- Email: [email protected]
Effect of various surface protections on the margin microleakage of resin-modified glass ionomer cements
Effect of various surface protections on the margin microleakage of resin-modified glass ionomer cements Shu-Fen Chuang, DDS,a Ying-Tai Jin, DDS, MS,b Pei-Fen Tsai, DDS,c and Tung-Yiu Wong, DDSd National Cheng Kung University Hospital, Tainan City, Taiwan Statement of problem. Because conventional glass ionomer cements are moisture sensitive, a surface coating is recommended during the initial setting stage. It is unknown whether resin-modified glass ionomer cements also need surface protection. Purpose. This study investigated the effect of various surface protections on microleakage with Class V resin-modified glass ionomer restorations. Material and methods. Forty extracted molars with buccal and lingual Class V cavity preparations were restored with a resin-modified glass ionomer (Fuji II LC). The occlusal margin of each restoration was on enamel and the cervical margin on dentin. After immediate finishing and polishing, the teeth were divided into 4 groups according to the following surface protection treatments: group I, unprotected; group II, Fuji varnish; group III, resin adhesive; and group IV, acid etching and resin adhesive. After these procedures, all teeth were stored in isotonic saline for 24 hours, thermocycled 1500 times at 5°C to 60°C, and soaked in dye solution for 24 hours. The teeth then were longitudinally sectioned and observed under a stereomicroscope. The degree of dye penetration was recorded and analyzed with the Kruskal-Wallis and Mann-Whitney tests (P<.05) Results. None of the 4 groups demonstrated complete margin sealing at either the occlusal or cervical margins. Groups II and III displayed the least microleakage at cervical margins; a significant difference existed between groups I and III (P=.034). Compared with the other 3 groups, group IV showed significantly greater microleakage at the cervical margins. Conclusion. Although resin-modified glass ionomers can be finished immediately, they remain moisture sensitive. Within the limitations of this study, the results suggest that resin adhesive should be used as a surface protection to reduce margin microleakage of resin-modified glass ionomer restorations. (J Prosthet Dent 2001;86:309-14.)
CLINICAL IMPLICATIONS Findings from this in vitro study suggest that surface protection with a resin adhesive provides improved margin sealing in Class V resin-modified glass ionomer restorations.
C
onventional glass ionomer cements (GIC) have been advocated as restorative materials because of their ability to chemically bond to tooth structure and release fluoride.1 They are widely used in dentistry for restoration, as a liner or base, and as luting cements. A survey on the use of glass ionomer cements showed that 94% of general dentists in the United States currently use or have used them.2 Conventional GICs are moisture-sensitive restorative materials. Immediately after the aluminosilicate glass powder is mixed into an aqueous solution of a Supported by NCKUH Grant No. 87-079, National Cheng-Kung University Hospital. aAttending Staff, Department of Operative Dentistry. bChief and Professor, Department of Pathology. cAttending Staff, Department of Pediatric Dentistry. dChief and Lecturer, Department of Dentistry. SEPTEMBER 2001
polymer or copolymer of acrylic acid, the chemical acid-base reaction starts. During the initial state, hydrated protons of the acid attack the periphery of the glass particles and release metal ions. Initially, some soluble salts such as calcium polyacrylate are formed; these gradually are replaced by insoluble aluminum polyacrylate salts, which cause gelation and hardening of the cement.3 During these reactions, both water uptake and water loss can compromise the physical properties of the restoration. Gemalmaz et al4 found that when GIC restorations were contaminated by moisture, their mechanical strength decreased and the surface of the material eroded or wore rapidly. Provisions must be made to maintain the water balance of restorations for the first 24 hours.5 Previous studies have discussed the necessity for and types of surface protection during the initial setting of THE JOURNAL OF PROSTHETIC DENTISTRY 309
THE JOURNAL OF PROSTHETIC DENTISTRY
conventional GICs. Cocoa butter, waterproof varnish, and even nail varnish have been recommended as surface coating agents.6-8 Recently, light-polymerized resin adhesive has been considered the optimal surface protecting agent. Hotta et al9 found that the use of light-polymerized bonding or glazing agents limited water movement across the setting cement surface. In an SEM study, Watson and Banerjee10 demonstrated the effectiveness of light-polymerized resin adhesives as surface protection. Moreover, the American Dental Association Council on Dental Materials, Instruments, and Equipment (1990) declared the importance of varnish or light-polymerized bonding agents for conventional GIC restorations.11 During the 1980s, resin-modified glass ionomer cements (RMGIC) were developed to replace conventional GICs. According to McLean et al,12 RMGICs are materials that set concurrently via a dominant acidbase reaction and auxiliary photopolymerization. With the addition of resin monomer (2-hydroxyethyl methacrylate [HEMA]), about 4.5 wt%,13 and lightpolymerized initiators, RMGICs are polymerized immediately after visible light irradiation. Compared with conventional analogs, RMGICs have been characterized as having a longer working time, a rapid set, improved appearance and translucency, and higher early strength.14,15 However, RMGICs retain some properties of their conventional counterparts. Additional resin monomer and supplementary photopolymerization have not significantly reduced the susceptibility of RMGICs to dehydration problems.16 Thus, the maintenance of water balance in the modified cements is important. Only a few studies have addressed the importance of surface protection for RMGICs. Ribeiro et al17 proved the effectiveness of surface protection for the prevention of dye uptake (staining) of 3 brands of RMGIC. Another study by Miyazaki et al18 reported the influence of surface coatings on the flexural properties of both conventional and resin-modified GICs. Their results indicated that RMGICs should be protected from water for at least 1 hour after cement mixing. In contrast, most manufacturers’ instructions indicate that RMGICs can be used with or without surface protection. Given that current dental restorative materials exhibit some degree of microleakage, the importance of surface protection seems to be underestimated. The presence of microleakage may lead to postoperative problems such as bacterial accumulation, fluid flow in the gap, and detachment of the restoration.19 The purpose of this study was to investigate the effects of various surface protections (GIC varnish and lightpolymerized resin adhesives) on the microleakage of an RMGIC in vitro. The microleakage of occlusal mar-
310
CHUANG ET AL
gins and cervical margins with different surface protections was evaluated separately.
