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Marginal adaptation of glass-ionomer cements
Marginal adaptation of glass-ionomer cements Anna B. Fuks, D.D.S.,* Zvia Hirschfeld,
D.M.D.,**
and Rafael Grajower, Ph.D.***
The Hebrew University, Hadassah Faculty of Dental Medicine, Jerusalem, Israel
G
lass-ionomer cements bond with enamel and dentin.lm3 Temperature changes that occur in the oral cavity from mouth breathing and the consumption of food of various temperatures may induce stressesat the cement-enamel interface that could impair the bond between these materials. In addition, if the glassionomer cement undergoes dimensional changes or deteriorates due to the environment, a gap may develop at the cement-enamel interface. The use of a glass-ionomer cement as a restorative material has been advocated primarily for restoring cervical erosion and abrasion. However, the application of these materials for restoration of Class II cavities in deciduous teeth has also been reported.4 In addition, there is a general recommendation for restoring primary teeth with glass-ionomer cement.5
MATERIAL
AND METHOD
Class II cavities were prepared in the conventional manner in 12 sound young premolar teeth that were extracted for orthodontic purposes. Restorations were made of the cements Aspa (L. D. Caulk Co., Milford, Del.) and Fuji (G-C’s type II, Dental Industrial Co., Tokyo, Japan) according to the manufacturers’ instructions. The enamel was etched with a citric acid solution (50%) supplied with Aspa; no enamel etching was applied for Fuji restorations. A celluloid matrix was fitted around the tooth and kept firmly in place so that no cement could escape from the cavity during insertion.
Preparation of replicas Impressions of the teeth were made with a vinyl silicone impression material (Reprosil, L. D. Caulk Co.) restrained in copper bands that were closed at one end with impression compound. Two impressions were made for each tooth. The first impression was discarded since artifacts were discerned on the replicas
RESULTS
*Lecturer, Department of **Senior ***Head,
356
Pedodontics. Lecturer, Department of Oral Unit for Dental Materials.
made with these impressions. Positive casts were prepared by pouring an epoxy resin (Araldite, Ciba, Base& Switzerland) in the impressions and allowing it to cure for 24 hours.6 The restored teeth were subjected to thermocycling. The thermocycling apparatus consisted of a plastic cross that was turned by a motor so that during each cycle the arms of the cross passed through a water bath of 60” C for 4% minutes and through air for 5% minutes. The water bath was covered with a Styrofoam lid provided with small openings that allowed the crossarms with the attached teeth to pass through the water. Cooling of the teeth above the bath was enhanced with an airstream. The temperature on the tooth surface was measured in preliminary experiments with a copper-constantan thermocouple of 0.4 mm diameter that was attached to a tooth surface with a thin layer of epoxy resin. Minimum temperatures of 15” to 17” C and maximum temperatures of 59” to 62” C were recorded. The minimum temperatures were below room temperature due to evaporation of water in the airstream. Thermocycling was carried out for 1 day (140 cycles) for six teeth and for 6 days (840 cycles) on the other six. After thermocycling, new replicas were prepared as described above. The teeth and replicas were gold plated for inspection in the scanning electron microscope (JSM 35, Jeol, Tokyo, Japan). The quality of the replica technique was verified by comparing the surface texture of the replicas with that of the original teeth at a magnification of X1,000. No differences in surfaci texture were observed. The adaptation of the cements to the cavity margins was evaluated along the proximobuccal and proximolingual surfaces of the restorations. Only the middle and cervical third of these margins were examined because these were retained by the matrix band and remained untouched; the occlusal third may have been affected by the carving and was therefore not studied.
Rehabilitation.
The distinct margin between enamel and cement was observed for most interfaces, and overlaps of the
MARCH
1983
VOLUME
49
NUMBER
3
MARGINAL
ADAPTATION
OF GLASS-IONOMER
CEMENTS
Fig. 1. Effect of thermocycling on marginal adaptation. A, Aspa before thermocycling. 8, Aspa after thermocycling. C, Fuji before thermocycling. D, Fuji after thermocycling. (Magnification x50.) En = Enamel; As = Aspa; Fu = Fuji.
cement onto the enamel surface occurred only in minute areas. Scanning electron micrographs of the cement-enamel interfaces are shown in Figs. 1 to 3. Fig. 1 shows the interfaces before and after thermocycling for 6 days. No appreciable effect of thermocycling on the marginal adaptation was observed after 1 to 6 days. Gaps along the entire cement-enamel interface were not observed.
