Dent Mater 8:351-353, November,1992
Effect of water-soluble photoinitiator on the adhesion between composite and tooth substrate T. Hayakawa, K. Horie Department of Dental Materials, Nihon University School of Dentistry at Matsudo, Matsudo Chiba, Japan
Abstract. The effectiveness of a water-soluble photoinitiator in a dentin primer was examined by measuring the tensile bond strength between the composite and tooth substrate treated with the primer. The water-soluble photoinitiator, 2-hydroxy-3-(3,4 dimethyl-9-oxo-9 H-thioxanthe n-2-yloxy)-N, N, N-trimethyl- 1propanaminium chloride (QTX) was dissolved into an aqueous solution of methoxy-nonaethyleneglycol monomethacrylate (M9G) or poly-N-vinylpyrrolidone (PNVP), and these aqueous solutions were used as primers. The combination of 0.5 M EDTA pretreatmerit and 1% QTX - 35% PNVP aqueous solution priming produced the highest bond strength. A mixture of dentin fractures and interfacial failure between the dentin and the resin was observed in the test specimen. This dentin priming combination was also effective in improving the bond strength to enamel pretreated with EDTA. INTRODUCTION The application of a dentin primer to the dentin surface is one useful method for improving the adhesion of dental resins to dentin (Munksgaard and Asmussen, 1984; Asmussen and Bowen, 1987; Tagami et al., 1987; Hayakawa et al., 1989; Chigira et al., 1989; 1991; Bowen et al., 1989; Munksgaard, 1990; Manabe et al., 1991). The dentin primer treatment increases the diffusibility or permeability of monomers into dentin (Nakabayashi and Takarada, 1992; Sugizaki, 1991). The diffusion of monomers into dentin and subsequent polymerization are major contributors to the formation of a strong adhesion between the restorative resins and the dentin (Nakabayashi, 1985; Nikaido, 1989). The polymerization initiator in a dentin primer containing methacrylate monomers will improve the degree of polymerization or conversion of diffused monomers inside the dentin; it will also improve the copolymerization between the dentin primer monomers, the monomers in the bonding agent and the composite, resultingin strong adhesion. C amphorquinone (CQ) is widely used as a photoinitiator of dental resins. It is doubtful that CQ can sufficiently initiate the polymerization of the diffused monomers inside the dentin because of the water content of dentin and lower partition coefficient of CQ in dentin than in resin. In this study, the bonding efficacy of mixtures containing a water-soluble photoinitiator was evaluated by measuring the tensile bond strengths between the composite and the dentin mediated by these agents. Moreover, the effectiveness ofthe primer containing water-soluble photoinitiator on enamel adhesion was also examined.
MATERIALS AND METHODS The components of the examined dentin primers are listed in Table 1. The main component of these dentin primers was either methoxy-nonaethyleneglycol monomethacrylate (M9G) (Shin-Nakamura Chemical, Wakayama, Japan) or poly-Nvinylpyrrolidone (PNVP, Tokyo Kasei, Tokyo, Japan). The viscosity-average molecular weight of PNVP is about 10,000 units. The water soluble photo-polymerization initiator, 2hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)N,N,N-trimethyl-l-propanaminium chloride (QTX) (Ward Blenkinsop, Cheshire, England, UK) was dissolved into an aqueous solution of M9G or PNVP, according to the concentrations listed in Table 1. For comparison with QTX, mixtures containing CQ (Aldrich Chemical, Milwaukee, WI, USA) were investigated. The structural formulas of the components of primers are shown in Fig. 1. The general procedures for making the test samples were previously reported (Hayakawa et al., 1989). Bovine anterior teeth were stored at -70°C after extraction from the mandibles. Their enamel was removed using No. 100 waterproof abrasive paper (Sankyo Rikagaku, Tokyo, Japan), and a flat dentin surface was prepared by wet grinding, using No. 800 and No. 1000 grinding stones (King, Tokyo, Japan) under running water. The dentin