MATERIAL AND METHODS Thirty human extracted molars without decay or previous restoration were chosen for this study. They were stored in normal saline before use within 4 months after extraction. The teeth were scaled and cleaned with pumice. To keep the cavity preparation on dentin, the cervical cementum over the cervical portion of the root was removed with a sharp scalpel. The exposed root surface was polished with Sof-Lex paper disks (3M, St Paul, Minn.). Two Class V cavity preparations with a mesiodistal width of 4 mm, an occlusogingival height of 3 mm, and a depth of 2 mm, without retention lock, were prepared on the buccal and lingual surfaces of each tooth. Diamond burs (440M and 411, Shofu Inc, Tokyo, Japan) were used for the cavity preparations; each bur was used to prepare 5 cavities. The occlusal margins of the cavities were located on enamel and the cervical margins on dentin. All cavosurface angles were kept at 90 degrees without bevel designs. The teeth were randomly assigned to 3 groups such that each group had 10 teeth with a total of 20 cavities. One RMGIC (Fuji II LC; GC Corp, Tokyo, Japan) was chosen as the restorative material because of its popularity and margin sealing quality demonstrated in previous studies.20,21 Three different surface treatment regimens were designed: group I teeth received no surface protection, group II teeth were treated with Fuji Varnish (GC Corp), and group III teeth were treated with the light-polymerized resin adhesive Scotchbond Multipurpose No. 3, which contains BISGMA, HEMA, and light-cured activator. All restorative and adjunctive materials used in the study are listed in Table I. According to the manufacturer’s instructions, Dentin Conditioner (GC Corp) was applied to all cavity preparations with a light scrubbing motion22 for 20 seconds; the preparations were rinsed with water for 20 seconds and then air dried. Fuji II LC was mixed according to the recommended powder/liquid ratio (3.0/1.0 g) and manufacturer’s instructions, then placed into the cavities and light polymerized with a Curing Light 2500 machine (3M) for 40 seconds to assure complete polymerization. The cavities on buccal and lingual surfaces were filled separately. The restored cavities were finished with a scalpel and fine diamond burs, then polished with Sof-Lex paper disks. After finishing and polishing, the teeth in group I were immersed in isotonic saline in a 37°C water bath for 24 hours.23 Immediately after polishing, the restorations in group II were lightly air dried, coated with a layer of
VOLUME 86 NUMBER 3
CHUANG ET AL
THE JOURNAL OF PROSTHETIC DENTISTRY
Table I. Experimental and adjunctive materials used in this study Material
Manufacturer
Type
Composition
Powder: fluoroaluminosilicate Liquid: polyacrylic acid, HEMA 10% polyacrylic acid Rosin BIS-GMA, HEMA, light-polymerized initiator 35% phosphate acid
Fuji II LC
GC Corp, Tokyo, Japan
Restorative material
Dentin Conditioner Fuji Varnish Scotchbond Multipurpose No. 3
GC Corp GC Corp 3M, St. Paul, Minn.
Dentin conditioner Surface protection Surface protection
Ultraetch
Ultradent Inc, South Jordan, Utah
Acid-etching gel
HEMA = 2-hydroxyethyl methacrylate.
Table II. Experimental groups and their treatments Group
Dentin preconditioning
Restoration
I II III IV
Dentin Dentin Dentin Dentin
Fuji Fuji Fuji Fuji
conditioner conditioner conditioner conditioner
II II II II
LC LC LC LC
Surface treatment
None Fuji Varnish Scotchbond Multipurpose No. 3, Light polymerized for 20 s Acid etched for 5 s, rinsed, and air dried. Scotchbond Multipurpose No. 3 applied and light polymerized for 20 s.
Fuji Varnish, and gently air dried. The restorations in group III were treated with Scotchbond Multipurpose No. 3, which was air thinned and then light polymerized for 20 seconds. If a glossy surface was not obtained over group II and III restorations, an additional surface coating was applied. The teeth in groups II and III then were immersed in isotonic saline for 24 hours in the same manner as group I specimens. The surfaces of the restorations were somewhat contaminated by the use of burs and other instruments during finishing and polishing procedures. The effect of acid etching on RMGICs has not been reported, although studies in the literature do address acid etching of GICs. With the use of the “sandwich technique,” the exposed surface of GICs and enamel margins have been acid etched before the placement of resin composites.24 An SEM study from Smith,25 however, revealed rapid surface deterioration with crack formations in conventional GIC after short-term acid etching. To study the effect of acid etching on the RMGIC used in this study, an additional 10 teeth were prepared and designated group IV. These teeth had prepared cavities and were filled as previously mentioned. After finishing and polishing, they were acid etched with 35% phosphoric acid (Ultraetch, Ultradent Inc, Utah) for 5 seconds, rinsed, and lightly air-dried. Scotchbond Multipurpose No. 3 was applied on the etched surfaces and light polymerized for 20 seconds. These teeth then were immersed in 37°C normal saline as previously
SEPTEMBER 2001
