Microleakage Evaluation in Amalgam Restorations Used with Bases Gerard Wieczkowski Jr., D.D.S.,* Xin Yi Yu, M.M.,' Robert B. Joynt, D.D.S.,+Elaine L. Davis,Ph.D.'

Marginal leakage in amalgam restorations often precedes the development of secondary caries. One potential way to improve the marginal seal of such restorations, and thus minimize the risk of caries development, is to apply a glassionomer base prior to amalgam placement. This study compared microleakage resistance among amalgam restorations placed with and without light-cured glass-ionomer base materials. Preparations were made in extracted human molar teeth. Four groups were studied, including copal varnish, which was used as a control. All specimens were restored with amalgam. Results indicated signllicantly greater leakage at the cavity wall/base interface for restorations with a copal varnish cavity liner than for those with a glass-ionomer base. Leakage dinerences among bases were also found at the amalgam/base interface. Best results were obtained with a dual-cure resin-based system. These samples showed minimal leakage at both the cavity wall/base and the base/amalgam interfaces. These findings suggest that light-cured glassionomer bases can be effective in the prevention of microleakage in amalgam restorations.

C ing

aries have been reported as the main reason for replacement of amalgam restorations, accountfor 50 to 60 percent of all restorations placed.'. A major reason for this is failure to either establish or maintain an adequate marginal seal. Microleakage can occur at the cavity wall/amalgam interface, resulting in marginal breakdown and the developmentof secondary caries. Glass-ionomer has been recommended as a base for composite resin and amalgam restoration^.^ Its high available fluoride content is thought to increase caries re~istance.~ While this is clearly advantageous, glassionomer cement also has a number of disadvantages. The material is sensitive to moisture contamination and desiccation while setting. In addition, postoperative sensitivity may d e v e l ~ pThe . ~ shorter setting time and higher bond strength reported for the light-cured glassionomer cements6have resolved some of these disadvantages.

The purpose of this study was to compare the resistance to microleakage of amalgam restorations used with several light-cured glass-ionomer bases. Class V cavity preparations were created in the buccal and lingual surfaces of extracted molars. Followingrestoration with either a glass-ionomer base or copal varnish h e r and amalgam, all specimens were stressed thermally and placed in fuchsin dye. Microleakage was determined by measuring the amount of dye penetration along the cavity wall.

MATERIALS AND METHODS The materials evaluated in this study were Geristore (Den-Mat, Santa Maria, CA), Vitrabond (3M Dental Products Division, St. Paul, MN). Vitrabond with Silver Seal (R Defelice, Geneva, NY), and Copalite (Cooleyand Cooley, Houston, TX). Geristore is a dual-cure, resinbased glass-ionomer, whereas Vitrabond is a modifled, polyacrylic acid, light-cured glassionomer. Silver Seal is a dual-cure proprietary resin developed specificallyfor the improvement of the bond between Vitrabond and amalgam. Copalite is a copal varnish and was included in this study as a control. Twenty-four freshly extracted human mandibular molar teeth, stored in a saline solution, were used. Class V cavity preparations, approximately 4 mm long x 4 mm wide x 2 mm deep, were prepared on both the buccal and lingual surfaces of each tooth. Cavity preparations

*AssociateRofessor and Chairman: t Assistant Professor: Department of Operative Dentistry. School of Dental Medicine. State Universityof New York at Buffalo, Buffalo. New York Presented at the International Association for Dental Research annual meeung. Acapulco, Mexico, Aprlll991. AddressrrprfntnqueststoXinYiYu.M.M..SchoolofDtntalMedicine.235 Squire Hall.University at Buffalo, Buffalo, NY 14214 0 1992 Decker periodicals Inc.

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JOURNAL OF ESTHETIC DENTISTRY VOLUME 4. NUMBER 2 March/April 1992

Table 1. Mean Microleakage (mm) by Base Material and Interface

were initiated with a #56bur rotating at high speedwith air-water coolant and completed with the #56 bur in a conventional speed handpiece. Preparations were located such that the occlusal margins were placed on enamel and the gingival margins were on cementum. A total of 12 preparations were made for each of the four treatment groups. All materials were placed in accordance with the manufacturers' recommendations. Geristore was not cured with light prior to amalgam placement. Vitrabond was cured for 40 seconds with a Prisma Lite [LD Caulk, Milford, DE). For the Vitrabond/Silver Seal group, Silver Seal was applied followingthe application and set of Vitrabond. Silver Seal is a two-paste system that is mixed in equal amounts to a homogeneous consistency prior to placement. It has a dual-cure polymerization system that allows approximately 4 to 5 minutes of working time. Amalgam (Valiant Ph.D. XT, LD Caulk, Milford, DE) was triturated and placed in all prepared specimens. Specimen apices were then sealed with a composite resin to prevent leakage. The entire tooth, with the exception of the restoration and tooth surface within 1 mm of the margin, was sealed with nail polish to limit dye contact to the area of study. Teeth were stored in 100 percent humidity at 37°C for 24 hours, then thermocycled 1500times. Each cycle consisted of 15 seconds each at 37°C. 54°C. 37T. and 4°C. After thermocycling, specimens were stored in 2 percent basic fuchsin dye for 24 hours and then completely embedded in self-cure acrylic resin. The resin was allowed to set and specimens were sectioned longitudinally at the center of the restoration with a low speed diamond saw (Buehler Ltd, Lake Bluff, IL). Microleakage was determined by measuring the axial penetration of the dye stain at both tooth/base and base/amalgam interfaces. Tooth sections were examined at 30 x magnification under an optical microscope, with the extent of leakage measured in millimetersfrom both the occlusal and gingival margins.

lnterface (n = 12) Base Material

Base Amalgam

Cavifv Wa/l/Base Mean (SO) Mean Rank'

Copalitet 3.86 (2.04) .61 (.86) Vitrabond .87(1.16) Geristore Vitrabondt Silver Seal+

28.75

Mean (SD) Mean Rank

2.36 (1.38)

30.25

.llC.26)

12.67

14.17

-

'Mean ranks connected by a vertical line do not differ statistically at the 0.05 significance level. Lower rank indicates less microleakage. t This group not included in base/amalgam evaluationsince this interface could not be seen under the microscope. $ This group not included in tooth surface/base interface evaluation since it duplicated the Vitrabond base material group.

A second Kruskal-Wallis analysis was used to test differences in leakage in the base/amalgam interface. Copal varnish specimens were not included in the analysis because the interface could not be distinguished in the optical microscope. This analysis indicated significant differences in leakage at the base/ amalgaminterface(x2=27.01,p

Microleakage evaluation in amalgam restorations used with bases.

Marginal leakage in amalgam restorations often precedes the development of secondary caries. One potential way to improve the marginal seal of such re...
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