Effect of water sorption and thermal stress on cavity adaptation of dental composites T. Koike T. Hasegawa A. Manabe K. Itob S. Wakumoto
Department of Operative Dentistry School of Dentistry Showa University 2-1-1 Kitasenzoku, Ohta-Ku Tokyo 145, Japan Received August 25, 1989 Accepted March 7, 1990 Dent Mater 6:178-180, July, 1990
Abstract-The effect of water sorption of composite and thermal stress on the marginal adaptation to the dentin cavity wall was evaluated by measurement of the gap width between composite fillings and the dentin cavity wall. The wall of a cylindrical dentin cavity prepared in the proximal surface of extracted human molars was cleaned with neutralized 0.5 M EDTA and pre-treated with one of three experimental dentin primers [35% hydroxyethyl methacrylate (HEMA), 35% HEMA containing 5% glutaraldehyde, and 35% glyceryl methacrylate]. A lightactivated composite (Silux, 3M Co., St. Paul, MN) was used to fill the cavity after application of a bonding agent (Clearfil New Bond, Kuraray Co., Osaka, Japan). The marginal gap width was measured after the specimens were immersed in water and thermal-cycled. The initial contraction gap of the tested bonding systems was closed completely by the water sorption of the composite for six hours, and such a marginal adaptation was not interrupted by 60 thermal cycles between 10 and 45°0. Among the dentin primers tested, only the 35% aqueous solution of glyceryl methacrylate mediated gap-free fillings in all specimens.
he adaptation of a composite to the dentin cavity wall is affected by the efficacy of the dentin bonding system employed, although most of the marketed bonding systerns are not able to overcome the contraction stress of the composite during polymerization (Yanagawa et al., 1989; Munksgaard et al., 1984, 1985; Kato et al., 1988; Itoh and Wakumoto, 1987). Such a contraction stress produces a gap between the dentin cavity wall and the composite which may be closed by subs e q u e n t w a t e r s o r p t i o n of the composite (Asmussen, 1975). This volume change is considered to be desirable to improve the adaptation of the composite to the cavity wall, although the mechanical properties may deteriorate (SSderholm et al., 1984). It has previously been eraphasized by Asmussen (Asmussen and J~rgensen, 1972) that the initial contraction gap between a composite and the dentin cavity wall could not be closed by water sorption after the specimens were stored in water for up to 32 days. Therefore, he suggested that polishing of the composite restoration should be postponed until hygroscopic expansion closed the contraction gap. This is because the portion of the margin that is not supported by the cavity wall will easily fracture during polishing. Due to enamel etching and the development of dentin bonding systems, the adaptation of the composite to both enamel and the dentin cavity wall has been improved significantly, and some contraction-gap-free systems have been reported (Yanagawa et al., 1989; Munksgaard et al., 1985; Chigira et al., 1989). Hansen and Asmussen recently reported that the marginal gap width between the composite and the dentin cavity wall was reduced by immersion of the specimen in water for only 60 rain (Hansen and Asmussen, 1988). The purpose of the present study
T
178 KOIKE et al./WATER SORPTION AND THERMAL STRESS OF COMPOSITE
was to evaluate the effect of volume change of composite caused by water sorption on adaptation to the dentin cavity wall. MATERIALS AND METHODS