mentioned. The experimental groups and their treatments are listed in Table II. All teeth were placed in a 5°C ± 0.2°C to 60°C ± 0.2°C thermocycling machine for 1500 cycles (20 seconds for each dwelling). The apex of each tooth was sealed with sticky wax, and the whole tooth, except 1 mm beyond the margin of the restoration, was coated with nail varnish to prevent dye penetration from neighboring dentin. The teeth were soaked in 2% basic fuchsin dye for 24 hours. After being removed from the dye solution, they were embedded with epoxy resin and sectioned in a buccal-lingual direction along their long axis with a low-speed saw (Isomat 2000, Buehler Ltd, Chicago, Ill.). Both halves of each sectioned tooth were observed with a ×50 stereomicroscope (Stemi SV 6, Carl Zeiss, Oberkochen, Germany) and scored for dye penetration. One examiner who was not informed of the treatment procedure examined the specimens randomly. During the analysis, the examiner was unaware of the nature of the specimen. The degree of margin microleakage at the tooth–restoration interface was scored as follows: 0 = no dye penetration; 1 = dye penetration up to dentinoenamel junction (DEJ) in occlusal margin, or up to one third full length of cervical margin wall; 2 = dye penetration beyond DEJ and up to two thirds full length of occlusal margin wall, or between one and two thirds full length of cervical margin wall; 3 = dye penetration beyond two thirds full length of occlusal or cervical wall but not involving axial wall; and 4 = extensive dye penetration extending
311
THE JOURNAL OF PROSTHETIC DENTISTRY
CHUANG ET AL
used in groups III (1 of 20) and IV (0 of 20). Because the defective restoration surfaces were rough and unevenly stained, the flaking coatings of the varnish or resin bonding agent were gently scrubbed off, and the restorations were rinsed with tap water before the teeth were immersed in dye solution. One half of a tooth in group IV was excluded because of damage during the sectioning procedure. Thus, the specimen halves numbered 40 in each of the groups I through III but only 39 in group IV. None of the 4 groups demonstrated complete margin sealing at either the occlusal or cervical margins. The distribution of dye penetration scores is displayed in Figure 2. Analyzed with the Kruskal-Wallis test, the data indicated no statistical differences in microleakage among the 4 groups at the occlusal margins. With regard to cervical margins, group III exhibited the best margin sealing, followed in sequence by groups II, I, and IV. Statistical differences existed between groups I and III (P=.034; significant), groups I and IV (P=.000), groups II and IV (P=.000), and groups III and IV (P=.000). The margin sealing of cervical margins in group IV was significantly inferior to the other 3 groups. The Mann-Whitney test was used to examine the microleakage between occlusal and cervical margins in each group (Table III). All unetched groups exhibited better sealing at the cervical margin than occlusal margin (P=.008, .001, and .000 for groups I, II, and III, respectively). In contrast, group IV specimens exhibited better sealing at the occlusal margin (P=.000). Fig. 1. Score system for degrees of dye penetration. 0 = no dye penetration; 1 = dye penetration up to DEJ in occlusal margin, or up to one third full length of cervical margin wall; 2 = beyond DEJ and up to two thirds full length of occlusal margin wall, or between one and two thirds full length of cervical margin wall; 3 = beyond two thirds full length of occlusal or cervical wall but not involving axial wall; and 4 = extending to axial wall.
to axial wall (Fig. 1). The scores were analyzed with the Kruskal-Wallis test to identify statistical differences in margin microleakage among the 4 groups. The MannWhitney test was also performed to compare the sealing quality at occlusal and cervical margins in each group. The level of significance was P<.05.
RESULTS A total of 80 restorations were prepared. After the restorations were removed from the thermocycling machine, it was discovered that the coating materials (varnish or resin bonding agent) had partially peeled off the surfaces of some restorations. Fuji Varnish (group II) exhibited more defects after thermocycling (5 of 20 restorations) than the resin bonding agent 312
DISCUSSION Ribeiro et al17 proved the effectiveness of surface protection, especially with the use of a light-polymerized resin adhesive, for the prevention of surface staining of RMGICs. In this study, the best margin sealing was obtained in specimens with resin adhesive protection and without prior acid surface cleansing. The resin adhesive coating reduced staining and microleakage more effectively than the other materials tested. Thus, when clinicians use a RMGIC as a restorative material, they should consider applying resin adhesive and adequately light polymerizing it after finishing the restorations. The unetched (I-III) and etched (IV) groups showed different results for microleakage at the occlusal and cervical margins. In the former, the restorations exhibited better margin sealing at the cervical (dentinal) margins than at the occlusal (enamel) margins. This finding disagrees with previous studies. In a microleakage study of RMGIC in Class V and Class II sandwich restorations, Sjödin et al26 found that dentinal gingival margins exhibited greater leakage than enamel margins. Contradictory results may exist because of different thermocycling tests and total immersion times. Only VOLUME 86 NUMBER 3
CHUANG ET AL
THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 2.Distribution of dye penetration scores for 4 experimental groups. Kruskal-Wallis test (significance level P=.05) demonstrated no significant differences among 4 groups at occlusal margins. At cervical margins, statistical differences existed between groups I and III (P=.034), I and IV (P=.000), II and IV (P=.000), and III and IV (P=.000). *Specimen number in group IV was 39; 1 specimen was damaged.
Table III. Comparisons of occlusal and cervical margin microleakage in each of the 4 experimental groups Group
I II III IV
Margin
Mean rank
Mann-Whitney U test
P value
Occlusal Cervical Occlusal Cervical Occlusal Cervical Occlusal Cervical
46.70 34.30 48.30 32.70 49.42 31.58 25.24 53.76
552.0
.008*
488.0
.001*
443.0
.000*
204.5
.000*
*Statistical difference in all 4 groups (Mann-Whitney U test, significance P=.05).