THE JOURNAL
OF PROSTHETIC
DENTISTRY
In many specimens small gaps were present in part of the interface or in the cement itself (Fig. 2). These phenomena were more prevalent for Aspa than for Fu,ji. Deterioratio:n of part of the cemenr surface was observed after thermocycling (Fig. 3). This: occurred for Aspa after thermocycling for 1 day but did not become more severe after 6 days. For Fu-
357
FLJKS, HIRSCHFELD,
AND
CRAJOWER
Fig. 2. Marginal adaptation. Nontypical interfaces. A, Aspa before thermocycling. Deep furrow and gap at cement-enamel interface. (Magnification x50.) B, Magnification x500. C, Fuji after thermocycling. Good adaptation. (Magnification x50.) D, Magnification ~2,600. E, Aspa after thermocycling. Good adaptation. (Magnification x500.) F, Fuji after thermocycling. Poor adaptation. (Magnification X100.) En = Enamel; As = Aspa; Fu = Fuji.
358
MARCH
1983
VOLUME
49
NUMBER
3
MARGINAL
ADAPTATION
OF GLASS-IONOMER
CEMENTS
Fig. 3. Defects in cements. A, Furrows in Aspa before thermocycling. 8, Furrows in Fuji before thermocycling. C, Gap and deterioration of Aspa after thermocycling. D, Deterioration of Fuji after thermocycling. (Magnification X500 [A, C, D]; Xl00 [B]“j En = Enamel; As = Aspa; Fu = Fuji. ji, surface deterioration 6 days.
was observed only
after
DISCUSSION Thermocycling is commonly conducted between 5” and 60” C.7 However, this temperature range requires extensive equipment. The absence of a cooling bath in the present method eliminated the need for cooling
THE JOURNAL
OF PROSTHETIC
DENTISTRY
equipment and simplified the cycling method. The effect of the present method on the interface between restorative materials was demonstrated for “bonded pontics.“* The load causing fracture at the interface between the bonding resin and the pontic decreased significantly after thermocycling. The results showed that only minor discrepancies occurred at the enamel-glass-ionomer cement interface
359
FUKS, HIRSCHFELD,
and no marginal gaps resulted from thermocycling. The almost imperceptible enamel-cement transition observed at high magnification after thermocycling indicated hydrolytic stability of the cements and established that the enamel-cement bond was not severed by temperature variations. The gaps in the cement as well as at the interface were probably formed during insertion of the cement or during carving, but not subsequently. Excellent marginal adaptation of glass-ionomer cement was also reported by Hembree and Andrews.9 They found that after thermocycling the marginal leakage around restorations for simulated cervical abrasion was less for a glass-ionomer cement than for composite resin retained by etched enamel. Nordenvall et al.” reported that Aspa provided better adaptation than composite resins but found that a combination of a bonding resin followed by a restorative resin applied to etched enamel gave the same results as Aspa. Crisp et al. ” demonstrated that Aspa samples absorbed water during the first week after carving but that the weight of immersed samples subsequently remained rather constant. They found that silica, sodium ions, and fluoride ions that did not contribute to the matrix structure were continuously eluted from the cement during repeated immersion in water for 15 weeks. However, the elution of matrix forming aluminum and phosphate ions ceased after 1 day, whereas calcium ions were detected in the eluate only after insufficient carving. In agreement with this chemical study of solubility, the present results showed only minor deterioration of the Aspa surface, which was similar after 1 and 6 days of thermocycling. The temperature of 60” C and the movement of the sample through water during thermocycling in this study constitute more severe erosive conditions than stationary immersion in water at 37” C as employed by Crisp et al.,” but this did not appear to affect the period during which the cement is vulnerable to erosion. Deterioration of Fuji became apparent only after 6 days of thermocycling, which may indicate that the setting mechanism of this material differs from that of Aspa. The localized nature of surface erosion may possibly be attributed to imperfect mixing, although care was taken to mix the materials thoroughly. The
360
AND
GRAJOWER
clinical significance of the erosion of the cements remains to be determined. SUMMARY
AND
CONCLUSIONS
The effect of thermocycling on the marginal adaptation of two glass-ionomer cements was determined by means of scanning electron microscopy. Small gaps in the cement as well as at the enamel-cement interface were observed after curing, but these phenomena were not enhanced by thermocycling. Localized areas of surface deterioration were observed for both cements after thermocycling. REFERENCES 1
2.