surface was pretreated with one of three procedures: 1) neutralized 0.5 M EDTA for 60 s; 2) 10% citric acid, 10% citric acid - 3% FeC13 (10-3); or 3) 10% phosphoric acid solution for 30 s. After washing and drying, the primer was applied to the pretreated dentin surface for 60 s. Any excess amount of primer was removed with compressed air for 10 s. A silicone ring, 3.2 mm diameter x 3.2 mm thick, was placed on the primed dentin surface. Then bonding agent (Clearfil Photobond, Kuraray, Osaka, Japan) was applied inside the ring and was irradiated for 10 s with Quick Light (Morita, Tokyo, Japan). The ring was filled with composite (Photoclearfil A, Kuraray) and irradiated for 40 s. Specimens without any primer treatment were also prepared. After curing the composite, the silicone ring was removed, and each specimen was stored in water at 37°C for 24 h. A brass attachment was fixed to the upper part of the cured resin and the tensile bond strength was measured with a universal testing machine (TOM10000X, Shinkoh, Tokyo, Japan) at a cross head speed of 2 mm/min. The data were tested for significant differences by an analysis of variance and by Scheff~'s test for a multiple comparison among the means (p = 0.05). The same general procedure was used to test the bond
Dental Materials~November 1992 351
CH3 CH2=C.C.(OCH2CH2)9.OCH 3 ,
--(- CH2-CH I "°
o
Primer MgG aq.
M9G
I
TABLE 1" COMPOSITIONOF PRIMERS
,o,
PNVP
el.3 "0"3
~,,~S~CH
3 OH OH3 QTX
OH3
1"
CH3~CHI~.,3CH3
c,"
Fig. 1. Structuralformulaeof componentsof dentin primers.
strength to the bovine enamel. The bovine enamel surface was polished and ground using No. 800 and No. 1000 grinding stones, under running water and then pretreated with 0.5 M EDTA or 40% phosphoric acid for 60 s. After washing and drying, PNVP aqueous or QTX(1)/PNVP was applied for 60 s. After drying with compressed air, the bonding agent and composite were applied as described above. The tensile bond strength after 24 h immersion in 37°C water was also measured. The data were also tested for significant differences by an analysis of variance and by Scheff~'s test for a multiple comparison among the means (p = 0.05). RESULTS
Table 2 presents the results of the tensile bond strengths between the composite and dentin pretreated with EDTA. Without any primer application, the mean bond strength was 2.8 MPa. Although the mean bond strengths were slightly increased by the addition of QTX and M9G aqueous solution, there were no significant differences among the bond strengths. Most of the bond failures were at the interface between the dentin and resin. The primer, consisting of 1% QTX added to PNVP aqueous solution, produced the highest mean value; with this primer, the bond failures were a mixture of dentin fracture and fracture at the interface between the dentin and resin. Subsequently, the effectiveness of QTX(1)/PNVP on the dentin pretreated with several kinds of acids was examined. The results are presented in Table 3. No remarkable increase in the bond strengths was evident in dentin pretreated with acids, compared to the bond strength obtained when the QTX(1)/PNVP primer was used on dentin pretreated with EDTA. Table 4 presents the results of tensile bond strengths between composite and enamel pretreated with EDTA or phosphoric acid. On enamel pretreated with EDTA, QTX(1)/ PNVP application significantly increased the mean bond strengths, which were almost equal to those of phosphoric acid etching. DISCUSSION
The strong adhesion between restorative resins and dentin is thought to occur due to the diffusion and polymerization of monomers in the dentin. Shibuya and Hayakawa (1991) reported that M9G and PNVP improved the adhesion of chemical-cured resin to dentin pretreated with EDTA. In this 352 Hayakawa & Horie/Effect of water soluble photoinitiator
50% MgG aqueous solution
CQ(0.5)/M9G
0.5% CQ + 50% M9G aqueoussolution
QTX(0.5)/M9G
0.5% QTX + 50% MgG aqueoussolution
QTX(1)/M9G
1% QTX + 50% M9G aqueous solution
QTX(2)/M9G
2% QTX + 50% M9G aqueous solution
PNVP aq.