180 thermocycling tests were performed in the study by Sjödin et al.26 In this study, more thermocycles (1500 total) and a longer immersion time were assigned to simulate the aging process. Enamel and dentin have a higher and lower modulus of elasticity, respectively. It has been reported that 4.7% volumetric expansion occurs with RMGICs after 24 hours of water immersion.27 Dentin under the restorations may have had a great enough stress-absorbing capacity to buffer the expansion of the RMGIC material. However, this hypothesis needs further investigation. Crim20 showed that some enamel adjacent to RMGIC cracked during thermocycling. Although no obvious enamel cracking was detected in this study, enamel microcrazing may have been another cause of microleakage. At the end of thermocycling, some coating materials on the restoration surfaces were partially peeled away. The flaking of Fuji Varnish (group II; 5 of 20) was more evident than the flaking of the resin bonding agent (group III; 1 of 20). The finding is consistent with a study by Hotta et al,9 in which the varnish material SEPTEMBER 2001
(Ketac varnish) peeled after water immersion but the resin bonding coatings remained intact. Because mechanical brushing motion was not included in this study, the breakdown of the coating materials was attributed to the impact of thermocycling or hydrolysis. Information about the wear resistance and protection duration of the coating materials in vivo was not reported in this study; these topics need further investigation. Information about the effect of acid etching on RMGICs is rare. In this study, the occlusal and cervical margins of group IV restorations displayed different degrees of microleakage after 5 seconds of 35% phosphoric acid etching. A study by Smith25 suggested that GIC materials, including RMGICs, deteriorate after even short-term acid etching. Dye penetration at the cervical margin, generally extending to the axial wall, suggested the breakdown of the bond between the RMGIC and dentinal margin after acid etching. If etched dentin surfaces are sealed with a resin adhesive but not treated with a dentin bonding agent, microleakage will occur in the restored interfaces. 313
THE JOURNAL OF PROSTHETIC DENTISTRY
The results of this study suggest that resin adhesive can be used as a surface protection agent to improve margin sealing. Acid etching the RMGIC restoration to clean the surface resulted in extensive cervical margin microleakage and should be avoided. Some current resin adhesives, such as 1-component dentin bonding agents and self-etching primers, contain polyacrylic acid or other organic acids. Whether these acids would deteriorate the surface of GIC or RMGIC restorations is debatable. Until further research is performed, they should be avoided as surface protection agents.
CONCLUSIONS Within the limitations of this study, the following conclusions were drawn: 1. Surface protection, especially with the use of resin adhesive agents, should be added to resin-modified glass ionomer cement restorations. 2. The use of 35% phosphoric acid to clean RMGIC restorations negatively and severely affected cervical margin sealing and should be avoided. We thank Miss Ling-Fan Ho for her help with the statistical analyses.
REFERENCES 1. Wilson AD, McLean JW. Glass ionomer cement. London: Quintessence Publishing; 1988. p. 83-99, 126-8. 2. Reinhardt JW, Swift EJ Jr, Bolden AJ. A national survey on the use of glassionomer cements. Oper Dent 1993;18:56-60. 3. Wilson AD, McLean JW. Glass ionomer cement. London: Quintessence Publishing; 1988. p. 43-54. 4. Gemalmaz D, Yoruc B, Ozcan M, Alkumru HN. Effect of early water contact on solubility of glass ionomer luting cements. J Prosthet Dent 1998;80:474-8. 5. Mount GJ, Makinson OF. Glass-ionomer restorative cements: clinical implications of the setting reaction. Oper Dent 1982;7:134-41. 6. Asmussen E. Opacity of glass-ionomer cements. Acta Odontol Scand 1983;41:155-7. 7. Earl MS, Hume WR, Mount GJ. Effect of varnishes and other surface treatments on water movement across the glass-ionomer cement surface. Aust Dent J 1985;30:298-301. 8. Rodrigues Garcia RC, De Goes MF, Del Bel Cury AA. Influence of protecting agents on the solubility of glass ionomers. Am J Dent 1995;8:294-6. 9. Hotta M, Hirukawa H, Yamamoto K. Effect of coating materials on restorative glass-ionomer cement surface. Oper Dent 1992;17:57-61. 10. Watson T, Banerjee A. Effectiveness of glass-ionomer surface protection treatments: a scanning optical microscope study. Eur J Prosthodont Restor Dent 1993;2:85-90.
314
CHUANG ET AL
11. Using glass ionomers. Council on Dental Materials, Instruments, and Equipment. J Am Dent Assoc 1990;121:181-8. 12. McLean JW, Nicholson JW, Wilson AD. Proposed nomenclature for glass-ionomer dental cements and related materials. Quintessence Int 1994;25:587-9. 13. Mount GJ. Buonocore Memorial Lecture. Glass-ionomer cements: past, present and future. Oper Dent 1994;19:82-90. 14. Mitra SB. Adhesion to dentin and physical properties of a light-cured glass-ionomer liner/base. J Dent Res 1991;70:72-4. 15. Uno S, Finger WJ, Fritz U. Long-term mechanical characteristics of resinmodified glass ionomer restorative materials. Dent Mater 1996;12:64-9. 16. Sidhu SK, Sherriff M, Watson TF. The effects of maturity and dehydration shrinkage on resin-modified glass ionomer restorations. J Dent Res 1997;76:1495-501. 17. Ribeiro AP, Serra MC, Paulillo LA, Rodrigues Junior AL. Effectiveness of surface protection for resin-modified glass ionomer materials. Quintessence Int 1999;30:427-31. 18. Miyazaki M, Moore BK, Onose H. Effect of surface coatings on flexural properties of glass ionomers. Eur J Oral Sci 1996;104:600-4. 19. Kidd EA. Microleakage: a review. J Dent 1976;4:199-206. 20. Crim GA. Marginal leakage of visible light-cured glass ionomer restorative materials. J Prosthet Dent 1993;69:561-3. 21. Toledano M, Osorio E, Osorio R, Garcia-Godoy F. Microleakage of Class V resin-modified glass ionomer and compomer restorations. J Prosthet Dent 1999;81:610-5. 22. Barakat MM, Powers JM, Yamaguchi R. Parameters that affect in vitro bonding of glass-ionomer liners to dentin. J Dent Res 1988;67:1161-3. 23. Crim GA, Garcia-Godoy F. Microleakage: the effect of storage and cycling duration. J Prosthet Dent 1987;57:574-6. 24. McLean JW, Powis DR, Prosser HJ, Wilson AD. The use of glass-ionomer cements in bonding composite resins to dentine. Br Dent J 1985;158:410-4. 25. Smith GE. Surface deterioration of glass-ionomer cement during acid etching: an SEM evaluation. Oper Dent 1988;13:3-7. 26. Sjödin L, Uusitalo M, van Dijken JV. Resin modified glass ionomer cements. In vitro microleakage in direct class V and class II sandwich restorations. Swed Dent J 1996;20:77-86. 27. Cattani-Lorente MA, Dupuis V, Payan J, Moya F, Meyer JM. Effect of water on the physical properties of resin-modified glass ionomer cements. Dent Mater 1999;15:71-8. Reprint requests to: DR SHU-FEN CHUANG DEPARTMENT OF DENTISTRY NATIONAL CHENG-KUNG UNIVERSITY HOSPITAL 138 SHENG-LI ROAD TAINAN 70428 TAIWAN FAX: (886)6-276-6626 E-MAIL: [email protected] Copyright © 2001 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2001/$35.00 + 0. 10/1/116133
doi:10.1067/2001.116133
VOLUME 86 NUMBER 3
CLINICAL IMPLICATIONS Findings from this in vitro study suggest that surface protection with a resin adhesive provides improved margin sealing in Class V resin-modified glass ionomer restorations.