Measurement of the Volume Expansion of Composite by Water Sorption. - The cavity adaptation of a visible-light-cured composite (Silux) was evaluated by measurement of the wall-to-wall contraction gap in cylindrical dentin cavities. The proximal enamel of freshly extracted human molars was removed on wet carborundum paper, grit number 220, and a cylindrical cavity 3 mm in diameter and 1.5 mm in depth was prepared in the exposed dentin. The cavity wall including the surrounding dentin surface was cleaned with neutralized 0.5 M EDTA for 60 s and then rinsed and dried thoroughly. F o r the control, a cavity was slightly overfilled with a visible-lightactivated composite without use of a dentin primer or an intermediate resin. The resin surface was covered with a plastic matrix under gentle pressure on a glass plate and irradiated by a visible-light-lamp unit (Quick Light, Morita, Kyoto, Japan) for 40 s. The specimens were then stored in water at room temperature (24 _ 1°C). After 0.5, 24, and 48 hours of storage in water, the cavity margin was exposed by being polished on wet carborundum paper followed by an alumina slurry on linen. The width of the contraction gap every 45° along the cavity margin was measured by use of a screw micrometer (Eyepiece Digital, Leitz, Wetzlar, W. Germany) mounted on the ocular lens of a light microscope (Metaloplan, Leitz, Wetzlar, W. Germany) at a magnification of 1024 x. The maximum contraction of the composite was indicated in percent of the cavity diameter as de-
scribed in a previous p a p e r (J0rgensen et al., 1985). Ten specimens were measured in each group. In the experimental groups, the dentin was cleaned with EDTA and p r e - t r e a t e d with one of t h r e e experimental dentin primers: aqueous solution of 35% h y d r o x y e t h y t m e t h a c r y l a t e (HEMA), aqueous mixture of 35% HEMA and 5% glutaraldehyde, or aqueous solution of 35% glyceryl methacrylate (GM) for 60 s. The cavity was then dried by a blast of compressed air, and a commercial dentin bonding agent (Clearfil New Bond) was applied prior to the composite filling. The irradiation and the measurement of the contraction gap was performed using the same method as that of the control group. The width of the contraction gap was measured after one-, two-, four-, and six-hour storage in water. Ten specimens were measured in each group.
Measurement of the Marginal Gap after Thermal Cycling.- The effect of thermal stress on the marginal adaptation of the composite was evaluated by measurement of the contraction gap after thermal cycling. The specimens were prepared by the same method as that employed in the abovementioned experimental groups and stored in water at a temperature of 10°C for one, two, four, and six h. Specimens were then cycled thermally 60 times by being immersed in two baths filled with water at temperatures of 10 and 45°C for 30 s, respectively. Immediately after the thermal cycling, the width of the contraction gap was measured by the same method as described above. Ten specimens were prepared in each group. RESULTS The specimens in the control group, in which neither dentin primers nor dentin bonding agents were used, showed that the initial contraction gap was closed completely by water sorption after 48 h (Table 1). Use of the dentin primers and the dentin bonding agent significantly reduced the initial contraction gap. In the group representing the experiments with GM, a complete seal was obrained in all the tested specimens one h after polymerization of the com-
TABLE 1 WALL-TO-WALL POLYMERIZATIONCONTRACTIONOF LIGHT-ACTIVATED COMPOSITEIN CYLINDRICAL DENTIN CAVITIES (%) Storage Mean Range 0.5 hour 0.177 (0.133-0.231) 24 hours 0.026 ( 0 -0.047) 48 hours 0 ( 0 ) n=10. *GF: Number of gap-free specimens. Dentin cavity wall was cleaned with 0.5 M EDTAfor 60 s. Specimens were stored in water at room temperature of 24°C before measurement.
