- Email: [email protected]
Effect of glass-ionomer base on composite resin hardness
Effect of glass-ionomer base on composite resin hardness J.M. Berrong* R.L. Cooley E.S. Duke University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, Texas 78284-7914, USA Received September 11, 1987 Accepted March 1, 1988 *To whom correspondence and reprint requests should be addressed Dent Mater 5:38-40, January, 1989
Abstract-The effect of the glassmm, and 3 mm thicknesses were placed over glass-ionomer bases, and the microhardness of the external surface was compared with that of controls without a base. A significant reduction in surface hardness (p<0.05) was determined only for the 1-mm test specimens.
he use of glass-ionomer bases in conjunction with composite resins has been advocated. A technique has been described in which a veneer of composite resin filling material is placed over an etched glassionomer cement base in restoration of both anterior and posterior teeth. This laminated restoration is suggested by McLean et al. (1985) as a technique which overcomes the problem of establishing an adequate marginal seal in those Class V restorations ending in thin or irregular cervical tooth enamel. Histopathological pulpal changes observed after the placement of composite resin fillings (Goto and Jordan, 1972; Stanley et al., 1975; Macko et al., 1978) provide another rationale for using the composite-resin/glass-ionomer laminate (Jordan, 1986) in conservative restorations, since the glass ionomer has been found to be biocompatible with the dental pulp (Tobias et al., 1978; Kawahara et al., 1979; Yakushiji et al., 1979; Wilson and Prosser, 1982). Knight (1984) suggests the use of this technique in repairing worn surfaces of glass-ionomer restorations and f r a c t u r e d cusps of teeth, where esthetic considerations are paramount. Marshall et al. (1982) studied the effects of various bases on three brands of composite resin. They demonstrated that composite resin surfaces cured against a glass-ionomer base resulted in a decrease in hardness. The nonadjacent surface of the composite resin was not tested; therefore, the effect of a glass-ionomer base on this surface was not determined. This study was undertaken to examine the effect of the compositeresin/glass-ionomer-laminate technique on the hardness of the composite resin surface exposed to the oral environment.
T
MATERIALS AND METHODS Thirty, light-cured, composite resin test samples were used in this study. 38
Fifteen of these samples were placed and cured over glass-ionomer bases, while the other 15 served as controls which did not have a base material. The test specimens were made by placement of the composite material (Silux, Batch Number 5502, Universal Shade, 3M Dental Products, St. Paul, MN 55144) in a Teflon ring with an inside diameter of 10 mm. In order for the effect of the base material on v a r i o u s t h i c k n e s s e s of composite resin to be evaluated, Teflon rings were fabricated to create samples 1 mm, 2 mm, and 3 mm thick. Five controls and five test disks were made in the l-mm, 2-mm, and 3-mm Teflon rings. These three thicknesses permitted an evaluation of thickness on microhardness of the composite samples to be made. The controls, which had no base, were cured against a plastic block (Fig.). The composite samples with a base were formed by use of a plastic block containing a "well" in the center that measured 3 mm deep × 10 mm (Fig.). The "well" was filled with a glass-ionomer base (KetacBond, Batch Number 0010, ESPEPremier, Norristown, PA 19401), mixed according to manufacturer's instructions, allowed to set for four minutes, etched for 60 seconds with a phosphoric acid gel, rinsed with distilled water, and coated with a dual-cured bonding agent (Scotchbond Light Cured Dental Adhesive, 3M Dental Products, St. Paul, MN 55144), which was cured separately for 20 seconds. The Teflon ring was placed over the glass-ionomer base, filled with the composite resin, and cured with a visible-light-curing unit (Coe-Lite, Coe Laboratories, Chicago, IL 60658). In order to ensure minimum variability in the quality of cure, we exposed each sample to visible light for 40 seconds per 1 mm of resin thickness. This curing time was chosen based on a study by Swartz et al. (1983), who determined that 40 seconds of exposure to the light source satisfactorily cured both dark