C
onventional glass ionomer cements (GIC) have been advocated as restorative materials because of their ability to chemically bond to tooth structure and release fluoride.1 They are widely used in dentistry for restoration, as a liner or base, and as luting cements. A survey on the use of glass ionomer cements showed that 94% of general dentists in the United States currently use or have used them.2 Conventional GICs are moisture-sensitive restorative materials. Immediately after the aluminosilicate glass powder is mixed into an aqueous solution of a Supported by NCKUH Grant No. 87-079, National Cheng-Kung University Hospital. aAttending Staff, Department of Operative Dentistry. bChief and Professor, Department of Pathology. cAttending Staff, Department of Pediatric Dentistry. dChief and Lecturer, Department of Dentistry. SEPTEMBER 2001
polymer or copolymer of acrylic acid, the chemical acid-base reaction starts. During the initial state, hydrated protons of the acid attack the periphery of the glass particles and release metal ions. Initially, some soluble salts such as calcium polyacrylate are formed; these gradually are replaced by insoluble aluminum polyacrylate salts, which cause gelation and hardening of the cement.3 During these reactions, both water uptake and water loss can compromise the physical properties of the restoration. Gemalmaz et al4 found that when GIC restorations were contaminated by moisture, their mechanical strength decreased and the surface of the material eroded or wore rapidly. Provisions must be made to maintain the water balance of restorations for the first 24 hours.5 Previous studies have discussed the necessity for and types of surface protection during the initial setting of THE JOURNAL OF PROSTHETIC DENTISTRY 309
THE JOURNAL OF PROSTHETIC DENTISTRY
conventional GICs. Cocoa butter, waterproof varnish, and even nail varnish have been recommended as surface coating agents.6-8 Recently, light-polymerized resin adhesive has been considered the optimal surface protecting agent. Hotta et al9 found that the use of light-polymerized bonding or glazing agents limited water movement across the setting cement surface. In an SEM study, Watson and Banerjee10 demonstrated the effectiveness of light-polymerized resin adhesives as surface protection. Moreover, the American Dental Association Council on Dental Materials, Instruments, and Equipment (1990) declared the importance of varnish or light-polymerized bonding agents for conventional GIC restorations.11 During the 1980s, resin-modified glass ionomer cements (RMGIC) were developed to replace conventional GICs. According to McLean et al,12 RMGICs are materials that set concurrently via a dominant acidbase reaction and auxiliary photopolymerization. With the addition of resin monomer (2-hydroxyethyl methacrylate [HEMA]), about 4.5 wt%,13 and lightpolymerized initiators, RMGICs are polymerized immediately after visible light irradiation. Compared with conventional analogs, RMGICs have been characterized as having a longer working time, a rapid set, improved appearance and translucency, and higher early strength.14,15 However, RMGICs retain some properties of their conventional counterparts. Additional resin monomer and supplementary photopolymerization have not significantly reduced the susceptibility of RMGICs to dehydration problems.16 Thus, the maintenance of water balance in the modified cements is important. Only a few studies have addressed the importance of surface protection for RMGICs. Ribeiro et al17 proved the effectiveness of surface protection for the prevention of dye uptake (staining) of 3 brands of RMGIC. Another study by Miyazaki et al18 reported the influence of surface coatings on the flexural properties of both conventional and resin-modified GICs. Their results indicated that RMGICs should be protected from water for at least 1 hour after cement mixing. In contrast, most manufacturers’ instructions indicate that RMGICs can be used with or without surface protection. Given that current dental restorative materials exhibit some degree of microleakage, the importance of surface protection seems to be underestimated. The presence of microleakage may lead to postoperative problems such as bacterial accumulation, fluid flow in the gap, and detachment of the restoration.19 The purpose of this study was to investigate the effects of various surface protections (GIC varnish and lightpolymerized resin adhesives) on the microleakage of an RMGIC in vitro. The microleakage of occlusal mar-
310
CHUANG ET AL
gins and cervical margins with different surface protections was evaluated separately.