3.
4.
5.
6. 7.
8.
9.
10.
11.
hlcCabe, J. F., and Wilson, H. J.: Some properties of a glass-ionomer cement. Br Dent J 9279, 1979. Maldonado, A., Swartz, M. L., and Phillips, R. W.: An in vitro study of certain properties of a glass-ionomer cement. J Am Dent Assoc 96:785, 1978. Levine, R. S., Beech, D. R., and Garton, B.: A rapid technique for improving the bond strength of polyacrylate cements to dentine. Br Dent J 143~274, 1977. Vlietstra, J. R., Plant, C. G., Shovelton, D. S., and Bradnock, G.: The use of glass-ionomer cements in deciduous teeth. Br Dent J 145:164, 1978. McLean, J. W., and Wilson, A. D.: The clinical development of the glass-ionomer cement. II. Some clinical applications, Aust Dent J 22:120, 1977. Grundy, J. R.: An intra-oral replica technique for use with the scanning electron microscope. Br Dent J 13&l 13, 1971. Crim, G. A., and Mattingly, S. L.: Evaluation of two methods for assessing marginal leakage. J PROSTHET DENT 45~160, 1981. Grajower, R., Stern, N., Zamir, S., and Kohavi, D.: Temporary space maintainers retained with composite resin. Part II: Fracture load in vitro. J PRCETHETDENT 45:49, 1981. Hembree, J. H., and Andrews, J. T.: Microleakage of several Class V anterior restorative materials: A laboratory study. J Am Dent Assoc 97:179, 1978. Nordenvall, K. J., Br%tnstriim, M., and Torstensson, B.: Pulp reactions and microorganisms under Aspa and Concise composite fillings. ASDC J Dent Child 46:449, 1979. Crisp, S., Lewis, B. G., and Wilson, A. D.: Glass-ionomer cements: Chemistry of erosion. J Dent Res 55:1032, 1976.
Keprznt
reques1.5 to:
DR. ANNA B. FUKS THE HEBREWUNIVERSITY HADASSAHFACULTY OF DENTAL MEDICINE POB 1172 JERUSALEM,ISRAEL
MARCH
1983
VOLUME
49
NUMBER
3
D.M.D.,**
and Rafael Grajower, Ph.D.***
The Hebrew University, Hadassah Faculty of Dental Medicine, Jerusalem, Israel
G
lass-ionomer cements bond with enamel and dentin.lm3 Temperature changes that occur in the oral cavity from mouth breathing and the consumption of food of various temperatures may induce stressesat the cement-enamel interface that could impair the bond between these materials. In addition, if the glassionomer cement undergoes dimensional changes or deteriorates due to the environment, a gap may develop at the cement-enamel interface. The use of a glass-ionomer cement as a restorative material has been advocated primarily for restoring cervical erosion and abrasion. However, the application of these materials for restoration of Class II cavities in deciduous teeth has also been reported.4 In addition, there is a general recommendation for restoring primary teeth with glass-ionomer cement.5
MATERIAL
AND METHOD
Class II cavities were prepared in the conventional manner in 12 sound young premolar teeth that were extracted for orthodontic purposes. Restorations were made of the cements Aspa (L. D. Caulk Co., Milford, Del.) and Fuji (G-C’s type II, Dental Industrial Co., Tokyo, Japan) according to the manufacturers’ instructions. The enamel was etched with a citric acid solution (50%) supplied with Aspa; no enamel etching was applied for Fuji restorations. A celluloid matrix was fitted around the tooth and kept firmly in place so that no cement could escape from the cavity during insertion.
Preparation of replicas Impressions of the teeth were made with a vinyl silicone impression material (Reprosil, L. D. Caulk Co.) restrained in copper bands that were closed at one end with impression compound. Two impressions were made for each tooth. The first impression was discarded since artifacts were discerned on the replicas
RESULTS
*Lecturer, Department of **Senior ***Head,
356
Pedodontics. Lecturer, Department of Oral Unit for Dental Materials.
