Method: Sixty class I cavities were prepared. Teeth were divided into 6 groups of permanent teeth (n=10 for each group) and restored using (Group 1) resin modified glass ionomer cement (Vitrebond Plus, 3M-ESPE), (Groups 2, 3, 4, 5 accordingly) flowable resins with special characteristics as bases (Fusio Liquid Dentin, Pentron Clinical, Surefil SDR Flow, Dentsply, Beautifil Flow Plus F03, Shofu Dental, Beautifil Flow Plus F 00, Shofu Dental). Cavities were then restored with composite resin (Tetric Ceram, Ivoclar, Vivadent). Specimens were thermocyled (1500 cycles, 15’’ dwell time, in temperatures 5oC – 37oC – 55oC – 37oC) to mimic the oral environment and microleakage was assessed via methylene blue penetration degree, using a classification according to the surfaces influenced.
Result: Statistical analysis showed that Group 2 exhibited the lowest mean microleakage values (2.0, 0.6325). Groups in increasing microleakage values were as follows: 2=<1<4=5<3. Comparison between the different materials exhibited significant statistical difference between Groups 2 and 3 (p<0.01). All the other comparisons exhibited no statistical difference.
Conclusion: We concluded that the use of a base material under composite restorations, exhibits varying results in terms of microleakage, according to the type of material used. Chemical composition seems to play an important role when comparing flowable composite resins, but superiority against resin modified glass ionomer cement was not proven. Viscosity of the base material does not seem to affect microleakage values.