MATERIAL AND METHODS Thirty human extracted molars without decay or previous restoration were chosen for this study. They were stored in normal saline before use within 4 months after extraction. The teeth were scaled and cleaned with pumice. To keep the cavity preparation on dentin, the cervical cementum over the cervical portion of the root was removed with a sharp scalpel. The exposed root surface was polished with Sof-Lex paper disks (3M, St Paul, Minn.). Two Class V cavity preparations with a mesiodistal width of 4 mm, an occlusogingival height of 3 mm, and a depth of 2 mm, without retention lock, were prepared on the buccal and lingual surfaces of each tooth. Diamond burs (440M and 411, Shofu Inc, Tokyo, Japan) were used for the cavity preparations; each bur was used to prepare 5 cavities. The occlusal margins of the cavities were located on enamel and the cervical margins on dentin. All cavosurface angles were kept at 90 degrees without bevel designs. The teeth were randomly assigned to 3 groups such that each group had 10 teeth with a total of 20 cavities. One RMGIC (Fuji II LC; GC Corp, Tokyo, Japan) was chosen as the restorative material because of its popularity and margin sealing quality demonstrated in previous studies.20,21 Three different surface treatment regimens were designed: group I teeth received no surface protection, group II teeth were treated with Fuji Varnish (GC Corp), and group III teeth were treated with the light-polymerized resin adhesive Scotchbond Multipurpose No. 3, which contains BISGMA, HEMA, and light-cured activator. All restorative and adjunctive materials used in the study are listed in Table I. According to the manufacturer’s instructions, Dentin Conditioner (GC Corp) was applied to all cavity preparations with a light scrubbing motion22 for 20 seconds; the preparations were rinsed with water for 20 seconds and then air dried. Fuji II LC was mixed according to the recommended powder/liquid ratio (3.0/1.0 g) and manufacturer’s instructions, then placed into the cavities and light polymerized with a Curing Light 2500 machine (3M) for 40 seconds to assure complete polymerization. The cavities on buccal and lingual surfaces were filled separately. The restored cavities were finished with a scalpel and fine diamond burs, then polished with Sof-Lex paper disks. After finishing and polishing, the teeth in group I were immersed in isotonic saline in a 37°C water bath for 24 hours.23 Immediately after polishing, the restorations in group II were lightly air dried, coated with a layer of
VOLUME 86 NUMBER 3
CHUANG ET AL
THE JOURNAL OF PROSTHETIC DENTISTRY
Table I. Experimental and adjunctive materials used in this study Material
Manufacturer
Type
Composition
Powder: fluoroaluminosilicate Liquid: polyacrylic acid, HEMA 10% polyacrylic acid Rosin BIS-GMA, HEMA, light-polymerized initiator 35% phosphate acid
Fuji II LC
GC Corp, Tokyo, Japan
Restorative material
Dentin Conditioner Fuji Varnish Scotchbond Multipurpose No. 3
GC Corp GC Corp 3M, St. Paul, Minn.
Dentin conditioner Surface protection Surface protection
Ultraetch
Ultradent Inc, South Jordan, Utah
Acid-etching gel
HEMA = 2-hydroxyethyl methacrylate.
Table II. Experimental groups and their treatments Group
Dentin preconditioning
Restoration
I II III IV
Dentin Dentin Dentin Dentin
Fuji Fuji Fuji Fuji
conditioner conditioner conditioner conditioner
II II II II
LC LC LC LC
Surface treatment
None Fuji Varnish Scotchbond Multipurpose No. 3, Light polymerized for 20 s Acid etched for 5 s, rinsed, and air dried. Scotchbond Multipurpose No. 3 applied and light polymerized for 20 s.
Fuji Varnish, and gently air dried. The restorations in group III were treated with Scotchbond Multipurpose No. 3, which was air thinned and then light polymerized for 20 seconds. If a glossy surface was not obtained over group II and III restorations, an additional surface coating was applied. The teeth in groups II and III then were immersed in isotonic saline for 24 hours in the same manner as group I specimens. The surfaces of the restorations were somewhat contaminated by the use of burs and other instruments during finishing and polishing procedures. The effect of acid etching on RMGICs has not been reported, although studies in the literature do address acid etching of GICs. With the use of the “sandwich technique,” the exposed surface of GICs and enamel margins have been acid etched before the placement of resin composites.24 An SEM study from Smith,25 however, revealed rapid surface deterioration with crack formations in conventional GIC after short-term acid etching. To study the effect of acid etching on the RMGIC used in this study, an additional 10 teeth were prepared and designated group IV. These teeth had prepared cavities and were filled as previously mentioned. After finishing and polishing, they were acid etched with 35% phosphoric acid (Ultraetch, Ultradent Inc, Utah) for 5 seconds, rinsed, and lightly air-dried. Scotchbond Multipurpose No. 3 was applied on the etched surfaces and light polymerized for 20 seconds. These teeth then were immersed in 37°C normal saline as previously
SEPTEMBER 2001
mentioned. The experimental groups and their treatments are listed in Table II. All teeth were placed in a 5°C ± 0.2°C to 60°C ± 0.2°C thermocycling machine for 1500 cycles (20 seconds for each dwelling). The apex of each tooth was sealed with sticky wax, and the whole tooth, except 1 mm beyond the margin of the restoration, was coated with nail varnish to prevent dye penetration from neighboring dentin. The teeth were soaked in 2% basic fuchsin dye for 24 hours. After being removed from the dye solution, they were embedded with epoxy resin and sectioned in a buccal-lingual direction along their long axis with a low-speed saw (Isomat 2000, Buehler Ltd, Chicago, Ill.). Both halves of each sectioned tooth were observed with a ×50 stereomicroscope (Stemi SV 6, Carl Zeiss, Oberkochen, Germany) and scored for dye penetration. One examiner who was not informed of the treatment procedure examined the specimens randomly. During the analysis, the examiner was unaware of the nature of the specimen. The degree of margin microleakage at the tooth–restoration interface was scored as follows: 0 = no dye penetration; 1 = dye penetration up to dentinoenamel junction (DEJ) in occlusal margin, or up to one third full length of cervical margin wall; 2 = dye penetration beyond DEJ and up to two thirds full length of occlusal margin wall, or between one and two thirds full length of cervical margin wall; 3 = dye penetration beyond two thirds full length of occlusal or cervical wall but not involving axial wall; and 4 = extensive dye penetration extending
311
THE JOURNAL OF PROSTHETIC DENTISTRY
CHUANG ET AL
used in groups III (1 of 20) and IV (0 of 20). Because the defective restoration surfaces were rough and unevenly stained, the flaking coatings of the varnish or resin bonding agent were gently scrubbed off, and the restorations were rinsed with tap water before the teeth were immersed in dye solution. One half of a tooth in group IV was excluded because of damage during the sectioning procedure. Thus, the specimen halves numbered 40 in each of the groups I through III but only 39 in group IV. None of the 4 groups demonstrated complete margin sealing at either the occlusal or cervical margins. The distribution of dye penetration scores is displayed in Figure 2. Analyzed with the Kruskal-Wallis test, the data indicated no statistical differences in microleakage among the 4 groups at the occlusal margins. With regard to cervical margins, group III exhibited the best margin sealing, followed in sequence by groups II, I, and IV. Statistical differences existed between groups I and III (P=.034; significant), groups I and IV (P=.000), groups II and IV (P=.000), and groups III and IV (P=.000). The margin sealing of cervical margins in group IV was significantly inferior to the other 3 groups. The Mann-Whitney test was used to examine the microleakage between occlusal and cervical margins in each group (Table III). All unetched groups exhibited better sealing at the cervical margin than occlusal margin (P=.008, .001, and .000 for groups I, II, and III, respectively). In contrast, group IV specimens exhibited better sealing at the occlusal margin (P=.000). Fig. 1. Score system for degrees of dye penetration. 0 = no dye penetration; 1 = dye penetration up to DEJ in occlusal margin, or up to one third full length of cervical margin wall; 2 = beyond DEJ and up to two thirds full length of occlusal margin wall, or between one and two thirds full length of cervical margin wall; 3 = beyond two thirds full length of occlusal or cervical wall but not involving axial wall; and 4 = extending to axial wall.