made with these impressions. Positive casts were prepared by pouring an epoxy resin (Araldite, Ciba, Base& Switzerland) in the impressions and allowing it to cure for 24 hours.6 The restored teeth were subjected to thermocycling. The thermocycling apparatus consisted of a plastic cross that was turned by a motor so that during each cycle the arms of the cross passed through a water bath of 60” C for 4% minutes and through air for 5% minutes. The water bath was covered with a Styrofoam lid provided with small openings that allowed the crossarms with the attached teeth to pass through the water. Cooling of the teeth above the bath was enhanced with an airstream. The temperature on the tooth surface was measured in preliminary experiments with a copper-constantan thermocouple of 0.4 mm diameter that was attached to a tooth surface with a thin layer of epoxy resin. Minimum temperatures of 15” to 17” C and maximum temperatures of 59” to 62” C were recorded. The minimum temperatures were below room temperature due to evaporation of water in the airstream. Thermocycling was carried out for 1 day (140 cycles) for six teeth and for 6 days (840 cycles) on the other six. After thermocycling, new replicas were prepared as described above. The teeth and replicas were gold plated for inspection in the scanning electron microscope (JSM 35, Jeol, Tokyo, Japan). The quality of the replica technique was verified by comparing the surface texture of the replicas with that of the original teeth at a magnification of X1,000. No differences in surfaci texture were observed. The adaptation of the cements to the cavity margins was evaluated along the proximobuccal and proximolingual surfaces of the restorations. Only the middle and cervical third of these margins were examined because these were retained by the matrix band and remained untouched; the occlusal third may have been affected by the carving and was therefore not studied.
Rehabilitation.
The distinct margin between enamel and cement was observed for most interfaces, and overlaps of the
MARCH
1983
VOLUME
49
NUMBER
3
MARGINAL
ADAPTATION
OF GLASS-IONOMER
CEMENTS
Fig. 1. Effect of thermocycling on marginal adaptation. A, Aspa before thermocycling. 8, Aspa after thermocycling. C, Fuji before thermocycling. D, Fuji after thermocycling. (Magnification x50.) En = Enamel; As = Aspa; Fu = Fuji.
cement onto the enamel surface occurred only in minute areas. Scanning electron micrographs of the cement-enamel interfaces are shown in Figs. 1 to 3. Fig. 1 shows the interfaces before and after thermocycling for 6 days. No appreciable effect of thermocycling on the marginal adaptation was observed after 1 to 6 days. Gaps along the entire cement-enamel interface were not observed.
THE JOURNAL
OF PROSTHETIC
DENTISTRY
In many specimens small gaps were present in part of the interface or in the cement itself (Fig. 2). These phenomena were more prevalent for Aspa than for Fu,ji. Deterioratio:n of part of the cemenr surface was observed after thermocycling (Fig. 3). This: occurred for Aspa after thermocycling for 1 day but did not become more severe after 6 days. For Fu-
357
FLJKS, HIRSCHFELD,
AND
CRAJOWER
Fig. 2. Marginal adaptation. Nontypical interfaces. A, Aspa before thermocycling. Deep furrow and gap at cement-enamel interface. (Magnification x50.) B, Magnification x500. C, Fuji after thermocycling. Good adaptation. (Magnification x50.) D, Magnification ~2,600. E, Aspa after thermocycling. Good adaptation. (Magnification x500.) F, Fuji after thermocycling. Poor adaptation. (Magnification X100.) En = Enamel; As = Aspa; Fu = Fuji.
358
MARCH
1983
VOLUME
49
NUMBER
3
MARGINAL
ADAPTATION
OF GLASS-IONOMER
CEMENTS
Fig. 3. Defects in cements. A, Furrows in Aspa before thermocycling. 8, Furrows in Fuji before thermocycling. C, Gap and deterioration of Aspa after thermocycling. D, Deterioration of Fuji after thermocycling. (Magnification X500 [A, C, D]; Xl00 [B]“j En = Enamel; As = Aspa; Fu = Fuji. ji, surface deterioration 6 days.