BERRONG et al./EFFECT OF GLASS-IONOMER B A S E ON COMPOSITE R E S I N H A R D N E S S
Controls Composite Resin Plastic Block
Composite Samples Composite Resin 1 mm, 2mm, 3 m m
Plastic Block
J
Glass Ionomer
Fig. Plastic blocks and Teflon rings which were used to fabricate samples. Top: The composite samples were cured against the plastic to simulate absence of base, Bottom: The "well" in the plastic block was filled with a glass-ionomer base and then with the composite resin sample in three thicknesses cured over the base. and light shades of two composite resins to a depth which equaled or exceeded 1 mm. The cure time was 40 seconds for the l-mm sample, 80 seconds for the 2-mm sample, and 120 seconds for the 3-ram sample. Curing was performed in 40-second increments. The test specimens were stored as constructed in distilled water for seven days at 37°C. Each sample remained in contact with the base upon which it was constructed, while five m i c r o h a r d n e s s t e s t s were performed on the resin surface not adjacent to the base. Surface hardness was determined with a Micromet (Buehler, Inc., Evanston, IL 60204) microhardness tester, which gave measurements in microns. The micron measurements were converted to Knoop Hardness Numbers (KHN). RESULTS The mean Knoop Hardness Numbers for both the controls and test specimens are listed in the Table. We
obtained these mean scores by averaging the KHN from the five microhardness tests performed on each sample and then a v e r a g i n g each group. The mean Knoop Hardness Numbers for all three thicknesses of controls (l-ram, 2-mm, and 3-ram) were higher than the mean scores for the test samples with glass-ionomer bases. When the data were subjected to a two-way Analysis of Variance, there was a significant difference (p<0.05) between the microhardness of the controls and that of the test specimens, but no significant difference was found among the microhardnesses of the three thicknesses (l-ram, 2-ram, and 3-ram). A Duncan's Multiple Range Test indicated that there was a significant difference (p<0.05) in surface hardness between the l-mm control and the l-mm test specimens, but there were no significant differences between the controls and test specimens of the 2-mm and 3-mm samples.
TABLE
MEAN KNOOPHARDNESSNUMBER (KHN) OF COMPOSITESAMPLES Controls Mean KHN 1-mm 2-mm 3-mm * p < 0.05.
26.89* 25.73 26.66
S.D. 3.54 4.91 4.37
Test Specimens Mean KHN S.D. 20.35 24.65 23.51
4.05 3.24 3.10
DISCUSSION An earlier study by Marshall et al. (1982) demonstrated that glass-ionomer bases could result in a major reduction in the surface hardness of a composite resin. This reduction in surface hardness occurred on the surface in intimate contact with the glass-ionomer base. Color stability was also evaluated with calorimetric determinations, and it was found that one brand of composite resin exhibited a color change. The authors did not discuss what effect the reduction in internal surface hardness would have on the restorations' intra-oral serviceability. However, they did fred that the polyacrylic acid inhibited polymerization of the composite and would also plasticize set resin if allowed to remain in contact with it. This study found that the campusite resin surface remote from the glass-ionomer base had a significantly reduced surface hardness occurring in the l-mm-thick samples. However, there was no significant difference in surface hardness between 2-ram- and 3-mm-thick samples and that of the controls. The clinical significance of these findings has not been investigated; however, it would appear that glass ionomers would affect external surface hardness only in thin restorations (thickness, 1 mm or less). This may occur in Class II or Class V restorations in which the glass-ionomer base is extended or feathered out to or near the cavo-surface margin, resulting in a thin laminate of campusite resin material. Since surface hardness values are shown to be adversely affected, other properties-such as color stability, stain resistance, and wear resist a n c e - m a y be adversely affected, thus decreasing the longevity of the restoration. Further studies of these properties need to be conducted.
