| Objective: To observe and compare the microleakage of four base materials(GI-1 glass-ionomer,3M Vitrebond light-cured glass-ionomer,Urbical LC light-cured calcium hydroxide and Ionosit-Baseliner light-cured glass-ionomer) bonding to dentin, and contrast with the microleakage of Charisma resin. This paper aims at choosing the best base materials for deep caries.Methods: Fifty intact, caries-free, subfissure-free, extracted human molars were cleaned and were preserved in distilled water of -20°C. The cavities were prepared with carbide burs in a high-speed handpiece equipped with water spray.The occlusal enamel of all specimens was grinded with silicon carbide burs in a high-speed handpiece equipped with water spray, to expose the dentin surface. Then, typical cavities (approximately 3 mm in diameter and 2 mm deep) on the occlusal surfaces of dentin were prepared. Fifty specimens were randomly divided into four experimental groups and one control group. The cavities were filled with five different materials as following.Group1. Clearfil SE-Bond agents and Charisma resin (control group);Group2. GI-1 glass-ionomer;Group3. 3M Vitrebond light-cured glass-ionomer;Group4. Urbical LC light-cured calcium hydroxide;Group5. Ionosit-Baseliner light-cured glass-ionomer.Group 2 to group 5 was used as experimental group.After all the cavities have been filled, fifty specimens were putted into normal saline at ordinary temperature for 24 hours. Then, the teeth were putted into 5°C and 55°C water alternately 1min in each bath. A total of 720 cycles was used for all specimens. The apical foramen of all teeth were closed with wax, then the entire tooth, except for the restoration and 1 mm of the tooth surface adjacent to the restoration, was coated with nail varnish.The teeth were then placed in a 50% ammoniacal silver nitrate aqueous solution for 24 hr in total darkness. They were rinsed in running water until no black particle can be seen, immersed in photodeveloping solution, and exposed to a fluorescent light for 8 hr so that silver ion reduction would be completed. After removal from the developing solution, the teeth were rinsed thoroughly in running water for 5 min.All specimens were divided into two parts along the long axis of teeth with silicon carborundum discs in low-speed handpiece. The extreme of microleakage in each section was measured with a vernier caliper, and was scored. Kruskal-Wallis test was used to analyze the difference microleakage among five groups; LSD-t test were used for multiple-comparison. Asα= 0.05, if p value is <0.05, there is difference statistically.One specimen was chosen from every group for SEM observation. Combining specimen noumenal pictures, scan-ning electronic micrographs and statistics results, we eval-uate the character of four base materials in this study. Results: A nonparametric one-way analysis of variance (Kruskal-Wallis test) showed a significant difference in the extent of microleakage among the five groups (H = 69.855, p<0.001).A post hoc nonparametric multiple-comparison procedure (LSD-t test) further indicated that the microleakage between group 1 and group 5 was not statistically significant (p >0.05). The same was observed for group 2 and group 4(p>0.05). But the microleakage of group 3 was different from the other four groups (p<0.0001), group 1 and group 5 were different from group 2 or group 4(p<0.0001).From the specimens noumenal pictures, we can hardly see any silver microleakage in group 1, the circumstance was similar in group 5, there were little silver staining. On the other hand, group 2 and group 3 showed much more silver microleakage, and silver grains leaked from the base materials- elves, group 2 was more serious than group 3. In group 4, microleakage invaded from the adhesive interface of dentin and Urbical LC, and some reached the bottom of the cavity, indicating that Urbical LC light-cured calcium hydroxide had a weaker sealing function in dentin bonding.Through 40 times scanning electronic micrographs, group 1 and group 5 remained little silver staining, and there was no fissure between dentin and materials, but Ionosit Baseliner present many uniformly distributed micropores in itself, like sponge someway. In group 4, separation of the Urbical LC and dentin was observed, as demonstrated by the presence of silver grains along the cavosurface margin. Group 2 and group 3 showed wider gaps between base materials and dentin, gaps presented in some part of base materials, too. Silver microleakage distributed in gaps and bases like spot or floss.From high-power scanning electronic micrographs, group 1 and group 5 showed a little nanoleakage at some area, but the adhesive interfaces didn't present any gap. The shapes of the pores in group 5 were irregular, and nanoleakage seldom present in pores. In group 4, a long strip of microleakage was seen obviously at the dentin-ULC interface, and a little silver grain got into the dentinal tubules and ULC. Silver microleakage could be seen in Group 2 and 3 in materials and in gaps, moreover, the silver staining can be seen clearly in some dentinal tubules. Otherwise, in the gaps between dentin and base materials, we could see that most of the dentin tubules were sealed by the two base materials, so we think the base materials in group 2 and 3 have a good capability of sealing dentinal tubules. Conclusion:1 Ionosit-Baseliner showed the least microleakage in the four test groups, and had no statistically difference with the control group.2 GI-1 glass-ionomer and Urbical LC light-cured calcium hydroxide showed similar microleakage in depth, and had no statistically difference with each other, but there was statistically difference as compared with control group.3 The microleakage of 3M Vitrebond was less than GI-1 glass-ionomer and Urbical LC light-cured calcium hydroxide, but more than Ionosit-Baseliner and the control group.4 GI-1 glass-ionomer and 3M Vitrebond had many pores, in which the microleakage presented. Urbical LC light-cured calcium hydroxide showed long strip microleakage in the interface with dentin. Ionosit-Baseliner showed very slight the microleakage.
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