was observed only
after
DISCUSSION Thermocycling is commonly conducted between 5” and 60” C.7 However, this temperature range requires extensive equipment. The absence of a cooling bath in the present method eliminated the need for cooling
THE JOURNAL
OF PROSTHETIC
DENTISTRY
equipment and simplified the cycling method. The effect of the present method on the interface between restorative materials was demonstrated for “bonded pontics.“* The load causing fracture at the interface between the bonding resin and the pontic decreased significantly after thermocycling. The results showed that only minor discrepancies occurred at the enamel-glass-ionomer cement interface
359
FUKS, HIRSCHFELD,
and no marginal gaps resulted from thermocycling. The almost imperceptible enamel-cement transition observed at high magnification after thermocycling indicated hydrolytic stability of the cements and established that the enamel-cement bond was not severed by temperature variations. The gaps in the cement as well as at the interface were probably formed during insertion of the cement or during carving, but not subsequently. Excellent marginal adaptation of glass-ionomer cement was also reported by Hembree and Andrews.9 They found that after thermocycling the marginal leakage around restorations for simulated cervical abrasion was less for a glass-ionomer cement than for composite resin retained by etched enamel. Nordenvall et al.” reported that Aspa provided better adaptation than composite resins but found that a combination of a bonding resin followed by a restorative resin applied to etched enamel gave the same results as Aspa. Crisp et al. ” demonstrated that Aspa samples absorbed water during the first week after carving but that the weight of immersed samples subsequently remained rather constant. They found that silica, sodium ions, and fluoride ions that did not contribute to the matrix structure were continuously eluted from the cement during repeated immersion in water for 15 weeks. However, the elution of matrix forming aluminum and phosphate ions ceased after 1 day, whereas calcium ions were detected in the eluate only after insufficient carving. In agreement with this chemical study of solubility, the present results showed only minor deterioration of the Aspa surface, which was similar after 1 and 6 days of thermocycling. The temperature of 60” C and the movement of the sample through water during thermocycling in this study constitute more severe erosive conditions than stationary immersion in water at 37” C as employed by Crisp et al.,” but this did not appear to affect the period during which the cement is vulnerable to erosion. Deterioration of Fuji became apparent only after 6 days of thermocycling, which may indicate that the setting mechanism of this material differs from that of Aspa. The localized nature of surface erosion may possibly be attributed to imperfect mixing, although care was taken to mix the materials thoroughly. The
360
AND
GRAJOWER
clinical significance of the erosion of the cements remains to be determined. SUMMARY
AND
CONCLUSIONS
The effect of thermocycling on the marginal adaptation of two glass-ionomer cements was determined by means of scanning electron microscopy. Small gaps in the cement as well as at the enamel-cement interface were observed after curing, but these phenomena were not enhanced by thermocycling. Localized areas of surface deterioration were observed for both cements after thermocycling. REFERENCES 1
2.
3.
4.
5.
6. 7.
8.
9.
10.
11.
hlcCabe, J. F., and Wilson, H. J.: Some properties of a glass-ionomer cement. Br Dent J 9279, 1979. Maldonado, A., Swartz, M. L., and Phillips, R. W.: An in vitro study of certain properties of a glass-ionomer cement. J Am Dent Assoc 96:785, 1978. Levine, R. S., Beech, D. R., and Garton, B.: A rapid technique for improving the bond strength of polyacrylate cements to dentine. Br Dent J 143~274, 1977. Vlietstra, J. R., Plant, C. G., Shovelton, D. S., and Bradnock, G.: The use of glass-ionomer cements in deciduous teeth. Br Dent J 145:164, 1978. McLean, J. W., and Wilson, A. D.: The clinical development of the glass-ionomer cement. II. Some clinical applications, Aust Dent J 22:120, 1977. Grundy, J. R.: An intra-oral replica technique for use with the scanning electron microscope. Br Dent J 13&l 13, 1971. Crim, G. A., and Mattingly, S. L.: Evaluation of two methods for assessing marginal leakage. J PROSTHET DENT 45~160, 1981. Grajower, R., Stern, N., Zamir, S., and Kohavi, D.: Temporary space maintainers retained with composite resin. Part II: Fracture load in vitro. J PRCETHETDENT 45:49, 1981. Hembree, J. H., and Andrews, J. T.: Microleakage of several Class V anterior restorative materials: A laboratory study. J Am Dent Assoc 97:179, 1978. Nordenvall, K. J., Br%tnstriim, M., and Torstensson, B.: Pulp reactions and microorganisms under Aspa and Concise composite fillings. ASDC J Dent Child 46:449, 1979. Crisp, S., Lewis, B. G., and Wilson, A. D.: Glass-ionomer cements: Chemistry of erosion. J Dent Res 55:1032, 1976.
Keprznt
reques1.5 to:
DR. ANNA B. FUKS THE HEBREWUNIVERSITY HADASSAHFACULTY OF DENTAL MEDICINE POB 1172 JERUSALEM,ISRAEL
MARCH
1983
VOLUME
49
NUMBER
3