CQ
Composition
35% PNVP aqueous solution
CQ(0.3)/PNVP
0.3% CQ + 35% PNVP aqueous solution
QTX(0.5)/PNVP
0.5% QTX + 35% PNVP aqueous solution
QTX(1)/PNVP
1% QTX + 35% PNVP aqueous solution
QTX(2)/PNVP
2% QTX + 35% PNVP aqueous solution
TABLE 2: EFFECTOF PRIMERS ON BOND STRENGTH TO DENTIN PRETREATED WITH EDTA Primers ..... M9G aq. CQ(0.5)/M9G QTX(0.5)/M9G QTX(1)/M9G QTX(2)/M9G PNVP aq. CQ(0.3)/PNVP QTX(0.5)/PNVP QTX(1)/PNVP QTX(2)/PNVP
Tensile Bond Strength (MPa) Mean _+SD 2.8 _+1.3 5.4 _+2.3 6.6 + 1.6 6.3 + 1.6 6.1 + 2.9 7.0 + 3.6 5.3 + 1.7 3.6 + 0.9 7.0 _+3.3 8.6 + 3.5 4.6 __.1.9 ]
Numberof Specimens 14 9 6 6 12 10 6 6 7 10 11
Vertical lines indicate no statisticaldifference. TABLE 3: EFFECT OF QTX(1)/PNVPON BOND STRENGTH TO DENTIN PRETREATED WITH ACID
Acid
Primer
Tensile Bond Strength (MPa) Mean __.SD
10% Citric Acid
..... QTX(1)/PNVP ..... PTX(1)/PNVP ..... QTX(1)/PNVP
3.8 + 1.5 5.2 + 2.2 4.4 + 2.1 6.6 + 3.1 3.9 _+2.7 5.8 + 1.4
10- 3 10% PhosphoricAcid
Numberof Specimens 6 12 6 12 9 10
Vertical lines indicate no statistical difference between the specimens that received and did not receivethe primer when the same pretreatmentreagent was used. TABLE 4: EFFECT OF QTX(1)/PNVPON BOND STRENGTH TO ENAMEL
Pretreatment EDTA EDTA EDTA Phosphoric Acid Phosphoric Acid Phosphoric A c i d
Primer ..... PNVP aq. QTX(1)/PNVP ..... PNVP aq. QTX(1)/PNVP
Tensile Bond Strength (MPa) Mean _+SD 8.3 _+3.5 10.4 + 3.5 14.0 + 3.1 16.1 + 3.9 14.8 _+4.3 16.5 + 5.4
Numberof Specimens 7 7 9 10 7 7
Vertical lines indicate no statistical difference between the specimens that received and did not receivethe primer when the same pretreatmentreagent was used.
study, it was expected that M9G and PNVP promoted the diffusion of monomers into dentin, and QTX sufficiently initiated the polymerization of diffused monomers in dentin. QTX has an absorption maximum at 402 nm and is used for direct silk screen photoemulsion (Davis et al., 1986). Contrary to our expectations, the copolymerization between M9G and monomers of the bonding agent did not occur due to the preferential homopolymerization of M9G. QTX initiated the polymerization of the diffused monomers of bonding agent into dentin when it was combined with PNVP. Sugizaki (1991) reported that the bond strength of Photobond to dentin pretreated with EDTA was increased about 1.6 times by SA(N-methacryloyl-5-aminosalicylic acid) priming. In this study, the bond strength was increased about 3 times by QTX(1)/PNVP priming. Hayakawa et al., (1989) reported that acid etching produced deeper decalcified dentin layers than EDTA pretreatment. Therefore, the interpenetration of PNVP into acidetched dentin was not sufficient, and the bond strengths were not improved by QTX(1)/PNVP priming. On the enamel pretreated with EDTA, QTX(1)/PNVP was also effective for improving the bond strengths. It was presumed that QTX improved the degree of conversion of the polymerization of the bonding agent at the subsurface of enamel. The effects of QTX(1)/PNVP were not obvious on enamel etched with phosphoric acid because of the large etching effect of phosphoric acid which produced the mechanical interlocking of the resin tags. Imai et al., (1991) pointed out that the interfacial initiation of polymerization is the key to strong adhesion of dental resin to dentin. In this study, the increased adhesion bond strengths were thought to be due to the polymerization of diffused monomers inside the dentin or subsurface of enamel by using QTX. QTX is a useful photoinitiator of the polymerization in the presence of water and has a possibility for wider applications, for example, in dental resins or cements.
