Despite the popularity of resin based composites, bonding to dentine remains questionable and limits the clinical success of these materials. Objectives: To evaluate and compare the cervical sealing ability of Class II sandwich restorations with a composite restoration placed in vitro. Materials and Methods: Class II preparations with cervical margins equally distributed between dentine and enamel, were cut in 100 sound human molar teeth. In the sandwich groups, Ketac Molar, Ketac Molar set with ultra-sound (US), Ketac Nano and Vitremer were used to fill the interproximal box, while the rest of the cavity was filled with Z250. Z250 bonded with ScotchBond MultiPurpose was used as control. Half of each group underwent thermocycling for 500 cycles between 5 and 55 °C with a dwell time of 30 seconds. All specimens were immersed in 0,5% basic fuchsin for 24 hours. Cleaned teeth were embedded in clear self-curing acrylic and sectioned 3 times with an Accutom-2 precision saw. Sections were examined under light microscope and the extent of microleakage scored as: 0 = no microleakage, 1 = dye penetration less than half the cervical floor, 2 = more than half the cervical floor and 3 = penetrating up to the axial wall. Results: The sandwich technique significantly reduced microleakage of cervical margins placed in dentine, with Ketac Molar US performing the best. Conclusions: Conventional glass-ionomers or resin-modified glass-ionomers should be used to restore the gingival margin of Class II cavities when it is placed in dentine.
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