanser, dentin primer, and composite used in the investigation. It is considered to be most important that the optimum materials and techniques be e m p l o y e d in all of t h e s e steps. GLUMA, a mixture of aqueous solutions of glutaraldehyde and hydroxyethyl methacrylate (HEMA), improved the bond between the composite and dentin pre-treated with the 0.5 M E D T A solution (Munksgaard and Asmussen, 1984). The efficacy of this dentin primer, GLUMA, was f u r t h e r improved when combined with the commercial dentin bonding agent (Munksgaard et al., 1985). The glutaraldehyde in GLUMA could be eliminated, because the 35% aqueous HEMA solution was comparable with GLUMA when both were used in combination with Clearfil New Bond (Itoh et al., 1985). These bonding systems, however, might be unacceptable for clinical use
because of their complex handling procedures. The purpose of the present investigation was to simplify the bonding procedures by combining the dentin cleanser and dentin primer.
T
MATERIALS AND METHODS
The functional monomers tested are listed in the Fig. The experimental dentin primers were prepared by dilution of each of these four monomers separately in the 35% aqueous HEMA solution at the concentrations of 0.1 M, 0.2 M, and 0.3 M, producing 12 kinds of experimental dentin primers. Flat dentin was prepared on the proximal surfaces of freshly ext r a c t e d human molars by being ground on wet carborundum paper, and cylindrical cavities, approximately 3 mm in diameter and 1.5 mm deep, were prepared in the exposed dentin. The cavity walls and the surrounding dentin surface were treated with the experimental dentin primers for 60 s, then with Clearfil New Bond, followed by being slightly overfilled with a light-curing composite (Si-
TABLE MAXIMUM CONTRACTION GAP IN CYLINDRICAL DENTIN CAVITY PRE-TREATEDWITH VARIOUS EXPERIMENTAL ETCHING PRIMERS Pre-treated by Control (EDTA, HEMA) MES 0.1 M - HEMA 2.9 M MES 0.2 M - HEMA 2.9 M MES 0.3 M - HEMA 2.9 M
Number of Gap-free Specimens* 5 8 8 9
Maximum Contraction Gap (Mean +_ S.D.) 0.06 _+ 0.13 0.02 +_ 0.07 0.02 _+ 0.05 0.01 _+ 0.02
DMEP 0.1 M - HEMA2.9 M DMEP 0.2 M - HEMA 2.9 M DMEP 0.3 M - HEMA 2.9 M
6 6 7
0.07 +_ 0.12 0.08 _+ 0.10 0.03 _+ 0.06
TBAS 0.1 M - HEMA 2.9 M TBAS 0.2 M - HEMA 2.9 M TBAS 0.3 M - HEMA 2.9 M
5 7 8
0.03 +_ 0.05 0.04 +_ 0.06 0.01 +_ 0.03
4-META 0.1 M - HEMA2.9 M 7 0.14 ___ 0.20 4-META 0.2 M - HEMA2.9 M 5 0.07 _+ 0.08 4-META 0.3 M - HEMA2.9 M 7 0.02 _+ 0.04 * Per 10 specimens. 2.9 M HEMA = 35% HEMA (V%). Control specimens were treated with 2.9 M HEMA for 60 s after being cleansed with 0.5 M EDTA for 60 s.
408 HASEGAWA et al./INVESTIGATION OF SELF-ETCHING D E N T I N PRIMERS
lux). The surface of the composite was gently compressed on the glass plate mediated by a plastic matrix and irradiated for 40 s by a lamp unit (Focus Activator Light, Teledyne Getz, USA). After the specimens were stored in water at room temperature for 10 min, the excess composite was eliminated, and the cavity margin was exposed by being ground on wet carborundum paper, followed by being polished with an alumina slurry on linen. The width of the maximum contraction gap was measured to the accuracy of 0.1 ~m by use of a screw micrometer mounted on the ocular lens of a light microscope, and the magnification was calculated as the maximum contraction in percent of the cavity diameter measured to the accuracy of 0.1
Mono-methacryloxyethyl
succinate
(MES)
CH 3
CH2=C-C-O-CH2CH2-O-C-CH2CH2-C-OH O O O
Dimethacryloxyethyl
C
phosphate
(DMEP
?H3
cm.
Tertiarybutylacrylamide
In the same way as stated in the previous paper (Hasegawa et ~., 1988), for the control group, the dentin cavities were cleansed and pre-treated for 60 s with neutralized 0.5 M EDTA and 35% aqueous HEMA solution, respectively, prior to the application of the bonding agent. Ten specimens were prepared for each group at a room temperature of 24 -+ 1°C.