GF* [0] [3] [10]
TABLE 2 WALL-TO-WALL POLYMERIZATIONCONTRACTION OF LIGHT-CURED COMPOSITEIN CYLINDRICAL DENTIN CAVITIES (%) Storage* 35% HEMA** 35% HEMA ÷ 5% CA*** 35% GM**** I hour 0.027 (0-0.077) [ 5] 0.007 (0-0.074) [ g] 0 (0) [10] 2 hours 0.005 (0-0.045) [ 9] 0.003 (0-0.031) [ 9] 0 (0) [10] 4 hours 0.002 (0-0.020) [ 9] 0 ( 0 ) [10] 0 (0) [10] 6hours 0 ( 0 )[10] 0 ( 0 )[10] 0(0)[10] Mean, range in ( ) , and number of gap-free specimens in [ ]. n=10. *Storage: Storage time of specimens in water at a temperature of 10°C before measurement. **HEMA: Hydroxyethyl methacrylate. ***CA: Glutaraldehyde. ****GM: Glyceryl methacrylate. The dentin cavity wall was cleansed with neutralized 0.5 M EDTA for 60 s and treated with listed dentin primers, and a light-activated composite was used as filling mediated by a dentin bonding agent. TABLE 3 WALL-TO-WALL POLYMERIZATIONCONTRACTIONOF LIGHT-CURED COMPOSITE IN CYLINDRICAL DENTIN CAVITIESAFTER THERMAL CYCLING (%) Storage* 35% HEMA 35% HEMA ÷ 5% GA 35% GM 1 hour/TC** 0.018 (0-0.130) [7 ] 0.007 (0-0.044) [8 ] 0 (0) [10] 2 hours/TC 0.012 (0-0.075) [8 ] 0 ( 0 )[10] 0 (0) [10] 4 hours/lC 0.002 (0-0.020) [9 ] 0 ( 0 )[10] 0 (0) [10] 6hours/TC 0 ( 0 )[10] 0 ( 0 )[10] 0(0)[10] Mean, range in ( ) , and number of gap-free specimens in [ ]. n =10. *Storage: Storage time in water before thermal cycling. **T/C: Thermally cycled 60 times between thermostated baths at 10 and 45°C for 30 s at each temperature.
posite. Furthermore, such tight adaptation mediated by this dentin primer was not destroyed after thermal cycling (Tables 2, 3). In two other expeI~nental groups, the initial contraction gap was closed rapidly, and after six hours of storage in water and thermal-cycling, no marginal gap was observed (Table 3). DISCUSSION
The primary requirement for a dentin bonding system is to obtain complete adaptation between the dentin and the resin materials just after polymerization of the composite. Most of the bonding systems available on the market, however, cannot over-
come the contraction stress of the composite. Therefore, volumetric expansion of the composite by water sorption is required to close the initial contraction gap, although such a marginal seal is not considered to be consistent with bonding but only with mechanical contact between the dentin cavity wall and the resin. The light-activated composite employed in this study exhibited volumetric expansion in the dentin cavity without any dentin primers or dentin bonding agents after up to 48 h of storage in water. The storage time required to close the contraction gap was reduced when the experimental dentin bonding system was applied,
Dental Materials/J~ely 5990
179
and it was supposed that the composite continued to expand elastically. Therefore, elastic stress in the resin toward the dentin cavity wall might have been caused by water sorption after the initial contraction gap was closed. Such elastic stress may resist marginal gap formation when subjected to thermal contraction stress. In this study, it was revealed that the marginal adaptation of the composite to the dentin cavity wall, which was mediated by a highly efficient dentin bonding system, was not destroyed by the contraction stress of thermal-cycling between 10 and 45°C after six h of storage in water. The storage time required to close the initial contraction gap evaluated in this study was significantly reduced compared with that in a previous r e p o r t ( A s m u s s e n and J¢rgensen, 1972). In addition, it was possible to conclude that a dentin bonding system composed of a dentin cleanser of 0.5 M EDTA, a dentin primer of 35% aqueous solution of GM, a commercial dentin bonding
180
agent, and a light-activated composite exhibited a bonding efficacy high enough to compensate for both the polymerization and the thermal contraction stress of the composite.