SUMMARY The effect of the glass-ionomer/composite-resin-laminate technique on the hardness of external composite resin surfaces was studied. The mean hardness of the 1-mm test specimens was significantly less than that of the l-ram controls. Surface hardness values for the 2-mm- and 3-mm-thick samples were not significantly different from those of their controls. Dental Materials~January 1989
39
REFERENCES GOTO, G. and JORDAN, R.E. (1972): Pulpal Response to Composite Resin Materials, J Prosthet Dent 28: 601-606. JORDAN, R.E. (1986): Esthetic Composite Bonding Techniques and Materials. Burlington, Ontario: B.C. Decker, Inc., pp. 228-230. KAWAHARA, H.; IMANISHI, Y.; and OSHINA, H. (1979): Biological Evaluation of Glass Ionomer Cements, J Dent Res 58: 1080-1086. KNIGHT, G.M. (1984): The Use of Adhesive Materials in the Conservative Restoration of Selected Posterior Teeth, AuNt Dent J 29: 324-331. MACKO, D.J.; RUTBERG, M.; and LANGELAND, g. (1978): Pulpal Re-
sponse to the Application of Phosphoric Acid to Dentin, Oral Surg Oral Med Oral Pathol 45: 930-946. MARSHALL, S.J.; MARSHALL, G.W.; and HARCOURT, J.K. (1982): The Influence of Various Cavity Bases on the Microhardness of Composites, AuNt Dent J 27: 291-295. MCLEAN, J.W.; PROSSER, H.J.; and WILSON, A.D. (1985): The Use of Glass Ionomer Cements in Bonding Composite Resins to Dentine, Br Dent J 158: 410-414. STANLEY, H.R.; GOING, R.E.; and CHAUNCEY,H.H. (1975): Human Pulp Response to Acid Pretreatment of Dentin and to Composite Restoration, J A m Dent Assoc 91: 817-825.
SWARTZ, M.L.; PHILLIPS, R.W.; and RHODES, B. (1983): Visible Light-activated Resins-Depth of Cure, J A m Dent Assoc 106: 634-637. TOBIAS, a.s.; BROWNE, R.M.; PLANT, C.G.; and INGRAM,D.Y. (1978): Pulpal Response to a Glass Ionomer Cement, Br Dent J 144: 345-350. WILSON, A.D. and PROSSER, H.J. (1982): Biocompatibility of the Glass Ionomer Cement, J Dent Assoc S Afr 37: 872879. YAKUSHIJI, M.; KINUMATSU, T.; FUCHINO, T.; and MACHIDA,Y. (1979): Effects of Glass Ionomer Cement on the Dental Pulp and Its Efficacy as a Base Material, Bull Tokyo Dent Coll 20: 47-59.
40 BERRONG et al./EFFECT OF GLASS-IONOMER BASE ON COMPOSITE RESIN HARDNESS
Abstract-The effect of the glassmm, and 3 mm thicknesses were placed over glass-ionomer bases, and the microhardness of the external surface was compared with that of controls without a base. A significant reduction in surface hardness (p<0.05) was determined only for the 1-mm test specimens.
he use of glass-ionomer bases in conjunction with composite resins has been advocated. A technique has been described in which a veneer of composite resin filling material is placed over an etched glassionomer cement base in restoration of both anterior and posterior teeth. This laminated restoration is suggested by McLean et al. (1985) as a technique which overcomes the problem of establishing an adequate marginal seal in those Class V restorations ending in thin or irregular cervical tooth enamel. Histopathological pulpal changes observed after the placement of composite resin fillings (Goto and Jordan, 1972; Stanley et al., 1975; Macko et al., 1978) provide another rationale for using the composite-resin/glass-ionomer laminate (Jordan, 1986) in conservative restorations, since the glass ionomer has been found to be biocompatible with the dental pulp (Tobias et al., 1978; Kawahara et al., 1979; Yakushiji et al., 1979; Wilson and Prosser, 1982). Knight (1984) suggests the use of this technique in repairing worn surfaces of glass-ionomer restorations and f r a c t u r e d cusps of teeth, where esthetic considerations are paramount. Marshall et al. (1982) studied the effects of various bases on three brands of composite resin. They demonstrated that composite resin surfaces cured against a glass-ionomer base resulted in a decrease in hardness. The nonadjacent surface of the composite resin was not tested; therefore, the effect of a glass-ionomer base on this surface was not determined. This study was undertaken to examine the effect of the compositeresin/glass-ionomer-laminate technique on the hardness of the composite resin surface exposed to the oral environment.