ACKNOWLEDGEMENTS We are grateful to Mr. Kidokoro, Dainippon Ink and Chemical, for his offer of QTX. This study was supported in part by Grantin-Aid for Scientific Research 1991(A-03771464), from the Ministry of Education, Science, and Culture, Japan. Received March 21, 1992/Accepted October 22, 1992 Address correspondence and reprint requests to: T. Hayakawa Department of Dental Materials Nihon University School of Dentistry at Matsudo 2-870-1 Sakaecho Nishi Matsudo Chiba 271, Japan
REFERENCES Asmussen E, Bowen RL (1987). Effect of acidic pretreatment on adhesion to dentin mediated by Gluma. J Dent Res 66:1386-1388. Bowen RL, Eichmiller FC, MarjenhoffWA, Rupp NW (1989). Adhesive bonding of composites. J A m Coll Dent 56:10-13. Chigira H, Manabe A, Itoh K, Wakumoto S, Hayakawa T (1989). Efficacyofglycerylmethacrylate as a dentin primer. Dent Mater J 8:194-199. Chigira H, Itoh K, Wakumoto S (1991). Marginal adaptation of nine commercial intermediate resins. Dent Mater 7: 103-106. Davis MJ, Grawne G, Green PN, Green WA (1986). Spec Chem 6:3-12. Hayakawa T, Endo H, Nagatsuka A, Horie K (1989). Studies on adhesion to tooth substrate. VI. The adhesion ofcomposite resin mediated by the dentin primer containing MTYA. Dent Mater J 8:155-163. Imai Y, Kadoma Y, Kojima K, Akimoto T, Ikakura K, Ohta T ( 1991). Importance ofpolymerization initiator systems and interfacial initiation of polymerization in adhesive bonding of resin to dentin. J Dent Res 70:1088-1091. Manabe A, Katsuno K, Itoh K, Wakumoto S, Miyasaka T (1991). Bonding efficacy of erythritol methacrylate solutions as dentin primers. JDent Res 70:1294-1298. Munksgaard EC (1990). Amine-induced polymerization of aqueous HEMA/aldehyde during action as a dentin bonding agent. J Dent Res 69:1236-1239. Munksgaard EC, Asmussen E (1984). Bond strength between dentin and restorative resins mediated by mixtures of HEMA and glutaraldehyde. J Dent Res 63:1087-1089. Nakabayashi N (1985). Bonding of restorative materials to dentin: the present status in Japan. Int Dent J 35:145-154. Nakabayashi N, Takarada K (1992). Effect of HEMA on bonding to dentin. Dent Mater 8:125-130. Nikaido T (1989). Formulation ofphotocurable bonding liner and adhesion to dentin: Effect of photoinitiator, monomer, and photoirradiation. J Jpn Dent Mater 8:862-876. Shibuya I, Hayakawa T (1991). Studies on adhesion between the composite resin and the dentin- effect of various dentin primers. J Jpn Dent Mater 10:566-575. Sugizaki J (1991). The effect of the various primers on the dentin adhesion of resin composites - SEM and TEM observations of the resin impregnated layer and adhesion promoting effect of the primers. J Jpn J Conserv Dent 34:228-265. Tagami J, Hosoda H, Imai Y, Masuhara E (1987). An evaluation of a new adhesive liner as an adhesive promoter and a desensitizer on hypersensitive dentin. Dent Mater J 6:201-208.
