Porcelain-composite interface microleakage with various porcelain surface treatments J,A. Sorensen S,K. Kang S.P. Avera School of Dentistry University of California Los Angeles, CA 90024 Received March 22, 1990 Accepted February 8, 1991 This project was supported in part by BRSG S07 RR05304 awarded by the Biomedical Research Support Grant Program, Division of Research Resources, National Institutes of Health, Bethesda, MD. Dent Mater 7:118-123, April, 1991
Abstract-This study evaluated the effects of various porcelain surface treatments on the microleakage of the porcelain-composite interface. The experimental model isolated and evaluated only the porcelain-composite interface without the presence of a bond to tooth structure. Four types of porcelain were fired into circular porcelain tabs 1.0 mm thick by 8.5 mm in diameter. The groups of porcelain were divided into subgroups for treatment with hydrofluoric acid-etching and silane. A jig standardizing composite thickness to 0.2 mm was used to photopolymerize composite to porcelain. The margins were finished and polished with burs and disks. Samples were stored in 37°C water thermocycled 1000X, placed in AgN03 solution, embedded in epoxy, and cross-sectioned every 90° for measurement of stain penetration at the composite-porcelain interface. Occasional crazing of porcelain from composite polymerization shrinkage was observed. Porcelain surface treatment significantly increased the specimens' ability to withstand water storage and thermal-cycling procedures. Porcelain surface treatment with silane alone did not reduce microleakage, but, in combination with etching, reduced microleakage significantly.
icroleakage has been defined as the passage of bacteria, fluids, molecules, or ions between a cavity wall and the restorative material applied to it (Kidd, 1976). Loss of integrity of the marginal seal of adhesive restorations manifested as microleakage is accountable for secondary caries (Nelson et al., 1952; Going and Sawinski, 1966), post-operative sensitivity (Nelson et al., 1952; Qvist, 1975), staining (Asmussen, 1974; Tyas et at., 1986), and plaque accumulation (Theilade and Theilade, 1986; Mej~re et al., 1979; Sorensen, 1989). Marginal percolation occurs due to the mismatch of coefficient of thermal expansion between tooth struct u r e and r e s t o r a t i v e materials (Nelson et al., 1952). Therefore, some form of thermal stressing should be incorporated for in vitro microleakage research (Kidd, 1976; Peterson et al., 1966). Previous research by the authors with 37°C water storage and thermal cycling of samples found that silane application to etched porcelain had no significant effect on shear bond strength of composite to porcelain (Sorensen et al., 1991). The application of silane to porcelain was found to decrease microleakage of composite repair material (Ferrando et al., 1983; Bello et al., 1985). However, these researchers did not thermocycle their specimens. The purpose of this study was to evaluate the effects of various porcelain surface treatments on the microleakage of the porcelain-composite interface. MATERIALS AND METHODS Porcelain disks 1.0 mm thick and 8.5 mm in diameter were fabricated according to manufacturers' instructions for four brands of porcelain (Table 1). The samples were fired on the respective porcelain manufacturer's refractory die material (VTN,
118 SORENSEN et a/./PORCELAIN-COMPOSITE MICROLEAKAGE
GCA, CRN) or platinum foil (CER). Porcelain samples were de-vested with 25-~m aluminum oxide abrasion at 2.8 kg/cm2 pressure to a uniform surface. The porcelain disks were ground with 180-, 220-, and 300grit silicon carbide sandpaper on an abrasive wheel (Ecomet III Grinder, Buehler Ltd., Evanston, IL) under water coolant to a thickness of 1.0 ram. Specimens were evaluated under 20 × magnification and discarded if any cracks were observed. All porcelain samples were abraded with 25-~m aluminum oxide at 2.8 kg/cm2 pressure to a uniform surface. Each sample was then steamcleaned. For each brand of porcelain, 40 samples were made, divided into four groups of 10, and subjected to the following treatments: subgroup (1) control, (2) sfiane, (3) etched with 20% hydrofluoric acid (Stripit, National Keystone Products, Philadelphia, PA) for three min, and (4) etched and silane application. Each of the silane and adhesive materials was manipulated in strict accordance with the directions of the manufacturer (Table 1). A jig standardizing composite thickness to 0.2 mm was used to photopolymerize composite to porcelain. The respective composite was applied to the treated porcelain surface, seated on the positioning jig (Fig. 1), and a clear mylar strip was wrapped around the sample so that the material would be contained while the composite was photopolymerized (Fig. 2). The margins were finished with carbide finishing burs (Esthetic Trimming, E.T.6, Brasseler USA, Savannah, GA) and polished with SofLex disks #1982M, 1982F, and 1982SF (3M Dental Products, St. Paul, MN) under water spray. Specimens were stored in 37°C water for seven days and thermocycled 1000 times between 5°C and 50°C, with a 30-second dwell time and
a 20-second transport time between immersion baths. The specimens were evaluated for interface microleakage by a modified silver nitrate staining technique similar to that described by Wu et al. (1983, 1987). The samples were placed in a 50% solution of AgN03 for 45 rain, rinsed with distilled water, placed in a developer solution (T-MAX Developer, Kodak, Rochester, NY), and exposed under a 150watt photo fioodlamp for eight h, causing the areas of silver nitrate penetration to turn black. The specimens were embedded in epoxy resin and allowed to cure for 24 h. The porcelain-composite disks were crosssectioned every 90° with a diamond blade (Isomet, Buehler Ltd., Evanston, IL). The sectioned sides of the samples were again exposed under the 150-watt floodlamp for five rain so that complete silver reaction would be ensured. The degree of porcelain-composite interface microleakage was determined by the penetration of the silver nitrate stain from the external porcelain-composite interface toward the center of the cylinder (Fig. 3). Microleakage was recorded in terms of distance of stain penetration as measured at 250X magnification on an Olympus Metallurgical Microscope Model BHMJ (Olympus Optical Co., Ltd., Tokyo, Japan). A Mitutoyo Digimatic Head 164 series (Mitutoyo Mfg. Co. Ltd., Tokyo, Japan) digital traveling micrometer with an accuracy _+ 3 ~m was used to make three measurements at each
point. As the porcelain-composite disks were sectioned twice at 90 ° through their centers, eight composite-porcelain interface measurement points were produced for each sample (Fig. 3). Ten samples were made for each group, which should yield 80 microleakage measurements for each treatment subgroup. Each interface was measured three times by three individuals, and the mean, median, standard deviation, and stand a r d e r r o r of the m e a n s w e r e calculated. Chi-square analysis was used to test for independence for survivor frequency of water storage and thermocycling for surface treatment modality and porcelain brands. A level of p < 0.05 was accepted for statistical significance. The data were subjected to a Kruskal-Wallis oneway ANOVA and Tukey's Studentized Range method for multiple comparison of microleakage related to surface treatment modality and type of porcelain.
RESULTS Crazing of the porcelain disks was observed for some groups. All porcelain specimens were examined at 20X magnification, and findings are recorded in Table 2. The CER group had the majority of specimens exhibiting crazing in the control and etched treatment groups. Several of the specimens did not survive the thermal-cycling treatment, resulting in partial or total delamination of the composite layer (Table 3). Chi-square analysis re-
vealed significant differences in survival rates between the porcelain surface treatment subgroups (p < 0.001) (Table 4). None of the control group specimens survived the thermal cycling. There were also significant differences among the different porcelains that survived water storage and thermal cycling (p