REFERENCES ASMUSSEN, E. (1975): Composite Restorative Resins. Composition versus Wall-to-Wall Polymerization Contraction, Acta Odontol Scand 33:337-344. ASMUSSEN, E. and J¢RGENSEN, K.D. (1972): A Microscopic Investigation of the Adaptation of Some Plastic Filling Materials to Dentin Cavity Walls, Acta Odontol Scand 30:3-21. CHIGIRA, H.; MANABE, A.; ITOH, K.; WAKUMOTO, S.; and HAYAgAWA,T. (1989): Efficacy of Glyceryl methacrylate as a Dentin Primer, Dent Mater J 8:194-199. HANSEN, E.K. and ASMUSSEN,E. (1988): Effect of Postponed Polishing on Marginal Adaptation of Resin used with Dentin-bonding Agent, Scand J Dent Res 96:260-264. ITOH, K. and WAKUMOTO,S. (1987): Momentary Pretreatment by 35% HEMA Solution Combined with Five Marketed Bonding Agents, Dent Mater J 6:15-21.
KOIKE et al./WATER SORPTION A N D T H E R M A L STRESS OF COMPOSITE
J~RGENSEN,K.D.; ITOH, K.; MUNKSGAARD, E.C.; and ASMUSSEN,E. (1985): Composite Wall-to-Wall Polymerization Contraction in Dentin Cavities Treated with Various Bonding Agents, Scand J Dent Res 93:276-279. KATO, H.; ITOH, K.; and WAKUMOTO,S. (1988): The Bonding Efficiency of Chemically and Visible Light Cured Composite Systems, Dent Mater J 7:13-18. MUNKSGAARD,E.C.; HANSEN, E.K.; and ASMUSSEN, E. (1984): Effect of Five Adhesives on Resin in Dentin Cavities, Scand J Dent Res 92:544-548. MUNKSGAARD, E.C.; ITOH, K.; ASMUSSEN, E.; and J¢RGENSEN, K.D. (1985): Effect of Combining Dentin Bonding Agents, Scand J Dent Res 93:377-380. SODERHOLM, K.J.; ZIGAN, M.; RAGAN, M.; FISCHLSCHWEIGER, W.; and BERGMAN,M. (1984): Hydrolytic Degradation of Dental Composites, J Dent Res 63:1248-1254. YANAGAWA, T.; ITOH, K.; and WAKUMOTO, S. (1989): A Study of Dentin Adhesive Containing 4META-The Effect of Cleanser on Bonding Efficacy,Dent Mater J 8:200205.
Department of Operative Dentistry School of Dentistry Showa University 2-1-1 Kitasenzoku, Ohta-Ku Tokyo 145, Japan Received August 25, 1989 Accepted March 7, 1990 Dent Mater 6:178-180, July, 1990
Abstract-The effect of water sorption of composite and thermal stress on the marginal adaptation to the dentin cavity wall was evaluated by measurement of the gap width between composite fillings and the dentin cavity wall. The wall of a cylindrical dentin cavity prepared in the proximal surface of extracted human molars was cleaned with neutralized 0.5 M EDTA and pre-treated with one of three experimental dentin primers [35% hydroxyethyl methacrylate (HEMA), 35% HEMA containing 5% glutaraldehyde, and 35% glyceryl methacrylate]. A lightactivated composite (Silux, 3M Co., St. Paul, MN) was used to fill the cavity after application of a bonding agent (Clearfil New Bond, Kuraray Co., Osaka, Japan). The marginal gap width was measured after the specimens were immersed in water and thermal-cycled. The initial contraction gap of the tested bonding systems was closed completely by the water sorption of the composite for six hours, and such a marginal adaptation was not interrupted by 60 thermal cycles between 10 and 45°0. Among the dentin primers tested, only the 35% aqueous solution of glyceryl methacrylate mediated gap-free fillings in all specimens.