Dental Materials~November 1992 353
Effect of water-soluble photoinitiator on the adhesion between composite and tooth substrate T. Hayakawa, K. Horie Department of Dental Materials, Nihon University School of Dentistry at Matsudo, Matsudo Chiba, Japan
Abstract. The effectiveness of a water-soluble photoinitiator in a dentin primer was examined by measuring the tensile bond strength between the composite and tooth substrate treated with the primer. The water-soluble photoinitiator, 2-hydroxy-3-(3,4 dimethyl-9-oxo-9 H-thioxanthe n-2-yloxy)-N, N, N-trimethyl- 1propanaminium chloride (QTX) was dissolved into an aqueous solution of methoxy-nonaethyleneglycol monomethacrylate (M9G) or poly-N-vinylpyrrolidone (PNVP), and these aqueous solutions were used as primers. The combination of 0.5 M EDTA pretreatmerit and 1% QTX - 35% PNVP aqueous solution priming produced the highest bond strength. A mixture of dentin fractures and interfacial failure between the dentin and the resin was observed in the test specimen. This dentin priming combination was also effective in improving the bond strength to enamel pretreated with EDTA. INTRODUCTION The application of a dentin primer to the dentin surface is one useful method for improving the adhesion of dental resins to dentin (Munksgaard and Asmussen, 1984; Asmussen and Bowen, 1987; Tagami et al., 1987; Hayakawa et al., 1989; Chigira et al., 1989; 1991; Bowen et al., 1989; Munksgaard, 1990; Manabe et al., 1991). The dentin primer treatment increases the diffusibility or permeability of monomers into dentin (Nakabayashi and Takarada, 1992; Sugizaki, 1991). The diffusion of monomers into dentin and subsequent polymerization are major contributors to the formation of a strong adhesion between the restorative resins and the dentin (Nakabayashi, 1985; Nikaido, 1989). The polymerization initiator in a dentin primer containing methacrylate monomers will improve the degree of polymerization or conversion of diffused monomers inside the dentin; it will also improve the copolymerization between the dentin primer monomers, the monomers in the bonding agent and the composite, resultingin strong adhesion. C amphorquinone (CQ) is widely used as a photoinitiator of dental resins. It is doubtful that CQ can sufficiently initiate the polymerization of the diffused monomers inside the dentin because of the water content of dentin and lower partition coefficient of CQ in dentin than in resin. In this study, the bonding efficacy of mixtures containing a water-soluble photoinitiator was evaluated by measuring the tensile bond strengths between the composite and the dentin mediated by these agents. Moreover, the effectiveness ofthe primer containing water-soluble photoinitiator on enamel adhesion was also examined.
MATERIALS AND METHODS The components of the examined dentin primers are listed in Table 1. The main component of these dentin primers was either methoxy-nonaethyleneglycol monomethacrylate (M9G) (Shin-Nakamura Chemical, Wakayama, Japan) or poly-Nvinylpyrrolidone (PNVP, Tokyo Kasei, Tokyo, Japan). The viscosity-average molecular weight of PNVP is about 10,000 units. The water soluble photo-polymerization initiator, 2hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)N,N,N-trimethyl-l-propanaminium chloride (QTX) (Ward Blenkinsop, Cheshire, England, UK) was dissolved into an aqueous solution of M9G or PNVP, according to the concentrations listed in Table 1. For comparison with QTX, mixtures containing CQ (Aldrich Chemical, Milwaukee, WI, USA) were investigated. The structural formulas of the components of primers are shown in Fig. 1. The general procedures for making the test samples were previously reported (Hayakawa et al., 1989). Bovine anterior teeth were stored at -70°C after extraction from the mandibles. Their enamel was removed using No. 100 waterproof abrasive paper (Sankyo Rikagaku, Tokyo, Japan), and a flat dentin surface was prepared by wet grinding, using No. 800 and No. 1000 grinding stones (King, Tokyo, Japan) under running water. The dentin