T
MATERIALS AND METHODS Thirty, light-cured, composite resin test samples were used in this study. 38
Fifteen of these samples were placed and cured over glass-ionomer bases, while the other 15 served as controls which did not have a base material. The test specimens were made by placement of the composite material (Silux, Batch Number 5502, Universal Shade, 3M Dental Products, St. Paul, MN 55144) in a Teflon ring with an inside diameter of 10 mm. In order for the effect of the base material on v a r i o u s t h i c k n e s s e s of composite resin to be evaluated, Teflon rings were fabricated to create samples 1 mm, 2 mm, and 3 mm thick. Five controls and five test disks were made in the l-mm, 2-mm, and 3-mm Teflon rings. These three thicknesses permitted an evaluation of thickness on microhardness of the composite samples to be made. The controls, which had no base, were cured against a plastic block (Fig.). The composite samples with a base were formed by use of a plastic block containing a "well" in the center that measured 3 mm deep × 10 mm (Fig.). The "well" was filled with a glass-ionomer base (KetacBond, Batch Number 0010, ESPEPremier, Norristown, PA 19401), mixed according to manufacturer's instructions, allowed to set for four minutes, etched for 60 seconds with a phosphoric acid gel, rinsed with distilled water, and coated with a dual-cured bonding agent (Scotchbond Light Cured Dental Adhesive, 3M Dental Products, St. Paul, MN 55144), which was cured separately for 20 seconds. The Teflon ring was placed over the glass-ionomer base, filled with the composite resin, and cured with a visible-light-curing unit (Coe-Lite, Coe Laboratories, Chicago, IL 60658). In order to ensure minimum variability in the quality of cure, we exposed each sample to visible light for 40 seconds per 1 mm of resin thickness. This curing time was chosen based on a study by Swartz et al. (1983), who determined that 40 seconds of exposure to the light source satisfactorily cured both dark
BERRONG et al./EFFECT OF GLASS-IONOMER B A S E ON COMPOSITE R E S I N H A R D N E S S
Controls Composite Resin Plastic Block
Composite Samples Composite Resin 1 mm, 2mm, 3 m m
Plastic Block
J
Glass Ionomer
Fig. Plastic blocks and Teflon rings which were used to fabricate samples. Top: The composite samples were cured against the plastic to simulate absence of base, Bottom: The "well" in the plastic block was filled with a glass-ionomer base and then with the composite resin sample in three thicknesses cured over the base. and light shades of two composite resins to a depth which equaled or exceeded 1 mm. The cure time was 40 seconds for the l-mm sample, 80 seconds for the 2-mm sample, and 120 seconds for the 3-ram sample. Curing was performed in 40-second increments. The test specimens were stored as constructed in distilled water for seven days at 37°C. Each sample remained in contact with the base upon which it was constructed, while five m i c r o h a r d n e s s t e s t s were performed on the resin surface not adjacent to the base. Surface hardness was determined with a Micromet (Buehler, Inc., Evanston, IL 60204) microhardness tester, which gave measurements in microns. The micron measurements were converted to Knoop Hardness Numbers (KHN). RESULTS The mean Knoop Hardness Numbers for both the controls and test specimens are listed in the Table. We
obtained these mean scores by averaging the KHN from the five microhardness tests performed on each sample and then a v e r a g i n g each group. The mean Knoop Hardness Numbers for all three thicknesses of controls (l-ram, 2-mm, and 3-ram) were higher than the mean scores for the test samples with glass-ionomer bases. When the data were subjected to a two-way Analysis of Variance, there was a significant difference (p<0.05) between the microhardness of the controls and that of the test specimens, but no significant difference was found among the microhardnesses of the three thicknesses (l-ram, 2-ram, and 3-ram). A Duncan's Multiple Range Test indicated that there was a significant difference (p<0.05) in surface hardness between the l-mm control and the l-mm test specimens, but there were no significant differences between the controls and test specimens of the 2-mm and 3-mm samples.
TABLE
MEAN KNOOPHARDNESSNUMBER (KHN) OF COMPOSITESAMPLES Controls Mean KHN 1-mm 2-mm 3-mm * p < 0.05.