he adaptation of a composite to the dentin cavity wall is affected by the efficacy of the dentin bonding system employed, although most of the marketed bonding systerns are not able to overcome the contraction stress of the composite during polymerization (Yanagawa et al., 1989; Munksgaard et al., 1984, 1985; Kato et al., 1988; Itoh and Wakumoto, 1987). Such a contraction stress produces a gap between the dentin cavity wall and the composite which may be closed by subs e q u e n t w a t e r s o r p t i o n of the composite (Asmussen, 1975). This volume change is considered to be desirable to improve the adaptation of the composite to the cavity wall, although the mechanical properties may deteriorate (SSderholm et al., 1984). It has previously been eraphasized by Asmussen (Asmussen and J~rgensen, 1972) that the initial contraction gap between a composite and the dentin cavity wall could not be closed by water sorption after the specimens were stored in water for up to 32 days. Therefore, he suggested that polishing of the composite restoration should be postponed until hygroscopic expansion closed the contraction gap. This is because the portion of the margin that is not supported by the cavity wall will easily fracture during polishing. Due to enamel etching and the development of dentin bonding systems, the adaptation of the composite to both enamel and the dentin cavity wall has been improved significantly, and some contraction-gap-free systems have been reported (Yanagawa et al., 1989; Munksgaard et al., 1985; Chigira et al., 1989). Hansen and Asmussen recently reported that the marginal gap width between the composite and the dentin cavity wall was reduced by immersion of the specimen in water for only 60 rain (Hansen and Asmussen, 1988). The purpose of the present study
T
178 KOIKE et al./WATER SORPTION AND THERMAL STRESS OF COMPOSITE
was to evaluate the effect of volume change of composite caused by water sorption on adaptation to the dentin cavity wall. MATERIALS AND METHODS
Measurement of the Volume Expansion of Composite by Water Sorption. - The cavity adaptation of a visible-light-cured composite (Silux) was evaluated by measurement of the wall-to-wall contraction gap in cylindrical dentin cavities. The proximal enamel of freshly extracted human molars was removed on wet carborundum paper, grit number 220, and a cylindrical cavity 3 mm in diameter and 1.5 mm in depth was prepared in the exposed dentin. The cavity wall including the surrounding dentin surface was cleaned with neutralized 0.5 M EDTA for 60 s and then rinsed and dried thoroughly. F o r the control, a cavity was slightly overfilled with a visible-lightactivated composite without use of a dentin primer or an intermediate resin. The resin surface was covered with a plastic matrix under gentle pressure on a glass plate and irradiated by a visible-light-lamp unit (Quick Light, Morita, Kyoto, Japan) for 40 s. The specimens were then stored in water at room temperature (24 _ 1°C). After 0.5, 24, and 48 hours of storage in water, the cavity margin was exposed by being polished on wet carborundum paper followed by an alumina slurry on linen. The width of the contraction gap every 45° along the cavity margin was measured by use of a screw micrometer (Eyepiece Digital, Leitz, Wetzlar, W. Germany) mounted on the ocular lens of a light microscope (Metaloplan, Leitz, Wetzlar, W. Germany) at a magnification of 1024 x. The maximum contraction of the composite was indicated in percent of the cavity diameter as de-
scribed in a previous p a p e r (J0rgensen et al., 1985). Ten specimens were measured in each group. In the experimental groups, the dentin was cleaned with EDTA and p r e - t r e a t e d with one of t h r e e experimental dentin primers: aqueous solution of 35% h y d r o x y e t h y t m e t h a c r y l a t e (HEMA), aqueous mixture of 35% HEMA and 5% glutaraldehyde, or aqueous solution of 35% glyceryl methacrylate (GM) for 60 s. The cavity was then dried by a blast of compressed air, and a commercial dentin bonding agent (Clearfil New Bond) was applied prior to the composite filling. The irradiation and the measurement of the contraction gap was performed using the same method as that of the control group. The width of the contraction gap was measured after one-, two-, four-, and six-hour storage in water. Ten specimens were measured in each group.