surface was pretreated with one of three procedures: 1) neutralized 0.5 M EDTA for 60 s; 2) 10% citric acid, 10% citric acid - 3% FeC13 (10-3); or 3) 10% phosphoric acid solution for 30 s. After washing and drying, the primer was applied to the pretreated dentin surface for 60 s. Any excess amount of primer was removed with compressed air for 10 s. A silicone ring, 3.2 mm diameter x 3.2 mm thick, was placed on the primed dentin surface. Then bonding agent (Clearfil Photobond, Kuraray, Osaka, Japan) was applied inside the ring and was irradiated for 10 s with Quick Light (Morita, Tokyo, Japan). The ring was filled with composite (Photoclearfil A, Kuraray) and irradiated for 40 s. Specimens without any primer treatment were also prepared. After curing the composite, the silicone ring was removed, and each specimen was stored in water at 37°C for 24 h. A brass attachment was fixed to the upper part of the cured resin and the tensile bond strength was measured with a universal testing machine (TOM10000X, Shinkoh, Tokyo, Japan) at a cross head speed of 2 mm/min. The data were tested for significant differences by an analysis of variance and by Scheff~'s test for a multiple comparison among the means (p = 0.05). The same general procedure was used to test the bond
Dental Materials~November 1992 351
CH3 CH2=C.C.(OCH2CH2)9.OCH 3 ,
--(- CH2-CH I "°
o
Primer MgG aq.
M9G
I
TABLE 1" COMPOSITIONOF PRIMERS
,o,
PNVP
el.3 "0"3
~,,~S~CH
3 OH OH3 QTX
OH3
1"
CH3~CHI~.,3CH3
c,"
Fig. 1. Structuralformulaeof componentsof dentin primers.
strength to the bovine enamel. The bovine enamel surface was polished and ground using No. 800 and No. 1000 grinding stones, under running water and then pretreated with 0.5 M EDTA or 40% phosphoric acid for 60 s. After washing and drying, PNVP aqueous or QTX(1)/PNVP was applied for 60 s. After drying with compressed air, the bonding agent and composite were applied as described above. The tensile bond strength after 24 h immersion in 37°C water was also measured. The data were also tested for significant differences by an analysis of variance and by Scheff~'s test for a multiple comparison among the means (p = 0.05). RESULTS
Table 2 presents the results of the tensile bond strengths between the composite and dentin pretreated with EDTA. Without any primer application, the mean bond strength was 2.8 MPa. Although the mean bond strengths were slightly increased by the addition of QTX and M9G aqueous solution, there were no significant differences among the bond strengths. Most of the bond failures were at the interface between the dentin and resin. The primer, consisting of 1% QTX added to PNVP aqueous solution, produced the highest mean value; with this primer, the bond failures were a mixture of dentin fracture and fracture at the interface between the dentin and resin. Subsequently, the effectiveness of QTX(1)/PNVP on the dentin pretreated with several kinds of acids was examined. The results are presented in Table 3. No remarkable increase in the bond strengths was evident in dentin pretreated with acids, compared to the bond strength obtained when the QTX(1)/PNVP primer was used on dentin pretreated with EDTA. Table 4 presents the results of tensile bond strengths between composite and enamel pretreated with EDTA or phosphoric acid. On enamel pretreated with EDTA, QTX(1)/ PNVP application significantly increased the mean bond strengths, which were almost equal to those of phosphoric acid etching. DISCUSSION
The strong adhesion between restorative resins and dentin is thought to occur due to the diffusion and polymerization of monomers in the dentin. Shibuya and Hayakawa (1991) reported that M9G and PNVP improved the adhesion of chemical-cured resin to dentin pretreated with EDTA. In this 352 Hayakawa & Horie/Effect of water soluble photoinitiator
50% MgG aqueous solution
CQ(0.5)/M9G
0.5% CQ + 50% M9G aqueoussolution
QTX(0.5)/M9G
0.5% QTX + 50% MgG aqueoussolution
QTX(1)/M9G
1% QTX + 50% M9G aqueous solution
QTX(2)/M9G
2% QTX + 50% M9G aqueous solution
PNVP aq.