CH ~:C-C-NH-C-CH~-SO ~ H
sulfonic
acid
(TBAS)
HI
4-Methacryloxyethyl
trimellitic
anhydride
(4-META)
RESULTS The maximum contraction for each series of measurements and the numher of gap-free specimens are shown in the Table. By analysis of variance, no significant difference was observed among the experimental and control groups, because more than five out of ten specimens showed complete marginal adaptation in all groups. The purpose of using dentin bonding agents is to prevent the complete f o ~ a t i o n of contraction gap in the composite fillings in all of the specimens. Therefore, it is reasonable to evaluate the efficacy of the dentin primer by comparing the numbers of gap-free specimens in each group. Among the primers tested, the best result was obtained with the 0.3 M MES diluted in the 35% HEMA solution, since a minute contraction gap was observed in only one specimen out of ten. The bonding ability mediated by these four thnctional monomers diluted in the 35% HEMA solution was increased with the increase in concentration from 0.1 M to 0.3 M. This bonding might be improved if the concentrations of these
CH
CH =C-C-O-CH
5
CH -O-C-(Q~-C=O
6--(Q-Ol 0
Fig. Chemical structure of functional acidic monomer. monomers could be increased even more. However, it was impossible for the 4-META to be increased to more than 0.3 M in the HEMA.
DISCUSSION In order for a tight adaptation to be obtained between the composite and the cavity wall in the filling, some s t e p s - s u c h as enamel etching, dentin cleansing, pre-treatment with the dentin primer, and the application of the dentin bonding a g e n t - a r e required prior to placement of the composite filling. These procedures, however, are not easy to undertake,
and it is desirable for the steps to be reduced as much as possible. The acidic monomers tested in this investigation were expected to be effective, both in removing the smear layer on the dentin and improving the efficacy of the bonding agent. In the previous paper, the aqueous solution of the glutaric acid and HEMA was reported to be as effective as the s e l f - e t c h i n g d e n t i n p r i m e r (Hasegawa et al., 1988), although any potential harmful effect was not discussed. However, the irritation by the dentin primers should be examined carefully, because the cavities are not washed after the application
Dental Materials/No~,embe~. 1989 409
of the dentin primer. The acidic monomers examined in this investigation are considered to be more desirable for clinical use because they can be polymerized after application. If the improved bonding with the single application of the selfetching dentin primers can be used, as in this investigation, it is possible to reason that the acidic and methacrylic groups appear to be effective in removing the smear layer and in polymerization. By the results observed in this in-
vestigation, it may be concluded that the two steps of dentin cleansing and dentin primer may be combined. However, the procedures needed to place composite restorations and their bonding to dentin are still complex and require further investigation.
REFERENCES HASEGAWA~ T.; MANABE, A.; ITOH, K.; and WAKUMOTO,S. (1988): The Effect of an Experimental Dentin Primer Composed of 35% HEMA and Glutaric Acid, Jpn J Consew Dent 31:451-456
410 HASEGAWA e$ al./INVESTIGATION OF SELF-ETCHING DENTIN PRIMERS
(in Japanese). ITOH, K.; HASHIMOTO, K.; and WAKUMOTO,S. (1985): Effect of GLUMA Concentration on Adhesion to Dentin, Jpn J Consew Dent 28:895-901 (in Japanese). MUNKSGAARD, E.C. and /~MUSSEN, E. (1984): Bond Strength Between Dentin and Restorative Resins Mediated by Mixture of HEMA and Glutaraldehyde, J Dent Res 63: 1087-1089. MUNKSGAARD, E.C.; ITOH, K.; ASMUSSEN, E.; and JORGENSEN, K.D. (1985): Effect of Combining Dentin Bonding Agents, Scand J Dent Res 93: 377-380.