Measurement of the Marginal Gap after Thermal Cycling.- The effect of thermal stress on the marginal adaptation of the composite was evaluated by measurement of the contraction gap after thermal cycling. The specimens were prepared by the same method as that employed in the abovementioned experimental groups and stored in water at a temperature of 10°C for one, two, four, and six h. Specimens were then cycled thermally 60 times by being immersed in two baths filled with water at temperatures of 10 and 45°C for 30 s, respectively. Immediately after the thermal cycling, the width of the contraction gap was measured by the same method as described above. Ten specimens were prepared in each group. RESULTS The specimens in the control group, in which neither dentin primers nor dentin bonding agents were used, showed that the initial contraction gap was closed completely by water sorption after 48 h (Table 1). Use of the dentin primers and the dentin bonding agent significantly reduced the initial contraction gap. In the group representing the experiments with GM, a complete seal was obrained in all the tested specimens one h after polymerization of the com-
TABLE 1 WALL-TO-WALL POLYMERIZATIONCONTRACTIONOF LIGHT-ACTIVATED COMPOSITEIN CYLINDRICAL DENTIN CAVITIES (%) Storage Mean Range 0.5 hour 0.177 (0.133-0.231) 24 hours 0.026 ( 0 -0.047) 48 hours 0 ( 0 ) n=10. *GF: Number of gap-free specimens. Dentin cavity wall was cleaned with 0.5 M EDTAfor 60 s. Specimens were stored in water at room temperature of 24°C before measurement.
GF* [0] [3] [10]
TABLE 2 WALL-TO-WALL POLYMERIZATIONCONTRACTION OF LIGHT-CURED COMPOSITEIN CYLINDRICAL DENTIN CAVITIES (%) Storage* 35% HEMA** 35% HEMA ÷ 5% CA*** 35% GM**** I hour 0.027 (0-0.077) [ 5] 0.007 (0-0.074) [ g] 0 (0) [10] 2 hours 0.005 (0-0.045) [ 9] 0.003 (0-0.031) [ 9] 0 (0) [10] 4 hours 0.002 (0-0.020) [ 9] 0 ( 0 ) [10] 0 (0) [10] 6hours 0 ( 0 )[10] 0 ( 0 )[10] 0(0)[10] Mean, range in ( ) , and number of gap-free specimens in [ ]. n=10. *Storage: Storage time of specimens in water at a temperature of 10°C before measurement. **HEMA: Hydroxyethyl methacrylate. ***CA: Glutaraldehyde. ****GM: Glyceryl methacrylate. The dentin cavity wall was cleansed with neutralized 0.5 M EDTA for 60 s and treated with listed dentin primers, and a light-activated composite was used as filling mediated by a dentin bonding agent. TABLE 3 WALL-TO-WALL POLYMERIZATIONCONTRACTIONOF LIGHT-CURED COMPOSITE IN CYLINDRICAL DENTIN CAVITIESAFTER THERMAL CYCLING (%) Storage* 35% HEMA 35% HEMA ÷ 5% GA 35% GM 1 hour/TC** 0.018 (0-0.130) [7 ] 0.007 (0-0.044) [8 ] 0 (0) [10] 2 hours/TC 0.012 (0-0.075) [8 ] 0 ( 0 )[10] 0 (0) [10] 4 hours/lC 0.002 (0-0.020) [9 ] 0 ( 0 )[10] 0 (0) [10] 6hours/TC 0 ( 0 )[10] 0 ( 0 )[10] 0(0)[10] Mean, range in ( ) , and number of gap-free specimens in [ ]. n =10. *Storage: Storage time in water before thermal cycling. **T/C: Thermally cycled 60 times between thermostated baths at 10 and 45°C for 30 s at each temperature.