CQ
Composition
35% PNVP aqueous solution
CQ(0.3)/PNVP
0.3% CQ + 35% PNVP aqueous solution
QTX(0.5)/PNVP
0.5% QTX + 35% PNVP aqueous solution
QTX(1)/PNVP
1% QTX + 35% PNVP aqueous solution
QTX(2)/PNVP
2% QTX + 35% PNVP aqueous solution
TABLE 2: EFFECTOF PRIMERS ON BOND STRENGTH TO DENTIN PRETREATED WITH EDTA Primers ..... M9G aq. CQ(0.5)/M9G QTX(0.5)/M9G QTX(1)/M9G QTX(2)/M9G PNVP aq. CQ(0.3)/PNVP QTX(0.5)/PNVP QTX(1)/PNVP QTX(2)/PNVP
Tensile Bond Strength (MPa) Mean _+SD 2.8 _+1.3 5.4 _+2.3 6.6 + 1.6 6.3 + 1.6 6.1 + 2.9 7.0 + 3.6 5.3 + 1.7 3.6 + 0.9 7.0 _+3.3 8.6 + 3.5 4.6 __.1.9 ]
Numberof Specimens 14 9 6 6 12 10 6 6 7 10 11
Vertical lines indicate no statisticaldifference. TABLE 3: EFFECT OF QTX(1)/PNVPON BOND STRENGTH TO DENTIN PRETREATED WITH ACID
Acid
Primer
Tensile Bond Strength (MPa) Mean __.SD
10% Citric Acid
..... QTX(1)/PNVP ..... PTX(1)/PNVP ..... QTX(1)/PNVP
3.8 + 1.5 5.2 + 2.2 4.4 + 2.1 6.6 + 3.1 3.9 _+2.7 5.8 + 1.4
10- 3 10% PhosphoricAcid
Numberof Specimens 6 12 6 12 9 10
Vertical lines indicate no statistical difference between the specimens that received and did not receivethe primer when the same pretreatmentreagent was used. TABLE 4: EFFECT OF QTX(1)/PNVPON BOND STRENGTH TO ENAMEL
Pretreatment EDTA EDTA EDTA Phosphoric Acid Phosphoric Acid Phosphoric A c i d
Primer ..... PNVP aq. QTX(1)/PNVP ..... PNVP aq. QTX(1)/PNVP
Tensile Bond Strength (MPa) Mean _+SD 8.3 _+3.5 10.4 + 3.5 14.0 + 3.1 16.1 + 3.9 14.8 _+4.3 16.5 + 5.4
Numberof Specimens 7 7 9 10 7 7
Vertical lines indicate no statistical difference between the specimens that received and did not receivethe primer when the same pretreatmentreagent was used.
study, it was expected that M9G and PNVP promoted the diffusion of monomers into dentin, and QTX sufficiently initiated the polymerization of diffused monomers in dentin. QTX has an absorption maximum at 402 nm and is used for direct silk screen photoemulsion (Davis et al., 1986). Contrary to our expectations, the copolymerization between M9G and monomers of the bonding agent did not occur due to the preferential homopolymerization of M9G. QTX initiated the polymerization of the diffused monomers of bonding agent into dentin when it was combined with PNVP. Sugizaki (1991) reported that the bond strength of Photobond to dentin pretreated with EDTA was increased about 1.6 times by SA(N-methacryloyl-5-aminosalicylic acid) priming. In this study, the bond strength was increased about 3 times by QTX(1)/PNVP priming. Hayakawa et al., (1989) reported that acid etching produced deeper decalcified dentin layers than EDTA pretreatment. Therefore, the interpenetration of PNVP into acidetched dentin was not sufficient, and the bond strengths were not improved by QTX(1)/PNVP priming. On the enamel pretreated with EDTA, QTX(1)/PNVP was also effective for improving the bond strengths. It was presumed that QTX improved the degree of conversion of the polymerization of the bonding agent at the subsurface of enamel. The effects of QTX(1)/PNVP were not obvious on enamel etched with phosphoric acid because of the large etching effect of phosphoric acid which produced the mechanical interlocking of the resin tags. Imai et al., (1991) pointed out that the interfacial initiation of polymerization is the key to strong adhesion of dental resin to dentin. In this study, the increased adhesion bond strengths were thought to be due to the polymerization of diffused monomers inside the dentin or subsurface of enamel by using QTX. QTX is a useful photoinitiator of the polymerization in the presence of water and has a possibility for wider applications, for example, in dental resins or cements.
