| objective:Composite resins have become one of the most commonly used direct restorative materials for anterior and posterior teeth, but one of the inevitable drawbacks of dental composites is shrinkage. Polymerization shrinkage stresses have the potential to initiate failure of composite-tooth interface, causing microleakage, secondary caries, which may result in postoperative sensitivity. Therefore the study about reducing microleakage is the major problem that clinician care about. The purpose of this study was to evaluate the microleakage of composite resins with different clinical technique in vitro, and find an effective way to reduce the microleakage of resin repair and then provide theoretical basis for clinical operation.Methods:Experiment 1:? type cavities were prepared on buccal surface of 48 freshly extracted molars. Teeth were randomly divided into 3 groups:A. restore cavities with 3MZ350 resins under normal temperature; B. restore cavities with 3MZ350 resins after 3MZ350 resins been preheated to 60?; C. restore cavities with 3MZ350 resins after 3MZ350 resins been precooled to 4?; After thermal cycling, all teeth were then immersed in fuchsine solution. The degree of microleakage was assessed as the ratio of the extent of dye penetration at the tooth restoration interface under stereomicroscope.Experiment 2:? type cavities were prepared on buccal surface of 48 freshly extracted molars. Teeth were randomly divided into 3 groups:A. restore cavities with 3MZ350 resins under normal temperature; B. restore cavities with 3MZ350 resins after 3MZ350 resins been preheated to 60?; C. restore cavities with 3MZ350 resins inlays. After thermal cycling, all teeth were then immersed in fuchsine solution. The degree of microleakage was assessed as the ratio of the extent of dye penetration at the tooth restoration interface under stereomicroscope.Experiment 3:? type cavities were prepared on buccal surface of 48 freshly extracted molars. Teeth were randomly divided into 4 groups:A. restore cavities with 3MZ350 resins under normal temperature; B. place preformed composite megafiller and then restore cavities with 3MZ350 resins under normal temperature; C. restore cavities with 3MZ350 resins after 3MZ350 resins been preheated to 60?; D. place preformed composite megafiller and then restore cavities with 3MZ350 resins after 3MZ350 resins been preheated to 60?.After thermal cycling, all teeth were then immersed in fuchsine solution. The degree of microleakage was assessed as the ratio of the extent of dye penetration at the tooth restoration interface under stereomicroscope.Experiment 4:? type cavities were prepared on buccal surface of 48 freshly extracted molars. Teeth were randomly divided into 4 groups:A. Low intensity lights (400 mw/cm2×40 s)B. High intensity lights (800 mw/cm2×20 s) C Soft-Start (100 mw/cm2×10 s+800 mw /cm2×15 s) D. Intermittent light (800 mw/cm2×40 s,2 s on,2 s off).After preheating,3MZ350 resins were filled cavities. Then light curing in different light curing modes. After thermal cycling, all teeth were then immersed in fuchsine solution. The degree of microleakage was assessed as the ratio of the extent of dye penetration at the tooth restoration interface under stereomicroscope.Results:1.The result of microleakage showed that there were all statistically significant differences among the three different groups (P<0.05). And the result of microleakage of the preheat group was higher than that of the precooled one.2.The result of microleakage showed that there were no statistically significant differences between the preheat group and the inlays group, which was significantly lower than that of the direct restorations with Z350 resin (P<0.05)3.The microleakage values in groups C and D were significantly lower than groups A and B (P<0.05).And there were no statistically significant differences between groups A and groups B (P>0.05). And there were no statistically significant differences between groups C and groups D (P>0.05)4.The microleakage values of high intensity light groups were significantly lower than the other groups (P<0.05). And there were no statistically significant differences between the low intensity light groups, the intermittent light groups and the soft-start light groups (P>0.05)Conclusions:1.Temperature have an influence on microleakage between the resin and the wall of the cavity. After preheated to 60?, resin filling may reduce microleakage between the resin and the wall of the cavity. While after precooled to 4?, resin filling may increase the microleakage.2.Using preheating resin and inlays to restore cavities can both reduce microleakage between the resin and the wall of the cavity effectively.3.Use of prepolymerized composite megafiller, no matter normal temperature or been preheated, could not decreased the marginal gaps between the tooth and composite restorations.4. After composite resin preheated, the use of low intensity light, intermittent light and soft-start light will reduce the marginal seal between the resin and the wall of the cavity. |
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