posite. Furthermore, such tight adaptation mediated by this dentin primer was not destroyed after thermal cycling (Tables 2, 3). In two other expeI~nental groups, the initial contraction gap was closed rapidly, and after six hours of storage in water and thermal-cycling, no marginal gap was observed (Table 3). DISCUSSION
The primary requirement for a dentin bonding system is to obtain complete adaptation between the dentin and the resin materials just after polymerization of the composite. Most of the bonding systems available on the market, however, cannot over-
come the contraction stress of the composite. Therefore, volumetric expansion of the composite by water sorption is required to close the initial contraction gap, although such a marginal seal is not considered to be consistent with bonding but only with mechanical contact between the dentin cavity wall and the resin. The light-activated composite employed in this study exhibited volumetric expansion in the dentin cavity without any dentin primers or dentin bonding agents after up to 48 h of storage in water. The storage time required to close the contraction gap was reduced when the experimental dentin bonding system was applied,
Dental Materials/J~ely 5990
179
and it was supposed that the composite continued to expand elastically. Therefore, elastic stress in the resin toward the dentin cavity wall might have been caused by water sorption after the initial contraction gap was closed. Such elastic stress may resist marginal gap formation when subjected to thermal contraction stress. In this study, it was revealed that the marginal adaptation of the composite to the dentin cavity wall, which was mediated by a highly efficient dentin bonding system, was not destroyed by the contraction stress of thermal-cycling between 10 and 45°C after six h of storage in water. The storage time required to close the initial contraction gap evaluated in this study was significantly reduced compared with that in a previous r e p o r t ( A s m u s s e n and J¢rgensen, 1972). In addition, it was possible to conclude that a dentin bonding system composed of a dentin cleanser of 0.5 M EDTA, a dentin primer of 35% aqueous solution of GM, a commercial dentin bonding
180
agent, and a light-activated composite exhibited a bonding efficacy high enough to compensate for both the polymerization and the thermal contraction stress of the composite.
REFERENCES ASMUSSEN, E. (1975): Composite Restorative Resins. Composition versus Wall-to-Wall Polymerization Contraction, Acta Odontol Scand 33:337-344. ASMUSSEN, E. and J¢RGENSEN, K.D. (1972): A Microscopic Investigation of the Adaptation of Some Plastic Filling Materials to Dentin Cavity Walls, Acta Odontol Scand 30:3-21. CHIGIRA, H.; MANABE, A.; ITOH, K.; WAKUMOTO, S.; and HAYAgAWA,T. (1989): Efficacy of Glyceryl methacrylate as a Dentin Primer, Dent Mater J 8:194-199. HANSEN, E.K. and ASMUSSEN,E. (1988): Effect of Postponed Polishing on Marginal Adaptation of Resin used with Dentin-bonding Agent, Scand J Dent Res 96:260-264. ITOH, K. and WAKUMOTO,S. (1987): Momentary Pretreatment by 35% HEMA Solution Combined with Five Marketed Bonding Agents, Dent Mater J 6:15-21.
KOIKE et al./WATER SORPTION A N D T H E R M A L STRESS OF COMPOSITE
J~RGENSEN,K.D.; ITOH, K.; MUNKSGAARD, E.C.; and ASMUSSEN,E. (1985): Composite Wall-to-Wall Polymerization Contraction in Dentin Cavities Treated with Various Bonding Agents, Scand J Dent Res 93:276-279. KATO, H.; ITOH, K.; and WAKUMOTO,S. (1988): The Bonding Efficiency of Chemically and Visible Light Cured Composite Systems, Dent Mater J 7:13-18. MUNKSGAARD,E.C.; HANSEN, E.K.; and ASMUSSEN, E. (1984): Effect of Five Adhesives on Resin in Dentin Cavities, Scand J Dent Res 92:544-548. MUNKSGAARD, E.C.; ITOH, K.; ASMUSSEN, E.; and J¢RGENSEN, K.D. (1985): Effect of Combining Dentin Bonding Agents, Scand J Dent Res 93:377-380. SODERHOLM, K.J.; ZIGAN, M.; RAGAN, M.; FISCHLSCHWEIGER, W.; and BERGMAN,M. (1984): Hydrolytic Degradation of Dental Composites, J Dent Res 63:1248-1254. YANAGAWA, T.; ITOH, K.; and WAKUMOTO, S. (1989): A Study of Dentin Adhesive Containing 4META-The Effect of Cleanser on Bonding Efficacy,Dent Mater J 8:200205.