to axial wall (Fig. 1). The scores were analyzed with the Kruskal-Wallis test to identify statistical differences in margin microleakage among the 4 groups. The MannWhitney test was also performed to compare the sealing quality at occlusal and cervical margins in each group. The level of significance was P<.05.
RESULTS A total of 80 restorations were prepared. After the restorations were removed from the thermocycling machine, it was discovered that the coating materials (varnish or resin bonding agent) had partially peeled off the surfaces of some restorations. Fuji Varnish (group II) exhibited more defects after thermocycling (5 of 20 restorations) than the resin bonding agent 312
DISCUSSION Ribeiro et al17 proved the effectiveness of surface protection, especially with the use of a light-polymerized resin adhesive, for the prevention of surface staining of RMGICs. In this study, the best margin sealing was obtained in specimens with resin adhesive protection and without prior acid surface cleansing. The resin adhesive coating reduced staining and microleakage more effectively than the other materials tested. Thus, when clinicians use a RMGIC as a restorative material, they should consider applying resin adhesive and adequately light polymerizing it after finishing the restorations. The unetched (I-III) and etched (IV) groups showed different results for microleakage at the occlusal and cervical margins. In the former, the restorations exhibited better margin sealing at the cervical (dentinal) margins than at the occlusal (enamel) margins. This finding disagrees with previous studies. In a microleakage study of RMGIC in Class V and Class II sandwich restorations, Sjödin et al26 found that dentinal gingival margins exhibited greater leakage than enamel margins. Contradictory results may exist because of different thermocycling tests and total immersion times. Only VOLUME 86 NUMBER 3
CHUANG ET AL
THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 2.Distribution of dye penetration scores for 4 experimental groups. Kruskal-Wallis test (significance level P=.05) demonstrated no significant differences among 4 groups at occlusal margins. At cervical margins, statistical differences existed between groups I and III (P=.034), I and IV (P=.000), II and IV (P=.000), and III and IV (P=.000). *Specimen number in group IV was 39; 1 specimen was damaged.
Table III. Comparisons of occlusal and cervical margin microleakage in each of the 4 experimental groups Group
I II III IV
Margin
Mean rank
Mann-Whitney U test
P value
Occlusal Cervical Occlusal Cervical Occlusal Cervical Occlusal Cervical
46.70 34.30 48.30 32.70 49.42 31.58 25.24 53.76
552.0
.008*
488.0
.001*
443.0
.000*
204.5
.000*
*Statistical difference in all 4 groups (Mann-Whitney U test, significance P=.05).
180 thermocycling tests were performed in the study by Sjödin et al.26 In this study, more thermocycles (1500 total) and a longer immersion time were assigned to simulate the aging process. Enamel and dentin have a higher and lower modulus of elasticity, respectively. It has been reported that 4.7% volumetric expansion occurs with RMGICs after 24 hours of water immersion.27 Dentin under the restorations may have had a great enough stress-absorbing capacity to buffer the expansion of the RMGIC material. However, this hypothesis needs further investigation. Crim20 showed that some enamel adjacent to RMGIC cracked during thermocycling. Although no obvious enamel cracking was detected in this study, enamel microcrazing may have been another cause of microleakage. At the end of thermocycling, some coating materials on the restoration surfaces were partially peeled away. The flaking of Fuji Varnish (group II; 5 of 20) was more evident than the flaking of the resin bonding agent (group III; 1 of 20). The finding is consistent with a study by Hotta et al,9 in which the varnish material SEPTEMBER 2001
(Ketac varnish) peeled after water immersion but the resin bonding coatings remained intact. Because mechanical brushing motion was not included in this study, the breakdown of the coating materials was attributed to the impact of thermocycling or hydrolysis. Information about the wear resistance and protection duration of the coating materials in vivo was not reported in this study; these topics need further investigation. Information about the effect of acid etching on RMGICs is rare. In this study, the occlusal and cervical margins of group IV restorations displayed different degrees of microleakage after 5 seconds of 35% phosphoric acid etching. A study by Smith25 suggested that GIC materials, including RMGICs, deteriorate after even short-term acid etching. Dye penetration at the cervical margin, generally extending to the axial wall, suggested the breakdown of the bond between the RMGIC and dentinal margin after acid etching. If etched dentin surfaces are sealed with a resin adhesive but not treated with a dentin bonding agent, microleakage will occur in the restored interfaces. 313
THE JOURNAL OF PROSTHETIC DENTISTRY
The results of this study suggest that resin adhesive can be used as a surface protection agent to improve margin sealing. Acid etching the RMGIC restoration to clean the surface resulted in extensive cervical margin microleakage and should be avoided. Some current resin adhesives, such as 1-component dentin bonding agents and self-etching primers, contain polyacrylic acid or other organic acids. Whether these acids would deteriorate the surface of GIC or RMGIC restorations is debatable. Until further research is performed, they should be avoided as surface protection agents.