ACKNOWLEDGEMENTS We are grateful to Mr. Kidokoro, Dainippon Ink and Chemical, for his offer of QTX. This study was supported in part by Grantin-Aid for Scientific Research 1991(A-03771464), from the Ministry of Education, Science, and Culture, Japan. Received March 21, 1992/Accepted October 22, 1992 Address correspondence and reprint requests to: T. Hayakawa Department of Dental Materials Nihon University School of Dentistry at Matsudo 2-870-1 Sakaecho Nishi Matsudo Chiba 271, Japan
REFERENCES Asmussen E, Bowen RL (1987). Effect of acidic pretreatment on adhesion to dentin mediated by Gluma. J Dent Res 66:1386-1388. Bowen RL, Eichmiller FC, MarjenhoffWA, Rupp NW (1989). Adhesive bonding of composites. J A m Coll Dent 56:10-13. Chigira H, Manabe A, Itoh K, Wakumoto S, Hayakawa T (1989). Efficacyofglycerylmethacrylate as a dentin primer. Dent Mater J 8:194-199. Chigira H, Itoh K, Wakumoto S (1991). Marginal adaptation of nine commercial intermediate resins. Dent Mater 7: 103-106. Davis MJ, Grawne G, Green PN, Green WA (1986). Spec Chem 6:3-12. Hayakawa T, Endo H, Nagatsuka A, Horie K (1989). Studies on adhesion to tooth substrate. VI. The adhesion ofcomposite resin mediated by the dentin primer containing MTYA. Dent Mater J 8:155-163. Imai Y, Kadoma Y, Kojima K, Akimoto T, Ikakura K, Ohta T ( 1991). Importance ofpolymerization initiator systems and interfacial initiation of polymerization in adhesive bonding of resin to dentin. J Dent Res 70:1088-1091. Manabe A, Katsuno K, Itoh K, Wakumoto S, Miyasaka T (1991). Bonding efficacy of erythritol methacrylate solutions as dentin primers. JDent Res 70:1294-1298. Munksgaard EC (1990). Amine-induced polymerization of aqueous HEMA/aldehyde during action as a dentin bonding agent. J Dent Res 69:1236-1239. Munksgaard EC, Asmussen E (1984). Bond strength between dentin and restorative resins mediated by mixtures of HEMA and glutaraldehyde. J Dent Res 63:1087-1089. Nakabayashi N (1985). Bonding of restorative materials to dentin: the present status in Japan. Int Dent J 35:145-154. Nakabayashi N, Takarada K (1992). Effect of HEMA on bonding to dentin. Dent Mater 8:125-130. Nikaido T (1989). Formulation ofphotocurable bonding liner and adhesion to dentin: Effect of photoinitiator, monomer, and photoirradiation. J Jpn Dent Mater 8:862-876. Shibuya I, Hayakawa T (1991). Studies on adhesion between the composite resin and the dentin- effect of various dentin primers. J Jpn Dent Mater 10:566-575. Sugizaki J (1991). The effect of the various primers on the dentin adhesion of resin composites - SEM and TEM observations of the resin impregnated layer and adhesion promoting effect of the primers. J Jpn J Conserv Dent 34:228-265. Tagami J, Hosoda H, Imai Y, Masuhara E (1987). An evaluation of a new adhesive liner as an adhesive promoter and a desensitizer on hypersensitive dentin. Dent Mater J 6:201-208.
Dental Materials~November 1992 353