26.89* 25.73 26.66
S.D. 3.54 4.91 4.37
Test Specimens Mean KHN S.D. 20.35 24.65 23.51
4.05 3.24 3.10
DISCUSSION An earlier study by Marshall et al. (1982) demonstrated that glass-ionomer bases could result in a major reduction in the surface hardness of a composite resin. This reduction in surface hardness occurred on the surface in intimate contact with the glass-ionomer base. Color stability was also evaluated with calorimetric determinations, and it was found that one brand of composite resin exhibited a color change. The authors did not discuss what effect the reduction in internal surface hardness would have on the restorations' intra-oral serviceability. However, they did fred that the polyacrylic acid inhibited polymerization of the composite and would also plasticize set resin if allowed to remain in contact with it. This study found that the campusite resin surface remote from the glass-ionomer base had a significantly reduced surface hardness occurring in the l-mm-thick samples. However, there was no significant difference in surface hardness between 2-ram- and 3-mm-thick samples and that of the controls. The clinical significance of these findings has not been investigated; however, it would appear that glass ionomers would affect external surface hardness only in thin restorations (thickness, 1 mm or less). This may occur in Class II or Class V restorations in which the glass-ionomer base is extended or feathered out to or near the cavo-surface margin, resulting in a thin laminate of campusite resin material. Since surface hardness values are shown to be adversely affected, other properties-such as color stability, stain resistance, and wear resist a n c e - m a y be adversely affected, thus decreasing the longevity of the restoration. Further studies of these properties need to be conducted.
SUMMARY The effect of the glass-ionomer/composite-resin-laminate technique on the hardness of external composite resin surfaces was studied. The mean hardness of the 1-mm test specimens was significantly less than that of the l-ram controls. Surface hardness values for the 2-mm- and 3-mm-thick samples were not significantly different from those of their controls. Dental Materials~January 1989
39
REFERENCES GOTO, G. and JORDAN, R.E. (1972): Pulpal Response to Composite Resin Materials, J Prosthet Dent 28: 601-606. JORDAN, R.E. (1986): Esthetic Composite Bonding Techniques and Materials. Burlington, Ontario: B.C. Decker, Inc., pp. 228-230. KAWAHARA, H.; IMANISHI, Y.; and OSHINA, H. (1979): Biological Evaluation of Glass Ionomer Cements, J Dent Res 58: 1080-1086. KNIGHT, G.M. (1984): The Use of Adhesive Materials in the Conservative Restoration of Selected Posterior Teeth, AuNt Dent J 29: 324-331. MACKO, D.J.; RUTBERG, M.; and LANGELAND, g. (1978): Pulpal Re-
sponse to the Application of Phosphoric Acid to Dentin, Oral Surg Oral Med Oral Pathol 45: 930-946. MARSHALL, S.J.; MARSHALL, G.W.; and HARCOURT, J.K. (1982): The Influence of Various Cavity Bases on the Microhardness of Composites, AuNt Dent J 27: 291-295. MCLEAN, J.W.; PROSSER, H.J.; and WILSON, A.D. (1985): The Use of Glass Ionomer Cements in Bonding Composite Resins to Dentine, Br Dent J 158: 410-414. STANLEY, H.R.; GOING, R.E.; and CHAUNCEY,H.H. (1975): Human Pulp Response to Acid Pretreatment of Dentin and to Composite Restoration, J A m Dent Assoc 91: 817-825.
SWARTZ, M.L.; PHILLIPS, R.W.; and RHODES, B. (1983): Visible Light-activated Resins-Depth of Cure, J A m Dent Assoc 106: 634-637. TOBIAS, a.s.; BROWNE, R.M.; PLANT, C.G.; and INGRAM,D.Y. (1978): Pulpal Response to a Glass Ionomer Cement, Br Dent J 144: 345-350. WILSON, A.D. and PROSSER, H.J. (1982): Biocompatibility of the Glass Ionomer Cement, J Dent Assoc S Afr 37: 872879. YAKUSHIJI, M.; KINUMATSU, T.; FUCHINO, T.; and MACHIDA,Y. (1979): Effects of Glass Ionomer Cement on the Dental Pulp and Its Efficacy as a Base Material, Bull Tokyo Dent Coll 20: 47-59.
40 BERRONG et al./EFFECT OF GLASS-IONOMER BASE ON COMPOSITE RESIN HARDNESS