Abstract- In order to simplify the dentin bonding procedures by combining the dentin cleansing and dentin primer steps, we investigated the efficacy of the four acidic monomers-monomethacryloxyethyl succinate (MES), dimethacryloxyethyl phosphate (DMEP), tertiary butylacrylamide sulfonic acid ('rBAS), and 4-methacryloxyethyl trimellitic anhydride (4-META), diluted in 35% hydroxyethyl methacrylate (HEMA) solution- by measuring the maximum contraction gap of the visible-light-curing composite (Silux 3M, St. Paul, MN, USA) in the cylindrical dentin cavity mediated by the bonding agent (Clearfil New Bond, Kuraray Co., Osaka, Japan). More than five of the ten specimens which were pre-treated with an aqueous mixture of 35% HEMA and four functional monomers at the concentrations of 0.1 M, 0.2 M, and 0.3 M showed a complete marginal adaptation, and this result was the same as in the control group in which the cavities were cleansed and pre-treated with 0.5 M EDTA and 35% HEMA, respectively. Moreover, the procedures were simpler. Therefore, these four monomers are considered to be effective as self-etching primers.
he adaptation of the composite to the dentin cavity wall is affected not only by the ability of the bonding agent used but also by the combination of the dentin cleanser, dentin primer, and composite used in the investigation. It is considered to be most important that the optimum materials and techniques be e m p l o y e d in all of t h e s e steps. GLUMA, a mixture of aqueous solutions of glutaraldehyde and hydroxyethyl methacrylate (HEMA), improved the bond between the composite and dentin pre-treated with the 0.5 M E D T A solution (Munksgaard and Asmussen, 1984). The efficacy of this dentin primer, GLUMA, was f u r t h e r improved when combined with the commercial dentin bonding agent (Munksgaard et al., 1985). The glutaraldehyde in GLUMA could be eliminated, because the 35% aqueous HEMA solution was comparable with GLUMA when both were used in combination with Clearfil New Bond (Itoh et al., 1985). These bonding systems, however, might be unacceptable for clinical use
because of their complex handling procedures. The purpose of the present investigation was to simplify the bonding procedures by combining the dentin cleanser and dentin primer.
T
MATERIALS AND METHODS
The functional monomers tested are listed in the Fig. The experimental dentin primers were prepared by dilution of each of these four monomers separately in the 35% aqueous HEMA solution at the concentrations of 0.1 M, 0.2 M, and 0.3 M, producing 12 kinds of experimental dentin primers. Flat dentin was prepared on the proximal surfaces of freshly ext r a c t e d human molars by being ground on wet carborundum paper, and cylindrical cavities, approximately 3 mm in diameter and 1.5 mm deep, were prepared in the exposed dentin. The cavity walls and the surrounding dentin surface were treated with the experimental dentin primers for 60 s, then with Clearfil New Bond, followed by being slightly overfilled with a light-curing composite (Si-
TABLE MAXIMUM CONTRACTION GAP IN CYLINDRICAL DENTIN CAVITY PRE-TREATEDWITH VARIOUS EXPERIMENTAL ETCHING PRIMERS Pre-treated by Control (EDTA, HEMA) MES 0.1 M - HEMA 2.9 M MES 0.2 M - HEMA 2.9 M MES 0.3 M - HEMA 2.9 M
Number of Gap-free Specimens* 5 8 8 9
Maximum Contraction Gap (Mean +_ S.D.) 0.06 _+ 0.13 0.02 +_ 0.07 0.02 _+ 0.05 0.01 _+ 0.02
DMEP 0.1 M - HEMA2.9 M DMEP 0.2 M - HEMA 2.9 M DMEP 0.3 M - HEMA 2.9 M
6 6 7
0.07 +_ 0.12 0.08 _+ 0.10 0.03 _+ 0.06
TBAS 0.1 M - HEMA 2.9 M TBAS 0.2 M - HEMA 2.9 M TBAS 0.3 M - HEMA 2.9 M
5 7 8
0.03 +_ 0.05 0.04 +_ 0.06 0.01 +_ 0.03
4-META 0.1 M - HEMA2.9 M 7 0.14 ___ 0.20 4-META 0.2 M - HEMA2.9 M 5 0.07 _+ 0.08 4-META 0.3 M - HEMA2.9 M 7 0.02 _+ 0.04 * Per 10 specimens. 2.9 M HEMA = 35% HEMA (V%). Control specimens were treated with 2.9 M HEMA for 60 s after being cleansed with 0.5 M EDTA for 60 s.
408 HASEGAWA et al./INVESTIGATION OF SELF-ETCHING D E N T I N PRIMERS
lux). The surface of the composite was gently compressed on the glass plate mediated by a plastic matrix and irradiated for 40 s by a lamp unit (Focus Activator Light, Teledyne Getz, USA). After the specimens were stored in water at room temperature for 10 min, the excess composite was eliminated, and the cavity margin was exposed by being ground on wet carborundum paper, followed by being polished with an alumina slurry on linen. The width of the maximum contraction gap was measured to the accuracy of 0.1 ~m by use of a screw micrometer mounted on the ocular lens of a light microscope, and the magnification was calculated as the maximum contraction in percent of the cavity diameter measured to the accuracy of 0.1
Mono-methacryloxyethyl
succinate
(MES)
CH 3
CH2=C-C-O-CH2CH2-O-C-CH2CH2-C-OH O O O
Dimethacryloxyethyl
C
phosphate
(DMEP
?H3
cm.