CONCLUSIONS Within the limitations of this study, the following conclusions were drawn: 1. Surface protection, especially with the use of resin adhesive agents, should be added to resin-modified glass ionomer cement restorations. 2. The use of 35% phosphoric acid to clean RMGIC restorations negatively and severely affected cervical margin sealing and should be avoided. We thank Miss Ling-Fan Ho for her help with the statistical analyses.
REFERENCES 1. Wilson AD, McLean JW. Glass ionomer cement. London: Quintessence Publishing; 1988. p. 83-99, 126-8. 2. Reinhardt JW, Swift EJ Jr, Bolden AJ. A national survey on the use of glassionomer cements. Oper Dent 1993;18:56-60. 3. Wilson AD, McLean JW. Glass ionomer cement. London: Quintessence Publishing; 1988. p. 43-54. 4. Gemalmaz D, Yoruc B, Ozcan M, Alkumru HN. Effect of early water contact on solubility of glass ionomer luting cements. J Prosthet Dent 1998;80:474-8. 5. Mount GJ, Makinson OF. Glass-ionomer restorative cements: clinical implications of the setting reaction. Oper Dent 1982;7:134-41. 6. Asmussen E. Opacity of glass-ionomer cements. Acta Odontol Scand 1983;41:155-7. 7. Earl MS, Hume WR, Mount GJ. Effect of varnishes and other surface treatments on water movement across the glass-ionomer cement surface. Aust Dent J 1985;30:298-301. 8. Rodrigues Garcia RC, De Goes MF, Del Bel Cury AA. Influence of protecting agents on the solubility of glass ionomers. Am J Dent 1995;8:294-6. 9. Hotta M, Hirukawa H, Yamamoto K. Effect of coating materials on restorative glass-ionomer cement surface. Oper Dent 1992;17:57-61. 10. Watson T, Banerjee A. Effectiveness of glass-ionomer surface protection treatments: a scanning optical microscope study. Eur J Prosthodont Restor Dent 1993;2:85-90.
314
CHUANG ET AL
11. Using glass ionomers. Council on Dental Materials, Instruments, and Equipment. J Am Dent Assoc 1990;121:181-8. 12. McLean JW, Nicholson JW, Wilson AD. Proposed nomenclature for glass-ionomer dental cements and related materials. Quintessence Int 1994;25:587-9. 13. Mount GJ. Buonocore Memorial Lecture. Glass-ionomer cements: past, present and future. Oper Dent 1994;19:82-90. 14. Mitra SB. Adhesion to dentin and physical properties of a light-cured glass-ionomer liner/base. J Dent Res 1991;70:72-4. 15. Uno S, Finger WJ, Fritz U. Long-term mechanical characteristics of resinmodified glass ionomer restorative materials. Dent Mater 1996;12:64-9. 16. Sidhu SK, Sherriff M, Watson TF. The effects of maturity and dehydration shrinkage on resin-modified glass ionomer restorations. J Dent Res 1997;76:1495-501. 17. Ribeiro AP, Serra MC, Paulillo LA, Rodrigues Junior AL. Effectiveness of surface protection for resin-modified glass ionomer materials. Quintessence Int 1999;30:427-31. 18. Miyazaki M, Moore BK, Onose H. Effect of surface coatings on flexural properties of glass ionomers. Eur J Oral Sci 1996;104:600-4. 19. Kidd EA. Microleakage: a review. J Dent 1976;4:199-206. 20. Crim GA. Marginal leakage of visible light-cured glass ionomer restorative materials. J Prosthet Dent 1993;69:561-3. 21. Toledano M, Osorio E, Osorio R, Garcia-Godoy F. Microleakage of Class V resin-modified glass ionomer and compomer restorations. J Prosthet Dent 1999;81:610-5. 22. Barakat MM, Powers JM, Yamaguchi R. Parameters that affect in vitro bonding of glass-ionomer liners to dentin. J Dent Res 1988;67:1161-3. 23. Crim GA, Garcia-Godoy F. Microleakage: the effect of storage and cycling duration. J Prosthet Dent 1987;57:574-6. 24. McLean JW, Powis DR, Prosser HJ, Wilson AD. The use of glass-ionomer cements in bonding composite resins to dentine. Br Dent J 1985;158:410-4. 25. Smith GE. Surface deterioration of glass-ionomer cement during acid etching: an SEM evaluation. Oper Dent 1988;13:3-7. 26. Sjödin L, Uusitalo M, van Dijken JV. Resin modified glass ionomer cements. In vitro microleakage in direct class V and class II sandwich restorations. Swed Dent J 1996;20:77-86. 27. Cattani-Lorente MA, Dupuis V, Payan J, Moya F, Meyer JM. Effect of water on the physical properties of resin-modified glass ionomer cements. Dent Mater 1999;15:71-8. Reprint requests to: DR SHU-FEN CHUANG DEPARTMENT OF DENTISTRY NATIONAL CHENG-KUNG UNIVERSITY HOSPITAL 138 SHENG-LI ROAD TAINAN 70428 TAIWAN FAX: (886)6-276-6626 E-MAIL: [email protected] Copyright © 2001 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2001/$35.00 + 0. 10/1/116133
doi:10.1067/2001.116133
VOLUME 86 NUMBER 3