Tertiarybutylacrylamide
In the same way as stated in the previous paper (Hasegawa et ~., 1988), for the control group, the dentin cavities were cleansed and pre-treated for 60 s with neutralized 0.5 M EDTA and 35% aqueous HEMA solution, respectively, prior to the application of the bonding agent. Ten specimens were prepared for each group at a room temperature of 24 -+ 1°C.
CH ~:C-C-NH-C-CH~-SO ~ H
sulfonic
acid
(TBAS)
HI
4-Methacryloxyethyl
trimellitic
anhydride
(4-META)
RESULTS The maximum contraction for each series of measurements and the numher of gap-free specimens are shown in the Table. By analysis of variance, no significant difference was observed among the experimental and control groups, because more than five out of ten specimens showed complete marginal adaptation in all groups. The purpose of using dentin bonding agents is to prevent the complete f o ~ a t i o n of contraction gap in the composite fillings in all of the specimens. Therefore, it is reasonable to evaluate the efficacy of the dentin primer by comparing the numbers of gap-free specimens in each group. Among the primers tested, the best result was obtained with the 0.3 M MES diluted in the 35% HEMA solution, since a minute contraction gap was observed in only one specimen out of ten. The bonding ability mediated by these four thnctional monomers diluted in the 35% HEMA solution was increased with the increase in concentration from 0.1 M to 0.3 M. This bonding might be improved if the concentrations of these
CH
CH =C-C-O-CH
5
CH -O-C-(Q~-C=O
6--(Q-Ol 0
Fig. Chemical structure of functional acidic monomer. monomers could be increased even more. However, it was impossible for the 4-META to be increased to more than 0.3 M in the HEMA.
DISCUSSION In order for a tight adaptation to be obtained between the composite and the cavity wall in the filling, some s t e p s - s u c h as enamel etching, dentin cleansing, pre-treatment with the dentin primer, and the application of the dentin bonding a g e n t - a r e required prior to placement of the composite filling. These procedures, however, are not easy to undertake,
and it is desirable for the steps to be reduced as much as possible. The acidic monomers tested in this investigation were expected to be effective, both in removing the smear layer on the dentin and improving the efficacy of the bonding agent. In the previous paper, the aqueous solution of the glutaric acid and HEMA was reported to be as effective as the s e l f - e t c h i n g d e n t i n p r i m e r (Hasegawa et al., 1988), although any potential harmful effect was not discussed. However, the irritation by the dentin primers should be examined carefully, because the cavities are not washed after the application
Dental Materials/No~,embe~. 1989 409
of the dentin primer. The acidic monomers examined in this investigation are considered to be more desirable for clinical use because they can be polymerized after application. If the improved bonding with the single application of the selfetching dentin primers can be used, as in this investigation, it is possible to reason that the acidic and methacrylic groups appear to be effective in removing the smear layer and in polymerization. By the results observed in this in-
vestigation, it may be concluded that the two steps of dentin cleansing and dentin primer may be combined. However, the procedures needed to place composite restorations and their bonding to dentin are still complex and require further investigation.
REFERENCES HASEGAWA~ T.; MANABE, A.; ITOH, K.; and WAKUMOTO,S. (1988): The Effect of an Experimental Dentin Primer Composed of 35% HEMA and Glutaric Acid, Jpn J Consew Dent 31:451-456
410 HASEGAWA e$ al./INVESTIGATION OF SELF-ETCHING DENTIN PRIMERS
(in Japanese). ITOH, K.; HASHIMOTO, K.; and WAKUMOTO,S. (1985): Effect of GLUMA Concentration on Adhesion to Dentin, Jpn J Consew Dent 28:895-901 (in Japanese). MUNKSGAARD, E.C. and /~MUSSEN, E. (1984): Bond Strength Between Dentin and Restorative Resins Mediated by Mixture of HEMA and Glutaraldehyde, J Dent Res 63: 1087-1089. MUNKSGAARD, E.C.; ITOH, K.; ASMUSSEN, E.; and JORGENSEN, K.D. (1985): Effect of Combining Dentin Bonding Agents, Scand J Dent Res 93: 377-380.